The Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP) Version 1 aerosol extinction retrieval algorithm: theoretical basis

Loughman, Robert; Bhartia, P. K.; Chen, Zhong; Xu, Philippe; Nyaku, Ernest; Taha, Ghassan

doi:10.5194/amt-11-2633-2018

Cited by 55 publications

(72 citation statements)

References 82 publications

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“…The measurement vector y m i represents the measured ASI m at tangent height h i = z i . The Gauss-Seidel limb scattering (GSLS) radiative transfer model (Herman et al, 1994(Herman et al, , 1995Loughman et al, 2004Loughman et al, , 2015 calculates the ASI c vector y c i at each iteration, using the extinction profile given by x 1.37 * f c is the coarse-mode fraction, which is the ratio of the number of particles of the coarse mode to the total number of particles for a bimodal lognormal distribution . product provides extinction profiles from cloud-top height to 40 km.…”

Section: Lp Algorithm Descriptionmentioning

confidence: 99%

Improvement of stratospheric aerosol extinction retrieval from OMPS/LP using a new aerosol model

et al. 2018

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The Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP) has been flying on the Suomi National Polar-orbiting Partnership (S-NPP) satellite since October 2011. It is designed to produce ozone and aerosol vertical profiles at ∼ 2 km vertical resolution over the entire sunlit globe. Aerosol extinction profiles are computed with Mie theory using radiances measured at 675 nm. The operational Version 1.0 (V1.0) aerosol extinction retrieval algorithm assumes a bimodal lognormal aerosol size distribution (ASD) whose parameters were derived by combining an in situ measurement of aerosol microphysics with the Stratospheric Aerosol and Gas Experiment (SAGE II) aerosol extinction climatology. Internal analysis indicates that this bimodal lognormal ASD does not sufficiently explain the spectral dependence of LP-measured radiances. In this paper we describe the derivation of an improved aerosol size distribution, designated Version 1.5 (V1.5), for the LP retrieval algorithm. The new ASD uses a gamma function distribution that is derived from Community Aerosol and Radiation Model for Atmospheres (CARMA)-calculated results. A cumulative distribution fit derived from the gamma function ASD gives better agreement with CARMA results at small particle radii than bimodal or unimodal functions. The new ASD also explains the spectral dependence of LP-measured radiances better than the V1.0 ASD. We find that the impact of our choice of ASD on the retrieved extinctions varies strongly with the underlying reflectivity of the scene. Initial comparisons with collocated extinction profiles retrieved at 676 nm from the SAGE III instrument on the International Space Station (ISS) show a significant improvement in agreement for the LP V1.5 retrievals. Zonal mean extinction profiles agree to within 10 % between 19 and 29 km, and regression fits of collocated samples show improved correlation and reduced scatter compared to the V1.0 product. This improved agreement will motivate development of more sophisticated ASDs from CARMA results that incorporate latitude, altitude and seasonal variations in aerosol properties.

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Section: Lp Algorithm Descriptionmentioning

confidence: 99%

Improvement of stratospheric aerosol extinction retrieval from OMPS/LP using a new aerosol model

et al. 2018

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“…The effect of this constant unimodal particle size assumption was estimated to a degree by Rieger et al (2015), but a limited number of geometries and cases were tested. More recently, Loughman et al (2018) estimated the impact of particle size assumptions based on estimates of the phase function, but they did not fully propagate the error through the retrievals. This work extends these previous analyses to additional conditions and geometries and estimates the impact on the retrieved extinction.…”

Section: Particle Sizementioning

confidence: 99%

“…For decades, monitoring of stratospheric aerosols from satellite observations was largely the domain of occultation instruments such as Stratospheric Aerosol and Gas Experiment (SAGE) II. However, since the 2000s aerosol extinction has been retrieved from limb scatter instruments such as the Optical Spectrograph and InfraRed Imaging System (OSIRIS) (Llewellyn et al, 2004;Bourassa et al, 2012, and references therein), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIA-MACHY) (Burrows et al, 1995;Bovensmann et al, 1999;von Savigny et al, 2015, and references therein) and the Ozone Mapping and Profile Suite Limb Profiler (OMPS-LP) (Flynn et al, 2006;Loughman et al, 2018). While limb scatter provides greatly improved global coverage over occultation satellites, it requires additional assumptions and computationally expensive forward models to perform the inversions.…”

