Investigate the Use and Impact of “Electronic Means Complementing Visual Observation in Tower Control” on the ATCO

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Investigate the Use and Impact of “Electronic Means Complementing Visual Observation in Tower Control” on the ATCO

46TH ANNUAL CONFERENCE, Istanbul, Turkey, 16-20 April 2007

WP No. 160

Investigate the Use and Impact of “Electronic Means Complementing Visual Observation in Tower Control” on the ATCO

Presented by PLC


1.1 The aim of the paper is to address the use of electronic means within the control tower environment and their impact on the controller.


2.1  Firstly, is there a need for increased technology in the predominantly visual environment of the tower and any need for increased automation?

2.2  Current Air Traffic Management (ATM) has serious limitations with current and expected air transport growth. The goal of any ATC system is to satisfy and balance the two critical goals of safety and efficiency. All current forecasts concur about a substantial increase in aircraft numbers. Even the most efficient current air traffic control systems cannot remain as they are, because they were never designed to cope with such increases in traffic nor cater for the level of safety now demanded. Human participants in the system must make continuous adjustments in the flight scheduling and traffic patterns to maximize efficiency without compromising safety. The many redundant components in the system and the smooth communication between operators have generally been allowed to recover gracefully from failures without accident. Because ‘perfect system’ reliability can never be assumed, it is important that planners not change the system in ways that will destroy the critical failure recovery aspects that already exist.

2.3  Increases in air traffic density and complexity have led to substantial demands on the mental workload of controllers. Very high workload can affect performance and set an upper limit on traffic handling capacity. Very low workload may result in boredom and reduced alertness, with the consequent implications for handling emergencies. Evidence linking ATC operational errors to performance and workload are generally during either low or high workload situations. Such conditions increase the demands on controller monitoring and vigilance and they could increase further if systems become more automated.

2.4  Identifying the need for system enhancement

2.4.1 Automation of ATC systems and the synthetic replacement or enhancement of reality, means achieving minimum accidents and maximum efficiency. However, these goals can potentially be in conflict. It is important that in such circumstances, safety remains the number one priority. Unclear definitions of efficiency as well as lack of knowledge about the effects of proposed system enhancements on the cognitive tasks of controllers, inhibits the predictive assessment of whether and to what extent proposed improvements to equipment and automated features will actually contribute to either safety or efficiency.

2.5 Human Machine Interface

2.5.1 It is important for ATM to consider an overall design philosophy when making the liveware (the controller), hardware connection. Controllers develop strategic plans for traffic flow; monitor these plans with visual inputs to update the “big picture” of all traffic and communicate heavily with pilots and other controllers to ensure continued safety and efficiency. Controllers in towers depend heavily on direct visual sightings of traffic in the vicinity of the airport. Like all controllers, they must be prepared to deal with unanticipated events, for example, equipment failure, weather, emergency or pilot non-compliance with instructions, in a flexible manner that preserves safety even if it temporarily disrupts efficiency.

2.6 Human Factors

2.6.1  Human factors regarding technological enhancements combine the impact of ergonomics on the controller, accessing, interpreting and subsequently using information to perform our primary objective. Whatever enhancements are made, it is the total combination of all systems on the individual’s thought processes, together with the visual landscape that must be considered. By analysing the cognitive tasks of the controller both strengths and weaknesses have been identified along with a number of vulnerabilities inherent in human information processing.(Flight to the Future, 2006) The strengths include the ability to bring experiences stored in long-term memory to bear in solving novel and unexpected problems. Weaknesses include vulnerability in detecting subtle and infrequent events, in predicting events occurring in three-dimensional space and in temporarily storing and sometimes communicating information. Considerable human factors knowledge exists as to how these vulnerabilities can be addressed by design and training.

2.6.2  It is therefore imperative that changes to the ATC systems should include not only efforts to retain and capitalise on the controller’s cognitive strengths, but also efforts to compensate for weaknesses. Such compensation includes making subtle and infrequent events more prominent, providing explicit predictive displays whenever possible, providing redundant communications and visual backup for working memory when errors can be critical, providing visible feedback for state changes, and using display techniques to improve individual and shared situation awareness, both among controllers and between controllers and pilots.

