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The digital elevation model based on SRTM is very convenient for a wide range of studies but requires correction due to the influence of forest vegetation. The present study was conducted to analyse the effect of boreal forests on altitudes, aspects and slopes calculated from the SRTM. A DEM based on topographic maps at 1:100 000 scale was used as a reference. The linear regression analysis showed low data correlation in forested areas. The presence of different types of forests and felling in the woods leads to a complex distribution of deviations from the SRTM. A simple correction method was proposed, using a forest mask, built according to Landsat, and forest heights indicated on the topographic maps. After correction, the correlation coefficient between the altitudes increased by 0.05–0.14, the share of matching aspects by 1–4% and the share of matching slopes by 2–8%.

Urban populations are expanding rapidly and so are cities. Remote sensing offers a convenient means of monitoring this expansion as it covers a period of 40 years in the case of the LANDSAT satellite. In some parts of the globe, this is probably the only viable means of monitoring due to the lack of other types of data. In order to monitor expansion, first, urban land has to be separated from other land-cover types. Although this can be done by standard classification processes, it is much more efficient to establish an urban index UI analogous to the widely used normalized difference vegetation index NDVI for vegetation. Existing efforts to establish such a UI are reviewed and compared in a common context. Following this, a novel, more efficient UI is introduced. The calculation of the new index is straightforward, based on combining the NDVI with the normalized difference built-up index. The results are promising as the index can efficiently segment urban areas, even in the presence of excessive bare land. The proposed method is evaluated on two test sites selected in different LANDSAT scenes. The new index is valid only for sensors with the same bands as those of LANDSAT.