Satellite Altimetry andSatellite Altimetry andGravimetryGravimetry: : Theory and ApplicationsTheory and Applications

C.K. ShumC.K. Shum1,21,2, Alexander Bruan, Alexander Bruan2,12,1

1,21,2Laboratory for Space Geodesy & Remote SensingLaboratory for Space Geodesy & Remote Sensing 2,12,1Byrd Polar Research CenterByrd Polar Research Center

The Ohio State UniversityThe Ohio State UniversityColumbus, Ohio, USAColumbus, Ohio, USA

ckshum@osu.ckshum@osu.eduedu, , braunbraun.118@.118@osuosu..edueduhttp://geodesy.eng.ohio-state.http://geodesy.eng.ohio-state.eduedu

Norwegian Univ. of Science and TechnologyTrondheimTrondheim, Norway, Norway

2121––25 June, 200425 June, 2004

Space Geodesy:Space Geodesy: An AnInterdisciplinary Science in theInterdisciplinary Science in the

21st Century21st CenturyC.K. Shum, Alexander BraunC.K. Shum, Alexander Braun

Laboratory for Space Geodesy & Remote SensingLaboratory for Space Geodesy & Remote Sensing

The Ohio State UniversityThe Ohio State UniversityNorwegian Univ. of Science and Technology

TrondheimTrondheim, Norway, Norway2121––25 June, 200425 June, 2004

Satellite Altimetry andSatellite Altimetry and Gravimetry Gravimetry::Theory and ApplicationsTheory and Applications

Wednesday, 23 June 2004Wednesday, 23 June 2004

•• Space Geodesy: An Interdisciplinary ScienceSpace Geodesy: An Interdisciplinary Science (AM)(AM)C.K. ShumC.K. Shum

•• 20th Century Sea Level Rise20th Century Sea Level Rise (AM) C.K. Shum(AM) C.K. Shum

•• Determination of Vertical Motion Using Satellite AltimetryDetermination of Vertical Motion Using Satellite Altimetryand Tide Gaugesand Tide Gauges ((PM) Alexander BraunPM) Alexander Braun

Space Geodesy: An Interdisciplinary ScienceSpace Geodesy: An Interdisciplinary Sciencein the 21st Centuryin the 21st Century

•• What is Geodesy?What is Geodesy?•• Earth science applications using Space GeodesyEarth science applications using Space Geodesy

–– GPSGPS ((atmosphereatmosphere, climate, ionosphere, geodynamics, navigation,, climate, ionosphere, geodynamics, navigation,water level, GPS altimetry, positioning, etc)water level, GPS altimetry, positioning, etc)

–– Synthetic Aperture Radar Synthetic Aperture Radar InterferometryInterferometry (tectonics, (tectonics, DEMsDEMs,,volcano, volcano, ice velocity/ mass balanceice velocity/ mass balance, subsidence, current/wave), subsidence, current/wave)

–– Satellite altimetrySatellite altimetry ((circulationcirculation, gravity, , gravity, tides, sea leveltides, sea level, hydrology,, hydrology,ionosphere, ice mass balance, sea ice, bathymetry, ionosphere, ice mass balance, sea ice, bathymetry, vertical motionvertical motion))

–– Space Space gravimetrygravimetry ((hydrology, oceanographyhydrology, oceanography, ice sheet mass, ice sheet massbalance, glaciology, balance, glaciology, geodynamics, postglacial reboundgeodynamics, postglacial rebound))

•• ConclusionsConclusions

A science discipline toA science discipline todetermine the size (gravity),determine the size (gravity),shape (volume), and theirshape (volume), and theirchanges of the Earth (andchanges of the Earth (andplanets); and positions andplanets); and positions andmotions of a pointmotions of a pointanywhere on the surface oranywhere on the surface orin space.in space.

What Is Space Geodesy?What Is Space Geodesy?What Is Space Geodesy?

Credit: Cartoon modified from a figure by K. Lambeck

GPS Buoy Water Level

GPS Buoy System

• Equip GPS capability to the buoy/vessel tosurvey the water level.

