Ground-Based Remote Sensing of Cloud Properties ...
365
for qualitative studies of cloud behavior, as well as quantitative determinations of cloud boundaries. However, the real power of radar lies in combining reflectivity and Doppler velocity
measurements with !idar cloud base and passive radiometric measurements. Radiometric measurements typically provide integral measurements of total condensed phase. By using these
as constraints on cloud particle retrievals from the active sensors, we can devise methods that
allow us to define the vertical distribution of cloud particle size and condensed water content.
This is a remarkable achievement. Further, the instruments currently being developed are much
more robust than their earlier counterparts. Millimeter-wave radar and smalllidar systems can
be run continuously and unattended, as can passive radiometers. Various investigators have
demonstrated this capability with individual instruments, and now the Atmospheric Radiation Measurement (ARM) program, sponsored by the United States Department of Energy, is
putting instruments systems together for long term operations.
Given this progress, development of routine signal processing techniques for radars and retrieval
algorithms for instrument systems must be viewed as high priority research. Much like satellites
provide measurements of spatial variability, these suites of groundbased instruments can be
used to continuously measure cloud statistics, provided that algorithms are available to process
the raw data streams. These statistics will have many uses, including model verification and
satellite retrieval validation. Most importantly, the unique perspective on cloud properties
provided by these retrievals and statistics will improve our understanding of cloud physics and
cloud processes.
Acknowledgments
We are indebted to many colleagues for their help as we have delved into radar signal processing and interpretation. We are especially indebted to Bruce Albrecht, whose efforts were
instrumental in the development of a millimeter-wave cloud radar here in the Department of
Meteorology at the Pennsylvania State University. Robert Peters engineered the radar system,
with supporting help from J. Thomas Treaster, and he has patiently answered all of our questions about its operation. Gerald Mace has worked unceasingly to collect important data sets
with the radar and, as we begin to apply cloud retrievals of the sort described in this document
to these data sets, his contributions will become increasingly apparent. The core of this paper
originated with a number of discussions with our colleague Hans Verlinde as he designed and
taught a Radar Meteorology course for the first time here in the Department of Meteorology.
The number of references to various scientists in the National Atmospheric and Oceanic Administration attests to their significant contributions to this field of research. This work would
not have been possible without early support from the National Aeronautics and Space Administration (NAG-I-999) and sustained support from the Department of Energy Atmospheric
Radiation Measurements Program (DE-FG02-90ER61071).
13.10 References
Atlas D, Ed (1990) Radar in Meteorology. American Meteorological Society, Boston, Massachusetts
Battan LJ (1973) Radar Observation of the Atmosphere. University of Chicago Press, Chicago,
Illinois
Bohren CF, Huffman DR (1983) Absorption and Scattering of Light by Small Particles.
John Wiley and Sons, New York, New York
365
for qualitative studies of cloud behavior, as well as quantitative determinations of cloud boundaries. However, the real power of radar lies in combining reflectivity and Doppler velocity
measurements with !idar cloud base and passive radiometric measurements. Radiometric measurements typically provide integral measurements of total condensed phase. By using these
as constraints on cloud particle retrievals from the active sensors, we can devise methods that
allow us to define the vertical distribution of cloud particle size and condensed water content.
This is a remarkable achievement. Further, the instruments currently being developed are much
more robust than their earlier counterparts. Millimeter-wave radar and smalllidar systems can
be run continuously and unattended, as can passive radiometers. Various investigators have
demonstrated this capability with individual instruments, and now the Atmospheric Radiation Measurement (ARM) program, sponsored by the United States Department of Energy, is
putting instruments systems together for long term operations.
Given this progress, development of routine signal processing techniques for radars and retrieval
algorithms for instrument systems must be viewed as high priority research. Much like satellites
provide measurements of spatial variability, these suites of groundbased instruments can be
used to continuously measure cloud statistics, provided that algorithms are available to process
the raw data streams. These statistics will have many uses, including model verification and
satellite retrieval validation. Most importantly, the unique perspective on cloud properties
provided by these retrievals and statistics will improve our understanding of cloud physics and
cloud processes.
Acknowledgments
We are indebted to many colleagues for their help as we have delved into radar signal processing and interpretation. We are especially indebted to Bruce Albrecht, whose efforts were
instrumental in the development of a millimeter-wave cloud radar here in the Department of
Meteorology at the Pennsylvania State University. Robert Peters engineered the radar system,
with supporting help from J. Thomas Treaster, and he has patiently answered all of our questions about its operation. Gerald Mace has worked unceasingly to collect important data sets
with the radar and, as we begin to apply cloud retrievals of the sort described in this document
to these data sets, his contributions will become increasingly apparent. The core of this paper
originated with a number of discussions with our colleague Hans Verlinde as he designed and
taught a Radar Meteorology course for the first time here in the Department of Meteorology.
The number of references to various scientists in the National Atmospheric and Oceanic Administration attests to their significant contributions to this field of research. This work would
not have been possible without early support from the National Aeronautics and Space Administration (NAG-I-999) and sustained support from the Department of Energy Atmospheric
Radiation Measurements Program (DE-FG02-90ER61071).
13.10 References
Atlas D, Ed (1990) Radar in Meteorology. American Meteorological Society, Boston, Massachusetts
Battan LJ (1973) Radar Observation of the Atmosphere. University of Chicago Press, Chicago,
Illinois
Bohren CF, Huffman DR (1983) Absorption and Scattering of Light by Small Particles.
John Wiley and Sons, New York, New York