A new snow-level detection radar

Snow-level detection by radar is a very useful tool for hydrologic applications, especially in mountainous watersheds. As part of NOAA's Hydrometeorological Testbed (HMT) field operations, vertically pointing radars routinely determine the snow level in various locations of California. This presentation describes a new, low-cost radar for snow-level detection.

During the winter of 2008/2009 a prototype of this Doppler FM-CW radar was field tested at the HMT site in Colfax, California. A 915-MHz pulsed Doppler wind profiler, rain gage, and disdrometer were also located at this site, so direct comparisons of snow level and reflectivity were possible. The prototype FM-CW radar measured vertical profiles of Doppler spectra with a spatial resolution of 50 m and a temporal resolution of 36 s. Automatic detection of the snow level was performed ever 10 minutes. During the observing period, the prototype FM-CW radar measured snow levels between 175 m and 2200 m above the radar.

This S-band (2.835 GHZ) FM-CW radar is a low-cost alternative to the pulsed radars currently used by NOAA for this purpose. This radar is not as sensitive as the pulsed radars currently being used, but it can be constructed at a fraction of the cost. Operating at S-band to minimize attenuation, this radar is small and low-powered. To develop this new radar, previous FM-CW equipment and pulsed Doppler hardware and software were used to create a robust instrument. The prototype radar utilizes commonly available parts to create a 0.2 W transmit signal, and is bi-static, using two existing 1.2 m diameter parabolic dish antennas from previous experiments. The prototype data system uses a commercial data-acquisition system combined with control circuits from a pulsed radar system to digitize the received signals. The software for the radar utilizes the same Doppler processing used in the other HMT vertically-pointing radars. The automatic snow-level detection algorithm used in the pulsed Doppler systems was modified slightly for this radar, since it is not as sensitive as the pulsed systems.

Results from the first observations, as well as technical details of the prototype FM-CW radar will be presented.