Ultrawideband normalized radar cross sections of distributed clutter

Theoretical and empirical formulas have been derived to compute the normalized radar cross section (NRCS) of distributed clutter targets for remote sensing applications. These formulas are usually parameterized in terms of the center frequency, and are therefore frequency-dependent. In recent years, high resolution measurements are being investigated for improved terrain characterization using ultrawideband (UWB) radar systems. In such cases, the NRCS value at the center frequency is generally used for calculations. This approximation does not cause too great an error when the system operates over a narrow frequency band, typically less than 10%. However, under UWB conditions, errors as large as a few decibels can occur under this assumption. We derive an expression for the UWB NRCS of distributed clutter as a function of the NRCS value at the center frequency and the fractional bandwidth. We show the application of these results in deducing the UWB signal-to-clutter ratio (SCR) for representative targets. It is seen that the UWB SCR increases with increasing fractional bandwidth initially, and then tends to level off at higher fractional bandwidths.