Landsat 5 TM Image for Calculating the Spatial Evapotranspiration with Penman's Basic Method and GIS Technology Analysis at Jakarta and Surroundings

Evapotranspiration as a combination of surface evaporation and plants transpiration, is one of the main elements in the hydrologic cycle. Penman method is used to calculate the evapotranspiration, the equation is {EP = C[W.Rn + (1-W).f(u).(ea – ed)]} where, EP is potential evapotranspiration, mm/hari, W is weighting factor, Rn is net radiation, cal/cm2/aK), f(u) is wind function, (ea – ed) is saturated water vapor difference, and C is wind effect correction factor by day and night. For getting the more accuration and to obtain the spatial evapotranspiration distribution, the calculation benefiting with the Landsat 5 TM composite 5,4,2 and band 6 images, the research area and topography maps of Jabotabek (Jakarta and surroundings). The others are meteorological data : air temperature, air humidity, solar radiation and wind velocity from five meteorological stasions : Jakarta Observation, Tanjung Priok, Halim Perdana Kusuma, Ciledug and Dermaga Bogor. The Landsat image processing of Jabotabek research area, obtain the land used, land slide, land surface temperature, air temperature estimated, saturated vapor pressure, wind function and air humidity maps. All of the maps was digitalized, spatial calculating and analysing by GIS technology with Penman method to obtain the spatial tematic evapotranspiration of Jabotabek research area. The result is spatial evapotranspiration between 4.257 until 5.402 mm/day which is divided into 1308 classes and reclassify into 258 classes. The evapotranspiration distribution pattern is shown in the thematic map layout which produced by GIS technology. The spatial evapotranspiration distribution pattern shows significantly a likeliness with the wind velocity distribution pattern and land use classification. The highest value is distributed in the field crops and wet land areas in the east and west of the Jakarta center, and the lowest in the urban and warm land areas of Jakarta city. Keywords : Penman Method, Meteorological data, Landsat 5 TM image – Spatial Evapotranspiration