Detecting turbulence remains a key challenge of modern-day aviation, with reports submitted by pilots often being very inaccurate. However, due to being the least expensive method, it is the most frequently used for trying to predict where it will occur.
A team from the Faculty of Physics, University of Warsaw, have shown that there is every indication that data allowing pilots to avoid turbulence and even to forecast such occurrences are already being routinely recorded, and has been recorded for many years. Jacek Kopec, a doctoral student at the Faculty of Physics, has managed to extract this valuable information from the flight parameters routinely broadcast by the transponders installed in most modern commercial aircraft. What is most promising is that this new method for detecting turbulence is not only original but also potentially very easy to implement.
‘Today's commercial aircraft fly at altitudes of 10 to 15 km, where the temperatures fall to -60 °C. Conditions for measuring atmospheric parameters are very difficult, which explains why such measurements are not taken systematically or extensively,’ commented Kopec. ‘A lack of sufficiently accurate and up-to-date information not only exposes aircraft and their passengers to danger, it also restricts the development of theories and tools for forecasting turbulence.’
Overcoming cost hurdles
Presently pilot reports (PIREPs) are relayed by radio and provided to pilots of other aircraft by air traffic controllers are a basic source of turbulence data. As these reports are based on the subjective opinions of pilots, the data collected in this fashion are often marred by substantial inaccuracies concerning both the area of turbulence and its intensity. More accurate readings are provided by aircraft involved in the Aircraft Meteorological Data Relay (AMDAR) programme. This method is nonetheless costly, so data collected at cruising altitudes are transmitted relatively rarely. In practice, this prevents such reports from being used to detect and forecast turbulence.
Passenger aircraft are fitted with sensors that record a variety of flight parameters. Unfortunately, most of the data is not made publicly available. Publicly available reports include only the most basic parameters such as the position of the aircraft (ADS-B transmissions, which are also used by the popular website FlightRadar24) or its speed relative to the ground and the air (Mode-S data). Meanwhile, detecting turbulence requires knowledge of the vertical acceleration of aircraft. ‘Vertical accelerations are especially strongly felt both by the passengers and by the aircraft," Kopec explained. ‘Unfortunately, there is no access to materials regarding vertical accelerations. That was why we decided to check if we could extract such data from other flight parameters, accessible in Mode-S and ADS-B transmissions.’
The research team tested three algorithms of turbulence detection. The first relied on information about the position of aircraft (ADS-B transmissions). However, preliminary tests and their comparison against the parameters registered in the same area by the research aircraft failed to produce satisfactory results. As for the remaining two algorithms, each of them used, though in somewhat different ways, the parameters received approximately every 4 seconds through Mode-S transmissions. In the second approach, the parameters were analysed using the standard theory of turbulence. In the third approach, the scientists adapted a method for determining turbulence intensity previously used to measure turbulence on a very small scale in the understory of forests.
Once wind velocity in the vicinity of the aircraft was determined and its changes were analysed in successive readings, it was possible to use the latter two theoretical approaches to locate turbulence areas with an error of only 20 km. Passenger aircraft need around 100 seconds to travel this distance, so this level of accuracy would allow pilots to manoeuvre their aircraft to effectively avoid turbulence.
An easy system to implement
By harnessing the existing data, this system of turbulence detection therefore requires no significant investments in aviation infrastructure. To be operational, it just requires adequate software and a computer connected in a simple way to the devices that receive Mode-S transmissions from the transponders onboard aircraft, which are standard equipment. In essence, passenger aircraft act as sensors by creating a dense network of measurement points above Europe.
Over the coming months, the research team plans to improve upon this software but have already shown how this new method for detecting turbulence really works. The data for the research was collected in a flight test campaign that formed part of the DELICAT project, which finished in March 2014. The results detailing the new system have been published in the May 2016 issue of ‘Atmospheric Measurement Techniques’ with further details released by the University of Warsaw in August 2016.
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