Study On Farmland Moisture Estimation And Thermal Effect Based On UAV Thermal Infrared Remote Sensing

With the continuous development of agricultural modernization,higher requirements have been put forward for the irrigation and management of farmland crops.The UAV thermal infrared remote sensing has the advantages of real-time,cheap and convenient,etc.It can reverse interpret the changes of crop evapotranspiration and soil moisture content in the field efficiently and accurately,and put forward new research methods in the field thermal effect.In summer maize field as the research object,this study applied unmanned aerial vehicle(UAV)thermal infrared remote sensing platform for crop canopy temperature image,and inversion of summer corn evaporation(evapotranspiration,ET),the field Soil water(Soil moisture),at the same time to collect the vorticity field(Campbell Scientific Inc,USA)data,meteorological data,crop canopy and land surface temperature,the field Soil moisture content and summer corn crop phenotypic information data,and the summer corn evaporation and Soil moisture inversion accuracy field validation.Finally,relevant data obtained from the inversion are combined with elevation and vegetation coverage to comprehensively study the thermal effect of farmland and analyze the influence of different land types,elevation and vegetation coverage indexes on the regional heat of farmland.The main results are as follows:(1)The inversion accuracy of thermal infrared temperature image is over 95%,the correlation coefficient between measured value and simulated value R2=0.83,and the measured value and simulated value are mostly concentrated at about 31℃.The thermal infrared temperature fluctuant(±1℃)between different pixels in a small region(measuring range ≤1m).The differences in summer maize growth status,leaf area index(LAI)and vegetation coverage(NDVI)at each pixel affect the temperature value.(2)The crop evapotranspiration model based on UAV thermal infrared canopy temperature can accurately and quickly estimate the daily evapotranspiration of field scale crops.The lowest value of evapotranspiration(3.42mm/d)appears in the seedling stage,and the highest value(10.94mm/d)appears in the grouting stage.Through correlation analysis of evapotranspiration and its influencing factors,the leaf area index is the most important biological factor of summer maize farmland,and the leaf area index is linearly positively correlated with evapotranspiration,with the determining coefficient R2=0.70.Aerodynamic impedance is the most important environmental driving factor,and is linearly negatively correlated with evapotranspiration(R2= 0.696).(3)The fitting results of crown temperature difference method and soil moisture content showed that the correlation between surface soil moisture content(10cm,20cm)and crown temperature difference was the best(R2 was 0.82,0.81,respectively),and that the soil moisture content decreased with the increase of soil depth,while the correlation between deep soil moisture content and crown temperature difference was poor.The accuracy was verified by the measured values,and the accuracy of the soil moisture content of the thermal infrared temperature inversion reached more than 90%,R2=0.80.It shows that the UAV thermal infrared remote sensing combined with the canopy temperature difference method can well reflect the surface soil moisture distribution.Under the same water and fertilizer treatment,the soil moisture content values of different pixels were different,and the surface soil moisture content(10cm)had a good negative correlation with the temperature difference of the thermal infrared crown.In the traditional ground soil moisture monitoring,the difference of soil moisture between different points is obfuscated by the method of data processing of soil moisture content.(4)The thermal effect of farmland area is the result of the interaction of various indicators.The negative correlation between vegetation coverage(NDVI)and temperature during the whole growth period of summer maize indicates that vegetation has the function of mitigating the farmland heat effect.The thermal infrared temperature distribution of ETc calculated by the crop evapotranspiration model was in good agreement with the thermal infrared temperature distribution of summer corn,and the evapotranspiration in the farmland area was positively correlated with the temperature(R2=0.84).There was a negative correlation between the surface soil moisture content and the thermal infrared temperature in the test area(R2=0.83),indicating that the higher the soil moisture content,the lower the corresponding temperature value,and the higher the soil moisture content directly affected the thermal movement of the farmland,which was closely related to the thermal effect of the farmland.