基于互补相关模型和IKONOS数据的农田蒸散时空特征分析

Temporal-spatial analysis of farmland evapotranspiration based on complementary relationship model and IKONOS data

获取田块内高分辨率农田实际蒸散信息对于精准农业中制定灌溉计划、变量处方实施及评价水分利用效率等具有重要参考价值,将传统方法与遥感结合并生成精细田块尺度的农田蒸散成为当前研究热点方向。本文基于互补相关模型和北京2011年3-6月份间内气象观测数据进行了冬小麦实际蒸散估算,并利用大型蒸渗仪对结果进行了验证和分析。最后将互补相关模型与高空间分辨率遥感数据结合实现了田块尺度农田瞬时蒸散估算,并结合蒸发比率不变法实现了日尺度蒸散扩展。结果表明:在2011年3-6月间试验区内冬小麦总耗水量达到469.12mm,其中在灌浆期5月份耗水比重最大,占到总量近二分之一;互补相关模型估算精度整体较高,其中在5月份估算精度最高(R2=0.863,RMSE=0.103mm);扩展后的日尺度蒸散量与实测结果非常一致(R2=0.937,RMSE=0.668mm)。上述结果表明在没有土壤温、湿度数据及高分辨率热红外遥感数据条件下,仅利用互补相关模型,并结合气象观测数据和高分辨率遥感数据即可估算出精细尺度农田蒸散。

Mapping high spatial-temporal resolution evapotranspiration （ET） over large areas is important for water resources planning, precision irrigation and monitoring water use efficiency. Recently accurate estimation of ET is becoming available via a number of methods using surface meteorological and sounding observations, which are used to represent only local processes, meet insuperably difficulty to mapping ET in large areas due to land surface heterogeneity and the dynamic nature of the heat transfer processes. Satellite remote sensing is a promising tool for this purpose. Nevertheless, most of the existing techniques of ET estimation from satellite remote sensing are not satisfactory, because satellite monitoring of ET has not been feasible at high pixel resolution. Therefore, using traditional measurements and high resolution image data to generate high spatial-temporal resolution ET is becoming an important research direction. In this paper, the complementary relationship model （CR） was employed together with meteorological data to estimate actual ET, and the results were validated by lysimeter observation. Furthermore, CR model was combined with high resolution image, IKONOS data, to estimate instantaneous field scale ET and they also were transferred into daily ET. The cumulative evapotranspiration （ET） of winter wheat during the reproductive phase from March to June of 2011 was 469.12 mm, essentially corresponding to the annual precipitation in the Beijing area. The most high accuracy of estimated ET by CR model is also on May（R 2 =0.863,RMSE=0.103 mm）. The daytime ET accounted for 86% of the total ET for the four-month period, while the nighttime ET constituted the remaining 14% of the total. Therefore, the nighttime ET must also be considered. The transferred daily ET by self-preservation of evaporative fraction（EF） method were consistent with lysimeter measurements for all four months（R 2 =0.937,RMSE=0.668 mm）. The estimated daily ET by the EF method was consistent with lysimeter measurement for each of the four months. The IKONOS image-based instantaneous and daily ET over vegetation-covered area increased with increment of leaf area index （LAI） and decreased with increment of albedo. It was proved in this study that CR model can be used to estimate precision field scale ET with meteorological data and high resolution remote sensing data together in a region with limited ground data availability, e.g. without soil moisture and surface temperature .