Picture of NASA Gulfstream III with pod configured for Ka-band interferometry. Lower insert shows close-up with details of the two antennas. Photo credit: Chun-lun (Ernie) Chuang, JPL.

Jakobshavn Isbrae Mosaic: Shaded Relief
May 5 and 6, 2009 - 84km x 84km area

Jakobshavn Isbrae Mosaic: Height Map 80m Wrap
May 5 and 6, 2009 - 84km x 84km area

In May 2009, a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year (IPY) activities [1]. The demonstration occurred using the airborne glacier and ice surface topography interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer implemented as an adaptation to the Jet Propulsion Laboratory (JPL) L-band uninhabited airborne vehicle synthetic aperture radar (UAVSAR) [2] (see images on top right). Although the technique of using radar interferometry for mapping terrain has been demonstrated before, this was the first such application at millimeter-wave frequencies.

GLISTIN-A performance indicates swath-widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. During the 2009 campaign collaborative flights were made with NASA’s Airborne Topographic Mapper lidar on board the NASA P3 to evaluate effective penetration of the interferometric signal into the snow cover. Furthermore GLISTIN-A produced high-resolution maps over Jakobshavn Isbrae (see images on lower right, click images to enlarge).

Further to assessment of the IPY data collections, the GLISTIN-A system has been funded under the NASA Earth Science Technology Office (ESTO) Airborne Innovative Technology Transition (AITT) program for system performance upgrades and modifications to transition this system to an operational capability for NASA. The AITT implementation will incorporate two distinct changes that improve performance and also enable unpressurized and autonomous operation. Table 1 summarizes the modifications. While the peak transmit power is equivalent, the TWTA used during IPY required pressurized operation. Additional advantages of the SSPA is a reduction in front-end losses since it is located in the pod next to the antennas and there is no hard duty cycle limit like that imposed with tube amplifiers. The second performance upgrade is the addition of ping-pong capability which improves the height precision by a factor of two. Reflected in Table 1, with these modifications we can collect data at higher altitudes of operation for increased swath for the same range of incidence angles (near, mid and far swath correspond to look angles of 15°, 31° and 50° respectively). The height precisions quoted indicate an equivalent height performance for GLISTIN-A, but covering a nominal swath of 10km rather than 6km. (Notionally one could also degrade the swath for a higher precision product.)

Table 1: Summary of changes from IPY to GLISTIN-A and performance/swath advantage (highlighted)

Parameter	Units		IPY	GLISTIN-A
Peak transmit power (at antenna)	W		40 (TWTA)	40 (SSPA)
Receive Losses	dB		5	2
Ping-pong			No	Yes
Nominal Flight Altitude (AGL)	km		7	11
Nominal Swath	km		6	10
Height Precision (30x30m posting)	M	15° 31° 50°	0.06 0.14 0.50	0.10 0.11 0.49

Partners and Related Technologies and Missions:

• JPL
• NASA Airborne Science
• NASA ESTO

References:

[1] Moller, D.; Hensley, S.; Sadowy, G. A.; Fisher, C. D.; Michel, T.; Zawadzki, M.; Rignot, E.; , “The Glacier and Land Ice Surface Topography Interferometer: An Airborne Proof-of-Concept Demonstration of High-Precision Ka-Band Single-Pass Elevation Mapping,” Geoscience and Remote Sensing, IEEE Transactions on , vol.PP, no.99, pp.1-16, 0 doi: 10.1109/TGRS.2010.2057254

[2] P. A. Rosen, S. Hensley, K. Wheeler, G. Sadowy, T. Miller, S. Shaffer, R. Muellerschoen, C. Jones, H. Zebker, S. Madsen, “UAVSAR: A New NASA Airborne SAR System for Science and Technology Research,” Proc. IEEE Conference on Radar, 24-27 April 2006, pp8.

Contact RSS for more information.