Device for detecting, by a drone, at least one manned aircraft on approach and associated detection method

Abstract

A device for detecting, by a drone, at least one manned aircraft, the manned aircraft (N) transmitting at least one positioning message including at least one altitude data point (ZN), the detection device comprising a receiver for receiving the positioning message and for measuring its reception power (P), a computer (11) configured to compare (E2) an altitude deviation (ΔZ) to a first threshold (S1) to activate a first alert state (V1) in case of exceedance, to compare (E3) the reception power (P) to a second threshold (S2) to activate a second alert state (V2) in case of exceedance, and to generate (E4) at least one collision warning signal (A) if the first alert signal (V1) and the second alert signal (V2) are active simultaneously. Abstract figure: Figure 4

Description

Title of the invention: Device for detecting, by a drone, at least one manned aircraft approaching and associated detection method Technical field

[0001] The present invention relates to the field of unmanned aircraft, known as drones. The invention relates more particularly to a method for detecting aircraft located in the vicinity of a drone in order to enable their avoidance, in particular, at altitudes below 152 m (approximately 500 feet).

[0002] It is known to use a drone for carrying out various missions such as capturing images or transporting loads. The presence of drones in the airspace is set to increase, which increases the risk of collision with manned aircraft.

[0003] To reduce the risk of collision, it is known to equip a drone with a video camera in order to observe the vicinity of the drone. The images collected are then analyzed by an operator or by computer, which in theory makes it possible to detect any aircraft in the vicinity. In practice, it is complex to monitor the vicinity of the drone from images alone. This is all the more complex since the drone and / or aircraft located in the vicinity may be moving with significant speed and / or velocity.

[0004] In practice, to know their respective positions, manned aircraft periodically transmit positioning messages following an interrogation from a radar or another manned aircraft. These positioning messages contain in particular the altitude of the transmitting aircraft as well as an identifier of said aircraft. This allows manned aircraft to know the relative position of other manned aircraft.

[0005] Currently, for security reasons, a drone is not authorized to interrogate a manned aircraft. Also, it is known to equip a drone with an incoming cooperative surveillance system (known by its English acronym "ADS-B In") configured to listen to the positioning messages sent by the different manned aircraft. This advantageously allows the drone to know if manned aircraft are moving at an altitude close to its own. In fact, the altitude data generally contains inaccuracies which, in spaces with a high density of aircraft, generates a large number of false alarms, which presents a disadvantage. The different manned aircraft transmit positioning messages, known to those skilled in the art under the designation "Mode S", which only contain the altitude and identifier information of the manned aircraft.

[0006] The invention thus aims to eliminate at least some of these drawbacks. PRESENTATION OF THE INVENTION

[0007] The invention relates to a device for detecting, for a drone, at least one manned aircraft, the manned aircraft transmitting at least one positioning message comprising at least one item of altitude data, the drone having a drone altitude; the detection device comprising: At least one receiver configured to receive the positioning message from the manned aircraft, At least one computer configured to compare an altitude difference, determined between the altitude of the drone and the altitude of the manned aircraft, with a first threshold so as to activate a first state of vigilance in the event of exceeding.

[0008] The invention is remarkable in that, the receiver being configured to measure the reception power of the received positioning message, the calculator is configured to: Compare the reception power of the positioning message to a second threshold so as to activate a second vigilance state in the event of exceeding it, and Generate at least one collision alert signal if the first alert signal and the second alert signal are active simultaneously.

[0009] Thanks to the invention, the number of false alarms is reduced by using the reception power of the positioning message. The reception power is advantageous since it is accessible passively without interrogation of the manned aircraft, which meets IT security requirements. Furthermore, the reception power is correlated with the separation distance between the manned aircraft and the drone, which forms a relevant criterion for avoiding a collision.

[0010] Preferably, the computer is configured to filter the reception power of the positioning message prior to its comparison with the second threshold, preferably with a Kalman filter. This makes it possible to filter the reception power measurements and to improve the relevance of the comparison with the second threshold.

