The method of geoinformation-mapping morfokomplexes on a basis of the morphometric parameters and supervised classifications (for example, the typical areas of south-western Siberia)
Chupina D.A.
V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia
dasha.chupina@gmail.com
The science of the Earth has received a new source of information and powerful tools for their research with the advent of geographic information systems (GIS) and digital elevation models (DEM). GIS technology is actively used in the geomorphology for zoning of the territory, mapping forms and types of terrain. The practical aspect of GIS introduce in geomorphological mapping is to develop the standard procedures that would enable to replicate it for the solution of industrial problems, particularly for geological and landscape mapping.
GIS technology has decided to the technical difficulties of morphometric studies. So it has given the impetus to the development of modern explanatory morphometry of the relief, which is focused on a disclosure of quantitative characteristics of the relief and its origin. It seems timely, development of techniques that would allow recognize the genetic types of the terrain with morphometric indices. The methodology promising in this aspect are implemented in the digital image processing systems. It repeatedly tested for the mapping and the monitoring of landscapes, natural-territorial complexes, geological objects and other. The author offers the technology of mapping morfocomplexes on a basis of using the supervised classifications for the key morphometric characteristics (for example, the terrain of Chuy valley).
The different sources can be used as a basis for the construction of DEM. However, the using of the sharing DEM are significantly reduced the difficulty of research. In our case, the digital elevation model SRTM was taken on with the resolution of 90x60 meters, and reduced to the size of pixels 90x90 m. Some of shapes of the Earth's surface can totally get into the pixel of this size, and some of them only partially. Morphometric parameters are calculated with the method of the sliding window. The size of the sliding window is chosen so that it got the basic forms of the earth's surface. So it is possible to obtain a grid-mean morphometric parameters that reflect the most common types of the relief. The window's size was chosen from the series of experiments and amounted to 1260 m (the diameter of the window is 14 pixels).
The modern morphological structure in the mountains were formed not only as a result of a variety of exogenous processes. The latest movements of tectonic blocks have had a great influence too. It is necessary to consider the mapping the genetic types of relief. This has reflected in the values of absolute morphometric parameters - heights, aspects and slopes. If the relief was formed under the influence of neotectonic movements, at the beginning it is necessary to zone it. Further studies are mainly based on relative morphometric parameters. It is representing the difference of maximum and minimum values of variable (range), calculated within a sliding window. In our case, the 8 most common indicators are used to highlight the morfocomplexes. These are the mean values of slope, the mean values of heights, the mean values of submeridian aspects, the mean values of sublatitudinal aspect, range of slope, range of heights (vertical dissection), range of values sublongitudinal aspects, range of values sublatitudinal aspect. It has directly calculated from DEM with the ArcMap software package.
The analysis of each morphometric parameters has found out similar for some of these genetic types of a relief to each other and join together in groups. Also analysis have detected the parameters which help to separate the genetic types of a relief with greater or lesser degree of reliability. The branching scheme of dichotomous splitting of a relief to separate types and their groups is thus built. The most efficient morphometric parameters, or combinations thereof are selected for each point of the branching. The morphometric parameters selected are normalized to maximum and converted into the TIF format. The images are then loaded in the form of channels in ENVI software package for further classification with the training on the reference sites. According to the dichotomous scheme the general classification of all morfocomplexes is not used at once, it is used branched series of classifications.
The recognition of terrain types is carried out for each neotectonic segment. At first, the segment is divided to the dissected and flat areas. Further, the masks are constructed on base of allocated sites. It's the area where classification will be applied. It is improve the accuracy of classifications. Space of recognition and amount allocated classes of relief are reduced at each step.
The proposed approach has some limitations. On the one hand, not all the genetic types of relief detected in the field conditions can be recognized on only the morphometric features. On the other hand, some morfocomplexes can be statistically stay apart by the morphometric parameters, if they were not considered significant for some reason in another feature space. The possibility of the separation and detection morfocomplexes largely controlled by the spatial resolution of DEM. It not always is possible to identify the genetic type of the relief, consisting of the small forms or having a limited areal distribution.
The proposed method is automatically enabled the mapping of morfocomplexes of Chu steppes, which isn't inconsistent with the geomorphological precursors studies [3]. The summary diagram of morphological complexes as a result of consecutive series of classifications are shown in the picture.
Fig. Symbols: 1 — glacial trough-ridge, 2 — talus-proluvial, 3- erosion gully-ravine, 4 — limnetic at the aleurite -sand base, 5 — limnetic with a bars, 6 — limnetic at the moraine base, 7 — alluvial of the Chu river valley, 8 — thermokarst, 9 — alluvial of incised valleys, 10 — alluvial of tributaries.
This studies has shown advisability of aggregation methods of processing raster images (ENVI) and grids modeling (ArcGis) to mapping morfokomplexes. The using of relative morphometric parameters allowed to move out from the mapping of landforms and their elements to the mapping of types of relief, which are the natural combination of typical geomorphological sites. And finally, the using of supervised classifications does propose the technology easily accessible and replicated. The proven technology is promising for the medium-scale geomorphological map construction at the landscape and geological mapping
References:
Simonov JG. Explanatory morphometry of relief. - Moscow: GEOS, 1999. - 263 p.
Zolnikov ID, Lyamina VA, Glushkov, NV.The basics of using GIS and RS technology for solving typical problems of Geology and Geoecology: Textbooks / Novsib. State. University v.2. Novosibirsk, 2011, 94 p.
Zolnikov ID, EV Deev, VA Lyamina. New data on Quaternary morpholithogenesis in the Chuya basin (Gorny Altai)// Geology and Geophysics, 2010, V.51, № 4. P. 437-449.