An Unattended Gamma Monitor for the Determination of Snow Water Equivalent (SWE) Using the Natural Ground Gamma Radiation

A custom γ radiation monitor, named "GMON" has been developed to accurately measure the snow water equivalent of the snow pack in order to predict the stream flow originating from snowmelt and also for hydrologic investigations. It is based on a 3 by 3 inches NaI(Tl) detector and newly developed electronics able to function at ambient temperatures ranging from −40°C to 45°C. The gain is firmware compensated for temperature over the full range. The GMON is designed for unattended operation in remote areas. It runs on solar power, is hermetically tight, and transmits its data over a modem or satellite link. The GMONs are equipped with a lead collimator, defining a 60° angle of view. The collimator and detector casing also shields partially the crystal against cosmic rays. The results of field tests with the apparatus compared with a multitude of snow cores taken simultaneously will be presented.