Beyond visual line of sight (BVLOS) Operation of unmanned aerial vehicles (UAVs) for Antarctic Sea ice data collection.
The snow radar has recently been developed to non-intrusively measure Antarctic snow depth from an unmanned aerial vehicle (UAV), a vast practical improvement on traditional methods. Improvements in sensing methods is a critical step towards an automated and more effective collection of snow depth m...
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| Format: | Article in Journal/Newspaper |
| Language: | English |
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University of Canterbury
2020
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| Online Access: | https://dx.doi.org/10.26021/10402 https://ir.canterbury.ac.nz/handle/10092/101339 |
| Summary: | The snow radar has recently been developed to non-intrusively measure Antarctic snow depth from an unmanned aerial vehicle (UAV), a vast practical improvement on traditional methods. Improvements in sensing methods is a critical step towards an automated and more effective collection of snow depth measurements, and therefore ice volume by inference. The research focus is to realise the potential of the snow radar by providing an autonomous, reliable and rapid means of surveying an expansive area. UAVs must operate at low-altitudes (5 m – 15 m) to gather accurate snow depth readings. Operational ranges of data collection UAVs are to extended past 10 km, far beyond the visual line of sight (BVLOS). Implementation of a proof-of- concept (PoC) communications architecture was explored for enabling BVLOS data collection missions. A mesh networking protocol called DigiMesh was implemented as a replacement for point-to-point (PtP) telemetry links. This protocol uses IEEE 802.15.4 based media access control layer (MAC) specifications, and a proprietary physical layer (PHY) implementation. Python middleware was written to utilise DigiMesh compatible radios, as they are not directly supported by the open-source UAV ecosystem. Network bottle-necking between ground control station (GCS) and relay UAV was found to be a constraint of the original design. Higher bandwidth radios using IEEE 802.11n PHY/MAC specifications were implemented for this link, with DigiMesh remaining for the inter-UAV network. The physical channel was investigated by simulating the two-ray model. The theoretical maximum range between GCS and relay UAV varied between 2 km to 55 km, depending on the modulation coding scheme (MCS) used. In addition it was shown, that under ideal conditions with a perfectly flat sea ice cover, the spatial position of the relay UAV can be locally optimised with respect to received signal strength. A method for empirically determining channel characteristics with software defined radios (SDRs) is described. An autonomous centre frequency offset (CFO) correction algorithm was implemented within the GNURadio data collection script, improving the quality of channel data. Recommendations were made for future work on a BVLOS data collection system, most notably replacing RF equipment with IEEE 802.11ah compatible hardware. This standard describes sub 1 GHz (S1G) mesh wireless local area networks (WLANs) with much greater data- rates than DigiMesh. For these reasons, IEEE 802.11ah was deemed the most optimal open networking standard for BVLOS data collection missions. Finally, regulatory recommendations are provided for BVLOS UAV operations in Antarctica, including a telemetry data benchmark, and maximum packet loss threshold. This thesis forms the theoretical and practical basis for realistic tests and BVLOS data collection missions in Antarctica. |
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