92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 9:30 AM
CrIS NPP Full Spectral Resolution Test
Room 343/344 (New Orleans Convention Center )
Mark Esplin, Space Dynamics Laboratory, North Logan, UT; and L. L. Strow, G. Bingham, V. Zavyalov, D. K. Scott, and C. Fish

The Cross-track Infrared Sounder (CrIS) Flight Model One (FM1) sensor will be flown on the NPP spacecraft. The CrIS sensor is a Michelson interferometer with detectors for three spectral bands: LWIR 650-1095 cm-1, MWIR 1210-1750 cm-1 and SWIR 2155-2550 cm-1. The spectral resolution of the LWIR band is 0.625 cm-1, but due to bandwidth consideration the spectral resolution of the MWIR was limited to 1.25 cm-1 and the SWIR band to 2.5 cm-1. Limited spectral resolution results in a loss of science data, particularly in the SWIR band. The spectral resolution of a Michelson interferometer is determined by the length of scan of the interferometer moving mirror. For CrIS, a single interferometer scan mechanism is used for all three spectral bands. The length of the scan was determined by the LWIR spectral resolution requirement. The MWIR and SWIR bands only use part of interferometer mirror scan. The MWIR and SWIR detectors are active during the entire scan, but the signal processing electronics only uses part of the data. CrIS spectral resolution for the MWIR and SWIR bands can be enhanced to be the same as the LWIR band by simply reconfiguring the signal processing electronics with no hardware changes required. During the NPP spacecraft level testing a full resolution test of the MWIR and SWIR bands was performed using the CrIS FM1 sensor.

Increasing the spectral resolution will result in significant gains in the value of the CrIS sensor science data as well as simplifying operations. Without higher spectral resolution in the SWIR it is extremely difficult to use measurements of atmospheric spectral lines to provide spectral calibration. Without accurate spectral calibration the very important 4.3 μm CO2 R branch data is not very usable. In addition higher spectral resolution would give the US a long term CO monitoring capability from space, which is important for monitoring atmospheric chemistry. Finally, full spectral resolution in the SWIR band would make it possible to use CO instead of HBr for ground spectral characterization. HBr is a very corrosive and dangerous gas that proved very problematic during FM1 ground thermal vacuum testing.

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