• Buoy position and water level is processed withDGPS in kinematic mode

• Buoy design and implementation vary from oneapplication to another

• Coastal applications (within 100 km off shore fora few cm–decimeter accuracy in water height):geocentric water surface height measurementsand radar altimeter calibrations

Some GPS Buoy Designs

GFZ Ruggedized buoy

ETH Zurich(GGL) buoy

UTas buoy

NOAA/NGS Autonomous Buoy

Credit: G. Mader

OSU Waverider GPS Buoy

• Life-saver type buoy.• Choke Ring GPS

antenna.• Tethered to a ship or on

shore where receiverand battery reside.

• Plastic radomeprevents water fromentering the centercompartment.

OSU Waverider GPS Buoy

• Marks on 4 sides.

• Offsets from the marks toARP are measured in thelaboratory.

• Observing water line withmarks during eachdeployment in order to getthe height of ARP above thewater line.

Marks

Waverider GPS Buoy Deployment

Antenna Reference PointHeight

up component from user

offset from ant_info.002

xyz from user

antennareferencepoint (ARP)

L1 phase center

KARS Height Solution (an example)

Equipments

Bottom pressure gauge GPS buoy

NOAA acoustic tidegauge

Lake Erie Calibration Sites(Marblehead and Cleveland)

Cleveland

GPS buoy campaign for Marblehead Site

October 20-21, 2001. 3 TP/Jason nominal footprints (call Bin) on Pass 76 were surveyed

with GPS buoy. GPS occupation:

1 hr of 1Hz GPS data at each location. Mean lake surface

gradient estimate: ~20 cm over 18.4 km from Marblehead to Bin B with formal error <1cm. Geoid height at TG:

-35.293 m with formal error < 1cm. (8 hr of 1Hz GPS data).

GPS buoy data processing withTGO - Trimble Geomatics OfficeKARS – Kinematic And Rapid Static (Mader, 1986).

GPS buoy solution at a tide gauge

GPS Occultation:- Precision orbit determination <0.1 mm/yr near-real time 3-Dvelocity- Global pressure improvement

GPS OccultationGPS Occultation

- POD (0.1 mm/sec 3-D velocity accuracy)

- Potential pressure field improvement

Figure credit: GFZ

GPS OCCULTATION MISSIONSGPS OCCULTATION MISSIONS

Micro-LabMicro-Lab(GPS-Met),(GPS-Met),

19951995

OrstedOrsted, 1999, 1999

SunsatSunsat, 1999, 1999

CHAMP, launched CHAMP, launched July 15,2000July 15,2000

SAC-C, June 2000SAC-C, June 2000

GRACE, launchedGRACE, launched16 March 200216 March 2002

COSMIC, COSMIC, 787800-85-8500

inclination, inclination, 6 satellite-6 satellite-constellation with nodalconstellation with nodalplanes separated by ~30planes separated by ~3000,,2005 launch, 5 yr mission2005 launch, 5 yr mission

ACE+, 2007 (proposed)ACE+, 2007 (proposed)4 satellites4 satellites

NCEP-ECMWF PRESSURENCEP-ECMWF PRESSUREDIFFERENCESDIFFERENCES

6-hour (May 2001) NCEP-ECMWF surface pressure6-hour (May 2001) NCEP-ECMWF surface pressuredifferences using NCEP topography (up to >8 differences using NCEP topography (up to >8 hPahPain the S. Ocean and -6 to -7 in the S. Ocean and -6 to -7 hPa hPa over Antarctica)over Antarctica)

Effect of Atmospheric Aliasing on MonthlyEffect of Atmospheric Aliasing on MonthlyGRACE Gravity Field RecoveryGRACE Gravity Field Recovery

Simulated aliasing as 6 hr. - 3 day NCEP mean pressureSimulated aliasing as 6 hr. - 3 day NCEP mean pressure(scaled, 30x30 model). Monthly averaged atmospheric(scaled, 30x30 model). Monthly averaged atmosphericload error (height anomalies at altitude) has high-load error (height anomalies at altitude) has high-frequency component in S. Ocean and Antarctica)frequency component in S. Ocean and Antarctica)

