Overlapping seabed images collected at Looe Key coral reef, Florida, 2022

IMAGE & POSITION ACQUISITION Images were collected in TIFF (.tif) format in synchronized quintets by the SQUID-5 system while towed at a speed of approximately 3 knots behind the USGS research vessel (R/V) Sallenger during USGS field activity 2022-314-FA. The image-collection frequency was 1 hertz (Hz), and GNSS positions were recorded at 10 Hz. Image-gain settings were adjusted, as needed, depending on water depth and lighting conditions. Aperture and shutter speed were consistent for each group of images at a study site. Image files were named programmatically and conform to the following naming convention: CAM##-YYYYMMDDhhmmss_fff-n[nnn].tif, where ## comprise the last 2 digits of the serial number of the camera that captured the image, YYYYMMDD represents the year (YYYY), month (MM) and day (DD) of capture; hhmmss_fff is the time of capture as hours (hh), minutes (mm), seconds(ss) and fractional seconds (fff) in Universal Coordinated Time (UTC) and n[nnn] is a sequence number (image counter) which is reset at the beginning of each survey line. For example, 'CAM13-20210717163118_000-330.tif' indicates camera 13, July 17, 2021, 16:31:18.000 (UTC), collection event number 330 of the survey line.

SQUID-5 NAVIGATION PROCESSING Raw GNSS data received by the antenna mounted atop the SQUID-5 were recorded at 10 Hz by a dual-frequency survey-grade GNSS receiver, which was post-processed and differentially corrected against a local base station located 14 kilometers (km) from the survey site, in NovAtel's GrafNav software to produce 10-Hz SQUID-5 trajectories. The SQUID-5 trajectories, in combination with precisely recorded image capture event times, were used to generate SQUID-5 GNSS antenna positions at the moment of each image capture and can be found in the accompanying text file (FL_2022_LooeKey_Image_Locations.txt). The positions in the SQUID-5 navigation file represent the position of the SQUID-5 GNSS antenna reference point (ARP), not the position of the cameras or features imaged. To determine actual image positions, photogrammetric software such as Agisoft Metashape can be used to apply the lever arm offsets (in the camera frame of reference) from the GNSS antenna reference point to the camera lens. The following values for each camera were calculated for x, y, and z (in meters). Camera 13, 0.033 m(x), 0.036 m(y), 0.739 m(z); Camera 01, -0.32 m(x), -0.205 m(y), 0.823 m(z); Camera 39, 0.17 m(x), -0.280 m(y), 0.838 m(z); Camera 75, 0.047 m(x), 0.396 m(y), 0.698 m(z); Camera 82, -0.11 m(x), -0.69 m(y), 0.675 m(z). The methodology by which the original lever arm measurements were determined is described in Hatcher and others (2020). Those values were then refined during the SfM process. For more information about quality assurance/quality control (QA/QC) procedures completed for this process step, refer to the SQUID-5 DCP metadata record associated with this collection effort (Kranenburg and others, 2023).

IMAGERY HEADERS Georeferencing, copyright, and other relevant information were added to the imagery headers of each image using Phil Harvey’s ExifTool . To extract the information from the image headers using ExifTool, the following command can be used (tested with ExifTool version 11.88): exiftool -n -csv *.tif > allheaders.csv The -csv flag writes the information out in a comma-delimited format. The -n option formats the latitude and longitude as signed decimal degrees. For the exact scripts used to populate the imagery headers in this process step, refer to the SQUID-5 DCP metadata record associated with this collection effort (Kranenburg and others, 2023).

KMZ CREATION In order to provide a visual map of the survey extent, image capture locations and to aid in completing the geospatial information in the collection-level metadata, a Keyhole Markup Language Zipped file (.kmz) is created from the image positions text file for each collection using Global Mapper.