Determination of Mars Clouds’ Altitude on Amateur Images and Implication on New Types of Clouds

Amateur astronomers image clouds on Mars surface regularly. While clouds on illuminated surface are usually well known, transient ones appearing on the night side at dawn or dusk, or above the limb, are of special interest and have been studied lately in [1] and [2]. Determining their altitude is a key element for studying their characteristics, but unfortunately cannot be derived simply on a 2D image. We describe here two methods used to estimate altitudes of such features, and scientific studies using those estimations.MethodWhat can be measured on observations are (see figure 1): * the “apparent (i.e., projected) terminator altitude” of a feature above the terminator when it is on the night side (whether below or above the limb) * the “apparent limb altitude” of a feature above the limb * the apparent latitude and longitude of the feature when it is visible on the surface of the planet.