3.4.1 Image Pre-Processing
3.4.1.1 Selecting and Cropping Data
The aim of selecting data is to get the free cloud-cover image data. Furthermore, to get the efficiency in image processing, the selected data are cropped for the
study area.
3.4.1.2 Radiometric and Geometric Correction
Radiometric and geometric errors are the most common types of error encountered in remotely sensed imagery. To remove or minimize the error the
following should be done: 1.
Radiometric correction, using histogram adjustment 2.
Geometric correction is the basic operation in geometric rectification which covers collecting ground control point GCP, transformation and
resampling. The topographic map from Bakosurtanal of Karawang district with the scale of 1:25.000 is used to correct the image data.
3.4.2 Data Processing and Analysis
Satellite imagery data is analyzed using ER Mapper 7 and vector data is processed using ArcView 3.3. Field data are collected from surveys and position
of the location is taken by using GPS. Field data is used to verify result of land cover. Result analysis is thematic images of evaporative fraction from 2003 until
2006.
3.4.3 Energy Balance Modeling
Energy balance estimation has been performed using daily meteorological data from surface station and daily remote sensing data from Landsat. The flow
diagram modeling of energy balance is presented in Figure 4.
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Remote Sensing Data
Climate Data
NDVI Ts
α Ta
U
2
Rs
Net Radiation Rn
4
16 .
273 1
+ −
+ −
= Ts
Rl Rs
Rn
εσ α
Net Radiation Rn
4
16 .
273 1
+ −
+ −
= Ts
Rl Rs
Rn
εσ α
Sensible Heat Flux H
273 900
2
Ta Ts
U Ta
H −
+ =
λ γ
Sensible Heat Flux H
273 900
2
Ta Ts
U Ta
H −
+ =
λ γ
Soil Heat Flux G
0.98NDVI -
1 007
. 0.0038
4 2
α α
α +
= Ts
Rn G
Soil Heat Flux G
0.98NDVI -
1 007
. 0.0038
4 2
α α
α +
= Ts
Rn G
Energy Evapotranspiration λE
H G
Rn E
− −
= λ
Energy Evapotranspiration λE
H G
Rn E
− −
= λ
Evaporative Fraction EF
G Rn
E EF
− =
λ
Evaporative Fraction EF
G Rn
E EF
− =
λ
Figure 4. Flow diagram of energy balance modeling
3.4.4 Development of Web GIS
In this research we also develop a web GIS to publish the spatial information of energy balance Figure 5. Developing web GIS is divided into
three major steps. First, is the design data information of drought indicator. Second, is building web page based on drought information. The last step is
publishing the spatial drought information through the internet.
Figure 5. Schema to build and publish information
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The raw materials for information system are data input, i.e. the representation of facts or concepts that becomes usable when processed. Data is
required to produce information which is needed by users. There are conceptual, logical and physical database designs. Conceptual design focuses on what data
should be stored in the database, while the function model deals with how the data is processed. To put this in the context of the relational database, the data model
is used to design the relational tables. The functional model is used to design the queries that will access and perform operations on those tables. Logical database
design focuses on constructing a model of information used in an enterprise based on specific data model. Logical model explains the logic of database which is the
process of constructing a model of information used in an enterprise based on specific data model, but independent of particular DBMS and other physical
considerations. Physical design describes the physic of database visualization, which allows the designer to make decisions on how the database is to be
implemented. Physical model describes the data physically where entity is set based on database software.
This phase building web page also applies to the programs which process the database. In the system development approach, the parallel activities could be
observed. The designed web page of the system is divided into two parts. 1.
Design of spatial modeling includes spatial data selection and spatial data manipulation.
2. Design of output includes map, graph and table.
The last step is implementation to improve the system. A standard web browser will be used as the web page. The browser connects to the server, which contains
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spatial database. The server sends back a result of request to the client. An interface will be developed which allows user to query the spatial database. The
result is returned to the user’s browser as an HTML file that contains the dataset
in image format usually .pnggif format.
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IV. RESULTS AND DISCUSSION
4.1. Energy Balance
The component is analyzed from Landsat-7 and climate data. Landsat-7 ETM+ image data used is from 2003 to 2006. Mosaic process is applied only to
data 2006 to see land cover condition. The data actually was invalid since 2003 and a lot of striping data cannot be analyzed. Climate data are obtained from
BMG air temperature and wind velocity data acquisition 1995 to 2002 and from
PJT-II Jatiluhur rainfall data acquisition 2004 to 2006. 4.1.1.
Existing Land Use
The exiting land use map is obtained by interpreting Landsat-7 ETM+ image in October 2006. The land use map consists of paddy field, industrial area,
residential area, fish pond, vegetation cover, unirrigated land and water body. Table 5 shows Karawang district where 22 of the total area is paddy field area
and 1.8 industrial area. Because in October 2006 usually start of the rainy season, but there was no rainfall observed. Based on data form BPS Karawang
total area paddy field at 2006 is 82,285 ha. So existing paddy field detected is low and partly detected is unirrigated land. Data used is Landsat-7 ETM+ after mosaic
process. Table 5. The existing land use of Karawang district
No Land Use
Area ha Area
1 Paddy Field 42,424
22 2 Industry
3,476 2
3 Residential 10,282
5 4 Fish Pond
14,777 8
5 Vegetation 51,889
27 6 Unirrigated Land
69,891 36
7 Water 357
Total 193,097
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4.1.2. Albedo
The albedo of an object is the extent to which it reflects light, defined as ratio of reflected to incident electromagnetic radiation. Its value depends on the
frequency of radiation unqualified, it usually refers to same appropriate average across the spectrum of visible light. In general, the albedo depends on the
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