HotPlate™

A joint research venture between the Desert Research Institute (DRI) and the National Center for Atmospheric Research (NCAR) has produced an improved meteorological apparatus and method for measuring—in real-time—precipitation reaching the earth’s surface at a given location. The device, called the HotPlate™ Total Precipitation Sensor, rapidly measures (within one minute) both liquid and frozen precipitation, making it especially useful in characterizing freezing rain and snow at airports. The Aviation Weather Research Program within the Federal Aviation Administration sponsored the HotPlate™ research and development project co-led by John Hallett with the DRI and Roy Rasmussen with NCAR. Other researchers involved in the HotPlate™ project include Jeff Cole, Matt Tryhane, and Scott Landolt with NCAR and Rick Purcell with DRI.

Precipitation measurements are used to determine the quantity of moisture falling at a known location during a given time interval. For technical reasons, only a fraction of the observation area is evaluated, yet conclusions are drawn for the total area. The measurement equates with the amount of liquid precipitation that would have covered the ground surface if the liquid would not have penetrated the ground, evaporated, or run off. Since the water supply of the world is nearly exclusively replenished by precipitation, measurements are extremely important for agriculture and forestry as well as for general use. For example, it is necessary to know precipitation conditions when managing water supply services, planning hydroelectric generating stations and sewage systems, or issuing flood warnings.

Hot-plate precipitation-measuring systems work by measuring the extra power needed to evaporate precipitation falling on the upper sensor plate as compared with the lower reference plate (which needs about 1 watt per 0.004 inch of water-equivalent precipitation per hour). A small correction (8%) is necessary to measure ice as compared with water because of the difference in the latent heat associated with evaporation. The upper and lower plates are thermally isolated from each other and are heated separately.

The power needed to maintain each plate at a high temperature (sufficient for evaporation and to discourage birds) subsequently is measured. Each plate is cooled almost equally by the wind, depending on speed and temperature; the system accounts for a small correction in solar radiation when passing showers occur. The HotPlate™ precipitation-measuring system is also capable of measuring wind speed.

The HotPlate™ system can operate in an accumulation of precipitation equivalent to about 2 inches of water per hour depending on conditions. The system has no moving parts, requires no maintenance, and is software controlled. Fifty to several hundred watts are needed to operate the HotPlate™ depending on atmospheric conditions. In the event of a power outage, the system is capable of “sleeping” while power is not available and will recover when power is restored. The system is also capable of storing up to one month of data.

The HotPlate™ system has advanced the science of characterizing the physical environmental processes (temperature, wind speed, precipitation rate) of precipitation events with application to various practical scenarios such as measuring airport snow and basin precipitation, especially in situations having potential for high levels of runoff. Technological advances developed by DRI and NCAR researchers allow this instrument to overcome distinct disadvantages inherent in existing rain and snow gauges. In 2002, a patent was granted, and then in October 2003, Yankee Environmental Systems was awarded an exclusive manufacturing license to produce the promising HotPlate™.