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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
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