Co-registration of laser altimeter tracks with digital terrain models and applications in planetary science

Abstract

We have derived algorithms and techniques to precisely co-register laser altimeter profiles with gridded Digital Terrain Models (DTMs), typically derived from stereo images. The algorithm consists of an initial grid search followed by a least-squares matching and yields the translation parameters at sub-pixel level needed to align the DTM and the laser profiles in 3D space. This software tool was primarily developed and tested for co-registration of laser profiles from the Lunar Orbiter Laser Altimeter (LOLA) with DTMs derived from the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) stereo images. Data sets can be co-registered with positional accuracy between 0.13 m and several meters depending on the pixel resolution and amount of laser shots, where rough surfaces typically result in more accurate co-registrations. Residual heights of the data sets are as small as 0.18 m. The software can be used to identify instrument misalignment, orbit errors, pointing jitter, or problems associated with reference frames being used. Also, assessments of DTM effective resolutions can be obtained. From the correct position between the two data sets, comparisons of surface morphology and roughness can be made at laser footprint-or DTM pixel-level. The precise co-registration allows us to carry out joint analysis of the data sets and ultimately to derive merged high-quality data products. Examples of matching other planetary data sets, like LOLA with LRO Wide Angle Camera (WAC) DTMs or Mars Orbiter Laser Altimeter (MOLA) with stereo models from the High Resolution Stereo Camera (HRSC) as well as Mercury Laser Altimeter (MLA) with Mercury Dual Imaging System (MDIS) are shown to demonstrate the broad science applications of the software tool.

A New Realization of the Global Lunar Reference Frame Based on Co-Registered Lola Tracks

“…For our study we created two polar DTMs of ten meter per pixel resolution and with an extent of 200 by 200 km centered on the poles using co-registration techniques (Gläser et al, 2013). Each DTM was then co-registered with the common 4,116 LOLA tracks and the resulting offset was applied to ensure global alignment between them (Figures 1, 2).…”

“…However, at this high resolution, the remaining orbit errors and consequently errors in the relative positional accuracy of ground points become relevant. To overcome these errors, we previously presented a co-registration technique (Gläser et al, 2013) which greatly improved the relative accuracy. The purpose of co-registering LOLA tracks in our previous work was to derive polar DTMs of high relative consistency for illumination studies (Gläser et al, 2014.…”

“…The algorithm is implemented for General Purpose Computation on Graphics Processing Unit (GPGPU) using OpenCL (Gaster et al, 2011) which runs the grid search in parallel on the GPU. The benefit of this approach in comparison to the one shown in (Gläser et al, 2013) is that we now determined a set of seven parameters, dx, dy, dz, ω, φ, κ and µ which describes the best (global) fit of a track to both polar DTMs at the same time.…”

Implementation of a Self-Consistent Stereo Processing Chain for 3D Stereo Reconstruction of the Lunar Landing Sites

“…This is followed by a least squares fit of the track with respect to the DTM to obtain sub-pixel accuracy for the fit. More information about the LOLA co-registration can be found in Gläser et al (2013). Results of the fit between DTMs and LOLA tracks are shown in table 2.…”

Extracting accurate and precise topography from LROC narrow angle camera stereo observations

“…These observations are paving the way towards future robotic and crewed missions to the surface ( Chin et al 2007 ). Among the instruments are the Lunar Reconnaissance Orbiter Camera (LROC) and the Lunar Orbiter Laser Gläser et al (2013) enabled a comparison of surface morphology and surface roughness at both the laser footprint and DTM scales by co-registering NAC DTMs and LOLA profiles. The NAC DTMs enable investigations of elevation, slope, volume, roughness, and other parameters to place constraints on complex geologic processes (impact cratering, volcanism, tectonism) over time that have shaped the lunar surface ( Ashley et al 2012;Jolliff et al 2011;Watters et al 2012;Lawrence et al 2013;Braden et al 2014;Stopar et al 2014;Mahanti et al 2014;French et al 2015 ).…”