Sensitivity of aerosol retrieval to geometrical configuration of  ground-based sun/sky radiometer observations

Torres, Benjamín; Dubovik, Оleg; Toledano, Carlos; Berjón, A.; Cachorro, Victoria E.; Lapyonok, T.; Litvinov, Pavel; Goloub, Philippe

doi:10.5194/acp-14-847-2014

Cited by 51 publications

(65 citation statements)

References 30 publications

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“…The fine mode r eff retrieved by both methods ranges between 0.10 and 0.13 µm. Differences between fine mode r eff retrieved by GRASP and AERONET are below 0.02 µm, which are within the uncertainty of the inversions Torres et al, 2014). For the coarse mode, the r eff values obtained by GRASP were 0.03 µm higher than those retrieved by AERONET but the differences are within the uncertainty range.…”

Section: Rascado Et Al 2009supporting

confidence: 50%

Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign

et al. 2017

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Abstract. In this study, vertical profiles and columnintegrated aerosol properties retrieved by the GRASP (Generalized Retrieval of Atmosphere and Surface Properties) algorithm are evaluated with in situ airborne measurements made during the ChArMEx-ADRIMED field campaign in summer 2013. In the framework of this campaign, two different flights took place over Granada (Spain) during a desert dust episode on 16 and 17 June. The GRASP algorithm, which combines lidar and sun-sky photometer data measured at Granada, was used to retrieve aerosol properties. Two sun-photometer datasets are used: one co-located with the lidar system and the other in the Cerro Poyos station, approximately 1200 m higher than the lidar system but at a short horizontal distance.Column-integrated aerosol microphysical properties retrieved by GRASP are compared with AERONET products showing a good agreement. Differences between GRASP retrievals and airborne extinction profiles are in the range of 15 to 30 %, depending on the instrument on board the aircraft used as reference. On 16 June, a case where the dust layer was coupled to the aerosol layer close to surface, the total volume concentration differences between in situ data and GRASP retrieval are 15 and 36 % for Granada and Cerro Poyos retrievals, respectively. In contrast, on 17 June the dust layer was decoupled from the aerosol layer close to the surface, and the differences are around 17 % for both retrievals. In general, all the discrepancies found are within the uncertainly limits, showing the robustness and reliability of the GRASP algorithm. However, the better agreement found for the Cerro Poyos retrieval with the aircraft data and the vertical homogeneity of certain properties retrieved with GRASP, such as the scattering Ångström exponent, for cases with aerosol layers characterized by different aerosol types, shows that uncertainties in the vertical distribution of the aerosol properties have to be considered.The comparison presented here between GRASP and other algorithms (i.e. AERONET and LIRIC) and with airborne in situ measurements shows the potential to retrieve the optical and microphysical profiles of the atmospheric aerosol properties. Also, the advantage of GRASP versus LIRIC is that GRASP does not assume the results of the AERONET inversion as a starting point.

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Section: Rascado Et Al 2009supporting

confidence: 50%

Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign

et al. 2017

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“…We limit ourselves to these polarization-specific sources of uncertainty and defer to the far more detailed investigations in publications such as Torres et al (2014) and Li et al (2010) for other sources of uncertainty.…”

Section: Appendix A: Uncertainty For Instruments With Linear Polarizersmentioning

confidence: 99%

Cloud thermodynamic phase detection with polarimetrically sensitive passive sky radiometers

et al. 2015

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Abstract. The primary goal of this project has been to investigate if ground-based visible and near-infrared passive radiometers that have polarization sensitivity can determine the thermodynamic phase of overlying clouds, i.e., if they are comprised of liquid droplets or ice particles. While this knowledge is important by itself for our understanding of the global climate, it can also help improve cloud property retrieval algorithms that use total (unpolarized) radiance to determine cloud optical depth (COD). This is a potentially unexploited capability of some instruments in the NASA Aerosol Robotic Network (AERONET), which, if practical, could expand the products of that global instrument network at minimal additional cost.We performed simulations that found, for zenith observations, that cloud thermodynamic phase is often expressed in the sign of the Q component of the Stokes polarization vector. We chose our reference frame as the plane containing solar and observation vectors, so the sign of Q indicates the polarization direction, parallel (positive) or perpendicular (parallel) to that plane. Since the fraction of linearly polarized to total light is inversely proportional to COD, optically thin clouds are most likely to create a signal greater than instrument noise. Besides COD and instrument accuracy, other important factors for the determination of cloud thermodynamic phase are the solar and observation geometry (scattering angles between 40 and 60 • are best), and the properties of ice particles (pristine particles may have halos or other features that make them difficult to distinguish from water droplets at specific scattering angles, while extreme ice crystal aspect ratios polarize more than compact particles).We tested the conclusions of our simulations using data from polarimetrically sensitive versions of the Cimel 318 sun photometer/radiometer that compose a portion of AERONET. Most algorithms that exploit Cimel polarized observations use the degree of linear polarization (DoLP

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“…Nonetheless, there is still a large amount of data that do not contain the sky-radiance scans necessary for full AERONET inversions of size distributions, complex re-PM x has a detrimental effect on human health, and is commonly monitored at the ground level in worldwide networks (Rohen et al, 2011;Bennouna et al, 2016). For these reasons, many studies in recent decades use τ a retrieved by satellite sensors to estimate and forecast the surface PM x (Kacenelenbogen et al, 2006;Koelemeijer et al, 2006;Van Donkelaar et al, 2010Vidot et al, 2007;Rohen et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Advanced characterisation of aerosol size properties from measurements of spectral optical depth using the GRASP algorithm

et al. 2017

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Abstract. This study evaluates the potential of using aerosol optical depth (τ a ) measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with different aerosol loads. The direct numerical simulations (selfconsistency tests) indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the finemode radius, width and volume concentration are stable and precise if the real part of the refractive index is known. The coarse-mode properties are less accurate, but they are significantly improved when additional a priori information is available. The tests with random simulated errors show that the uncertainty in the bimodal log-normal size distribution parameters increases as the aerosol load decreases. Similarly, the reduction in the spectral range diminishes the stability of the retrieved parameters. In addition to these numerical studies, we used optical depth observations at eight AERONET locations to validate our results with the standard AERONET inversion products. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as moon photometry. Comparisons of the mode median radii between GRASP-AOD and AERONET indicate average differences of 0.013 µm for the fine mode and typical values of 0.2-0.3 µm for the coarse mode. The dominant mode (i.e. fine or coarse) indicates a 10 % difference in mode radii between the GRASP-AOD and AERONET inversions, and the average of the difference in volume concentration is around 17 % for both modes. The retrieved values of the fine-mode τ a (500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the AERONET spectral deconvolution algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon photometry and the airborne PLASMA sun photometer during the ChArMEx summer 2013 campaign in the western Mediterranean.

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Sensitivity of aerosol retrieval to geometrical configuration of ground-based sun/sky radiometer observations

Cited by 51 publications

References 30 publications

Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign

Comparative assessment of GRASP algorithm for a dust event over Granada (Spain) during ChArMEx-ADRIMED 2013 campaign

Cloud thermodynamic phase detection with polarimetrically sensitive passive sky radiometers

Advanced characterisation of aerosol size properties from measurements of spectral optical depth using the GRASP algorithm

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