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Polar Radar for Ice Sheet Measurements

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Home>PRISM Update>Radar Team>A mirror-like (specular) wet bedrock...


A mirror-like (specular) wet bedrock surface limits the radar reflectivity in areas of ice streams and glaciers.

Picture of John Paden  



Part One of Two

Audio version - Part 1 (12.7 MB) - .wav format
Video version - Part 1 (21.6 MB) - .mov format

Part Two of Two

Audio version - Part 2 (10.8 MB) - .wav format
Video version - Part 2 (18.3 MB) - .mov format
Speaker: John Paden, graduate student, EECS, University of Kansas, 2002.

Modified Part One Transcript: To understand why we need to use bistatic radar to measure a whole swath of bedrock, rather than a single line, you have to understand what the bedrock looks like to the radar. A good analogy to illustrate this situation is to imagine a laser pointer as the transmitter of the radar. If you think of the bedrock as a mirror and if you shine your light straight down, the only energy reflected is going to be reflected straight back at you. If you were to stand just the slightest bit away from the source of light, you wouldn't see the light coming back at you. This shows if you want to measure a kilometer swath of the bedrock, then a measurement has to occur at every point along that kilometer swath, because you are only seeing right beneath you. If you want to see a thousand meters over, then you have move a thousand meters over on the ice. This is an extremely slow process.

Modified Part Two Transcript: If the surface were truly specular, or mirror-like, it wouldn't matter if we used monostatic or bistatic radar. Normally, on a mirror, if you shine your laser pointer, or transmitter at a 45 degree angle you would expect the energy to go down, strike the bedrock and be reflected away from you at a 45 degree angle. You would only receive energy at a certain point. In actuality the surface isn't perfectly specular, the bedrock doesn't act like a mirror, it is more like aluminum foil that has been crinkled a little bit. Since the bedrock acts like aluminum foil that has been crinkled a little bit, most of the energy is focused at one point, but you do get some energy back at what are called off-specular angles. This means if you move a little bit from the main focus of the energy, you can still receive some of the energy, but if you move more, you don't receive any energy.


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