ASA 127th Meeting M.I.T. 1994 June 6-10

5pUW9. Improved empirical descriptions of the dependence of surface backscatter on air-sea environmental descriptors.

Michael Nicholas

Peter M. Ogden

Fred T. Erskine

Naval Res. Lab., Code 7142, 4555 Overlook Ave. SW, Washington, DC 20375-5350

Between August 1988 and March 1992 six at-sea experiments were performed in which sea surface backscattering strengths were measured from ~70 to ~1000 Hz utilizing explosive (SUS) charges. (These were part of the Critical Sea Tests.) The latter of the six experiments (CST-7) was particularly interesting in that wind speeds as high as 17.5 m/s (at 10-m height) were encountered, which is 4 m/s higher than in any of the earlier experiments. Here, results obtained from CST-7 will be compared with those from the five earlier tests, and some important differences will be presented. Some new empirical formulas will be presented that describe the results from all six of the CST tests better than the Ogden--Erskine algorithm. (The Ogden--Erskine algorithm was formulated using data from the first five tests only and is now widely regarded as a much better description than the older Chapman--Harris formula.) Possibilities for improving still further the prediction of surface scattering strengths will be discussed. [Work supported by ONR.]