Reflectivity Calibration and Radial Wind Correction for HIAPER Cloud Radar

Presentation Type: 
Jothiram Vivekanandan (National Center for Atmospheric Research)

Obtaining an accurate system calibration for reflectivity and radial wind is essential for airborne cloud radar s scientific mission related to climate science application. Cloud liquid, ice water contents and mean particle sizes are estimated using reflectivity and vertical fall velocity spectrum. Since non-precipitating cloud reflectivity is

Both an absolute calibration, which includes reflection measurements from a target of known radar cross-section, and an internal calibration, which tracks changes in receiver gain with temperature are used in reflectivity calibration. For a polarimetric radar system, internal calibration is important to track changes in the receiver gains. Common calibration schemes, namely, calibrated test signals, noise source, or injection of a small part of the transmitted signal into both receivers are used. Using a transmitted signal to track differential changes in the receiver allows monitoring of the transmitted pulse. This is important when using frequency modulation since one can then compensate for phase nonlinearities due to the transmitter in the compression filter.

Retrieval of the radial velocity related to cloud particles from airborne Doppler measurements requires compensation for aircraft motion. The amount of aircraft motion contribution to airborne Doppler measurements is determined by aircraft velocity along the radar beam pointing direction. This requires precise estimates of the antenna pointing angle and aircraft attitude and velocity.

This paper describes calibrations of reflectivity and fall velocity for measurements of HIAPER Cloud Radar (HCR) fixed-beam configuration. The HCR is an airborne, millimeter-wavelength, dual-polarization, Doppler radar that serves the atmospheric science community by providing cloud remote sensing capabilities. The pod based HCR is mounted on a modified Gulfstream V aircraft, which is operated and maintained by the National Center for Atmospheric Research (NCAR) on behalf of the National Science Foundation (NSF). The aircraft is called the High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER). Currently, the radar system is capable of collecting observations between zenith and nadir in a fixed scanning mode.

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