Ocean current observations by infrared and visual Large Scale Particle Image Velocimetry (LSPIV)

The natural dynamics of tidal currents continuously change the appearance of the Wadden Sea. Especially coastal regions and bays with shallow waters are strongly influenced by tidal dynamics. Meanwhile, in offshore study areas with harsh environmental conditions as well as dynamic ocean currents and water levels, continuous in-situ investigations of the prevailing current conditions requires a high effort. In-situ measurement technology is thereby maintenance-intensive and partly limited in time or space by limited accessibility or restricted by the measurement method. In hence, remote sensing techniques based on video image information, such as Large Scale Particle Image Velocimetry (LSPIV) for sensing, and computer vision algorithms for long-term investigation of the prevailing dynamic near-surface ocean flow conditions, have become highly relevant. However, in some environmental situations there may be not sufficient or significant natural textures evaluable in the visual camera images, or only insufficient contrast ratio under varying ambient illumination at the water observation site, to perform image based velocimetry. Thus, we consider with this study an extended approach of visual and infrared video data analysis by an automated LSPIV measurement technique under real offshore deployment conditions. The treatise of this paper first introduces the reader to the subject area and technologies as well as the principles of the LSPIV measurement method. Followed by the depiction of the motivation for an extended approach to visual and infrared video data analysis by an automated LSPIV measurement method in real offshore applications. Subsequently, related research is discussed. Thereafter, the remote sensing setup and sensor-test-bed-system for offshore deployment on an observation platform is presented, therein we also addresses routines of necessary calibration procedures for camera sensors. We then depict details of our automated LSPIV measurement procedure. This is followed with an overview of the preceding validation procedures and LSPIV multispectral remote sensing results of long-term monitoring of horizontal flow dynamics over several days. Finally, we discuss uncertainties of the LSPIV velocity measurement method encountered in real applications and conclude with a brief outlook on further developments and applications.