Long term observation of soil moisture by the in situ stations and AMSR/AMSR2 a 1.1º by 1.1º study area on the Mongolian Plateau since 2001
Abstract:Soil moisture behavior has a strong influence on water cycle (especially, interaction between soil and atmosphere) and surface natural environments in semi-arid and arid areas with highly variable rainfall. Recently, as the Mongolian Plateau has been affected by global warning, it has been facing several times severe droughts. So, it is very important to measure continuously and precisely the surface soil moisture.
We have been successfully carrying out the in situ soil moisture and meteorological observations using some automatic stations (from 13 to 16 stations) in a 1.1º by 1.1º flat surface land (study area) covered with pasture/shrubs, and a daily large-scale soil moisture observation on the Mongolian Plateau by AMSR-E (Advanced Microwave Scanning Radiometer-EOS) of AQUA and AMSR2 (Advanced Microwave Scanning Radiometer 2) of GCOM-W1 (Global Change Observation Mission-Water 1) since 2001 with making a validation of the AMSR-E/AMSR2 soil moisture products in every year.
As a result, we have obtained a few new findings about soil moisture dynamics in the study area. Concretely, there was a decreasing trend of the surface soil moisture in the study area during the period from 2001 to 2008 with the drought development and inversely it started to increase slightly in 2009 with the increase of rainfall in summer. The ratio of evapotranspiration to rainfall from April to September was estimated to be more than about 95 %, and the rainfall condition in summer controlled the amount of annual precipitation and the wet condition on the soil surface.
We also knew that AMSR-E/AMSR2 can continuously and successfully conduct a long term monitoring observation of the surface soil moisture on the Mongolian Plateau with the high measurement accuracy between 4 and 5 % on a large scale. This fact suggests that AMSR-E/AMSR2 soil moisture observation is useful for studies of water cycle over large areas of grass.
Keywords: soil moisture, rainfall, in situ observation, AMSR-E/AMSR2, Mongolian Plateau