13 Jun 2023
 | 13 Jun 2023
Status: this preprint is currently under review for the journal AMT.

The Langley Ratio method, a new approach for transferring photometer calibration from direct sun measurements

Antonio Fernando Almansa, África Barreto, Natalia Kouremeti, Ramiro González, Akriti Masoom, Carlos Toledano, Julian Gröbner, Rosa Delia García, Yenny González, Stelios Kazadzis, Stephane Victori, Óscar Álvarez, Virgilio Carreño, Victoria Eugenia Cachorro, and Emilio Cuevas

Abstract. This article presents a new method for transferring calibration from a reference photometer, referred to as the "master'', to a secondary photometer, referred to as the "field'', using a synergetic approach when master and field instruments have different spectral bands. The method was first applied between a PFR, (Precision Filter Radiometer) instrument from the World Optical Depth Research and Calibration Center (WORCC) considered the reference by the WMO (World Meteorological Organization), and a CE318-TS photometer, the standard photometer used by AERONET (AErosol RObotic NETwork). These two photometers have different optics, sun-tracking systems and spectral bands. The Langley Ratio method (LR) proposed in this study was used to transfer calibration to the closest spectral bands for 1-minute synchronous data, for airmasses between 2 and 5, and was compared to the state of the art Langley calibration technique. The study was conducted at two different locations, Izaña Observatory (IZO) and Valladolid, where measurements were collected almost simultaneously over a six-month period under different aerosol regimes. In terms of calibration aspects, our results showed very low relative differences and standard deviations in the calibration constant transferred in Izaña from PFR to Cimel, up to 0.29 % and 0.46 %, respectively, once external factors such as different field-of-view between photometers or the presence of calibration issues were considered. However, these differences were higher in the comparison performed at Valladolid (1.04 %) and in the shorter wavelengths spectral bands (up to 0.78 % in Izaña and 1.61 % in Valladolid). Additionally, the LR method was successfully used to transfer calibrations between different versions of the CE318-T photometer, providing an accurate calibration transfer (0.17 % to 0.69 %) in the morning LRs, even when the instruments had differences in their central wavelengths (Δλ up to 91 nm). Overall, our results indicate that the LR method is a useful tool not only for transferring calibrations but also for detecting and correcting possible instrumental issues. This is exemplified by the temperature dependence on the two Cimel UV spectral bands, which was estimated by means of the LR method to be ~ -0.09x10-2/° in the case of 380 nm and ~ -0.03x10x10-2/° in the case of 340 nm. This estimation served us to implement the first operative temperature correction on ultraviolet (UV) spectral bands.

Antonio Fernando Almansa et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-108', Anonymous Referee #1, 17 Jul 2023
  • RC2: 'Comment on amt-2023-108', Anonymous Referee #2, 28 Jul 2023
  • RC3: 'Comment on amt-2023-108', Anonymous Referee #3, 22 Aug 2023

Antonio Fernando Almansa et al.

Antonio Fernando Almansa et al.


Total article views: 440 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
355 71 14 440 9 9
  • HTML: 355
  • PDF: 71
  • XML: 14
  • Total: 440
  • BibTeX: 9
  • EndNote: 9
Views and downloads (calculated since 13 Jun 2023)
Cumulative views and downloads (calculated since 13 Jun 2023)

Viewed (geographical distribution)

Total article views: 438 (including HTML, PDF, and XML) Thereof 438 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 23 Sep 2023
Short summary
This paper applies sun-photometer synergies to improve calibration transference between different sun-photometers and also enhance their quality assurance and quality control. We have validated this technique using different instrumentation, the WMO-GAW and NASA-AERONET references, under different aerosol regimes using the standard Langley calibration method as a reference.