KEYWORDS: Sensors, Equipment, Calibration, Black bodies, Temperature metrology, Detector arrays, Infrared radiation, Data acquisition, Temperature sensors
The Atmospheric Infrared Sounder (AIRS) was launched on May 4, 2002 on the NASA Earth Observing System (EOS) Aqua spacecraft. AIRS measures the hyperspectral upwelling spectral radiance of the Earth in the infrared from 3.7- 15.4μm in 2378 channels. Instrument raw digital counts are converted to radiances using a hybrid physical, empirical approach that maintains high measurement accuracy with SI traceability. Before launch, a comprehensive On-board Calibration Plan was developed that configures the AIRS instrument into certain modes that enable characterization and/or validation of various performance parameters. Ten of the eleven on-board tests have been performed on-orbit with varying frequencies. This paper addresses three of the tests that focus on the radiometric performance of the instrument including instrumental gain and noise, non-linearity, non-Gaussian noise and stray light effects on the On-Board Calibrator (OBC) Blackbody and Space View (SV), respectively. The Guard Test, C1, uploads A only and B only detector redundancy gain tables that allow characterization of the noise and gain in normal operational mode. The Space View Noise Test, C8, stops the scan mirror while AIRS views space, providing a long, continuous, measurement of a cold target for characterization of instrumental noise and drift. The OBC Float Test, C5, turns off the OBC blackbody to provide a range of observational temperatures to the instrument for calibration of the nonlinearity. All tests show excellent stability of the instrument response, albeit regular non-automated adjustments to the detector redundancy has been required throughout the mission due to normal instrumental aging and radiation hits. Despite the changes, the AIRS Calibration Team has managed to maintain the number of active channels to the values experienced shortly after launch for the life of the mission.
The AIRS instrument was launched in May 2002 into a polar sun-synchronous orbit onboard the EOS Aqua Spacecraft. Since then we have released three versions of the AIRS data product to the scientific community. AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), produces temperature profiles with 1K/km accuracy on a global scale, as well as water vapor profiles and trace gas amounts. The first version of software, Version 2.0 was available to scientists shortly after launch with Version 3.0 released to the public in June 2003. Like all AIRS product releases, all products are accessible to the public in order to have the best user feedback on issues that appear in the data. Fortunately the products have had exceptional accuracy and stability. This paper presents the improvement between AIRS Version 4.0 and Version 5.0 products and shows examples of the new products available in Version 5.0.
KEYWORDS: Calibration, MATLAB, Data archive systems, Data centers, Data processing, Space operations, Binary data, Microwave radiation, Databases, Inspection
The Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU-A), and the Humidity Sounder for Brazil (HSB) instruments were launched aboard NASA's Aqua spacecraft on May 4, 2002 into near-polar Earth orbit with a 1:30 PM ascending equator crossing. The AIRS instrument measures 2,378 infrared and four visible/near-infrared channels, while the 15-channel AMSU-A and four-channel HSB instrument provide simultaneous observations in the microwave region from 23.8-89 GHz and 150-189 GHz, respectively. Together these instruments produce thousands of measurements per second for a mission expected to last 7 years.
This paper describes the challenges of identifying and monitoring, among the approximately 1,500 available engineering and quality assessment parameters, a representative subset for tracking each instrument's performance. A software system has been developed which autonomously extracts key items from the voluminous project database, performs data analysis and creates web-based daily summary reports with links to these archived results. Independently, a second process autonomously monitors these trending data products and notifies team members by e-mail if parameters exceed their trending-specific monitoring limits. Finally, this paper describes how this system has been used to predict long-term instrument performance trends, investigate previous flight anomalies and maintain the instrument within calibration specifications.
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