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PSD Testing Snow-Level Radar Prototype

December 29, 2008

Picture of the bistatic (dual antenna) prototype FM-CW snow-level radar deployed at Colfax, CA. The radar electronics and data acquisition system are housed in the trailer.

Sample time-height cross section of Dopper vertical radial velocity (m s-1; positive downward) from the prototype snow-level radar deployed at Colfax, CA. The retrieved 10-min average snow levels are indicated by the black dots.

Engineers at ESRL's Physical Sciences Division have developed and are field-testing a prototype frequency modulated-continuous wave (FM-CW) radar to detect and monitor the snow level during winter storms. The first-ever observations of the snow-level from this prototype radar were collected on 22 December 2008, as shown in the bottom-right image. Comparison with an independent, snow-level data set from a co-located wind profiler confirm the accuracy of the prototype. The snow level is an important variable for stream flow prediction in mountainous regions because it determines how much of a particular mountain basin will experience rain as opposed to snow. The prototype (a.k.a. snow-level radar) is currently installed in the American River basin near Colfax, CA, where ESRL operates other meteorological instruments for NOAA's Hydrometeorological Testbed (HMT) program. The snow-level radar development work is part of a joint project between ESRL, the California Department of Water Resources, and Scripps Institution for Oceanography to provide 21st century observation, modeling, and display capabilities to bear on the state's water resource and flood protection issues.

The current snow-level radar prototype uses two vertically-pointed antennas, one for transmission and one for reception. These two four-foot diameter antennas with enclosures are visible on the ground in the attached photograph. The radar only transmits a small amount of energy because it is continuously transmitting, unlike pulsed radars that send out successive short bursts containing significantly greater amounts of energy. A new profile of cloud and precipitation is obtained every 35 seconds, and currently a snow level is reported every 10 minutes. The highest altitude that the prototype is set to record data is 10.4 km above the ground. The sensitivity of the radar has not been fully determined and the radar return signals are not calibrated yet. However, the snow-level algorithm does not require calibrated data, and the radar is sensing the snow level as intended. A second snow-level radar prototype that uses a single antenna is being developed and tested by ESRL engineers.

Real-time measurements of the snow level in mountainous regions will help verify stream flow predictions and assist forecasters in providing more accurate and timely forecasts of winter storms, flooding, and debris flows. Other potential users of this information include road maintenance crews, emergency managers, electric utilities, aviators, and the ski industry.

Contact: Allen White