94 GHz Doppler Cloud Radar

Millimeter-wavelength radars are among the new research tools that have been developed during the past 10 years for studying the properties of boundary layer clouds and the processes that affect those properties. Millimeter-wavelength cloud radars (MMCRs) can detect most could droplets and the radar beam penetrates clouds of all types, except during periods of heavy rain.

Most of the time the Miami MMCR will operate in a vertical pointing mode providing an excellent tool for the observation and study of the vertical sturcture of clouds and especially "weak" meteorological targets (non precipitating) which normally are undetectable by a conventional weather radar(cm-wavelength radar).

Its main advantages over the use of centimeter radar are:

1. Increased space resolution (~30m) compared to 500m for the weather radar.
2. Its abliity to interact with smaller size particles (due to their small wavelength), so the observations are no longer limited to precipitation systems.
3. Enhanced velocity resolution (0.031m/s).
4. Excellent mobility of the system due to the lightweight MMCR components.

Roger Lhermitte (1987) describes a radar system operating at 3mm (94 GHz). Recently, a portable single antenna 94 GHz cloud radar was designed, constructed and tested here at the Rosensteil School of Marine and Atmospheric Science (RSMAS). Transmitter components from the orignial radar developed by Lhermitte were combined with a newly designed T-R switch to form this single antenna unit under the supervision of Dr. Bruce Albrecht.

MMCRs, depending on the type of Digital Signal Processor (DSP), can provide us with the three moments of the Doppler Spectrum S(v) (Autocovariance or Pulse Pair Processing) or with the full Doppler Spectra (FFT or Spectral Processing). The University of Miami radar will be upgraded with a next generation signal processor using the Bittware dual DSP board that was recently acquired by our group. The new DSP will increase the time resoultion, and provide spectra at 2 second intervals. Combined with other surface-based remote sensors like lidars, ceilometers, and passive infrared and microwave radiometers, the 94 GHz abliity to detect cloud sturcture and microphysics is enhanced substantially.