Diurnal and seasonal changes in evapotranspiration (ET) of sweet potato and the crop coefficient (ET/reference ET) were studied during the period from the transplanting time to the time when crop development terminated following first hoar frost, at a location in the southern part of Kyushu. The ET was measured using the Bowen ratio heat balance method. ET from a grass field was also measured with the same method to check the applicability of the modified Penman model (Doorenbos and Pruitt, 1977) for estimating reference ET to the southern part of Kyushu. The results obtained through the observations and data analysis can be summarized as follows.
1) Reference ET calculated from the modified Penman model agreed with the measured one at the grass field, showing that the modified Penman model is applicable to the southern part of Kyushu without turning the coefficients in Eq. A-1.
2) The daily mean of albedo in the sweet potato field increased curvilinearly with the growth of sweet potato, varying from about 0.08 of the transplanting time to 0.24 of the stage at the maximum leaf area index. These threshold values agreed well with the ones obtained by Ito et al. (1984). After the sweet potato field was damaged by the first hoar frost on 22 October, the albedo decreased drastically to about 0.13 on the next day.
3) The daily values of evapotranspiration measured for the growing period were in a range from 1mm to 9mm with the average of 3.67mm, agreeing well with average evapotranspiration (ET=3.71mm) for a paddy field measured with a lysimeter in the same district (Iwakiri, 1965). The daily ET on clear days (25<Q≤30MJ·m^-2) fell into a range from 7mm to 9mm for 3/4 of these days.
4) The daily crop coefficients of sweet potato calculated from the measured ET and the reference ET showed smaller variation than those based on the radiation model (Eq. A-2). The mean value of the crop coefficient obtained on the basis of the modified Penman model was 1.18 (Fig. 5).
5) There was good agreement between the actual ET measured at the sweet potato field using the Bowen ratio heat balance method and ET calculated from Morton model (Fig. 8). This agreement implies that the Morton model is applicable to the estimate of actual evapotranspiration from sweet potato field with the meteorological data collected at one level above the canopy.

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Detection of the hazard areas for frost damage was attempted by using numerical terrestrial data and NOAA/AVHRR data. The areas in this analysis were the regions around the foot of Mt. Youtei (referred to here as Youtei), Ishikari plain (referred to here as Sorachi), the Tokachi plain (referred to here as Tokachi) and the Nayoro basin (referred to here as Nayoro). The study areas were 60km×50km.
The following three methods were employed for detecting valleys and basins using numerical terrestrial data; 1) Counting the number of negative gradient values of the altitude between a center cell and its eight adjacent cells (the 8 adjacent cells method); 2) Counting the number of negative gradient values between a center cell and its sixteen surrounding cells that are one cell width apart from it (the 16 adjacent cells method); 3)-A Counting the number of valleys that drain into a single cell (the contiguous maximum gradient method). This method involves tracing the maximum negative gradient values from cell to cell until a low point is reached from which only positive gradient values radiate. This technique was repeated for each cell in the entire grid. That is, each cell was used as a starting point, and the valley emanating from it was traced until a basin was reached; 3)-B Determining the number of adjacent cells for which the negative gradient value is greatest between the adjacent cell itself and the center cell (the maximum gradient method).
Two methods were employed to detect areas having low temperatures using NOAA/AVHRR data; 1) Counting the number of negative difference in temperature between the center cell and the eight adjacent cells (the 8 adjacent temp. method); 2) Locating cells with temperatures lower than the threshold temperature (the threshold temp. method).
The topographic data and temperature data for Youtei were then combined on a cell by cell basis to find how well the two types of data matched. The 16 adjacent cells method gave the same results as the 8 adjacent cells method.
The valleys and basins detected by the 8 adjacent cells method matched well with the low temperature areas located by both low temperature detecting methods. However, the 8 adjacent temperature method revealed which cells were more likely to get cold due to the local topography. On the other hand, the threshold temperature method revealed where valleys and basins with low temperatures were located.
The valleys and basins detected using the maximum gradient method did not match well with the areas of low temperature detected by either method.
The analysis discussed above was performed on the data for Youtei only. In order to compare the data obtained in all four areas, the coincidence index was calculated for each of the four study areas. The coincidence index is defined as the ratio of cells which represent either valleys or basins and have temperatures below threshold values, to the total number of cells with temperatures below the threshold.
The results indicated that these methods are effective for detecting hazard areas for frost damage in Youtei and Nayoro. However, the effectiveness of these methods is reduced for Sorachi and Tokachi. The small coincidence index in Sorachi is caused by a smooth and flat topography. In Tokachi hilly areas are separated by plains at a distance greater than can be covered by a center cell and its 8 adjacent cells.
The standard deviations in altitude between each cell and its 8 adjacent cells for which low temperatures were detected were calculated to determine topographic differences in each region. The results are shown in Table 4. The regions of Youtei and Nayoro have large standard deviations. On the other hand, the values for Sorachi and Tokachi are small. This demonstrates that low temperatures occur in smooth and flat areas in Sorachi and Tokachi.
The incidence matrix of the ranges for altitude in these regions and the inertial momentum around the diagonal

