airswot : a calibration/validation platform for the swot mission
DESCRIPTION
AirSwot : A Calibration/Validation Platform For The SWOT Mission Delwyn Moller, Ernesto Rodriguez, James Carswell , Daniel Esteban-Fernandez. Outline. Ka-band SWOT Phenomenology Airborne Radar ( KaSPAR): AirSWOT ’ s radar payload Instrument configuration Performance - PowerPoint PPT PresentationTRANSCRIPT
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AirSwot:
A Calibration/Validation Platform For The SWOT
Mission Delwyn Moller, Ernesto Rodriguez,
James Carswell, Daniel Esteban-Fernandez
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• Ka-band SWOT Phenomenology Airborne Radar (KaSPAR): AirSWOT’s radar payload– Instrument configuration– Performance– Processing and products– Hardware heritage and development status
• AirSWOT calibration/validation Platform– Auxiliary sensors– Platform– Timeline
Outline
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Ka-band SWOT Phenomenology Airborne Radar (KaSPAR)
Calibration/Validation Sensor
• The high-precision swath elevation mapping capability will enable calibration and validation of SWOT with 3D measurements not currently achievable
Primary measurement product:• High accuracy elevation maps with ~5km
swath (at 35kft) over ocean- Traditional altimeter height retrieval to
provide tie points for swath edges
Dedicated Science Campaigns: TBD
Phenomenology
• Multiple (elevation & temporal) baselines replicate and fully characterize SWOT sampling and geometry
• Gather pre-mission data for SWOT over specific and varied science targets for:
- Classification (land/water and further)- Predicting performance and interpretability to
extend the science impact beyond the mission requirements
- Penetration into snow for cryospheric applications
• Provide high resolution spatial measurements of:- Water temporal correlation - Elevation (both land and water)- Surface backscatter - Vegetation attenuation
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Swath Performance
• Two sets of transmit antennas:1. Illuminate inner (SWOT geometry) & outer swath to provide wide-swath coverage2. Overlapping beams for inter-calibration
Random error across swath
Parameter Value Unit
Center Frequency 35.75 GHz
Peak Transmit Power 40 W
Platform Height 35 kft
Swath Coverage “inner” “outer”
1.45.0 km
Bandwidth “inner” “outer”
200 (min)80 (min) MHz
Mean height error “inner” “outer”
1.2*
2.3** cm
Incidence angles “inner” “outer”
1-54-27 deg
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Measurements and Processing
KaSPAR will make the following measurements*:1. Surface elevation maps of the water and land (land accuracy will be lessened)
• Swath of up to 5km depending on water state• Resolution variable but innate instrument 1-look resolution is 10’s of cm along-track
and 10-5m range• Precision for ~50x50m posting is sub-3cm mean and assumes an ocean surface with
6m/s or greater winds
2. Corresponding backscattered power and correlation maps 3. For outer incidence angles - surface radial velocity 4. Surface temporal correlation estimates
*all simultaneous including both “SWOT-like” and “mapping” swaths
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Technology Support for SWOT: Calibration Loop
To meet the phase calibration goals outlined above KaSPAR will implement calibration loops to verify a new technique SWOT plans to employ for channel phase calibration.
• This is to enable loopback phase calibration to greater accuracy than required strictly for KaSPAR(0.2o budgeted)
• Rather this will demonstrate calibration knowledge to millidegrees-Matched filter tracks phase-changes in real-time by recording transmitted pulse through full transceiver path
-SNR and stringent signal to leakage ratio requirements
Success impact in terms of SWOT:
verify proposed SWOT calibration loop which enables relaxation of
phase stability requirements since the method corrects for drift
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AirSWOT Technology Heritage and Infusion
Multichannel, high-throughput digital system compatible with unpressurized unattended operation
First demonstration of mm-wave SAR interferometry
• technology development & technique demonstration
• Processor development is direct heritage for KaSPAR/AirSWOT
GLISTIN slotted waveguide DBF array produced IPY/AITT
antenna design.
HiWRAP: IIP & NASA SBIR
GLISTIN-A: IPY & AITT
AirSWOT SWOT cal/val sensor: ESTO & NASA SBIR
Compact integrated assembly compatible across platforms (e.g. NASA King Air, Ikhana, Global Hawk, DC8).
