02445naa a2200205 a 450000100080000000500110000800800410001910000160006024501100007626000090018652018290019565000190202465000190204365000250206265300220208770000180210970000200212770000160214777300760216315645862002-04-02       1999    bl ---       0--  u    #d1 aPOST, D. F.  aUse of hand-held radiometers to evaluate the cover and hydrologic characteristics of semiarid rangelands.  c1999  aThe spectral reflectance characteristics of 11 rainfall simulator plots were measured with a hand-held radiometer on semiarid rangeland surfaces, of the U.S. Departament of agriculture, agricultural research service, walnut gulch experimental rangeland watershed, tombstone, arizona. Rainfall simulations were made in may and june 1984 for plots characterized by natural vegetation, natural vegetation clipped and removed, and natural vegetation clipped and rock fragments maior 5 mm removed. In 1994, reflectance and cover data were collected on the same plots to evaluate changes over time. Measurements were taken at 38-43º and 74-77º sun elevation angles with a four-band hand-held radiometer (blue 0.45-0.52, green 0.52-0.60, red 0.63-0.69, and near-infrared 0.76-0.90). Correlation and regression relationships were computed between spectral reflectance and percent soil, rock, and vegetative cover percent runoff; and eroded sediments. Highly significant correlations were measured between vegetative cover and percent runoff; relationships with soil rock cover and eroded sediment were poorly correlated. The normalized diference vegetation index (NDVI) was the best predictor of percent vegetative cover, with shrubs forbs being most strongly correlated to reflectance. The regression relationships between 1984 and 1994 spectral reflectance and vegetative cover were very different, even though cover percentages were similar. The amount of standing live and dead biomass and the proportion of green biomass strongly affect spectral reflectance, and the 1984 and 1994 conditions were quite different. Spectral reflectance data can be used to predict rangeland cover characteristics, which in turn, can be used to determine parameters needed for models that predict hydrologic processes on the rangeland surfaces.  aremote sensing  asemiarid zones  aSensoriamento Remoto  aRegiao semi-arida1 aMARTIN, E. S.1 aSIMANTON, J. R.1 aSANO, E. E.  tArid Soil Research and Rehabilitation, Londongv. 13, p. 201-217, 1999.