DOI: 10.5285/463ea06f-6c49-4d6e-a80b-21c88a71c3da
title: Aerial survey of Hound Bay, South Georgia, elephant seal colony during the 2023/24 season, flight DLPUS_214_20

description: Aerial survey of Hound Bay elephant seal colony, Mirounga leonina, during the 2023/24 season conducted using a remotely piloted aerial system (RPAS).

The aerial survey was conducted as part of the Darwin Plus (DPLUS) 214 project: Southwest Atlantic Elephant Seal Population Assessment (SAESPA).

Dataset includes the original images and log files, the original RINEX GNSS (global navigation satellite system) base station files, the post-processed global navigation satellite system 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_214_20 which was carried out on 2024-10-25.

This work was supported by the Overseas Territories Environment and Climate Fund under Grant Darwin Plus ref: DPLUS214: Southwest Atlantic Elephant Seal Population Assessment (SAESPA).
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 forward overlap of 80% and a side overlap of 60%. The target altitude during acquisition was 95 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 and which was then used to process the eBee X's onboard GNSS receiver using post-processed kinematic (PPK) processing to improve the accuracy of the camera centres captured during flight.

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 onboard GNSS solution 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.
description: Data collection equipment:

Unmanned aerial vehicle (UAV):
Manufacturer: AgEagle
Model: eBee X
Sensor: AgEagle SODA 3D
Flight management software: eMotion (version 3.23.0)

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 3.23.0)
Photogrammetry software:
Pix4D (version 4.9.0.).
description: Coordinate reference system for outputs:
Projection: UTM Zone 23S
Horizontal datum: WGS84
Vertical datum: MSL (mean sea level), EGM2008 geoid

Resolution of final outputs:
DSM (2.1 cm)
Orthorectified mosaic (2.1 cm)

The camera is placed in the centre of the central component of the drone, with the LiDAR ground sensor immediately below it and offset from the camera. The GNSS antenna is at the front of the drone, offset in the opposite direction.

The sampling rate varied throughout the flight, depending on the speed of the platform.

Calibration was accounted for in processing.