Snow Depth Measurement using GPS on Karasawa Cirque, Japanese Northern Alps

In the mountainous area of Japan, snow depth is known to increase so as to become of high altitude. However, the snow depth distribution are hardly measured in the high mountain. It is significant to clarify the snow depth distribution based on actual measurement of snow depth in order to calculate the water equivalent of snow in its hydrographic basin. The measurement using GPS is attracted to attentions because the method of the GPS measurement is simple and high resolution. Especially, the Kinematic GPS measurement using two GPS receivers with high resolution antenna make possible to the measurement a wide area in a short time. We aim to clarify the snow depth distribution in Karasawa cirque where is one of the biggest cirque in Japan, based on the Kinematic GPS measurement on the snow surface during snow ablation season in 2012 and 2013. Karasawa cirque (36°17' N, 137°40' E), is located at the Hodaka massif in the Japanese Northern Alps where is one of the snowy mountains in Japan. The altitude of the cirque bottom is 2300 m to 2350 m. Snowfall season in the Karasawa cirque start at early November, and snow ablation in the cirque start at late April. In this study, we obtain the coordinates of the snow surface using the GPS receiver, to determine the snow depth from the difference between the ground surface elevation and snow surface elevation. Method of positioning is the kinematic positioning system, which is higher reliability for the interferometric positioning of the observation. This method is capable of recording the observations at any point in short and constant time intervals. Therefore, we can be obviously distribution of snow depth by GPS positioning at multipoint on the snow surface. On the other hand, the ground surface coordinates are obtained from airborne laser scanning data. The Maximum snow depth is measured about 23 m on the cirque bottom at late April, 2012 and 2013. Snow depth of the late April is greater than late March for both 2013 and 2012. On the cirque bottom, snow depth is increasing by avalanche debris in addition to snowfall. Since late April, snow surface is decreasing 10-15 cm per day. The maximum snow depth in early August is about 10 m.