IMPROVED AIRCRAFT DOCKING SYSTEM

Field of the Invention

The present invention relates to an aircraft docking system located at a docking site, said system comprising distance determining means configured to determine at least a distance between the system and an aircraft.

Description of related art

In recent years demand at airports for efficient operation has increased and with that has arisen at many airports a need to replace manual marshalling of aircraft to the gate by automatic aircraft docking systems.

Automatic docking systems are typically based on techniques, which are more or less affected by reduced visibility, e.g. due to fog and precipitation. The expression "visibility" is to be interpreted as atmospheric trans- mittance of electromagnetic radiation at a relevant wavelength. One example of such a system is disclosed in US Patent 6,563,432 in which a system for detecting and determining a distance to aircraft scans an area at a gate with laser pulses . The reflected laser pulses are analyzed in order to detect solid objects and also to distinguish between solid objects and fog or precipitation.

Another example of an automatic docking system, which is affected by visibility conditions, is disclosed in US patent 6,542,086. The system in US 6,542,086 utilizes a video camera as a sensor.

A drawback with such systems is that they do not always allow docking in all weather conditions during which the airport is open for traffic. The aircraft may need guidance at a distance of 80 - 100 meters away from the nearest location where a docking system can be mounted, typically at a gate, while the airport may still be open for traffic at a visibility less than 80-100 meters. A result of this is that, during the conditions when automatic docking is impossible due to fog or precipitation, the dockings has to be carried out manually by marshal- lers . A problem with such a situation is that the need for manual marshalling may not be apparent until an aircraft is approaching a gate, and it turns out that the fog or precipitation is too dense for the docking system to be able to give guidance. At a large airport this may happen at several gates at the same time and as it is not planned it may cause disturbances of the airport operation with associated problems such as added cost or decreased safety.

While the system disclosed in the US Patent 6,563,432 detects, identifies and docks aircrafts and also determines whether a detected object is solid or whether fog or precipitation is present, it does not determine whether automatic docking is impossible or not.

Generally, measurement of visibility is performed at airports by the use of visibility meters located near to runways. The output of the existing visibility meters is, however, typically not very representative of the conditions at the docking systems as these normally are located at gates in close vicinity of terminal buildings, and as the density of fog usually vary very much over an airport. Moreover, installing such a visibility meter at

each gate is not an optimal solution. The output of the meter may still not be representative of the conditions that governs the performance of the docking system as fog often exists in patches and as the operating area for the system is a sector extending about 100 meters out from the system. Another disadvantage with such a solution is the added cost of providing a plurality of expensive visibility meters.

Summary of the invention

Hence, from the above discussion of drawbacks related to prior art systems it turns out that a need exists in the art for an aircraft docking system with the ability to determine whether the visibility conditions allow docking with the system or not.

An object of the present invention is therefore how to configure a docking system to determine the visibility conditions within its working area and to provide a signal when these conditions no longer allow docking with the system.

To achieve this object the present invention provides, in a first aspect, an aircraft docking system configured to be located at a docking site. The system comprises distance determining means configured to determine, using electromagnetic radiation signal reception means, at least a distance between the system and an aircraft. The distance determining means are further configured to measure at least one property of a receiver signal received by said signal reception means, said property being related to the visibility at the docking site, compare said measure of the at least one receiver signal property with a threshold value, and depending on said comparison,

provide a signal indicative of whether or not the visibility at the docking site is good enough to allow safe docking with the system.

In a second aspect, the invention provides a method for controlling aircraft docking in an aircraft docking system located at a docking site. The system comprises distance determining means configured to determine, using electromagnetic radiation signal reception means, at least a distance between the system and an aircraft and the distance determining means perform the steps of measuring at least one property of a receiver signal received by said signal reception means, said property being related to the visibility at the docking site, comparing said measure of the at least one receiver signal property with a threshold value, and depending on said comparison, providing a signal indicative of whether or not the visibility at the docking site is good enough to allow safe docking with the system.

In a third aspect, the invention provides a computer program comprising software instructions that, when executed in a computer performs a method as discussed above .

In a fourth aspect, the invention provides a use of an aircraft docking system for controlling operations at an airport.

In other words, a system according to the present invention is configured to check the visibility conditions of the working area of the docking system before and/or during docking of an aircraft. The system measures characteristics which are related to the visibility at the docking site and which limits the performance of the

system. The measuring results are used as a determining factor in determining whether the visibility conditions allow safe docking or not.

