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Old 03-25-2018, 08:57 PM   #1203 (permalink)
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Originally Posted by Fat Charlie View Post
Well yeah, water gravity is different than rock gravity. Makes perfect sense to me.

NASA Operation Icebridge


However the gravity of the Earth is not homogeneously distributed since different topographic features, such as mountain, plains, valleys or ocean trenches, have different masses.
Since water has less mass than rock it has less gravitational pull.
DC-8 flying over a glacier resting on land. As the aircraft flies over the glacier the instruments are collecting multiple pieces of information: Laser will provide surface imaging of the ice; Radar will provide internal imaging of the ice layers down to the underlying bedrock, and can thus be used to calculate ice thickness; Gravity will measure the difference in mass between flying over dense bedrock and a thick glacial ice sheet. The graphic here shows the drop in gravity as the plane moves from flying over bedrock to flying over ice.[
DC-8 flying over a floating glacier. The laser surface imaging data collected flying over a glacier floating on water will be the same whether the subsurface is bedrock or water. The radar will successfully image through the ice layers, but will not penetrate the water beneath the glacier, so the image return will differ from radar collected over bedrock. These images can be used to detect that there is a wet surface under the ice sheet, and to calculate the surface area, but not the depth. This is where the gravity data can be used to collect essential information. Since water has less mass than bedrock, as the plane moves over the floating glacier the gravity will drop with the reduction in mass. This reduction in gravity can be used to calculate the area of underlying water.