DIGITAL CAMERA-POLE PHOTOGRAPHY: A USEFUL RESEARCH TOOL FOR OUTCROP-SCALE GEOLOGIC MAPPING

A telescoping aluminum pole with an adjustable tripod head, digital camera and remote triggering mechanism was designed to generate hi resolution, low elevation aerial imagery that can reveal geologic detail in mesoscale structures. These structures and relationships are too large to grasp on the outcrop surface and too small to be seen in typical aerial photographs. The camera pole includes up to nine 6-foot-long telescoping aluminum tubes (6063-T832 drawn aluminum tubing with 0.058” wall thickness; 1-2” diameters in 0.125” increments). Cross-bolt stops in the ends of the larger tubes allow a 1.5 ft overlap between sections to a give a maximum elevation of ~40 ft (12m). The remote triggering mechanism uses an air ball release with a custom mini-tripod head to hold a plunger over the shutter button on the camera. The 20 ft (6m) camera pole rig can be operated by a single person. The full 40 ft (12m) pole assembly requires a four-person team that includes an anchor/camera release person to hold the base and take the shot, two rope handlers spread in a V and attached mid-pole for stability and control, and a spotter/catcher to help orient the camera properly and to secure the camera end of the pole as it is lowered down. A 9.0 megapixel digital camera at the full 40 ft (12m) height yields hi resolution images with ground measured pixel sizes of 4x4 mm and an ~ 26 x 33 foot (8 x 10m) field of view. Overlapping shots are put together in Adobe Photoshop to give seamless photo-mosaics. These combined images can be georeferenced in ArcGIS to a set of surveyed reference markers in each of the photomosaics, for which position coordinates were determined using Trimble 5700 RTK GPS units with a precision of +/- 1 cm. On-screen digitizing of outcrop structural features within these georeferenced photomosaics using ArcMap's edit and zoom functions produces shape files that can be augmented with other digital survey data and GPS-positioned orientation data. These final digital maps allow the accurate representation and analysis of new, never-before-seen outcrop-scale geologic structures. Field examples from coastal Maine show details of asymmetric boudinage, syntectonic granite deformation and brittle fault zone geometry offering an important new perspective on crustal deformation.