Information contents of satellite aerosol extinction measurements and accuracy of aerosol microstructure retrieval.
Abstract
The airborne and satellite solar-occultation measurements (MK-IV, SAGE-II, III, HALOE, etc.) as well as limb atmospheric emission measurements (CLAES, ISAMS) allow the retrieving of spectral and altitudinal aerosol extinction coefficients (AEC). The aerosol size distribution function (SDF) and it's integral parameters such as total concentration N, surface area S and volume V of aerosol optically active particles can also be retrieved from the AEC measurements. In our study, the solution of the inverse problem with respect to microphysical parameters is assumed to be belonged to the statistical ensemble. On the basis of a statistical model of background aerosol microstructure in the stratosphere (large ensembles of SDF and complex refractive index (CRI)) the AEC values by Mie algorithms have been calculated. The appropriate covariance matrices for the aerosol microstructure and AEC have been constructed and analyzed. The information content of AEC satellite measurements (Shannon information, etc.) and the accuracy of retrieving the aerosol SDF and its integral functional (N, S and V) from AEC measurements using the various a priori information have been analyzed for different spectral measurement schemes (SAGE- II and III, HALOE, ISAMS, CLAES, IR interferometer). It has been shown that the use of the modeled aerosol statistics as a priori information (optimal estimation algorithm) yields the highest SDF retrieval accuracy from SAGE measurements but the input of AEC measurements in the solution of the inverse problem is rather small (10-20%). When general a priori information is used (e.g., the method of minimal a priori information), the input of AEC measurements is higher (25-65%), but the accuracy of SDF retrieval is worse. The accuracy of the microphysics retrieval from the AEC measurements of different satellite instruments and combined schemes with a wide spectral range from 0.38 to 16m has been studied. The scheme of combined measurements in two spectral ranges (visual and IR) makes it possible: - to enlarge the aerosol size dispersion for which the SDF is retrieved with good accuracy (better than V 50-100% relative accuracy) from 0.11-0.61m (SAGE III) and 0.11-3.1m (IR measurements) to 0.06-3.1m (combined measurements); - to enhance considerably the S and V retrieval accuracy and to a lesser degree the N retrieval accuracy. The examples of S and V retrievals from the AEC SAGE-III and HALOE measurements have been shown. Systematic discrepancy in retrieved profiles of S and V obtained from HALOE and SAGE-III AEC measurements is observed and analyzed. It has been shown that retrieval of the SDF integral parameters is weakly dependent on the used a priori aerosol statistics.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.A33C0933T
- Keywords:
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- 1610 Atmosphere (0315;
- 0325);
- 1640 Remote sensing (1855)