Íslenskar landbúnaðarrannsóknir - 01.03.1980, Side 16

14 ÍSLENZKAR LANDBÚNAÐARRANNSÓKNIR
Figure 2. Spectral acceptance of'the radiometer‘s probes. Each probe consists of'a silicon photodiode that
\ iews the vegatated plot through a custom-made interference filter (f'rom Pearson el al. 1976).
operator with the probes over the plot or
area in question, operating the instru-
ment, and recording the two radiance val-
ues takes approximately 20 to 30 seconds.
The radiance values are read instantane-
ously. The largest portion of the time
spent in field operation is in positioning
the operator‘s body to avoid reading their
shoe(s) or feet, being the desired height
above the pasture scene, and to a lesser
extent scaling the radiometer read-out.
Because the procedure is so fast, the plot
in question can be reread several times if
any questions arise without significantly
increasing the time involved.
Field use
The field biomass estimation method
most commonly used with the instrument
METHODS AXD AXALYSIS
Study Location
The site selected for the stud) was at the
Agricultural Research Institute in Iceland
which is located approximately 5 km east
involves a double sampling procedure.
First, 20 to 30 plots from the grassland in
question are measured with the radiome-
ter and clipped. The size of the circular
clipped plots can vary from a diameter of
~30 cm to that of~60 cm. After or while
the calibration clipping is proceeding, the
operator can then begin the survey of the
pasture in question. Many plots can be
read at the usual rate of approximately
one every minute. The nonclipped plots
can be expressed in terms of biomass by
using the relationship developed between
the radiance ratios for the clipped plots
and the biomass values determined in the
laboratory. In this way, the nondestruc-
tive spectral measurements are translated
into biomass values.
from Reykjavík, the capital of the country.
The site is at 64° northern latitude, the
annual mean temperature is 5.0°C, the
mean temperature of May through Sep-