Method for observing an environment with a method for resolving ambiguity and a method for listening and associated devices

Abstract

Method for observing an environment with a method for resolving ambiguity and a listening method and associated devices. The present invention relates to a method for observing an environment (12) comprising the implementation of several recurrences of a signal emission and reception step, at least one sequence of recurrences comprising, for two integers N and M, comprising: - N first recurrences comprising the emission of pulses in a first direction at a first frequency and the reception of the echoes emitted following this emission, - M recurrences comprising the emission of pulses in a second direction at a second frequency, and - N second recurrences comprising the emission of pulses at a repetition period in the second direction at the second frequency, and the reception of the echoes emitted following this emission. Figure for the abstract: Figure 1

Description

Title of the invention: Method for observing an environment with a method for resolving ambiguity and a listening method and associated devices

[0001] The present invention relates to a method of observing an environment by means of radar. It also relates to devices adapted for implementing such a method, namely a radar, an observation system and an aircraft.

[0002] Distance unambiguity resolution modes, notably Doppler, involve the emission and reception of a number of recurrences consisting of a "dead time" and a "useful time" for analysis.

[0003] The dead time corresponds to the propagation time of the echoes corresponding to the maximum instrumented distance desired for the application, so that all received echoes can be processed consistently over all analysis recurrences.

[0004] There is therefore a need for a method to exploit or eliminate said dead-time recurrences without degrading detection performance.

[0005] To this end, the description relates to a method for observing an environment, the method being implemented by an observation system comprising a radar and including the implementation of several recurrences of a signal emission and reception step, the method comprising at least one sequence of recurrences comprising, for N and M two integers:

[0006] - N first recurrences comprising a step of:

[0007] - emission of pulses at a repetition period in a first direction to a first frequency, and

[0008] - reception of echoes emitted at the first frequency in the first direction,

[0009] - M recurrences following the first N recurrences and comprising a step of:

[0010] - emission of pulses at the repetition period in a second direction at a second frequency, the second direction being different from the first direction and the second frequency being different from the first frequency, and

[0011] - listening to echoes emitted at the first frequency in the first direction, and

[0012] - N second recurrences following the M recurrences and comprising a step of:

[0013] - emission of pulses at the repetition period in the second direction to the second frequency, and

[0014] - reception of echoes emitted at the second frequency in the second direction.

[0015] According to other advantageous aspects of the invention, the monitoring method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0016] - the method comprises the implementation of P sequences, each sequence being implemented implemented at a respective rehearsal period.

[0017] - each sequence comprises an additional series of:

[0018] - M additional recurrences following N recurrences and comprising

[0019] a step of:

[0020] - emission of pulses at the repetition period in an additional direction to an additional frequency, the additional direction being different from the directions of the previous recurrences and the additional frequency being different from the frequencies of the previous recurrences, and

[0021] - listening to the echoes emitted at the frequency and direction of the echoes received during the step of receiving the N recurrences that the additional M recurrences follow, and

[0022] - N additional recurrences following the M additional recurrences and including a step of:

[0023] - emission of pulses at the repetition period in the additional direction to the additional frequency, and

[0024] - reception of echoes emitted at the additional frequency in the direction additional,

[0025] the sequence comprising additional series for K directions observed by the radar, K being an integer greater than or equal to 3.

[0026] - during each emission step, at least one emitted pulse comprises a phase random respective introduced by the radar and each stage of receiving an echo received from at least one pulse emitted with a random phase includes compensation for the phase shift related to the random phase introduced.

[0027] - the method includes a step of processing the received echoes to determine at least one of the following: a distance from a target and a speed of a target in the environment.

[0028] - the method includes a step of analyzing the echoes heard during a listening session to to obtain electromagnetic behavior in the direction and frequency of the echoes listened to.

[0029] - the processing step takes into account the electromagnetic behavior obtained at the analysis stage.

[0030] The description also relates to a radar suitable for implementing several recurrences of a signal transmission and reception step, at least one sequence of recurrences comprising, for N and M two integers:

[0031] - The first N recurrences during which the radar is specific to:

[0032] - emit pulses at a repetition period in a first direction to a first frequency, and

[0033] - receive echoes emitted at the first frequency in the first direction,

[0034] - M recurrences following the first N recurrences and during which the radar is specific to:

[0035] - emit pulses at the repetition period in a second direction at a second frequency, the second direction being different from the first direction and the second frequency being different from the first frequency, and

[0036] - listening for echoes emitted at the first frequency in the first direction, and

[0037] - N second recurrences following the M recurrences and during which the radar is specific to:

[0038] - emit pulses at a repetition period in the second direction to the second frequency, and

[0039] - receive echoes emitted at the second frequency in the second direction.