Day 1,Day 1,00 hr00 hr

Day 30,Day 30,00 hr00 hr

Day 15,Day 15,12hr12hr

Geoid Geoid and height anomalies (mm) at altitude shownand height anomalies (mm) at altitude shown

GLOBAL COMPARISONS OF ECMWF ANDCHAMP OCCULATION PROFILE

-4 -3 -2 -1 0 1 2 3 40

5

10

15

20

25

30CHAMP vs. ECMWF Pressure Difference, day001-093, 2003 (5376 profiles)

Pressure (mbar)

MSL altitude (km) mean of ECMWF-CHAMP

std of ECMWF-CHAMP

-4 -3 -2 -1 0 1 2 3 40

5

10

15

20

25

30CHAMP vs. ECMWF Pressure Difference, day001-093, 2003 (7856 profiles)

Pressure (mbar)

MSL altitude (km) mean of ECMWF-CHAMP

std of ECMWF-CHAMPIncludeprofilespenetratewithin 1km aboutMSL

• CHAMP data (source: UCAR) period: Jan –March 2003 (except 4 days)• Data interpolated/extrapolated for 0-30 km(above MSL) at 1-km intervals

hPa

2 km case

hPa

km

Lowest occultation altitude –ECMWF topography

Radar penetration better over polarregions and S. Ocean

SAR Interferometry- Digital Elevation Models- Digital Elevation Models- Earthquake deformation- Earthquake deformation- Land subsidence- Land subsidence- Ice stream velocity- Ice stream velocity- - Ocean tides over sea-ice covered oceansOcean tides over sea-ice covered oceans

SRTM C-bandShaded Relief ImageViti Levu , Fiji Islands

This image was generatedusing topographic data fromthe SRTM and shows thelargest island in the Fiji Islandgroup (10,429 sq km).

Colors show the elevation asmeasured by SRTM. Colorsrange from green at the lowestelevations to pink at thehighest elevations. Water isblack.

Suva, the capital city, lies onthe southeast shore. TheNakauvadra, the ruggedmountain range running fromnorth to south, has severalpeaks rising above 900 meters.Mount Tomanivi, in the uppercenter, is the highest peak at1324 meters.Size: 192 km x 142 km Location: 17.8° S, 178.0° EOrientation: North at topOriginal Data Resolution: 30 metersDate Acquired: 19 Feb 00Date Released to Media: 21 Feb 00

Shuttle RadarShuttle RadarTopographyTopographyMission DerivedMission DerivedTopographyTopographyUsing X-SARUsing X-SAR

Courtesy: DLRCourtesy: DLR

SAR Interferometry Principle

B : BaselineBn : Perpendicular baselineBp : Parallel baselineφ : Incidence angle

(Repeat-Pass interferometry)

Image swath~ 100 km

Bn Bp

S1S2

Bφ

C

Interferogram = phase difference between S1-C and S2-C.

Horizontal Velocity Field:Horizontal Velocity Field:Nivlisen Nivlisen Ice Shelf, Ice Shelf, Dronning Dronning Maud LandMaud Land

BBäßäßlerler,, Detrich Detrich, Shum [2003], Shum [2003]

Max. displacement of thePotsdam Glacier ~120m/yr; close to thegrounding zone.Grounding zone locationis confirmed to besignificantly affected byocean tides

Flightdirection

Look direction

Weddell Sea

AmunsenSea

SulzbergerBay

EdwardVIIPeninsula

CapeColbeck

Study area

Study Area : Sulzberger Ice Shelf

Sulzberger ice shelf : 76.5 S ~ 77.5 S 153 W ~ 156 W

Ross Sea

N

Interferogram (I) : Track 424

(a) Interferogram between ERS1 23959 & ERS2 4286 Bn = -121 m(b) Interferogram between ERS1 24875 & ERS2 5202 Bn = -6.2 m

(a)

(c)