7
GLISTIN: IIP
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KaSPAR Development Status
• Currently funded under a Phase II and Phase III NASA SBIR’s and NASA ESTO
• Phase II started April 2010 with radar design and RF
development for key assemblies
• Complementary activities for digital development
• Recent ESTO funding for system-level and processor development
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Antenna Summary
Narrow Beam Wide Beam
Size 21.2 cm x 4.0 cm 21.2 cm x 14.5 cm
Realized Gain 35.5 dBi 28.7 dBi
HPBW: Ecut 4.0 deg 17.2 deg Hcut 3.2 deg 2.6 deg
SLL: Ecut < -23 dB < -22 dB
Hcut < -23 dB < -23 dBI
Low CTE panel• Radome not shown integrated with antennas• Patterns verified, measured on near-field range
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Downconverters (4 of 7)
Upconverter
Transmitter IF
RF Subassemblies
• Subassembly development complete and CW tested
• Further characterization – eg temperature sensitivity underway
x2
Upconverter
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LO distribution
Internal Calibration
• Subassembly development complete and CW tested
RF Subassemblies (cont)
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Solid-State Power Amplifier
SSPA under development•Based on existing unit but accommodating new higher power MMIC’s with same combiner. •Timeline – November 2011•Thermal assessment underway (complementary with GLISTIN-A activities)
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Digital Receiver System
Radar Controller / Waveform GeneratorRadar Controller / Waveform Generator 3.6 GSa/s – 12-bit ADC Board3.6 GSa/s – 12-bit ADC Board
• Conduction Cooled 3U solution.• Deployed on Global Hawk and ER-2
(HIWRAP system).• Support 4 FPGA Processing Modules
(FPM) per system.• Each FPM can support up to 400
MHz bandwidth (100% duty).• Four Gigabit interfaces support > 400
MB/s sustained data recording rates.• ADC module is embedded in
transceiver providing 3.6 GSa/s 12-bit sampling.
• 5 Gbps fiber communication between ADC module and FPM.
• DDS/CTU supports synching of up to 8 ADC modules.
• DDS/CTU supports arbitrary amplitude tapering, LFM, NLFM, fixed frequency and CW waveforms.
• Fabrication will be completed in August/September 2011.
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AirSWOT: Payload SensorsTwo NASA airborne science facility sensors will be integrated with KaSPAR for the AirSWOT assembly:1. State-of-the-art Applanix 510 IMU (possibly 610) 2. DCS Near IR camera in aft port (cover field of view of radar with meter-
level pixel size at 35kft). • Map inundation extent using both KaSPAR and the DCS
• Spatial resolutions of 50 cm – 1 m.
• Frames synchronized with the IMU and radar.• It will include a near-infrared band, ideal for mapping
inundation
Map of water-land interface pixels for the Tanana River, AlaskaAt each red pixel, there is potential for classification error in KaSPAR data.
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AirSWOT: Platform considerations
P3 GulfstreamKing Air GlobalHawk/C130
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Initial Platform: NASA King Air B200
• Two available (DFRC and LARC) with nadir ports ready modified
• Altitude 35kft
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Near-term plans
• System-level I&T starting Winter 2011
• First engineering flights targeted for Spring 2012
• We need to formulate deployment plan for deployments pre-mission through SWOT calibration and validation (ie starting after engineering checkout ~ Fall 2012)- Draft will be compiled for SWG meeting in October
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Backups
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Example of Backscatter Dependence on Wind
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Aircraft considerations: NASA Global Hawk
• Best for mimicking SWOT geometry
• KaSPAR design is compatible with UAV deployment in the long-term
• Altitude 65kft• Long duration• Payload area 120”long x 56” wide• ER2 also a possibility
Payload area
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The backscattered power as a function of incidence angle was used to solve for the normalized radar cross-section using the radar range equation:
We know the antenna pattern and we assumed the following geometric optics approximation for 0:
Where s2 is the mean-square slope and hs is the small scale roughness.
Estimation of 0 near-nadir
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Airborne Velocity MappingIdeal for targeted response (search and
rescue, flood regions, pollutant spills, tidal flow patterns)
• two antennae separated by an along-track baseline B• one antenna transmits and one or both receive
• images from each receive channel are interpolated to the same spatial locations
• resultant images (separated in time by = B/v, where v is the platform velocity) are interfered
• the interferometric phase is related to the radial scene velocity u as
Right: C-band radial velocity image over San Francisco bay. Pixel resolution ~10m and velocity precision ~10cm. Swath ~8-10km
u
B
swath
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Example Products/Data
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KaSPAR Along-track Capability
• 50 x 80 m posting - no ping-pong and 6m/s wind• Good for assimilation and discharge estimation modeling• Also for eddy dynamics, sea-ice etc
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Processing and ProductsThe products available from KaSPAR will be the following:
1. Surface elevation maps of the water and land (land accuracy will be lessened)
• Swath of up to 5km depending on water state
• Resolution variable but innate instrument 1-look resolution is 10’s of cm along-track and 10-5m range
• Precision for ~50x50m posting is sub-3cm mean but assumes an ocean surface with 6m/s or greater winds
2. Surface temporal correlation
3. For outer incidence angles - surface radial velocity
4. Corresponding backscattered power and correlation maps
InSAR processing will build on the GLISTIN interferometric processor and calibration. Instrument and data calibration will provide greater challenges to achieve the accuracies wanted. The IMU and corrections for aircraft attitude is critical.
