High Resolution Digital Elevation Models of Mars from Moc Narrow Angle

Introduction: In this abstract we report on our initial experiences performing stereotopographic mapping of Mars with high-resolution images from the Mars Global Surveyor Mars Orbiter Camera Narrow-Angle subsystem (MGS MOC-NA; [1]). Accurate topog-raphic information, and, in particular, high-resolution digital elevation models (DEMs) are of intense interest at all phases of Mars exploration and scientific investigation , from landing site selection to the quantitative analysis of the morphologic record of surface processes. Unfortunately, the availability of extremely high resolution topographic data has hitherto been limited. The current "gold standard" for martian topog-raphic data, the Mars Orbiter Laser Altimeter (MOLA; [2]) has collected data globally with astonishingly high accuracy, but the resolution of this dataset is only about 300 m along track and, in many places near the equator, adjacent MOLA ground tracks are separated by gaps of one to several kilometers. Viking Orbiter images provide stereo coverage of the entire planet at low resolution and expected vertical precision (EP, a function of image resolution and stereo viewing geometry) but highest resolution stereo coverage only of limited areas [3]. Given that the minimum separation of independent stereo measurements is about 3 pixels because of the necessity of matching finite-sized image patches, the highest resolution Viking images, at about 8 m/pixel, support stereomapping only at horizontal resolutions >24 m. Photoclinometry, or shape-from-shading [4] can be used to produce DEMs at the pixel resolution from single images but the results depend on the accuracy of atmospheric and surface radiative transfer models [5]. Calibration of photoclinometry against MOLA data [6,7] promises to reduce uncertainties about the inferred scale of relief, but albedo variations can still lead to artifacts in the resulting DEMs. The MOC-NA camera, with a maximum resolution of 1.5 m/pixel [1], offers the prospect of stereotopog-raphic mapping at a horizontal resolution of ~5 m and EP ~ 1 m. MOC-NA stereo coverage is limited because most images are obtained with nadir pointing and are not targeted to overlap one another, but at least tens of MOC-MOC stereopairs do exist and further stereo imaging of Mars Exploration Rover (MER) candidate landing sites is an objective of the MGS extended mission. It is also likely that some MOC images will provide useful stereo coverage when paired with oblique Viking Orbiter images. A capability for stereomapping with the MOC-NA images is therefore