A REVISED PLANET-WIDE DIGITAL ELEVATION MODEL OF THE MOON

 

 

 

Description:

This data set is a revised version of a Digital Elevation Model (DEM) that was generated from Clementine ultraviolet-visible (UVVIS) camera along track stereo coverage at the Center for Earth and Planetary Studies, National Air and Space Museum, Washington D.C. in May 2000 and shall be referred to as NASM1KM. It was found that this product did not register spatially with the earlier USGS Clementine Basemap Mosaic (CBM). This was caused by NASA1KM using the original spacecraft pointing and CBM using a revised set of angles for the spacecraft pointing. The offset between the two products ranged from 0 to 15 km and this large offset called into questions the revised set of spacecraft angles used in the CBM. A new adjustment of the spacecraft angles was preformed and this resulted in the Unified Lunar Control Network 2005 (ULCN 2005).add link

 

The ULCN 2005 was used to revise the Clementine mosaic. Web page for ULCN 2005 report. Web page for revised Clementine mosaic.

 

To revise the NASA1KM DEM we started with the individual stereo models that went into the NASA1KM DEM. Based on the revised spacecraft camera angles we recomputed the ground intersection points for each of the stereomodels that had images in common with the ULCN 2005. Of the ~350,000 stereomodels in NASA1KM DEM we used 31,201 stereomodels that were in common with images used in the ULCN 2005 ( there were 441 stereomodels in common that we rejected based on number of points being less than 100 or elevation values that were not plausible.) The NASA1KM DEM covered 69% of the lunar surface and the revised model covers 38% of the lunar surface.

 

The ground point data in individual stereomodels were recomputed based on the revised camera angles obtained from the ULCN 2005 solution. These points were screened to remove elevation values with an absolute elevation value greater than 15 km. The recomputed ground point values were used to create ISIS cubs for each stereomodel. The ground resolution was set to ~237 m (128 pixels/degree), so each point would occupy one pixel in the cub. The ISIS equalizer program was used to vertically align the stereomodels with the ULCN 2005 elevation values. The stereomodels were then mosiced into a global DEM with ~1km resolution (32 pixels/degree), this 4 to one reduction was used to help reduce the noise in the elevation values.

 

There is LPSC abstract with more detail.

Rosiek et al. (2007) LPSC #2297

 

See this journal article for more information about Clementine photogrammetry that was used for the NASA1KM DEM.

Cook et al. (1996) Planet. Space Sci., 44,

 

 

 

 

Blending the nasm_usgs_1km DEM with the ULCN 2005 was bit tricky because of the differences in the point distribution in the two data sets. Figure 1 shows a portion of the nasm_usgs_1km DEM as a color coded image and the control points from the ULCN 2005 as black dots. The nasm_usgs_1km DEM has elevation values at a 1km spacing clustered into tiles that overlap. The ULCN 2005 points are distributed where images overlapped and are not uniformly distributed. ULCN 2005 points that were in common with the nasm_usgs_1km were already used to level the elevation of those tiles, so that are not included in the blended product. In trying to blend the data as point products the difference in the point distribution caused the blended product to lose the high resolution information from the nasm_usgs_1km or to have artifacts introduced in trying to interpolate from the tile to the ULCN 2005 points.

 

Instead of basing the blend on the point data we used the raster data. Using the nasm_usgs_1km DEM a mask was developed to clip from the ULCN 2005 DEM a raster data set that would fill-in the missing parts of the nasm_usgs_1km DEM and would have about a pixel of overlap between the two data sets. Figure 2 shows the two DEMS prior to blending. Each DEM is shown with a transparency of 50% that allows the overlap are between the two DEMs to be shown as darker line that outlines the tiles in the nasm_usgs_1km DEM.

 

Text Box: Figure 1 - example of nasm_usgs_1km DEM and ULCN 2005 points.

Text Box: Figure 2 - raster blend of nasm_usgs_1km DEM and DEM based on the ULCN 2005 control points