Laurence Gray

After joining the Canada Centre for Remote Sensing in 1975, Dr. Laurence Gray pioneered the study of radar signatures from different types of Arctic sea ice. This work was instrumental in the adoption of airborne and satellite synthetic aperture radar (SAR) for operational ice and cold ocean surveillance and also provided a strong justification for Canada’s first Earth Observation satellite, RADARSAT-1, launched in 1995.

Gray led the Canadian R&D on the ocean radar backscatter signatures as a function of wind speed and direction. Based on the combined international effort in this field, NASA and ESA (European Space Agency) developed specialized satellite radar systems to provide ocean wind field information to operational weather agencies.

Gray was key in the development and use of the CCRS airborne radar facility (the `SAR-580′). He was the first to demonstrate repeat-pass interferometry with airborne SAR, recovering the movement of a radar target to an accuracy of a few millimeters. Also, using this facility he developed and demonstrated cross-track interferometry for DEM generation, and along-track interferometry for target motion. This facility is now part of the collection of aircraft in the Canada Aviation and Space Museum.

After the 1997 CSA-NASA RADARSAT Antarctic Mapping Mission (AMM), Gray showed that glacial ice motion in polar regions could be mapped using a new technique now referred to as ‘speckle tracking’. Working with US collaborators, this has led to the discovery in Antarctica of new ice streams and ‘tributary’ systems. One of these, the Blackwall Ice Stream, is now named after the first Canadian scientist, Hugh Blackwall Evans, to overwinter in Antarctica.

Gray developed techniques for 3-dimensional terrain displacement using satellite SAR interferometry and applied these to polar glacial ice movement. This led to the discovery by Gray of episodic movement of pockets of subglacial water under Antarctic ice streams. Through the work on polar interferometry, Gray discovered that some previously assumed ‘processing artifacts’ in both the ESA ERS radar satellites and RADARSAT were not artifacts at all but were the results of auroral zone fluctuations in electron density in the ionosphere. As a result, it is now possible to better predict the impact of the ionosphere on the performance of satellite radars operating at different frequencies.

Gray derived a Digital Elevation Model (DEM) over the western part of the Devon Ice Cap in Nunavut Canada using a new technique called ‘swath processing’ of data collected by the ESA satellite Cryosat. Since the commissioning in 2010, Gray has continued to develop new processing techniques for CryoSat, showing that the derived height change data could help in monitoring mass balance change from Arctic ice caps.


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