不同参考温度取值对三温模型反演植被蒸腾精度的影响

Effects of different reference temperature values on the accuracy of vegetation transpiration estimation by three-temperature model

参考温度的参数化过程一直是三温模型反演蒸散发及其蒸发、蒸腾组分的关键和难点。该研究基于典型城市草坪的波文比与热红外观测数据,对三温模型植被蒸腾子模型中涉及的输入变量进行敏感性分析和误差分析,确定对三温模型反演植被蒸腾精度最为关键的变量,而后量化和对比输入变量参数化方法对三温模型计算草坪蒸腾的影响,由此确定最佳的参考温度取值。结果表明:1)参考叶片温度选择为整个纸片温度的最大值时反演效果最好(R^(2)=0.91,均方根误差(RMSE)=0.078 mm·h;);2)采用植被冠层温度的最大值为参考温度时,直接假定了植被最高温度冠层蒸腾为0(实际存在一定的蒸腾速率),所以容易低估实际蒸腾量,造成三温模型反演精度略低于取值参考叶片温度最大值的方法,但反演效果仍然较好(R^(2)=0.87, RMSE=0.080 mm·h;)。因此,考虑到参考叶片设置的局限性,如果在实际应用中无法或者没有实际测量参考叶片温度时,使用植被最大温度为参考温度也可达到较好的反演效果。

Aims Parameterization of reference temperature has always been the key and difficult part in calculating evapotranspiration and its evaporation and transpiration components by using three-temperature model.In this paper,the best value of reference temperature was determined by quantifying and comparing the influence of different reference temperature values on the accuracy of transpiration estimation by three-temperature model.Methods Based on the Bowen ratio and thermal infrared observation data of a typical urban lawn,sensitivity analysis and error analysis were carried out on the input variables involved in the sub-model of the three-temperature model to determine the most critical variables for the accuracy of transpiration estimation.Then the influence of input variables parameterization on the calculation of transpiration was quantified and compared to determine the best value of reference temperature.Important findings When using the three-temperature model,the best estimation is to select the maximum temperature of the whole piece of paper as the reference leaf temperature(R^(2) = 0.91,root mean square error(RMSE) = 0.078 mm·h;).When the maximum value of the vegetation canopy temperature was used as the reference temperature,it is directly assumed that the transpiration at the maximum temperature of the vegetation is zero(there is a certain transpiration rate in fact).Therefore,it is easy to underestimate the actual transpiration,resulting in that the estimation accuracy of the three-temperature model was slightly lower than the accuracy of using the maximum value of the reference leaf temperature,but the estimation effect is still good(R^(2) = 0.87,RMSE = 0.080 mm·h;).Therefore,considering the limitations of the reference leaf settings,if the reference leaf temperature cannot be measured in practical applications,the maximum temperature of the vegetation canopy as the reference temperature can be used to achieve good estimate results.