Section: Introductionmentioning

confidence: 99%

A study of the approaches used to retrieve aerosol extinction, as applied to limb observations made by OSIRIS and SCIAMACHY

et al. 2018

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Abstract. Limb scatter instruments in the UV-vis spectral range have provided long-term global records of stratospheric aerosol extinction important for climate records and modelling. While comparisons with occultation instruments show generally good agreement, the source and magnitude of the biases arising from retrieval assumptions, approximations in the radiative transfer modelling and inversion techniques have not been thoroughly characterized. This paper explores the biases between SCIAMACHY v1.4, OSIRIS v5.07 and SAGE II v7.00 aerosol extinctions through a series of coincident comparisons as well as simulation and retrieval studies to investigate the cause and magnitude of the various systematic differences. The effect of a priori profiles, particle size assumptions, radiative transfer modelling, inversion techniques and the different satellite datasets are explored. It is found that the assumed a priori profile can have a large effect near the normalization point, as well as systematic influence at lower altitudes. The error due to particle size assumptions is relatively small when averaged over a range of scattering angles, but individual errors depend on the particular scattering angle, particle size and measurement vector definition. Differences due to radiative transfer modelling introduce differences between the retrieved products of less than 10 % on average, but can introduce vertical structure. The combination of the different scenario simulations and the application of both algorithms to both datasets enable the origin of some of the systematic features such as high-altitude differences when compared to SAGE II to be explained.

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“…Typically, the phase function is determined by assuming an aerosol composition of spherical sulfate droplets consisting of ≈75% H 2 SO 4 and 25% H 2 O with a unimodal lognormal particle size distribution, as given by the equation

\frac{normald n false(r false)}{normald r} = \frac{N}{\sqrt{2 π} \ln false(σ_{g} false) r} \exp - \frac{{false(\ln r - \ln r_{g} false)}^{2}}{2 \ln^{2} false(σ_{g} false)},

where r g is the median radius, σ g the distribution width, and N the aerosol number density concentration. However, bimodal and gamma distributions have also been used (Chen et al, ; Loughman et al, ). Errors in these assumptions translate to errors in the phase function used in the radiative transfer and carry through to errors in the retrieved extinction.…”

Section: Introductionmentioning

confidence: 99%

“…Limb scatter aerosol retrievals often use an altitude normalized radiance profile as the measurement vector (e.g., Bourassa, Rieger, et al, ; Loughman et al, ). The altitude normalization decreases sensitivity to upwelling radiation from surface and multiple scattering as well as biases in absolute calibration and radiative transfer modeling.…”

Section: Introductionmentioning

confidence: 99%

A Multiwavelength Retrieval Approach for Improved OSIRIS Aerosol Extinction Retrievals

et al. 2019

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The Optical Spectrograph and InfraRed Imaging System (OSIRIS) on board the Odin satellite has been used to provide vertically resolved aerosol extinction since 2001. The OSIRIS version 5.07 aerosol product has been used in numerous studies and now provides a 17‐year record of global stratospheric aerosol. This work presents the new version 7 OSIRIS aerosol extinction retrieval. A multiwavelength aerosol extinction algorithm has been developed to reduce measurement geometry biases and improve extinction retrieval in the upper troposphere and lower stratosphere. The Chen et al. (2016, https://doi.org/10.5194/amt-9-1239-2016) cloud detection algorithm has been adapted for the OSIRIS wavelength range for improved cloud screening and polar stratospheric cloud detection, and comparisons after volcanic eruptions and with the CALIPSO‐GOCCP product show promising results. The version 7 product shows comparable agreement with version 5.07 when compared to coincident SAGE II and SAGE III measurements, and improved agreement with CALIPSO time series. The algorithm has been applied to the complete set of OSIRIS measurements, and the new data set is now publicly available.

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The Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP) Version 1 aerosol extinction retrieval algorithm: theoretical basis

Cited by 55 publications

References 82 publications

Improvement of stratospheric aerosol extinction retrieval from OMPS/LP using a new aerosol model

Improvement of stratospheric aerosol extinction retrieval from OMPS/LP using a new aerosol model

A study of the approaches used to retrieve aerosol extinction, as applied to limb observations made by OSIRIS and SCIAMACHY

A Multiwavelength Retrieval Approach for Improved OSIRIS Aerosol Extinction Retrievals

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