Post on 03-Jan-2016
transcript
SWOT
Near Nadir Ka-band SAR Interferometry:SWOT Airborne Experiment
Xiaoqing Wu, JPL, California Institute of Technology, USA
Scott Hensley, JPL, California Institute of Technology, USA
Ernesto Rodriguez, JPL, California Institute of Technology, USA
Delwyn Moller, Remote Sensing Solutions, Barnstable, USA
Ronald Muellerschoen, JPL, California Institute of Technology, USA
Thierry Michel, JPL, California Institute of Technology, USA
IGARSS 2011 SWOT Session , July 27, 2011
SWOT
Background
• SWOT (Surface Water Ocean Topography) is a planned NASA and CNES joint mission for monitoring Earth’s surface water.
• The major instrument of SWOT is KaRIn (a single pass Ka-band Radar Interferometrer)
• To measure sea surface heights and terrestrial water heights with a total 120 km width swath from both left and right sides
• To cover +90 % of Earth’s surface
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SWOT
KaRIn system and Ka-band airborne system
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System parameters KaRIn Airborne system
Platform height 970 km ~12 km
Carrier frequency 35.7 GHz 35.7 GHz
Signal bandwidth 200 MHz 80 MHz
Peak transmit power 1.5 kW 35 W
PRF (per channel and side) 4420 Hz ~800 Hz
Antenna boresight in elevation 2.7o 31o
Antenna azimuth beamwidth 0.12o 0.9o
Baseline length (physical) 10 m 25 cm
Baseline angle 0 45o
Roll angle to achieve near nadir geometry for airborne system NA 6o ~ 9o
Ground range swath (one side) 10 – 70 km 2 – 6 km
SWOT
Verification and validation through airborne experiments
• Characterize power return of water surface with near nadir geometry
• Test and Verify SWOT ground processing algorithms
• Evaluate and predict performances of KaRIn system
Need to overcome issues of airborne systems
• multi-path due to reflection from antenna fairings
• possible interferometric phase drift due to lack of calibration signals
• Baseline calibration – particularly baseline orientation angle
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SWOT
Magnitude pattern after flattening
Antenna data derived interferogram after flattening
Antenna mount
Phase residual from multi-path
SWOT
Dependency of cross track ripples on along track (Greenland)A
long
trac
k 22
0 km
Phase drift as a function of along-track estimated from comparison with ATM height
Near rangeFar range Absolute phase
SWOT Residual Baseline orientation angle estimation and correction
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Height map wrapped in 10 m After residual roll correction
7 km
SWOT Water and land power comparison and application for water land classification
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Water surface
Land
Pow
er (
db)
classification image (left) based on magnitude image and cross range dependent threshold. White: water surface; black: land surface
SWOT
Summary• Demonstrated techniques to correct phase residuals in
airborne system from:– Multi-paths due to antennas– unknown interferometric phase drift – unknown residual baseline orientation angle
• Characterized the near nadir water surface reflectivity
• Height measurements from airborne system match very well with SRTM DEM within 10 meters for land areas.
• The water surface height measurement accuracy of about 25 cm at near range is achieved.
• Some techniques will be verified again with AirSWOT airborne system in near future and incorporated into SWOT ground data processing system.
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