Evaluation of Remotely Operated Vehicle -mounted imaging and positioning techniques for topographic measurements under river ice cover.

The ability to perform measurements in rivers underneath seasonal ice cover is valuable as it allows relatively non-invasive survey of river ice and bed morphology over a large area, during a period when boats or other commonly used survey vessels can’t access the river. Remotely Operated Vehicles (ROVs) have been extensively used for the deployment of sensors in studies of marine ice, to assess ice thickness and properties, krill and algal biomass, and radiation transfer through sea ice, but applications on shallow inland waters, such as rivers, are rarer. 
This methodological study aims to evaluate the effectiveness of different imagery collection (multibeam echosounder and stereo-camera imagery processed with shape-from-motion) and 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.
Two BlueROV2 Remotely Operated Vehicles (ROVs) are tested in a high latitude, ice covered river in northern Finland. Both ROVs are identical other than their equipment load; ROV-a is equipped with an Oculus imaging sonar and DVL while ROV-b is equipped with a pair of stereo-cameras and a USBL system linked to a GPS to determine absolute position. Both imaging systems were used to survey a short reach of the subarctic Pulmanki River (nr 69°55'13.3"N 28°01'58.1"E). The surfaces derived from each ROV’s survey are compared to each other, and 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 morpho dynamics in ice covered rivers.