Study On Remote Sensing Inversion Of Soil Moisture And The Relationship Between Soil Moisture And Land-use In Hebei Plain Area

Soil moisture (SM) plays an important role in land surface and atmospheric interactions. A wide-range monitoring of soil moisture is the main component of agricultural process research and evaluation of environmental factors; and soil moisture is the direct water source during the process of crop growth and development, which plays a key role in the growth of crops. Consequently, large-scale monitoring of soil moisture may be helpful to the reasonable arrangements for agricultural produce.Traditional methods of obtaining soil moisture, such as the gravimetry method, soil hygrometer method, lysimeter method, resistivity method and neutron instrument measuring method have the advantages of multi-soil-layer determination, large depth and high precision, and can ignore the impact of atmosphere and vegetation, however, they are limited in obtaining enough sample plots and real-time data, the dynamic of data was difficult to be ensured, and the labor force and financial resources will be consumed largely. Compared with traditional soil moisture monitoring methods, the rapidly developed remote sensing technology for soil moisture monitoring has many irreplaceable advantages, can rapidly, real-time, long-term, dynamically monitor large area and has a good space-time resolution.Hebei plain area is one of the most important production regions for grain and cotton in Hebei province; and the sown area of grain covers more than 80% of the sown area of all the crops. Hebei plain area belongs to the warm-temperature zone; with a climate of semiarid-sub humid and monsoon, affected by the monsoon climate, the spatial and temporal distribution of precipitation and river runoff are badly uneven; 70-80% of the precipitation and river runoff are centralized in June, July and August; high flow year is greatly different from low flow year; and the natural characteristics of dry spring and waterlogged autumn are formed. Moreover, the water utilization of Hebei plain area greatly exceeds the water resources carrying capacity, thus leading water resource abnormally lacks. Therefore, it is necessary to implement large scale soil moisture monitoring on Hebei plain area to instruct agricultural production and reasonably arrange irrigation.Apparent thermal inertia (ATI) and vegetation water supply index (VSWI) model are two main methods for domestic vocational soil moisture monitoring. Thermal inertia method needs a plurality of physical parameter; however, simplified apparent thermal inertia method can obtain good inversion effect for bare soil and low-vegetation-covered area because of its simple parameter, easy obtaining and easy operation, and is widely applied particularly in soil moisture monitoring in arid area. But there are certain defects existing in this method. In high vegetation-covered area, surface temperature of the soil cannot be well obtained because of the effect of vegetation, thus leading the application of apparent thermal inertia method affected by certain restriction. Vegetation water supply index method is one of the soil moisture monitoring methods based on vegetation index, is mainly applied for soil moisture monitoring in high-vegetation covered area. This study is mainly based on these two methods, adopts the method of NDVI partition and uses vegetation water supply index model for areas of NDVI≥0.3 for ten days, and uses apparent inertia model to implement inversion for area of NDVI<0.3, avoids the subjectivity of dividing application range by man power, is capable of giving full play to the maximum advantages of the two kinds of models, and can obtain a more reasonable soil moisture inversion results.This article applies MODIS1B data with a spatial resolution of 1000m and measured soil moisture data, 23 ten-days-composite images of soil moisture inversion results can be obtained by substituting all kinds of inversion data obtained by using interactive IDL language programming to uniformly process remote sensing images under supporting of ENVI 4.6 technical platform into apparent inertia model and vegetation water supply index model, and significantly analyses relationship between soil moisture and land use types, respectively compares variation trends of value of ten days of irrigable land and arid land in each research area by using the methods of division analysis. From the comparison, we can find that irrigation is the main factor affecting soil moisture of different land use types without considering natural factors in the same region.Innovations of this article:1,Using the established linear regression equation by ten days to inverses the soil moisture.2,Analyzes the corresponding relationship between soil moisture and land use types of Hebei plain area .3,Improved the time resolution of irrigation effects on soil moisture in the plain area.