The Atmospheric Infrared Sounder (AIRS) was launched on May 4, 2002 on the NASA Aqua Satellite. AIRS measures the infrared spectrum in 2378 channels with a very high spectral resolution of approximately 1200. In this paper, the spatial properties of the infrared channels are presented in their flight configuration. The spatial response for any single channel is slightly irregular and rotates off nadir due to image rotation in the scan mirror. AIRS has several channels with the same spectral frequencies but different spatial responses. These channels are used to demonstrate the efficacy of resampling using standard techniques to improve the co-registration
The Atmospheric Infrared Sounder (AIRS), a hyperspectral infrared sounder, was launched onboard NASA's Aqua spacecraft on May 4, 2002 into sun-synchronous polar Earth orbit for a mission expected to last 7 years. By monitoring calibration data from views of deep space and two on-board calibrators, we have identified a number of effects attributed to in-orbit radiation. Transient effects include 1. steps in the output level of individual channels, attributed to injection of charge into a large capacitor in the read-out electronics integrated circuit (ROIC); and 2. spikes in the calibration data and, by inference, in the scene data, attributed to the passage of ionizing radiation through the active region of the HgCdTe detectors. On-board signal processing corrects for most of the spike effects, and ground processing smoothes the hot and cold calibration data and provides a system of flags to alert the user in cases where the calculated radiances are still suspect. Persistent effects include 1. extremely rare degradations of channels due to large charge injection events; and 2. slow increases in noise levels for a small number of channels, attributed to bias shifts due to the slow accumulation of radiation dose in the ROIC input cells for some channels. In addition to these detector effects, two operational anomalies have been attributed to the high radiation levels in the South Atlantic Anomaly (SAA), one an unplanned cooler shut-down, the second an unplanned stopping of the scan mirror. This paper presents statistics on the frequency and location of these radiation events, and provides a description of the mechanisms by which such events are identified and accounted for. It should be emphasized that the vast majority of the 2378 AIRS infrared channels, and the instrument as a whole, have shown excellent stability and operability throughout the mission.
We investigate uncertainties in the Atmospheric Infrared Sounder (AIRS) radiances based on in-flight and pre-flight calibration algorithms and observations. The global coverage and spectral resolution (~ 1200) of AIRS enable it to produce a data set that can be used as a climate data record over the lifetime of the instrument. Therefore, we examine the effects of the uncertainties in the calibration and the detector stability on future climate studies. The uncertainties of the parameters that go into the AIRS radiometric calibration are propagated to estimate the accuracy of the radiances and any climate data record created from AIRS measurements. The calculated radiance uncertainties are consistent with observations. Algorithm enhancements may be able to reduce the radiance uncertainties by as much as 7%. We find that the orbital variation of the gain contributes a brightness temperature bias of < 0.01 K. Although this can be removed by algorithm enhancements, it is smaller than uncertainty of the gain for most channels.
The Atmospheric Infrared Sounder (AIRS) was launched in May 2002. Along with two companion microwave sensors, it forms the AIRS Sounding Suite. This system is the most advanced atmospheric sounding system to date, with measurement accuracies far surpassing those available on current weather satellites. The data products are calibrated radiances from all three sensors and a number of derived geophysical parameters, including vertical temperature and humidity profiles, surface temperature, cloud fraction, cloud top pressure, and ozone burden. These products are generated under cloudy as well as clear conditions. An ongoing calibration/validation effort has confirmed that the system is very accurate and stable, and most of the geophysical parameters have been validated. AIRS is in some cases more accurate than any other source and can therefore be difficult to validate, but this offers interesting new research opportunities. The applications for the AIRS products range from numerical weather prediction to atmospheric research - where the AIRS water vapor products near the surface and in the mid to upper troposphere will make it possible to characterize and model phenomena that are key for short-term atmospheric processes, such as weather patterns, to long-term processes, such as interannual cycles (e.g., El Niño) and climate change.
The application of hyper spectral radiometric data to climate research requires very high absolute radiometric accuracy and stability. We use cloud-free tropical ocean data from the Atmospheric InfraRed Sounder (AIRS) Calibration Data Subset (ADCS) to show that the radiometric precision and stability required for climate applications has been achieved. The sea surface skin temperatures derived from the AIRS 2616cm-1 super window channel are stable relative to the RTG.SST at the better than 8 mK/year level, and the spectral calibration is stable at the 1 ppm/year level. The excellent stability and accuracy are the result of the implementation of AIRS as a grating array spectrometer, which is cooled and stabilized within 10 mK at 155 K. Analysis of daily measurements of the temperature gradient between the surface and 7 km altitude show that the AIRS Calibration Data Subset has applications which extend its original intent for calibration support to climate research.
