The ultimate vertical accuracy assessment of the third generation Turkish 1:25000 quad maps; under canopy vs. no canopy

Abstract

Elevation, vertical accuracy of any topographic Earth representation, e. g. stereo surface models, topo maps, DEMs, etc., is important if such data will be the base of further projects or development plans. The main form of these types of data in Türkiye is “1:25000” scaled quad maps. The third generation such maps were produced via digital stereo air-photo capture and photogrammetry capabilities as opposed to the previous two analogue based releases. Through this long-adapted scale, land cover types, hydrological formations, surface features, down to house rooftops, can be depicted in these maps. Elevation integration are also provided through the contour lines drawn in 10 m elevation difference showing intervals. They are the most frequently addressed topographic data type in forestry education as well as in profession. With the establishment of county-wide active GNSS network, very high precision elevation verification has become available for multitude of purposes. In this study, four dam reservoirs intensively surveyed using CORS-GPS were used to assess the vertical accuracies of the corresponding quad-map based DEMs produced in different resolutions. RMSEs ranged from 5.49 m to 14.22 m when the entire quad sheets were used while they ranged from 2.58 m to 8.95 m when the quads were purposely cut. Canopy closure apparently worsened the results.