STATUS - TelenorWhen Børge Ousland reached the North Pole on April 22, 1994, after 52 days of...

Guest editorial, Jan Hassel 1

Telecommunications in the Arctic, Mathias Bjerrang 3

Measurements of atmospheric effects on satellite linksat very low elevation angle, Odd Gutteberg 8

NORSAT – Isfjord – a satellite station in the wilderness,Martin Jarl Lode and John R Veastad 14

Satellite navigation and positioning, Ingar Skjønhaug 18

Very Long Baseline Interferometry in the Arctic, Bjørn Ragnvald Pettersen 29

Air pollution monitoring in the Arctic, Geir O Braathen and Elin Dahlin 35

Operation and maintenance of telecommunicationnetworks and services in Arctic conditions, Klaus Grimstad 38

Telecommunications’ importance for safety at Svalbard,Viggo Bj Kristiansen 44

Experiences from Arctic telecommunications, Gunnar Christiansen 46

Telecommunications in Greenland – challenges andsolutions, Per Danker 48

The INUKSAT system and its alternatives – a de-scription of satellite communications in Greenland, Peter Malmberg 51

The challenge of building a digital radio relay system inGreenland, Anders Klose Frederiksen 55

International research and standardisation activities intelecommunication: Introduction, Tom Handegård 8 6

EU’s research programme ACTS, Eliot J Jensen 87

The CIO project, Gabriela Grolms 92

Status report from ITU-TSB Study Group 1, Service Definition, Elisabeth Tangvik 98

Future mobile communications, Ole Dag Svebak 105

UPT – Service concept, standardisation and theNorwegian pilot service, Frank Bruarøy and Kjell Randsted 109

Telektronikk

Volume 90 No. 3 - 1994ISSN 0085-7130

Editor:Ola EspvikTel. + 47 63 80 98 83

Status section editor:Tom HandegårdTel. + 47 63 80 98 00

Editorial assistant:Gunhild LukeTel. + 47 63 80 91 52

Editorial office:TelektronikkNorwegian Telecom ResearchP.O. Box 83N-2007 Kjeller, Norway

Editorial board:Ole P Håkonsen, Senior Executive Vice PresidentKarl Klingsheim, Vice President, ResearchBjørn Løken, Vice President, Market and Product Strategies

Graphic design:Design Consult AS

Layout and illustrations:Gunhild Luke, Britt Kjus, Åse AardalNorwegian Telecom Research

FEATURE:

STATUS:

Development of telecommunications in the county ofMurmansk, E N Mesjtsjerjakov 58

Norwegian Telecom’s efforts in Nort-West Russia –development of a dedicated network in Murmansk, AtleAndersen 60

Norwegian Telecom’s involvement in the Barentsregion, Svein Martin Pedersen 64

Map of Svalbard 66

The first years and messages across, Jan Hassel 67

RESEARCH

Contents:

In this issue of Telektronikk thefocus is set on the developmentand history of telecommunicationin the Arctic. Activities in threedifferent areas are reported:Greenland, where Greenland Tele-com serves a very long coastlineof this enormous island; Svalbard,with its long tradition of wirelesscommunication covering largeparts of the Arctic Ocean; and theRussian–Norwegian project forreconstruction of the telephonenetwork in the Barents area.

Telecommunications in the Arcticregion have a great potential andare increasingly important. Overthe decades there has been agrowth in capacity and servicesaccording to the technologicaldevelopment of telecommunica-tions and the demands for com-munications in the area. At Sval-bard, we offer high qualitytelecommunication services to allnations. This is to continue and beextended in accordance withdemands in the region.

The existing infrastructure and the geographical position ofSvalbard provide excellent conditions for communication viasatellites in polar orbits. Satellite passages are frequent andobservation times long. Large amounts of data can be inter-changed and transferred on-line for processing anywhere in theworld. The satellite connection up to 80 degrees latitude, whichwas established in 1969, was a technological breakthrough forgeostationary satellites – moving the limits of what was thoughtfeasible at the time.

Telecommunications to Svalbard started in 1911, when thewireless telegraph service was established and offered to allnations operating at Svalbard and the surrounding areas of theArctic Ocean. The coastal radio service is still of importance forcommunication and safety to ships, trawlers, explorers and oth-ers who travel and trade in the area.

Svalbard is sometimes referred toas an international part of Nor-way. Even though Norwegianlaws and regulations apply, theSvalbard Treaty gives rights to allcountries who have signed thetreaty to operate at Svalbard. Formore than 80 years the policy ofNorwegian Telecom has been tooffer modern telecommunicationsto everyone concerned in theSvalbard region.

In the Arctic, excellent telecom-munications is of the utmostimportance. It is provided at Sval-bard and it can be in other Arcticregions. What to do, and the gutsto do it, still often depends uponfar-seeing directors and pioneersas in former days. The digitizationof the telephone network atLongyearbyen in 1990 gave avery significant rise of quality andperformance. This was a result ofdecisions made by today’s pio-neers. There is, however, still ademand for NMT or GSM forcommercial and safety reasons.

The telecommunication technology has become fundamental toman. And man is always behind the technology. Usually, peopleare not mentioned when we report on technology, solutions,progress, development, and milestones. In this issue of Telek-tronikk we also try to highlight the daily life of those who haveserved in Arctic telecommunications through the decades.

The Arctic is still a challenge to expeditions and loners. Thanksto the development of telecommunications, today’s expeditionsare far from being as risky and lonesome as in those early dayswhen the first pioneers were travelling. A recent one-man walkto the North Pole, supported by Norwegian Telecom, is reportedhere. Pioneers still exist.

1

Guest editorial

B Y J A N H A S S E L

When Roald Amundsen reached

the South Pole on December 14,

1911, he had to wait until he had re-

turned to Hobart, Australia, on

March 7, 1912, before he could

telegraph that the South Pole had

been reached nearly three months

previously.

When Børge Ousland reached the

North Pole on April 22, 1994, after

52 days of walking across the ice

from Kapp Arktichesky in Siberia,

he could immediately inform of his

achievement via the ARGOS satel-

lite transmitter.

During the 80 odd years separating

these two events, telecommunica-

tions have advanced tremendously

and have been of great importance

to both shipping and aviation, as

well as for the development of

communications in Arctic regions

as well as everywhere else in the

world.

Telecommunications

before 1911

At the beginning of this century therewas much exploration activity in the Arc-tic regions. Journeys were undertaken tothe North Pole on skis, by plane and byair ship, as well as commercial expedi-tions searching for profits in whateverthe Arctic had to offer. The company ASSpitsbergen of Tønsberg was establishedwith a whaling station at Finneset atGreen Harbour, Svalbard in 1905.Tourism and coal industry were in theirinfancy. Vesteraalens Dampskibsselskap(steam ship company) built their ownhotel at Hotellneset in the Advent Valleyin 1896, while the American Arctic CoalCompany started extracting coal in 1906.At this time Svalbard was “No-man’sland”, and nobody had the responsibilityfor what went on there.

Until 1911 communications betweenSvalbard and the mainland was largelydone in writing, and the letters were sentby boat in the summer. The Post Officewas first established in the summer sea-son of 1897 with the post office AdventBay. More post offices appeared after awhile: Bell-Sound 1907, Green Harbour1908. Spitsbergen Radio’s telegraphmanagers took on the all year round jobof post office clerk from 1911 onwards,with an annual wage of NOK 200.

First radio contact

Svalbard – Norway 1911

Telecommunication with radio wavesstarted in the early 1900s. Norway hadthe second radio telegraph connection inthe world; that was the connectionbetween Røst and Sørvågen opened onMay 1, 1906. It was the important fish-eries in the area which prompted theopening. Not long after, radio telegraphyto ships in the open seas was started.

On May 3, 1911, the Storting (Parlia-ment) instructed Norwegian Telecom tobuild a radio station at Svalbard. Alreadyon November 22 the same year the firstradio telegraphy signals from Spitsber-gen Radio were received at Ingøy Radionear Hammerfest, and the first telecom-munications between Svalbard and themainland were established. The stationplayed a vital role when Norwegianindustry and habitation made headway inthe years to follow, and particularly inthe great polar years of the 1920s. Thatwas when the radio station was in thefocus of the entire world press. The factthat Norwegian Telecom and the PostOffice were already established at Sval-bard was one of the most important argu-ments for Norway obtaining custody ofthe whole archipelago at the peace con-ference in Paris in 1920.

Ships to and from the mining communi-ties, fishing and hunting vessels, polarexpeditions, cruise liners, weather obser-vations, post office; these were the mostimportant jobs of Norwegian Telecom atGreen Harbour radio station, in additionto contact with the mainland.

Development to

the present day

Until 1949 all radio communications toand from Svalbard were transmitted asradio telegrams; no voice communicationwas possible. A radio telephone point-to-point connection on short-wave radiowas established in 1949 between Sval-

bard Radio and Harstad Radio. Thisfinally included Svalbard in the Norwe-gian national telephone network.

In 1978 communication by satellite to themainland was established and finally, in1981, Svalbard was connected to thenational and international subscriberdialling telephone system.

The offer of telecommunication servicesat Svalbard today is the same as on themainland, with the exception of mobiletelephone – that will probably never bedeveloped at Svalbard. The telecommu-nication services have been made possi-ble via a satellite in a geostationary orbitkeeping it over the same point (some36,000 km over the equator) on earth allthe time (ref. Figure 2).

Radio wave distribution

and northern lights

When the radio technique came into pub-lic use in the inter-war years, it was soonexperienced that radio communication atlatitudes in the extreme north was verydifficult during bursts of northern lights.Radio communication over distancesgreater than 300 km are based on theatmosphere’s ability to reflect radiowaves from areas where there are freeelectrons in sufficient amounts, the iono-sphere.

