Preprints
https://doi.org/10.5194/amt-2022-283
https://doi.org/10.5194/amt-2022-283
 
24 Oct 2022
24 Oct 2022
Status: this preprint is currently under review for the journal AMT.

Precipitable water vapor retrievals using a ground infrared sky camera in subtropical South America

Elion Daniel Hack1, Theotonio Pauliquevis2, Henrique Melo Jorge Barbosa1,3, Marcia Akemi Yamasoe4, Dimitri Klebe5, and Alexandre Lima Correia1 Elion Daniel Hack et al.
  • 1Institute of Physics, University of Sao Paulo, Sao Paulo, Brazil
  • 2Department of Environmental Sciences, Federal University of Sao Paulo, Diadema, Brazil
  • 3Department of Physics, University of Maryland Baltimore County, Baltimore, USA
  • 4Instituto de Astronomia, Geofísica e Ciências Atmosféricas, University of Sao Paulo, Sao Paulo, Brazil
  • 5Solmirus Corporation, Colorado Springs, CO, USA

Abstract. The atmospheric precipitable water vapor (PWV) is a critical quantity in fast-changing weather processes. Current retrieval techniques lack the spatial and/or temporal resolution necessary for a full PWV characterization. Here we investigate a retrieval method using an all-sky ground camera comprising a 14-bit 644 x 512-pixel microbolometer sensor array. The radiometrically calibrated infrared downwelling spectral radiance, Lλ, was acquired at rates of up to 3 min−1. For the studied site (23.56° S, 46.74° W, 786 m asl) and spectral interval, Lλ is sensitive to the PWV, the vertical distribution of humidity, and their temporal, spatial, or seasonal variations. By comparing measured and simulated Lλ, we show the PWV can be retrieved from prior knowledge about the local humidity profile. This information can originate from radiosonde data or statistical analysis of past vertical humidity distributions. Comparison with sunphotometer PWV retrievals, for stable atmospheric conditions, showed an agreement of the average PWV within 2.8 % and a precision of subsequent retrievals of 1.9 %. The PWV was also retrieved as a bidimensional array, allowing the investigation of spatial inhomogeneities of humidity distribution. The method can be used for day or nighttime retrievals, under partly cloudy sky conditions. Potential applications include studies on convection initiation processes.

Elion Daniel Hack et al.

Status: open (until 02 Jan 2023)

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  • RC1: 'Comment on amt-2022-283', Anonymous Referee #1, 25 Nov 2022 reply

Elion Daniel Hack et al.

Elion Daniel Hack et al.

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Short summary
Water vapor is a key factor when seeking to understand fast-changing processes when clouds and storms form and develop. We show here how images from a calibrated infrared camera can be used to derive how much water vapor there is in the atmosphere at a given time. Comparing our results to an established technique, for a case of stable atmospheric conditions, we found an agreement within 2.8 %. Water vapor sky maps can be retrieved every few minutes, day or night, and under partly cloudy skies.