Measurements at 13.9 GHz of the radar backscattering cross section of the North Sea covered with an artificial surface film

The reduction of the Ku-band (13.9 GHz) normalized radar cross section (NRCS) by an artificial monomolecular surface film (oleyl alcohol) on the sea surface was measured in the North Sea during the 1975 Joint North Sea Wave Project, JONSWAP 75 experiment. The aim of the surface film experiment was to simulate natural surface films which often occur on the ocean surface and are produced by plankton or fish. NRCS measurements were obtained from an aircraft at incidence angles of 41 deg and 47 deg at vertical and horizontal polarizations. For winds between 3.5 and 4.4 m/sec the maximum measured reduction was 7.3 plus or minus 3.5 dB relative to the mean. In-situ measurements showed that the oleyl alcohol film reduced the surface tension from 74 to 43 dyne/cm.