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.
The Atmospheric Infrared Sounder (AIRS) has been operating since Sept. 2002 and is being used operationally by several weather centers. Routine retrieval processing is done by NASA. Daytime AIRS measurements in the 4.3um region show large (upto 12 K) brightness temperature shifts compared to nighttime observations. The daytime shifts result from the preferential absorption of solar radiance in the upper atmosphere by CO2 and other molecules. This energy is transferred to many of the 4 um CO2 bands, driving them into a state of Non-Local Thermodynamic Equilibrium (NLTE). We present comparisons of observations against the results of a Fast Model we developed for the AIRS instrument, that includes this effect. This algorithm is fast enough to be used for retrievals, and will be especially useful for the 4.3um R branch head channels that are used for temperature sounding.
Large thunderstorms can be identified in the AIRS data as areas where the brightness temperature of the 1231 cm-1 atmospheric window channel in non-polar areas is less than 210 K. Each day about 6000 large thunderstorms are identified by this test, almost exclusively within 30 degrees of the equator. Since the size of the AIRS footprint at nadir is 13.5 km, a brightness temperature of less than 210 K indicates that the top of the anvil of the thunderstorm protrudes well into the tropopause. Such objects are commonly referred to as Deep Convective Clouds (DCC). Our interest in DCC was motivated by the question "Are severe weather events increasing due to global warming". Each DCC is a severe weather event, although not on the scale of the much less frequent hurricanes, which can be identified in the AIRS data as clusters of several hundred DCC. For the past four years the number of DCC per day has been fairly stable for all tropical oceans combined, but a significant increase can be seen day and night in the Atlantic Ocean. This increase may be related to the slowing of the Atlantic meridional overturning circulation. The most prominent features in brightness temperature spectra of DCC are due to stratospheric CO2, Ozone and Methane. In the channels with weighting functions below the stratosphere the brightness temperature is typically 205 K, with a characteristic 1 to 2.5 K drop between 1000 and 750 cm-1, equivalent to a 2-4 % drop in emissivity. This is likely due to the presence of cirrus (ice) particles. Firmer conclusions about the significance of the DCC count require a considerably longer data set than the currently available four years from AIRS. We plan to continue this analysis with AIRS data. Extension of the analysis to past operational sounders in polar orbit requires independent validation of the stability and absolute accuracy of the radiometric calibration at 210 K.
AIRS is an imaging hyperspectral grating-array spectrometer on the EOS Aqua spacecraft, launched on May 4, 2002.
We present an intercomparison of retrieved dust parameters obtained from
analyzing AIRS and MODIS satellite data. Recent papers have highlighted
using AIRS data to retrieve dust top (layer) height, loading and particle size.
Different methods have been used, such as assuming a fixed particle size
and dust top height before fitting radiance
data from selected AIRS channels, or using lookup tables to retrieve dust
loading, height and particle size. In this paper we use the combination
of dust retrievals from MODIS visible and AIRS thermal infrared channels
to provide information on dust top height by forcing the error term (or
intercept of the linear regression of dust optical depths retrieved from
MODIS and AIRS) to zero. When available, GLAS measurements will be used to
validate dust top height. Collocated ship based M-AERI observations, obtained in March 2004 during the AEROSE campaign will also be analyzed to verify this
approach.
The Atmospheric Infrared Sounder (AIRS) has been operating since Sept. 2002 and AIRS radiance data is being used operationally by several weather centers. A significant fraction of AIRS observations are contaminated by dust blowoff from arid areas. The almost continous spectral coverage of AIRS in both the 10-12 and 3.7 micron atmospheric windows allows excellent detection of the presence of dust. Dust signals can often survive the cloud-clearing process used in the retrieval system for AIRS, thereby contaminating the low-altitude temperature and water vapor retrieval products. We present techniques being developed to both operationally detect and mitigate the effects of dust on AIRS retrieval products.
