Impact of Pointing Aberration in Geolocation of Mercury Laser Altimeter (MLA) Time of Flight Measurements

Kurzfassung

Laser altimeters (LAs) have been extensively used in a wide range of planetary research [1,2,3,4,5]. Besides the peculiarities of the measurement process of an altimeter, the data reduction can be also rather involving, in particular, when relativistic effects are taken into account. This paper discusses the geoprocessing step, which converts the time of flight (ToF) measurements, when supplied with trajectory and pointing information as well as appropriate planet rotation models, to geodetic coordinates of the footprints. We first propose four progressively refined geolocation models and then apply them to available laser altimeter data frm space missions to investigate the effects of different approximations. These data include Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) Precision Experiment Data Records (PEDR)(where instrument was nadir pointed from a circular orbit) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Mercury Laser Altimeter (MLA) Reduced Data Records (RDR) MESSMLA2001 (with measurements characterized by large off-nadir pointing from an eccentric orbit). We demonstrate that for a spacecraft on a highly eccentric orbit the effect of pointing aberration, caused by the relative velocity of the spacecraft with respect to the observer, can lead to significant lateral and radial shifts of the footprint position.