Gauges
ADG
The acoustic depth gauge (ADG) measures the distance from the gauge to the snow. The distance to the snow surface in mm and the air temperature used to calculate the speed of sound for the distance measurement are recorded in a memory module at 1 hour intervals along with the hour and the Julian day of the year. The snow accumulation is calculated by subtracting the ADG depth from the initial distance to the snow. Figure 1 shows the June 1992 ADG record at the time of installation. The July 1992 record shows that the snow surface may be exposed for long time periods without significant snow accumulation. Once the snow surface is covered with additional snow without being exposed later the layer can be considered stored. Sampling the previously exposed surface should give an idea of the dry fall and sampling the snow between exposed layers should give information about the wet fall. The accumulation between previously exposed layers may be precipitation or it could be snow trans ported to the site. A similar approach is planned for Siple Dome and the new drilling site near Byrd Station. Additional information available at http://igloo.gsfc.nasa.gov/wais/pastmeetings/abstracts99/stearns.html [Summary provided by NASA]