A facility near-IR camera will provide coregistered shoreline demarcation for classification verification
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Variability of 0(i)
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Swath Mapping Performance
Error Sources modeled Quantity Unit
random
SNR Derived from system radar-range equation for ocean at 6m/s wind
Unitless ratio
Geometric Derived for each baseline
ISLR/MNR -13 dB
Zero-range ambiguity Relative gain of 2-way antenna pattern from opposite side
Unitless ratio
systematic
Receiver phase drift knowledge error
0.2 degrees
Baseline deviation 20 microns
Range timing accuracy 3 ns
Mean height error performance (35kft, ocean)
Inner subswath 1.8 cm
Outer swath 2.3* cm
*
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Predicted Height Accuracy for “SWOT” Subswath
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Predicted Height Accuracy Across Swath
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Processing and ProductsThe products available from KaSPAR will be the following:
1. Surface elevation maps of the water and land (land accuracy will be lessened)
• Swath of up to 5km depending on water state
• Resolution variable but innate instrument 1-look resolution is 10’s of cm along-track and 10-5m range
• Precision for ~50x50m posting is sub-3cm mean but assumes an ocean surface with 6m/s or greater winds
2. Surface temporal correlation
3. For outer incidence angles - surface radial velocity
4. Corresponding backscattered power and correlation maps
InSAR processing will build on the GLISTIN interferometric processor and calibration. Instrument and data calibration will provide greater challenges to achieve the accuracies wanted. The IMU and corrections for aircraft attitude is critical.
A facility near-IR camera will provide coregistered shoreline demarcation for classification verification
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Strategies for Validation of KaSPAR Hydrologic Measurements
Water Level and Slope: • Install pressure transducer water level loggers in rivers and lakes,
recording water level changes every 15 minutes with mm-level precision. • Use differential GPS to obtain absolute elevations for each sensor. • Compare temporal and spatial variations in water surface elevation
between KaSPAR and field data.
Solinst Pressure Transducer Water Level Logger
Setup for a pressure transducer sensor installed in a lake
Examples of pressure transducer data for two river channels, Peace-Athabasca Delta, Canada
Differential GPS Equipment used for surveying water levels in rivers and lakes.
Sensor
Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill
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Strategies for Validation of KaSPAR Hydrologic Measurements
River Discharge and Flow Velocity: • With help from the U.S. Geological Survey, obtain Acoustic Doppler
Current Profiler (ADCP) measurements of river discharge coincident with AirSWOT data collection.
• Use discharge measurements from existing river gauging stations to validate AirSWOT discharge algorithms.
Photo courtesy USGS
An Example of ADCP Data
Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill
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AirSWOT support for SWOT pre-mission
• Multiple (elevation & temporal) baselines replicate and fully characterize SWOT sampling and geometry
• Gather pre-mission data for SWOT over specific and varied science targets for:
- Classification (eg: land/water, wet-land/water, ice/water etc)- Discharge algorithm validation- Water temporal correlation - Elevation (both land and water)- Surface backscatter - Vegetation attenuation- Elevation retrieval over vegetated water- Sea ice height measurement- Penetration into snow for cryospheric applications- …
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Strategies for Validation of KaSPAR Hydrologic Measurements
Inundation Extent:
• Map inundation extent using both KaSPAR and the high-resolution Digital Cirrus Camera (DCS) that will be included on AirSWOT.
• The DCS will collect data at spatial resolutions of 50 cm – 1 m. It will include a near-infrared band, which will be ideal for mapping inundation.
• Additionally, cross-river transects of inundation extent will be surveyed in the field using traditional surveying techniques.
Map of water-land interface pixels for the Tanana River, AlaskaAt each red pixel, there is potential for classification error in KaSPAR data.
Digital Cirrus Camera to be included on AirSWOT
Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill