Camera Calibration Techniques for Accurate Measurement Underwater

Abstract

Calibration of a camera system is essential to ensure that image measurements result in accurate estimates of locations and dimensions within the object space. In the underwater environment, the calibration must implicitly or explicitly model and compensate for the refractive effects of waterproof housings and the water medium. This chapter reviews the different approaches to the calibration of underwater camera systems in theoretical and practical terms. The accuracy, reliability, validation and stability of underwater camera system calibration are also discussed. Samples of results from published reports are provided to demonstrate the range of possible accuracies for the measurements produced by underwater camera systems. This is a revised version based on a paper originally published in the online access journal Sensors (Shortis 2015).

Investigation of Chromatic Aberration and Its Influence on the Processing of Underwater Imagery

“…In addition to radial lens distortion, there often is decentering distortion. As pointed out by [19] alignment errors between the optical axis and housing port can be absorbed as decentering lens distortion parameters. This distortion is asymmetric about the principal point and is normally much smaller in magnitude compared to the radial lens distortion.…”

“…The underwater and in-air images were captured in quick succession without altering the camera-housing setups in any way. Therefore, following the suggestion from [19], the cameras in their housings are seen as one "unit".…”

“…In [19], the need to correct or model refraction effects in underwater environments is discussed, pointing out that by far the most common approach is to correct the refraction effect using absorption by the physical calibration parameters. The primary effect can be absorbed by the radial lens distortion parameters.…”

DepthLearn: Learning to Correct the Refraction on Point Clouds Derived from Aerial Imagery for Accurate Dense Shallow Water Bathymetry Based on SVMs-Fusion with LiDAR Point Clouds

“…Even though aerial imagery is well established for monitoring and 3D recording of dry landscapes and urban areas, when it comes to bathymetric applications, errors are introduced due, mainly, to the water refraction. According to the literature [7][8][9], thorough calibration is sufficient to correct the effects of refraction in the case of in-water photogrammetric procedures. On the contrary, in through-water (two-media) cases, the sea surface undulations due to waves [10,11] and the magnitude of refraction, which differ practically at each point of every image, lead to unstable solutions [12,13].…”

A protocol for the large‐scale analysis of reefs using Structure from Motion photogrammetry

“…our recommended process for SfM-derived reef model creation. For in-depth discussion on camera trade-offs, optimal calibration, processing/alignment error mitigation and post-process error reduction while using underwater SfM techniques (seeAgisoft LLC, 2020;Bryson et al, 2017;James & Robson, 2014;Lange & Perry, 2020;Lavy et al, 2015;Marre, Holon, Luque, Boissery, & Deter, 2019;Neyer et al, 2019;Nocerino et al, 2019;Shortis, 2019;Suka et al, 2019).…”