Monday, 3 June 2002
The Hot Plate Snowgauge
A hotplate snowgauge has been jointly developed by the National Center for Atmospheric Research (NCAR) and Desert Research Institute (DRI) that provides a method to measure liquid equivalent snowfall rates every minute. One of the main motivations for this work is the need for improved methods to measure liquid equivalent snowfall rates in support of aircraft deicing operations at airports. The hotplate snowgauge does not require glycol or oil or a wind shield, typical requirements of current weighing snowgauges. It is also expected to be relatively inexpensive in terms of initial cost and for maintenance. The principle of operation is to measure the amount of heat necessary to melt and evaporate all the snow or rain striking the top surface of the hotplate. The system has an upper and lower plate heated to nearly identical constant temperatures (near 75 °C). The lower plate is place directly underneath the upper plate with an insulator in between. The plates are maintained at constant temperature during wind and precipitation conditions by increasing or decreasing the current to the plate heaters. During normal windy conditions without precipitation, the plates cool nearly identically due to their identical size and shape. During precipitation conditions, the top plate has an additional cooling effect due to the melting and evaporation of precipitation. The difference between the power required to cool the top plate compared to the bottom plate is proportional to the precipitation rate. The initial design of the plates had a smooth upper and lower surface. It was determined that snow would "skate" off the upper surface during high wind conditions and underestimate the snowfall rate during these periods. In order to overcome this problem, three concentric walls were added to both the top and bottom plates. These concentric walls help prevent snow or rain impacting the plate at an angle from sliding off during high wind conditions. This modificatioan greatly increased the catch efficiency of the gauge. The hotplate has undergone two years of testing at Marshall (a site near Boulder) and at Mt. Washington, NH. This paper will report on the results of this testing, including an algorithm to adjust for wind undercatch.