Sensitivity of vegetation indices to substrate brightness in hyper-arid environment: the Makhtesh Ramon Crater (Israel) case study

The influence of soil background on most vegetation indices (VIs) derived f rom remotely sensed imagery is a well known phenomenon, and has generated i nterest in the development of indices that would be less sensitive to this influence. Several such indices have been developed thus far. This paper fo cuses on testing and comparing the sensitivity of seven intensively used, L andsat Thematic Mapper (TM) derived, VIs (NDVI, SAVI, MSAVI, PVL WDVI, SAVI (2). and TSAVI) to bare Surface variation with almost no vegetation signal. The study was conducted on a terrain composed of a high variety of bare su rface materials of which basalt and gypsum are two extremely dark and brigh t substrates respectively. It was found that SAVI and MSAVI respond to bare surface material very similarly. Such close similarity was also found betw een PVI and WDVI, and between SAVI(2) and TSAVI. NDVI tends to be overestim ated on dark surfaces, while SAVI, PVI and TSAVI show more sensitivity to b right surfaces. Comparison between Delta (VI) (the difference between pairs of VIs) and the brightness of the different surface materials showed a hig h correlation in each case, which underlines the Fact that the response of different VIs to bare surface variation is mainly related to the surface br ightness.