The use of terrestrial monoscopic time-lapse cameras for surveying glacier flow velocity

Glacier flow velocity is crucial information to assess the impact of global warming on glaciers since it is related to the ice thickness, its variations provide information on mass balance and, in general, on the current state of glacier “health”. Moreover, flow anomalies are often an indicator of glacier instabilities. Therefore, more attention has been dedicated to surveying glacier kinematics. Historically, flow velocity was the first quantitative variable measured on glaciers since the 19th century. In the last decades, terrestrial monoscopic time-lapse digital cameras have permitted to conduct automatic surveying at high spatial and temporal resolutions using digital image correlation. Even though terrestrial time-lapse imagery is currently a consolidated technique in glacier monitoring, possible strategies, limitations and potentialities have never been systematically reviewed. This work aims to illustrate the typical procedures required to monitor glacier flow velocity using terrestrial monoscopic time-lapse cameras. We describe possible inconveniences that can arise during the survey and provide some guidelines to minimise such issues. We present six study cases in the European Alps (Mont Blanc and Bernina massifs) that feature different monitoring equipment, site geometry and glacier morphodynamics to illustrate possible solutions for terrestrial imagery monitoring. The results of this review highlight the high benefit-to-cost ratio of terrestrial time-lapse cameras in glacier flow surveying.