Monitoring of shoreline change by using satellite images in Cuulong river estuaries
Methodology
Shoreline in this study is understood as a mean high water line. For coast, where is there a mangrove a outward boundary is considered to be a shore line.
Because of different spectral characteristics of water, land and vegetation we can discern very well water from other objects in infrared band. Hence for this study we used mainly LANDSAT band? and SPOT band 2. Naturally the rest bands also give a lot of use full information.
Because satellite sensors are not in the same geometric construction and photographic products contain much distorsion, geometric processing is very important in drafting shoreline from images into map. We have attempted to use both graphic and digital methods for transfering of interpreted shoreline from image prints into maps. Both methods are described in detail as following.
- Graphic method
Used graphic method is so called a local transformation one. Sufficient numbers of topographic control features were selected on both maps and prints. Control points have to be distincly observed on both prints and maps and they have been chosen like crossing of transportation network. Crossing of canal network atd. By this way system of control points new shore lines were transferred from prints into maps part by part on ZOOMTRANSFERSCOP. These land water boundaries of maps and prints will contain the erosion and accretion area of the change detection maps.
- Digital method
In order to applicant this method it is necessary to have a pc computer with the following configuration.
Fig. 1. PC - computer configuration used
for digital method
There are so many ways to executive it but following approach is applied jointly with the AutoCAD programme package. Whole transformation is divided into four steps.
- step - Control point four steps
Do the same as described in the graphic method
- step - Shoreline digitalization by digitizer
- step - Digital processing
This step is done by three separate programmes: FDXFOUT, TRANSF and FDXFIN. First thing to be done is convertion from AutoCAD file. DWG by command DXFOUT to file. DXF and by FDXFOUT programme coordinates x, y, are extracted and stored in appropriate files ready for transformation. The chosen transformation is based on planne affine one and it is programmed in FORTRAN 77. This programme can process unlimited number of coordinates. Listing of programme can TRANSF is given in Appendix 1. After transformation all corrected coordinates are stored back into AutoCAD file. DWG by FDXFIN programme and DXFIN command.
- Step - Ploting
Corrected shoreline can be regenerated on screen and plotted on plotter by using utilities of AutoCAD.
Advantages of the above described methodology are that all powerfull graphic abilities of AutoCAD can be used either during digitizaing or in editting and plotting. Further more all results are stored and they can be replotted or edited comfortably at any time.
