The image at right is from Lunar Calculator, after simulating the view from Earth. It demonstrates how features near the limb of the Moon are distorted (foreshortened), and why direct Clementine imagery has its limitations.
NASA's Clemetine spacecraft orbited the Moon in 1994. Among its mission objectives was mapping the whole surface in a range of wavelengths. Scientists then processed the images, accounting for lens distortions and perspective, to produce a set of cartographically accurate sections, or tiles. Each pixel can now be mapped to its latitude and longitude down to a high degree of accuracy. For much of the Moon, a tile looks like an overhead view of each area. For example, at left is a low resolution image of the region near Grimaldi (upper right) with Mare Orientale to the lower left.
The image at right is from Lunar Calculator, after simulating the view from Earth. It demonstrates how features near the limb of the Moon are distorted (foreshortened), and why direct Clementine imagery has its limitations.
One of the results from NASA’s Clementine spacecraft program was a complete map of the moon at constant illumination. Full phase was chosen with the sun as high in the lunar sky as possible. A low sun angle highlights topographic differences, while a high sun angle highlights albedo, or reflectivity differences. Albedo information is important for studying surface composition. At full moon, many craters disappear because there are no shadows. Albedo information at a range of wavelengths allows scientists to study surface (mineralogical) composition.
Clementine was not able to provide 100% coverage of the moon at full phase. To keep the dataset pure, the scientists decided not to merge in low resolution or low sun angle data.
The images of most interest to amateur astronomers fill 15 CD-ROMs, yet they are only a small part of the complete dataset! 14 CDs contain high resolution data, at 100m/pixel (1/16 mile per pixel). Volume 15 (the one included on the Lunar Calculator CD) has global coverage at 500m/pixel (5/16 mile per pixel). For a typical Earth-Moon distance this 500m/pixel resolution is about 1/4 arcsecond, pretty hard to achieve at the telescope!
More information on the Clementine mission can be found at NASA's planetary science node.
As mentioned above, the visual dataset is presented as a series of tiles. Each tile is roughly 2000x2000 pixels. For faster "browsing" access, NASA also produced the tiles in smaller sizes of 1000x1000 ("large"), 500x500 ("medium"), and 250x250 ("small"). The image sizes listed here are approximate. These browse images are individually contrast stretched by NASA.
When Lunar Calculator 2 was being initially developed, computers were slower and hard drive space was more limited, so to avoid bogging down the memory and keeping as much information on the CD as possible, the browse images were stitched together, creating abrupt changes from one tile to another.
Once I figured out how to manipulate the full tiles, I could get Lunar Calculator to produce a seamless stitch with no abrupt changes in contrast.
Yes, you must use the Contrast/Brightness window, which you access through the Edit menu.
On the Volume 15 CD-ROM, you can access the image tiles as JPGs. Click on INDEX.HTM on the CD-ROM to view the images in your favorite web browser. While this is useful, as an amateur astronomer I found that interface lacking, so I developed the freeware "Clementine Skimmer" to access the images more quickly and provide additional features such as a database and measuring utilities. The full resolution images 2000x2000 pixels are not accessible through the browser though NASA does have programs to view them - check the internet. Skimmer provides access to them on-the-fly with built-in image enhancement. You can install Skimmer from the CD-ROM or retrieve it from my website.
There are 4 main ways that Lunar Calculator portrays the Moon. There is a simple "wire frame" view that displays very quickly. The Clementine spacecraft view shows the Moon under high solar illumination, that is at full phase. Another view uses the classic USGS (United States Geological Survey) shaded relief "texture" map, which shows craters and highlights with a "morning solar illumination" which is great for the evening terrestrial observer. The best overall view is with the USGS-Clementine blend, because it more closely approaches the view in a telescope, with relief features (e.g. craters) near the terminator and albedo features farther away.
The dynamic shading of the USGS relief map ensures that the simulation on days following full phase doesn't suffer from looking like sunlight coming the "wrong way". This extra refinement does extoll a tax on the speed of the rendering, but it's well worth it.