A Novel Iterative Water Refraction Correction Algorithm for Use in Structure from Motion Photogrammetric Pipeline

Dimitrios Skarlatos,Panagiotis Agrafiotis

doi:10.3390/jmse6030077

Dimitrios Skarlatos, Panagiotis Agrafiotis

Open Access

https://doi.org/10.3390/jmse6030077

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Abstract

Photogrammetry using structure from motion (SfM) techniques has evolved into a powerful tool for a variety of applications. Nevertheless, limits are imposed when two-media photogrammetry is needed, in cases such as submerged archaeological site documentation. Water refraction poses a clear limit on photogrammetric applications, especially when traditional methods and standardized pipelines are followed. This work tries to estimate the error introduced to depth measurements when no refraction correction model is used and proposes an easy to implement methodology in a modern photogrammetric workflow dominated by SfM and multi-view stereo (MVS) techniques. To be easily implemented within current software and workflow, this refraction correction approach is applied at the photo level. Results over two test sites in Cyprus against reference data suggest that despite the assumptions and approximations made the proposed algorithm can reduce the effect of refraction to two times the ground pixel size, regardless of the depth.

Highlights

In 1989 Karara stated “ through-water depth determination from aerial photography is a much more time consuming and costly process, it is still a more efficient operation than ship-borne sounding methods in the shallower water areas
The work presented in this paper proposes a novel and simplified algorithm for water refraction correction within an existing photogrammetric pipeline
This algorithm could be used for coastal mapping applications and accurate and detailed bathymetry of the seabed in shallow waters

Summary

Introduction

In 1989 Karara stated “ through-water depth determination from aerial photography is a much more time consuming and costly process, it is still a more efficient operation than ship-borne sounding methods in the shallower (less than 10 m deep, say) water areas. A permanent record is obtained of other features in the coastal region such as tidal levels, coastal dunes, rock platforms, beach erosion, and vegetation” [1], a statement that has held true until today, despite the fact that many alternatives for bathymetry [2] have arose since. This is especially the case for the coastal zone of up to 6 m depth, which concentrates most of financial activities, is prone to accretion or erosion, and is ground for development, where there is no affordable and universal solution for seamless underwater and overwater mapping. Despite the excellent depth map provided by LiDAR, the sea bed orthophoto generation is prohibited due to the refraction effect, leading to another missed opportunity to benefit from a unified seamless mapping process

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