[0040] The description also relates to an observation system comprising a radar such as previously described.

[0041] The description also relates to an aircraft comprising a radar as previously described or an observation system as previously described.

[0042] In this description, the expression "specific to" means interchangeably "suitable for", "adapted to" or "configured for".

[0043] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0044] - [Fig. 1] [Fig. 1] is a schematic representation of an aircraft exhibiting a environmental observation system,

[0045] - [Fig.2] [Fig.2] is a schematic illustration of an example implementation of an observation method using the observation system, and

[0046] - [Fig.3] [Fig.3] is a representation of a flowchart for processing radar signals visible on the [Fig.2].

[0047] An aircraft 10 is schematically represented in [Fig.1].

[0048] Aircraft 10 is used here to observe the environment 12.

[0049] Aircraft 10 seeks, in particular, to detect the presence of potential targets.

[0050] The aircraft 10 is equipped with an observation system 14, the observation system 14 comprising a radar 16 interacting with a computer 18.

[0051] The radar 16 allows, for example, the detection of the position and / or speed of targets by observation of the environment in Doppler mode.

[0052] More generally, the radar is suitable for implementing any unambiguous detection mode.

[0053] For this purpose, as explained later, radar 16 implements several recurrences of a signal transmission and reception step.

[0054] By recurrence, it is understood here as a time interval comprising a portion dedicated to transmission and a portion dedicated to reception. This does not require that the radar 16 actually transmit radar pulses or actually receive echoes.

[0055] The computer 18 is, for example, implemented as a programmable circuit of the FPGA (Field Programmable Gate Array) type and / or of the ASIC (Application-Specific Integrated Circuit) type. In addition or alternatively, the computer 18 is implemented at least partially as software executable by a processor and stored in memory.

[0056] The specific operation of the radar 16 is now illustrated with reference to [Fig.2] which shows an example of the implementation of an environmental observation method 12 which the observation system 14 is capable of implementing.

[0057] This case corresponds to a simple implementation example allowing a clear understanding of the operating principle of radar 16, the generation of this process to any case being detailed afterwards.

[0058] As can be seen in this [Fig.2], a sequence of recurrences of a radar 16 is schematically represented.

[0059] This sequence comprises successively N first recurrences, M recurrences and N second recurrences.

[0060] N and M are integers, generally greater than or equal to 2, typically greater than or equal to 4.

[0061] The first N recurrences include a pulse emission step with a repetition period TRi in a first direction DI at a first frequency Fel.

[0062] The first direction DI corresponds to a first direction identified in azimuth and elevation by the pair (Azl, Eli).

[0063] The first N recurrences also include the reception of echoes from the environment 12 emitted at the first frequency Fel in the first direction DI in response to the emitted pulses.

[0064] From the point of view of the Doppler mode, the reception achieved during the first N recurrences corresponds to a useful time.

[0065] The M recurrences which follow the first N recurrences include a step of emission of pulses at the repetition period TRi in a second direction D2 at a second frequency Fe2.

[0066] The second direction D2 being different from the first direction DI.

[0067] The second direction D2 corresponds to a second direction located in azimuth and elevation by the pair (Az2, E12).

[0068] In the case of a sweep of neighboring directions, one of the coordinates Az2 or E12 of the second direction D2 is identical to one of the coordinates Azl or Eli of the first direction DI but it is quite possible to apply the sequence on two non-contiguous directions DI and D2.

[0069] The second frequency Fe2 is also different from the first frequency Fel.

[0070] The M recurrences do not receive echoes of the pulses emitted in the second direction D2 due to the propagation time required for the pulses to reach the target and return to the radar 16.

[0071] In this sense, for the Doppler mode to resolve distance ambiguity, the M recurrences correspond to a dead time for reception.

[0072] The M recurrences of "dead time" correspond to the round-trip time of the echoes at the maximum instrumented distance.

[0073] The number M of such recurrences can be obtained by applying the following formula:

[0074] M =

[0075] Where: • ceil denotes the upper integer, • is the maximum instrumented distance, • c denotes the speed of light, and • TR denotes the repetition period.

[0076] As an order of magnitude, for a maximum instrumented distance of Dlnax = 150 km, a repetition period TR corresponding to an average repetition frequency of 10 kHz, this leads to a value of M = 10.

[0077] In this example, this leads to a time interval of 1 ms.

[0078] According to the invention, the M recurrences are used to implement a listening to the echoes emitted at the first frequency Fel in the first direction DI.

[0079] A dead time in Doppler mode is thus taken advantage of to obtain additional information on the environment 12.

