Leading the way with LiDAR

A vital if unsung hero in the tools we use, LiDAR measures the distance to a target by illuminating the target with laser light and measuring the reflected light with a sensor. Differences in laser return times and wavelengths can then be used to make digital 3D representations of the target. By repeating this in quick succession, the instrument builds up a complex 'map' of the surface it is measuring.

Our LiDAR story began in 2007, when we first deployed a Lockheed Martin WindTracer LiDAR at Frankfurt airport for the European CREDOS project – Crosswind-reduced Separation for Departure Operations to analyse crosswind impact on wake decay.

In specific crosswind conditions, wake vortices are blown away from the trajectory of other aircraft and so no longer pose a safety risk. We used the LiDAR to measure the vortices of departing aircraft, resulting in recommendations to adapt crosswind criteria to reduce or suspend departure wake separation.

At Paris Charles de Gaulle (CDG), we used LiDAR to measure wind hazards and wake turbulence between their two closely spaced runway pairs, in order to measure the impact of wake turbulence from landing traffic on one runway on departing aircraft on the parallel runway. The goal was to establish whether wake constraints could be lifted, improving departure queue management and runway throughput, and reducing taxiway congestion.

This saw the WIDAO project (Wake-Independent Departure and Arrival Operations) undertook an extensive data-gathering exercise, collecting more than 6,000 heavy aircraft wake tracks and 25,000 tracks from medium aircraft.

In parallel, radar post-processing algorithms were used to collect more than 80,000 aircraft departure rolling distances and more than 75,000 landing separation distances on approach from different radar systems. WIDAO defined the first wake risk assessment methodology metrics applied by EUROCONTROL and as a result, CDG now operates its closely spaced parallel runways independently. WIDAO has been in operation since 2010, delivering a 5% increase in runway throughput.

EUROCONTROL also used its LiDAR to collect data to support the operational implementation of Time-Based Separation (TBS) at London Heathrow (LHR).

Over 120,000 tracks were collected during four years. Additional tracks were collected at Twickenham in London to measure wake at higher altitudes on the glideslope.

TBS uses time instead of distance to separate aircraft in strong headwind wind conditions that slow aircraft down on approach, reducing an airport’s landing rate. In strong winds, wake decay is faster and wake is quickly dispersed. The key principle underlying the concept is to define a distance separation as a function of headwind. This means that landing aircraft can be separated safely using time instead of distance, so maintaining runway throughput.

TBS was successfully implemented at Heathrow in March 2015, and has been in continuous operation ever since. Results have been very successful with a reduction of over 60% in arrival ATFM delays due to headwinds resulting in a marked improvement in overall airport punctuality.

Our work on wake turbulence has led to some very successful spinoffs. Perhaps the most useful is the re-categorisation of aircraft types, RECAT. ICAO has three wake separation categories, and in RECAT we developed a six category separation scheme.

So, LiDAR has been a highly successful tool for helping European aviation improve capacity safely - and we are currently developing a method of detecting and analysing wake vortices in real time to safely reduce separation minima by identifying the location and characterisation of wake turbulence’s strength.