Seasonal snow and ice thickness measured by SIMBA thermistor string based ice mass-balance buoy on an Arctic lake

A thermistor-string-based Snow and Ice Mass Balance Array (SIMBA) has been used for monitoring snow and ice mass balance in Lake Orajärvi in northern Finland since 2009. The environment temperature (ET) and heating temperature (HT) have been measured vertically every 2 cm by temperature sensors that have a minimum resolution of ±0.0625°C. The first- and second-order spatial derivatives (FOD/SOD) of SIMBA-ET, i.e. temperature changes, in 2 cm fixed interval were calculated and used to identify the air/snow, snow/ice and ice/water interfaces. The derivative threshold values were adapted from an existing SIMBA-algorithm. 
We first investigated SIMBA data obtained in winters 2011/2012, where in situ snow and ice thickness were available. The snow depth and ice thickness calculated by our method and from manual analyses were close to each other. Both results were comparable with in situ observations. The snow and ice thickness were, then, derived from SIMBA data observed since 2009. An upward-moving snow/ice interface was detected for all winters. Snow-ice contributed around 30 - 65% of the total average lake ice thickness. The snow depth on lake ice was only one-third of that on land nearby. The SIMBA-HT was capable to identify snow/ice and ice/water interfaces that were visible form SIMBA-ET profiles during cold conditions.