A Technique for Obtaining Sea Ice Thickness Measurements from Aircraft
Authors: McIntosh J.A. , Young C. Wayne 
Published: October 2008

The problem of developing instrumentation or techniques for measuring sea ice thickness remotely is a difficult one. Recent efforts at solving this problem have involved radio phase-interference, surface conductivity at radio frequencies, temperature measurements in the microwave and infrared bands, and various sonic techniques. These. techniques, at least to date, either work only under special conditions or require other, additional information to resolve ambiguities. For example, the sonic technique appears to work reasonably well when sounding upwards from the water-side, but poorly when sounding downwards from the airside. Examining this situation, we felt that the only chance to significantly improve this situation lay in the development of a completely different approach. (Although we were not aware of any previous work or proposals of this sort at the time the project was begun, we later became aware of a proposal prepared by a private firm for submission to the U.S. Army that is quite similar to the work described. here and predated it by several years.)

We eventually decided on tests to examine the feasibility of an air-dropped penetrometer which, of course, involved completely different phenomena than had been. used heretofore and which did not appear to require any prior knowledge (or assumptions) .. of the ice. Although the penetrometer provides only a point measurement, we believe that this will prove to be quite satisfactory when a significant number of these point measurements are properly combined with the output of imaging sensors such as the side-looking airborne radar. another area of concern is the fact that in this technique hardware is expended. One is naturally reluctant to throw things out of airplanes, no doubt due to the cost and the finality of it. However, if one considers all of the costs involved obtaining sea ice thickness measurements in the Arctic, particularly measurements whose locations are not influenced by the type and roughness of the ice itself, the cost of one or two hundred dollars per instrument (i.e., measurement) is not unreasonable.

In making inquires about this project, the Coast Guard discovered that Sandia Laboratory, which is a prime contractor to the U.S. Atomic Energy Commission, has done extensive work with air-launched, instrumented projectiles for earth penetration. The technology involved in these projectiles, which includes instrumentation that will survive and operate in a high It environment, has been under refinement at Sandia Laboratory for anumber of years. The Coast Guard contracted with Sandia Laboratory to perform a series of feasibility tests from an icebreaker off the coast of Alaska in Feb., 1970.

For reasons of economy and convenience it was decided that existing Sandia earth penetration projectiles would be modified as necessary for the sea ice feasibility tests, even though they were not suitable (as to cost or design) for extensive, operational use. To verify projectile design and proper system operation, several additional tests were performed prior to those in Alaska.