Intercomparison of Aerosol Optical Depth from Brewer Ozone spectrophotometers and CIMEL sunphotometers measurements

Cheymol, A.; Sotelino, L. Gonzalez; Lam, Ka Se; Kim, Jhoon; Fioletov, Vitali; Siani, Anna Maria; Backer, H. De

doi:10.5194/acp-9-733-2009

Cited by 16 publications

(13 citation statements)

References 30 publications

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“…Gröbner et al, 2001;Kerr, 2002;Marenco et al, 2002;Cheymol and De Backer, 2003;Arola and Koskela, 2004;Kazadzis et al, 2005;Cheymol et al, 2006Cheymol et al, , 2009De Bock et al, 2010, only one work exists to our knowledge which employs measurements of visible radiation (Gröbner and Meleti, 2004). Although this imbalance is likely to be ascribed to the predominant interest in the aerosol properties in the UV region, several factors could justify further investigation of AODs derived at visible wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens

et al. 2016

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Abstract.A MkIV Brewer spectrophotometer has been operating in Athens since 2004. Direct-sun measurements originally scheduled for nitrogen dioxide retrievals were reprocessed to provide aerosol optical depths (AODs) at a wavelength of about 440 nm. A novel retrieval algorithm was specifically developed and the resulting AODs were compared to those obtained from a collocated Cimel filter radiometer belonging to the Aerosol Robotic Network (AERONET). The series are perfectly correlated, with Pearson's correlation coefficients being as large as 0.996 and with 90 % of AOD deviations between the two instruments being within the World Meteorological Organisation (WMO) traceability limits. In order to reach such a high agreement, several instrumental factors impacting the quality of the Brewer retrievals must be taken into account, including sensitivity to the internal temperature, and the state of the external optics and pointing accuracy must be carefully checked. Furthermore, the long-term radiometric stability of the Brewer was investigated and the performances of in situ Langley extrapolations as a way to track the absolute calibration of the Brewer were assessed. Other sources of error, such as slight shifts of the wavelength scale, are discussed and some recommendations to Brewer operators are drawn. Although MkIV Brewers are rarely employed to retrieve AODs in the visible range, they represent a key source of information about aerosol changes in the past three decades and a potential worldwide network for present and future coordinated AOD measurements. Moreover, a better understanding of the AOD retrieval at visible wavelengths will also contribute in improving similar techniques in the more challenging UV range.

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Section: Introductionmentioning

confidence: 99%

Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens

et al. 2016

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“…The scatter plot of the compared AODs still showed the presence of a few outliers (highlighted in red in Fig. 3), causing the rather low correlation coefficient compared to the one obtained by Cheymol et al (2009) (correlation coefficient of 0.96 for the comparison between Brewer#016 at 320 nm and Cimel at 340 nm). These remarkable outliers require further examination.…”

Section: Comparison Between Brewer Spectrophotometer and Cimel Sunphomentioning

confidence: 99%

“…For this linear regression technique, the calibration quality clear days in the time period for which the AOD is to be calculated, have to be selected. The criteria from Cheymol et al (2009) had to be adapted so that they could be applied on sun scan measurements instead of direct sun measurements. Also, a new criterion, based on the ratio of the observed and expected irradiance for a certain day, was added since the adapted criteria were not sufficient.…”

Section: Discussionmentioning

confidence: 99%

“…This leads to different criteria for the selection of the days on which the LPM can be applied (calibration quality clear days). Cheymol et al (2009) proposed the following criteria:…”

