B. K. Bhattacharya and V. K. Dadhwal
Crop Inventory and Modeling Division, RESA
Space Applications Centre, Gujarat, Ahamedabad – 380015
Retrieval of land (soil-vegetation cover complex) surface temperature (LST) from thermal infrared observations of the Earth’s surface acquired from a satellite platform have been recognised as a valuable key input for evaluating the surface energy and water budget over large geographical region. The present study was aimed to derive LST over Kheda District of Gujarat using thermal bands (channel 4 and 5) of NOAA AVHRR images and validate them using field observations made during Land Surface Processes Experiment (LSPEX) carried out during 13th – 17th of December and May during 1997 at five sites (Anand-22035/ N, 720 55/ E; Derol – 220 40/N, 730 45/ E; Arnej – 220 40/N, 720 15/ E; Sanand – 30 04 /N, 720 22/ E; Khandha – 220 02/ N, 730 11/ E) at 10:00 and 9:30 GMT respectively.
Twelve images were acquired, calibrated and geometrically registered and LST was estimated using split window technique of Becker and Li (1990). Emissivities were computed using algorithm of Valor and Casselles (1995) with and without atmospherically corrected NDVI. Atmospheric corrections were done by running SMAC algorithm of (Rahman and Dedieu, 1994). The estimated LST were compared with measured air temperature (AT) and surface soil temperature (ST). Comparison of algorithms of fractional estimation of temperature at vegetation canopy and soil surface is planned for further investigation. The satellite derived LSTs were found to vary from 30.6 to 37.10C during December ’97, whereas the LSPEX field observed air temperatures (AT) and soil surface temperatures (ST) were ranging from 26.7 to 29.00C and from 33.4 to 42.50C. During May’97, the retrieved LSTs were higher and showed a variation in the range of 45.0 to 58.00C whereas the values of ATs and STs varied from 39.7 to 45.00C and 55.1 to 59.00C respectively. During both the seasons, LSTs were found to lie between STs and ATs, but the LSTs were close to STs during May which may be due to less effect by the presence of poor vegetation canopy growth.
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