PhixCam: A Tool to Georeference Images Captured by Visible Cameras with Applications for Volcano Monitoring

Highlights: What are the main findings? Inadequate calibration of visible cameras can induce significant effects on our estimates of column height or the position of ballistic products and, therefore, on any derived volcanological parameter. PhixCam is a user-friendly program that allows volcanologists to georeference in the 3D space the position of objects tracked in visible camera frames, when a given transport plane is assumed. What is the implication of the main findings? We have shown the operative potential of Phixcam, which provides data to volcano observatories that can be used to interpret the height of volcanic products when they are dispersed in specific directions, as well as the associated uncertainty. This program can be adopted to analyze historical pictures of volcanic events and estimate their eruption source parameters. Visible cameras are widely adopted low-cost instruments for volcano monitoring. Images can be used to characterize volcanic activity of variable intensity and style and to estimate key eruption source parameters that are essential for assessing volcanic hazards. Nevertheless, the analysis of images from visible cameras is subject to significant sources of uncertainty and operational limitations. In addition to visibility issues caused by meteorological phenomena and variable illumination, assigning the pixel position of an object of interest (e.g., volcanic plumes, ballistic projectiles) to a specific geographic location and elevation is not straightforward, introducing substantial uncertainty in the estimation of eruption parameters. We present PhixCam, a Python tool that allows the user to georeference in the 3D space the visual field of surveillance cameras from minimal input data: a DEM, the camera position, and a reference image where the framed relief can be outlined. The software includes functions to construct conversion matrices that can be adopted to translate the position of pixels into elevation above sea level when different emission directions of volcanic products are considered, thereby allowing users to assess the confidence of the results. This code was tested on a series of cameras of the Chilean Volcanic Surveillance Network, showing its operative potential in volcanic observatories, and on historical pictures, allowing us to estimate data of interest in volcanology for poorly monitored volcanic events.