Evaluation of Different Topographic Parameters Extracted from the Digital Elevation Measurements with the Use of Geostatistical Interpolation Methods

Gradient slope, aspect slope, profiling and contourlines are important topographic parameters that can be derived from digital elevation data obtained from different sources with exploitation of different interpolation techniques. Geostatistical interpolation methods such as ordinary kriging models constitute reliable alternatives to deterministic approaches in creation of continuous surface models from discrete elevation data. This research aimed at extraction, analysis, and evaluation of different terrain parameters elevation measurements with the use of different ordinary kriging models including the linear model, the circular model, the spherical model, the exponential models, and the Gaussian model. Different ordinary kriging models under ESRI ArcView 3.3 package along with its 3D analyst and Spatial analysis extensions have been exploited in extraction of gradient slope maps, aspect slope maps, and hillshade maps in addition to contourline maps from a sample of elevation data. Visual analysis of the gradient slope maps shows great similarities between the slope maps from the linear, circular, spherical, and exponential OK models, however, that from OK Gaussian models look very different as different sizes and arrangements of the colour patches, referring to different tones and different textures where smooth tones and smooth textures dominate the gradient slope map from the OK Gaussian model. Thus, gradient slope degradation and smoothing are considerably high in the gradient slope map from Gaussian model compared to the slope maps from the other four OK models. Also, the mean slope in the Gaussian model records the lowest value with the lowest value of the standard deviation of slopes in the same map reflecting less structured and highly smoothed gradient slope map compared to the slope maps from the other OK models. Thus, similar sizes of the colour patches and similar tones and similar texture dominate the different aspect slope maps. This is not the case in Figure 2(e) which depicts the aspect slope map extracted with the use of the Gaussian OK model where the smooth colour patches, smooth tones and smooth textures can be observed. Also, the Aspect map, hillshade map and the contourline map from Gaussian OK model are visually and statistically different from their corresponding maps created with the other four OK models. Finally, analysis of extracted two groups of profiles shows that the profiles extracted with the use of linear, circular, spherical, and exponential OK models run close and show highly corrugated and varied terrain. This is different from the profiles with the use of the Gaussian model which are less corrugated and tend to smooth and approximate different parts of the terrains.

Mapping of Planation Surfaces in the Southwest Region of Hubei Province,China——Using the DEM-Derived Painted Relief Model

Planation surfaces （PS） play a major role in reconstruction of the evolutionary history of landforms in local areas. Thus, objective and consistent mapping of planation surfaces from remotely sensed data （e.g., satellite imagery, digital elevation models （DEMs）） is paramount for interpreting the geomorphological evolution. Due to the lack of dated sedimentary covers and the difficulties of com-prehensive field work, the number and age of planation surfaces in the Southwest Hubei （湖北） Prov-ince of China are still controversial. In order to map the PS in the study area, four data visualization techniques including ETM＋ false color composite, grey-scale DEM, shaded relief model （SRM） and painted relief model （P M） were examined. It is found that the PRM is the most optimal technique for planation surface mapping. The study area was successfully mapped by visual interpretation of a PRM derived from ASTER GDEM. The mapped PS was divided into five classes in terms of elevation ac-cording to previous studies, varying from 1 700-2 000 （PS1）, 1 300-1 500 （PS2）, 1 000-1 200 （PS3）, 800-900 （PS4） to 500-600 （PS5） m. The results were partially compared with the published works. It is revealed that this method of mapping enjoys a higher accuracy and can reduce the time and ef- fort required in the traditional mapping to a large extent. The results also demonstrated that the PRM is an effective tool for geomorphological fea-ture mapping with considerable accuracy. The pre- liminary results can serve to facilitate locating rep-resentative samples for the planation surfaces dating, thus to determine the ages of PS in the study areas.

Fixing an illusion–an empirical assessment of correction methods for the terrain reversal effect in satellite images

Identifying land forms and land cover classes are important tasks in image interpretation.Sometimes,a phenomenon called terrain reversal effect(TRE)causes an inverted perception of 3D forms.When this inversion occurs,valleys appear as ridges and vice versa.While the TRE can severely impair the ability to identify 3D land forms,‘correcting’for the TRE in imagery can introduce new problems.Importantly,one of most commonly-proposed methods–shaded relief map(SRM)overlay–appears to impair the ability to identify land cover classes.In this paper,we report a comparative empirical evaluation of an SRM overlay solution,and its‘enhanced’versions supported by various other cues(stereopsis,motion,labels).In response to the different solutions,we measure the effectiveness,efficiency,confidence and preferences of our participants in land form and land cover identification tasks.All examined methods significantly improve the ability to detect land forms accurately,but they also impair the ability to identify the land cover classes to different degrees.Additionally,participants’visualization preferences contradict their performance with them,calling for reflection on the visual effects of the applied correction methods.Based on the study,recommendations concerning the correction of the TRE are drawn,and gaps are identified.