2.7 System Development

2.7.1 Successful human factors programs closely link research and development activities to ensure that research activities are responsive to developmental needs. There has recently been a great deal of discussion of the concept of human-centred automation, which is viewed by many as a critical issue to the successful introduction of automation. Unfortunately, however, there are many different attributes that researchers have identified with this concept and not all these are consistent with one another. Furthermore, not all of them are necessarily consistent with the goal of attaining the best (i.e. safe and expeditious) system performance. Detailed consideration of the human- centred automation must therefore become the focus of all system design.

2.7.2  A number of components of automation have been introduced into the air traffic control system over the past decades in the areas of sensing, warning, prediction and information exchange. These automated systems have provided a number of benefits and the attitude of controllers has generally been positive. There are also a series of lessons that have been learned from other domains about the appropriate and inappropriate implementation of automation as it affects the human user or supervisor of that automation. Of concern, is the controller’s possible loss of alertness and awareness of automated functions and system functioning, which may become critical if sudden manual intervention is necessary. Humans may distrust the automation because they fail to understand its complexities and it is possible that reliance on automation may lead to loss of human proficiency in the skills that the automation replaces.

2.7.3  In many countries there is a lack of research pertaining to ATC teamwork, selection, training, performance appraisal, communication, cognitive behaviour, shared situation awareness, workload and the focus of this paper, system design. It is important that lessons learned from other domains be carefully heeded in the further introduction of air traffic control automation. Cockpit resource management (CRM) has proved effective in improving task management for flight crews. The close alignment with such programs should provide similar enhancement in all ATC workplace environments.

2.7.4  Several factors are critical to system design (Flight to the Future: Human Factors in Air Traffic Control): Extensive user input into the design process at all stages, extensive involvement of human factors specialists, who are knowledgeable about human factors design and are able to assess techniques that capitalise on users expertise; frequent opportunities for the behavioural testing (not just expert opinion) of interfaces and for the refinement of those interfaces at several points throughout the design cycle. The evolution of human-computer interaction characteristics of new systems therefore often relies on user evaluations of these characteristics as the design progresses. User participation, however, is not a substitute for the expert knowledge of the human factors specialist. The two should operate as a complementary team. (Christopher D. Wickens, Anne S. Mavor, and James P. McGee, editors)

2.8 Available and pending technologies

2.8.1 Facilities in ATM are generally governed by two factors. The prime determining factor is the category and volume of traffic handled by a facility. The second consideration is the ability or desire of the Air Navigation Service Provider to fund facilities for ATC. In turn, funding is generally driven by two aims, either for safety or as a commercial transaction for return on investment. There is no ICAO or mandated minimum equipment list required to provide ATC from a control tower. With the advent of private ownership of airfields and the commercial pressure to improve profitability, airfield operators are now more willing to contribute towards technologies that contribute to increasing aircraft movement rates. Efficiency generally has a direct correlation to profitability.

2.8.2 The following is a list divided by category of equipment used in ATC including those technologies that are still in the implementation stage. Some equipment, whilst similar in performance and capability can be described many ways by commercial propriety. The following is intended as generalisation of equipment available in the market place. It is not intended as definitive list.

Tactical Displays

  • Airborne Radar, presented in the form of a Situation Data Display (SDD)
  • Surface Movement Radar (SMR) depicting a plan view of the airfield
  • Surface Movement Guidance and Control System (SMGCS)
  • Advanced Surface Movement Guidance System (ASMGCS)
  • Automatic Dependent Surveillance-Broadcast (ADS-B)
  • Wide Area Surveillance Systems
  • Closed Circuit Television displays (CCTV)
  • Low Light Cameras

Information Based Displays

  • Electronic Flight Progress Strips (EFPS)
  • Airfield Ground Lighting (AGL) including stop bars and sectionalised lighting


  • Speech Processor Equipment (SPE)
  • Controller-Pilot Datalink Communication (CPDLC)
  • Aircraft Communications Addressing and Reporting System (ACARS)
  • Mode S interoperable links
  • Airborne Collision Avoidance System (ACAS)
  • ADS-B (Automatic Dependant Surveillance-Broadcast)

Weather Information

  • Airfield Meteorological Operating Systems (AMOS)
  • Wind Shear and Turbulence Warning Systems (WTWS)
  • Terminal Doppler Weather Radar (TDWR)
  • Light Detection and Ranging (LIDAR)
  • Lightning Detection


Alarms can be either visual or aural or both. Some require interaction by the controller to cancel or rectify a situation.

