基于遥感蒸散发模型的净灌溉水量测算空间尺度研究

Using Remote Sensing to Estimate Evapotranspiration from Terrestrial Ecosystems at Different Scales

【目的】农业用水总量和灌溉水有效利用系数是最严格水资源管理考核总量红线和效率红线控制的重要指标。目前遥感蒸散发模型在珠江片区域蒸散发量估算和净灌溉水量评估的应用度不高,对其空间适用尺度缺乏研究。【方法】以广西区为例,通过试验观测-遥感解译等技术计算不同空间尺度遥感蒸散发量,并与相应尺度直接量测的净灌溉水量建立线性相关关系,根据相关系数,得出误差最小的空间尺度,从而建立一套更准确、快速、有效的最优空间尺度下,根据遥感蒸散发量进行区域净灌溉水量估算的方法。【结果】在较大的广西区、片区尺度,净灌溉用水量和遥感蒸散发量之间存在明显的线性相关关系,相关系数在0.8以上;对比广西区和桂中片区净灌溉用水量实测结果与遥感估算结果,误差均在0.5%以内。【结论】在片区和广西区等较大尺度,遥感测算结果的可信度较高,遥感蒸散发模型适用性较强,其估算结果可为最严格水资源管理考核和农业水资源科学管理提供科学支撑。

【Background and objective】Evapotranspiration is an important component in the hydrological cycle and provides a nexus between water, carbon and surface energy exchanges in terrestrial systems. It is difficult to measure in situ at large scales. Remote sensing can plug this gap and has seen rapid application over the past three decades.The purpose of this paper is to test the feasibility of remote sensing to estimate evapotranspiration at provincial and sub-provincial scales in Guangxi province of China.【Method】We established a model to calculate evapotranspiration using remote sensing data first and then compared it with ground-true data. It was then used to estimate the net irrigation water measured at different scales using a regression model. Based on the correlation coefficient between the measurements and estimations at different scales, we found the optimal scale for application of the model and established an accurate and effective method to estimate net irrigation water using remote sensing data.【Result】There is a linear correlation between net irrigation water and the remote sensing evapotranspiration at both provincial and sub-provincial scale, and the correlation coefficient was higher than 0.8. Comparison with measured results revealed that the errors of the evapotranspiration estimated using the remote sensing data was less than 0.5%at provincial and sub-provincial scales.【Conclusion】 At large scales, remote sensing provides a reliable alternative to estimate evapotranspiration and be used to help improve irrigation and agricultural managements.