A Four-Year Lidar–Sun Photometer Aerosol Study at São Paulo, Brazil

Landulfo, Eduardo; Papayannis, Alexandros; Torres, Ani Sobral; Uehara, Sandro Toshio; Pozzetti, Lucila Maria Viola; Matos, Caio Alencar de; Sawamura, Patrícia; Nakaema, Walter M.; Jesus, Wellington De

doi:10.1175/2007jtecha984.1

Cited by 8 publications

(5 citation statements)

References 15 publications

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“…In this regard, however, the São Paulo site, located in the southeastern region of Brazil, presents challenges in the analysis of measurements. Given the number of distinct aerosol sources within the city, combined with those brought by long-and mid-range regional transport, the São Paulo atmosphere is frequently filled by an amalgam of many different types of aerosols (Miranda and Andrade, 2005;Landulfo et al, 2008).…”

Section: Validation Methodologymentioning

confidence: 99%

Evaluating CALIPSO's 532 nm lidar ratio selection algorithm using AERONET sun photometers in Brazil

2013

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Abstract. Since the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite first began probing the Earth's atmosphere on 13 June 2006, several research groups dedicated to investigating the atmosphere's optical properties have conducted measurement campaigns to validate the CALIPSO data products. Recently, in order to address the lack of CALIPSO validation studies in the Southern Hemisphere, and especially the South American continent, the Lasers Environmental Applications Research Group at Brazil's Nuclear and Energy Research Institute (IPEN) initiated efforts to assess CALIPSO's aerosol lidar ratio estimates using the AERONET sun photometers installed at five different locations in Brazil. In this study we develop a validation methodology to evaluate the accuracy of the modeled values of the lidar ratios used by the CALIPSO extinction algorithms. We recognize that the quality of any comparisons between satellite and ground-based measurements depends on the degree to which the instruments are collocated, and that even selecting the best spatial and temporal matches does not provide an unequivocal guarantee that both instruments are measuring the same air mass. The validation methodology presented in this study therefore applies backward and forward air mass trajectories in order to obtain the best possible match between the air masses sampled by the satellite and the ground-based instruments, and thus reduces the uncertainties associated with aerosol air mass variations. Quantitative comparisons of lidar ratios determined from the combination of AERONET optical depth measurements and CALIOP integrated attenuated backscatter measurements show good agreement with the model values assigned by the CALIOP algorithm. These comparisons yield a mean percentage difference of −1.5 % ± 24 %. This result confirms the accuracy in the lidar ratio estimates provided by the CALIOP algorithms over Brazil to within an uncertainty range of no more than 30 %.

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Section: Validation Methodologymentioning

confidence: 99%

Evaluating CALIPSO's 532 nm lidar ratio selection algorithm using AERONET sun photometers in Brazil

2013

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“…Finally, the Fernald-Klett method extends when considering two different aerosol layers. We will refer to the inversion using aerosol optical depth (AOD) measurements in a single layer (the surface layer) (Marenco et al, 1997;Takamura et al, 1994;Landulfo et al, 2008;Kovalev and Eichinger, 2005) as the one-layer method and to the use of AOD measurements in two atmospheric layers as the twolayer method. In the latter methodology we include measure- Figure 1.…”

Section: Introductionmentioning

confidence: 99%

A 10-year characterization of the Saharan Air Layer lidar ratio in the subtropical North Atlantic

