High-resolution Lunar Topography (SLDEM2015)
Michael Kenneth BarkerDownload SLDEM2015:
http://imbrium.mit.edu/DATA/SLDEM2015/
Global maps (for latitudes between 60 deg South and 60 deg North) can be downloaded from the following links:
FLOAT IMG format:
JPEG2000 format:
512, 256, and 128 pixels per degree
Alternatively, if you are interested in just a few specific regions, then you can download the maps split up into tiles at these links:
FLOAT IMG format:
JPEG2000 format:
Acknowledging this work:
If using this dataset, please cite the following paper:
Barker, M. K., Mazarico, E., Neumann, G. A., Zuber, M. T., Haruyama, J., Smith, D. E. "A new lunar digital elevation model from the Lunar Orbiter Laser Altimeter and SELENE Terrain Camera," Icarus, Volume 273, p. 346-355. http://dx.doi.org/10.1016/j.icarus.2015.07.039
Introduction
The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) has collected over 6.3 billion measurements of surface height with a vertical precision of ~10 cm and an accuracy of ~1 m. The ability of LOLA to obtain measurements under uniform illumination conditions and in shadowed regions globally provides an advantage over passive stereoscopic imaging, particularly at high latitudes (poleward of 60°) where imaging is hindered by low solar incidence angles. This has allowed LOLA to produce the highest resolution and most accurate polar terrain models to date. In addition, LOLA provides the necessary geodetic framework with which lunar stereo imaging-based models must be controlled. However, due to LRO’s polar orbit, gaps in the LOLA coverage still persist especially near the equator where some can be as wide as a few km.
Here we present the results of an effort to improve the LOLA coverage by incorporating topographic information from the independently-derived and highly complementary SELENE Terrain Camera (TC) dataset (Haruyama et al., 2012). This dataset, called SLDEM2013, was controlled with an older version of the LOLA data geolocated with a gravity field made prior to the Gravity Recovery and Interior Laboratory mission (GRAIL; Zuber et al., 2013). In Barker et al. (2015), we co-registered the TC data to the newer, more accurate GRAIL-based LOLA geodetic framework creating a merged product, called SLDEM2015, which can be downloaded from the Planetary Data System LOLA data node. In addition to having many geophysical and exploration applications, the SLDEM2015 will improve the orthorectification and co-registration of diverse lunar datasets to the latest LRO/LOLA/GRAIL geodetic system without the gaps normally present between LOLA groundtracks.
Data
We used the 43,200 1°x1° TC DEM tiles covering latitudes within ±60°. The LOLA data coverage is sufficiently dense for most purposes at latitudes outside this range. During the SELENE mission lifetime (November 2007 to June 2009), the TC acquired stereo imagery for over 99% of the surface (Haruyama et al., 2012). The effective horizontal resolution of the TC DEM dataset is about 60 - 100 m.
Methods
We followed a two-step approach when co-registering the TC tiles to the LOLA data. In step (1), we derived a 5-parameter coordinate transformation between every TC tile and the full resolution LOLA data in that tile (unbinned point cloud with ~100,000 points). Thus, the tile-averaged transformation parameters compensate predominantly for the Kaguya/TC orbital, pointing, and camera model errors. In step (2), we fit a 3-dimensional (3D) offset to each LOLA profile segment in the transformed TC tile. These offsets reflect primarily the LOLA geolocation errors, which arise from uncertainties in the LRO orbit and LOLA boresight with a secondary contribution from Kaguya/TC errors not completely removed by the transformation in step (1) due to the restricted number of degrees of freedom.
Results
The top panel in Fig. 1 shows the spatial distribution of initial RMS vertical residuals between the LOLA and TC data while the bottom panel shows the RMS distribution after applying the tile-averaged transformation in step (1). Most of the vertical residuals are reduced to 3-4 m after step (1). The fraction of residuals <5 m increased from ~50% prior to registration, to ~90% after registration. After step (2), the 90th percentile further decreases from ~5.0 m to 3.4 m while the median RMS residual decreases from 3.2 m to 2.6 m.
Two areas with particularly high residuals include the South Pole Aitken basin (SPA; 45–60°S, 140–210°E) and the western edge of Orientale basin (45°S–15°N, 230–260°E). The large errors in SPA are due to lower-resolution Multi-band Imager DEMs included in the TC dataset to fill in areas TC did not observe. In Orientale, reaction wheel troubles on Kaguya led to degraded orbit reconstruction on those observation dates. The tile-averaged transformation also significantly improved some areas on the far side, especially between ± 30° latitude and 180–200°E longitude. These areas have initial RMS residuals of ~8 to 18 m, and have less vertically-oriented shapes than the regions mentioned previously. We attribute the initially high residuals in these far side areas to differences in gravity field models used by the reference LOLA data; SLDEM2013 was referenced to LOLA data based on pre-GRAIL gravity field LLGM-2 whereas in this work we used the much higher resolution and more accurate GRAIL GRGM900B (see Mazarico et al. (2013) for discussion).
Fig. 2 compares 3 different DEMs of the region around the landing site of the Chang’e 3 spacecraft: Fig. 2a shows LOLA data alone, after continuous curvature interpolation between ground tracks. Fig. 2b is our new SLDEM2015 merged product. Fig. 2c shows the GLD100 DEM, which was produced from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) stereo imagery (Scholten et al., 2012). The SLDEM2015 (Fig. 2b) reveals surface detail not sampled by the LOLA ground-tracks and below the ~1 km resolution limit of the GLD100.
Summary
In this study, we co-registered 43,200 TC DEM tiles to the latest GRAIL-based LOLA geodetic framework to produce a combined topographic map of the Moon at a resolution of 512 ppd. The bulk of the co-registered TC tiles have vertical residual with the LOLA data of 3 to 4 m. The co-registered TC data were used to estimate and remove orbital and pointing errors (typically amounting to <10 m horizontally and <1 m vertically) from the LOLA altimetric profiles. By combining both datasets, gaps in the LOLA data can be filled without the need for interpolation. Given the high (~1 m) absolute vertical accuracy of the LOLA data found in orbit overlap analysis (Mazarico et al., 2013), we conclude that the typical vertical accuracy of the SLDEM2015 is 3 to 4 m. SLDEM2015 is available for download from the PDS LOLA data node. This product has many geophysical and cartographic applications in lunar science, as well as exploration and mission design. Studies requiring the high geodetic accuracy of the LOLA data and the excellent spatial coverage of the TC data will especially benefit from this merged data product.
References
Barker, M.K. et al., 2016. A new lunar digital elevation model from the lunar orbiter laser altimeter and SELENE terrain camera, Icarus, 273, pp. 346-355. http://dx.doi.org/10.1016/j.icarus.2015.07.039
Haruyama, J. et al., 2012. Lunar global digital terrain model dataset produced from SELENE (Kaguya) terrain camera stereo observations. In: Lunar and Planetary Science Conference, p. 1200.
Mazarico, E. et al., 2013. Improved precision orbit determination of Lunar Orbiters from the GRAIL-derived lunar gravity models. In: 23rd AAS/AIAA Space Flight Mechanics Meeting, pp. 13-274.
Scholten, F. et al., 2012. GLD100: The near-global lunar 100 m raster DTM from LROC WAC stereo image data, J. Geophys. Res. (Planets), 117, CiteID E00H17. http://dx.doi.org/10.1029/2011JE003926
Zuber, M. T. et al., 2013. Gravity field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission, Science, 339, pp. 668-671. http://dx.doi.org/10.1126/science.1231507