Optimum choice of pulse pair spacing

A pulse pair waveform can be transmitted in order to estimate the mean of the wake velocity power spectrum at a given range sampling station of an object reentering the atmosphere. It is shown here how one may select the spacing between pulses in a pair so as to minimize the predicted variance of the mean velocity estimate. This variance is a function of the radar wavelength, the pulse signal-to-noise ratio, and the true spread of the wake power spectrum to be measured. These parameters are all assumed known a priori or available from previous data. For a given wavelength and power spectrum, the optimum pulse pair spacing to be used depends only on the signal-to-noise ratio and not on the number of pairs. Therefore, one can simply send, at the optimum spacing, the fewest pulse pairs required to achieve the necessary accuracy and thus minimize the radar energy required as well.