基于地面观测和Sentinel-2数据的玉米实际蒸散发估算

基于遥感技术估算作物蒸散发(Evapotranspiration,ET)对农业用水效率评价和精量灌溉决策具有重要意义。结合Sentinel-2数据和农田连续地面观测资料,利用混合双源蒸散发模型(Hybrid dual-source scheme and trapezoid framework-based evapotranspiration model,HTEM)对宁夏回族自治区中卫市2019年两个试验田玉米主要生育期(5—8月)的蒸散发量进行估算,并用水量平衡法对遥感估算结果进行验证和评价。结果表明:Sentinel-2数据具有高时空分辨率,能够与研究区复杂的种植地块相匹配,减少了混合像元的数量;遥感反演参数与地面观测数据拟合度较高,研究区2019年遥感反演的玉米田净辐射量均方根误差为36.256 W/m²。利用HTEM模型估算可得,主要生育期内研究区两个玉米试验田的日均实际蒸散发量分别为4.269 mm/d和4.339 mm/d,实际蒸散发总量分别为525.114 mm和533.690 mm,其中植被蒸腾量分别为363.483 mm和358.196 mm,生育初期主要以土壤蒸发形式消耗水分,随着作物的生长,在生育中后期主要以植被蒸腾的形式消耗水分。ET遥感反演结果与水量平衡结果之间差别不显著,两个观测点绝对误差分别为13.533 mm和7.774 mm。因此,结合地面连续观测系统和Sentinel-2数据估算研究区玉米生育阶段蒸散发量具有较高的精度,可为作物耗水规律研究及区域农业水管理提供技术支撑。

Estimation of Maize Evapotranspiration Based on Field Continuous Monitoring System in Site and Sentinel-2 Data

It is a useful and powerful tool to estimate crop evapotranspiration (ET) based on remote sensing technology for evaluation of water use efficiency and precision agriculture. To improve the accuracy of estimation, field continuous monitoring system and remote sensing data of Sentinel-2 were employed here to figure up the maize evapotranspiration. The hybrid dual-source scheme and trapezoid framework-based evapotranspiration model (HTEM), was selected as ET estimating model. The experimental fields located in Zhongwei City, Ningxia Hui Autonomous Region, and the main observations of the study area were during maize growing season (from May to Aug.) in 2019. Sentinel-2 data and observed canopy temperature data were the key input data of the HTEM model. Water balance method was also used for comparisons and evaluation of remote sensed ET. Results showed that Sentinel-2 data had high spatial and temporal resolution, which can match the complex planting plots in the study area, reducing the presence of mixed pixels. Remote sensing inversion parameters fit well with ground observation data. The root mean square error (RMSE) of net radiation over study area during study period was 36.256W/m2. Daily evapotranspiration of two maize experimental fields based on HTEM model were 4.269mm/d and 4.339mm/d, respectively. And total ET of study area were 525.114mm and 533.690mm during main growing period, respectively. The absolute error between remote sensed ET and calculated ET based on water balance method were 13.533mm and 7.774mm, respectively. Evaporation and transpiration can be also obtained based on HTEM model. According to the results, total transpiration of maize during study period were 363.483mm and 358.196mm, respectively. Water was mainly consumed by soil evaporation during the early growth phase. In the middle and late growth phase, transpiration became the main water consumption way. Thus it can be seen that Sentinel-2 data associated with site canopy temperature system would be more available in regional maize evapotranspiration estimation with high precision. These results could also provide technical support for regional crop evapotranspiration research and agricultural water management.