SVS: CGI Moon Kit
Sección: Astronomía Machadines y Exploración Espacial
Creado: 10-09-19 (Actualizado: 28-01-20)
These color and elevation maps are designed for use in 3D rendering software. They are created from data assembled by the Lunar Reconnaissance Orbiter camera and laser altimeter instrument teams.
Color
For the color map here, the visualizer modified and combined three of the seven wavelength bands of the LROC color data to more closely match what the human eye sees. The red channel contains the 643 nm band, while green and blue were created from different linear combinations of the 566 and 415 nm bands to more nearly center them on 532 nm (green) and 472 nm (blue). A gamma of 2.8 was applied (the LROC data is linear), and the channels were multiplied by (0.935, 1.005, 1.04) to balance the color. The intensity range (0.16, 0.4) was mapped into the full (0, 255) 8-bit range per channel. Small data dropouts near the top and bottom were inpainted using Photoshop's content-aware spot healing brush.
The source data covers the lunar globe from 70°N to 70°S. Because the Moon's axial and orbital tilts are both small, many areas outside these latitudes remain shrouded in shadow, even after thousands of passes by LRO's camera, so they are left out of the LROC mosaic. For this color map, the missing latitudes were filled in with a combination of monochromatic LROC data and an albedo map (LDAM) from LRO's laser altimeter. When rendered with realistic shadows, these parts of the map aren't particularly visible, and while they comprise more than 20% of the map's pixels, they represent only 6% of the Moon's surface.
This image is optimized for aesthetics, not science. Scientific applications should use the source data.
Displacement
The reference surface for all LRO data is a sphere of radius 1737.4 km. LOLA's gridded elevation data is published as signed 16-bit integers in units of half-meters relative to this radius. For the floating-point TIFFs, the source data was divided by 2000. For the unsigned 16-bit TIFFs, the source data was offset by +20,000 (10 km) so that all of the values are positive. This latter format is provided for software that doesn't work well with either floating-point or signed integer files.
How These Maps Are Used
Each pixel in these texture maps corresponds to a point on the lunar surface defined by a longitude-latitude pair. Pixels in the color map contain the base color
of the surface, before applying the effects of varying light and camera angles (called incidence angle i and emission angle e in the technical description). Pixels in the displacement map contain the height of the surface at the corresponding locations.
More Data
These maps are a tiny subset of the data publicly archived by the LRO instrument teams. All of the data is in standard and fairly simple PDS file formats (files with.IMGfilename extensions). Although not typically supported by general-purpose computer graphics software, these formats are directly readable by some GIS programs. The data formats are documented in PDS labels, which are either separate text files with a
.LBLfilename extension or embedded as fixed-length headers. Other than the possible header, most .IMG files are uncompressed 2D binary arrays of numbers. Some data is also available in TIFF or JPEG2000 formats.
As of this writing, the best global-scale elevation data for equatorial and mid-latitude regions of the Moon, at resolutions up to 512 pixels per degree, is SLDEM2015. For regions near the poles, where the density of laser shots is much higher, the GDR data in polar stereo projection reaches resolutions of five meters per pixel.
The LROC narrow-angle camera (NAC) has imaged most of the Moon's surface at a resolution of one meter per pixel or better. LROC imagery can be explored graphically using its Quickmap interface and searched on its RDR Product Select page. Of particular interest are the Topographic Products (menu option in the upper left of the page), which are matched with high-resolution DEMs derived from stereo image pairs. This dataset includes all of the Apollo landing sites and dozens of other locations of interest.
https://svs.gsfc.nasa.gov/4720