AirSwot : A Calibration/Validation Platform For The SWOT Mission

1. AirSwot: A Calibration/Validation Platform For The SWOT Mission Delwyn Moller, Ernesto Rodriguez, James Carswell, Daniel Esteban-Fernandez

2. Outline • 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

3. Ka-band SWOT Phenomenology Airborne Radar (KaSPAR) 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 scienceimpact 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 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

4. Swath Performance Random error across swath • Two sets of transmit antennas: • Illuminate inner (SWOT geometry) & outer swath to provide wide-swath coverage • Overlapping beams for inter-calibration

5. KaSPAR will make the following measurements*: • 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 • Corresponding backscattered power and correlation maps • For outer incidence angles - surface radial velocity • Surface temporal correlation estimates Measurements and Processing *all simultaneous including both “SWOT-like” and “mapping” swaths

6. 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

7. AirSWOTTechnology Heritage and Infusion HiWRAP: IIP & NASA SBIR GLISTIN-A: IPY & AITT GLISTIN: IIP • First demonstration of mm-wave SAR interferometry • technology development & technique demonstration • Processor development is direct heritage for KaSPAR/AirSWOT Multichannel, high-throughput digital system compatible with unpressurized unattended operation GLISTIN slotted waveguide DBF array produced IPY/AITT antenna design. AirSWOT SWOT cal/val sensor: ESTO & NASA SBIR Compact integrated assembly compatible across platforms (e.g. NASA King Air, Ikhana, Global Hawk, DC8).

8. 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

9. 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 • Radome not shown integrated with antennas • Patterns verified, measured on near-field range Low CTE panel

10. RF Subassemblies Transmitter IF Upconverter x2 Upconverter • Subassembly development complete and CW tested • Further characterization – eg temperature sensitivity underway Downconverters (4 of 7)

11. RF Subassemblies (cont) LO distribution • Subassembly development complete and CW tested Internal Calibration

12. 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)

13. Digital Receiver System • 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. Radar Controller / Waveform Generator 3.6 GSa/s – 12-bit ADC Board

14. AirSWOT: Payload Sensors • Two NASA airborne science facility sensors will be integrated with KaSPAR for the AirSWOT assembly: • State-of-the-art Applanix 510 IMU (possibly 610) • 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, Alaska At each red pixel, there is potential for classification error in KaSPAR data.

15. AirSWOT: Platform considerations P3 King Air Gulfstream GlobalHawk /C130

16. Initial Platform: NASA King Air B200 • Two available (DFRC and LARC) with nadir ports ready modified • Altitude 35kft

17. 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

18. Backups

19. Example of Backscatter Dependence on Wind

20. 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

21. Estimation of 0 near-nadir 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.

22. Airborne Velocity Mapping • Ideal 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 jis related to the radial scene velocity u as u swath B Right: C-band radial velocity image over San Francisco bay. Pixel resolution ~10m and velocity precision ~10cm. Swath ~8-10km

23. Example Products/Data

24. 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

25. The products available from KaSPAR will be the following: • 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 • Surface temporal correlation • For outer incidence angles - surface radial velocity • 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 Processing and Products

26. Variability of 0(i)

27. Swath Mapping Performance *

28. Predicted Height Accuracy for “SWOT” Subswath

29. Predicted Height Accuracy Across Swath

30. The products available from KaSPAR will be the following: • 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 • Surface temporal correlation • For outer incidence angles - surface radial velocity • 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 Processing and Products

31. 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. Examples of pressure transducer data for two river channels, Peace-Athabasca Delta, Canada Sensor Solinst Pressure Transducer Water Level Logger Setup for a pressure transducer sensor installed in a lake Differential GPS Equipment used for surveying water levels in rivers and lakes. Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill

32. 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. An Example of ADCP Data Photo courtesy USGS Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill

33. 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 • …

34. 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. Digital Cirrus Camera to be included on AirSWOT Map of water-land interface pixels for the Tanana River, Alaska At each red pixel, there is potential for classification error in KaSPAR data. Viewgraph credit: Tamlin Pavelsky UNC-Chapel Hill