A reexamination of the pulse length dependence of backscattered power observed by VHF radars at vertical incidence

The dependence of Fresnel scatter on the pulse length in the lower VHF region is studied using observations from two VHF radars. Vertical profiles of the power reflection are determined for both radars for 150, 300, 1000, and 2400-m range gates and 4 and 16-microsecond pulses. The observations indicate the existence of a complex day-to-day variation in the dependence for range gates shorter than 1 km. The pulse-length dependence of Fresnel scatter was also found to be a Delta-R dependence in the majority of the comparisons, though (Delta-R)-square dependence was observed in 25-30 percent of the comparisons.