For today’s blog post we will look at a case study where AUV technology has been implemented; the investigative search of the plane that went missing in 2014, flight MH370. This was a large operation lead by the Australian government department, Australian Transport and Safety Bureau (ATSB) who were publishing ongoing reports on their website. The end of flight search area analysis was conducted by the Australian Defence and Science Technology group (DST). The drift analysis and landfall of debris involved collaboration with an oceanographer from the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The survey operations was contracted out to ocean survey company Fugro, with a base in Perth, on the West Coast of Australia.
The story of this aircraft is a standard Malaysian airlines flight on 7th March 2014 heading from Kuala Lumpur to Beijing. There were communications between air traffic control from flight departure with final radar return 100 minutes into the flight after already deviating from the planned flight path, the plane continued to fly for 6 hours. During this time there was a series of ‘handshakes’ between the Ground Earth Station (GES) and the plane via satellite. These crucial pieces of information included satellite communication (SATCOM) data and their timing and frequency metadata. Burst timing offset(BTO) and burst frequency offset(BFO) could then be used to calculate the plane location.
A search area was later refined after analysis. The methods used included Bayesian filtering on information such as plane dynamics and drift analysis and performing backward calculations to determine the probable final accident location. The initial 60,000 square kilometres search area was expected to take 12 months. The Bayesian method performed by DST included SATCOM data, aircraft dynamics and environmental effects, produced a probability density function of the location of the aircraft. This is visualised in the image below by DST.
The drift analysis measured aircraft parts relative to ‘oceanographic drifters’. This used the existing archive from the Global Drifter Program by NOAA of satellite tracked buoys. The drift study did an analysis on a flaperon, confirmed from the plane, which was found on the coast of La Reunion Island July 2015. The analysis used the the oceanographic drifter models, as well as the lack of debris on the west coast of Australia, to lower the search area of the sea surface in 2014.
Maps can be found through here.
The initial search area had a first priority of 20 nautical miles either side of the 7th arc and around 700 kilometres along it. The 7th arc is a certain distance from which the plane was in communication via satellite to ground control. It is inferred from burst timing offset and is the 7th communication since losing contact. The enormity of the search area means that the technology of AUVs have helped make it realistic. Previously, the search would have taken a decade. The initial bathymetry survey needed to be done as this remote area is lacking in detailed ocean mapping. The depths that were to be reached could be at least 6000 metres, the information obtained would inform on what is involved and planning for the underwater search and which sensor types that would be used.
While the search was a joint agreement between Australia, Malaysia and China, Australia was the leading investigator and here we will focus on their deployed equipment. Fugro was contracted by ATSB for the initial bathymetry survey in mid May and later contracted for the extensive underwater search in August 2014. There were three survey vessels that were used over the search period. The vessels included deep tow systems, EM 2040 multibeam sonar that had the ability to reach 6000 metres in depth and a Kongsberg Hugin AUV. The three vessels were the Fugro Equator, Fugro Discovery, Fugro Supporter.
The initial bathymetric survey commencing in June 2014 to December 2014, would build on low resolution seafloor topology information mainly gained from satellite altimetry data, which can estimate water depth. (A link to an article on satellite altimetry and an example of its use.) The survey vessel for this was the Fugro Equator that was equipped with a multibeam system and sub-bottom profiler, which found some significant differences to the existing data.
Following the initial bathymetry was the extensive area search for the final accident location. This commenced in October 2014 with the Fugro Discovery. The search area later expanded to 120000 square kilometres. The AUV had several missions during the search operation and could be deployed in areas that had more complex terrain than where the deep tow could survey. The initial proposal had the AUV involved once the debris field had been found and it could then do the detailed mapping and optical imaging to be provided to aircraft engineers. As the terrain became too complex for the deep tows, an AUV was then deployed, being self propelled with an endurance of around 24 hours before having to re-surface and recharge. This was done from the Fugro Supporter commencing January 2015. Outlining this equipment shows the extensive resources taken up by this operation, lasting over 2 years with the search being suspended just in January, 2017. It is not surprising then, that this is the most expensive aircraft search in history. This video from Fugro summarizes features utilized by the AUV.
This is an impressive project with documentation from ATSH, CSIRO, DST and Fugro with the survey focus. ATSB providing updates and search area analysis with some media interest. While this is a non commercial project and therefore being government funded, such large scale projects can test capabilities of equipment. It also has a human interest, exploring a mystery and mapping largely unmapped underwater areas, but also affects the people impacted by the tragedy.
- Griffin, DA, Oke, PR and Jones, EM (2016). The search for MH370 and ocean surface drift. CSIRO Oceans and Atmosphere, Australia. Report number EP167888. 8 December 2016.
- Davey et al. 2016, Bayesian Methods in the Search for MH370, SpringerBriefs in Electrical and Computer Engineering
- ATSB (2016) MH370 — First Principles Review. ATSB, 20 December 2016
- ATSB (2015) MH370 – Definition of underwater search areas. ATSB, 3, 10 December 2015.
- Millar, D, 2015, The Search for MH370: Challenges in performing an underwater search in a remote area of the deep ocean. US Hydro. March 16-19, Maryland USA.