Relationship between the ground surface temperature by NOAA-AVHRR and environmental factors
Preparation of data set
As shown in Fig. 2 the test site was specified to the Tohoku district of Japan with an area of 600x200km. Its east side and west side face to the pacific ocean and the sea of Japan, respectively. Oou mountains, of which highest part is about 2,000m, runs from north to south in the central part. The site has a rather complicated geography because there are many rivers from the mountain areas formulating valleys, basins and plains.
The analysis was applied to the two AVHRR image data in
Table 1.
Fig. 2 and Fig. 3 show the pseudo-color and the temperature displays of the images. As the test site has been covered by traveling high pressure before the data acquisitions, those images represent typical data of the spring and the early summer under the stable clear sky conditions.
Table 1. Acquisition time of AVHRR data used in the analysis
| |
Local time |
Date |
#NOAA |
| Image-A |
15:12 |
1988.4.17 |
NOAA-9 |
| Image-B |
14:03 |
1986.6.12 |
NOAA-9 |
Figure 2: The map of Japan. The test site is the region inside the rectangle.
Figure 3: Pseudo color displays of AVHRR data used in the analysis.
This district was divided into square meshes with 5km distance, and sample points were specified at the center of each mesh. At each sample point, values of each variable were read out or calculated as follows .
ST (AVHRR ground surface temperature) : After the geometric correction of the original images, the temperatures were calculated by the method in Lauristein (1979). Then they were calibrated by the SST estimation function of Yokohama (1988).
ELE (elevation): This was read out from the digital geographical data set of Japan (DGDSJ). As the mesh size of DGDSJ I s250m and the ground resolution of AVHRR is 1.1km ELE was calculated as the mean of 5x5 neighborhood pixels in DGDSJ
Cos
g : This was calculated from DGDSJ and the sun position.
VI (Vegetation index ) : This was calculated from Ch. 1 and Ch. 2 data of AVHRR as
VI = ch.2 - ch.1 / ch.2 + ch.1 x 100
Lat (latitude coordinate) : This was read out from DGDSJ.
AL (albedo in the visible ch.1 of AVHRR) : This was calculated by following to the definition in Lauristein (1979).
In the preparation of the final data set, sample points accepting one of the following conditions were exempted
- A sample point of which neighboring points with 1.0 km were
covered by cloud, snow or noises.
- A sample point of which neighboring points within 1.0 km include a point in water.
- A sample point at which values in the neighbor hood points are very variable. The threshold value were determined from the histogram of the standard deviation of neighborhood points.
Table 2 shows the statistics of the final data set. Since the high elevation areas in image A had been covered by snow, its total number of final sample points and the mean of ELE is smaller than those of Image-B because most of deciduous trees, grasses and crops had not grown their elves yet in the middle of April.
Table 2: Statistics of the final data set for the regression analysis
| Image data |
#of samples |
ELE [m] |
Cosg |
VI |
LAT |
AL |
ST[°C] |
| Image-A |
1345 |
195.14
258.89 |
0.06
0.54 |
5.17
21.77 |
1.11
38.98 |
0.79
6.25 |
2.10
19.53 |
| Image-B |
1712 |
266.50
377.17 |
0.05
0.78 |
11.81
51.83 |
1.14
38.88 |
0.92
6.56 |
3.02
26.81 |
