Wide-angle infrared cloud imaging for cloud cover statistics
Nugent, Paul Winston
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The Infrared Cloud Imager (ICI) is a radiometrically calibrated thermal infrared imaging instrument currently in development at Montana State University to measure cloud cover statistics. This instrument was developed originally as part of a joint U.S.-Japan effort to study the arctic atmosphere. The ICI provides localized high-resolution data relative to satellites images and, in contrast to visible imaging systems, provides continuous day and night operation. While the original instrument proved the capabilities of using radiometrically calibrated thermal infrared images to produce cloud coverage measurements, this instrument was limited. These limits were primarily the instrument's large size, relatively high cost, narrow field of view, and need to recalibrate the camera for each image. The work presented here covers work conducted to develop two prototypes of a second-generation ICI instrument, and the work which laid the groundwork for the development of a fully deployable version of these systems. These systems are to be used to measure cloud cover statistics for the characterization of optical communication paths by the Optical Communication Group at NASA JPL.The second-generation ICI, based around the FLIR Photon camera, expands the field of view (fov) from 20° to 50° in the early prototype and up to 100° in the latest version, reduces instrument size, reduces instrument cost, and implements a novel internal shutter-based calibration technique. Increasing the fov has required the modification of the routines to process ICI data, in particular to accommodate the angular dependence of atmospheric emission from a clear sky. These processing routines have also been extended to provide cloud type classification in addition to only cloud presence as in the original system. Versions of this instrument have been deployed at Bozeman, Montana, and at JPL's Table Mountain Facility (TMF). During the deployment at Bozeman these instruments have been shown to be accurately calibrated, and that they produce the same data (after accounting for bandwidth and fov differences) while viewing the same scene. Much of the continued work needed to complete this project can be conducted during an extended deployment of these systems, which should take place during early 2008 at JPL's TMF.