CAN GIGAPAN IMAGES BE USED AS AN ALTERNATIVE TO LIDAR TO MEASURE EROSION RATES?: AN EXPERIMENT ON GLACIAL TILL AT CHIMNEY BLUFFS STATE PARK, HURON, NY

Focused erosion along the southern edge of Lake Ontario has dissected drumlins left behind as glaciers melted at the end of the Wisconsinan Stage of the Laurentide glaciation (~10 ka). Chimney Bluffs State Park in Wayne County, NY, contains several exposures of dissected drumlins whose eroded till produces steep faces, rivulets, and spires. While ground-based LiDAR techniques have been shown to accurately determine modern erosion rates, we wanted to see if the detail captured in Gigapan imagery could be used as an alternative to LiDAR. Using a Canon Rebel T3i and Gigapan, images of the bluffs were taken at monthly intervals starting from Fall 2017 to capture erosional changes on the faces of the bluffs over time. The Gigapan stitches together multiple overlapping photos to create one large image. We noticed that the stitching process caused noticeable perspective distortion to the resulting image, which could affect interpretations of erosion. To combat this, a test picture of a brick wall was taken to calculate the amount of distortion. We measured the differences in dimensions of center and corner bricks using Adobe Illustrator and Adobe Photoshop. We found that stitching produced pincushioning of the image that rotated objects and decreased the height of objects by 0.76 cm and the width of objects by 3.55 cm over a distance of 4.82 m from the center of the image. We corrected the images and applied image differencing to the distortion-free Gigapan imagery. The monthly images were warped to coincide with the original image from October in ENVI to facilitate comparison. We identified disparities between the images using a differencing layer in Photoshop. Image differences were quantified and mapped to illustrate erosion patterns. We found that a significant amount of material was eroded from the face of the bluffs including larger clasts due to heavy precipitation during the fall months. This is evident due to the material on the shore in the December picture. While we are able to use the Gigapan to notice differences between monthly images, it is still unclear if the Gigapan is capable of detecting millimeter scale differences.