Abstract
Abstract. The Lunar Reconnaissance Orbiter Camera (LROC) consists of two imaging systems that provide synoptic and high resolution imaging of the lunar surface. The Wide Angle Camera (WAC) is a seven color push frame imager with a 90° field of view in monochrome mode and 60° field of view in color mode. From the nominal 50 km polar orbit, the WAC acquires images with a nadir pixel scale of 75 m for each visible band and 384 m for the two ultraviolet bands. The Narrow Angle Camera (NAC) consists of two identical cameras capable of acquiring images with a pixel scale of 0.5 to 1.0 m from a 50 km orbit. Each camera was geometrically calibrated prior to launch at Malin Space Science Systems in San Diego, California. Using thousands of images acquired since launch in June of 2009, improvements to the relative and absolute pointing of the twin NACs were made allowing images on the surface to be projected with an accuracy of 20 meters. Further registration of WAC and NAC images allowed the derivation of a new distortion model and pointing updates for the WAC, thus enabling sub-pixel accuracy in projected WAC images.
Highlights
The Lunar Reconnaissance Orbiter (LRO) is a remote sensing precursor designed to facilitate scientific and engineering-driven mapping of the lunar surface for future robotic and human missions [Vondrak et al, 2010]
Unlike the Narrow Angle Camera (NAC), which can be directly tied to human artefacts on the lunar surface, the Wide Angle Camera (WAC) in-flight geometric calibration was based on registration with map projected NAC images that have been processed with the latest calibration updates
A custom MATLAB function was composed that calculated a root mean squared (RMS) error of the difference between the corrected pixel location defined by the NAC image and the corrected pixel location calculated from the distorted pixel location in the WAC image for a camera model with a given set of parameters
Summary
The Lunar Reconnaissance Orbiter (LRO) is a remote sensing precursor designed to facilitate scientific and engineering-driven mapping of the lunar surface for future robotic and human missions [Vondrak et al, 2010]. Recent precision orbit determination derived from radiometric data and altimetric crossovers improved the known position of the spacecraft to within 20 meters [Mazarico et al, 2011] With this updated ephemeris, the LROC team is improving the pointing for both the Narrow and Wide Angle Cameras as well as deriving an improved distortion model for the WAC. The WAC acquires framelets for all seven bands, due to limitations in the readout rate of the CCD array, only the center 704 samples are read out for each 14 line visible band. The 512 samples and 16 lines are summed in 4 × 4 pixel boxes resulting in a 128 × 4 pixel framelet, which increases the signal to noise ratio for the UV bands Due to this configuration, in monochrome mode the WAC has a ~90° FOV and in color mode a ~60° FOV. Typical WAC observations contain 36 to 1,800 evenly spaced frames
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