Figure 2 shows the earth in relation tosatellite orbits and the atmosphere whichwe assume is some 400 – 500 km inthickness and which only makes up thethickness of the line in the circle illustrat-ing the earth. Figure 3 shows a smalldetail of the atmosphere with reflectinglayers.

The atmosphere receives enormousamounts of energy from space and fromthe sun in the form of electric particlesand radiation. Gases in the atmosphereare electrically charged and various typesand degrees of ionization occur at differ-ent heights. When the radio waves pene-trate these layers they are partly deflected

3

Telecommunications in the Arctic

B Y M A T H I A S B J E R R A N G

Figure 1 Post marks from Svalbard ca. 1900

and reflected, which we try to make thebest possible use of.

As the sun is the main ionizationcause, ionization will vary fromday to day, from season to sea-son – not least because of

solar activity. When sunspotactivity is high theradiation from thesun is high and astronger ionizationwill occur in theatmosphere. The

sunspot activity peaks app-roximately every 11 years.

When the sunspot activity isnear the peak we have good radio

conditions. The last sunspot peakwas in 1991 and we are now heading

for worse conditions for short-wave com-munications. As the sun rotates aroundits own axis in 27.5 days, the sunspotactivity will change over the same periodof time.

We divide the atmosphere into threespheres, see Figure 3. The nearest is thetroposphere, which extends some 10 km

out. This is where wefind winds, cloud for-

mations, storms andgreat variations intemperature. Thestratosphereextends between 10and 50 km from theearth, and the tem-perature here ismore or less con-stant. Long dis-tance flights nor-mally fly in thislayer. The iono-sphere extendsfrom 50 km and out

to 500 km, and as the name indicates,this is where we find the ionized layersreflecting radio waves. The lowest is theD-layer at a height of some 80 km, thenthe E-layer at about 120 km, and furthestout is the F-layer, which we have divided

into the F1-layer at about 200 km and theF2-layer between 300 and 400 km fromthe earth. This is the daytime status, butafter dark the influence from the sunceases; the D- and E-layers disappear andthe F1- and F2-layers merge into onelayer at a height of some 250 km.

Figure 4 shows how transmitted radiowaves are reflected in the ionized layers.Space waves at high frequencyVHF/UHF/SHF are normally notreflected, but pass right through and dis-appear into space. Space waves in the 1 –5 MHz frequency will, in the daytime,first hit the D-layer which absorbs andreflects these frequencies. Strong solaroutbursts may lead to the D-layer becom-ing so strongly ionized that all signals areabsorbed. What we call SID (SuddenIonospheric Disturbance) then occurs,and we may have a total break-down inradio communications. SID may lastfrom a few minutes to several hours. TheF1-layer destroys some of the wave dis-tribution by absorbing radio waves whichotherwise would have been reflected inthe F2-layer. The F2-layer naturallyextends furthest, as it is on the outside.

In the Arctic there are areas of northernlights which consist of ionized air causedby electron bombardments in the earth’smagnetic field. There is a close linkbetween solar outbursts and northernlights / aurora. The northern lights occurat a height of some 80 – 110 km, and inthe daytime they are in the same heightas from the D-layer and nearly as high asthe E-layer. At night, they are also in the80 – 110 km area and almost “replace”the D- and E-layers, and only have themerged F1/F2-layer above. Radio signalsreflected from the northern lights belt arestrongly distorted and difficult to read.Telegraph signals sound like a pulsatingcrackle.

Figure 5 shows the degree of disturbancesfrom the northern lights zone with Roga-land Radio in the centre of an azimuthmap. Because of Rogaland Radio’s loca-tion close to the northern light zone, sev-eral areas will be disturbed. This mainlyapplies to connections along the border of

the northern light zone in thesector 20 – 40 degrees east, andalong the border of the sector280 – 320 degrees west. Secon-

4

Figure 2 The Earth with atmosphere and

satellite orbits

Figure 3 The atmosphere and reflecting

layers

Figure 4 Various paths between transmitter and receiver

Geostationarysatellite orbit

Satellites inlow orbit

Earth

Earth'satmosphere

0 20 000 40 000 km

400

300

200

100

0

Ionosphere

Stratosphere Troposphere

Earth

Heigth above Earth (km)

F2-layer

F1-layer

E-layer

D-layer

Day Night

F1/F2

Earth wave Dead zoneTransmitter

Spacewaves

Dead zone

One jumptransmission

Two jumptransmission

Receiver

darily, it applies to connections throughthe northern light zone in the sector 320degrees west to 20 degrees east.

Outbursts of aurora may be predictedwith a high degree of certainty, becausesudden bursts of solar activity are accom-panied by ejection of charged particlesfrom the sun. They travel in variousdirections, and some enter the earth’satmosphere, usually 24 to 36 hours afterthe event. When the solar particles enterthe earth’s atmosphere, they may reactwith the magnetic field to produce a visi-ble or radio aurora, the former if theirtime of entry is after dark. The visibleaurora is in effect fluorescence at E-layerheight – a curtain of ions capable ofrefracting radio waves in the frequencyrange above approx. 20 MHz. D-layerabsorption increases on lower frequen-cies during auroras. The exact frequencyrange depends on many factors: time,season, position with relation to theearth’s auroral regions and the level ofsolar activity at the time, to name a few.

Before I was hired for the job of respon-sible for communications for Radio 1’sNorth Pole expedition in 1993, the plan-ners thought it would be possible to usesatellite communications from the NorthPole directly to Radio 1’s studio in Oslo.The aim of the expedition was to cele-brate their 10 years anniversary bybecoming the first commercial radio sta-tion in the world to transmit directly fromthe North Pole.

Following my briefing on radio condi-tions in polar areas, one of the recurringquestions from my employer was “Canyou guarantee our radio connection withthe North Pole?” Naturally, I could not,but as we got nearer to departure for thePole and I had studied the propagationforecasts as well as aurora status for dateof landing, I indicated a 70 – 75 %chance of a connection. Luckily, I wasnot mistaken. Two days later I attemptedto do some amateur radio operation onshort-wave from Resolute Bay, but atthat time aurora conditions were bad, andthe result was poor.

On our North Pole expedition we used ashort-wave radio with a 600 Watts trans-mitter, inverted V dipole antenna and atransmitting frequency of 12.3 MHz viaRogaland Radio, and from there by tele-phone to Radio 1’s studio. We transmit-

ted directly for twohours and had acceptableconditions for about 80 %of transmission time.

During 1994, I madeagreements with twoNorth Pole expedi-tions to be theircommunication linkat Svalbard: BørgeOusland, who set outalone from the Rus-sian side, and theNAPE expedition(Mørdre & Co) fromthe Canadian side.Both expeditions hadthe same type ofshort-wave radio equip-ment (Racal BCC 39Bwith 50 Watts), the sameantenna and the same type ofLithium batteries (24 Volt 15 Ah). Iwas in contact with the NAPE expeditiononly once, while they were in trainingcamp at Frobisher Bay on Baffin Island,plus once from Eureka after they hadabandoned their expedition. I was in con-tact with Børge Ousland twice a weekduring the whole of his 52 day trip.

5

Figure 5 Degrees of disturbance from

the Northern Light zone

Less thanmaximum

0

maximum

maximum

much

much

less

least

less

20

40

60

90120

180

220

250

280

300

320

Sometimes conditions were so good thathe could have radio telephone conversa-tion of acceptable quality via SvalbardRadio with his family and his spokesman.

Figure 6 Børge Ousland in Sibiria, testing the radio equipment before setting out

Ph

oto

: Ma

thia

s B

jerr

an

g

The distances from Svalbard to bothexpeditions were largely the same, some1,300 – 1,400 km in a straight line. Whywere conditions reasonably good east-ward from Svalbard, while radio contactwestward from Svalbard was ratherpoor? We tried various frequencies atvarious times of the day and night, butnothing worked towards west, onlytowards east did we obtain contact. In myown time north of the Arctic circle withover 60,000 logged radio amateur con-tacts, I have experienced that when the

northern lights are in the south-west ordirectly overhead, contact eastward toJapan, Australia etc. is fairly easilyobtainable, but westward towards theUSA is almost impossible. When thenorthern lights are overhead or east ofSvalbard, contacts are difficult in alldirections. However, we may sometimeshave reflections from the northern lightsso that radio contact is possible to north-ern Norway, but these contacts are not tobe trusted because the northern lightsoften move at great speed and thereby the

reflection point changes constantly andthe contact is cut off. During long-lastingand strong northern lights we may atSvalbard experience total black-outs onall short-wave bands. This condition maylast for several days, and before Svalbardhad its satellite connection, we couldonly obtain contact via radio telegraphyto Norway on very low frequencies(about 150 kHz) under such conditions.

As will be known the northern lightsoccur in a ring around the North Mag-netic Pole in Canada. The NAPE expedi-tion was always some 800 km north ofthe North Magnetic Pole, while Ouslandwas some 2,600 km west of the NorthMagnetic Pole, which is probably the rea-son why he was less troubled by northernlights, although they were occasionallyvisible in the west.

Satellite communications have madegreat progress since first taken into use in1962. The maximum range for satellitesin geostationary orbits is 80 degrees northand 80 degrees south, but that requires thedown-link equipment in these areas to beconnected to a very large and fixedreflective antenna. At Isfjord Radio, Sval-bard, just over 78 degrees north, theantenna is 13 metres in diameter. AtEureka, Canada, near 80 degrees north,the antenna is 25 metres in diameter, butstill the military base at Alert, some 83degrees north, has a satellite connectionbecause radio relay is used (betweenAlert and Eureka) placed on the highestmountains on the Ellesmere Island. Shipsin Arctic areas with satellite equipmenton board often have difficulties commu-nicating via INMARSAT; the furthernorth they get, the poorer the connectionnaturally becomes.

