PRISM Multiband Multistatic SAR

Authors: J. Paden, D. Dunson, S. Mozaffar, T. Akins, C. Allen and S. Gogineni

The Polar Radar for Ice Sheet Measurements (PRISM) is a part of a large Information Technology Research (ITR) project, funded by NSF and NASA. As a part of this project, we developed a multiband, multistatic SAR that operates over three frequency bands (75-85 MHz, 140-160 MHz, and 330-370 MHz). Below are the results from one of the bands of the SAR system.

Goal: Image base of ice sheet using a multiband, multistatic, synthetic aperture radar operating in the VHF band.

• Multiband operation allows frequency dependent phenomenon like surface roughness to be determined.
• The multistatic approach is necessary to provide estimates of path loss through ice. Specifically, the following two effects on signal loss can be determined using a multistatic approach.
  • Path attenuation changes according to the bulk temperature and impurity content of the ice sheet.
  • Basal reflectivity changes according to the electrical permittivity of the base.
• SAR imaging provides bedrock resolutions capable of imaging water channels and smaller geographic features.

Refraction: As the electromagnetic wave propagates into the ice sheet at oblique incidence, it is refracted by the continuous change of snow into ice.

• The figure below shows the dielectric of the ice sheet at Summit, Greenland as a function of depth. The dielectric is found by using density and temperature information from the nearby GRIP ice core.
• The refraction is accounted for in the SAR processing by using look-up tables for efficiency.

	Weakly Directional Log-Periodic Antennas
	Directional TEM Horn Antenna Array

Antenna factor of the horn array projected on the bedrock. The horn array solves the left-right range ambiguity problem and also suppressed the nadir response (0 meter cross-track). The green circles represent the desired signal and the red circle represents the undesired signal. There is ≥ 18 dB of isolation between the two.

Bedrock measurements at the same location with (a) the log-periodic antennas and (b) the horn array. Note that the primary bedrock signal (assumed to be primarily from the near-nadir direction) is suppressed with the horn array.

Monostatic SAR images at four different locations plotted in dB. Two passes were made at each location (offset by several meters). The above images demonstrate the repeatability of the system.

Insert 4 images in the order given (2 part table with image and caption horizontal)

The mesh graphs shown here are the first ever monostatic SAR images through cold thick ice.

• The color represents the scattering power received from each pixel on a decibel (dB) scale.
• Along-track resolution: 12 m (500-m aperture)
• Cross-track resolution is between 30 to 15 m (range dependent).
• Radar Specs: 150 MHz, HH Polarization
• Location: Summit, Greenland - 2004

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