THE RELATIONSHIP BETWEEN CANOPY SURFACE TEMPERATURE w 
BY IR-THERMOMETER AND CANOPY STRUCTURE pi 
th 
Xiufeng WANG, lkuo HORIGUCHI and Takashi MACHIMURA se 
Dept. of Agricultural Engineering, Faculty of Agriculture, Hokkaido University 
Sapporo, Japan of 
(e 
Commission VI, Working Group 1 st 
or 
th 
KEY WORDS: Temperature, Surface, Vegetation, Structure, Infrared, Radiation n 
ABSTRACT: 
Various thermal phenomena on the surface of the earth have been analyzed by using surface 
temperature measurements from aircraft or satellites, because the preservation of the global Ur 
environment recently has become an issue. However, few basic studies on vegetation surface 19 
temperatures for such analysis have been performed. Therefore, lack of knowledge regarding surface me 
temperatures is an obstacle to analyzing data from aircraft or satellites. wl 
The purpose of this study is to analyze the characteristics of canopy surface temperature of crop + 
fields, to clarify the relationship between various thermal phenomena and these surface temperatures. of 
Study was performed for two different types of canopy structure, soybean (planophile) and corn ca 
(erectophile). The arrangements of leaves in the canopies were obtained for both crop fields, and an 
canopy surface temperatures and leaf temperatures were measured by IR-thermometer which uses the of 
same measuring principle as aircraft or satellite radiometers. The results of this study are summarized 
as follows: 2.1 
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 canopies leaf 24 
area is near the upper portion of the canopy. dis 
2) In contrast, canopy surface temperatures for the erectophile crop are affected by the leaf the 
temperature from the upper to the lower portion of the canopy. ple 
3) Therefore, in later stages of growth (dense vegetation cover), the maximum canopy surface ere 
temperature of the erectophile crop (corn) is lower than that of the planophile crop (soybean). pla 
4) Also, the directional variation and hourly variation of leaf surface temperature are larger for the Cai 
planophile crop (soybean) than for the erectophile crop (corn), because wind and solar radiation sky 
strongly influence the planophile crop. car 
5) At low intensities of solar radiation, however, surface temperature of leaves facing skyward is the 
lower for the planophile crop (soybean) than for the erectophile crop (corn). COI 
1. Introduction The purpose of this study is to obtain Dis 
M fundamental knowledge of remotely sensed surface ang 
Artificial satellites have recently been developed, temperature with regard to the canopy structure and dire 
and the surface temperature of the earth is ground measurements by IR thermometer. The 
measured regularly by launched radiometers. radiometric measurement of canopy surface 24. 
Furthermore, various thermal phenomena such as temperature over a crop field is affected by thermal terr 
heat budget and radiation budget on the earth have radiance emitted from soil and vegetation and is affe 
been analyzed by using surface temperature sensed as a composite surface temperature (we call kno 
measurements from these satellites or aircraft, this "canopy temperature") by the IR thermometer. tem 
because the preservation of the global environment Kimes, et al. (1980), Kimes (1980) and Heilman, el Spe 
recently has become an issue. Also, crop field al. (1981) have evaluated the canopy temperature tem 
surface temperature measurement by satellites is by using vegetation surface temperature, soil per 
useful for many agricultural applications including surface temperature and the probability of gap Or Soy 
evapotranspiration models, soil moisture detection, percent vegetation cover. However, this canopy ü 
plant stress detection and yield prediction. Most temperature is a function of the geometric upp 
studies have focused on remotely sensed canopy structure of the plant canopy, such as spatial tem 
surface temperature to infer the water status of the distribution of leaves within canopy and frequency 
vegetation for soil moisture detection and plant distributions of leaf orientation and angle, as well 24. 
stress detection. However, few basic studies have as plant surface temperature, soil surface tem 
been performed on the relationship between temperature and percent plant cover. Hatfield et al. thos 
remotely sensed canopy surface temperatures and (1984) reported about changing the canopy wer 
canopy structures for the analysis of thermal temperature due to change morphological structure 
phenomena. of the canopy, that is the canopy temperatures of Max 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996