Satellites in low polar orbits are todayused for navigation, positioning, etc.Some time in the future it may becomepossible to cover the whole of our planetwith satellite connections, but to date thisis not possible. Arctic communicationsare still dependent on short-wave com-munications and probably will be for along time yet. The arguments againstsatellite coverage are hardly of a techni-cal kind, but rather that this type of com-munication has little economic use, asthere are very few people north of 80degrees north and south of 80 degreessouth.

6

Figure 7 EUREKA weather station 80° 00’ N 85° 56’ W

Figure 8 Radio tent on the North Pole

Mathias Bjerrang is Head of SvalbardRadio, Longyearbyen.

Ph

oto

: Wa

yn

e E

mo

nd

/Ka

wa

rth

a P

ost

Ca

rd C

o.

Ph

oto

: Ma

thia

s B

jerr

an

g

7

Figure 9 Børge Ousland on his lonely trip to the North Pole

Ph

oto

: Kje

ll O

ve S

torv

ik /

Bre

vig

Fo

rla

g a

s

8

Measurements of atmospheric effects on satellite links

at very low elevation angle

B Y O D D G U T T E B E R G

This article is a reprint of a report

published in 1984. It describes ex-

periments and results obtained

from propagation measurements

with the Orbital Test Satellites

(OTS) at the Arctic islands of Spits-

bergen (78° N). The elevation angle

to the satellite was 3.2° and the

frequency 11.8 GHz.

The experiments carried out

included measurements of atmo-

spheric scintillations, cross-polari-

sation discrimination and space

diversity improvements. The mea-

surements showed that the distri-

butions of the received satellite

beacon amplitude can be approxi-

mated by Rice-distributions. Large

diversity gain was obtained by

using horizontal spacing of 1 km. A

wide-band (TV) transmission

experiments was also performed

with good result.

1 Introduction

One of the prime parameters in geosta-tionary satellite system design is the mar-gin in signal level needed to take accountof signal attenuation by the atmosphere.At present, attention is focused on theknowledge of climatic variations and theinfluence of elevation angle on signalattenuation and cross-polarisation at fre-quencies above 10 GHz (1).

A considerable amount of data has beencollected on attenuation and cross-polari-sation statistics, measured at mid-lati-tudes. However, relatively little is knownon the characteristics of low-elevation

paths to high-latitude stations, such asstatistical properties of the fading, sea-sonal variations, cross-polarisationdegradation and possible space diversityimprovements.

To gain knowledge of these characteris-tics, propagation experiments at 11 GHzhave been performed at Isfjord Radio,Spitsbergen (78°N, 13.6°E), Figure 1,using the Orbital Test Satellite (OTS).

The different experiments were con-ducted during the period from April 1979to August 1982. Some of the results havebeen presented earlier (2).

Isfjord Radio

Gre

enla

nd

Svalbard

Pack-ic

e limit

70o N

OTSα=183.8o

ε=3.2o

20oW70

o N0o

20o E

80o N

Nor

way

Location: Isfjord Radio, Spitsbergen

Coordinates: 13.64°E / 78.06°N

Elevation angle (OTS, 10°E): 3.2°

Azimuth angle (OTS, 10°E): 183.8°

Station type:

Station parameters A B Units

Beacon frequency 11.786 11.575 GHz

Polarisation Circular Linear

Antenna system

Antenna type Cassegrain Cassegrain

Diameter 3 1 metre

Gain 49.5 39.6 dB

Beamwidth 0.6 2.0 deg

Cross-polarisation isolation > 35 - dB

De-icing power 8 none kW

Receiving system Copol Xpol

Clear sky signal level

at receiver input ~-104 ~-139 ~-123 dBm

G/T 20.5 24.7 11.6 dB

Noise temperature 800 300 630 °K

Level detector type PLL PLL PLL

Locking range ±200 ±200 ±40 kHz

Dynamic range ~20 ~25 ~15 dB

Post detection bandwidth 10 1 1 Hz

Data acquisition system

Sampling rate 10 1 2 Hz

Tape recorder Tandberg TDC-3000 Tandberg TDC-3000

Strip chart recorder Gould 816 hp 7130A

Table 1 Stations characteristics

Figure 1 Location of the experimental site, Isfjord Radio,

78°N, 13.6°E. Elevation and azimuth angles are given for

OTS positioned at 10°E

Figure 2 Plots of co- and cross-polar signals at Isfjord

Radio, 25 July 1979. XPD ≈ 38 dB

Copolar

Crosspolar

25 July 1979

5 min

1000 GMT

2 dB

9

2 Description of

experiments

The OTS satellite is positioned at5°E (until 14 April 1982 at 10°E),which means that the satellite isalmost seen at the maximum ele-vation angle from Isfjord Radio.The geometric elevation angle is3.2°, with an average ray bendingof 0.2°. Assuming a troposphericheight of 8 km, the ray propagatesthrough more than 120 km of thetroposphere. One should thereforeexpect the received signal to beinfluenced by scattering andreflections due to turbulent airmasses. At this very low elevationangle, temperature inversionscould also cause duct transmis-sions.

The first experimental earth sta-tion was put into operation inApril 1979, receiving both the co-and cross-polar components of the11.8 GHz circularly polarised satellitebeacon. The station was equipped with a3 metre Cassegrain antenna and phase-locked receivers. The station characteris-tics are summarised in Table 1 (stationA).

During the spring of 1982 two additionalsmall earth stations for site diversitymeasurements were installed. The twoequally small OTS terminals were receiv-ing the linear polarised telemetry beaconat 11.6 GHz. The stations were equippedwith 1 metre Cassegrain antennas andphase locked receivers. Other stationcharacteristics are given in Table 1 (sta-tion B).

Low angle space diversity measurementsperformed in Arctic Canada at 6 GHz(3,4) showed poor diversity gain withhorizontal spacing up to 500 metres. Inour experiment it was therefore decidedto use a spacing of more than 1 km.

For a further investigation of the scintil-lation phenomena, an acoustic sounder(SODAR) were used during the diversityexperiment at Spitsbergen in the summerof 1982. The SODAR was placed almostunder the beam, 7 km away. Thus theradio and the acoustic beams intersectedat an approximate height of 450 metres.

The beacon measurements at Spitsbergenin 1979 and 1980 showed large scintilla-tions of the received signal. However,there existed little knowledge of the pos-sible coherent bandwidth that could bereceived at such a low elevation angle.Therefore a wide band experiment wasperformed during July 1982. A fre-quency-modulated TV signal with27 MHz bandwidth was transmitted viaOTS and received at Isfjord Radio. Thereceive earth station used in this experi-ment was a modified version of stationA, Table 1.

3 Experimental results

3.1 Atmospheric scintillations

Due to variations of the temperature andhumidity within small volumes of theatmosphere, the refractive index profilewill, at certain heights, depart from itsnormal exponential decay. This maycause bending, scattering and reflectionsof the ray. At very low elevation angleone should therefore expect the receivedsignal to be heavily influenced by turbu-lent air masses.

Figure 2 shows an example of therecorded co- and cross-polar signals atIsfjord Radio. This is a typical plot of the

signal variations (scintillations) duringthe Arctic summer months (July/August)with peak-to-peak variations around5 dB. A compressed time plot of thereceived signal for an 87 hours period, isshown in Figure 3.

In Figures 4 and 5 are shown the cu-mulative amplitude distributions of thescintillations. As seen, there are largeannual variations. During the Arctic win-ter (October–May), maximum fadingsare only about 5 dB. This is alsoexpected since the atmosphere is quitestable during the Arctic winter. However,in summer, deep fadings up to 20 dB areexperienced. This may be due to highrefraction index gradients.

The distribution for July/August 1979 iswell above the distributions for the sum-mer period 1980, probably due to theexceptional high mean temperature(7.6°C) during July 1979. The 30 yearJuly average is 4.9°C.

It would have been of great help for theplanning of earth stations in the Arctic, ifone could find a correlation between thefading level and a simple meteorologicalparameter, e.g. the ground temperature.

In Figure 6 is plotted the fading level at99.99% availability versus the mean tem-

Figure 3 Time-plot for OTS-I and OTS-II

Start: 25 July 82, 0500 GMT Stop: 28 July 82, 2045 GMT

Recording time: 5265 mins Sampling: 2 samples/sec

Smoothing: 5 sec Each: 100 points

+6

-3

26. July 82 27. July 82 28. July 82

Period with temperatureinversion

OTS - I

OTS - II

Time (hours)

amplitude (dB)

+3

-6

0

0 15 30 45 60 75 87

+3

0

-3

10

perature for each month. Thereseems to exist a strong dependencybetween the scintillations, at a certainreliability level, and the monthlymean ground temperature (or N0). Toa certain extent, we are therefore ableto predict the fading level, knowingthe mean ground temperature.

The received signal will consist of adirect one plus a scattered signal dueto turbulence activity. If we assumethat the scattered field consists ofseveral components with randomamplitude and phase, then the result-ing signal distribution could be de-scribed by a Rice-distribution, i.e. aconstant vector plus a Rayleigh dis-tributed vector.

