Focused synthetic aperture radar processing of ice-sounder data collected over the Greenland ice sheet

©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.We developed a synthetic aperture radar (SAR) processing algorithm for airborne/spaceborne ice-sounding radar systems and applied it to data collected in Greenland. By using focused SAR (phase-corrected coherent averaging), we improved along-track resolution by a factor of four and provided a 6-dB processing gain over unfocused SAR (coherent averaging without phase correction) based on a point-target analysis for a Greenland ice-sounding data set. Also, we demonstrated that the focused-SAR processing reduced clutter and enabled us to identify bedrock-interface returns buried in clutter. Using focused-SAR technique, we processed data collected over a key 360-km-long portion of the 2000-m contour line of southwest Greenland. To the best of our knowledge, these are the first high-quality radar ice thickness measurements over this key location. Moreover, these ice-thickness measurements have been used for improving mass-balance estimates of the Greenland ice sheet

Ice-sheet bed 3-D tomography

This is the published version. Copyright 2010 International Glaciological SocietyInformation on bed topography and basal conditions is essential to developing the next-generation ice-sheet models needed to generate a more accurate estimate of ice-sheet contribution to sea-level rise. Synthetic aperture radar (SAR) images of the ice–bed can be analyzed to obtain information on bed topography and basal conditions. We developed a wideband SAR, which was used during July 2005 to perform measurements over a series of tracks between the GISP2 and GRIP cores near Summit Camp, Greenland. The wideband SAR included an eight-element receive-antenna array with multiple-phase centers. We applied the MUltiple SIgnal Classification (MUSIC) algorithm, which estimates direction of arrival signals, to single-pass multichannel data collected as part of this experiment to obtain fine-resolution bed topography. This information is used for producing fine-resolution estimates of bed topography over a large swath of 1600m, with a 25m posting and a relative accuracy of approximately 10m. The algorithm-derived estimate of ice thickness is within 10m of the GRIP ice-core length. Data collected on two parallel tracks separated by 500m and a perpendicular track are compared and found to have difference standard deviations of 9.1 and 10.3m for the parallel and perpendicular tracks, respectively

Suppressing coherent noise in radar applications with long dwell times

A method to for suppressing internally produced coherent noise in radar applications is presented and experimentally demonstrated. The technique enhances conventional coherent averaging and involves interpulse phase modulation that is introduced digitally in the transmit waveform and removed digitally following digitization in the receiver. Experimental demonstration of this concept resulted in an additional noise floor reduction of 15 to 20 dB (compared to the conventional coherent averaging alone) when the number of coherent averages was between 1000 to 100 000, beyond which no significant suppression was observed

Coherent radar ice thickness measurements over the Greenland ice sheet

This is the published version, also available here: http://dx.doi.org/10.1029/2001JD900183.We developed two 150-MHz coherent radar depth sounders for ice thickness measurements over the Greenland ice sheet. We developed one of these using connectorized components and the other using radio frequency integrated circuits (RFICs). Both systems are designed to use pulse compression techniques and coherent integration to obtain the high sensitivity required to measure the thickness of more than 4 km of cold ice. We used these systems to collect radar data over the interior and margins of the ice sheet and several outlet glaciers. We operated both radar systems on the NASA P-3B aircraft equipped with GPS receivers. Radar data are tagged with GPS-derived location information and are collected in conjunction with laser altimeter measurements. We have reduced all data collected since 1993 and derived ice thickness along all flight lines flown in support of Program for Regional Climate Assessment (PARCA) investigations and the North Greenland Ice Core Project. Radar echograms and derived ice thickness data are placed on a server at the University of Kansas (http://tornado.rsl.ukans.edu/Greenlanddata.htm) for easy access by the scientific community. We obtained good ice thickness information with an accuracy of ±10 m over 90% of the flight lines flown as a part of the PARCA initiative. In this paper we provide a brief description of the system along with samples of data over the interior, along the 2000-m contour line in the south and from a few selected outlet glaciers

Mobile Robots for Harsh Environments: Lessons Learned from Field Experiments

Mobile robots for harsh environments provide useful means for automating the collection of research data in the field by reducing human involvement. MARVIN II has been designed and constructed to autonomously collect radar measurements to determine properties of the polar ice sheets. This paper discusses the lessons learned from a number of field experiments with its predecessor MARVIN, and how these lessons influenced the new design of MARVIN II

Suppressing Coherent Noise in Radar Applications with Long Dwell Times

A method for suppressing internally produced coherent noise in radar applications is presented and experimentally demonstrated. The technique enhances conventional coherent averaging and involves interpulse phase modulation that is introduced digitally in the transmit waveform and removed digitally following digitization in the receiver. Experimental demonstration of this concept resulted in an additional noise floor reduction of 15 to 20 dB (compared to the conventional coherent averaging alone) when the number of coherent averages was between 1000 to 100 000, beyond which no significant suppression was observed. Index Terms---Radar signal processing

Multiband Multistatic Synthetic Aperture Radar for Measuring Ice Sheet Basal Conditions

Abstract — Ice sheet models are necessary to understand ice sheet dynamics and to predict their behavior. Of the primary inputs to these models, basal conditions are the least understood. By observing the forward and backscatter across a wide frequency range (over two octaves) the basal conditions can be established with a high level of confidence. For this purpose, we developed a multistatic synthetic aperture radar system that operates on three frequency bands (75-85 MHz, 140-160 MHz, and 330-370 MHz). The radar system is designed to use pulse compression techniques and coherent integration to obtain high loop sensitivity (203 dB) necessary to overcome radio frequency losses in ice. The system will be tested at Summit, Greenland (72°34 ’ N, 38°29 ’ W) during July 2004. Keywords- ice, scattering, multistatic, synthetic aperture radar I