The Earth Science and Meteorological communities are taking great interest in a new instrument released by NASA. The Atmospheric Infrared Sounder (AIRS), launched on the EOS Aqua Spacecraft on May 4, 2002, is a high spectral resolution infrared imaging spectrometer with over 2300 distinct infrared wavelengths ranging from 3.7 μm to 15.4 μm. AIRS is unique in that it provides the highest infrared spectral resolution to date while also providing coverage of over 95% of the Earth's surface every day at 15 km spatial resolution. The AIRS project is currently managed by NASA's Jet Propulsion Laboratory in Pasadena, California1. The AIRS is providing a wealth of scientific data to the Earth Science community including upper atmospheric water vapor and atmospheric composition on key greenhouse gases. It is also improving weather forecasting and the studies of processes affecting climate and weather.
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 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.
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.
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