Wind monitoring Ludovic Thobois, scientific partnership and animation manager for meteorology and aviation, Leosphere

FLYING HIGH Obtaining detailed insights into upper air wind behavior above airports is now possible thanks to remote sensing technologies

90 • METEOROLOGICAL TECHNOLOGY INTERNATIONAL SEPTEMBER 2018 Wind monitoring

irports may be interested in the represent just 6% of flight time, it’s a sad fact same characteristics of wind as that 57% of accidents occur then – which is A other industries, but the why winds during these phases are the most significance of these factors to important to measure and forecast. the air traffic management (ATM) sector is crucial. Wind speed and direction are INTRODUCING WEATHER RADAR… principal factors, helping to determine the AND LIDAR landing and take-off configurations as well At Hong Kong (HKIA), as the procedures for approach and take-off, China, the wind sensor data gathered from such as the choice of the . anemometers and weather buoys is analyzed Windshear, for instance, refers to a change by the anemometer-based Windshear lasting several seconds in the direction and/ Alerting Rules – Enhanced (AWARE) system or speed of the wind. A decreased lift will to issue windshear alerts. cause the aircraft to drop below its intended HKIA also employs a Terminal Doppler flight path, while an increased lift will of Weather Radar (TDWR) system, which course have the opposite effect. A sustained continuously scans the high runway corridors change to the headwind or tailwind of 15kts to detect windshear and microbursts (intense is classed as significant windshear. It can small-scale downdrafts produced by a make planes on approach or departure much thunderstorm or rain shower). Being more difficult to control, and much more radar-based, TDWR works only when rain susceptible to the need for rapid corrective occurs. So, what can be done to measure action. According to the International Civil wind at altitude on dry days? Aviation Organization (ICAO), windshear At HKIA, the answer came in the phenomena have caused more than 1,400 form of a Doppler lidar system, capable deaths in aviation. Its unpredictability is also of detecting airborne particles as small as responsible for the disruption of air traffic 1.5μm and providing real-time detection management, which can have a substantial of windshear at up to 10km (6.2 miles) in business impact on airport operations. the glide slope. HKIA was the first airport Turbulence is another consideration, in the world to deploy a lidar sensor for referring to the rapid irregular motion of air. wind shear measurement. It brings about rapid bumps or jolts, but only Over the past 20 years, significant occasionally does it have a significant improvements have been made in lidar influence on an aircraft’s intended flight path. techniques, largely as a result of the However, in severe instances, abrupt changes introduction of optical fiber technology. in the altitude and attitude of the aircraft may The low cost and high reliability of its occur, the pilot may suffer a momentary loss components, which have led to their of control, and passengers may be injured. widespread use in the mainstream Finally, wake vortex is a form of telecommunications industry, are now being turbulence generated by all aircraft when appreciated in ATM. Examples of compact, flying. Wake vortices vary in relation to a reliable and accurate atmospheric lidar number of conditions, including the size of sensors that have been developed and the aircraft creating it and the airport’s own industrialized include those from ONERA, local wind and turbulence conditions. the French aerospace lab, and Leosphere, in As you’d expect, wind conditions are a the form of the Windcube product series. major concern for ICAO. At present, however, Further improvements in power, range and its current meteorological guidelines mention reliability are being made all the time. only conventional surface wind Working in conjunction with TDWR and measurements, measured at 33ft above the ground-based measurement systems, Doppler ground. They fail to address wind conditions lidar enables airports to create and sustain an in the upper air, especially along the initial all-weather 3D monitoring solution. Windcube 400S-AT take-off and final approach landing corridors monitoring (up to 1,640ft). If air traffic management is to : A CASE IN POINT windshear at operate at its most efficient levels, and if Dubrovnik has one of ’s busiest Dubrovnik Airport safety precautions are to be at their best, airports, handling more than two million for Croatia Control other measurement methods clearly need to passengers in 2016. The airport is around be employed. While landing and take-off 15km (9.3 miles) from the city center, near

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Schematic view of Bora winds on the Adriatic Coast

