Abstract: Soil moisture plays a significant role in agricultural monitoring and yield estimation. Monitoring soil moisture by remote sensing features such merits as fast effectiveness,strong dynamic contrast and large monitoring areas. Meanwhile,TVDI integrates the reaction of both vegetation growth state and land surface temperature to soil moisture,thus satisfying the demand of this study. The VIIRS,sensor carried by Suomi NPP,as the successor of MODIS/AVHRR,has not been used in soil moisture monitoring in domestic yet. VIIRS sensor data EDR daily surface reflectance product(GIGTO-VI1~5BO) is studied in this paper and the normalized differential vegetation index(NDVI) of the Regiment 125 of the Agricultural Division 7,the Xinjiang Production and Construction Corps,at Kuitun City,Xinjiang,China from June 29 to July 10,2015 is calculated. In addition,temperature vegetation dryness index(TVDI) is optimized and dry and wet edges are extracted to form characteristic space based on the EDR daily land surface temperature product(GMTCO-VLSTO) so as to calculate TVDI results. In the TVDI feature space,when NDVI is less than 0.1,TVDI cannot response soil moisture condition with no vegetation coverage;0.1 < NDVI < 0.7,respectively,Ts_max and Ts_min value decrease and increase with the increase of the vegetation coverage;0.7<NDVI,the sensitivity of TVDI is reduced,owning to the saturated NDVI. The measured ground soil moisture content data in the same period are adopted for verification and this model is promoted to the economic belt regions in the whole north slope of Tianshan Mountains. The study results show as follows:(1) The correlation index R² between TVDI result and measured ground data is 0.846;the uncorrelated two-tailed test value between them is smaller than 0.001. The soil moisture model built has sound reaction to water content in unsaturated farmland soil;(2) The characteristic space built shows excellent performance and the dry and wet edges are superior in conforming to theoretical triangular space distribution with better fitting result compared with the previously studied AVHRR/MODIS data;(3) The large breadth and fine-time resolution ratio of VIIRS data further improves timeliness of data processing in large area monitoring;only with 1-4 images can all areas in Xinjiang be completely covered for daily monitoring. This paper pioneers in China in the application of VIIRS sensor data product to realize soil moisture monitoring. This sensor,as an upgrade of AVHRR/MODIS sensor,has been optimized in performance,wave band setting and product format,thus rendering it with better performance. MODIS sensor is designed to serve until 2020s,thus the status of the VIIRS products will rise in the future. Therefore,the monitoring on soil water content in Xinjiang fields could be further strengthened with the application of VIIRS-TVDI to monitor soil moisture and is of certain practical value,which will fill a vacancy in the use of VIIRS data.

Key words: soil moisture, VIIRS, TVDI, Xinjiang