AN OPEN-SOURCE, DATA-LOGGING DEVICE FOR MARINE-BASED SURVEYS

Abstract. Observation, monitoring, and understanding of the marine environment, particularly seafloor mapping, have gained global attention. Underwater photogrammetry is a valuable technique for creating accurate seafloor orthomosaics and digital elevation models (DEMs). However, achieving accurate georeferencing in photogrammetry surveys is challenging in marine environments. To address this, a low-cost and open-source data collection device was developed for underwater photogrammetry projects. The device is affordable, flexible, lightweight, and capable of logging position, motion, and utilizing a laser for seafloor feature identification. This paper presents the validation and assessment of the system, focusing on the performance of the position and laser sensors. The study advances underwater photogrammetry and provides insights into the device's capabilities for marine research and mapping applications. The results show that the Post Processed Kinematic (PPK) technique achieves high accuracy, with RMSE values of 0.294 m (distance), 0.267 m (X-coordinate), and 0.12 3m (Y-coordinate) at the Fremantle car park and 0.278 m (distance), 0.16 8m (X-coordinate), and 0.222m (Y-coordinate) at the Fremantle near boat ramp. PPP exhibits acceptable accuracy, while GPS shows relatively lower accuracy. Echosounder measurements correlate well with bathymetric lidar and RTK Rover reference data, with RMSE values of 45 cm and 28 cm, respectively. The laser distance measurer provides accurate measurements between 25 and 60 cm, showing a good correlation with the echosounder (R = 0.77). After correction for offset and refraction, the laser measurements have an RMSE of 1.8 cm compared to the echosounder. This study further demonstrated the feasibility and effectiveness of low-cost and open-source platforms, like Raspberry Pi, for marine research and mapping applications. Further work will investigate integrating this data into photogrammetry surveys.