Real-time spectral observations of clouds and precipitation using a 94 GHz radar

A 94 GHz Doppler radar has been operating as an integral part of the cloud observing system developed by Penn State University (Albrecht et al, 1991). It became evident that in the need to observe and measure many of the microphysical processes of clouds and precipitation, the mean Doppler moments provided by pulse-pair processing did not provide sufficient information. However, a spectral method of processing, such as the Fast Fourier Transform (FFT), when used to process the complex linear video output of the radar could provide full use of the Doppler capabilities of the radar. The FFT technique was first used with a 94 GHz radar for precipitation studies by Lhermitte (1989), but limitations of the digitizing and processing hardware available allowed this to be accomplished only by storing the digitized Doppler radar signals and processing them at a later time. However, with the recent advances in digitizing hardware, digital signal processors and software, this process can now be done in real-time with relatively inexpensive and portable equipment.