Remote sensing methods in soil erosion assessment in the MÃ¡tra ...

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,/ ,.° -- ,...0 /", (l - ro- Eger oN°-J ( J-- , \.) Debrcccn ... "> BudQpe~t o j tO i \ ( i o-° / '-1- . ,;' ~ ' " '\ szeg '-- pecs ..-' '\. o ,J -', °-. ../ Figure 1 The situation of the catchment area in Hungary 90
The basic ecological conditions are not modified by the changes in ownership and th erefore a catchment area (Fig. 1) was chosen as the test site unit. Considering this fact, the USLE formula was applied to the catchment area. The main aim of the study was to locate those areas which are endangered by soil erosion independently of the borders of land parcels and to find areas in which the dynamic equilibrium is upset. METHODS In the investigation the unitied soil loss equation (USLE - Wischmeier, W. H. -Smith, D.D. 1978) was used. The USLE is an erosion model, which assesses the soilloss for a given site as the product of six major factors, whose most likely values at a particul ar location can be expressed numericaIly. The soilloss per unit area is (A): A=R*K*Ls*C*P where R - the rainfall and runoff factor (most important part is the rainfall erosioff index), K - the soil erodibility factor, Ls - slope length and steepness factor, C - surf ace covering and management factor, P - support practice factor. The two complicated factors K and C were controlled with the help of remote sensing methods. The K factor was simultaneously experimentally measured in the tieId using a tield-plot rainfall simulator. The K factor depends mainlyon soil type and texture, which allows the use of remote sensing methods. There are a lot of formulae to express the NDVI or the biomass value of a surface by measuring the vegetation cover characteristics and from these, the regional differences of the C factor can be assessed. The C value was also calculated from the suggested tables in Wischmeier and Smith (1978). AlI bands of the Landsat TM image recorded on 7 July, 1987 were used because the rainfall intensity (EI) and the predicted soil erosion give the highest rate in this early summer period. The LS values were measured using tieId methods. The maps were digitized in AutoCAD and the results were transferred to IDRlSI v. 4.0 (Eastman, J.R. 1992). In IDRISI the vector database was con verted into a raster database, and stored in GIS. The rasterized database was then used to compare tieid measurement data with the remotely sensed data. The best composite of different TM bands which substitute the slow process of the experimental tieid measurement data can then be distinguished . RES UL TS Some factors in the USLE formula can be easily calculated or, owing to the insigniticant differences, the factor value can be constant. For example, the P factor is equal to 1 for the entire catchment area because there was no special soil conservation management. Other factors, such as L and S, were measured at the test site: the value of steepness of land slope ranges from 10 to 12 %, while the length of land slope ranges from 300 to 500 m. The LS vaIues therefore, are more than 3 and less than 5. It may also be deduced that the steepness of the land slope is greater in the western part of the catchment than on the cultivated eastern part. 91
Page 1: ACTA Geographica Szegediensis Tomus
Page 5 and 6: a.. /1/ r A 3 A- Figure 3 7,4,2 (RG
Page 7 and 8: the catchment are similar). The NDV
Page 9 and 10: According to the histogram of pixel

Remote sensing methods in soil erosion assessment in the MÃ¡tra ...

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