Rice-distributions with different val-ues of K, where K is the ratio ofpower in the random component rel-ative to the steady component, havebeen drawn in Figure 7 together withthe monthly and “worst day” distri-butions. It is seen that the “worstday” distributions fit quite well aRice-distribution with K = -10 dB.The monthly distributions, which is asum of Rice-distributions with vary-ing standard deviations, will gener-ally not be a Rice-distribution. Thisis especially the case for large valuesof K, i.e. the summer months. If thescattered components, however, issmall relative to the direct compo-nent, the distribution will be similarto a Normal-distribution. Therefore,the distributions for the wintermonths will closely follow Rice-dis-tributions with small values of K.This supports the assumption that thereceived signal consists of one directcomponent and several scatteredcomponents, and that the fadings arenot due to beam bending effects.

Looking at the corresponding record-ings from the OTS receivers and theSODAR, one can see that the largepeak-to-peak values of scintillationsare clearly associated with the exist-ence of temperature inversions atabout 200 metres above sea level.During periods when no temperatureinversions were detected, the scintil-lations were much smaller. Figure 8shows an example of recordings fromthe SODAR, and the correspondingrecording of the beacon signal. We

1979

f = 11.8 GHz, Circular polarisationε = 3.2o

( ) = Number of registration days

OTS, Isfjord Radio

Precentage of time abcissa value is exceeded

100

10

1

0.1

0.01

0.001

0 2 4 6 8 10 12 14

April(29)

May (25)

Nov (18)

Des (22) Sep/Oct (23)

June (15)

July/Aug(20)

(dB9 att

1980

f = 11.8 GHz, Circular polarisationε = 3.2o


OTS, Isfjord Radio

Precentage of time abcissa value is exceeded

100

10

1

0.1

0.01

0.001

0 2 4 6 8 10 12 14

June (30)

July (31)

Aug (28)

July 82(16)lin.pol.

11.6 GHZ

DiversityJuly 82(16)

Lin.pol.11.6 GHZ

(dB9 att

Figure 4 Cumulative distributions of scintillations

(1979)


(1980 and 1982) and diversity (1982)

1979

1980

FAD (dB) at 99.99% reliability

12

8

4

-20 -16 -12 -8 -4 0 4 8

Apr

Dec

Sep/Oct

Nov

May

June

June

Aug

July

July/Aug

Monthly mean temperature (oC)

Figure 6

The fading

level at

99.99% of

time versus

monthly

mean

ground

tempera-

ture

can see two temperature layers aboveeach other. When they disappear atapproximately 1330 GMT, the signalvariations drop from approx. 6 dB peak-to-peak, down to less than 1 dB peak-to-peak. Another example is shown in Fig-ure 3, where a temperature inversionlayer at 200 metres height existed from0720 – 1220 on 27 July 1982.

3.2 Cross-polarisation due to

sleet and snow in the path

Cross-polarisation measurements wereonly systematically done during the sum-mer months of 1979 at Spitsbergen.

Figure 1 shows a recording of the co- andcross-polar signals on 25 July 1979 atIsfjord Radio. As seen, the scintillationsof co- and cross-polar levels are equal.This is generally the case, and there is nodegradation of the XPD. However, dur-ing overcast and sleet/ snow in the path,the XPD becomes worse. In Figure 9 isshown the cumulative distributions of thecross-polarisation discrimination. Alsofor the XPDs the summer months are theworst months.

The resulting distributions of attenuationand XPD for the period May– August1979 have been calculated. Using thesedistributions, the XPD value correspond-ing to the co-polar value for the sameprobability level, has been plotted in Fig-ure 10. It is seen that there seems to exista statistical relationship between theattenuation (ATT) and cross-polarisationdiscrimination (XPD) due to sleet/snowin the path, given by the equi-probabilityequation:

XPD (dB) = 27 - 8 lg ATT (dB)

3.3 Space diversity

For investigation of the space diversityimprovement, two “mini”-OTS terminalswere installed at Isfjord Radio in thesummer of 1982, receiving the linearpolarised telemetry beacon from OTS.One terminal was located at the radio-station (OTS-I) and the other (OTS-II)with a horizontal separation of 1,150metres, see Figure 11. The vertical sepa-ration was approximately zero. The mea-suring period was from 14 July to 2August 1982.

The acoustic sounder (SODAR) was putup under the beam of the OTS-II termi-nal, thus the acoustic radar and the earth

station were“seeing” a com-mon volume ofthe atmosphere.

Examples ofthe receivedsatellite signalsfrom the twostations areshown in Fig-ures 3, 8, and12. In Figure12, where thepaper speed is4.5 cm/min, wecan clearly seethat the shorttime variationsof the signalsare uncorre-lated. The sig-

11

16

14

12

10

8

6

4

2

0100 10 1 0.1 0.01

Att (dB)

K (d

B)

Precentage of time ordinate value is exceeded

April 79 (29)May 79 (25)June 79 (15)July 79 (14)Sep/Oct 79 (23)Nov 79 (18)Dec 79 (22)June 80 (30)July 80 (31)"worst day" 1979, 16th July"worst day" 1980, 1st July


Power in random componentPower in steady component

K =

OTS-I

OTS-II

Sig

na

l le

vel

2 d

B

He

igh

t (m

)

400

300

200

100

Temperature inversions

Time 19 July 1982 1330 GMT1 hour

Figure 8 Recordings of the signal levels from OTS-I and OTS-II and corresponding SODAR registra-

tion. Isfjord Radio, 19 July 1982

Figure 7 Rice-distributions for different values of K. Measured distributions

are plotted

nals were also recorded digitally on mag-netic tapes, and cumulative distributionsof the signal levels, both for each stationand for the site diversity system were cal-culated. The 87-hour period shown inFigure 3 is representative for the wholemeasuring period. The cumulativedistributions for this period is shown inFigure 13.

The single site distributions (OTS-I andII) are almost identical, as the scintilla-tions are random by nature, whereas asubstantial site diversity improvement isachieved. For example at a 3 dB fadinglevel, the single site reliability is 99%,

12

Figure 9 Cumulative distributions of

cross-polarisation discrimination, 1979

Figure 10 Statistical relationship be-

tween attenuation and cross-polar dis-

crimination

Transmit station: Goonhilly Downs, England

Receive station: Isfjord Radio, Spitsbergen

Frequencies

up/down: 14262.5/11600.0 MHz

Satellite: OTS, 5°E

Transponder: Channel 4 bar (saturated), gain step 7

Modulation: FM, frequency deviation 13.5 MHz/V,

energy dispersal 1.2 MHz peak-peak

EIRP (sat) 47.5 dBW (1)

Aspect angle loss 6.8 dB (2)

Down path loss 206.1 dB

Atmospheric absorption 1.0 dB (3)

Earth station G/T 24.0 dB (4)

Pointing loss 0.1 dB

Up-link noise 0.2 dB

Total link C/T -142.7 dBW/K

Receiver BW (27 MHz) 74.3 dBHz

C/N at receiver 11.6 dB

Notes:

(1) Beam centre EIRP; OTS report on in-orbit measure-

ments vol 1; p255 and 219.

(2) With OTS at 5°E, re-orientated in pitch bias by 0.4°,

ref Interim EUTELSAT, private correspondence.

(3) Calculated using equivalent height of oxygen 6 km

and water vapour 1.5 km, ref CCIR report 719, Geneva

1982.

(4) Measured value, assuming an antenna noise temper-

ature (clear sky) of 100°K and an antenna gain of 49

dB.

Table 2 Link budget, OTS-Spitsbergen

July/aug

June

May

April

100

10

1

0.122 26 30 34

XPD(dB)

Precentage of time abscissavalue is exceeded

July/Aug

1 2 4 6 8 10

20

24

28

XPD(dB)=27.3-7.6 log ATT(dB)

Copolar attenuation (dB)

Crosspolar discrimination (dB)

OTS, Isfjord Radio

PeriodFrequencyPolarisation

: Apri l- August 1979: 11.8 GHz: circular

and the site diversity reliability is99.92%.

The distributions for the total measuringperiod (17 July – 2 August 1982) isshown, together with the other distribu-tions, in Figure 5. Since the distributionsfor OTS-I and II are almost identical,only one single site distribution is plot-ted. Again it is seen that at a 3.2 dB fad-ing level the availability improves from99% to 99.9%, due to site diversity.

3.4 Wide-band transmission

As previously mentioned, little knowl-edge exists of the characteristics of selec-tive fading at very low elevation angle.Comprehensive measurements of selec-tive fading could be done by using multi-or swept frequency techniques. However,due to the limited time for planning andperforming such experiments, it wasdecided to perform a direct experiment,involving the reception of a wide-bandsignal (FM-modulated TV signal) atIsfjord Radio. As previously shown, themost severe fading is confined to the Arc-tic summer months. Accordingly, thisexperiment was conducted during July1982.

The transmit station was GoonhillyDowns in England. A frequency modu-lated TV signal (PAL) saturated one ofthe wide-band transponders of OTS to

give a receive frequency of 11.6 GHz.The frequency deviation used was13.5 MHz/V and receive filter bandwidthwas 27 MHz. The link budget is given inTable 2.

Due to the signal scintillations, thereceived C/N-ratio had large fluctuations.On 20 July 1982 the following valueswere measured between 2110 and 2225GMT:

C/Nmax = 12.3 dB

C/Nmin = 8.7 dB

The TV transmissions took place 13–23July, approximately 3 hours per day, con-taining colour bars, pulse and bar andvideo film sequences. Two hours wererecorded on video tape. The picture qual-ity was judged to be fair (Q = 3), andfrom observations of the colour bar spec-trum, there seemed to be no severe selec-tive fading during the experimentalperiod.

