Validation of the Atmospheric Infrared Sounder radiative transfer algorithm

Abstract

[1] Comparisons between observed AIRS radiances and radiances computed from coincident in situ profile data are used to validate the accuracy of the AIRS radiative transfer algorithm (RTA) used in version 4 processing at Goddard Space Flight Center. In situ data sources include balloon-borne measurements with RS-90 sensors and frost point hygrometers and Raman lidar measurements of atmospheric water vapor. Estimates of the RTA accuracy vary with wave number region but approach 0.2 K in mid-to lowertropospheric temperature and water vapor sounding channels. Temperature channel radiance biases using ECMWF forecast/analysis products are shown to be essentially identical to those observed with coincident sonde observations, with somewhat higher biases in water vapor channels. Some empirical adjustments to the RTA channel-averaged absorption coefficients were required to achieve these stated accuracies.

Matching radiative transfer models and radiosonde data from the EPS/Metop Sodankylä campaign to IASI measurements

“…In order to do this, we need to be absolutely certain that we have a very precise atmospheric state vector and surface properties or we need to have a sufficient number of observations to statistically reduce the noise in them (e.g., Strow et al, 2006).…”

Corrigendum to "First direct observation of the atmospheric CO<sub>2</sub> year-to-year increase from space" published in Atmos. Chem. Phys., 7, 4249–4256, 2007

“…In summary, we conclude that we would like to refer readers of our manuscript to information given in three other manuscripts not cited in Buchwitz et al (2007), namely Chédin et al (2002Chédin et al ( , 2003 and Strow et al (2006). We also conclude that the title of our paper now appears somewhat general and not sufficiently specific to atmospheric CO 2 columns.…”

“…We refer in the title of our manuscript to atmospheric CO 2 , in contrast to the mid tropospheric CO 2 observed by the TIR CO 2 retrievals, but we now think that it would have been clearer to explicitely mention in the title of our manuscript that our results refer to CO 2 columns (in our abstract this is mentioned). In conclusion, we would like to take this opportunity to cite and draw attention to the results provided in Chédin et al (2002Chédin et al ( , 2003 and Strow et al (2006), which we consider important examples of the use of remote sensing to understand the behavior of CO 2 in the atmosphere. Similarly we consider that one optimal way to obtain global information about CO 2 is to combine satellite NIR and TIR measurements as discussed in for example Burrows et al (2004) for several tropospheric trace gases.…”

“…In addition, both papers focus on the tropical region because this enables to better decorrelate CO 2 from temperature variations. Strow et al (2006) focusses on AIRS radiances and discusses differences to radiative transfer simulations based on ECMWF temperature profiles. Apart from the different temperature sensitivities there are several other important differences between the NIR and the TIR measurements.…”

Deriving clear-sky longwave spectral flux from spaceborne hyperspectral radiance measurements: a case study with AIRS observations

“…Compared with AIRS observations, MODTRAN 5 replicates AIRS brightness temperatures over 650-1600 cm −1 with a mean difference of ∼ 0.2 K (the AIRS noise equivalent delta temperature (NEDT) being 0.51 K over this band) (Anderson et al, 2007). AIRS radiances are generated by convoluting MODTRAN 5 output and tabulated spectral response functions of AIRS channels (Strow et al, 2006). The TOA spectral fluxes are computed using a three-point Gaussian quadrature (Clough and Iacono, 1995).…”