KEYWORDS: Sensors, Polarization, Polarimetry, Aerosols, Signal to noise ratio, Telescopes, Calibration, Short wave infrared radiation, Error analysis, Space telescopes
The Aerosol Polarimetry Sensor (APS) is the primary Earth observing instrument of the Glory Mission. It is expected to
launch into space in the 4th quarter of 2010. This paper summarizes results from the APS ground-testing, completed in
2009. Ground testing established that the instrument meets or exceeds performance requirements: SNR, dynamic range,
radiometric accuracy, polarimetric accuracy, response vs. scan angle, boresight co-alignment, and calibration sources
accuracy. The APS demonstrated excellent performance stability during sensor and spacecraft level testing over a wide
range of environmental conditions. The APS will be a significant improvement over existing sensors that measure
aerosols from space. It will provide the scientific community with new information about the distribution and properties
of aerosols around the globe. Scientists will use APS data to estimate the radiative forcing imposed on the Earth by
aerosols, to assess the effects of aerosols on the Earth's climate.
Future operational geosynchronous remote sensors will respond to a broad range of environmental and
military/intelligence mission needs. This paper describes initial system engineering design studies for 4th
generation operational geosynchronous remote sensors that address notional future mission requirements.
Two hyperspectral sensor architectures were considered: an imaging Fourier transform spectrometer and an
imaging prism spectrometer. While both imaging FTS and dispersive approaches are viable over a broad
trade space, each requires new technology that must be demonstrated low risk by 2017 to enable a mission
pathfinder by 2025. To reach this important objective requires that technology risk reduction start now.
Aerojet has developed high performance infrared (IR) cameras based on Kodak's 640 by 486 pixels platinum silicide (PtSi) array. Several versions of the camera have been developed for the various applications. The cameras have multiple field-of-view (FOV) optics, with the narrow FOV used for long range observation. The use of the large array of PtSi leads to very high image quality as well as high resolution. The operation in the medium-wavelength infrared (MWIR) allows observation at very long ranges in high humidity, warm atmospheres. Field tests have shown the advantage of these cameras, particularly in coastal and marine applications.
To minimize the noise of a PtSi IR camera we examined all the sources of radiation reaching the detector. In particular, we suspected that the cold shield which is supposed to be (nearly) 100% black -- was not. In long wavelength FLIRs where the scene radiation is the main source of noise this was never an issue. In MWIR cameras this could be a source of added noise. The problem was to evaluate the noise contribution of the reflected radiation from the cold shield by sensor measurements. To this end we replaced the lens by an equivalent black (painted) tube which was temperature controlled (heated) and was outside the FOV of the cold shield. The mean charge in the center of the FPA was evaluated as a function of the temperature of the tube. The analysis of the test data showed that the cold shield reflectance is one percent, a low value. As utilized in our IR camera, this commercially available cold shield was determined to be effective in keeping the noise low.
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