Thursday, September 24. 2009
As a student researcher at LROC, I (Steven Koeber) mosaic images from the Narrow-Angle Cameras (NACs) and the Wide-Angle Camera (WAC). Mosaics are composed of several individual images that are stitched together, permitting an investigator to explore the geophysical and compositional properties of the lunar surface on a global or regional scale. NAC and WAC mosaics are produced using a specialized image-processing package called ISIS, the Integrated System for Imagers and Spectrometers. ISIS has the unique capability for processing data from several NASA spacecraft missions, including the Lunar Reconnaissance Orbiter (LRO).
Mosaics are processed in ISIS in four stages. The first stage prepares the individual images for processing in ISIS by adding ancillary information, such as the spacecraft’s altitude, time of observation, spacecraft location relative to the Moon and other pertinent data required to rectify an image. The second stage removes instrumental artifacts such as dust located on the camera CCD or bad (noisy) pixels to produce an “ideal” image of the surface.
The third stage simultaneously corrects for camera distortions and maps the image to a selected projection. A map projection displays the spherical surface of the Moon on a plane. Images obtained near the north or south poles are often mapped in a polar stereographic projection, while an image near the equator could be projected in simple cylindrical or Mercator projection.
In the final stage, ISIS generates a blank image that represents the regional or global area that all the individual images cover. Then those images are moved one-by-one into the “blank image” to create the final mosaic. Depending on the size and desirable resolution of the mosaic, the entire process can take only five minutes or several days. Providing the science team with quality mosaics of the Moon to analyze is my priority.