4 Conclusions

In polar areas with low elevation angle(< 5°) the predominant type of fading isscintillation. The fading seems to becaused by a combination of scatteringand reflections from turbulent air masses.Deep fadings are, however, associatedwith temperature inversions in the atmo-sphere. The monthly distributions of thescintillations can be approximated byRice-distributions with average values ofthe power ratio of the random component

to the steady component of -20dB, -13 dB and -10 dB for thebest month, worst month, andworst day, respectively.

At very low elevation angle,large improvement by usingspace diversity can be obtained.With a horizontal separation ofthe two stations of app-roximately 1 km, the availabilityis increased from 99% to 99.9%at a 3 dB fading level.

In areas with little rain, as thepolar areas, cross-polarisationdue to sleet and snow in the pathmay be the most dominanteffect. In the measurements atSpitsbergen, a statistical relation-ship (equi-probability equation)between attenuation (ATT) andcross-polarisation (XPD) werefound.

XPD (dB)= 27 - 8 lg ATT (dB)

Selective fading over 27 MHzbandwidth was not observed atSpitsbergen, and reception offrequency modulated satelliteTV signals down to elevation angles of atleast 3° is possible with good quality.

5 Acknowledgements

The author expresses his sincere appreci-ation to M Osmundsen for valuableassistance with all parts of the experi-mental work; to the staff at Isfjord Radioand Goonhilly Downs for excellent co-operation, and to the National Meteoro-logical Institute for supplying the meteo-rological data. Thanks also to T Tjelta,N Åtland and T Heggelund for assistancewith analyzing the site diversity data.

Part of the work described was doneunder contract with European SpaceAgency, ESTEC Contract No 5032/82NL/GM(SC), technical management byG Brussaard.

6 References

1 CCIR. Propagation in non-ionizedmedia. Geneve, 1982. (CCIR Vol V,Report 564-2.)

2 Gutteberg, O. Measurements of tro-pospheric fading and cross-polarisa-tion in the Arctic using Orbital TestSatellite. IEE Conf. Publ. (Antennasand Propagation), No. 195, Part 2,71–75, 1981.

3 Strickland, J I. Site-diversity mea-surements of low-angle fading. 19thGeneral Assembly of URSI, Helsinki,Finland, 1978.

4 Strickland, J I. Site-diversity mea-surements of low-angle fading andcomparison with a theoretical model.URSI Commission F InternationalSymposium, Lennoxville, Quebec,1980.

13

Figure 11 Geometry of the space diversity experi-

ment at Isfjord Radio, 1982 (OTS 5°E). Both sta-

tions’ heights above sea level: 7 metres


for single sites (OTS-I and OTS-II) and the diver-

sity system.

Period: 25–28 July 1982 (5265 mins)

Time-plot for the same period is shown inFigure 3

Signal level

2 d

B

Time1631 GMT

1 min

OT

S-I

OT

S-I

I

OTS-I

OTS-II

0 dB OTS-I

0 dB OTS-II

100

10

1

0.1

0.01

0.001

0.00013 12 0 -1 -2 -4-3 -5 -6

Fading (dB)

Percentage of time

OTS-Isfjord1982

OTS-I

OTS-II

Diversity

Figure 12 Registration of the linear polarised beacon

from OTS. Space diversity experiment, Isfjord Radio,

14 July 1982

Odd Gutteberg is a Senior ResearchScientist working for the Satellites unit ofNorwegian Telecom.

14

NORSAT – Isfjord – a satellite station in the wilderness

B Y M A R T I N J A R L L O D E A N D J O H N R V E A S T A D

This article was first published in

Telektronikk in 1981. The reprint

gives a short historic back-view of

a technology that has become the

most important in long distance

telecommunications throughout

the world.

1 Introduction

Norwegian Telecom today operates anearth station at Isfjord Radio at Svalbard(Spitsbergen). The earth station is a partof the NORSAT system. This article isan explanation to the background for thesatellite station and how it was built.

2 The NORSAT system

When the oil companies drilling in theNorth Sea started to establish produc-tion platforms it became clear that con-ventional radio connections could notcover their communication needs. Theplatforms would need telephone, telex,telefax and transfer of data. Theywould also require a high level of relia-bility – 99.9 % or better. As distancescould vary between 150 and 600 kilo-metres there were only two possiblealternatives that could meet theirrequirements:

- troposcatter- satellite system.

Norwegian Telecom chose a satellitesystem. In the long run this would bethe least costly alternative, it is adapt-able and there was a recognition of thepossibilities for connecting Svalbard tothe automatic telephone network inmainland Norway. This was in 1974.

NORSAT employs half a transponderin one of INTELSAT’s satellites. Nor-wegian Telecom leases the halftransponder on a “preemptible basis”,i.e. INTELSAT may shift NORSAT’sallotted space around as INTELSAT’sprimary services need satellite capac-ity. The main station in the system is atEik in Rogaland. The system employsdelta modulation of the speech signals,so that necessary capacity for a tele-phone channel is 32 kbit/s. The digitalinformation then modulates the phaseto a carrier, 2-PSK. Each channel hasits own carrier, i.e. SCPC (SingleChannel Per Carrier), and the carrier isswitched on only when speech takesplace – speech activation. The effect ofthe NORSAT system is limited, with acapacity of 130–150 telephone chan-nels (two-way). At present, 38 two-way telephone channels are in use.

Operation statistics so far have shownthat the earth stations in the satellite sys-tem have a mean accessibility of

- Eik 99.96 %- Ekofisk 99.89 %- Frigg 99.56 %- Statfjord 98.91 %.

We note that the remote stations have arelatively low accessibility. In manycases, interruptions in accessibility havebeen caused by conditions related to thedrilling operation. On some occasions,drilling mud has got into the antenna sothat it had to be cleaned.

3 Telecommunications

with Svalbard

The archipelago of Svalbard obtainedtelecommunication connections withNorway in 1911 when Spitsbergen Radioat Green Harbour dispatched their firsttelegram to the mainland. In 1930 thestation was moved to Longyearbyen, andIsfjord Radio was built in 1933.

Public telephone traffic was opened inthe spring of 1949. The connection haspreviously been based on short-wavecommunication. The transmitter andreceiver plant at Svalbard has beenlocated at Longyearbyen and, since 1975,also at Isfjord Radio at Kapp Linne.From 1975 the capacity has comprised:

- 3 telephone connections- 4 telex channels.

Longyearbyen has some 1,000 inhabitantsand the local telephone network, which isowned and run by Store Norske Spitsber-gen Kulkompani AS, has approximately450 subscriber lines. Trunk trafficbetween Svalbard and the mainland hasbeen operator handled.

Telecommunications between Svalbardand the mainland can be said to havebeen unsatisfactory. Svalbard is so farnorth that radio signals have to travelthrough the so-called northern light belt.This produces disturbances in the distri-bution conditions for the signals, so thatlong break-downs may occur. Even ifNorwegian Telecom constantly haveimproved the technical equipment forshort-wave communications, the qualitycannot be improved beyond certain lim-its. These limits are given by nature, andare determined by the location of thearchipelago and ionospheric conditions,among other things. As a consequence ofthese disturbances the short-wave con-nections cut out for 10 % of the time. In

Figure 1 Block diagram of the NORSAT system

Figure 2 Isfjord Radio

Ph

oto

: No

rwe

gia

n T

ele

co

m M

use

um

15

the worst cases these “cut-outs” may lastfor several days. The result used to behour-long waits, either because of over-load, or because of poor radio connec-tions.

While a similar mining community inNorway, Sulitjelma, in the 1970s had 20reliable connections to the national tele-phone network, the Svalbard communityhad three connections of varying qualityat their disposal. The fact that this did notlead to strong reactions had several rea-sons. In the years 1911–1949 the onlyform of communication was by telegram.When the telephone connection wasopened in 1949 it was seen as a tremen-dous step forward. The effort and will ofthe telecom personnel to utilize the con-nection in the best possible way may alsohave contributed, most important,though, was the fact that the customersthemselves had a down-to-earth attitudeand great understanding for the limitedpossibilities available. In 1975 this atti-tude changed. Much of the reason for thiswas the knowledge that permanent con-nections of good quality could be estab-lished via NORSAT. Store Norske Spits-bergen Kulkompani had for years urgedNorwegian Telecom to provide moderncommunications. So had the fishing fleet,as fishing activities around Svalbardwere increased in the 1970s and therebythe needs for communication with themainland. In 1975 an airport was builtwhich required access to the telephonenetwork on the mainland and permanentdirect connections to other locations inthe air traffic service. On the basis ofthis, Norwegian Telecom assumed thatthere was a need for a radical increase inthe number of connections to Svalbard.There were three alternatives:

I Troposcatter with an intermediatestation on Bear Island

II Increase the number of short-waveconnections

III Establish connection via NORSAT.

For economic and operational reasons thetroposcatter alternative was abandonedquite early on, and a comparison betweenthe two remaining alternatives showedthat handling the traffic with the help ofshort-wave communication offered a farpoorer solution because it was quitecostly, waiting would be longer, and thedegree of service would be lower. Theshort-wave connections have poorer

speech quality and reliability.Because of the very few avail-able frequencies the possibili-ties for capacity expansion arevery limited. Last, but not least,the telephone and telex servicescannot be automated with themainland.

4 Problems

connected to

building an earth

station at Sval-

bard

Even if the satellite alternativewas the most favourable, a fewproblems were foreseen in con-nection with building an earthstation at Svalbard.

