Cloud profile radars use very short wavelength (mm) radar (typically 94 GHz) to detect scattering from non-precipitating cloud droplets or ice particles, thereby yielding information on cloud characteristics such as moisture content and base height.
A 94 GHz cloud profiling radar has the unique property of being able to penetrate ice clouds with negligible attenuation and providing a range-gated profile of cloud characteristics.
Rain radars use microwave radiation (centimetre wavelengths) to detect backscatter from water drops and ice particles in precipitating clouds, and to measure the vertical profile of such particles. One of the key challenges with such radars is suppressing the return from the Earth’s surface (ground clutter), which is inevitably much stronger than the rain echo. Recent instruments however, can map the 3D distribution of precipitating water and ice in a relatively narrow swath (around 200 km) along the track of a low altitude satellite, making it possible to infer more precise estimates of instantaneous rainfall.
The Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM), launched in 1997, was the first radar in space with the capability to measure rainfall. PR provided three-dimensional maps of storm structure and invaluable information on the intensity and distribution of rain, rain type and storm depth. NASA’s CloudSat uses an advanced 94 GHz radar to ‘slice’ through clouds to see their vertical structure, providing a completely new observational capability from space. These instruments are the first to study cloud profiles on a global basis, and to look at their structure, composition and effects. From 2013, the Global Precipitation Measurement (GPM) mission – an international cooperative programme – will provide more frequent and complete sampling of the Earth’s precipitation using a constellation of satellites. As of 2013, the Japanese instrument onboard the ESA-JAXA EarthCARE mission, the 94 GHz CPR, will continue providing cloud profile observations, with increased sensitivity and additional Doppler capability to observe vertical motion.