What smart pebbles can and cannot do: A discussion on the common notions regarding IMU sensors and the prospect of using them in (fluvial) geomorphological research.

During the last decade, many scientists developed and deployed ‘’smart- pebbles’’ in fluvial (and other rapidly changing environments) in an attempt to monitor sediment dynamics. In parallel, Inertial Measurements Units (IMUs) have been tested in laboratory experiments focusing mainly on fluvial single grain entrainments and sort-term motions (simulating either costal or river hydrodynamics). Despite the innovation in the above applications, only a small number of those investigated the errors inherited in the IMU measurements. Although all the IMUs are in principal the same (an assembly of micro-accelerometer, micro-gyroscope and micro-compass), the parameters that affect the results range from the sensor’s electrical and physical characteristics to the filtering of the derived measurements and from the modelling of inertial kinematics to the transformation of those to a coherent reference frame. In this presentation we will discuss: a) the key error sources in IMU sensing and its realistic range of applicability, b) the results from including a coherent error compensation in the developing of a smart pebble for sensing dynamics in natural streams, c) results from testing this sensor in a series of laboratory entrainment experiments and d) how these measurements alter the existing theoretical descriptions for fluvial sediment transport. Finally, we will discuss preliminary results from the deployment of two smart pebbles (one spherical and one elliptical) in a Scottish bedrock river (River Calder).

Dr Maniatis has a 5- year Diploma in Environmental Engineering, an M.Sc. in Freshwater Systems Science and a PhD in Geography and Computing Science. However, he believes that he is a geomorphologist. During his PhD he developed a smart pebble for monitoring fluvial sediment transport. His main concern was the understanding of the relevant errors and the contextualising of this new measurement in the theory of sediment transport.  Currently, he is employed as a Fluvial Geomorphology RA in the School of Geographical and Earth Sciences of the University of Glasgow working for a national scale erosion susceptibility study dedicated to the protection of critical water infrastructure.