Isfjord is located at 78° 04' Nand 13° 38' E. This implies thatthe antenna at best has an ele-vation angle of 3° towards ageostationary satellite. Becauseof the location of satellites thestation ought to be able to oper-ate with an elevation angle aslow as 1°. Geostationary satellites arenormally not employed for elevationangles smaller than 5°. Consequently,there was little documentation availableon the expected distribution conditions.The signals from the satellite have a longdistribution path through the atmosphereand are exposed to atmospheric attenua-tion, refraction and fading. These wereconditions that had to be quantified.

In the summer of 1974 Norwegian Tele-com demonstrated that it was possible touse satellite connection for telephony.This was achieved by establishing a con-nection between Tanum and Svalbardwith the help of a small, mobile earth sta-tion at Isfjord. Measurements were car-ried out at this station for two consecutivesummers – 1974 and 1975. In 1975 thedistribution measurements were expandedand Norwegian Telecom erected anexperimental station with an antenna 4.5metres in diameter. These measurements,which were then started in 1975, lasteduntil April 1980. Tracking signals fromthe Symphonie satellite and from one ofthe INTELSAT satellites were used. Inthis way, two elevation angles were mea-sured: 3° and 1.7°.

At an elevation of 1.7° the atmospherecauses a refraction giving a directionalerror less than 0.03°. At elevation angleslarger than 1° the deflection is approxi-mate to a linear function of the refractionindex measured on the ground. Therefraction index is dependent on meteo-rological parameters, e.g. temperature.As it is fairly cold at Isfjord, sufficientdirection accuracy can be achieved byletting a basic microcomputer steer thedirection of the antenna. Antenna steer-ing at Isfjord will take place accordingto:

- manual steering

- program steering

- step track (at times this is unsuitablebecause of fading).

The atmospheric attenuation is also verydependent on temperature. On the basisof temperature measurements carried outat Isfjord, atmospheric attenuation wasestimated at approx. 1.5 dB at 1° eleva-tion. The biggest obstacle was assumedto be the fading conditions. As a conse-quence of temperature and dampnessfluctuating considerably within smallvolumes of the atmosphere, the signal is

Histogrammet viser % av tidensom signalstyrken ikke går under viser terskelverdier.Elevasjonsvinkelen er 1.7o

Signalstyrke rel. referense (dB)

12

10

8

6

4

2

0

juni juli august november desembertid

99%99.9%99.99%

Figure 3 Diagram of the fading conditions at Isfjord during a time

span of five months

16

deflected, scattered and reflected. Thesignal that reaches the antenna will con-sist of the direct and the scattered signal.Depending on phase and amplitude con-ditions of the scattered signal, rapid vari-ations in the received signal level mayarise. Fading conditions are, as expected,

worst during the summer months.The collected volumes of data arebeing studied, but there has been anearly indication that it was possibleto obtain 99 % accessibility on thedown-link with a fading margin ofapprox. 4 dB at 1.7° elevation.

Up-link fading is another problem –it may be solved by varying theeffect from the antenna in relation tofading: up-link effect control.

Access to Isfjord Radio is by boat inthe summer and by snow scooter inthe winter. Helicopter may be usedall the year round, weather permit-ting. This may cause problems forthe operation of the earth station. Itis for example difficult to transport

large objects. Operational staff arerecruited among technical engineersin Norwegian Telecom. Normal timeof employment is one or two years,but a third year may be applied for.Because of the relatively shortemployment period it is difficult andexpensive to give the engineers spe-cial training in the operation of theearth station; it is even unrealisticbecause all other types of equipmentneed to be maintained as well. It hastherefore become necessary to makespecific considerations for the relia-bility of the equipment.

5 The earth station

at Isfjord

Based on the tests, Norwegian Tele-com entered in May 1978 into a con-tract with Elektrisk Bureau, divisionNERA, on the building of an earthstation at Svalbard. On July 1, 1979,the equipment arrived at IsfjordRadio and the earth station was com-pleted by December 1 the same year.

A Cassegrain antenna with a diame-ter of 13 metres is employed, on afoundation anchored to the per-mafrost. The low noise amplifiersare uncooled, parametric amplifiersand have a noise temperature lessthan 45 K. Considering NorwegianTelecom’s reliability requirements,two amplifiers are mounted in paral-lel, one of them serving as a warm

reserve. Low noise amplifiers are usuallymounted directly on the antenna. This isdone in order to minimize the noise con-tribution from the feeder cable, i.e. one

tries to minimize the length of the waveconductor from the antenna to the ampli-fiers. With the weather conditionsexpected at Isfjord, it would have beenvery difficult to carry out maintenance onthe amplifiers if they were mounted inthe antenna. The decision was thereforemade to mount them in a cabin some dis-tance from the antenna.

The station has a quality factor, G/T, bet-ter than 32.7 dB/K at 4 GHz and 10° ele-vation. At 1.7° elevation G/T = 31.5dB/K at 4 GHz.

The rest of the equipment has beenhoused in a new extension to the stationbuilding. The transmitter consists ofredundant klystron tube amplifiers withan output effect of 1.5 kW. The fre-quency converter equipment is alsoredundant and employs double convert-ing. Isfjord has the same channel equip-ment as the other remote stations, i.e. theoil production installations.

This is decided by the modulationmethod in the NORSAT system, and sofar, only Fujitsu can deliver this equip-ment (July 1980).

A high degree of reliability will most ofall demand reliable power supplies. AtIsfjord power has to be generated on thespot. Because of the difficult access,diesel may only be bunkered for shortperiods of the year; a large diesel tank istherefore necessary. The tank at Isfjord is400 m3.

The station is powered by a 200 kVAdiesel generator. De-icing of the antennaalso requires a generator, and there isanother joint reserve generator. So alto-gether there are three similar diesel gen-erators.

The power is connected via an inverterdevice which provides non-stop power,with a stand-by battery producing powershould the generators cut out. The powersupply is probably the most sensitive sys-tem component at Isfjord.

6 Telecommunication

services via satellite

to Svalbard

The satellite connection with Svalbardwas opened by Prime Minister Nordli onDecember 19, 1979, and the station hassince been open for public traffic. Tele-phone traffic to Svalbard operates at pre-

Figure 4 Block diagram of the radio frequency equipment at

Isfjord

Figure 5 The earth station antennas at Isfjord

Ph

oto

: No

rwe

gia

n T

ele

co

m M

use

um

sent over 8 connections. 5 of these areconnected to Gjøvik trunk exchange. Theremaining three are connected to thetrunk exchange in Oslo. Operator trunkcalls are available to the staff at SvalbardRadio, and telephone traffic from Sval-bard is handled this way. Traffic to Sval-bard is manually set up via Oslo trunkexchange. During the first four months of1980, 18,299 calls were handled fromSvalbard – this may be compared to the7,400 calls handled in the same period in1978 over the short-wave connections,i.e. an increase of some 250 %.

The earth station has suffered from some“teething trouble”, yet its accessibilityhas reached 99.58 %. There are alsospare radio connections should the earthstation cut out. We may therefore con-clude that telecommunications with Sval-bard are very reliable. Test operation of asmall number of telephone channels viathe experimental station was started inDecember 1978. Traffic handling in theperiod from December 1978 up till nowhas shown that fading conditions areunder control.

The earth station has given NorwegianTelecom the possibility to connect Sval-bard to the automatic telecommunica-tions network on the mainland. The telexservice is planned to be automated bySeptember 1980. The telex lines will beconnected to Oslo Telex III (newexchange). The telephone service will beautomated when Longyearbyen gets itsnew automatic exchange in 1981.

The transmission of radio programmesfrom the mainland to Svalbard via satel-lite has for some time been considered.Norwegian Telecom has run a test opera-tion in a telephone channel and therebyconfirmed that it is possible. The trans-mitted programme has not had a satisfac-tory quality during the test operation;music has particularly suffered. Norwe-gian Telecom are now working on anoffer to the Norwegian BroadcastingCorporation of permanent transmissionof radio programmes. Contained in theoffer is a plan to increase bandwidth inorder to improve the quality. The leasedsatellite capacity is large enough to han-dle this. The case is somewhat differentregarding transmission of television pro-grammes. In order to do that, morecapacity in the satellite will have to be

leased. With the lease of an additionalhalf a transponder, preliminary estimatesshow that the fading margin will be neg-ligible. However, Norwegian Telecomaim to carry out tests in order to ascertainwhether it is technically feasible to trans-mit television to Svalbard. A possibletransmission may be costly: INTELSATare asking for NOK 2.5 mill per year perhalf transponder. A broadband linkbetween Isfjord and Longyearbyenwould also be necessary.

Svalbard still does not have the sameoffer of telecommunication services asthe mainland, but a leap forward hasbeen taken to achieve it.

Reference

Osen, O. Satellittkommunikasjon tilSvalbard. Telektronikk, 75 (3), 1979.

17

Figure 6 Block diagram of a channel unit in the NORSAT system

Figure 7 Isfjord Radio seen from the south-west. The earth station equipment is placed in the build-

ing on the left. The diesel tank can also be seen

John R Veastad is a Consultant working for the Satellitesunit of Norwegian Telecom.Martin Jarl Lode is an Engineer who, when this articlewas first published, was working in the Technical Depart-ment of Norwegian Telecom.

Ph

oto

: No

rwe

gia

n T

ele

co

m M

use

um

18

Satellite navigation and positioning

B Y I N G A R S K J Ø N H A U G

The satellite based Global

Positioning System NAVSTAR,

developed by the Department of

Defense in the USA and the Norwe-

gian implementation project

SATREF are described. Availability

and accuracy of positioning depend

on national data processing and

broadcasting of reference (correc-

tion) data. The Geodetic Institute, a

part of the Norwegian Mapping

Authority, in co-operation with

Norwegian Telecom, are designing

a complete national network for

GPS. This includes a reference sta-

tion at Spitsbergen, offering

research and commercial position-

ing facilities.