[0011] Preferably, the calculator is configured to: Calculate a derivative of the reception power of the positioning message between two consecutive time instants, Compare the derivative of the receive power to a third threshold so as to activate a third vigilance state in case of exceedance, and Generate the collision alert signal if the first vigilance signal, the second vigilance signal and the third vigilance signal are active simultaneously.

[0012] The number of false alarms is further reduced by using the derivative of the reception power of the positioning message. The derivative of the reception power is advantageous since it allows the variation of the separation distance between the manned aircraft and the drone to be measured indirectly and passively. Thus, knowledge of a rapid reduction in the separation distance is a relevant criterion for avoiding a collision.

[0013] Preferably, the calculator is configured to filter the derivative of the reception power prior to its comparison with the third threshold, preferably with a Kalman filter. This makes it possible to filter the measurements of the derivative of the reception power and to improve the relevance of the comparison with the third threshold.

[0014] According to one aspect, the calculator is configured to: • Count the number of consecutive collision warning signals generated over time, • Emit the collision warning signal if said number of consecutive collision warning signals is greater than or equal to a first predetermined number of occurrences, and • Keep the collision warning signal if the said number of consecutive collision warning signals is less than the first predetermined number of occurrences

[0015] Thus, a collision alert signal is only emitted after a certain number of occurrences, which makes it possible to validate the risk of collision and avoid emitting untimely alerts.

[0016] According to another aspect, the calculator is configured to: • Determine a percentage of collision warning signals over a given period, • Issue the collision alert signal if the percentage of collision alert signals is greater than or equal to a first predetermined threshold, and • Keep the collision alert signal if the percentage of collision alert signals is below the first predetermined threshold.

[0017] According to another aspect, the calculator being configured to generate at each time instant a collision warning signal or a safety signal, the calculator is configured to: • Count the number of consecutive safety signals generated during the time, Emit a safety signal if said number of consecutive safety signals is greater than or equal to a second predetermined number of occurrences, and

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[0023] • Keep the safety signal if the said number of consecutive safety signals is less than the second predetermined number of occurrences. Thus, a safety signal is only emitted after a certain number of occurrences, which allows for reliable validation of an alert being raised. According to another aspect, the calculator is configured to: • Determine a percentage of security signals over a given period, • Issue the safety signal if the percentage of safety signals is greater than or equal to a second predetermined threshold, and • Keep the safety signal if the percentage of safety signals is below the second predetermined threshold. The invention also relates to a drone comprising a detection device as presented previously. The invention also relates to a method for detecting, by a drone, at least one manned aircraft, the manned aircraft transmitting at least one positioning message comprising at least one altitude datum, the drone having a drone altitude, the detection method comprising steps consisting of: • Receive the positioning message from the manned aircraft, • Measure the reception power of the received positioning message, • Compare an altitude difference, determined between the altitude of the drone and the altitude of the manned aircraft, to a first threshold, • Activate a first state of vigilance in the event of exceeding the first threshold, • Compare the reception power of the positioning message to a second threshold, • Activate a second state of vigilance in the event of exceeding the second threshold, and • Generate at least one collision alert signal if the first alert signal and the second alert signal are active simultaneously. Preferably, the method comprises steps consisting of: • Calculate a derivative of the reception power of the positioning message between two consecutive time instants, • Compare the derivative of the reception power of the positioning message to a third threshold, • Activate a third state of vigilance in case the third threshold is exceeded, and • Generate the alert signal if the first vigilance signal, the second vigilance signal and the third vigilance signal are active simultaneously. The invention also relates to a computer program type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by this processor, causes the steps of the method to be carried out as presented previously.

[0024] The invention also relates to a computer-readable medium comprising the computer program type product as presented above. PRESENTATION OF FIGURES

[0025] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0026] [Fig.l] is a schematic representation of a drone and a manned aircraft transmitting a positioning message.

[0027] [Fig.2] is a schematic representation of a detection device for a drone according to the invention.

[0028] [Fig. 3] is a schematic representation of the reception power of a positioning message transmitted by the manned aircraft.

[0029] [Fig.4] is a schematic representation of a first example of implementation of a detection method according to the invention.

[0030] [Fig.5] is a schematic representation of a second example of implementation of a detection method according to the invention.

