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

Abstract

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.

Vapor d\'água atmosférico a partir de imagens radiométricas no infravermelho

“…Parte dos resultados apresentados neste trabalho corresponde a um artigo publicado na revista Atmospheric Measurement Techniques (Hack et al , 2023)…”