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

Bock, Veerle De; Backer, H. De; Mangold, Alexander; Delcloo, Andy

doi:10.5194/amt-3-1577-2010

Cited by 23 publications

(34 citation statements)

References 50 publications

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“…The CIMEL sun photometer at Uccle, Brussels, was (AOD) retrievals by comparison with the co-located Brewer spectrophotometer AOD observations (De Bock et al, 2010). Here, CIMEL IWVs are compared with IWVs of the IGS site "BRUS".…”

Section: Cimel Sun Photometermentioning

confidence: 99%

A multi-site intercomparison of integrated water vapour observations for climate change analysis

et al. 2014

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Abstract. Water vapour plays a dominant role in the climate change debate. However, observing water vapour over a climatological time period in a consistent and homogeneous manner is challenging. On one hand, networks of groundbased instruments able to retrieve homogeneous integrated water vapour (IWV) data sets are being set up. Typical examples are Global Navigation Satellite System (GNSS) observation networks such as the International GNSS Service (IGS), with continuous GPS (Global Positioning System) observations spanning over the last 15+ years, and the AErosol RObotic NETwork (AERONET), providing long-term observations performed with standardized and well-calibrated sun photometers. On the other hand, satellite-based measurements of IWV already have a time span of over 10 years (e.g. AIRS) or are being merged to create long-term time series (e.g. GOME, SCIAMACHY, and GOME-2).This study performs an intercomparison of IWV measurements from satellite devices (in the visible, GOME/SCIAMACHY/GOME-2, and in the thermal infrared, AIRS), in situ measurements (radiosondes) and ground-based instruments (GPS, sun photometer), to assess their use in water vapour trends analysis. To this end, we selected 28 sites world-wide for which GPS observations can directly be compared with coincident satellite IWV observations, together with sun photometer and/or radiosonde measurements. The mean biases of the different techniques compared to the GPS estimates vary only between −0.3 to 0.5 mm of IWV. Nevertheless these small biases are accompanied by large standard deviations (SD), especially for the satellite instruments. In particular, we analysed the impact of clouds on the IWV agreement. The influence of specific issues for each instrument on the intercomparison is also investigated (e.g. the distance between the satellite ground pixel centre and the co-located ground-based station, the satellite scan angle, daytime/nighttime differences). Furthermore, we checked if the properties of the IWV scatter plots between these different instruments are dependent on the geography and/or altitude of the station. For all considered instruments, the only dependency clearly detected is with latitude: the SD of the IWV observations with respect to the GPS IWV retrievals decreases with increasing latitude and decreasing mean IWV.

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Section: Cimel Sun Photometermentioning

confidence: 99%

A multi-site intercomparison of integrated water vapour observations for climate change analysis

et al. 2014

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“…Since Brewer #001 has never been moved to a high-altitude and pristine site, which would satisfy the hypothesis of constant AOD during the day actually needed for a Langley plot, a long-term analysis of the data recorded on site was preferred, as often done in the literature (e.g. Cheymol and De Backer, 2003;Cheymol et al, 2006Cheymol et al, , 2009De Bock et al, 2010Gröbner and Meleti, 2004). Also, since only a few AOD measurements per day were scheduled for the Brewer during this period, we cannot perform the Langley plot with such a small number of clear-sky days.…”

Section: In Situ Langley Etc Extrapolationmentioning

confidence: 99%

“…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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“…An additional very likely reason for the good agreement is the fact that both instrument types measure at close wavelengths in the UVB. In earlier studies in which AOD was determined from Brewer DS measurements the validation has so far only been done against measurements at UVA or even VIS wavelengths (Marenco et al, 2002;Cheymol and De Backer, 2003;Cheymol et al, 2006;Gröbner and Meleti, 2004;Kazadzis et al, 2005Kazadzis et al, , 2007De Bock et al, 2010;Kumharn et al, 2012). Also, earlier comparisons of AOD from Brewers of different type have shown larger differences than between the UVPFR and the MkIII Brewer in this study (Kazadzis et al, 2005;Kumharn et al, 2012).…”

mentioning

confidence: 65%

“…The Brewer spectrophotometer is an instrument initially designed for providing total column ozone (TCO) measurements based on the use of direct sun (DS) irradiance measured at specific wavelengths in the short UVA and in the UVB range (e.g., Kerr et al, 1985). During the past years, several attempts have been presented in the literature, which showed the use of the abovementioned Brewer measurements in order to retrieve AOD in the UVB (e.g., Marenco et al, 1997Marenco et al, , 2002Cheymol and De Backer, 2003;Cheymol et al, 2006;Gröbner and Meleti, 2004;Kazadzis et al, 2005Kazadzis et al, , 2007Meleti et al, 2009;De Bock et al, 2010Kumharn et al, 2012). In addition, Arola and Koskela (2004) have discussed the uncertainties and possible systematic errors linked with the Brewer related DS retrieval for AOD.…”

Section: Introductionmentioning

confidence: 99%

Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

et al. 2017

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Abstract. The determination of aerosol properties, especially the aerosol optical depth (AOD) in the ultraviolet (UV) wavelength region, is of great importance for understanding the climatological variability of UV radiation. However, operational retrievals of AOD at the biologically most harmful wavelengths in the UVB are currently only made at very few places. This paper reports on the UVPFR (UV precision filter radiometer) sunphotometer, a stable and robust instrument that can be used for AOD retrievals at four UV wavelengths. Instrument characteristics and results of Langley calibrations at a high-altitude site were presented. It was shown that due to the relatively wide spectral response functions of the UVPFR, the calibration constants (V 0 ) derived from Langley plot calibrations underestimate the true extraterrestrial signals. Accordingly, correction factors were introduced. In addition, the instrument's spectral response functions also result in an apparent air-mass-dependent decrease in ozone optical depth used in the AOD determinations. An adjusted formula for the calculation of AOD, with a correction term dependent on total column ozone amount and ozone air mass, was therefore introduced. Langley calibrations performed 13-14 months apart resulted in sensitivity changes of ≤ 1.1 %, indicating good instrument stability. Comparison with a high-accuracy standard precision filter radiometer, measuring AOD at 368-862 nm wavelengths, showed consistent results. Also, very good agreement was achieved by comparing the UVPFR with AOD at UVB wavelengths derived with a Brewer spectrophotometer, which was calibrated against the UVPFR at an earlier date. Mainly due to non-instrumental uncertainties connected with ozone optical depth, the total uncertainty of AOD in the UVB is higher than that reported from AOD instruments measuring in UVA and visible ranges. However, the precision can be high among instruments using harmonized algorithms for ozone and Rayleigh optical depth as well as for air mass terms. For 4 months of comparison measurements with the UVPFR and a Brewer, the root mean squared AOD differences were found < 0.01 at all the 306-320 nm Brewer wavelengths.

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

Cited by 23 publications

References 50 publications

A multi-site intercomparison of integrated water vapour observations for climate change analysis

A multi-site intercomparison of integrated water vapour observations for climate change analysis

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

Aerosol optical depth determination in the UV using a four-channel precision filter radiometer

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