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4.Field measurment of spectral signature of wheat by using hand 
spctroradiometer 
The possibility of using the remote sensingdata to forecast 
the grain yield of wheat has worldwidely investigated, such as 
LACIE project. So, we have measured the reflectance of wheat canopy 
and examined the relationship among spectral signature, wheat 
growht and grain yield. 
The test site was chosen on three different soils of a test 
area of the National Agriculture Experiment Station at Hokkaido. 
Eleven ten by ten meters fields with wheat, which were fertilized 
by three kinds of fertilizers, phosphoric, potash, and nitrogenous 
fertilizers were prepared. 
Reflection measurements were performed at May 27, June 28, July 
27, 1977, during the maturing period, and dry weights of wheat were 
also every 25 days since seeding. 
In order to avoid the effect of the soil reflectance, the 
reflection from these field was always measured for an observation 
angle of 30 and a solar angle of 30 from the place of 2.5 m higher 
avobe the soil level. 
Fig.4-1 shows the radiance factor of the wheat canopy at June 
28, when wheat ears began to grow after coming to ear. From the 
figure, wheat canopy on the soil where potash fertilizer was not 
added, apeared lighter, and for the soil lacked of nitrogenous 
fertilizer, looked darker. 
Generally radiance factor at 650 nm decreased as wheat grow 
thicker,and at 850 nm radiance factor decreased, so dry weight and 
grain yield of wheat was plotted against the difference of radiance 
factor of 450 nm and 650 nm, that IR/R value as shown in Fig.4-2 
and Fig.4-3. 
From those figures, both dry weight and grain yield were 
Linearly varied with the IR/R value, but two regression lines of 
the different gradients were drawn. 
This seems to be occured by the differences of the wheat growth 
due to the different condition of soil. Following correlation 
coefficients were obtained. 
Dry volucanic Alluvial soil Total 
(SV) soil (AV) 
dry weight 0.933 0.749 0.851 
grain yield 0.812 0.824 0.831 
The correlation coefficient of the grain yield to the dry weight 
was 0.883 and a bit larger than that to the value IR/R. 
It is reasonable to use the dry weight for forecasting the grain 
yield of wheat, but it is not practical to measure the dry weight over 
the large area of wheat. So, the value IR/R is a good index of 
estimating the yield. 
Fig.4-4 and 4-5 also show the relation among these three parameters 
caluculated from the data on JUne 28. Both the dry weight and the 
grain yield were varied linearly with the IR/R, without being affected 
by the reflectance of soil, and their correlation coefficients had 
higher values than 0.90. 
This means that the IR/R value can be used for forecasting the 
grain yield of wheat.