  • Short Term Conflict Alert (STCA)
  • Minimum Safe Altitude Warning (MSAW)
  • Runway incursion
  • Crash Alarm
  • Go-round alarm
  • Equipment failures, RADAR, radio and lighting
  • Lightning Warning
  • Windshear
  • Communications panel

2.9 Known advantages or shortcomings with current technology

2.9.1 SDD The use of Primary Radar and Secondary Surveillance Radar (SSR) for coverage in the Terminal Area (TMA) is a primary tool to assist the controller in the provision of separation. The raw data available, giving speed and altitude, the history display of target motion and predictive ability, give rapid situation awareness to multiple users. It is invaluable in providing position information beyond visual range, and for accurate separation information where it cannot be provided visually in the azimuth. It is just as useful to the controller to provide spacing information, determining accurately wake turbulence standards and closure rates.

2.9.2 SMR  SMR targeting is provided by transmitting on a set frequency. Different frequencies have different properties. The K or KU-band SMR (Air Traffic Safety Electronic Engineers of Hellenic Civil Aviation Authority) has a higher resolution than the X-band SMR during good weather. During heavy rain the X-band, (Future Airports) however is of better performance since the KU-band has a limited ability to penetrate rain. Therefore it is preferable X- band is used or that the two systems are operated in tandem to overcome gaps in coverage during adverse weather.  For existing K or KU- band SMRs, they present the controller with a constant dilemma. The equipment works well in good visibility, but has poor or no performance in adverse conditions, when the demand on the system can be at a peak. Secondly, both the K- band Radars have a tendency to present false targets, lose and swap labels when traffic operates in close proximity to each other. This can be extremely disconcerting to the controller in a high workload situation if system integrity is not guaranteed. If recognition of corrupt data is not determined, it can quickly escalate into an incident or accident.  Obviously, a raw display has very limited capability to assist the controller. With a labelled display, a significant disadvantage is that the controller is required to manually assign a data tag. At large airfields, high workload, at night and during reduced visibility, this contains the inherent risk of possible misidentification of traffic by incorrect labelling.  Situation awareness is obviously a significant issue for the controller and if lost, can have catastrophic results. As can be seen from the Singapore accident in Taipei in 2000 where the aircrew lost situational awareness and commenced take-off from the wrong runway and in Linate, where a Cessna business jet crossed an active runway and collided with a departing MD-87. If situational awareness had been maintained by the controllers, it is highly probable neither incident would have occurred. This would indicate that had SMR been operational in both circumstances both accidents would have been prevented.

2.9.3 A-SMGCS  The target information provided to the controller with this technology is a composite of feeds from multiple sensors around the airfield together with one or more SMRs (Northrop Grumman). The process of multilateration, by interrogating aircraft and vehicle transponders, provides reliable identification and location information to the controller with accuracy to within 5 metres. Other textual and graphical information is also available, providing, incursion alarms to runways and conflict alerts. Integration with collaborative decision making tools, such as the AMAN and DMAN, can be of great assistance to assist the controller with tactical decision making. These tools can achieve a significant reduction in fuel burn by minimising time with engines operating. This is a directive incentive for the airlines and airfield operators to contribute towards their implementation.  The SMR coverage is included to cater for system redundancy. The disadvantages with a stand alone SMR in the areas of target loss, label swapping and false targets are virtually eliminated with the introduction of A-SMGCS.  A-SMGCS is also designed to couple with the AGL to enable a “follow the greens” concept by using the routing and guidance functions in the Radar Data Processor (RDP). The system can support all vehicles and aircraft with routing and guidance.  The next development is the integration of Datalink and cockpit displays in airfield ground operations. Surface operations during high traffic volumes are inefficient and prone to excessive radio frequency congestion. Suitably equipped vehicles and aircraft can however operate with less voice communication load, providing situation awareness, (all participants in the system can be presented with moving map presentation of all relevant targets and potential conflicts) with less restriction in both control function and during low visibility conditions.  The technology is available to Datalink clearances to aircraft and that information is then able to be displayed on a moving map in the cockpit. One overriding concern with this technology is that en-route studies have revealed that pilots are slower to react to Datalink than voice commands (Becky L. Hooey). This may have important implications for surface operations as dynamic route amendments, hold instructions and expedited runway crossings are frequent. However, surprisingly, the impact of Datalink on surface operations remains untested.

