Vegetation Health Method

Abstract

Vegetation health (VH) method was developed for space-based monitoring of moisture and thermal and total health conditions in vegetation. This chapter is very important in explaining the theoretical and practical principals of the new development. The method stems from the properties of green vegetation to reflect sunlight and emit absorbed solar radiation in the visible (VIS) and near-infrared (NIR) parts of solar spectrum. In drought-free years, vegetation is normally healthy being very green (contains much chlorophyll) and vigorous (contains much water). Such vegetation reflects very little solar radiation in the VIS and much in the NIR parts of solar spectrum. As a result, the normalized difference vegetation index (NDVI), calculated from VIS and NIR, has a very high value, symbolizing good vegetation health, moisture, and thermal conditions. Healthy vegetation also emits less absorbed thermal infrared (IR) radiation, resulting in a lower brightness temperature (BT) and a cooler canopy. Drought depresses vegetation greenness and vigor and makes the canopy hot due to an increase in VIS (due to depletion of chlorophyll), decrease in NIR (due to a drop in water content), a reduction of NDVI, and an increase in BT making canopy hot. Therefore, NDVI and BT serve as indicators of healthy/non-healthy vegetation. Their data are composited and processed to reduce noise related to clouds, aerosols, water vapor, sun-sensor geometry, orbit degradation, satellite position, sensor deterioration, random noise, and other errors. Further, processing includes a development of NDVI and BT multiyear climatology and three indices in the form of deviation from that climatology. The indices are vegetation condition index (VCI), temperature condition index (TCI) and vegetation health index (VHI), combining the first two together. They characterize vegetation moisture (VCI), thermal (TCI), and total health (VHI) conditions. These indices were based on the three biophysical laws: the Leibig’s Law of Minimum, the Shelford’s Law of Tolerance, and the Principal of Carrying Capacity. This chapter describes the three indices and their applications for monitoring vegetation moisture, thermal, and health conditions.