A critical analysis of the Stratospheric Aerosol and Gas Experiment II spectral inversion algorithm

Fussen, D.

doi:10.1029/97jd03737

Cited by 6 publications

(4 citation statements)

References 12 publications

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“…The problem of retrieving species density profiles from the measured intensity data can be divided into two distinct steps (e.g., Kyrölä et al, 1993;Fussen et al, 1997;Fussen, 1998): First, transmission data from a number of wavelength channels are used in a "spectral inversion" in order to estimate the composition of the atmospheric gas for each individual sounding ray, i.e., for each tangent height. Having subsequently performed this for all rays (data points) of an occultation event, this yields along-ray columnar content profiles for all species included.…”

Section: Introductionmentioning

confidence: 99%

Error analysis for mesospheric temperature profiling by absorptive occultation sensors

Rieder

Kirchengast

2001

Ann. Geophys.

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Abstract. An error analysis for mesospheric profiles retrieved from absorptive occultation data has been performed, starting with realistic error assumptions as would apply to intensity data collected by available high-precision UV photodiode sensors. Propagation of statistical errors was investigated through the complete retrieval chain from measured intensity profiles to atmospheric density, pressure, and temperature profiles. We assumed unbiased errors as the occultation method is essentially self-calibrating and straight-line propagation of occulted signals as we focus on heights of 50-100 km, where refractive bending of the sensed radiation is negligible. Throughout the analysis the errors were characterized at each retrieval step by their mean profile, their covariance matrix and their probability density function (pdf). This furnishes, compared to a variance-only estimation, a much improved insight into the error propagation mechanism. We applied the procedure to a baseline analysis of the performance of a recently proposed solar UV occultation sensor (SMAS -Sun Monitor and Atmospheric Sounder) and provide, using a reasonable exponential atmospheric model as background, results on error standard deviations and error correlation functions of density, pressure, and temperature profiles. Two different sensor photodiode assumptions are discussed, respectively, diamond diodes (DD) with 0.03% and silicon diodes (SD) with 0.1% (unattenuated intensity) measurement noise at 10 Hz sampling rate. A factor-of-2 margin was applied to these noise values in order to roughly account for unmodeled cross section uncertainties. Within the entire height domain (50-100 km) we find temperature to be retrieved to better than 0.3 K (DD) / 1 K (SD) accuracy, respectively, at 2 km height resolution. The results indicate that absorptive occultations acquired by a SMAS-type sensor could provide mesospheric profiles of fundamental variables such as temperature with unprecedented accuracy and vertical resolution. A major part of the error analysis also applies to refractive (e.g., Global Navigation Satellite System based)Correspondence to: G. Kirchengast (gottfried.kirchengast@kfunigraz.ac.at) occultations as well as to any temperature profile retrieval based on air density or major species density measurements (e.g., from Rayleigh lidar or falling sphere techniques).

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Section: Introductionmentioning

confidence: 99%

Error analysis for mesospheric temperature profiling by absorptive occultation sensors

Rieder

Kirchengast

2001

Ann. Geophys.

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“…Since the spectral variation of the 16 showed that the application of the Angstrom law to SAGE II aerosol extinction data could result in errors of 5-10 % in the extinction coefficient. According to the estimates given by Fussen 6 the operational SAGE II algorithm yields a 5-15% error in aerosol extinction at a wavelength of 0.6 µm. He showed how a cubic fit to the aerosol extinction spectral dependence could give noticeably better results.…”

Section: Review Of Available Methodsmentioning

confidence: 99%

Optimal eigenanalysis for the treatment of aerosols in the retrieval of atmospheric composition from transmission measurements

et al. 2003

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The separation of the individual contributions of aerosol and gases to the total attenuation of radiation through the atmosphere has been the subject of much scientific investigation since remote sensing experiments first began. We describe a new scheme to account for the spectral variation of the aerosol extinction in the inversion of transmission data from occultation measurements. Because the spectral variation of the aerosol extinction is generally unknown,the inversion problem is underdetermined and cannot be solved without a reduction in the number of unknowns in the set of equations used to describe the attenuation at each wavelength. This reduction can be accomplished by a variety of methods, including use of a priori information, the parameterization of the aerosol spectral attenuation, and the specification of the form of the aerosol size distribution. We have developed and implemented a parameterization scheme based on existing empirical and modeled information about the microphysical properties of aerosols. This scheme employs the eigenvectors from an extensive set of simulations to parameterize the aerosol extinction coefficient for incorporation into the inversion algorithm. We examine the accuracy of our method using data sets containing over 24,000 extinction spectra and compare it with that of another scheme that is currently implemented in the Polar Ozone and Aerosol Measurement (POAM) satellite experiment. In simulations using 80 wavelengths in the UV-visible-near-IR spectral range of the Stratospheric Aerosol and Gas Experiment III (SAGE) instrument, we show that, for our optimal parameterization, errors below 1% are observed in 80% of cases, whereas only approximately 20% of all cases are as accurate as this in a quadratic parameterization employing the logarithm of the wavelength.

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“…The aerosol optical depth parameterization described in was selected to keep the inversion linear. Fussen [1998] has shown that a polynomial interpolation of aerosol extinction with wavelength is preferable to methods that implicitly attempt to solve for the parameters of the underlying aerosol size distribution. For the nitrogen dioxide channels, a second order fit is done using the aerosol extinctions at 385, 441, and 521 nm, and for the midvisible ozone channels, a third order fit is done using the aerosol extinctions at 441, 521, 676, and 756 nm.…”

Section: Inversionmentioning

confidence: 99%

“…Previous studies [e.g., Steele and Turco , 1997a; Fussen , 1998] have shown that SAGE II retrievals of ozone are susceptible to biases related to the level of volcanic aerosol. The problem stems from uncertainty in separating the aerosol and gas contributions to the measured extinction.…”

Section: Simulated Retrievalsmentioning

confidence: 99%

A semisimultaneous inversion algorithm for SAGE III

Ward

2002

J.‐Geophys.‐Res.

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[1] The Stratospheric Aerosol and Gas Experiment (SAGE) III instrument was successfully launched into orbit on 10 December 2001. The planned operational species separation inversion algorithm will utilize a stepwise retrieval strategy. This paper presents an alternative, semisimultaneous species separation inversion that simultaneously retrieves all species over user-specified vertical intervals or blocks. By overlapping these vertical blocks, retrieved species profiles over the entire vertical range of the measurements are obtained. The semisimultaneous retrieval approach provides a more straightforward method for evaluating the error coupling that occurs among the retrieved profiles due to various types of input uncertainty. Simulation results are presented to show how the semisimultaneous inversion can enhance understanding of the SAGE III retrieval process. In the future, the semisimultaneous inversion algorithm will be used to help evaluate the results and performance of the operational inversion. Compared to SAGE II, SAGE III will provide expanded and more precise spectral measurements. This alone is shown to significantly reduce the uncertainties in the retrieved ozone, nitrogen dioxide, and aerosol extinction profiles for SAGE III. Additionally, the well-documented concern that SAGE II retrievals are biased by the level of volcanic aerosol is greatly alleviated for SAGE III.

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A critical analysis of the Stratospheric Aerosol and Gas Experiment II spectral inversion algorithm

Cited by 6 publications

References 12 publications

Error analysis for mesospheric temperature profiling by absorptive occultation sensors

Error analysis for mesospheric temperature profiling by absorptive occultation sensors

Optimal eigenanalysis for the treatment of aerosols in the retrieval of atmospheric composition from transmission measurements

A semisimultaneous inversion algorithm for SAGE III

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