MRSEI指数的合理性分析及其与RSEI指数的区别

遥感生态指数（RSEI）自提出以来，已得到广泛的应用。近年来，也有学者对其进行了修改。研究基于主成分变换的机理和应用实例，分析了修改的遥感生态指数（MRSEI）的合理性及其与RSEI的区别。结果表明：MRSEI指数将不具生态含义的第二主成分和第三主成分加入具有明确生态含义的第一主成分进行加权求和计算，其结果不仅降低了第一主成分的占比，无法增加原RSEI的信息量，而且还导致各主成分分量互相干扰，造成MRSEI结果的低估或高估。因此，这一修改缺乏合理性。研究同时还对用户在计算RSEI指数中碰到的一些问题进行分析。RSEI在使用中应注意采用植物生长季节的地表反射率数据；当研究区有大面积水体时，必须对水体进行掩膜；而只有当对生态起正面影响的绿度（NDVI）和湿度（Wet）指标在PC1的载荷为负值时，才必须进行“1 – PC1”的还原运算。

Rationality Analysis of MRSEI and Its Difference with RSEI

The Remote Sensing based Ecological Index （RSEI） has been widely used since its publication and was modified recently. In this paper， the differences between RSEI and the Modified Remote Sensing Ecological Index （MRSEI） are analyzed and compared based on the principle of the principal component analysis and an application case. The results show that the MRSEI index unreasonably adds the second principal component （PC2） and the third principal component （PC3） into the first principal component （PC1）， as PC2 and PC3 have no clear ecological meanings. The addition also reduces the weight of PC1. Therefore， the MRSEI does not improve the original RSEI， but reduces the value of RSEI as the added principal component components can cancel each other. Therefore， the modification made in MRSEI lacks rationality. This paper also analyzes and discusses some issues that users encountered in calculating and applying the RSEI index. The RSEI should be calculated using surface reflectance data rather than the top of atmospheric reflectance data or Digital Numbers （DNs）. Also， the imagery should be acquired in plant growing seasons. When there is large-area open water in study images， the water must be masked in advance. The "1–PC1" procedure can only be performed when the loadings of the greenness and wetness indicators in PC1 have negative signs.