The National Aeronautics and Space Administration (NASA) released a request for proposals (RFP) on January 09, 2007 for an Operational Land Imager (OLI). The RFP specified the OLI as the principal sensor for the Landsat Data Continuity Mission (LDCM), the successor mission to Landsat 7. The RFP provides requirements for OLI performance, special calibration tests, and mission assurance without specifying a particular technical design. The performance specifications derive from the heritage and societal benefits of data from the previous Landsat satellites, the high standards set by the performance of the Landsat 7 Enhanced Thematic Mapper-Plus, direction from the Executive Office of the President, cognizance of current technology, and an eye to the future of land remote sensing beyond the LDCM. The specification includes nine spectral bands (four visible, one near infrared, three shortwave infrared, and one panchromatic band), spatial resolution of 30 m with the exception of a 15 m panchromatic resolution, stringent radiometric performance and absolute calibration, and accurate image geolocation with precise band-to-band and multitemporal image-to-image registration. Proposals were due on February 23, 2007 with selection and contract award anticipated by June 2007. The RFP requires delivery of a well-characterized instrument for spacecraft integration within 39 months of contract award. This schedule leads to a target LDCM launch date of July, 2011.
The GOES Sounder is similar in appearance, size, and design to the GOES Imager. It provides independent radiomen-ic sounding of the atmosphere from GOES-East and GOES-West (GOES 8 and 9), which was accomplished on previous GOES by a single instrument with responsibility split between the functions of imaging and sounding. With 19 channels ranging from 0.70 m to 14.71 m, the Sounder probes the atmosphere to measure radiance at different depths (altitudes) while also monitoring surface and atmospheric temperatures, ozone, water vapor content, and cloud cover by means of the calibration of radiance data at selected wavelengths.Like the Imager, the Sounder scans the full earth, and can be commanded to scan local regions of interest. The scan mirror steps across the disk of the earth in synchronization with a dead zone on a filter wheel. The filters defme 18 of the channels as they rotate on the wheel in the path of light split into three beams traveling to detectors divided into longwave, midwave, and shortwave arrays. For visible (0.70 m) sounding of cloud cover, energy is split off ahead of the filter wheel and passed to the 19th channel and also to star sensing detectors used for instrument navigation.
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