Sunshine around the middle Earth: relief inversion less prevalent in satellite images in the near-south of the Equator than on the Equator

ABSTRACTInverted depth perception in satellite images is a well-known phenomenon. It has been previously verified that the illusion is prevalent in Northern Hemisphere (NH) images, while it is observed in Southern Hemisphere (SH) images to a much smaller extent. However, the equatorial zone has not been examined despite its interesting geometric position in relation to the Sun and satellite orbits. We present a user study (n = 313) in which participants were asked to identify landforms on 16 satellite images from the equatorial region. Our main findings are: (a) surprisingly, on the equatorial line and roughly ±1° of it in either direction, the results are consistent with the NH images; (b) instead, the expected variation/ambiguity occurs with the images 2–5° south of the Equator. These outcomes imply that based on illumination alone, the ‘middle’ (i.e. the Equator) might be somewhat more south from the perspective of the studied illusion. The observed effect surpasses various individual and group differences such as biological sex, expertise and education levels. Landcover cues such as snow, vegetation etc. do not appear to moderate the observed effect either. Our observations contribute towards a better understanding of the causes and prevalence of the relief inversion illusion.