An advantage of the present invention is hence that it provides to an operator of an airport an enhanced ability to determine whether or not it is possible to perform a docking operation when visibility is reduced to such an extent that there exists an uncertainty whether or not safe docking is possible or not. For example, prior art systems are typically unable to distinguish between dense fog or precipitation and parts of approaching aircraft. Needless to say, such lack of distinguishing capability may lead to dangerous situations. On the other hand, prior art systems may be configured to account for such lack of distinguishing ability and simply provide a signal to the effect that docking is impossible when the system is uncertain. This, however, means that the availability of prior art systems is not as high as the availability of a system according to the present invention.

Furthermore, an advantage is that it is possible to determine in real-time, and continuously, whether or not the density of the fog or the precipitation makes automatic docking impossible or not and keep the traffic controllers informed about it. The need for marshalling can be foreseen and thereby marshallers can be in place when the aircraft arrive and disturbances in terms of docking delays can be avoided. Efficient airport operation is thereby achieved, e.g. in terms of less waiting time for aircraft and faster and hence more efficient allocation of arriving aircraft to gates and terminals where automatic docking is possible.

Yet an advantage of the invention is that, by providing a solution to the problems as discussed above, an already existing docking system may be adapted to also provide a signal indicative of the visibility conditions at the docking site. Typically, an implementation will only entail re-programming of control software in the system, which means a large saving in cost when comparing with a situation in which a separate visibility system would be needed. There is no need to adapt any hardware of the existing docking system as the wavelength interval in which a docking system operates is also suitable for operation in connection with the determining of visibility conditions .

Embodiments of the invention include those where the distance determining means are configured to measure receiver signal properties in terms related to scattering of the electromagnetic radiation. For example, the distance determining means may comprise laser ranging means and the distance determining means may then be con- figured to measure scattering of the laser radiation.

Alternatively, the distance determining means may comprise radar ranging means and the distance determining means may then be configured to measure scattering of radar radiation. In further embodiments, backscattered electromagnetic radiation, or more precisely, a power distribution of the backscattered radiation, indicates the scattering.

Further embodiments include those where the distance determining means comprise signal reception means comp- rising imaging means configured to provide two-dimensional images of the docking site and where the distance determining means are configured to measure the at least

one property of the receiver signal at least in terms related to a contrast difference between at least two areas within an image. These image areas may correspond to predetermined locations, preferably at a same distance from the system, at the docking site.

In other words, where the docking system utilizes a two- dimensional imaging technique, the measure of visibility conditions is the contrast in an image. Analysing an image signal used for determining the location of the aircraft and determining the deterioration of this signal caused by the fog or precipitation provides a good indication of whether or not the visibility deterioration exceeds the level above which docking is unsafe or even impossible .

The imaging means may be configured to detect electromagnetic radiation in any of a visual wavelength interval and an infrared wavelength interval as well as detecting electromagnetic radiation in both of these wavelength intervals .

Brief description of the drawings

The invention will now be described in more detail with reference to the attached drawings on which:

Figure 1 schematically illustrates docking sites at which docking systems according to the invention are arranged.

Figure 2a schematically illustrates a docking system according to a first embodiment of the present invention.

Figure 2b is a graph of a response curve relating to a electromagnetic pulse reflected in fog.

Figure 3 schematically illustrates a docking system according to a second embodiment of the present invention.

Figures 4 and 5 are flow charts of methods according to the invention.

Preferred embodiments

Figure 1 illustrates schematically a view from above of a situation at an airport. A terminal 101, which may be a passenger terminal and/or a freight terminal, is. config- ured with a first aircraft docking system 115 and a second aircraft docking system 117. A first docking site 103 and a second docking site 105 are located at each docking system 115, 117 respectively. Although the docking sites are indicated by dashed lines in figure 1, these lines need not represent actual markings on the ground but should only be perceived as an aid in reading the present description.

Moreover, although figure 1 shows that both docking systems 115, 117 are attached to the terminal 101, alterna- tive configurations include those where a docking system is not directly attached to a terminal but to any other suitable means at a docking site. In fact, a docking site may not be directly associated with a specific terminal, and may also be associated with a designated docking site anywhere at an airport where airport operations allow docking.

