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

Rieger, Landon; Malinina, Elizaveta; Rozanov, A.; Burrows, J. P.; Bourassa, A. E.; Degenstein, D. A.

doi:10.5194/amt-11-3433-2018

Cited by 34 publications

(55 citation statements)

References 28 publications

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“…The two fitted parameters (α = 1.8 and β = 20.5) determined from the GD fit at 20 km produce an AE of 2.0 and a r eff of 0.18 µm. These values match the average values determined from SAGE II Version 7.0 data (Thomason et al, 2008;Damadeo et al, 2013) during the 2000-2005 period. Hereafter, this resultant ASD derived from the CARMA results will be labeled as V1.5 ASD, while the ASD assumed in LP V1 will be labeled as V1.0 ASD.…”

Section: Z Chen Et Al: Improvement Of Omps/lp Aerosol Retrievalsupporting

confidence: 83%

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: Z Chen Et Al: Improvement Of Omps/lp Aerosol Retrievalsupporting

confidence: 83%

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

et al. 2018

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“…The aerosol extinction coefficient is retrieved by employing the general approach as used for SCIAMACHY v1.4 stratospheric aerosol extinction product (Rieger et al, 2017). As a consequence of a coarser spectral resolution, the radiance measured at 750 nm is affected by the O 2 absorption band.…”

Section: Aerosol Treatmentmentioning

confidence: 99%

Retrieval of ozone profiles from OMPS limb scattering observations

et al. 2018

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Abstract. This study describes a retrieval algorithm developed at the University of Bremen to obtain vertical profiles of ozone from limb observations performed by the Ozone Mapper and Profiler Suite (OMPS). This algorithm is based on the technique originally developed for use with data from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument. As both instruments make limb measurements of the scattered solar radiation in the ultraviolet (UV) and visible (Vis) spectral ranges, an underlying objective of the study is to obtain consolidated and consistent ozone profiles from the two satellites and to produce a combined data set. The retrieval algorithm uses radiances in the UV and Vis wavelength ranges normalized to the radiance at an upper tangent height to obtain ozone concentrations in the altitude range of 12–60 km. Measurements at altitudes contaminated by clouds in the instrument field of view are identified and filtered out. An independent aerosol retrieval is performed beforehand and its results are used to account for the stratospheric aerosol load in the ozone inversion. The typical vertical resolution of the retrieved profiles varies from ∼  2.5 km at lower altitudes ( < 30 km) to ∼  1.5 km (about 45 km) and becomes coarser at upper altitudes. The retrieval errors resulting from the measurement noise are estimated to be 1–4 % above 25 km, increasing to 10–30 % in the upper troposphere. OMPS data are processed for the whole of 2016. The results are compared with the NASA product and validated against profiles derived from passive satellite observations or measured in situ by balloon-borne sondes. Between 20 and 60 km, OMPS ozone profiles typically agree with data from the Microwave Limb Sounder (MLS) v4.2 within 5–10 %, whereas in the lower altitude range the bias becomes larger, especially in the tropics. The comparison of OMPS profiles with ozonesonde measurements shows differences within ±5 % between 13 and 30 km at northern middle and high latitudes. At southern middle and high latitudes, an agreement within 5–7 % is also achieved in the same altitude range. An unexpected bias of approximately 10–20 % is detected in the lower tropical stratosphere. The processing of the 2013 data set using the same retrieval settings and its validation against ozonesondes reveals a much smaller bias; a possible reason for this behaviour is discussed.

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“…The Ångström exponent (AE) is derived from Equation (1) using the 525 nm and 1020 nm extinction coefficients (Nyaku, 2016 Comparison of the extinction coefficients derived from OPC measurements and SAGE II occultation have shown differences that vary by more than 50% depending on altitude and for a volcanic period and less that 50% on the average for non-volcanic periods (Kovilakam and Deshler, 2015). Also Rieger et al (2018) have shown that the differences in the lognormal parameters can induce errors of 30% in the aerosol extinction retrievals for OSIRIS geometries and 50% for SCIAMACHY geometries when the correct AE is used. These analyses illustrate the importance of the assumed value of P a (Θ) for LS retrievals of K ext , 80 and the limitations of using AE alone to estimate the value of P a (Θ).…”

Section: Ae =mentioning

confidence: 99%

A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from OPC measurements

Nyaku

Loughman

Bhartia

et al. 2019

Preprint

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A series of in situ measurements made by optical particle counters (OPC) at Laramie, Wyoming provides size-resolved stratospheric aerosol concentration data for the period of 2008-2017. These data are analyzed in this study for the purpose of assessing the sensitivity of the stratospheric aerosol phase function to the aerosol size distribution (ASD) model used to fit the measurements. The two unimodal ASD models investigated are the uni-modal lognormal (UMLN) and gamma distribution 5 models, with the minimum χ 2 method employed to assess how well each ASD fits the measurements. The aerosol phase function (APF) for each ASD is calculated using Mie theory, and is compared to the APF derived from the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics module. Comparing the χ 2 values for the fits at altitudes 20 km and 25 km shows that the UMLN distribution better represents the OPC measurements. The importance of data at aerosol radius below 0.1 µm is also demonstrated: When these data are not available from OPC measurements, the 10 gamma distribution provides a more stable derived APF. The gamma distribution also fits the CARMA model results better than the UMLN model, when the CARMA model results are binned to mimic the OPC measurement bins (and therefore measurements between 0.05 and 0.1 µm are excluded).

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

Cited by 34 publications

References 28 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

Retrieval of ozone profiles from OMPS limb scattering observations

A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from OPC measurements

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