Evaluating hand‐held radiometer derived vegetation indices for estimating above ground biomass

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Abstract
The potential for using vegetation indices developed from remote sensing devices, such as the GSFC Mark‐II hand‐held radiometer, to evaluate biomass has been examined in a number of studies. Relationships range from very good (r2=0.96) to very poor (r2=0.029). One problem with most of the studies is that the data were only collected during a single year, therefore, the usefulness of the relationships within and between years is difficult to evaluate. This study examined the usefulness of vegetation indices, calculated from data gathered by the GSFC Mark‐II radiometer, in assessing the amount of biomass on native grasslands. Vegetation indices derived from data gathered over two years (1989 and 1990) and during four periods throughout each growing season indicate that the ratio between near‐infrared and red spectral responses (ratio vegetation index) performed better then either the difference between the two bands or the normalized difference vegetation indices. Poor relationships were observed (r2=0.07 to r2=0.44) with the best relationships occurring in June and July. Results suggest a high degree of influence by the dead plant component and environmental factors such as sun angle, soil albedo, and atmospheric conditions. Further analysis is needed to evaluate indices acquired by other sources such as airborne‐multiband video and Landsat Thematic‐Mapper data.