Íslenskar landbúnaðarrannsóknir - 01.03.1980, Page 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