3. Assessment of thermal characteristics for different land cover types
Table 1 indicates the average temperature for different land cover categories which is calculated from AVHRR band 4. In Table 4 parameters Td4 and Tn4 show the temperature at day and night derived from AVHRR band 4, and DT4 shows the temperature difference between day and night. The result for each band has similar tendency, so only the result for band4 is shown as an example. Figure 2 describes the histogram of the surface temperature for paddy, forest and Grass land. In Table 1 and Fig. 2 is clearly indicated that the forest area has low temperature difference between day and night. However, the results for categories such as urban, Mine, Orchard, Water, Fish/Shrimp farm are not satisfactory enough, probably because of coarse spatial resolution, and because of the miss registration.

	Average
Category	Td4 (°C)	Tn4 (°C)	DT4 (°C)
Urban	24.5	19.9	5.6
Mine	24.1	19.8	5.5
Paddy	28.7	20.4	8.4
Crop	28.8	20.0	8.9
Orchard	26.0	20.0	6.6
Plantation	22.8	18.2	5.9
Mangrove	25.4	19.6	6.4
Idle land	26.0	19.5	6.8
Water	25.9	19.6	6.6
Fisth/Shrimp farm	25.5	19.4	6.3
Forest	24.4	18.7	5.9
Grasland	27.7	19.7	8.1

Table 1 Average of Td, Tn, DT of band 4 for each category
4. Conclusions
The average of night time temperature for most land-use categories have similar value. On the other land thee is significant difference in the average of day time temperature for most land-use categories. Thus the difference of temperature between day and night is dominated by the day time temperature. One distinct pattern observed is that while the average of day time temperature for Forest is low, that for Paddy field, Crop land and Grassland is significantly higher. It demonstrates that conversion of land from forest to grassland and agriculture effects in the increase in the day time temperature.

Further work is going on to make more robust analysis by performing seasonal analysis will more sets of NOAA AVHRR data and linking with observed meteorological parameters at various points.

In this study NOAA AVHRR data was provided by Asian Institute of Technology. Authors would like to express out thanks to Dr. S. Lurtlum and Dr. K. Honda of AIT for their kind support for the study.





Fig 2. Distribution of DT of band 4 for Paddy field, Forest and Grassland.
References

• Department of Land Development, Government of Thailand (1990), LANDUSE MAP OF THILAND