Calibration and validation of salt-resistant hyperspectral indices for estimating soil moisture in arid land

SummarySurface soil moisture information is needed for monitoring and modeling landscape processes at various spatial scales. Studies have shown that surface reflectance spectra of soils are often jointly controlled by soil moisture content (SMC) and salt content (SSC) but has not been sufficiently addressed. In this study, eight different index types of soil moisture hyperspectral indices were being examined for their sensitivities to SSC based on laboratory controlled experiments with a wide range of SMC and SSC (dataset I, 196 spectra in total). They were then validated using field in situ measurements (dataset II) as well as data extracted from the same locations from a Hyperion image (dataset III). The dD1300,1970 was identified as the robust salt-resistant index to estimate soil moisture, with R2 of 0.57 and 0.65 corresponding to Datasets I and II, respectively. However, the performance of the index somehow dropped when Dataset III (R2 = 0.29, P < 0.01) was used, mostly due to the quality of Hyperion data resulting from the propagated errors from atmospheric corrections. With improved accuracy from atmospheric corrections and development of new satellite-borne sensors, it is foreseen that the dD1300,1970 index identified in this study should have wide application in the mapping of soil moisture in saline soils of arid lands.

► The dD1300,1970 index is the most insensitive to salt contents. ► It can be applied to estimate soil moisture from reflectance spectra in arid land. ► Moisture and salinity greatly shaped soil surface reflectance in arid land. ► Hyperspectral indices are able to retrieve soil moisture even in arid land.