Description of

NAVSTAR GPS

NAVigation System with Timing AndRanging (NAVSTAR) Global Position-ing System (GPS) is a satellite basednavigation and positioning system devel-oped on behalf of the US Department ofDefense (DoD). The system is expectedto be operative by the end of 1993 with aconstellation of 21 operative satellitesplus three active ones in reserve, dis-tributed in six different orbits. There willbe four satellites in each orbit with an

inclination angle in relation to the equa-torial plane of 55 degrees (Figure 1).

For civilian use the system will have anaccuracy of approximately plus/ minus100 metres in the x, y plane and 150metres in altitude for kinematic use. Forstationary geodetic applications (staticuse) it is feasible by way of various post-processing techniques to achieve anaccuracy in the millimetre level. Thesatellite constellation enables the systemto have a global coverage 24 hours a daywith four to eight observable satellitessimultaneously, with an elevation angleof >15 degrees over the horizon. NAVS-TAR GPS may be used for navigation atsea, on land, and in the air in addition topositioning offshore and onshore.

NAVSTAR GPS may be divided intothree segments:

- Space segment- Control segment- User segment.

The space segment

The space segment consists of a satelliteconstellation as mentioned in the intro-duction. The satellites orbit approx.20,200 km above the earth and has anorbital speed of approx. 12 “siderealhours” (star time). In relation to UniversalTime (UT) this means that the satellites(in a given geometric position) will be inthe same position four minutes later eachday.

There are three classes or types of GPSsatellites. These are Block I, Block II,and Block IIR satellites. Eleven Block Isatellites with a specific weight of 845 kgwere launched in the period 1978 to1985. The life span for the Block I satel-lites was estimated at approx. 4.5 years,but some of these satellites have provedto have a much longer life span. ThreeBlock I satellites are actually operativetoday (SV9/ PRN13, SV10/PRN12 andSV11/ PRN03). All satellites have theirown unique PRN (PseudoRandom Noise)code in addition to an SV (Space Ve-hicle) number, and the oldest of thesesatellites was launched in June 1984. TheBlock I constellation is different fromBlock II, as the orbital plane is 63degrees in relation to the equatorialplane, while the Block II constellationhas an inclination of 55 degrees.

28 Block II satellites have been designedand produced for the first official opera-tional constellation. Of this total, 24 will

be launched (21 will be active, whilethree will be reserve). The Block II satel-lites have an estimated life span ofapprox. 7.5 years and a specific weight ofsome 1,500 kg. Price: approx. NOK 3mill. each. It is worth noting that whilethe signals from Block I satellites werefully accessible to civilian users, the sig-nals from Block II satellites are “classi-fied” (signals may without further noticebe encrypted). (General GPS constella-tion status from GPS-INFO BULLETIN06/93, Geodesic division of NorwegianMapping Authority is shown in Figure2.)

Block II satellites will gradually bereplaced by Block IIR satellites (R standsfor Replacement) with an estimated lifespan of some 10 years. The developmentof these satellites is still going on and isestimated to be completed in 1995. Thespecific weight of these satellites will beapprox. 2,000 kg, but the price is thoughtto be half of what Block II satellites cost.While Block II satellites have two rubid-ium and two cesium clocks on board (sta-bility of 10-13 in one day), Block IIR satel-lites will have four hydrogen clocks withconsiderably greater accuracy (stability of10-15 in one day). The clocks make up“the heart” of the satellite, as they producethe L-band frequency of 10.23 MHz (f0),which is fundamental in the GPS signals(Figure 3).

The signals from the GPS satellites arebased on the spread spectrum techniquewhich ensures a higher communicationsafety (the signal is distributed over alarger bandwidth than necessary). TheGPS signals consist of two components,Link 1 (L1) with a centre frequency of1575.42 MHz (154 f0) and Link 2 (L2)with a centre frequency of 1227.60 MHz(120 f0). Both L1 and L2 are modulatedwith a P-code (Precision code) which isequal to f0, while L1 is also modulatedwith a C/A-code (Coarse/ Acquisitioncode), which is a tenth of f0. The modu-lated signals are equated as follows:

L1(t) = a1P(t) D(t) cos(f1t)+ a1 C/A(t) D(t) sin(ft)

L2(t) = a2 P(t) D(t) cos(f2t)

Various types of satellite data or mes-sages are sent. The messages contain dataon things like clock correction, orbitparameters, PRN number, the “generalhealth” of the satellite, GPS time, etc.

- 21 satellites, plus 3 active spares- 6 orbit planes- 12 hour period- 20 000 km height- full coverage (24 hours per day everywhere in the world)

Figure 1 GPS constellation in 1993

19

There are mainly two methods of pre-venting civilian users gaining full accessto the GPS system by encryption of sig-nals: Selective Availability (SA) and

Antispoofing (A-S). The SA methodmeans that the clock frequency (dither-ing) of the satellites are regulated from amaster control unit, in such a way that

publicly available accuracy decreases.The second method (A-S) to prevent fullaccess to the GPS signals, is by encrypt-ing the P-code with a Y-code. Thisensures that only C/A code receivers maybe used.

Control segment

The control segment is an operationalcontrol system consisting of a MasterControl unit situated at ColoradoSprings, USA. In addition to the maincontrol station there are five monitoringstations all over the globe, receiving sig-nals from all visible satellites. Slave con-trol stations (basically a transmission sys-tem with antenna) is situated near to themonitoring stations and make up thetransmission link to the satellites. Byknowing the position of the monitoring

PRN SVN NORAD COSPAR Remarks

No. No. No. No.

04 01 10684 1978 020A No longer active







13 09 15039 1984 059A

12 10 15271 1984 097A

03 11 16129 1985 093A

14 14 19802 1989 013A

02 13 20061 1989 044A

16 16 20185 1989 064A

19 19 20302 1989 085A

17 17 20361 1989 097A

18 18 20452 1990 008A

20 20 20533 1990 025A

21 21 20724 1990 068A

15 15 20830 1990 088A

23 23 20959 1990 103A

24 24 21552 1991 047A

25 25 21890 1992 009A

28 28 21930 1992 019A

26 26 22014 1992 039A

27 27 22108 1992 058A

01 32 22231 1992 079A

29 29 22275 1992 089A

22 22 22446 1993 007A

31 31 22581 1993 017A

07 37 22657 1993 032A

09 39 22700 1993 042A

The satellite that would have been known as NAVSTAR 7 failed

to achieve orbit. The satellite that will be known as NAVSTAR

12 will be used as an experimental platform and not part of the

GPS constellation.

Global Positioning System satellites availability chart

Availability for Friday July 9, 1993 (MJD 49177)

Latitude: 60.00 deg, Longitude: 10.00 deg, Height: 0 m

Analysis interval every 30 minutes

Acceptable DOF less than 6

Mask angle 10.00 deg

24 transmitters (24 SVs) plus altitude aiding available

Time of day (hours UTC)

00 03 06 09 12 15 18 21 24

PRN 1 -----------------------��-------------------------��-------------------PRN 2 --��----------------------------------------��-----------------------PRN 3 ��--------------------------------��-------------------------------------��PRN 7 ---------------��--------------------------------------��------------PRN 9 ---------------��--------------------------------��------------------------PRN 12 -----------------��------------------------------��--------------------PRN 13 --------------------��--------------------------------------��---PRN 14 ----------------------------------��------------------------------��---PRN 15 --------------------��------------------------------------��---------------PRN 16 ��---------------------------��--------------------------------------��PRN 17 ----��-------------------------��--------------------------------------PRN 18 ��--------------------------------------��---------------------------------��PRN 19 ��-----------------------------------��------------------------------��PRN 20 --------------------------��-----------------------------------�------------PRN 21 ------------------��-------------------------��--------------------------PRN 22 �---------------------------------------��------------------------------��PRN 23 --------------��-----------------------��------------------------------PRN 24 ��---------------------------��----------------------------------------��PRN 25 -------------------------------��--------------------------��--------PRN 26 ----��---------------------------��----------------------------------PRN 27 ��-------------------------------------��------------------------------��PRN 28 ----��--------------------------------------��-----------------------------PRN 29 --------------------------------------��-----------------------------��PRN 31 -------��--------------------------------------��----------------------

Number of satellites available

Time of day (hours UTC)

00 03 06 09 12 15 18 21 24

11

10 +

9 + ++ +++ ++

8 +++ + +++ +++ ++ +++ ++ + +++

7 + +++++++++++++ +++ +++ + ++++ ++++++++++++++ ++++

6 ++++++++++++++++++++++ +++++++++++++ +++++++++++++++++++

5 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

4 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 ��

2 ��

1 ��

Usable: ��

n : Required minimum number of satellites available

+ : More than enough satellites available

Figure 2 a), b) and c) General GPS constellation status (from GPS-INFO BULLETIN 06/93)

Figure 2 b)Figure 2 a)

20

stations it is possible to estimate errors inmeasuring the distance to the satellites.This information is used by the MasterControl station, where errors inephemerides (satellite orbit data) and thesatellite clocks are estimated. The slavestations then receive the corrections andtransfer this information to the GPSsatellites via an S-band radio link oncedaily (Figure 4).

User segment

There are two main groups of users: mili-tary and civilian. The development ofNAVSTAR GPS was originally relatedto the US Department of Defense pro-gramme for a national defence plan. Allmilitary aircraft, ships, ground vehicles,and groups of infantry were to beequipped with GPS receivers in order toco-ordinate military activities. Part ofthis strategy was actually put into opera-

tion during the Gulf War in 1991. SA,which up till then had been activated,was switched off so that “ordinary” civil-ian hand receivers could be used in thedesert regions. The reason for this wasthe fact that at that point there were notenough military receivers available.

