Estimation of water quality using GIS data and Landsat TM data
Data and study area
Tokyo Bay as the study area serves as an entrances to the sea-borne traffic bound for Cosmopolitan Tokyo with direct bearings on the daily life of citizens. The bay itself is enclosed (surrounded by metropolitan Tokyo, Kanagawa and Chiba Prefectures), deep inside, and very narrow at its mouth restricting a free influx of outside sea water while allowing large volumes of pollutants into the bay via rivers, which in turn add to biological productivity to cause what is commonly known as "red water" a phenomenon caused by masses of dead planktons and observed every year.
The water quality of the bay, therefore, is characteristically subject to tidal currents and river waters and reflect the different aquatic environments along the coast sea and the inside sea. The characteristic was further examined in the present study by using Landsat TM data and the aquatic environment database built on ARC/INFO.
- TM data
The data were selected for study in such a manner that they were of the same dates as those of water quality data and from periods when atmospheric conditions ere relatively stable. The selected data were as follows.
Path-row : 107-035 and 107-036
Dates : 1) August 6, 1986
2) March 2, 1987
Correction : Status corrected
- Water quality data
The water quality of Tokyo bay has been monitored regularly at the 51 survey stations located in the surrounding Tokyo, Kanagwa and Chiba for the past five years. Based on these data as input, chronological and spatial analyses were made with respect to the study area.
Figure 1. Location map of survey stations
1 ~ 51 : Survey stations
Methodology
The study flow is schematically shown in Figure 2
- Preprocessing
Since the study area was covered by two scenes of TM data as purchased, mosaicking was performed in the lien direction, followed by geometric correction to make TM data properly correspond to water quality data on the 1/50,000 topographic map.
- Data input
Water quality data were input in a computer in a uniform format for chronological and spatial analyses that followed. The bathymetric map as digitized in polygons for input.
- Inner correlation
Inner correlation were computer to examine the distinctions between the bands of TM data and between the water quality survey items. Based on the computation results, the bands with lower values of correlation were applied for the analysis.
- Analysis of water quality
- Chronological analysis :
As Seasonal changes in the aquatic environment by developing graphs for such changes.
- Spatial analysis :
To identify the spatial characteristics of the study area, cluster classification was applied to the typical water quality data for summertime in an attempt to classify water masses. A similar attempt was made for the August 6, 1986 data.
