10
The dark object method was carried out upon Landsat images 2006 which is assigned as referenced data of normalization. Even the image was suffered from striping
caused by Scan Line Corrector SLC failure, the radiometric quality remains intact USGS, 2006. The complete process of atmospheric correction can be seen in the figure
below.
Figure 3.3. The Process Flow of Atmospheric Correction
D. DEM Generation
DEM Digital Elevation Model is one of raster data used in this study which generated from contour data. Contour data was came from topographic map Rupa Bumi
Indonesia map, sheet no. 1209-142 and 1209-231, with contour interval 12.5 m. DEM was generated through surfacing process by using non-linear rubber sheeting method. In
order to have same in resolution of data, DEM produced have a resolution as same as
Atmospheric Correction: dark object method
Data Preprocessing
Landsat 12265_ 2006
Landsat 12265_ 1991
12265_ 1994 12265_ 1997
12265_ 2001 12265_ 2004
RC Landsat 12265_ 2006
PIS Selection
STD of PIS of reference image σ
Rk
STD of PIS of subject image σ
Sk,y
Mean of PIS of reference Image R
k
Mean of PIS of subject image S
k,y
Note: PIS = Pseudo-invariant Set
STD = Standard Deviation RC = Radiometric Corrected
Transformation Transformation Coefficient
slope: m
k, y
= σ
Rk
σ
Sk,y
intercept: b
k, y
= R
k
- m
k, y
. S
k,y
Image Regression Model Y
y
= m
k, y
. X
k
+ b
k, y
Reference Image
Subject Images X
k
Landsat 12265_ 1991
12265_ 1994 12265_ 1997
12265_ 2001 12265_ 2004
Normalized ImagesY
y
11
LANDSAT data, that is 30 m x 30 m. In further step of analysis in this study, the DEM was converted to a slope map and then used as a one factor for estimate soil erosion.
III.6. D
ATA PROCESSING
There are three kinds of data processing are carried out to prepare the data for the main analysis in the study that is soil erosion analysis, comprise of image classification,
watershed delineation, and slope classes and length generation.
A. Watershed Delineation
The watershed delineation tool uses AVSWAT-2000 version 1.0, the extension for ArcView and Spatial Analysis. It is used to perform watershed delineation based on
SWAT Soil and Water Assessment Tool model. SWAT is a model developed to predict the impact of land management practices on water, sediment, and agricultural chemical
yields in large, complex watershed with varying soils, land use, and management conditions over long period of time Arnold et al., 1998. The delineation process requires
a Digital Elevation Model DEM in ArcInfo grid format. The diagram flow below illustrates the steps in the delineation process:
Figure 3.4. Delineation process
Topographic Data
Digital Elevation Model in Erdas format .img
Digital Elevation Model In ArcInfo grid format .grid
Surfacing
Export .img to .grid
Process in ERDAS
Outputs . shp file: 1.
Sub-watersheds area
2. The stream network
Load the DEM Preprocess the DEM
Specify the minimum sub-watershed area
catchments area Review and edit the
stream network points Delineation Process
Process in ArcView AVSWAT Ext.
Data Processing Data Preprocessing
12
Figure 3.5 shows the catchments area which generated from Digital Elevation Model DEM. Delineating process obtained three large watersheds, which overlapped
with Telaga Warna Nature Reserve, as follows: Ciliwung, Cigundul and Cibeet watersheds. However, the area study is limited on the catchments area part of
watershed that has an upper stream region on nature reserve area. Figure 3.5.b. shows that area study has eight catchments that have upper stream region on nature reserve
area.
Figure 3.5. Delineating catchments area
B. Slope Classes and Length Generation