The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua satellite was launched into polar orbit in May 2002. AIRS covers the spectral region from 640 to 2700 cm-1 with 2378 independent channels and represents the first of a new generation of hyper spectral resolution sounders in support of global sounding data for weather forecasting and climate research.
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.
The current performance of AIRS radiometric, spectral, and spatial calibration algorithms are described. Radiometric accuracy is validated to tenths of a kelvin. Spectral stability is better than 0.5% of the spectral response function FWHM. Geolocation accuracy is accurate to approximately 2 km at nadir. An algorithm has been implemented to correct for space views contaminated by the moon. Planned algorithm improvements include correcting the 2 km bias in geolocation.
JPL is currently managing the instrument operations, calibration and data system for the Atmospheric Infrared Sounder (AIRS) on the EOS Aqua spacecraft. Aqua was launched on May 4, 2002 from Vandenberg Air Force Base. AIRS has 2378 infrared channels with high spectral resolution (1200) covering the 3.7 to 15.4 micron wavelength range. AIRS data are used to produce temperature and humidity profiles useful in predicting weather and monitoring climate. We discuss lessons learned on AIRS in the development and operations as well as plans for next generation systems including SIRAS, a wide field hyperspectral infrared imaging spectrometer which offers AIRS spectral performance at 24x the spatial resolution.
The Atmospheric Infrared Sounder (AIRS) is a space-based hyperspectral infrared instrument designed to measure the Earth’s atmospheric water vapor and temperature profiles on a global scale. AIRS has 2378 infrared channels in the spectral range of 3.7 to 15.4 microns, with a spatial resolution of 13.5 km and 4 Vis/NIR channels from 0.4 to 0.8 microns with a spatial resolution of 2.3 km. AIRS is one of several instruments onboard the Earth Observing System (EOS) Aqua spacecraft launched May 4, 2002. AIRS has completed its Activation and Evaluation (A&E) phase and is currently in its operational mode. This paper summarizes the AIRS instrument radiometric, spatial, and spectral performance as measured in orbit during the A&E phase. Instrument noise performance, spectral alignment dependence on temperature and other factors, and spatial pointing accuracy are discussed.
The Atmospheric Infrared Sounder (AIRS) is a space based instrument developed for measurement of global atmospheric properties; primarily water vapor and temperature. AIRS is one of several instruments on board NASA's Earth Observing System Aqua spacecraft. AIRS operates in the 3.7 - 15.4 micron region and has 2378 infrared channels and 4 Vis/NIR channels. AIRS spatial resolution is 13.5 km from the orbit of 705 km and it scans ±49.5 degrees. AIRS has a set of on-board calibrators including a single infrared blackbody source, a parylene spectral calibration source, a space view and a Vis/NIR photometric calibrator. The on-board calibration subsystems are described along with a description of special test procedures for using them and results from several tests performed to date. Results are exceptional indicating that the instrument is performing better than expected.
Spectral characterization of the Atmospheric Infrared Sounder (AIRS) instrument during ground Thermal/Vacuum tests posed a number of difficult challenges due to the high spectral resolution and accurate knowledge requirements. A Fourier transform spectrometer was used in external step-scan mode to characterize the spectral response functions (SRFs) of the 2378 infrared detectors in the focal plane array which is part of the AIRS grating spectrometer. This paper summarizes the test development and characterization results. Special post-test data analysis was needed separately to determine the effects of interference in the order-separating entrance filters, which have a different temperature dependence from that of the otherwise unperturbed SRFs. This separation, which was successfully accomplished, provides calibration of the AIRS SRF shape over the full expected range of instrument temperatures.
The Atmospheric Infrared Sounder project will measure global atmospheric water vapor and temperature with unprecedented resolution and accuracy. AIRS is an infrared instrument covering 3.7-15.4 microns in 2378 IR channels. This paper describes the AIRS mission and science objectives, the instrument design and operation, the calibration plan, the in-flight operational scenario and the Science Processing System. All aspects of the program are addressed here to demonstrate that the AIRS program is ready to transition to the flight segment of the program. The AIRS instrument meets the majority of instrument design requirements established in order to meet the scientific objectives. A well-defined operational approach has been established, and a sound calibration plan has been developed to ensure optimal performance throughout the life of the mission.
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