To confirm the results, the variations of the
maximum surface temperature minus the maximum
air temperature for the measurement periods are
calculated and shown in Fig. 9. The same results
were indicated in Fig. 9.
In the latter growth stage of an erectophile crop,
the canopy temperature includes the low leaf
temperature of the under part within the canopy.
However, leaves of the planophile crop receive
much energy and the canopy temperature becomes
high.
4 , Conclusions
The results of this study are summarized as
follows:
1) Canopy surface temperatures of the planophile
crop (soybean) as measured by IR thermometer
are affected by the leaf temperatures of leaves in
the upper portion, because most of such canopy
leaf area is near the upper portion of the canopy.
2) In contrast, canopy temperatures for the
erectophile crop (corn) are affected by the leaf
temperature from the upper to the lower portion of
the canopy.
3) Therefore, in latter stages of growth (dense
vegetation cover), the maximum canopy temperature
of the erectophile crop (corn) is lower than that of
the planophile crop (soybean).
4) Also, the directional variation and hourly
variation of leaf surface temperature are larger for
the planophile crop (soybean) than for the
erectophile crop (corn), because wind and solar
radiation more influence the planophile crop.
5) At low intensities of solar radiation, however,
surface temperatures of leaves facing skyward are
lower for soybeans than for corn.
These results suggest that canopy temperatures
vary due to canopy structure: especially orientation
and distribution of leaves within canopies, and crop
spaces. Therefore, in the latter growth stage of
crops, vegetation cover ratio is not an important
factor for canopy temperature. In the latter growth
stage (dense vegetation cover), the canopy
temperature of the erectophile crop is lower than
that of the planophile crop in daytime.
This is important for analyzing thermal
phenomena using canopy temperature measured by
IR thermometer.
762
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996