13.1 INTRODUCTION

Indoor RCS measurement ranges offer advantages not possible on outdoor ranges. Probably the single most important disadvantage of outdoor measurements is the necessity of dealing with both the vagaries and the long-term effects of weather. Measurements cannot be made in the rain because of moisture collection on targets and target support columns and the backscatter from the raindrops in the measurement zone. Although many of the outdoor ranges listed in Table 12.5 are in the desert, where rain is rarely a problem, wind is a major concern. All outdoor ranges have requirements that limit operation in even moderate winds. If foam support columns are employed, light guy lines are almost always used to secure the target and prevent it from blowing off its support. Those guy lines contribute to the RCS, and even with lines providing additional support, measurements must often be halted when wind speeds approach 10 m/s. The weather encountered on outdoor ranges is also hard on range equipment exposed to the elements (support columns or pylons, turntables, RAM, antennas). For example, at RATSCAT over a period of time hygroscopic gypsum dust coats and penetrates the surface of support columns and the RAM used to shield turntables. The dust adversely affects scattering characteristics, particularly in wet or humid weather, requiring more frequent replacement of those components than on indoor ranges.

Moreover, outdoor measurements are subject to overhead observation by aircraft or satellites, a significant problem with sensitive targets. Although many ranges are in...