Asymmetric Doppler amplitudes in the surface scatter channel for crosswind transmitter–receiver geometry

Doppler asymmetries have been observed in model tank experiments in the signal received after being scattered from a wind‐driven surface. A distinct spectral shift was observed when the plane containing the transmitter and receiver was perpendicular to the wind direction. This paper examines the conjecture that this shift arises from the fundamental asymmetry observed in a wind‐driven surface, i.e., from the fact that the upwind slopes tend to be shallower than the downwind slopes. Three different situations are considered: (1) a deterministic surface, (2) a random surface with large Rayleigh parameter, (3) a random surface with small Rayleigh parameter. All three models show that the slope asymmetry results in Doppler asymmetry; however, the amount of this asymmetry corresponding to realistic values of surface parameters is very small. Hence the slope asymmetry does not completely explain the occasionally observed larger spectral shifts, and other mechanisms must be considered.