Predicting Differential Loran-C Performance in Boston Harbor

32nd International Loran Association November 3-7, 2003

Predicting Differential Loran-C Performance in Boston Harbor

Erik Johannessen

Andre Grebnev

Wouter Pelgrum


Context

Supports on-going LORIPP/LORAPP evaluations and analyses

Specifically part of a program to prototype Integrated GPS/Loran for Harbor Entrance and Approach

Program Participants


HEA Receiver Program Scope

Prototype Integrated Receivers Receiver/Integration Specification Antenna Design Cost Study 5 Deliverable Evaluation Units

Measurement Campaign On-the-Water Data Collection Reference Station Measurements Demonstration

Documentation


Reelektronika develops miniature integrated GPS/Loran-C receiver as OEM product for NELS (Northwest European Loran System)

Credit Card 85 x

54 mm

Front End & ADC77 x 47 mm

Signal Processor

77 x 51 mm

Prototype Integrated Receivers


Prototype Integrated Receivers (cont’d)

Replace MF Beacon Engine with Loran/GPS/WAAS

Modify H-Field Beacon Antenna To H-Field Loran


Measurement Campaign Overview

Envisioned as three steps leading to set up capable of formal demo in DC area

First step local to Megapulse resource availability

Temporal and spatial decorrelation measured, also local effects

Differential measurements by tightly time coupling a reference and rover

Method applicable to all modes Stored raw sample data permits comparison of

multiple envelope and carrier tracking points


Experimental Set-up – Step 1

Raw Data

Data recording(external FireWire

Harddisk)

Loran-CE-field antenna

Cesium Clock

Loran-C receiver

clock in

Antenna inTCP/IP

10MHz

Ca

libra

tion

Sig

na

l

UT

C c

oa

rse

+ p

osi

tion

+ G

PS

co

ntr

ol

Raw Data

Data recording(external FireWire

Harddisk)

1 PPS out

Cesium

1 PPS in

1 PPS outFreq outSerial IO

Loran-C simulator

signal out

Clock in

GPS antenna

GPS receiver

1 PPS outSerial IO

Antenna in

Loran-C receiver

clock in

Antenna inTCP/IP

H-field antenna

Reference Station at Megapulse Rover Receiving Equipment Suite


A lovely day for a sail?


Reference Station Data

0 50 100 150 200 250 300 350

-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

05930X

9960X

8970X

9960M

5930M

9960W

9960Y

time (minutes)

us

TOA-variations (5 sec integrated)

0 50 100 150 200 250 300 350

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

5930X

9960X

8970X

9960M

5930M

9960W

9960Y

time (minutes)

us


Measurement Date : June 20, 2003 1100-1800 ET

Recorded at Megapulse –(Nan, Sen, Crb, CB shown)

5 sec independent samples Non-moving average of 12 samples


Reference Station Data (cont’d)

180 200 220 240 260 280 300 320 340 360 380-0.085

-0.08

-0.075

-0.07

-0.065

-0.06

-0.055

-0.05

-0.045

9960X

8970X

9960M

5930M

9960W

9960Y

time (minutes)

us


50 100 150 200 250 300 350-0.34

-0.33

-0.32

-0.31

-0.3

-0.29

-0.28

-0.27

9960W

9960Y

time (minutes)

us


Note: discrete steps of 20 ns - LPAs or Other??

Nantucket – last 3.5 hours Caribou – 7 hours, 10nsec/div



105oW

90oW

75oW 60oW

45oW

24oN

36 oN

48 oN

60 oN

1000 2000 3000

Caribou

Nantucket

Cape Race

Fox Harbor

Comfort Cove

Cape Race

Fox Harbor

Malone Grangeville

Raymondville

Jupiter

Carolina Beach

Havre

Baudette Gillette

Dana

Malone

Seneca

Baudette

Boise City Boise City

Gillette

Raymondville

Grangeville

Seneca

Caribou

Nantucket

Carolina Beach

Dana

Carolina Beach Carolina Beach Carolina Beach Carolina Beach

Seneca

Caribou

Nantucket

Calibrated LoranIntegrated NavNovAtel POSA

Longitude Error (m)151050-5-10-15

Latit

ude

Err

or (

m)

15

10

5

0

-5

-10

-15

• Scatter plot created using 7 TOAs, 5 sec integrated/independent

• Repeatability of 7 hour set: 6.5m, 95% and 8.6m, 99%

• Slight offset from mean due to ASF variation



0 50 100 150 200 250 300 350-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

05930X

9960X

8970X

9960M

5930M

9960W

9960Y

time (minutes)

us

Pseudo-Differential TOA (5 sec integrated, corrected with 60 sec integrated TOA)


Longitude Error (m)20151050-5-10

Latit

ude

Err

or (

m)

15

10

5

0

-5

-10

-15

• Mean of 1st minute used to compensate next twelve 5 sec samples

• Repeatability improves slightly: 6.1m, 95% and 8.2m, 99%



0 50 100 150 200 250 300 350

-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

05930X

9960X

8970X

9960M

5930M

9960W

9960Y

time (minutes)

us

Pseudo-Differential TOA (5 sec integrated, corrected with 600 sec integrated TOA)


Longitude Error (m)151050-5-10

Latit

ude

Err

or (

m)

15

10

5

0

-5

-10

• Mean of ten minutes used to compensate next 120 samples

• Repeatability: 6.2m, 95% and 8.4m, 99%


Rover Receiver Results/Issues

Antenna related Phase error with orientation Include cable and attenuators as part of antenna

Receiver related Data grabber worked very well Need to lose some weight

Vessel related Alternator noise


Measurements-Step 2

Currently completing analysis of Step 1 Rover Results

Antenna related issues addressed via hardware upgrade and compensation in software

Ship Shape gone to FLA for winter, will need alternate vessel

Alternatively, SiTex resources in Tampa Expect to be on water again early December


Summary

Reference station and Rover data collection systems useful for post processing

High update rate of differential correction did not significantly improve position fix

Vessel related issues need resolution Measurement campaign has been critical input

to integrated receiver design

Predicting Differential Loran-C Performance in Boston Harbor

Documents

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