A New High Resolution Turbulence Profiling Fm-Cw Radar

Abstract

Most boundary layer studies of refmtive index fluctuations have centered on the use of tall tower or balloon-borne systems. Often there has beena lack of temporal/spatial resolution and continuity. The U.S. Army Atmospheric Sciences Laboratory (ASL) at White Sands Missile Range is now operating a new Frequency ModulatedContinuous Wave (FM-CW) radar for Boundary Layer (BL) studies. This radar can uniquely obtain continuous ultra-high resolution (1-2m) measurements of radar power return by sensing clear-air turbulent backscattered power from Bragg scattered 5cm turbulent cells from 5Om to 22OOm AGL. Using one antenna to transmit and one to receive, the radar uses an empirical calibration for the first 100 meters above the ante-, and a 1st principles calibration from there up to approximately 2 kilometers to obtain real-time C,2 values. When observing hydrometeor type backscatter, hardware gains can be adjusted to also obtain similar resolution of power return from Rayleigh scattered precipitation. FM-CW measurements can be applied to boundary layer dynamic theory, radio wave propagation, and studies of imaging and laser propagation. A system description describing various salient features, samples of episodal events, and comparison data with a tethered balloon system is shown. BACKGROUND AND INTRODUCTION The first high resolution meteorological FM-CW radar was operated in San Diego in 1969 (Richter, 1969). Originally designed to perform electromagnetic propagation studies for the Navy, the radar proved indispensable in "seeing" air mass layers such as marineldry air boundaries, KelvinHelmholtz (K-H) induced wave structures, and the (at that time) infamous dot angels. The resolution showed such a high level of spactial and temporal detail that often layers were: found to be only a few meters thick, rather than tens of meters (allured to in the Wallops Island multiwavelength radar experiments; Hardy, 1966, and Richter, 1974). Insects could be seen individually with their speed calculated as they were caught up in atmospheric wave motions (Atlas, 19709, and K-H instabilities producing "cat's eyes" were seen in incredible detail (Gossard, 1971). The NOAA Wave Propagation Laboratory, in Boulder, built the second FM-CW radar, adding Doppler winds capability (Chadwick, 19:76), and also calibrated the radar for Gz measurements. The third FMCW radar used for BL studies was delivered to ASL late last year, and incorporates most if not all features of the previous HM-CW radars, and also takes advantage of newer technologies. Following is a system description and discussion of sample data.