 JPL Earth Science Airborne Program
Critical to progress in understanding and modeling ice sheets, are: a better characterization of what ice sheets are doing at present, how fast they are changing, what are the driving processes controlling these changes, and how we can better represent these processes in numerical models to derive more realistic predictions of the evolution of glaciers and ice sheets in the future. Chief among these measurements, are detailed, enhanced and sustained measurements of ice sheet elevation, at high spatial resolution, with high vertical accuracy, over the entire ice sheets. These measurements provide critical information about long-term ice sheet dynamics (mass balance trends) and short-term variability (precipitation, ablation events, surface lowering of an accelerating glacier, etc.).
Ideally suited to making these measurements is GLISTIN, a Ka-band single pass interferometric synthetic aperture radar (InSAR). Proposed also as a spaceborne mission concept [1], the airborne GLISTIN-A serves as a proof-of-concept demonstration and science sensor. Key features include:
1. The Ka-band center frequency maximizes the single-pass interferometric accuracy (which is proportional to the wavelength), reduces snow penetration (when compared with lower frequencies), and remains relatively impervious to atmospheric attenuation.
2. Imaging capabilities that are important for mapping large areas. Imaging allows features to be tracked with time for estimation of ice motion and reduces data noise when measuring topographic changes over rough surfaces of glaciers and coastal regions of ice sheets.
To achieve this demonstration in a timely and cost-effective manner, NASA’s Jet Propulsion Laboratories’ (JPL) L-band UAVSAR (link) was adapted for Ka-band operation and successfully collected interferometric data in engineering checkout flights March 13, 16 and April 21 and 29 2009 aboard the NASA Dryden Gulfstream III. This was followed by a comprehensive campaign to Greenland May 1-May 13, 2009 where collaborative acquisitions with the NASA Wallops Airborne Topographic Mapper (ATM) laser altimeter (link or reference) occurred coincident with in situ observations at CIRES’ (Cooperative Institute for Research in the Environmental Sciences) Swiss Camp and calibration sites at both Swiss Camp and the National Science Foundation’s Summit station.
[1] D. Moller, B. Heavey, E. Rignot, G. Sadowy, M. Simard and M. Zawadzki, “A Novel Ka-band Digitally Beamformed Interferometric Synthetic Aperture Radar for Glacier and Ice-sheet Topographic Mapping: Concept and Technology Development,“, EUSAR 08, Friedrichshafen, Germany |
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Adapted from Original
(credit: John Sonntag,
NASA Wallops) |
5/5/09 ATM and 5/4/09 & 5/5/09 GLISTIN-A coincident flight path |
5/5/09 & 5/6/09 mapping over Jakobshavn took place on consecutive days. Flights were repeated six days later (5/11/09 & 5/12/09). - see initial qualitative observation below in Google EarthTM inserts. The ATM flew this region ~1 week prior to first flights. |
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| Corner reflector deployed at Greenland’s Summit Camp. Three reflectors were deployed at both Summit and Swiss Camp/JAR1 and precision surveyed for 3D location for GLISTIN-A calibration. |
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Pictorial of ATM operation on the P3. The ATM lidar is key to validation and calibration of GLISTIN-A since it is nadir viewing and does not penetrate snow cover (therefore systematic biases are minimal). Coincident and collaborative flights were conducted |
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Quicklook” processed imagery from 5/5/09 (top) and 5/11/09 flying North-South over Jakobshavn. Cursory evaluation reveals approximately 800m-1km horizontal movement of features in the 6 day elapsed over the observation time period. |
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Ka-band maps at 3m x 3m posting generated from data collected on May 1, 2009 near the Greenland coast. a) relative backscatter image and b) Ka-band radar elevation map. Elevation contours are color coded with a wrap of 800 m, i.e. from red to red represents an elevation change of 800 m.c) Interferometric correlation and d) height error map (right) generated from the correlation data. Note the height accuracy varies from 30 cm in the near range to about 3 m in the far range. The data if averaged to the 30 m posting as needed for glacial science application will meet the 50 cm height accuracy requirements almost everywhere in the swath |
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