Back-Scattering Characteristics of the Sea in the Region from 10 to 50 KMC

Measurements of radiation back scattering from the ocean have been made over the frequency range from 10 to 50 kmc by means of several cw, Doppler, microwave systems operating simultaneously. The systems were mounted on the bow of a ship and various antenna depression angles from 0° (horizontal) to 90° were used. Data were obtained for vertical, horizontal, and circular polarization, and for the cross-polarized component of vertically polarized radiation. Horn antennas of 20-db gain were used at all of the operating frequencies and, in addition, higher and lower gain antennas were used at certain selected frequencies. Signals recorded from a variety of sea conditions have been used to calculate the back-scattering cross section per unit area, σ°, and these calculations indicate that σ° is nearly constant with microwave frequency and increases as the antenna depression angle is increased. The Doppler frequency characteristics of the returned signals have also been obtained from these measurements. A comparison is made between the experimental results and the characteristics predicted from simple scattering mechanisms.