[0031] [Fig.6] is a schematic representation of curves of altitude deviation, reception power and the derivative of reception power.

[0032] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0033] With reference to [Fig.l], a drone D is shown, that is to say an unmanned aircraft, which moves in the air. In this example, a drone with a delta-type wing is shown, but it goes without saying that the invention applies to any type of drone D, in particular, a drone D having a plurality of rotors. The invention relates more particularly to a drone D configured to be piloted beyond the visual distance by an operator.

[0034] Still with reference to [Fig.l], there is shown a manned aircraft N, for example a commercial aircraft, which moves in the air. In a known manner, as presented in the preamble, a manned aircraft N conventionally comprises a transponder N1 for transmitting and receiving positioning messages M following an interrogation Q from another manned aircraft 101 or from a radar center 102.

[0035] In a known manner, each positioning message M transmitted by the manned aircraft N comprises several data items including altitude data ZN at a time instant t and an identifier IDN of the manned aircraft N. In practice, the positioning messages M transmitted by the manned aircraft N are broadcast widely and can be received by a drone D without the latter being authorized to interrogate the manned aircraft N.

[0036] According to the invention, with reference to [Fig.l], the drone D comprises a detection device 1 for receiving and processing the positioning messages M transmitted by the manned aircraft N located in the vicinity of the drone D.

[0037] In this example, as illustrated in [Fig.2], the detection device 1 comprises at least one receiver 10 configured to receive a positioning message M and at least one computer 11 configured to generate a collision alert signal A as a function of the positioning message M and an altitude of the drone ZD. Preferably, the altitude of the drone ZD is determined by an altimeter of the drone D or the like. Such an altimeter is known to those skilled in the art and will not be presented in further detail.

[0038] The collision warning signal A can be in various forms, in particular, a computer message which can be sent to a control station for the pilot of the drone N or to a navigation system of the drone D in order to adapt the trajectory of the drone D (avoidance maneuver).

[0039] The receiver 10 is configured to receive a positioning message M and read the data it contains. Preferably, the receiver 10 is configured to communicate on the frequency of 1090 MHz. The receiver 10 is also configured to measure a reception power P of the positioning message M that has been received. Preferably, the reception power P corresponds to an RSSI parameter for “Received Signal Strength Indicator”, that is to say, the signal-to-noise ratio of the positioning message M.

[0040] It nevertheless goes without saying that any parameter depending on the reception power P could be used. The calculation of an RSSI parameter is known to those skilled in the art and will not be presented in further detail.

[0041] As illustrated in [Fig. 3], when a manned aircraft N transmits a positioning message M, the reception power P is a function of the separation distance DN, that is to say, the distance between the receiver 10 of the drone D and the transponder N1 of the manned aircraft N. Thus, the further the drone D is from the manned aircraft N, the lower the reception power P. In other words, the reception power P makes it possible to estimate the separation distance DN between the drone D and the manned aircraft N. The present invention aims to take advantage of this correlation to make it possible to reduce the risk of collision without interrogating the manned aircraft N and thus comply with safety requirements.

[0042] Preferably, the correlation law between the reception power P (in particular the RSSI parameter) and the separation distance DN is determined beforehand, preferably statistically.

[0043] According to the invention, with reference to a first example of implementation represented in [Fig.4], the computer 11 is configured to implement the steps consisting of: • Determining El an altitude difference AZ between the altitude of the drone ZD and the altitude of the manned aircraft ZN, • Compare E2 the altitude difference AZ to a first threshold SI in order to activate a first state of vigilance VI in the event of an overshoot, • Compare E3 the reception power P of the positioning message M to a second threshold S2 so as to activate a second vigilance state V2 in the event of exceeding, and • Generate E4 at least one collision alert signal A if the first vigilance signal VI and the second vigilance signal V2 are active simultaneously.

[0044] Preferably, the computer 11 comprises a memory (not shown) in which the first threshold S1 and the second threshold S2 are stored. Preferably, the first threshold S1 and the second threshold S2 correspond respectively to an altitude threshold and to a reception power threshold. The thresholds S1, S2 are preferably predetermined in order to obtain the desired degree of collision alert A. Preferably, the thresholds S1, S2 are adapted dynamically according to the conditions, so as to maintain the desired degree of collision alert A in all circumstances.

