Íslenskar landbúnaðarrannsóknir - 01.03.1980, Side 19

Íslenskar landbúnaðarrannsóknir - 01.03.1980, Side 19
TEST OF A HAND-HELD RADIOMETER 1 7 TOTAL DRY BIOMASS (g/m2) TOTAL DRY BIOMASS (g/rn^) Figure 3. Plot of data values, regression determined equations, and associated r2 values for (A) red radiance, (B) IR radiance, (C) radiance ratio, (D) radiance difference, (E) radiance sum, and (F) vegetation index. computation. Regression output included the regression derived equation, regres- sion analysis of variance, correlation coef- ficient (r), coefficient of determination (r2), measures of central tendency, re- siduals, etc. (Dixon 1974). It should be noted that the coefficient of determination (r2) values for the trans- formed data using Equations 2, 3, and 4 approximate the actual statistic (s). This results from the introduction of a small amount of transformation error for small and large values of total dry biomass (Draper and Smith 1966). Variables evaluated In addition to evaluating the red radiance, near infrared radiance, and the IR/red radiance ratio, three other variables were transgenerated from the red and infrared radiance. These were the IR—red radiance difference, the IR+red radiance sum, and the vegetation index (VI) of Rouse et al. (1974). The VI is the IR— red radiance difference divided by the IR+red radiance sum and has been shown to have a high degree of utility for vegetational biomass remote sensing (Tucker 1979). Equation 2 was used for the red radiance data while Equation 4 was used for the IR radiance, the radiance ratio, radiance difference, and the VI. The radiance sum could not be consistently approximated with any of the four regres- sion models used. Experimental results Inspection of the regression results indi- cated that a substantial degree of simi- larity existed between the first five meas- urement trials (Table 2). Because it would be impractical to compare all six meas- urement trials by presenting the figures for each of six variables for the six trials, the complete results of the second trial 2

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