Snow and Ice
Arctic sea routes are lately a topic of great interest to many people. Satellite data will play a big role to play in the implementation of commercially viable shipping lanes, which have the potential to revolutionize world trade and international relations.
Monitoring of the ocean lane in winter by satellite data
In the coastal waters of Hokkaido, the Sea of Okhotsk is covered with sea ice in winter every year. The sea ice obstructs ship navigation and fishing. On March 1970, there was a large-scale maritime accident by drift ice in Hitokappu-wan, Etorofu-tou.
The accident led the 1st Regional Coast Guard Headquarters of Japan Coast Guard to organize the Ice Information Center in every year to distribute Sea Ice Condition Chart every day in the winter.
The Sea Ice Condition Chart is produced assembling various information and is released at 17:00 every day. In the information, information from satellites is also used as well as data from airplanes and ships. However, most of information is provided from optical sensors, sometime there happen to be no information of the Sea of Okhotsk due to bad weather condition in the winter.
Therefore, it is improved to distribute information of Sea Ice Condition Chart even in bad weather condition, using PALSAR synthetic aperture radar image data (in the figure) using microwave which can penetrate cloud cover to detect sea ice widely distributed on the sea.
The all-weather information is expected to be used to detect the watched open route through the Arctic Ocean covered with sea ice, and ALOS-2 is considered to have the potential to contribute for the information service on this purpose in the future.
Sea Ice Distribution in the Arctic Sea
The left figure is the sea ice distribution map of the minimum record of satellite-based observations, observed by Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard Global Change Observation Mission – Water (GCOM-W) “Shizuku” in 2012.
The right figure is the sea ice distribution map in the same season in 1980. In the recent map, the sea ice is largely shrinking along the coastal zone of the continent, and there are opening routes drawing attention in the world; Northwest Passage across the Archipelago in the north of Canada and the Northern Sea Route along the coastal zone of the Siberia, Russia.
AMSR2 is able to estimate geophysical parameters of the sea ice and water-related parameters such as sea surface temperature, perceptible water, soil moisture and so on.
Detection of Grounding line
While the global warming with climate change is getting one of serious challenges, the measurement of global water mass transfer is getting important. Among the ice on the ground, about 70% is conserved in ice sheet including Greenland. In case of melting of all these ice, the sea level rise is estimated to be 70 m and its effect will be profound.
For the quantitative understanding of these ice sheet dynamics or balance of accumulation and ablation, it is necessary to measure 1) velocity of glacier flow and ice shelf flow, 2) thickness of ice sheet and ice shelf, and 3) position of grounding line.
Grounding line is the boundary between the floating ice on the sea and the ice grounded on the bedrock. Understanding the location of the line is estimation of the ice amount flowing into the sea. The use of SAR is advantageous for the understanding of velocity of glacier flow and grounding line, and also significant tool for the polar science.