Photogrammetric monitoring of small streams under a riparian forest canopy

Abstract

The recent advent of digital photogrammetry has enabled the modeling and monitoring of river beds at relatively high spatial resolution (0·01 to 1 m) through the extraction of digital elevation models (DEMs). The traditional approach to image capture has been to mount a metric camera to an aircraft, although non-metric cameras have been mounted to a variety of novel aerial platforms to acquire river-based imagery (e.g. helicopters, radio-controlled motorized vehicles, tethered blimps and balloons). However, most of these techniques are designed to acquire imagery at fl ying heights above the riparian tree canopy. In relatively narrow channels (e.g. <20 m bankfull width), streamside trees can obscure the channel and limit continuous photogrammetric data acquisition of both the channel bed and banks, while still providing useful information regarding the riparian canopy and even spot elevations of the channel. This paper presents a technique for the capture and analysis of close-range photogrammetric data acquired from a vertically mounted non-metric camera suspended 10 m above the channel bed by a unipod. The camera is positioned under the riparian forest canopy so that the channel bed can be imaged without obstruction. The system is portable and permits relatively rapid image acquisition over rough terrain and in dense forest. The platform was used to generate DEMs with a nominal ground resolution of 0·03 m. DEMs generated from this platform required post-possessing to either adjust or eliminate erroneous cells introduced by the extraction process, overhanging branches, and by the effects of refraction at the air-water interface for submerged portions of the channel bed. The vertical precision in the post-processed surface generally ranged from ± 0·01 to 0·1 m depending on the quality of triangulation and the characteristics of the surface being imaged.

Topographic structure from motion: a new development in photogrammetric measurement

“…The production of high-resolution topographic datasets is of increasing concern and application throughout the geomorphic sciences (Butler et al, 2001;Hancock and Willgoose, 2001;Bird et al, 2010;Fonstad and Marcus, 2010). A wide range of topographic measurement methods have evolved to meet this production need.…”

Photogrammetry and Laser Scanning for the Earth Sciencesworking Group V6

“…Bird et al (2010) provides a recent account on this evolution, with a particular focus on the measurement and modelling of riverbeds, an area where the use of photogrammetry has become almost routine. Related work has developed for application in the more controlled laboratory flume environment (e.g.…”

Image analysis techniques to estimate river discharge using time-lapse cameras in remote locations

“…particle image velocimetry (Bradley et al, 2002;Hauet et al, 2008;Bird et al, 2010;Tsubaki et al, 2011). The latter requires markers and may involve the use of stereo cameras.…”