Windcube 400S-AT averaged data availability measured at Dubrovnik Airport

the shore of the Adriatic Sea, about 160m to 200m (656ft) under clear air conditions, Commission as a contribution to the (525ft) above sea . The Dinaric Alps, a and with a wind accuracy of better than SESAR2020 R&I program. mountain range rising to 1,000m (3,280ft), 0.3m/s (0.7mph). In addition to the submission, Croatia run closely parallel to the coastline, and slope The Dubrovnik Windcube installation Control is also working at a national level down to the airport and to the sea beyond. measures the crosswind created by the Bora, with airports, airlines and academia on the The prevailing winds are generally low, especially on the approach of Runway 12, on Bora Dubrovnik Project. Due to start in 2019, but in winter the airport is particularly which it has the greatest impact. It was deployed it’s a four-year program aimed at developing a susceptible to what is known as the Bora 1.35km (0.8 miles) away from the runway and Bora event decision support system. wind. This is a northern to northeastern close to its threshold. The maximum range “It’s good to see the spatial data that lidar katabatic (or down-slope) wind on the lee exceeds 10km (6 miles) and enables large scale obtains,” says Alen Sajko, director of the MET side of the Dinaric Alps and down to the monitoring around the airport. Division at Croatia Control. “It’s something Adriatic Sea. Bora events can last from a During the trial, 14 Bora events were you simply don’t get with anemometers. We couple of hours to several days, and can logged and measured at speeds of up to were never able to see patterns like these induce strong crosswinds of up to 70kts. 60kts. One of them lasted 1.5 days, with before. It’s very useful. For example, we These wind events have a major impact on the wind veering from the north to the discovered that one part of the skies above the air traffic control at Dubrovnik Airport and northeast and strengthening from 8 to 23kts airport is much more affected by Bora events. also at other airports on the Adriatic coast, – and gusting up to 35kts. Strong turbulence The positioning of the anemometers meant we causing many delays. They can sometimes and fluctuations along the vertical were couldn’t have picked this up in any other way. cause the airport at Dubrovnik to close, recorded, and on the RHI vertical slice, a “Lidar has also confirmed that when an necessitating the rerouting of all incoming strong wind was measured as well as a great aircraft is subjected to these events, its flights. Even more importantly, Bora winds deal of flow separation (turbulence) 2km (1.2 vertical speed can change dramatically in have huge implications for flight safety, and miles) away from the equipment, and thus just 20 seconds,” he continues. “It is vital need to be fully forecast and mitigated. close to the airport itself. information that we can pass on to pilots The meteorological department of Croatia Croatia Control is still analyzing the and to air traffic control, and that we can Control is interested in better characterizing data gathered during the exercise, and is also use to produce better forecasts.” the Bora winds and in improving forecasts at comparing the findings with measurements Dubrovnik Airport. It is currently working from on-site anemometers. It is working with WEATHER SYSTEM INTEGRATION on a four-year project to develop a Bora event the Department of Geophysics in the Faculty Lidar information can be readily integrated decision support system. As a result, last of Science at the University of . It will into weather systems. For example, Windcube winter it launched a wind measurement also be making a submission to the European data can be combined with IRIS software from campaign as part of its activities in the SESAR 2020 (Single European Sky ATM Research) Research and Innovation (R&I) program, Air traffic management: lidar benefits including a scanning Doppler Safety General conditions Performance optimization Windcube 400S-AT lidar Detailed data gathered at flying heights to show - Weather forecasts – - Better runway management system from Leosphere that real-time and trending conditions of: including fog prediction - Better air traffic control could characterize the winds - Windspeed and direction (currently at proof-of- management of distance in three dimensions. - Windshear concept stage) between aircraft on This equipment provides - Turbulence - Cloud base measurement approach and take-off remote measurements of - Wake vortices - Volcanic ash detection - Better noise reduction winds and aerosols/clouds - Air traffic management awareness of procedures inside the planetary unmanned aerial vehicles (UAVs, also known boundary layer (PBL) with a as drones) in the air near airports resolution from 75m (246ft)

92 • METEOROLOGICAL TECHNOLOGY INTERNATIONAL SEPTEMBER 2018 Wind monitoring

Samples of Bora wind measurement by the Windcube 400S-AT

Vaisala and Rainbow 5 software from Selex to there is simply no alternative. Lidar is defining the separation of aircraft as a display relevant and operational meteorological used for designing new wake turbulence function of wake behavior captured in the products such as windshear alerts. regulations, performing the safety assessment previous 10 minutes. The application is still to validate the potential implementation of an in development but it is on its way. ADDRESSING WAKE TURBULENCE existing wake turbulence regulation, and for Airports are interested in Doppler lidar for performing the risk monitoring. LIDAR MOMENTUM another reason. Around 40 years ago, ICAO Eurocontrol is also making use of lidar The interest international airports are standards defined wake turbulence categories to develop a separate, time-based separation showing in Doppler lidar is growing rapidly. and their separation distance minima to model. “Headwinds affect flight times and By the end of this year there will be four prevent the risk of wake vortex encounters. distance and so have a bearing on the times as many airports permanently Larger aircraft both create and can tolerate intervals needed between aircraft,” explains equipped with the technology as six years larger wake vortices – so minimum safe Vincent Treve, runway throughput and wake ago, and several more trials are taking place distances will depend on the size of the project manager at Eurocontrol. “We have an worldwide. It’s likely that as air traffic leading and following aircraft in the pattern. implementation at Heathrow, and another is volumes grow, so too will interest in the For more than 10 years, Eurocontrol, an in progress in .” detailed measurement of wind in general. intergovernmental organization working to In addition to trends calculated from the In addition, many other tasks can be build pan-European ATM performance, has offline analysis of data, many airports like to performed by Doppler lidars developed worked with ICAO and others to develop a cross-check wake data after deployment – so originally for wind: cloud base measurement new, optimized categorization of aircraft. Eurocontrol has developed a lidar-based and the characterization of aerosol hazards Approved by the European Aviation Safety platform for the continuous monitoring of such as ash plumes. Doppler lidars are also Agency (EASA), RECAT-EU aims to increase risk. In addition, the organization is merging expected to become the super ceilometer, airport capacity safely by redefining wake databases of data gathered from several sites with numerous functions for better mitigating turbulence categories and the minimum safe across Europe – it expects new concepts to adverse wind and aerosol hazards, and for distances between aircraft. emerge from this initiative. enhancing the weather resilience of ATM. To implement these new regulations, For Treve, lidar’s two principal ATM roles Combined with its benefits in terms of safety, wake vortex data must be collected by a lidar of monitoring risk and measuring wind will ATM efficiency, and increased insight, it’s sensor: in dry weather and at flying height, in time be joined by a third application: clear why lidar is about to take off. z

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