TABLE OF CONTENTS The reflectivity at vertical incidence is of importance in remote-sensing and in airborne radars where the altitude line echo enters the sidelobes of a sensitive airborne radar. Reflectivity is quite high for calm seas at 0 incidence (90 grazing), since the radar is looking downward onto a mirror-like flat plate with some curvature due to the spherical nature of the ocean surface. Thus, like a flat metallic plate, the ocean surface will have a gain factor and ? 0 will exceed unity. Unfortunately, the beamwidth of most measurement radars is relatively large and the earth's curvature must be taken into account. In addition, even 2 to 4 errors in knowing the vertical will yield significant errors. Thus, vertical incidence ? 0 data varies from + 10 to 26 dB for calm seas for either polarization. Values of + 15 to 20 dB for X- or K u band are appropriate for typical calm seas and small beamwidths. Note that with wavelengths of 2 to 3 cm, the sea would have to be extremely calm to emulate a flat plate. However, tank measurements by Uliana et al. [721] at 94 GHz yield ? 0 as high as + 26 dB for light winds. For calm seas at lower carrier frequencies ? 0 probably increases to above 20 dB until the carrier frequency is low enough that the waves penetrate the sea. Early measurements reported about + 16 dB at...