[0045] Preferably, the second threshold S2 is determined as a function of the minimum horizontal distance accepted between two aircraft during their flight (generally 9300m) and the correlation law linking the reception power P and the separation distance DN.

[0046] Thus, in a manner similar to the prior art, a first vigilance state V1 is activated if the manned aircraft N has an altitude ZN close to the altitude ZD of the drone D. Nevertheless, a collision alert signal A is only generated if the reception power P of the positioning message M is high (activation of the second vigilance signal V2). Indeed, as explained previously, the reception power P is correlated to the separation distance DN, it follows that a risk of collision is higher for neighboring altitudes and for a reduced separation distance DN. The use of the reception power P of the positioning message M thus makes it possible to significantly reduce the risk of false alarm while allowing optimal detection.

[0047] Preferably, the reception power P is filtered, for example with a Kalman filter, to smooth the measurements.

[0048] Preferably, the collision alert signal A comprises the identifier of the manned aircraft N present in the positioning message M.

[0049] With reference to a second exemplary implementation shown in [Fig. 5], the computer 11 is configured to implement additional steps. For the sake of clarity and conciseness, the steps presented for the first exemplary implementation will not be presented again.

[0050] The calculator 11 is thus configured to implement the steps consisting of: • Calculating E5 a derivative dP of the reception power P of the positioning message M between two consecutive time instants, • Compare E6 the derivative of the reception power dP to a third threshold S3 so as to activate a third vigilance state V3 in the event of exceeding, • Generate E4 the collision warning signal A if the first vigilance signal VI, the second vigilance signal V2 and the third vigilance signal V3 are active simultaneously

[0051] Preferably, the memory of the computer 11 stores the reception powers P(t) measured over time so as to calculate the reception power derivative dP. Preferably, the third threshold S3 is also stored in the memory. Preferably, the third threshold S3 corresponds to a reception power variation threshold. The thresholds S1, S2, S3 are preferably predetermined in order to obtain the desired collision alert degree A.

[0052] In this example, the derivative of the reception power dP corresponds to the difference between two RSSI parameters (P(tl), P(t)) between two consecutive time instants (tl,t).

[0053] Preferably, the reception power derivative dP is filtered, for example with a Kalman filter, to smooth the measurements.

[0054] Advantageously, in this second embodiment, the derivative of the reception power dP, i.e. its rate of variation, makes it possible to verify whether the separation distance DN tends to reduce and the speed at which the latter reduces. Thus, if a manned aircraft N is close in distance to the drone D but is moving away from it, the third vigilance signal V3 is not made active. Conversely, if a manned aircraft N is far from the drone D but is rapidly approaching it, the third vigilance signal V3 is made active.

[0055] Optionally, with reference to [Fig.5], in order to further reduce the number of false alarms, the computer 11 is configured, during a validation step E7, to: Count the number of consecutive collision warning signals A generated at the course of time, • Emit collision warning signal A if said number of consecutive warning signals is greater than or equal to a first predetermined number of occurrences, • Keep collision warning signal A if said number of consecutive warning signals is less than the first predetermined number of occurrences.

[0056] Thus, the collision warning signal A is not transmitted systematically but transmitted after a certain number of occurrences. Such validation of the collision warning signal A makes it possible to reduce the number of false alarms without affecting the responsiveness of the detection device 1.

[0057] The collision warning signal A can be generated and transmitted directly after its generation in order to warn an operator or a computer system of a risk of collision with a manned aircraft N.

[0058] Alternatively, the computer 11 is configured, during a validation step E7, to: • Determine a percentage of collision alert signals A over a given period (preferably a sliding time window), • Issue collision alert signal A if the percentage of collision alert signals A is greater than or equal to a first predetermined threshold, and • Keep collision alert signal A if the percentage of collision alert signals A is below the first predetermined threshold.

[0059] For example, a collision alert signal A is emitted if the percentage of collision alert signals is greater than a predetermined threshold, for example, 80% of the time over the last 10 seconds.