et al. 2019

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Abstract. Particle extinction-to-backscatter ratio (lidar ratio) is a key parameter for a correct interpretation of elastic lidar measurements. Of particular importance is the determination of the lidar ratio of the Saharan Air Layer mineral dust transported into the free troposphere over the North Atlantic region. The location of the two sun photometer stations managed by the Izaña Atmospheric Research Centre (IARC) on the island of Tenerife and a decade of available micropulse lidar (MPL) data allow us to determine the lidar ratio under almost pure-dust conditions. This result can be considered representative of the Saharan dust transported westward over the North Atlantic in the subtropical belt. Three different methods have been used to calculate the lidar ratio in this work: (1) using the inversion of sky radiance measurements from a sun–sky photometer installed at the Izaña Observatory (2373 m a.s.l.) under free-troposphere conditions; (2) the one-layer method, a joint determination using a micropulse lidar sited at the Santa Cruz de Tenerife sea-level station and photometric information considering one layer of aerosol characterized by a single lidar ratio; and (3) the two-layer method, a joint determination using the micropulse lidar and photometric information considering two layers of aerosol with two different lidar ratios. The one-layer method only uses data from a co-located photometer at Santa Cruz de Tenerife, while the two-layer conceptual approach incorporates photometric information at two heights from the observatories of Izaña and Santa Cruz de Tenerife. The almost pure-dust lidar ratio retrieval from the sun–sky photometer and from the two-layer method give similar results, with lidar ratios at 523 nm of 49 ± 6 and 50 ± 11 sr. These values obtained from a decade of data records are coincident with other studies in the literature reporting campaigns in the subtropical North Atlantic region. This result shows that the two-layer method is an improved conceptual approach compared to the single-layer approach, which matches the real lower-troposphere structure well. The two-layer method is able to retrieve reliable lidar ratios and therefore aerosol extinction profiles despite the inherent limitations of the elastic lidar technique. We found a lack of correlation between lidar ratio and Ångström exponent (α), which indicates that the dust lidar ratio can be considered independent of dust size distribution in this region. This finding suggests that dust is, under most atmospheric conditions, the predominant aerosol in the North Atlantic free troposphere, which is in agreement with previous studies conducted at the Izaña Observatory.

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“…While these two sensors are situated within 400 m of each other, analysis of measurements from the São Paulo site nevertheless faces challenges. Given the number of distinct aerosol sources within the city, combined with those brought by longand mid-range regional transport, the São Paulo atmosphere is frequently filled by an amalgam of many different types of aerosols (Miranda and Andrade, 2005;Landulfo et al, 2008).…”

Section: Validation Methodologymentioning

confidence: 99%

Assessment of the CALIPSO Lidar 532 nm version 3 lidar ratio models using a ground-based lidar and AERONET sun photometers in Brazil

Lopes¹,

Landulfo²,

Vaughan³

2013

Preprint

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Since the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite first began probing the Earth's atmosphere on 13 June 2006, several research groups dedicated to investigating the atmosphere's optical properties have conducted measurement campaigns to validate the CALIPSO data products. Recently, in order to address the lack of CALIPSO validation studies in the Southern Hemisphere, and especially the South American continent, the Lasers Environmental Applications Research Group at Brazil's Nuclear and Energy Research Institute (IPEN) initiated efforts to assess CALIPSO's aerosol lidar ratio estimates using two ground-based remote sensing instruments: a single elastic backscatter lidar system and the AERONET sun photometers installed at five different locations in Brazil. In this study we develop a validation methodology to assess the accuracy of the modeled values of the lidar ratios used by the CALIPSO extinction algorithms. We recognize that the quality of any comparisons between satellite and ground-based measurements depends on the degree to which the instruments are collocated, and that even selecting the best spatial and temporal matches does not provide an unequivocal guarantee that both instruments are measuring the same air mass. The validation methodology presented in this study therefore applies backward and forward air mass trajectories in order to obtain the best possible match between the air masses sampled by the satellite and the ground-based instruments, and thus reduces the uncertainties associated with aerosol air mass variations. Quantitative comparisons of lidar ratio values determined from the combination of AERONET optical depth measurements and CALIOP integrated attenuated backscatter show good agreement with the model values assigned by the CALIOP algorithm. These comparisons yield a mean percentage difference of −2% ± 26%. Similarly, lidar ratio values retrieved by the elastic backscatter lidar system at IPEN show a mean percentage difference of −2% ± 15% when compared with CALIOP's lidar ratio. These results confirm the accuracy in the lidar ratio estimates provided by the CALIOP algorithms to within an uncertainty range of no more than 30%

show abstract

A Four-Year Lidar–Sun Photometer Aerosol Study at São Paulo, Brazil

Cited by 8 publications

References 15 publications

Evaluating CALIPSO's 532 nm lidar ratio selection algorithm using AERONET sun photometers in Brazil

Evaluating CALIPSO's 532 nm lidar ratio selection algorithm using AERONET sun photometers in Brazil

A 10-year characterization of the Saharan Air Layer lidar ratio in the subtropical North Atlantic

Assessment of the CALIPSO Lidar 532 nm version 3 lidar ratio models using a ground-based lidar and AERONET sun photometers in Brazil

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