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SciTech Watch: Clouds in 3D

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Weather satellites have been around since the 1960s, but the data return has always been two-dimensional.  This week on SciTech Watch, we learn about the latest weather satellite and its three-dimensional capabilities.

Launched at the end of April by NASA, Cloudsat's mission is to investigate clouds using a radar system known as Cloud Profiling Radar (CPR).  Developed jointly by NASA/JPL and the Canadian Space Agency (CSA). The overall design of the CPR is based on technology used by earth-based and airborne radar systems. 

To achieve sufficient cloud detection sensitivity, a relatively low frequency (i.e., <94 GHz) radar would require an enormous antenna and high peak power. At frequencies much greater than 100 GHz, a large antenna and high peak power are also needed due to rapid signal attenuation through cloud absorption.  The 94-GHz frequency chosen by CPR offers the best compromise between performance and spacecraft resources.

Most existing airborne cloud radars operate at 94 GHz. These airborne radars provide extensive heritage for CPR on instrument design and technology, data processing, and retrieval algorithms. A primary frequency allocation of 94 GHz for spaceborne cloud radar sensing was formally approved at the 1997 World Radio Conference.

CPR is more than 1,000 times more sensitive than typical weather radar. It can observe clouds and precipitation in a way never before possible, distinguishing between cloud particles and precipitation.  Using CPR from orbit provides three dimensional data, which is used to reconstruct the interior structures of cloud formations associated with weather systems.  These radar data are expected to offer new insights into how fresh water is created from water vapor and how much of this water falls to the surface as rain and snow.

The CPR radar system was activated this week for the first time and immediately began returning radar images showing slices of cloud formations directly below the spacecraft's orbit.  CloudSat principal investigator, Dr. Graeme Stephens, a professor at Colorado State University, Fort Collins was enthusiastic:

CloudSat's radar performed flawlessly, and although the data are still very preliminary, it provided breathtaking new views of the weather on our planet.  All major cloud system types were observed, and the radar demonstrated its ability to penetrate through almost all but the heaviest rainfall.  We have now begun continuous radar operations, and we look forward to releasing our first validated data to the science community within nine months, hopefully sooner.

The data provided by CloudSat will contribute to our understanding of weather systems and changes in rainfall amounts and locations.  This, in turn, will aid our understanding and coping efforts as our earth undergoes climatic and geophysical changes.

CloudSat is managed by JPL, which developed the radar instrument with hardware contributions from the Canadian Space Agency. Colorado State University provides scientific leadership and science data processing and distribution. Ball Aerospace and Technologies Corp., Boulder, Colorado., designed and built the spacecraft. The U.S. Air Force and U.S. Department of Energy contributed resources. U.S. and international universities and research centers support the mission science team.

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