[0060] According to one aspect of the invention, the computer 11 is configured to generate at each time instant a collision warning signal A or a safety signal S. With reference to [Fig. 5], in order to avoid intermittent transmission of the collision warning signal, the computer 11 is configured, during a validation step E7, to: • Count the number of consecutive safety signals S generated during the time • Issue a safety signal S if said number of consecutive safety signals S is greater than or equal to a second predetermined number of occurrences, • Keep the safety signal S if said number of consecutive safety signals is less than the second predetermined number of occurrences.

[0061] In a similar manner to the collision warning signal A, a safety signal S is not transmitted systematically but transmitted after a certain number of occurrences. Such validation of the safety signal S makes it possible, by hysteresis, to emit alternative way of collision warning signals A and safety S, which improves the robustness and reliability of the detection system 1.

[0062] Alternatively, the computer 11 is configured, during a validation step E7, to: • Determine a percentage of safety signals S over a given period (preferably a sliding time window), • Issue the safety signal S if the percentage of safety signals S is greater than or equal to a second predetermined threshold, and • Keep the safety signal S if the percentage of safety signals S is lower than the second predetermined threshold.

[0063] For example, a safety signal S is emitted if the percentage of safety signals is greater than a predetermined threshold, for example, 80% of the time over the last 10 seconds.

[0064] Alternatively, the validation step E7 can implement a sliding window in order to smooth the collision alert signals A or safety S.

[0065] An example of implementation of a detection method according to the invention will now be presented with reference to [Fig.6].

[0066] The present example will refer to the situation of the invention represented in [Fig.l]. A drone D is hovering at a drone altitude ZD of 1500m. A manned aircraft N is moving at an altitude ZN lower than that of the drone D. As explained previously, the drone D does not have the authorization to interrogate the transponder NI of the manned aircraft N unlike the other manned aircraft 101 or the radar center 102 which are authorized to do so. Consequently, the drone D only receives the positioning message M passively from the manned aircraft N.

[0067] The receiver 10 of the detection device 1 of the drone D receives the positioning message M which includes at least the altitude ZN as well as its identifier ID. The receiver 10 can thus determine the reception power P.

[0068] As explained previously, with reference to [Fig.6], the computer 11 can thus determine over time t: • The altitude difference AZ (frame 6a of [Fig.6]) to compare it to the first SI threshold, for example, 300m; • The reception power P (frame 6b of [Fig.6]) to compare it to the second threshold S2; • The derivative of the reception power dP (frame 6c of [Fig.6]) to compare it with the third threshold S3.

[0069] With reference to the first frame 6a of [Fig.6], the altitude difference AZ is lower than the first threshold SI between the time instants tll and tl2. Also, between the time instants tll and tl2, the first vigilance signal VI is active (Vl=l) and is inactive in outside (Vl=0). The first vigilance signal VI alerts you to the fact that the manned aircraft N is flying at a nearby altitude.

[0070] Similarly, with reference to the second frame 6b of [Fig.6], the reception power P is greater than the second threshold S2 between the time instants t21 and t22. Also, between the time instants t21 and t22, the second vigilance signal V2 is active (V2=1) and is inactive outside (V2=0). The second vigilance signal V2 makes it possible to alert on a separation distance DN with the manned aircraft N.

[0071] Similarly again, with reference to the third frame 6c of [Fig.6], the derivative of the reception power dP is greater than the third threshold S3 between the time instants t31 and t32. Also, between the time instants t31 and t32, the third vigilance signal V3 is active (V3=1) and is inactive outside (V3=0). The third vigilance signal V3 makes it possible to alert on a reduction in the separation distance DN over time with the manned aircraft N.

[0072] With reference to the fourth frame 6d of [Fig.6], the computer 11 emits a collision alert signal A between the time instants t21 and t32 given that the vigilance signals VI, V2, V3 are simultaneously active. This significantly limits the number of false alarms compared to a detection device according to the prior art relying only on the altitude difference AZ (the collision alert signal A would have been emitted between the time instants t11 and t12). In order to make the detection system robust, a validation step can also be implemented as presented previously.

