detection when the blind range exceeds the radar horizon. Radial velocity Radial velocity is the speed along the line of sight of toward the radar and away from the radar. This kind of motion degrades cross section performance due to the following phenomenon. Scalloping Doppler ambiguity function Moving target indication blind velocities Instrumented range The instrumented range is the maximum distance at which a radar return may be displayed. This does not indicate an object will be detected at this range, but merely that beyond this range no returns will be displayed at all. Scan time The scan time is the time between re-scan of the same volume. For example, if a radar rotates at a fixed speed of 4 RPM, then the scan time is 15 seconds (60/4). Scan time performance interacts with high-speed objects. Excessive scan time allows high-speed objects to travel a large distance toward the radar without being detected. Altitude Altitude is the distance from the earth surface. This measure of performance interacts with elevation angle. The Kármán line is generally accepted as the boundary between air and space. This is 100 km (62.5 mile). There are two difficulties associated with altitude. The first difficulty is that the Outer Space Treaty requires international disclosure for space operations. This can include RF emissions from radar systems that can observe objects in space. The second difficulty is that there are millions of objects in low Earth orbit. Reflections from distances beyond the instrumented range can degrade performance. Elevation angle The elevation angle performance of a radar is determined by the type of antenna. High elevation The antenna panels used with phased array radar may be designed with an overlap that fills in any gap above a fully operational radar. The radiation pattern of a rotating truncated parabolic antenna for radar fixed pedestal has a fan shaped beam with a vertical gap in coverage. Objects located directly above the radar may not be detected. Low elevation Low elevation is a unique performance region. Pulse-Doppler radar and Continuous-wave radar are required for high performance in this area because these exclude low-velocity reflections. This is a critical measure of performance for the Littoral zone and land-based radar. Prevailing winds of about 15 mile/hour cover most of the surface of the earth. This constantly stirs up debris into the lowest several thousand feet of air, and each piece of debris creates a