DOI: 10.5285/eb210711-85e1-4671-97a8-8c2791979a19
title: Aerial survey of the Hound Bay, South Georgia, elephant seal colony during the 2022/23 season, flight number DPLUS_109_35

description: Aerial survey of the Hound Bay elephant seal colony during the 2022/23 season conducted using a RPAS (remotely piloted aerial system).
The aerial survey was conducted as part of the Darwin Plus (DPLUS) 109 project: Initiating Monitoring Support for the SGSSI-MPA Research and Monitoring Plan for the purpose of establishing a baseline population estimate of key indicator species around South Georgia.
Dataset includes the original images and log files, the original RINEX GNSS (global navigation satellite system) base station files, the post-processed GNSS and imagery data, along with the resulting georeferenced DSM (digital surface model) and an orthorectified mosaic of the imagery.
This dataset is from flight number DPLUS_109_35 and was carried out on 26/10/2022.
This work was supported by the Overseas Territories Environment and Climate Fund under Grant Darwin Plus ref: DPLUS109: Initiating monitoring support for the SGSSI-MPA Research and Monitoring Plan. Funding for this work was also received from the UK Blue Belt fund through GSGSSI.
description: Data collection:
Aerial survey conducted using a RPAS (AgEagle eBee X). The survey consisted of collecting overlapping imagery of the target area, with a minimum forward overlap of 80% and a side overlap of 60%. The altitude during acquisition was species specific, determined by the required ground sampling distance (GSD), but was generally between 80 m and 120 m AGL (above ground level). During the aerial surveys a geodetic Trimble GNSS base station receiver collected data.

Post flight processing:
Precise point positioning (PPP) was undertaken using the online Canadian Spatial Reference System PPP tool to generate the position of the base station during the survey. The PPP solution generated was then used to process the eBee X's onboard GNSS receiver using post-processed kinematic (PPK) processing within eMotion to improve the accuracy of the camera centres captured during flight. Once complete, the coordinates for each image was then updated in the EXIF data and reexported from eMotion as .jpg's.

Photogrammetry / final outputs:
Structure from motion photogrammetry was used to determine the exterior orientation (x, y, z, omega, phi and kappa (or roll, pitch, yaw)) of the camera during image acquisition using a combination of the PPK solutions and common points within the images. Once the camera centre and orientation for each image was determined, a dense point cloud was extracted of the surface within the target area. The dense point cloud was then transformed into a DSM, which in turn was used to resample the images onto a map projection, removing camera perspective and terrain distortions, in a process called ortho-rectification and resulted in a single complete mosaic of the imagery.

Please refer to Fenney et al. for further information on the data collection and post processing methodologies.
description: Data collection equipment:

UAV:
Manufacturer: AgEagle
Model: eBee X
Sensor: AgEagle Aeria X (RBG camera)
Flight management software: eMotion (version 3.20.0 and version 3.22.0)

GNSS base station:
Manufacturer: Trimble
Receiver model: R9s
Antenna model: Zyphr Model 2

Post-flight processing software:

Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP, Version 3)
eMotion (version 3.20.0 and version 3.22.0)
Photogrammetry software:
Agisoft Metashape (version 1.8.4 build 14671) or Pix4D (version 4.7.5.).
description: Please refer to Fenney et al. for further information on the data collection and post processing methodologies.

PPP processing accuracy is reported in the CSRS PPP processing report (.pdf).

PPK processing accuracy (by image) is reported in the eMotion camera centre geoinfo file (.txt).

Data resolution
Target GSD of aerial survey (1.9 cm).

Resolution of final outputs:
DSM (1.9 cm)
Orthorectified mosaic (1.9 cm)