The GPS receiver is passive and mustreceive signals from at least four satel-lites simultaneously. The receiver isequipped with a program carrying out thenecessary calculations. By multiplyingthe time delay (from the signals are trans-mitted from the satellites until they arereceived) by the speed of light (c), wehave the distance measurements to thesatellites (Ri). The position of thereceiver may then be found by using theknown positions of the satellites. The fol-lowing navigation equation can be done,

(xi - ux)2 + (yi - uy)2+ (zi - uz)2 = (Ri - cb)2 i = 1,2,3,4

where xi, yi, and zi are the positions offour satellites. These positions are trans-ferred from the satellites in the naviga-tion message and may be regarded asknown quantities. ux, uy, and uz are theunknown quantities in the position of thereceiver.

Up-to-date GPS receivers tend to use acrystal clock which is set approximatelyto GPS time. The clock in the receiverwill therefore have an offset from theGPS time in the satellite, and because ofthis the distance to the satellite will belonger or shorter than the “real” distance.This distance to the satellite is calledpseudo-range (R) and consists of a “real”distance plus/ minus an extra distance (b)

General status for GPS constellation

The general status of the Navstar GPS constellation as at 30 June 1993 is as follows. Note

that all mention of future launches has been removed from this table, since current infor-

mation is unclear.

Satellite No. Launched Plan Clock Status

SVN01 BLK.I-10 PRN04 22.02.1978 Withdrawn






SVN07 BLK.I-07 - 18.12.1980 Accident


SVN09 BLK.I-09 PRN13 13.06.1984 C1 Cesium Operational

SVN10 BLK.I-10 PRN12 08.09.1984 A1 Rubidium Operational

SVN11 BLK.I-11 PRN03 09.10.1985 C4 Rubidium Operational

SVN13 BLK.II-02 PRN02 10.06.1989 B3 Cesium Operational

SVN14 BLK.II-01 PRN14 14.02.1989 E1 Cesium Operational

SVN15 BLK.II-09 PRN15 01.10.1990 D2 Cesium Operational



SVN18 BLK.II-06 PRN18 24.01.1990 F3 Cesium Operational

SVN19 BLK.II-04 PRN19 21.10.1989 A4 Cesium Operational

SVN20 BLK.II-07 PRN20 24.03.1990 B2 Cesium Operational





SVN25 BLK.II-12 PRN25 23.02.1992 A2 Rubidium Operational



SVN28 BLK.II-13 PRN28 10.04.1992 C2 Cesium Operational



SVN37 BLK.II-20 PRN07 13.05.1993 C4 Cesium Operational

SVN39 BLK.II-21 PRN09 26.06.1993 A1 Cesium -

Figure 2 c) Figure 3 A GPS satellite

21

because of clock error in thereceiver and bias as a conse-quence of atmospheric, strato-spheric and ionospheric interfer-ence. Other errors may be inte-gral interference in the receiver,orbital errors, errors in the satel-lite clocks which may eventuallyinfluence the navigation accu-racy. Using differential GPSincreases this accuracyconsiderably.

There are many different GPSreceivers on the market todayfor civilian users, at an increas-ingly favourable price. GPSreceivers may be divided intothree groups: C/A code pseudo-range, C/A code carrier phase,and P-code carrier phase. P-codereceivers are the most accurate,and are reserved for military andauthorised users, while C/A-code receivers, being less accu-rate, are used for civilianapplications (Figure 5).

Differential use of

NAVSTAR GPS

Differential GPS (dGPS) is a techniquewhereby a GPS receiver placed at aknown point (point of reference) is usedfor determining errors/inaccuracies in thesatellite measurements (reference data).A dGPS user will then be able to utilisethe reference data (or correction data) forcorrecting his own measurements withina distance of several hundred kilometresaround a reference station. This willimprove the user’s positioning accuracyto better than 5 m (kinematic use). Asmentioned above, GPS alone has anaccuracy of plus/minus 100 m.

By employing two static receivers it ispossible to calculate the distance betweenthem very accurately. (Tests have shownaccuracies in the millimetre region onmeasurements of more than 180 km.)Such measurements utilise the phasemeasurement on the carrier wave of L1and L2.

The dGPS will be increasingly usedwithin the field of surveying, both geode-tic and other, and definitely within navi-gation on land, at sea, and in the air.SATREF (SATellite based REFerencesystem) will become such a service for

users of dGPS and will offer data toincrease the accuracy and reliability,and reduce costs connected topositioning (Figure 6).

SATREF – Satellite

based reference

system

Summary

The idea of a national satellite basedreference system was launched in1989 in the form of the publicdevelopment project SATREF.Today, SATREF is almost com-pleted and will now gradually moveinto an operational phase. Elevenreference stations in some Norwe-gian cities and at Spitsbergen will becompleted by 1993. Nine referencestations and control centres are alreadyin operation on a test basis, and SATREFcan therefore offer some services byarrangement.

Introduction

SATREF was started up in 1989 by theGeodetic Institute of Norwegian Map-ping Authority as a development projectaiming at establishing a national satellitebased reference system. Co-operation

partners have been the Norwegian Indus-trial and Regional Development Fundand the company Seatex in Trondheim.The Norwegian Mapping Authority istechnically and economically responsiblefor further development and operation ofthe system.

In 1991 a business plan for SATREF wasdrawn up. The conclusion of the plan isthat there is a basis, both in terms of

Havaii

ColoradoSprings

Ascencion DiegoGarcia

Kwajalein

Figure 4 GPS control stations

Position

GPS

Info

Inmarsat

Chart

Radar

Autopilot

Gyro Log

Figure 5 Electronic navigational chart system

22

users and economics, to implement apublic dGPS service. A national systemoffering reference data to a wide spec-trum of users would be beneficial interms of efficiency because many differ-ent user groups may use the same sys-tem. Quality and integrity control will bean important function in order to safe-guard satisfactory data and services.

Business idea

The business idea is to offer data and ser-vices in connection with the use ofdGPS, which will increase accuracy andreliability and reduce costs related topositioning. The area of business is bothreal time use (navigation) and data forpost-processing, and will thereby cover awide spectrum of accuracy levels. Thedistribution of data should be based onsolutions satisfying the requirements ofindividual users.

On its own, as well as in co-operationwith public partners, the Mapping Auth-ority will offer data and services directly

to the end user and to private firms whocan carry out value added services basedon SATREF. The main area of serviceswill be SATREF reference data andunprocessed GPS data, but the SATREForganisation will also be able to offervarious specialised products and services.

The need for improving the safety of navi-gation is considerable, and SATREF willbe a vital service together with the Map-ping Authority’s efforts in electronicmaps. The system will be based on usershaving to pay for the products and ser-vices offered by SATREF, but this has notyet been finalised.

Organisation

Two specialised groups in the GeodeticInstitute work with SATREF on a dailybasis. The specialised group SATREF isresponsible for sale, marketing, and dailyoperation. The specialised group Techno-logical Development (TU) work on fur-ther development and technical operation

of the system. Altogether, the specialisedgroups consist of 10–11 people. In addi-tion to this, SATREF may draw on theGeodetic Institute’s considerable GPSknowledge.

Background

SATREF is based on NAVSTAR GPS asdescribed above. The GPS system willoffer signals and data for two types ofusers, i.e. military and civilian. The mili-tary part of GPS is the most accurate andis called PPS (Precise Positioning Ser-vice). The use of PPS requires access toencryption equipment. Civilian usersmay use SPS (Standard Positioning Ser-vice). Using a satellite receiver, SPSusers will acquire a 100 metre navigationaccuracy in two dimensions.

However, this is insufficient for a greatmany users. With the help of a referencenetwork SATREF will improve accuracyand assure the quality of the data for itsusers. Typical figure for differentialaccuracy is 5 metres.

Reference network

The reference network SATREF consistsof six main elements (Figure 7): Refer-ence station, transmitter, monitor station,control centre and communication linesconnecting the various components. Inaddition, there are user units, which isequipment enabling the use of SATREFin connection with positioning and navi-gation. Such a unit may either be basedon the reception of reference data in“real” time, or be equipped with storagecapacity for post-processing.

The reference stations (Figure 8) consistof GPS receivers and processor units forthe calculation of corrections. The sta-tions will be connected both to transmit-ters and to a control centre with perma-nent communication lines. Referencedata from a reference station may be dis-tributed to one or more transmittingunits.

The reference stations will be continu-ously monitored by the control centrewhich assures the quality of all transmit-ted data. The stations will also pass onmessages generated by the control centre.These messages may contain informationon status, activities connected to theoperation of the system, the “generalhealth” of both the GPS and the SATREFsystem and on expected accuracy andperformance.

Figure 6 Major elements of a dGPS service

Reference stationand

integrity monitor

Broadcastmonitor

Geodeticmonument

Internal communicationsnetwork

Broadcastsite

DGPS user equipmentand

mission display

Broadcaststandard

Navstar GPS satellitesprovide basic navigation

signals and data

23

The Mapping Authority wish to utilisedata from the reference stations in its sci-entific work, within the fields of researchand global environmental changes,among other things. This means that thereference network must satisfy the strictrequirements to this

STATUS - TelenorWhen Børge Ousland reached the North Pole on April 22, 1994, after 52 days of...

Documents

Transcript of STATUS - TelenorWhen Børge Ousland reached the North Pole on April 22, 1994, after 52 days of...