An Improved Empirical Model for Radar Sea Clutter Reflectivity

A fundamental characteristic of radar sea clutter, important for radar performance evaluations, is its apparent reflectivity defined a σ^o (m²/m²). “Apparent” is used as a reminder that any measurement of sea clutter reflectivity includes the effects of propagation and shadowing close to the sea surface. Sea clutter reflectivity depends on many factors, including sea state, wind velocity, grazing angle, polarization, and radar frequency. An empirical sea clutter model proposed by Horst, et al. (1978), the so-called GIT model, has found widespread acceptance in the radar community. However, this model does not always agree with what is the most complete experimental database of sea clutter reflectivity available to the radar systems engineer. The 1991 edition of F. E. Nathanson´s book provides seven tables of measured sea clutter reflectivity data summarized from approximately 60 sources. The large deviation between the GIT model and this database, in particular at lower sea states, has prompted NRL to develop an improved model for sea clutter reflectivity based on these tables. The model is a function of radar frequency, polarization, sea state, and grazing angle. The functional form of this empirical model was chosen such that the average absolute deviation (in dB) between the model and the experimental data was minimized.