Remotely Operated Vehicle Stereo-camera photogrammetry and positioning techniques for topographic measurements under river ice cover.

Autonomous survey platforms operating under river ice cover allow ice and bed morphology to be measured in-situ with minimal disturbance to the ice cover, and hence to the fluvial conditions affecting the morphodynamics of the ice and bed sediment. This enables less invasive investigation of rivers during the morphologically important and under-studied winter season, when access by other survey vessels is impractical. Remotely Operated Vehicles (ROVs) are currently used to measure a range of qualities of- and under marine ice sheets, but so far applications in rivers are rarer.

This methodological study aims to evaluate the effectiveness of using high resolution stereo-camera imagery processed with structure-from-motion photogrammetry, and of two acoustic positioning systems (Doppler Velocimeter Log, DVL, and Ultra Short Base Line, USBL) systems for use in ice-covered rivers for the creation of digital models of both riverbeds and ice.

A BlueROV2 ROV is tested in a high latitude, ice covered river in northern Finland. The ROV is equipped with a pair of stereo-cameras and a USBL system linked to a GPS to determine absolute position, as well as a DVL. The system is used to survey a short reach of the Pulmanki River (nr 69°55'13.3"N 28°01'58.1"E). A range of lighting configurations are also tested. The surfaces derived from the ROV survey are compared to known topographic points taken with sub-centimetre accuracy RTK dGPS to determine their accuracies, and so the potential of these methodologies in studies of the critical dynamics of seasonal ice cover and morphodynamics in ice covered rivers.