A review of passive microwave observations of snow-covered areas over complex Arctic terrain

The Arctic is experiencing rapid environmental change due to climate warming, resulting in snow condition changes. Passive microwave observation is a useful tool to monitor these changes. However, the ground conditions in boreal regions, comprised of forest, permafrost, and lakes, are complex. The rapid change of season from winter to spring is also important information obtained through snow observations when studying the Arctic climate. This study introduces previous attempts to retrieve Arctic microwave observations, examples of flight observations, and the use of the low-frequency 6 GHz band to improve the assessment of snow conditions. Flight observations carried out over a forest, wetland, and lake using an airborne microwave radiometer provides detailed brightness temperature variations of the Arctic and winter ‒ spring changes. Flight and satellite microwave observations were used to monitor warming in spring and indicated the early warming of lowlands and late warming of mountainous areas. The diurnal amplitude variation (DAV) is useful to monitor snowmelt in the Arctic. During the short winter‒spring transition in the Arctic, microwave emissions showed local and temporal variations with forest, permafrost, and lake. They are available for further discussion on microwave observation of snow in the Arctic and implementation of changing Arctic cryospheric environment.