Journal of Glaciology, Vol. 59, No. 214, 2013 doi:10.3189/2013JoG12J126 275 Instruments and Methods Cameras as clocks Ethan Z. WELTY,1 Timothy C. BARTHOLOMAUS,2 Shad O’NEEL,3,1 W. Tad PFEFFER1 1Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA E-mail:
[email protected] 2Geophysical Institute, University of Alaska, Fairbanks, AK, USA 3Alaska Science Center, US Geological Survey, Anchorage, AK, USA ABSTRACT. Consumer-grade digital cameras have become ubiquitous accessories of science. Particu- larly in glaciology, the recognized importance of short-term variability has motivated their deployment for increasingly time-critical observations. However, such devices were never intended for precise timekeeping, and their use as such needs to be accompanied by appropriate management of systematic, rounding and random errors in reported image times. This study describes clock drift, subsecond reporting resolution and timestamp precision as the major obstacles to precise camera timekeeping, and documents the subsecond capability of camera models from 17 leading manufacturers. We present a complete and accessible methodology to calibrate cameras for absolute timing and provide a suite of supporting scripts. Two glaciological case studies serve to illustrate how the methods relate to contemporary investigations: (1) georeferencing aerial photogrammetric surveys with camera positions time-interpolated from GPS tracklogs; and (2) coupling videos of glacier-calving events to synchronous seismic waveforms. 1. INTRODUCTION procedures that extend their application and reliability as Digital cameras automatically record the capture date and scientific instruments would be useful developments, not just time of every image and video file. Such time-aware imagery for glaciologists but for the broader scientific community.