Since the automation of the meteorological observation network in the Netherlands in 2002, snow depth was not included anymore in the set of in-situ observations used for synoptic and climatological purposes. At present, the Royal Netherlands Meteorological Institute (KNMI) collects snow depth data only on a daily basis, using a network of around 325 voluntary precipitation observers. The lack of snow depth information in the international bulletins issued by KNMI has been recognized as a serious problem. The European Centre for Medium-Range Weather Forecasts (ECMWF) model, for example, relies almost exclusively on in-situ snow depth information that is routinely available via the Global Telecommunication System (GTS). Recent snowfall events in the Netherlands have demonstrated that large errors in the ECMWF 2 m temperature forecast were caused by errors in the snow analysis over Europe (ECMWF, 2010). In addition to this international need, also on a national scale there is an increasing demand for real-time and continuous snow depth information over the Netherlands, e.g. for the evaluation of weather alerts issued for heavy snowfall.
Although automated measurement techniques exist, the low frequency of occurrence and the limited depth and life time of a closed snow deck in the Netherlands form a serious obstacle in the developments towards automation. In view of the snow cover climatology calculated for the period 1961-1990 (Klein Tank, 1997), a closed snow deck occurs only 11 days a year on average. In addition, total snow depth exceeds 5, 10 and 20 cm for only 4.2, 1.5 and 0.1 days per year, respectively. A suitable snow depth sensor should therefore provide accurate measurements of the onset of snow cover and the first centimeters of snow. A recent inventory of commercially available snow depth sensors (De Haij, 2007), which were at that time all using an acoustic measurement principle, did not result in suitable candidates. The new Jenoptik SHM30 laser snow depth sensor, introduced in 2008, seems to overcome the problems that can be expected with sonic rangers under typical Dutch snow cover conditions. First reports of experiences with this sensor by National Meteorological and Hydrological Services (NMHSs) in Europe show largely positive results (e.g. Lanzinger et al., 2010a).
Supported by these positive experiences, KNMI has evaluated the Jenoptik SHM30 laser snow depth sensor in De Bilt from 16 December 2010 to 30 June 2011. The aim of this test was to get experience with the sensor in Dutch conditions and investigate whether the SHM30 is a suitable candidate for automated snow depth observations in the meteorological observation network. This report describes the results from the test and provides recommendations for further actions.
MJ de Haij. Field test of the Jenoptik SHM30 laser snow depth sensor