2.9.4 ADS-B ADS-B (Fly Light Flight Planning and Navigation) is an ATC surveillance technology currently under trial in both the USA and Australia, with the expectation that it can substantially contribute to ATC surveillance and separation, at a comparatively low cost. The Australian trial allows an SSR- like traffic separation service across current non radar airspace. The trials in Australia have recently uncovered problems with system integrity should unauthorised users input spurious information. Because of the continual transmissions required by the system, it has a direct application as a communication tool also.

2.9.5 CCTV/ Low Light cameras These applications provide assistance to fill in visibility gaps over large or restricted viewing areas. Low light and intelligent digital cameras can provide imagery regardless of atmospheric conditions or time of day. One of the problems for use in ATC is how to integrate these displays ergonomically into the console so that the controller can assimilate the information into a “real world” visual scan. If employed intuitively, these devices can overcome major design flaws in control tower design and poor line of sight areas on tarmacs.

2.9.6 EFPS  EFPS design has been driven by two requirements: functional requirements and human factors. (Nathan Doble) EFPS must support all the functionality of paper strips and have considerable levels of redundancy in the event of system degradation or failure. Many of the benefits of the paper strip have been noted (Mackay, 2000). These form the basis of the human factors requirements for EFPS. Namely such a system should minimise head-down time, maintain controller mobility with the tower cab and facilitate interaction between controllers. It is imperative to minimise the possible culture shock, that EFPS permit an intuitive adaptation from the paper environment.  The development of voice activated functions incorporated into EFPS by some manufactures is a very progressive step in reducing head-down time and permits intuitive adaptation from the paper environment.

2.9.7 CPDLC/ ACARS/Mode S Radar  This technology has the potential to significantly reduce workload in many aspects. It can also have a destabilising effect on the controller of not having the immediate response that exists with voice communications.  In efficiency terms, it allows multi tasking by the controller in a very short time frame. It also permits lack of corruption by incorporating the WYSIWYG (what you see is what you get) to both parties in the communication loop. Not only does this eliminate wrongly interpreted clearances or instructions, it has a direct correlation to increased efficiency and reduction in “say again”. It is particularly effecting in overcoming language problems involving non-native English aircrew or controllers.  Added advantages of these links are the seamless communication between cockpit and controller. In the case of WTWS (see below), all warnings can be sent direct to the flight deck. Similarly, with TCAS Resolution Advisories (RAs) it is now being trialled that advisories generated by airborne collision avoidance systems (ACAS II) be sent in near real time to the controller to keep ATC in the information loop, rather than out of it as in the current situation.

2.9.8 WTWS/ TDWR/ Lidar Windshear is an extreme form of weather and, if encountered at speeds and at an altitude in the flight envelope where there is little margin to maintain safe operations, it can rapidly result in an unsafe situation or accident. The advent of equipment then that can predict or forecast such conditions would seem a radical step forward.  A lot of the equipment (WTWS & Lidar) available though is still in a developmental stage and in many cases is being tuned by direct comparison between forecast and actual conditions by the use of algorithms. In practice, the information can be highly inaccurate. Often forecast windshear or turbulence doesn’t materialise and at the opposite end of the scale, when it is not forecast, it occurs. It is also common to have “caution windshear +20 knots on final” forecast by TDWR and then to have aircrew report and actual of -15 knots. In total, a differential of 35 knots from the expectation passed by ATC. When such circumstances occur, the information passed is totally counterproductive to the planned approach by aircrew.  The dilemma for the controller is if equipment indicates forecast windshear and a significant amount of traffic does not report any occurrences, should the warnings be issued? By continually advising pilots of the possible incidence of windshear at a location, it has the effect of de-sensitising aircrew if they continually fail to experience any. Secondly, if warnings are to occur at critical stages of flight, should these be passed considering the possible distraction to aircrew?  Lidar uses the same principle as RADAR. The Lidar instrument transmits light out to a target. The transmitted light interacts with and is changed by the target. Some of this light is reflected back to the instrument where it is analysed. The change in the properties of the light enables some property of the target to be determined. The time for the light to travel out to the target and back to the Lidar is used to determine the range. In the ATC application it is intended for the determination of turbulence and windshear.

