Introduction to Radar Remote Sensing (Page 7):

Ground Photos

One can also learn a lot about the information provided by radar by studying a few key areas on the ground at the same time that we look at the radar data. Here we show five ground photos, taken from places in the air photography.

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Even from the air, we get a different impression of the lava flow than when we are on the ground. The first view we should have is an overview from the top of the cliff (point #3 in the radar image , and air photos #2 , #3 , #4 , and #5 ). This picture shows the smooth pahoehoe flows as bright, and the aa flows as darker materials. Mauna Loa volcano in the distance.

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From the air ( air photo #3 ), it is hard to imagine the size of the fault scarp. This photo shows what it is like when you are standing at its base.

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Having a good "feel" for the size of features also includes their thickness. A pahoehoe flow close to the vent can be very thin -- perhaps 20 to 30 cm -- and yet it appears to be a very large unit from the air. Here we see a flow very close to the fissure from which it erupted. The location of this picture is point #7 in the air photo.

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Finally, let us see what the topography of the aa and pahoehoe lava flows is like. We can best do this by seeing the relief when we use a "roughometer" that uses plastic rods suspended from a horizontal bar. On the pahoehoe, we can see that there is only a few centimeters of relief. In contrast, there is almost 1 meter of variation on the aa flow. Radar would see these differences as dark (pahoehoe) and bright (aa).

Go on to Page 8 of this Remote Sensing Tutorial to see how we produce color radar images.

Author: Pete Mouginis-Mark

Copyright by P. Mouginis-Mark

Curator: Lori Glaze