On refinement of Water Resources Mapping and development of Flood Forecast Method, using Remote Sensing and Ground Data
II. Data and Methodology
For water resources assessment were used the remote sensing data in conjunction with the ground observation data of the Hydro meteorological Stations and available information, published reports and field survey data [5,9]. For the water resources mapping the various Remote Sensing Data were used to obtain direct and indirect characteristics on water resources and hydrologic regime for refining the previously compiled maps and field survey data. In other words they were used for obtaining the qualitative assessments.
Multiband images at scale of 1:250,000 to 1:1000,000 in visible and near infrared regions, obtained from the spaceraft “Soyuz”, the space laboratory “Salyut” and Meteorological Satellite “Meteor” were used for water Resources Thematic Mapping. The above image data were used as a photo base map and drainage pattern, structure, density and drainage boundaries in the run-off dispersion area, lake shorelines and locations of the present glaciers and snow pack were defined and refined on this photo base. As well as, run-off dispersion area, specific area for the ground water formation, boundaries of the Artesian Basins, ground water recharge and discharge areas were determined on the images. As is known, the water bodies are identified by their definite tone contrast with the surrounding objects on bands of 0.8 – 1.1 mm images where they appear relatively darker. Due to impossibility of the ground water availability to be identified directly on the space-acquired inmates, we used a Landscape Type Scheme developed by appropriate geo-morphological elements in relation with the different litho logy, hydro geological formations and processes.
Thus crystalline base origination and structure of a large area in band of 0.6 – 0.7 mm, tectonic cracks and line structures in band of 0.8 -1.1 mm and Quaternary Alluvial deposit in band of 0.5 – 0.6 mm were clearly delineated. In determination of the large Artesian Basins and Hydrogeological formations were used regional space images with 300-1000 m spatial and spectral resolutions at nadir. The interpretation of the images was resolutions at nadir. The interpretation of the images was resolutions at nadir. The interpretation of the images was carried out visually according to the established indicators or clues; shapes, pattern, tones, texture and structure of the clues; shapes, pattern, tones, texture and structure of the natural objects [5,6]. The Remote Sensing Data was selected,
widely depending on the natural objects to be identified and also physiographic, climate condition and season when the images were acquired.
For the study of Khovd River snow-melt run-off were used METEOR TV images with resolution of 0,2 – 1.2 km in the period of April and May, 1972-1982 and data on air temperature and precipitation of the Meteorological Stations as Yalalt (2148m), Uigil (171 om), and Knovd (1405m) located in the catechment and conventional river discharge data of the Hydrological Stations for the same period of 1972 – 1982. In addition, Hypsographic Curve of the catchment and Pyhsiographic and Landscape Maps of the study region were used as well.
The Khovd River catchement is situated in the Western Part of Mongolia and is related to a river type with spring – summer snow-melt floods and 60% of its annual run-off constitute snow-melt run-off [Fig.2]. The catchemtn area is 59,932 sq. km. The spring floods of the Khovd River usually begin in early April reaching their peaks in June-July and end up in late August.
Figure 2. Drainage network scheme of the Khovd River Basin
The established in the result of the study W = f (P,%) relationship was analysed by the ground records on precipitation, air temperature, river run-off and snow cover condition at the Hydro meteorological Stations located in the Khovd River catchment.
In selecting images consideration should be given to cloud condition, sun elevation and coverage of the catchments area at nadir. So the frequencies of the could free days in the Altai Mountain Region estimated by the Satellite Data during the period from April to May were 42 – 52 percent. The Satellite TV Image in visible band of 0.5 – 0.6mm and near infrared band of 0.7 – 1.1 mm were particularly suited to investigation and analysis of the snow-melt dynamics. The geographical fastening to the Topographic Base Map performed by the relief features e.g., mountain ranges, depressions, lakes and drainage network, which were easily and mapping of the snow cover were carried out visually on the basis of the specially developed interpretation indicators [5,6]. Because of impossibility of detecting absolute values of he spectral reflectance characteristics of the ground objects on the images by visual interpretation we used the relative interpretation indicators such as photo tone, texture, structure and image specifics [Fig. 4]. Measurement of the snow-covered area was made by using the ordinary methods i.e. plainer or special pattern (grid).
Figure 4. Scheme of snow covered area in Khovd River catchment, METEOR - 28 Satellite image aquired on 26 April, 1978
