USING GIGAPAN MEASUREMENT OF EROSION PINS TO MONITOR SURFACE CHANGES IN SAND

Regions of open sand on beaches and active dunes are dynamic yet fragile environments. They can respond dramatically both to natural events such as strong winds or waves and to human incursions such as vehicular or foot traffic, so sand surfaces are difficult to monitor without disturbing them. We use the GigaPan system to make photographic panoramas to unobtrusively measure and document an array of erosion pins in an active dune blowout at the Saugatuck Harbor Natural Area, Saugatuck, Michigan.

The GigaPan system features a robotic camera mount, photo-stitching software, and an on-line web hosting interface. It creates a gigapixel-sized image by merging a series of close-up, overlapping photos (up to 147 in our work, although more are possible) into a single panorama that is uploaded to the GigaPan website. Whereas the final image is too large to display on most personal computers, the website allows zooming in to any part of the panorama to examine details up to the resolution of the original photos. We zoom to view individual erosion pins, then use a screen ruler software tool to measure the exposed length of the pin as scaled to a known distance between marks on the pin. The erosion pins are alternating colored plastic jump rope beads, which provide highly visible, uniform distance increments, epoxied onto 122 cm fiberglass rods.

This method has many advantages over manual measurement of erosion pins. The GigaPan can photograph a scene in less than 15 minutes, speeding up data gathering in the field since measurement is done in the lab. The panorama permanently records the raw data, allowing reexamination of pins, and is spatially organized, allowing quicker reference to specific pins than does sorting through the set of original photos. Most importantly, the method avoids disturbance inherent in manual measurements, which can be quite significant when climbing steep slopes in open sand to measure pins. Data for individual pins may be lost, however, if vegetation or debris obscures the base of a pin in the images, and care must be taken to avoid measuring areas with image distortion if a pin crosses the stitching boundary between photos.