The "solar Constant" and Related Problems

Langley, S. P.

doi:10.1086/140999

Cited by 18 publications

(11 citation statements)

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“…single scattering albedo, refractive index, phase function, size distribution), which are needed to study the microphysicalchemical properties of the particles and their interaction with radiation, but all networks provide, at least, information about the aerosol optical depth (AOD). The latter serves as a concise index of the atmospheric turbidity, and thus of the aerosol burden, and can be simply determined by estimating the attenuation of the direct solar beam throughout the atmosphere compared to the exoatmospheric irradiance (Langley, 1903).…”

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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“…In those years the main observing sites were Washington, D.C. (39øN) [Langley, 1903b[Langley, , 1904 Abbe [1904] and Kimball [1913] petitioned astronomers to supply any unpublished extinction measurements of starlight. Unfortunately, the resulting sets of stellar data are of little practical value, being uncalibrated and very crude [Stothers, 1996].…”

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confidence: 99%

“…tieth century eruptions before Agung. In those years the main observing sites were Washington, D.C. (39øN) [Langley, 1903b[Langley, , 1904Abbot, 1903;Abbot and Fowle, 1908] and Mount Wilson, California (34øN) [Abbot and Fowle, 1908;Abbot et al, 1913Abbot et al, , 1922. The Washington observations covered the years 1901-1907, and the Mount Wilson ones 1905-1906 and 1908-1920. Two very short series of measurements made at Mount Whitney, California (37øN) in 1909-1910 and at Bassour, Algeria (36øN) in 1912 [Abbot et al, 1913] can be only approximately calibrated and so will not be utilized here.…”

mentioning

confidence: 99%

Stratospheric aerosol clouds due to very large volcanic eruptions of the early twentieth century: Effective particle sizes and conversion from pyrheliometric to visual optical depth

Stothers¹

1997

J. Geophys. Res.

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“…The calibration constant V 0 used to be found by linear extrapolation to zero air mass of measurements V , corrected to mean Sun-Earth distance, and plotted on a logarithmic scale versus air mass. This method is historically called Langley plot calibration (Langley, 1903). Using a single, common air mass m for all components of the total optical depth can lead to significant errors in ln(V 0 ) (e.g., Thomason et al, 1983;Forgan, 1988;Russell et al, 1993;Schmid and Wehrli, 1995;Slusser et al, 2000).…”

Section: Instrument Calibrationmentioning

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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The "solar Constant" and Related Problems

Cited by 18 publications

References 0 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

Stratospheric aerosol clouds due to very large volcanic eruptions of the early twentieth century: Effective particle sizes and conversion from pyrheliometric to visual optical depth

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

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