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Abstract
Visible and infrared binocular all-sky-view cameras can provide continuous and complementary ground-based cloud observations. Accurate angular calibration for every pixel is an essential premise to further cloud analysis and georeferencing. However, most current calibration methods mainly rely on calibration plates, which still remains difficult for simultaneously calibrating visible and infrared binocular cameras, especially with different imaging resolutions. Thus, in this study, we present a simple and convenient angular calibration method for wide field-of-view visible and infrared binocular cameras. Without any extra instruments, the proposed method only utilizes the relation between the angular information of direct sun lights and the projected sun pixel coordinates to compute the geometric imaging parameters of the two cameras. According to the obtained parameters, the pixel-view-angle for the visible and infrared all-sky images is efficiently computed via back projection. Meanwhile, the projected pixel coordinates for the incident lights at any angle can also be computed via reprojection. Experimental results show the effectiveness and accuracy of the proposed angular calibration through the error estimation of reprojection and back projection. As a novel application, we successfully achieve visible and infrared binocular image registration at the pixel level after finishing angular calibration, which not only verifies the accuracy of calibration results, but also contributes to further cloud parameter analysis under these two different imaging features. The registration results, to our knowledge, also provide a reference for the current blank in visible and infrared binocular cloud image registration.
Highlights
The complex interactions among clouds, aerosols, and radiation have significant impacts on climate change and the hydrological cycle [1,2]
The angular calibration of visible and infrared binocular all-sky-view cameras using sun positions and their accuracy experiments are performed
The results prove the feasibility of calculated through estimated imaging parameters (Section 3.2)
Summary
The complex interactions among clouds, aerosols, and radiation have significant impacts on climate change and the hydrological cycle [1,2]. Visible and infrared all-skyview cameras are powerful, ground-based cloud observation equipment [3,4,5], and some have been deployed on many meteorological observation networks dedicated to clouds–. The most common studies use all-sky-view cameras to detect clouds and derive the local cloud cover [6,7,8,9], as a comparison to and validation of human observation and satellite observation [10,11]. The combination of visible and infrared all-sky-view cameras provides complementary and continuous whole sky information and has better advantages for ground-based cloud observation through multi-channel imaging features.
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