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

Abstract

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.

Keywords

• terrain reversal effect
• satellite images
• correction methods
• shaded relief map
• stereoscopy
• motion