The situation illustrated in figure 1 is one in which a first aircraft 111 is approaching the first docking site 103 along a guiding line 107 on the ground. A second aircraft 113 is located at the second docking site 105,

having performed a successful docking operation and being connected to the terminal 101 via a passenger bridge 109.

The first docking site 103 is to a large extent covered by fog 119. The fog 119 extends in three spatial dimen- sions in the atmosphere at the docking site and is to be understood as being a potential obstacle that may prevent safe docking of the first aircraft 111 as it approaches the first docking system 115.

As is known, fog or precipitation affects visibility mainly in that incident electromagnetic radiation is scattered by the droplets in the atmosphere. During the scattering process, the illuminated droplets reemit some fraction of the incident electromagnetic radiation in all directions. The droplets then act as point sources of the reemitted energy. Some portion of the incident electromagnetic radiation is scattered backwards towards the radiation source, dependent on the relation between the droplet size and the radiation wavelength. The relation between visibility and scattered electromagnetic radia- tion is widely described in the literature, e.g. in

"Ground-based remote sensing of visual range / Visual- range lidar", Verein Deutscher Ingenieure VDI 3786, or in "Elastic Lidar: Theory, practise and analysis methods", V.A. Kovalev, W. E. Eichinger, Hoboken, N.J., Wiley, 2004.

For docking systems relying on electromagnetic emission means, e.g for emission of pulses, the scattering reduces the amount of received energy reflected from objects to be detected. For docking systems relying on imaging means, the scattering causes a reduction of contrast in the image used.

Turning now to figure 2a and 2b, a docking system 215 will be described, which utilizes electromagnetic radiation in terms of emission of pulses and reception of backscattered radiation of these pulses. The docking system 215 is configured to determine, in real-time, distances to an approaching aircraft 240 and also configured to indicate whether or not visibility at a docking site, located between the docking system 215 and the approaching aircraft 240, is good enough, to allow safe docking of the aircraft 240.

The docking system 215 of figure 2a, which may represent any of the docking systems 115, 117 discussed above in connection with figure 1, comprises a control unit 221, a transmitter 223 and a receiver 225. The transmitter 223 is configured, under the control of the control unit 221, to emit electromagnetic radiation pulses that is in the form of laser radiation (although other embodiments may comprise a transmitter/receiver pair that are configured to operate with radar pulses) . The radiation exits from the transmitter in a transmission beam 229 along a transmission beam direction 230, as schematically illustrated in figure 2a. Correspondingly, the receiver is configured, also under the control of the control unit 221, to receive backscattered radiation in a reception beam 231 along a reception beam direction 232 and to provide a representative signal of the backscattered radiation to the control unit 221.

The transmitter 223 and the receiver 225 are configured such that they, via a beam direction device 226 control- led by the control unit 221, can be directed in any desired spatial direction. As the skilled person will

realize, the beam direction device 226 may be realized in the form of mirrors, stepper motors etc.

The docking system 215 may, as indicated in figure 1, form part of a larger system arranged at an airport terminal and also be connected to an external control system 227 operated by airport staff.

Now follows a description of how the docking system 221 in figure 2 operates in order to provide an indication of whether or not safe docking is possible, where the dis- tance determining of the docking system 221 utilizes the transmitter 223 and the receiver 225 to emit and receive electromagnetic pulses in the form of either laser pulses or radar pulses. Reference will be made also to the flow chart in figure 4.

The graph in figure 2b shows a typical power distribution Z (r) of a range-corrected receiver signal of the system when a pulse has been emitted, in an emission step 401, towards homogenous fog and backscattered radiation has been receive by the receiver 225, in a reception step 403, in the form of a receiver signal having a power distribution P(r). Then follows a calculation step 405 during which a value for visibility V is calculated.

In the calculation step 405, the range-corrected power distribution Z (r) is initially calculated as Z (r) =r ² *P (r) to compensate for the fact that the receiver signal at long distances falls off as 1/r ² . r is the distance between the transmitter/receiver and the reflecting/scattering object.

The visibility V is then calculated from the range-cor- rected receiver signal Z (r) , e.g. by using an algorithm

disclosed in DE 19642967 or by using the so called method of asymptotic approximation. According to this method the visibility V can be calculated by the expression

where

c = speed of light ,

ro is the distance at which the field of view of the transmitter and the receiver begin to overlap fully,

T ₁ is the distance at which the signal has dropped to 10% of the maximum value at the distance ro, and

T ₂ = ri - r ₀ .

