Íslenskar landbúnaðarrannsóknir - 01.03.1980, Qupperneq 13

Íslenskar landbúnaðarrannsóknir - 01.03.1980, Qupperneq 13
ÍSL. LANDBÚN. J. AGR. RES. ICEL. 1980 12,1: 11—25 Test of a Hand-held Radiometer for Estimating Pasture Biomass in Iceland Campton J. Tucker Earth Resources Branch NASA/Goddard Space Flight Center Greenbelt, AID 20771 USA and Ingvi Thorsteinsson Agricultural Research Institute, Keldnaholt, V/Vesturlandsveg Reykjavík, Iceland ABSTRACT A hand-held digital radiometer configured for spectral estimation of herbaceous biomass has been field tested in Iceland on cultivated pastures. The method is inexpensive, fast, accurate, unaffected by soil/veg- etation moisture, and worked well under varying illumination conditions. Greater than 80 percent of variability between the red and ir radiances and the total dry biomass was accounted for using this method. Frequent recalibrations are necessary which is the principal disadvantage of the method. The results of the field test indicated this method may have application in field situations encountered in Iceland. INTRODUCTION Grassland scientists and other involved in the estimation of standing crop biomass have continually attempted to improve upon existing procedures for estimating herbage biomass accurately, inexpen- sively, and quickly. The existing methods most commonly used involve the hand clipping of a known area ofvegetation and weighing the resulting sample. The limi- tations of clipping need no emphasis in addition to being a destructive sampling technique. Several methods have been devised to estimate standing crop herbaceous biomass nondestructively using various teclmiques such as ocular estimation (Pechanec and Picikford 1937), /3-at- tenuation (Mitchell 1972), capacitance measurements (Neal and Neal 1973), and spectral reflectance or radiance measurements (Tucker et al. 1975). Pearson et al. (1976) reported on an inexpensive hand-held radiometer con- figured for estimating green biomass by measuring the reflected radiation in two wavelenght bands. The bands of 0.650 to 0.700 and 0.775 to 0.825 um were used. A ratio of the two bands was used to allow for instrument use independent of solar illumination levels. The hand-held radiometer, as originally coníigured, in- cluded a modified Tektronics J-16 digital photometer, a Hewlett-Packard model 35 pocket calculator, and a control and in- terface circuit which joined these two in- struments. The prototype instrument was
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