CS725, An Accurate Sensor for the Snow Water Equivalent and Soil Moisture Measurements

Abstract

The CS725 is manufactured by Campbell Scientific (Canada) Corp - CSC and patented by Hydro-Quebec. The CS725 is designed to determine four times a day the snow water equivalent (SWE) up to 600 mm and soil moisture by measuring the natural ground gamma radiation over an ar- ea of more than 100 m 2 . The performances of the CS725 sensor are highlighted according to the re- s ults collected over more than 5 years by Hydro-Quebec. The manual SWE reference data are mainly collected from the snow pit method. The snow core technique is also used, but has more drawbacks to produce reliable data under icy snow conditions. The CS725 delivers accurate SWE data regardless of soil type (inorganic or organic) through a calibration method that we have developed. We have learned that a long enough off-snow period must be investigated in order to set properly the CS725's parameters. We have also found that the soil moisture does not vary significantly during the winter season and it is considered constant thereby simplifying the mathematical equations. From all our in- vestigations, we have proved that CS725 is able to quantify the SWE of a snowpack at an accuracy level of 5±%.