DOI: 10.5061/dryad.63xsj3v4s
title: Crowd-sourced SfM: Best practices for high resolution monitoring of coastal cliffs and bluffs

description: Digital oblique photos of an approximately 2.0 km alongshore reach of
 seaward-facing coastal bluff faces on the Strait of Juan de Fuca,
 Washington State, were collected at least quarterly between 2016 and 2022.
 In total over 3900 photos were collected over 38 separate surveys. The
 photos were collected to support digital surface reconstructions using
 Structure-from-Motion (SfM) photogrammetry, and specifically to assess the
 quality of surfaces generated with photos collected using relatively
 simple techniques that could be accessible to community science programs.
 A secondary goal was to use the photos, and the digital surfaces generated
 with them, to evaluate patterns and rates of erosion on the bluff
 face. 
description: Photos were collected in one of two ways. The first method was
 with a point-and-shoot digital camera hand-held by a photographer on a
 boat, approximately 100-200 meters from the toe of the coastal bluff.
 Individual photos were manually collected approximately every 2 seconds as
 the boat moved along the shoreline at speeds of approximately 2-3 knots,
 with the camera facing straight towards the bluff face. The second method
 was with a point-and-shoot digital camera, collected by a photographer
 standing at the base of the beach, around the mean low water elevation
 contour, at a distance of approximately 30-50 meters from the toe of the
 coastal bluff. For photos collected on the beach, photos were collected
 approximately every 10-15 meters in alongshore distance along the reach.
 Of the 38 photo sets, 3 were collected with no spatial information
 associated with each photo and 13 were collected with camera position
 supplied only by the cameras internal GNSS sensor. For the remaining 22
 photo sets a ProMark 200 GNSS system, operating in Real-Time Kinematic
 mode (RTK-DGPS) was used to assign a high-accuracy position and elevation
 to the camera. For 7 of the photo sets camera positions are only know from
 the GNSS systems, whereas 15 of the photo sets include positions from both
 the camera's internal GNSS sensor and from the GNSS system. For those
 photos that were collected with high accuracy location and elevation
 information the camera was set on to a platform attached to a rover pole
 and positioned directly under the GNSS antennae, providing an estimated
 horizontal and vertical uncertainty for the camera position of
 approximately 15 cm. Three different handheld digital cameras were used
 during the project, a Canon D20 Powershot, a Fujifilm Finepix XP130, and a
 Motorola Moto G(6).
description: Where GNSS survey data were collected for each photo a separate
 .txt file is included for each survey. The .txt file includes a row for
 every photo, with 18 data columns. The relevant data columns
 are: Columns 1-3: XYZ referenced to Washington State
 Plane Zone North, metric units. Elevations in column 3 are relative to
 NAVD88 (Geoid18).<br>Columns 7-8: Latitude and
 Longitude<br>Column 9: Description attribute. The number in the
 description in this column matches to the number in the file name of the
 associated photo.  <br>Columns 10-16: A variety of position estimate
 quality and uncertainty metrics<br>Column 17-18: Date/Time (Pacific
 Time Zone, local time) The alongshore distance over
 which photos were collected for any given survey varied. In general photo
 sets collected by boat tended to image a greater alongshore length of the
 shoreline than those collected from the beach. Lighting and photo quality
 varied across surveys as well. The attached file,
 "Bluff_Photos_Metadata.csv" includes a table providing details
 associated with each individual survey.