Articles | Volume 11, issue 2
Research article
28 Mar 2017
Research article |  | 28 Mar 2017

Terrain changes from images acquired on opportunistic flights by SfM photogrammetry

Luc Girod, Christopher Nuth, Andreas Kääb, Bernd Etzelmüller, and Jack Kohler

Abstract. Acquiring data to analyse change in topography is often a costly endeavour requiring either extensive, potentially risky, fieldwork and/or expensive equipment or commercial data. Bringing the cost down while keeping the precision and accuracy has been a focus in geoscience in recent years. Structure from motion (SfM) photogrammetric techniques are emerging as powerful tools for surveying, with modern algorithm and large computing power allowing for the production of accurate and detailed data from low-cost, informal surveys. The high spatial and temporal resolution permits the monitoring of geomorphological features undergoing relatively rapid change, such as glaciers, moraines, or landslides. We present a method that takes advantage of light-transport flights conducting other missions to opportunistically collect imagery for geomorphological analysis. We test and validate an approach in which we attach a consumer-grade camera and a simple code-based Global Navigation Satellite System (GNSS) receiver to a helicopter to collect data when the flight path covers an area of interest. Our method is based and builds upon Welty et al. (2013), showing the ability to link GNSS data to images without a complex physical or electronic link, even with imprecise camera clocks and irregular time lapses. As a proof of concept, we conducted two test surveys, in September 2014 and 2015, over the glacier Midtre Lovénbreen and its forefield, in northwestern Svalbard. We were able to derive elevation change estimates comparable to in situ mass balance stake measurements. The accuracy and precision of our DEMs allow detection and analysis of a number of processes in the proglacial area, including the presence of thermokarst and the evolution of water channels.

Short summary
While gathering data on a changing environment is often a costly and complicated endeavour, it is also the backbone of all research. What if one could measure elevation change by just strapping a camera and a hiking GPS under an helicopter or a small airplane used for transportation and gather data on the ground bellow the flight path? In this article, we present a way to do exactly that and show an example survey where it helped compute the volume of ice lost by a glacier in Svalbard.