Section: Langley Plot Methodsmentioning

confidence: 99%

“…Arola and Koskela (2004) discussed the systematic errors in the AOD retrieval from Brewer DS measurements, which led to improvements of the conventional Langley Plot Method (e.g. Cheymol et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Aerosol Optical Depth measurements at 340 nm with a Brewer spectrophotometer and comparison with Cimel sunphotometer observations at Uccle, Belgium

et al. 2010

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Abstract. The Langley Plot Method (LPM) is adapted for the retrieval of Aerosol Optical Depth (AOD) values at 340 nm from Brewer#178 sun scan measurements between 335 and 345 nm (convoluted with the band pass function of the Cimel sunphotometer filter at 340 nm) performed in Uccle, Belgium. The use of sun scans instead of direct sun measurements simplifies the comparison of the AOD values with quasi-simultaneous Cimel sunphotometer values. Also, the irradiance at 340 nm is larger than the one at 320.1 nm due to lower ozone absorption, thus improving the signal to noise ratio. For the selection of the cloudless days (from now on referred to as calibration quality clear days), a new set of criteria is proposed. With the adapted method, individual clear sky AOD values, for which the selection criteria are also presented in this article, are calculated for a period from September 2006 until the end of August 2010. These values are then compared to quasi-simultaneous Cimel sunphotometer measurements, showing a very good agreement (the correlation coefficient, the slope and the intercept of the regression line are respectively 0.974, 0.968 and 0.011), which proves that good quality observations can be obtained from Brewer sun scan measurements at 340 nm. The analysis of the monthly and seasonal Brewer AODs at Uccle is consistent with studies at other sites reporting on the seasonal variation of AODs in Europe. The highest values can be observed in summer and spring, whereas more than 50% of the winter AODs are lower than 0.3. On a monthly scale, the lowest AOD are observed in December and the highest values occur in June and April. No clear weekly cycle is observed for Uccle. The current cloud-screening algorithm is still an issue, Correspondence to: V. De Bock (veerle.debock@meteo.be) which means that some AOD values can still be influenced by scattered clouds. This effect can be seen when comparing the calculated monthly mean values of the Brewer with the AERONET measurements.

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On the differences of ultraviolet and visible irradiance calculations in the Mediterranean basin due to model- and satellite-derived climatologies of aerosol optical properties

Nikitidou

Kazantzidis

2012

Int. J. Climatol.

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ABSTRACT:The variability of aerosol optical properties over the Mediterranean basin, in the ultraviolet (UV) and visible (VIS) spectral regions, is examined, using ground-based data from eight stations of the AErosol RObotic NETwork (AERONET), climatological values from the AeroCom (Aerosol Comparisons between Observations and Models) project and data from the MODerate resolution Imaging Spectroradiometer (MODIS) on-board the Terra and Aqua satellites. The aerosol optical properties from the three datasets are used as input data in a radiative transfer model, in order to estimate the differences in irradiance at the ground under cloud-free skies. The MODIS aerosol optical depth climatology shows better agreement with AERONET data. The highest difference in the monthly average values is equal to 0.09 at 550 nm, while the differences between the AERONET and the AeroCom climatologies reach 0.25 and 0.15 in the UV and VIS wavelengths, respectively. As a result, the AERONET modelled VIS and UV irradiances are closer to MODIS, with the absolute differences in average values reaching 15 (6%) and 2 W m -2 (6%), respectively, while absolute differences with AeroCom irradiances can reach up to 30 (12%) and 4.5 W m -2 (12%). The differences are higher in FORTH Crete, Nes Ziona, Sede Boker and Blida, which are influenced by desert dust aerosols. The separate effect on irradiances due to differences in aerosol optical depth and single scattering albedo from the three datasets has been also examined; according to results, the effect of aerosol optical depth is dominant. At this stage, the use of MODIS aerosol climatology would be recommended for calculations of UV and VIS irradiance in the Mediterranean basin. However, the AeroCom climatology, with some further improvements in the dust cycle, could be a valuable tool in future studies in this area, due to the provision of natural and manmade aerosol optical properties with higher spectral resolution.

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Intercomparison of Aerosol Optical Depth from Brewer Ozone spectrophotometers and CIMEL sunphotometers measurements

Cited by 16 publications

References 30 publications

Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens

Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens

Aerosol Optical Depth measurements at 340 nm with a Brewer spectrophotometer and comparison with Cimel sunphotometer observations at Uccle, Belgium

On the differences of ultraviolet and visible irradiance calculations in the Mediterranean basin due to model- and satellite-derived climatologies of aerosol optical properties

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