2.9.9 AMOS  Similar to the WTWS detection equipment, if the information is synthetic and processed and not a direct feed of actual information, controllers will lose faith in the system. This normally occurs where gust information or maximum deflection in a rapidly varying wind situation is not included in crosswind and downwind components generated by preset criteria. There are numerous instances where a quick mental calculation of wind speed and direction will give a significantly more dramatic outcome for crosswind and downwind components than computer generated results. Where aircraft are operating at critical weights and take-off data can be radically affected by small increments of wind, this puts the controller in a predicament where they may unintentionally pass inaccurate information that gives aircrew a misleading.  Similarly, in adverse weather and aircraft are operating at near maximum permissible crosswind limitations, the passing of inaccurate wind information can be critical. Again the controller is placed in a situation where a system has a level of automation to cover normal operating situations, but is seriously flawed in the worst possible case scenarios.

2.9.10 RVR RVR can have a significant impact on operations. It is not uncommon for the perceived visibility to be considerably different that detected by sensors. Again, if the controller loses faith with the accuracy of critical meteorological information such as wind speed readout, windshear warnings and visibility, what is our legal and or moral obligation towards transmitting such information?

2.10 Research required minimise the fragmentation of information provided

2.10.1  Due to the numerous ANSPs worldwide and the commensurate variance in financial capabilities, ATM does not present a unified front when providing equipment to controllers. The extensive research conducted in the airline industry towards flight deck operations by comparison demonstrates how uncoordinated global ATM is when adapting new technologies. Using Boeing and Airbus Industries act as models of systems integrators, they link several different technologies all geared towards aircrew performance. By contrast, in ATC technologies are generally developed independently of each other. ANSPs procure equipment based on a perceived requirement and usually with limited capital and as is quite often the case, system integration is compromised or nonexistent. Controllers are left to discover and close the technological gaps. In some cases these gaps are only highlighted by incidents or accidents because of the lack of human factors studies with one-off equipment purchases.

2.10.2  To get the best result from human factors contributions, they have to be planned and organised, with the resources and funding for appropriate contributions at each stage. There is nothing specific to human factors about this. If the management, planning, hardware or software is inadequate at any stage during system evolution, their inadequacy also will affect all subsequent stages. (Hopkins 1995)

2.11 The need for automation

2.11.1 2005/06 has seen record number of orders taken by both Boeing and Airbus Industries. With a different Marketing strategy by Boeing where they are promoting less hub and spoke operations with the efficiency of the B787, there is a high probability that many new routes will eventuate by pairing previously uneconomic destinations. Air traffic growth rates in China have been averaging 16% per year and are expected to continue until 2020. (Air transport Press Release). They are expected to double their current fleet of aircraft in 5 years. India has been recording similar traffic growth. With the traffic levels projected to increase significantly in the medium term, the rapid increase in Low Cost Carrier operations and the expected growth in the emerging Very Light Jet (VLJ) in the air taxi role, it will become harder for controllers, unaided, to manage traffic safely and efficiently. In particular as traffic levels increase there is a tendency for traffic conflicts to increase significantly (i.e. where there is a danger of losing required separation between two aircraft). (Kirwan 2002)

2.12 The mental model of the controller

2.12.1 Mental models embody stored long-term knowledge that can be called upon in direct problem solving and interaction with the relevant system when needed (Dubois & Gaussin, 1993; Endsley, 2000b). Within the ATC context, an accurate up to date mental model of system functioning is critical because it “provides a mechanism for guiding attention to relevant aspects of the situation, integrating information perceived to form an understanding of its meaning and projecting future states of the system based on its current state.

2.13 The picture

2.13.1  Using information from both external and internal sources, controllers build a comprehensive mental representation of the current traffic scenario. This representation is commonly referred to as the picture (Whitfield & Jackson, 1982). The controller’s picture consists of all that is perceived and is meaningful, interpreted in the context of recalled events and those predicted using professional knowledge and experience.

2.13.2  Which tasks should be allocated to the machine and sub-system and which to the human? (Isaac, Anne, R. & Ruitenberg, I. 1999) In reality it seems, as much as possible goes to the machines and the human does what is left. This is usually the result of engineering economics, in which the cost of a system is often the most important factor. There are, however, economic implications to all human factor decisions and they will affect both original and operating costs.