[0080] The N second recurrences involve the emission of pulses at the repetition period TR[ in the second direction D2 at the second frequency Fe2.

[0081] The N second recurrences also include the reception of echoes from the environment 12 emitted at the second frequency Fe2 in the second direction D2 in response to the emitted pulses.

[0082] Compared to the M recurrences where no emitted impulse has returned in the form of an echo, the N second recurrences can be seen as N recurrences of analysis.

[0083] The distinction between the different echoes is made using a phase code.

[0084] The distinction between echoes relating to the different distance ambiguity ranks on the first distance DI is made using a phase code. The phase code makes it possible to obtain as many power maps as there are distance ambiguity ranks associated with each distance ambiguity rank, isolated from the others.

[0085] The second direction D2 is nominally processed by the computer 18 with a power card and a detection on all ambiguity ranks folded on the same card if no phase code is used (first case) or in the same way (second case).

[0086] More specifically, at each transmission stage, an emitted pulse includes a respective random phase introduced by the radar and, at each reception stage, an echo received from at least one emitted pulse with a random phase includes the phase shift compensation related to the introduced random phase.

[0087] This impulse is the impulse for which the tiling is implemented, here the first impulse.

[0088] On the sequence which has just been illustrated, there is overlapping between the emissions / reception to overcome part of the dead time of the Doppler mode (that which takes place at the level of the M recurrences).

[0089] This saves listening time on a dead time in Doppler mode.

[0090] To achieve a Doppler mode, the sequence is repeated several times at a respective repetition period as schematically illustrated in the right part of [Fig.2] with a change in the value of the repetition period at the end of the sequence (transition from a first repetition period TRi to a second repetition period Tr2).

[0091] More specifically, P sequences are implemented.

[0092] The number P is chosen to allow for the removal of ambiguities.

[0093] A resolution of ambiguity is a detection extractor that performs a "K / N" test to confirm a detection on N detection maps obtained on N values ​​of repetition periods Tr.

[0094] Typically, K / N values ​​such as 2 / 2, 2 / 3 or 2 / 4, 3 / 5, 3 / 8 or 5 / 8 are found to resolve ambiguity.

[0095] In the simple example described, P is assumed to be equal to 2.

[0096] In other words, we will repeat the previous sequence between the two directions DI and D2 until the barrel of repetition periods is emptied to proceed to the resolution of ambiguity (distance, speed) by recombination of the repetition periods.

[0097] When each echo of a set of P sequences is obtained, it is possible to implement a processing of the received echoes to determine at least one of a distance of a target and a velocity of a target in the environment 12 in accordance with the desired Doppler mode.

[0098] This processing by the computer 18 is a parallel processing for each rank of ambiguity as schematically illustrated by [Fig.3].

[0099] The processing first includes an operation involving phase compensation and signal duplication (rectangle 20 on [Fig.3]) to obtain as many signals as there are ranks of ambiguity (i.e., M+1 and therefore 3 for M=2).

[0100] This operation is carried out for each direction, so that two rectangles 20 are visible on the [Fig.3].

[0101] It may be noted that for the first direction Dl, there is a shift in recurrences to be dealt with (the recurrences among M are progressively integrated) whereas, for the second direction D2, either the phase code is used by proceeding similarly to the first direction Dl or a single detection map is used by leaving the resolution of ambiguities to the extractor.

[0102] Each rank of ambiguity is also subject to processing implemented by a channel 22, so that there are here 3*2=6 channels 22.

[0103] The same processing is applied to each channel 22 and includes common operations such as a pulse compression operation (rectangle 24), a clutter rejection operation (rectangle 26), a Doppler processing operation (rectangle 28), an AC TF detection operation (rectangle 30) and an ambient noise measurement operation (rectangle 32).

[0104] At the output of each channel 22, a single extraction block 34 allows a combination of the different ranks of ambiguities to be made to obtain the speed and / or distance of the target(s) sought.

[0105] Alternatively, each channel 22 includes an extraction block 34 performing an extraction of the speed and / or the distance.

[0106] In each case, the extraction block(s) 34 are connected to a tracking block.

[0107] In the example of [Fig.3], the tracking block 36 allows for a synthesis information thus obtained for the purpose of tracking a target, that is to say that the tracking block 36 provides plots for a tracking system not shown.

[0108] The described process makes it possible to eliminate certain dead times, here for the first DL direction

[0109] Other uses of listening are nevertheless possible.

[0110] A non-limiting example is now described.

[0111] The ambient noise measurement operation (rectangle 32) is advantageously carried out here using the listening step.

[0112] For this purpose, the method also includes the analysis of the echoes listened to during a listening session in order to obtain an electromagnetic behavior in the direction and frequency of the echoes listened to.

