Keywords: deforestation, NOAAAVHRR, thermal band, band-use, temperature

Abstract
Large-scale deforestation has been a serious global environmental issue. It has been pointed out that large-scale changes in land cover conditions due to deforestation might give serious impact to local climatic characteristics including precipitating or temperature. However, it has not been fully investigated how the changes in land cover affect to local climate. In this study, taking the area around Thailand as the study area, fluctuations in land surface temperature for different land cover types were analyzed to asses the thermal characteristics of land surface by using NOAA AVHRR data and land-use data.

1.Introdution
Large-scale deforestation has been a serious environment issue, and it has been pointed out that the large-scale land cover change might give impact to local climate including the changes in precipitation or in temperature. However, the quantitative relations between the deforestation and the local climate have not been fully investigated. The objective of this study is to assess the impact of land cover change such as deforestation or land use change to local climate, in particular, surface temperature characteristics.

Taking the area around Thailand as the case study area, fluctuations in land surface temperature at day and night were analyzed for different land cover types by NOAA thermal band data and land use data. Land surface temperature at day and night was evaluated from AVHRR Band 3,4 and 5 data from day and night, and land cover data was obtained from land use data from the Land Development Department of Thailand which included 13 classes. The difference areas, and showed the impact of deforestation to local climatic conditions.

2.Methodoloy

21.Data used
Day and night time NOAA AVHRR thermal band data (band3, 4, 50 received in December 1998 covering Thailand area are used to evaluate land surface temperature. Each pixel size of AVHRR is around 1.1 km x 1.1 km. Land use map⁽¹⁾ inThailand including thirteen categories (1; urban, 2: Mine, 3: Paddy, 4:Crop, 5:Orchard, 6:Plantation, 7:mangrove, 8:ldle Land, 9:Water, 10: Fish/Shrimp Farm, 11:Forest, 12: Grasland, 13:Others) is also used to assess surface temperature dependency on land cover types. The original land use map is produced by Land Development Deparment of Thailand in 1990 and is a scale of 500,000. It is digitized into a digital into a digital land map with a grid of 200 m x 200 m (Fig.1).

Fig .1 Land use Map of Thailand, 1990
2.2 Registration
Geometrical rectification of night time NOAA AVHRR thermal band data and land-use in Thailand was made by polynomial transformation, using more than five ground points on the coast line, using day time NOAA AVHRR thermal band data which was rectified using UTM map projections. Since the pixel size of these data are different, the pixel size of land-use data (200 x 200m) is resampled to that of the NOAA AVHRR data (1.1 km x 1.1 km) using majority data as the value for the pixel after transformation.

2.3 Calculation of surface temperature
The difference in temperature between day and night is calculated using the NOAA AVHRR thermal band data as follows;

DTi = Tdi -Tni           (1)
DTi: the difference of temperature between day and night for each pixel of band i
Tdi = day time temperature for each pixel of band i
Tni : night time temperature for each pixel of band i.

For each category of land use, distribution and average of DTi is calculated for band 34 and 5 in NOAA AVHRR.