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The spectral reflectances of individual detached leaves at 15 wavelengths ranging from 400nm to 2300nm were measured versus leaf water content per unit leaf area (leaf water content; LWC; mgH₂O·cm^-2) for three dicotyledonous tree species, Viburnum awabuki (viburnum), Nerium indicum (oleander) and Cinnamomum camphora (camphor), in August and February. The spectral reflectances (γλ_i=1-15; %), their reciprocals (1/γλ_i=1∼15), and all combinations of ratio between two bands pair (γλ_i=1-15/γλ_j=1-15) were chosen as the independent variable (total 240 kinds), and LWC (mgH₂O·cm^-2) was the dependent variable. Regression analyses were conducted for each species and for the pooled species. The reflectance ratio (γ1650/γ1430) correlated best with leaf water content (Table 1), and the regressions differed little among three tree species. The regression equation for the pooled species in August was LWC=20.9(γ1650/γ1430)-22.8 (correlation coefficient, r=0.97; number of observations, n=90; see Fig. 3). The standard error of estimate of mean leaf water content was 1.0mgH₂O·cm^-2. The value equal to about 5% of the mean leaf water content per unit leaf area of all leaves examined. Thus, γ1650/γ1430 is a useful index for remotely sensing leaf water content per unit leaf area.

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Deviations in the horizontal distribution of soil temperatures beneath the film mulch were studied in relation to meteorological conditions. Three kinds of mulching, transparent PE film, violet PE film and black PE film were tested. The effects to raise soil temperatures were evaluated with the measured deviations of soil temperatures.
The results are as follows.
(1) It was revealed that the deviations of soil temperatures varied with the depth in soil and the time of day. Especially in the night, the deviations 0.2-0.8°C for the soil layers of 0-30cm in the mulched plot with transparent PE film were almost the same as those of 0.2-0.5°C in the bare plot. However, in the day, the deviations of soil temperatures reached 0.3-0.9°C for the layers excluding the surface in the mulched plot as compared with those of 0.1-1.7°C in the bare plot. The mulched plot showed a smaller variation of the deviations between the day and the night. (2) It was implied that the horizontal inhomogeneity of the soil moisture content at a depth influenced largely the soil temperature and caused such deviations. Further, the effect of each meteorological factor on the deviations of soil temperatures was different from the mulched plot to the bare plot. The main factor to cause the deviations of soil temperatures was the amount of insolation in the mulched plot with transparent PE film, but the soil moisture content in the bare plot. (3) A method was proposed to compare the effects between two mulched plots. The comparison was conducted in two cases. One was that soil temperatures were obtained at 10 points at a same depth (see Table 3), and the other was that soil temperatures were obtained at one point at each depth (see Table 4).

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