Development of the Millimeter-Wave Cloud Radar (MMCR):

An Unattended, Continuous Cloud Profiler for the U.S. Dept. of Energy's ARM Program

Prototype MMCR radar at the Southern Great Plains testbed in Oklahoma.
Spectra contours.

Cloud radars transmit radio-frequency signals with wavelengths that are about 10 times shorter than those used by conventional storm surveillance radars, such as NEXRAD. The shorter wavelength helps these radars detect the tiny water droplets and ice crystals which comprise clouds, in addition to the much larger raindrops and snowflakes that conventional precipitation radars can "see". Fine-scale depictions of cloud layer heights and thicknesses, including multiple layer situations, are readily obtained from the ground with these ground-based systems. The cloud radar measurements can also be used to estimate the microphysical properties of the clouds, including particle sizes and mass contents, especially when the radar data are combined with simultaneous radiometer measurements. The information on cloud structure is particularly valuable for understanding and modeling how clouds reflect, absorb, redirect, and transform radiant energy passing through the atmosphere. It is vital information for improving climate models and climate prediction.

NOAA/ETL designed the MMCR, a vertically pointing Doppler cloud radar, specifically to monitor clouds overhead at the Cloud and Radiation Testbed CART sites of the U.S. Department of Energy's Atmospheric Radiation Measurement (DOE/ARM) program. These radars monitor the clouds continuously at sites in Oklahoma, Alaska, and the Tropical Western Pacific Ocean. They are intended to operate at these sites with minimal manned assistance for at least a decade. An identical cloud radar called the NOAA Portable Cloud Observatory (NPCO), is operated by ETL with coincident radiometers for shorter periods on a variety of research field projects. The NPCO radar attains extraordinary sensitivity (as good as -50 dBZ at 5km height) for detecting extremely weak non-precipitating clouds through the use of a relatively large antenna (6-ft or 10-ft diameter), long sampling (~ 1 second), signal processing and pulse compression techniques, and the short wavelength (8.7 mm). Microwave and infrared radiometers in the same container provide additional measurements of cloud conditions overhead.

For additional information on the MMCR, see the article:
Moran et al., 1998: An unattended cloud-profiling radar for use in climate research.
Bulletin of the American Meteorological Society, 79, 443-455.