The integration time of I _r i is from to to t _± = t ₀ + δt and the integration time of I _r∑ is from tj to t _∑ - ti + δt where to, ti, t _∑ and δt are related to ro, r _± , r _∑ and δr as defined in figure 2b.

The calculated visibility V is then compared, in a comparison step 407, with a predetermined threshold value in order to give an indication, i.e. a signal, whether or not docking is possible. Specific values for the threshold are determined, e.g., empirically. If the visibility V is greater than the threshold value, an indication is

provided in an indication step 409 that the visibility is good and that safe docking is possible. If, on the other hand, the visibility V is less than the threshold value, an indication is provided in an indication step 411 that the visibility is bad and that safe docking is not possible .

Turning now to figure 3, a docking system 315 will be described, which utilizes imaging means in the form of a camera 324. As in the previous embodiment, the docking system 315 is configured to determine, in real-time, distances to approaching aircraft and also configured to indicate whether or not visibility at a docking site is good enough to allow safe docking of an aircraft 340.

The docking system 315 of figure 3, which may represent any of the docking systems 115, 117 discussed above in connection with figure 1, comprises a control unit 321 connected to the camera 324 and connected to an external control system 327, similar to the situation discussed above in connection with the embodiment of figure 2a.

The camera 324 is controlled to record an image of a contrast test object, illustrated by a dark spot 303 and a bright spot 304, located at a distance d from the docking system 315. As the skilled person will realize, the test object 304,305 may be any predetermined object or marking located at the docking site within the field of view of the docking system, e.g. a part of the painted guiding line 107. Fog 305 is illustrated in figure 3 as extending in the atmosphere between the docking system 315 and the approaching aircraft 340.

Now follows a description of how the docking system 315 in figure 3 operates in order to provide an indication of

whether or not safe docking is possible, where the distance determining of the control unit 321 utilizes the camera 324 to record images. In a recorded images a first pixel, denoted i, and a second pixel, denoted j, contain image data of a respective scene point, Pi and Pj that correspond to the respective spots 303, 304 of the calibration object. Reference will be made also to the flow chart in figure 5.

After recording an image in a recording step 501 the con- trast between the two pixels i and j in the camera image, corresponding to the two scene points P± and Pj at the same distance d from the camera, is calculated in a calculation step 503. The contrast is then, as will be described below, used as a measure of the performance degradation caused by reduced visibility.

The contrast in the camera image is affected by scattering of light by atmospheric particles in two ways, as shown in figure 3. Direct transmission 307 is the attenuated irradiance received by the camera sensor from the scene point 303,304 along the line of sight. Airlight 309 is the total amount of environmental illumination 311 (sunlight, skylight, ground light) reflected into the line of sight by atmospheric particles.

It is known that the following relations apply:

£«=/.p<V*+J _β (l-e- ^/l ')

E"> =1^ ^' » +I _βt (l-e-' ^u )

where:

E ^(1> and E ^<j> is the brightness at the two pixels i and j, respectively.

I- is the environmental illumination intensity,

p is the normalized radiance of the scene point 303,304, being a function of the scene point reflectance, normalized environmental illumination spectrum and the spectral response of the camera 324,

β is the backscatter coefficient of the atmosphere in front of the camera 324, and

d is the distance between the system 315 and the scene point 303,304.

The observed contrast between Pi and P ₃ can be defined as

EW-E ⁰⁾ _ p ^{ι) -p ^ω

£ ^w + E ^{ω "} p ^w +p ^ω +2(e^ -1)

This shows that the contrast degrades exponentially with the scattering coefficient β and the depths of scene points in a situation where the fog 305 is present.

The brightness E of the two pixels are measured and the contrast C(i _r j) between the two points is calculated as

rr λ.-£ ⁽ °-£ ^ω ^ ^>J) - _E ⁽ θ _{+ E} ϋ ⁾

The calculated contrast C is then compared, in a comparison step 505, with a predetermined threshold value in order to give an indication, i.e. a signal, whether or not docking is possible. Specific values for the threshold are determined, e.g., empirically. If the contrast C is greater than the threshold value, an indication is provided in an indication step 507 that the visibility is good and that safe docking is possible. If, on the other hand, the contrast C is less than the threshold value, an