[0073] Thanks to the invention, a reliable collision warning signal A can be emitted in order to alert an operator or a navigation system of the drone D in order to avoid any actual collision. Advantageously, the drone D does not emit interrogation requests to manned aircraft N, which guarantees safety.

Claims

Claims

1. Detection device (1), for a drone (D), of at least one manned aircraft (N), the manned aircraft (N) transmitting at least one positioning message (M) comprising at least one altitude datum (ZN), the drone (D) having a drone altitude (ZD); the detection device (1) comprising: • At least one receiver (10) configured to receive the positioning message (M) from the manned aircraft (N), • At least one computer (11) configured to: • Compare (E2) an altitude difference (AZ), determined between the altitude of the drone (ZD) and the altitude of the manned aircraft (ZN), with a first threshold (SI) so as to activate a first vigilance state (VI) in the event of exceeding, • Characterized by the fact that, the receiver (10) being configured to measure the reception power (P) of the positioning message (M) received,the calculator (11) is configured to: • Compare (E3) the reception power (P) of the positioning message (M) with a second threshold (S2) so as to activate a second vigilance state (V2) in the event of exceeding, • Calculate (E5) a derivative of the reception power (dP) of the positioning message (M) between two consecutive time instants, • Compare (E6) the derivative of the reception power (dP) with a third threshold (S3) so as to activate a third vigilance state (V3) in the event of exceeding, and • Generate (E4) at least one collision alert signal (A) if the first vigilance signal (VI), the second vigilance signal (V2) and the third vigilance signal (V3) are active simultaneously.,

2. Detection device (1) according to claim 1, in which the computer (11) is configured to filter the reception power (P) of the positioning message (M) prior to its comparison with the second threshold (S2), preferably with a Kalman filter.

3. Detection device (1) according to claim 1, wherein the cal- The controller (11) is configured to filter the derivative of the reception power (dP) prior to its comparison with the third threshold (S3), preferably with a Kalman filter.

4. Detection device (1) according to claims 1 to 3, wherein the computer (11) is configured to: • Determine a percentage of collision warning signals (A) over a given period, • Emit the collision warning signal (A) if the percentage of collision warning signals (A) is greater than or equal to a first predetermined threshold, and • Keep the collision warning signal (A) if the percentage of collision warning signals (A) is less than the first predetermined threshold.

5. Detection device (1) according to claims 1 to 4, wherein, the computer (11) being configured to generate at each time instant a collision warning signal (A) or a safety signal (S) corresponding to an absence of risk of collision, the computer (11) is configured to: • Determine a percentage of safety signals (S) over a given period, • Emit the safety signal (S) if the percentage of safety signals (S) is greater than or equal to a second predetermined threshold, and • Keep the safety signal (S) if the percentage of safety signals (S) is less than the second predetermined threshold.

6. Drone (D) comprising a detection device (1) according to one of claims 1 to 5.

7. Method for detecting, by a drone (D), at least one manned aircraft (N), the manned aircraft (N) transmitting at least one positioning message (M) comprising at least one altitude datum (ZN), the drone (D) having a drone altitude (ZD), the detection method comprising steps consisting of: Receive the positioning message (M) from the aircraft inhabited (N), Measure the reception power (P) of the received positioning message (M), Compare (E2) an altitude difference (AZ), determined between the altitude of the drone (ZD) and the altitude of the manned aircraft (ZN), to a first threshold (SI) Activate a first state of vigilance (VI) in the event of exceeding the first threshold (SI), Compare (E3) the reception power (P) of the positioning message (M) to a second threshold (S2), Activate a second vigilance state (V2) if the second threshold (S2) is exceeded, Calculate (E5) a derivative of the reception power (dP) of the positioning message (M) between two consecutive time instants, Compare (E6) the derivative of the reception power (dP) to a third threshold (S3) so as to activate a third vigilance state (V3) in the event of exceeding, and Generate (E4) at least one collision warning signal (A) if the first vigilance signal (VI), the second vigilance signal (V2) and the third vigilance signal (V3) are active simultaneously.

8. Computer program type product, comprising at least one sequence of instructions stored and readable by a processor and which, once read by this processor, causes the steps of the method according to claim 7 to be carried out.

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