Point measurements and the struggle of satellites
Although essential, measurements with snow poles are expensive and sometimes risky. Often entailing repeated climbs to high altitudes in difficult conditions. Today, some stations use more advanced systems such as ultrasonic sensors resulting in automated and more accurate measurements. Regardless of the technology, ground measurements do have a limitation: they only refer to a specific point. In the mountains this can be especially misleading, winds and highly differing solar exposure from slope to slope mean that snow is often distributed very unevenly. In order to get a more accurate picture, the areas where snow surfaces are measured would have to be pitted like Swiss cheese.
This is where satellite images, which provide data over larger areas, should be able to come to the rescue. However, this combination of ground and satellite data - which works well for other parameters such as the extent of snow cover - is more problematic here. Currently, satellite techniques use radar sensors. Researchers set the right frequency for incoming electromagnetic waves from the satellite to interact with the snow grains. It's a bit like researchers tuning the satellite radio to the snow channel. If the signal encounters water particles, it sends a recognisable signal back to the satellite. But not all snow is the same, if it’s wetter or more powdery, the flakes - technically called grains – differ in dimension.
The electromagnetic waves interact intensively with the water in the snow, preventing interaction with the dry part, this means that not all the snow can be detected. When the snow is only dry, in most cases it is transparent; in the presence of liquid water, the electromagnetic waves interact essentially with the water. The result is that the snow station, even though it communicates, doesn’t always tell the whole story on snow.