USE OF REMOTE SENSING AND GEOGRAPHIC INFORMATION SYSTEMS
FOR AQUACULTURE SITING STUDIES
presented at the
National Coordinators Meeting
FAO/UNDP Regional Seafarming Development
and Demonstration Project
Network of Aquaculture Centers in Asia
c/o National Inland Fisheries Institute
Kasetsart University Campus
Bangkhen, Bangkok 10900, Thailand
27th October 1987
by Dr. J.E. Lukens, Coordinator
Interdisciplinary Natural Resources Development and Management
(INRDM) Program
Asian Institute of Technology
G.P.O. Box 2754
Bangkok 10501, Thailand
USE OF REMOTE SENSING AND GEOGRAPHIC INFORMATION SYSTEMS
FOR AQUACULTURE SITING STUDIES
Outline
I. Introduction to Remote Sensing and Geographic Information Systems (GIS)
Definitions
A. Remote Sensing: Any non-contact method used to infer conditions near or at the earth's surface. Includes aerial photography, aerial magnetometry, and satellite imagery. The original data is usually simplified and presented as maps.
B. G.I.S. : A method for storing spatial information, usually maps and statistics related to a defined geographic area. This stored information is called a “data base”. The data base is highly organized and thus may be easily used to create models of the landscape. The models, in turn, offer a logical and rational device for helping planners predict outcomes of events occurring on the landscape.
In order to make the process of modelling as effective as possible, the data base usually consists of a series of “thematic” maps (such as geology or land use) having a common level of detail and spatial accuracy. This is usually achieved by referencing each thematic map to a “base map” of known accuracy (such as a topographic map).
Scope of GIS
GIS have been used for centuries; only the term GIS” is new. Formerly “visual” or “manual” methods were employed; as projects became more complex, and as the quantity of data increased, computer-assisted methods were used. Now that computers are becoming cheaper and more reliable, they are displacing manual methods even for simple tasks.
GIS Components
Every GIS consists of: 1.) a data base; 2.) a data base management system; and 3.) a landscape modelling system. The model is created when the relationships among the elements of the data base are defined. If new elements are added to the model (such as a proposed shrimp pond), the effects of the existing elements of the landscape upon the new element and the effects of the new element on the existing elements can then be predicted.
GIS Operations
A GIS uses the data base manager to find the maps and statistical data necessary to help a planner design a project. The process is:
INPUT → MANIPULATION → OUTPUT
The input may simply be one of the thematic maps from the data base. The output may simply be the same thematic map, or perhaps the map scale may be changed.
In more complex cases, the input may be a number of the thematic maps and statistics from the data base, plus all of the additional information necessary to create a special-purpose model of the landscape (such as locating the most suitable sites for a certain type of aquaculture operation). This information is then manipulated (synthesized) to produce the output (such as shrimp pond site suitability maps, given various assumptions about local aquaculture practices).
II. GIS Procedures
Manual
These methods generally use transparent thematic overlays to a base map, often a transparent base map on a light table. (Popularized by Ian L. McHarg in “Design with Nature”, Doubleday & Co., Garden City, New York, 1971, paperback.) Other techniques involve numerical methods, such as the FAO land classification system.
Computer-Assisted
These methods store the maps and statistical information in a digital data base, using either a “polygon” or a “grid cell” format to store, manipulate, and display or output the information. (These techniques are explained well by Kapetsky et al in “A Geographical Information System to Plan for Aquaculture”, FAO Fisheries Technical pap[er No. 287, Rome, 1987.) The grid cell techniques are becoming more widely used because of the ease with which the data are manipulated.
GIS today are available which run on main frame computers, mini-computers, and micro-computers. Of the latter, there are three levels of sophistication:
Simple grid cell programs which run on unaugmented IBM PC's (or compatibles). These systems provide baisc “overlay” operations, plus rapid “proximity” or “connectivity” operations;
Grid cell and/or polygon programs which run on IBM-PC's (or compatibles) with high-resolution color monitors and advanced graphic cards. These systems add the ability to work with linear and point data (i.e., points do not get lost within large grid cells); and
Grid cell and/or polygon programs which run on highly modified IBM PC's (or compatibles), using special processors and high-resolution display devices. These systems add special operations, such as the display of a thematic surface as a three-dimensional perspective view.
Peripherals for all of the PC-based systems should include a map digitizing tablet and a color printer. Projects with large amounts of data will require hard disks for additional data storage.
Many of these systems will directly accept digital maps created from remote sensing data, and some of the systems will also permit the use of GIS information to assist with the digital analysis of image data.
