Spectral-radiometric differentiation of non-photosynthetic vegetation and soil within Landsat and Sentinel 2 wavebands

ABSTRACT

We explore the comprehensive differentiation of non-photosynthetic vegetation (NPV) and soil using Landsat and Sentinel 2 wavebands through a spectral library approach. NPV and soil spectra from online spectral libraries and an Airborne Visible Infrared Imaging Spectrometer (AVIRIS) scene were convolved to Landsat 5 Thematic Mapper (TM), Landsat 8 Operational Land Imager (OLI), and Sentinel 2 bands. Several spectral-radiometric measurements, including the spectral reflectance of analogous Landsat and Sentinel bands, and a suite of spectral indices were tested for the separation of NPV and soil. Reflectance of individual bands is similar between the two categories, and vegetation indices such as Normalized Difference Vegetation Index (NDVI) and the Soil Adjusted Vegetation Index (SAVI) are incapable of such differentiation. For both reference and image spectra, the normalized difference tillage index (NDTI) based on the two shortwave infrared bands of Landsat and Sentinel instruments performed best among all spectral measurements. Classification results suggest an NDTI value of 0.1 to be a general threshold for separating NPV and soil, with higher values associated with NPV. Further tests based on AVIRIS-convolved imagery show that NDTI can dichotomize NPV and soil if either fractional cover is no less than 50%.

Additional information

Funding

This work was funded by National Aeronautics and Space Administration grant id 17-EARTH17F-337.