The Atmospheric Infrared Sounder (AIRS), launched in May 2002, is the first of a new generation of high-spectral resolution temperature and humidity sounders for numerical weather prediction and climate change studies. The accuracy of the AIRS radiances, and the validity of the clear sky AIRS Forward Model, have already been demonstrated. With daily global coverage by the instrument, the almost continuous wavelength coverage in the 10-12 micron and 3.7 micron atmospheric windows enables AIRS to excel at detecting cirrus clouds. This paper presents global retrievals of cloud top pressure, ice particle size and amount, using the AIRS radiances. Cloud optical depths lower than 0.1 (at 10 μm) have been detected. We also present comparisons between retrievals done using spherical particles to those done using nonspherical particles.
The Atmospheric Infrared Sounder (AIRS), launched in May 2002, is the first of a new generation of high-spectral resolution temperature and humidity sounders for numerical weather prediction and climate change studies. The accuracy of the AIRS radiances, and the validity of the clear sky AIRS Forward Model, have already been demonstrated. This paper presents global daytime measurements by the instrument, showing the effects of NLTE in the 4.3 μm CO2 band. Simulations using upper atmosphere NLTE temperatures are compared to actual AIRS measurements, for various solar angles.
The Atmospheric Infrared Sounder (AIRS) was launched in early May 2002. This new high-spectral resolution sounder is the first of a new generation of temperature and humidity sounders for numerical weather prediction and climate change studies. In addition, AIRS should be able to detect several minor gases, including ozone, carbon monoxide, methane and carbon dioxide. This paper presents a preliminary comparison between observed AIRS spectra and spectra computed from the ECMWF (European Center for Medium Range Forecasting) model fields. A key component of this comparison is the selection of clear fields of view, which we limited to night views over ocean, allowing the use of the relatively well known sea surface emissivity.
The Atmospheric Infrared Sounder (AIRS) was launched in early May 2002. The temperature and humidity fields retrieved from this new high-spectral resolution sounder will be used for numerical weather prediction and climate change studies. This paper presents a comparisons between observed AIRS spectra and spectra computed from profiles using the worldwide radiosonde network, as well as spectra computed from the ECMWF (European Center for Medium Range Weather Forecasts) model fields.
New high-spectral resolution satellite sounders will use channels located between CO2 lines for temperature retrievals. Transmittances for these channels are dominated by spectral line wings that are strongly influenced by line-mixing and duration-of-collision effects. Previous studies demonstrated the importance of Q-branch line mixing for atmospheric sounding in the 15 micrometer region. This work presents an improved model of P/R-branch line mixing and duration-of- collision effects on CO2 transmittances in the 4.3 micrometer and 15 micrometer regions, based on laboratory and spectroscopy data. Most line-by-line codes model non- Lorentzian behavior by using the Cousin chi-function. This empirical function incorporates both P/R line-mixing and duration-of-collision effects by using many parameters. It is common to use the Cousin model parameters obtained from the 4 micrometer band in the 15 micrometer region, overestimating the amount of line-mixing. Comparisons to radiance data taken with high resolution interferometers that fly on NASA's ER-2 partially validates our model. The biggest improvements are at 4.3 micrometer where the differences are reduced by more than 2K, compared to using the Cousin model.
A new monochromatic radiative transfer algorithm based on compressed lookup tables of pre-computed atmospheric molecular absorption coefficients has been developed. These compressed look-up tables are called the kCompressed Database. Our motivation is to compute monochromatic absorption coefficients for any realistic Earth atmospheric situation (pressure, temperature, gas amount) at the same accuracy as a line-by- line code, but faster. In addition, the procedure for producing atmospheric transmittances is extremely simple, and easy to code. Although the kCompressed Database was originally developed to compute layer-to-space transmittances that are needed to produce fast transmittance models for high spectral resolution infrared temperature and humidity sounders, we have now developed a complete (non-scattering) atmospheric radiative transfer code around the kCompressed Database, called kCARTA (for kCompressed Atmospheric Radiative Transfer Algorithm). In addition, Jacobians with respect to gas amount and temperature can be rapidly performed, providing the user insight to the regions to which the measured radiance is most sensitive.
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