(d)

(b)

(c) Differential interferogram before baseline scaling(d) Differential interferogram after baseline scaling [= (a) – 19x(b)]*

(c)

*19 is the baseline ratio (toremove topography effects

Geocoded Interferometric DEM(Land Only)(1) Find coast line using scaled differential interferogram (d)(2) Mask out sea and ice tongue from unscaled differential interferogram (c)(3) Baseline estimation & phase unwrapping(4) DEM generation over the land (grounded ice)

N

(c) (d)

Elevation Comparison:Interferometric DEM height & ICESat laser altimeter profile (C-D)

DC

Mean bias : 12.46 m 8 yr difference ellipsoidal height vs. approximated height

Relative Height

Standard deviation (in the middle) = 1.34 m

Standard deviation(for all the profile) = 5.12 m

Mean bias(12.46 m)removed

Interferogram (II) : Track 381

A

BD

C

(Left) Differential interferogram for track 381(Right) Classification for land glacier (LG), ice tongue (IT), grounding zone (GZ), ice stream (IS), and sea ice (SI)

LG

ITGZ

IS

SI

Deformation Change Measurement

A : 0.12 rad

B : 34.66 rad

) 23( angle Incidence :

difference rangeSlant :

changeelevation Surface :

cos

o=

Δ

Δ

Δ=Δ

α

α

r

z

rz

Where

cmcmz

7.162

6.5

2=×

Δ

π Deformation from InSAR = Tide + Atmosphere + Other

Predicted Ocean Tides by Model

4.2

5.3

2.0

-0.2

-6.2

-5.8

-2.6

-0.7

-2.2

-0.9

-0.3

-0.7

Solid EarthTide (cm)

-33.4-47.9-48.5-47.21996-4-24

-36.0-51.3-52.6-49.71996-4-23

-22.2-16.3-15.5-17.71996-4-18

-16.2-7.0-5.2-10.71996-4-17

-3.010.812.5-0.81996-3-17

-8.61.62.9-9.81996-3-16

-24.8-21.9-22.2-28.71996-3-14

-31.3-31.9-33.0-36.61996-3-13

-20.4-16.7-16.7-20.11996-2-14

-23.8-23.8-24.3-24.11996-2-13

-15.6-20.1-21.1-21.51996-2-11

-7.4-12.3-13.1-15.81996-2-10

GOTCATSTPXONAO99

Geocentric tide (cm)Date

-((-7.362-0.7)-(-15.623-0.3))+((-8.648-5.8)-(-3.027-6.2)) = -13.1GOT

-((-12.268-0.7)-(-20.086-0.3))+((1.643-5.8)-(10.768-6.2)) = -16.1CATS

-((-13.141-0.7)-(-21.124-0.3))+((2.944-5.8)-(12.483-6.2)) =-16.7TPXO

-((-15.779-0.7)-(-21.504-0.3))+((-9.822-5.8)-(-0.809-6.2)) = -13.9NAO

Predicted Tidal difference (cm)Model

Tide Change Prediction by Model

Deformation change obtained by SAR: -16.7 cm (Atmospheric effect or inverse barometric correction ignored)

TOPEXPOSEIDONand JASON

Credit: NASA/JPLCredit: NASA/JPL

Global Mean Sea Level andGlobal Mean Sea Level andEl Nino and La Nina MonitoringEl Nino and La Nina Monitoring

RMS Ocean Variability around MSSalong T/P Ground Tracks

Current Bathymetry from Altimetry

Observed Gravity Anomalies Predicted Bathymetry

Bathymetry from Satellite Altimetry

http://ibis.grdl.noaa.gov/SAT/Bathy.intro.html

Courtesy: Walter Smith

20-km-scale Bathymetry Steers OceanCurrents

Forecast models require correct global bathymetry

A single feature as small as 20 km across cansteer a major current (Kuroshio mean flow in U.S.Navy model at 1/16° [Metzger & Hurlburt, 2001]

Intrudesunnaturally

Approximatesnature

Model BathymetryChanged Only Here