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Development of the Millimeter-Wave Cloud Radar (MMCR):
An Unattended, Continuous Cloud Profiler
for the U.S. Dept. of Energy's ARM Program
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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.
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