Estimation of Annual Total Nitrogen Load to lake from Basin with Remote Sensing
2.3 Land Cover Classification with LANDSAT MSS
LANDSAT MSS data from 1979, 1984 and 1990 were analyzed to produce a land cover distribution map in the Lake Kasumigaura basin and to evaluate land cover changes. Usually maximum likelihood method is utilized for classifying land cover, the method is not accurate enough to extract land cover changes if we don't have a good ground truth data for each year. In this study, the following procedure were used [Oki, et.al., 1996].
(1) Data compression:
Combined MSS data from 1979 and 1984 (or 1990) was compressed by the principal component analysis (PCA), and then the first to n-th PCA components were extracted which gives more than 9 % of cumulative variance.
(2) Unsupervised classification:
The basin areas were classified into more than twenty classes with the unsupervised classification scheme by ISODATA method from the compressed MSS data (n components).
(3) Production of land cover distribution map:
The classification results with unsupervised classification were re-merged into five predetermined categories include urban area, paddy field, forest area, water area and field which seem to give main impact for nitrogen load. Land cover distribution in 1979, we determined categories based on database provided by Ibaraki Prefecture in 1980. furthermore, in order to produce land cover distribution in 1984 or 1990, we considered land cover change in the basin and determined categories based on database investigated by field work. Figure 3 shows the classification result at the Lake Kasumigaura basin. Extent of each land cover category and the ratio of mixing categories in each river basin were estimated (fig.2 and 3).
Fig.3 Classification of land cover at the Lake Kasumigaura basin
3. Estimation of Influent Annual Total Nitrogen Load
3.1 Data
In order to evaluate basic units of total nitrogen load from five land cover categories in the lake basin and influent annual total nitrogen load to the Lake, following data sets were collected in individual river basins were ten dominant river were selected.
(1) Annual mean total nitrogen concentration, N[mg/l]:
The annual mean total nitrogen concentration were calculated based on the data base provided by Ibaraki Prefecture. The each total nitrogen concentration in individual river basins were measured at the circle shown in Fig. 1.
(2) Annual precipitation, P[mm]:
The annual precipitation was estimated from meteorological report.
(3) Annual river discharge, Q[m3]:
The annual river discharge for each river was estimated from annual precipitation and run-off ratio of each river basin.
(4) Influent annual total nitrogen load to the lake, L[Kg/y]:
The influent annual total nitrogen load L was calculated as
L = N * 10
-3 X Q
(5) Lake basin area, A[Km2], land cover area of each category, A'[Km2], land
cover ratio of each category, r:
These data were calculated from land cover distribution map obtained in Chapter 2.