2.13.3  Initial outlay to implement a system should not be viewed in isolation. It can be seen that many new technological systems are often designed and installed with regard for the operator’s ergonomic requirements and no consideration from a systemic or operational stand point. In terms of the implications for these changes in the working environment, Weiner (1994) suggest the following:

“To consider human factors properly at the design stage is costly, but the cost is paid only once. If the operator must compensate for the incorrect design in his training programme, the price must be paid every day. And what is worse, we can never be sure that when the chips are down the correct response will be made.” (p20)


3.1  There is sufficient evidence that Human-Centred Automation is central to our ability to cope with increased traffic demand. As mentioned earlier in Human Factors, the controller should be supported by systems design to overcome known human weaknesses. It is recommended that systems be developed using predictive air traffic control workload models similar to those used for flight control and management tasks, and to initiate additional studies to rectify the relative paucity of studies of underload and boredom in air traffic control. This will become more relevant in highly repetitive actions as traffic levels increase.

3.2  The teaming of controllers with Human Factors specialists to integrate some or all of the technologies listed above into ergonomic work stations that match controller thought patterns, in the control tower environment, will match our goal of safe, efficient ATM. It is paramount that the controller does not become flooded with information or placed in a legally complex position by being in possession of too much information with the advent of new systems. Especially in the visual environment of the control tower, it is vital that systems design does not promote fixation on electronic information and inhibit the primary scan of the external environment. With the advent of Head-Up Displays (HUD) becoming common place in commercial aviation, there is obviously a perceived need to avoid fixation by aircrew when scanning flight instrumentation. Whilst this technology is emerging perhaps it would be advantageous to rapidly integrate it into the tower environment to provide similar benefits to the controller.


4.1 That this paper be accepted as information.


Air Traffic Safety Electronic Engineers of Hellenic Civil Aviation Authority.

Surface Movement Radar. KU band frequency diversity. Retrieved from web site:

Airtransport Press release: retrieved from web site:

Becky L. Hooey, Monterey Technologies/ NASA Ames Research Centre, Moffett Field, CA: Integrating Datalink and Cockpit Display Technologies into current and future taxi operations. PDF file retrieved from web site:

Christopher D. Wickens, Anne S. Mavor, and James P. McGee, editors.

Panel on Human Factors in Air Traffic Control Automation, Committee on Human Factors, Commission on Behavioural and Social Sciences and Education. NATIONAL ACADEMY PRESS, Washington, D.C. 1997.

Dubois, M. & Gaussin, J. (19930. How to fit the Man-Machine Interface and Mental Models of the Operators. Verification and Validation of Complex Systems: Human Factors Issues/ Wise, J., Kopkins, D. & Stager,P. Springer-Veralg, 110: 381-397.

Endsley, M.R. (2000b). Situation Models: An avenue to the modelling of Mental Models. Proceedings of the IEA/HFES 2000 Congress, San Diego, CA. Human Factors and Ergonomics Society.

Flight to the Future: Human Factors in Air Traffic Control. Cognitive tasks. Retrieved from web site:

Fly Light Flight Planning and Navigation, retrieved from web address: Kirwan B. Human Factors and Aerospace 2 (2), 2002 pp 105-146

Future Airports. System performance. Retrieved from web address

Hopkins, V.D. (1995) Human Factors in Air Traffic Control. London and Bristol, PA. Taylor & Francis.

Nathan Doble. An Interactive Electronic Flight Progress Strip Prototype. MIT International Center for Air Transportation, Room 35-217, 77 Massachusetts Ave., Cambridge MA, 02139 USA. Retrieved from web site:

Northrop Grumman, retrieved from web address:

Wiener, E.L. : Digital Woes: Why We Should Not Depend on Software. Reading, Mass: Addison-Wesley. 1994.

Whitfield, D., & Jackson, A. (1982) The Air Traffic Controller’s ‘picture’ as an example of a mental model. In G. Johannsen & J.E. Rijnsdorp (Eds), Analysis, Desgn and Evaluation fo Man-Machine Systems (pp 45-52) Düsseldorf, W. Germany: International Federation of Automatic Control.

WTWS & Lidar, Windshear and Turbulence Warning System, Hong Kong International Airport. Retrieved from web site:

Lidar Tutorial. Retrieved from web site:

Last Update: September 29, 2020  

April 12, 2020   824   Jean-Francois Lepage    2007    

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