[0113] Thus, the listening carried out during the M recurrences makes it possible to obtain an ambient map in the first direction DI at the first frequency Fel.

[0114] In other words, the processing step takes into account the electromagnetic behavior obtained in the analysis step.

[0115] This allows for a faster implementation of the process since it is not necessary to dedicate specific time to listening in addition to the recurrences used for the implementation of the Doppler mode.

[0116] It could also be considered to listen in the second direction D2 during the M recurrences.

[0117] This could allow us to react if the direction-frequency pair corresponds to a polluted frequency, in particular by changing the pair thanks to the listening carried out.

[0118] The described method is also compatible with observation from more than two directions.

[0119] The aim here is therefore to observe K directions with K an integer greater than or equal to 3.

[0120] For each of the additional directions observed (in addition to the two directions (previous), each sequence includes an additional series of recurrences comprising M additional recurrences following N recurrences and N additional recurrences following the M additional recurrences.

[0121] The additional M recurrences include a pulse emission step at the repetition period in an additional direction at an additional frequency, the additional direction being different from the directions of the previous recurrences and the additional frequency being different from the frequencies of the previous recurrences.

[0122] For K=3, this means that the additional M recurrences include a pulse emission step at the current repetition period in a third direction D3 at a third frequency Fe3, that the third direction D3 is different from the first and second directions DI and D2 and that the third frequency Fe3 is different from the first and second frequencies Fel and Fe2.

[0123] The additional M recurrences also include a step of listening to the echoes emitted at the frequency and direction of the echoes received during the reception step of the N recurrences that the additional M recurrences follow.

[0124] For the example described, this means that the additional M recurrences include listening for echoes at the second frequency Fe2 and in the second direction D2.

[0125] The N additional recurrences include a pulse emission step at the repetition period in the additional direction at the additional frequency.

[0126] For the example at K=3, this means that the radar 16 emits pulses at the current repetition period in the third direction D3 at the third frequency Fe3.

[0127] The N additional recurrences also include a step of receiving the echoes emitted at the additional frequency in the additional direction.

[0128] Still for the example described, this corresponds to the reception by the radar of the echoes emitted by the environment 12 in the third direction D3 at the third frequency Fe3.

[0129] For this sequence, 2 listening times are thus gained, corresponding to 2 dead times in Doppler mode.

[0130] More generally, one listening time is gained for each additional series, so that for K directions observed, (Kl) listening time is gained, corresponding to (Kl) dead times in the Doppler mode. Indeed, there is a dead time phase that cannot be gained at each change of repetition period.

[0131] In theory, a different and distinguishable phase code should be used for each direction. However, in practice, two different codes are sufficient since the echoes from the third direction D3 will not be picked up during reception on the first direction D1.

[0132] Implementing the method for K directions also involves adding 22 additional channels. In the general case, the processing involves using K*M different channels (if the last direction is treated like the others with phase codes).

[0133] This is not problematic, however, since these are identical routes.

[0134] It may also be stated here that the method is applicable to fixed or mechanically scanned radar architectures with one-plane or two-plane active antennas, as long as the conventional beamforming has sufficient channels available for digitization for the application.

[0135] Active electronically scanned array radars are often referred to by the abbreviation AESA, which refers to the corresponding English name "Active Electronically Scanned Array" (which literally means active electronically scanned array).

Claims

Demands

1. A method for observing an environment (12), the method being implemented by an observation system (14) comprising a radar (16) and comprising the implementation of several recurrences of a step of emitting and receiving signals, the method comprising at least one sequence of recurrences comprising, for N and M two integers: - N first recurrences comprising a step of: - emitting pulses at a repetition period in a first direction at a first frequency, and - receiving the echoes emitted at the first frequency in the first direction, - M recurrences following the first N recurrences and comprising a step of: - emitting pulses at a repetition period in a second direction at a second frequency, the second direction being different from the first direction and the second frequency being different from the first frequency, and - listening to the echoes emitted at the first frequency in the first direction,and - N second recurrences following the M recurrences and comprising a step of: - emission of pulses at the repetition period in the second direction at the second frequency, and - reception of the echoes emitted at the second frequency in the second direction.

2. A method according to claim 1, wherein the method comprises the implementation of P sequences, each sequence being implemented at a respective repetition period.

3. A method according to claim 1 or 2, wherein each sequence comprises an additional series of: - M additional recurrences following N recurrences and comprising a step of: - emitting pulses at the repetition period in an additional direction at an additional frequency, the additional direction being different from the directions of the preceding recurrences and the additional frequency being different from the frequencies of the previous recurrences, and - listening to the echoes emitted at the frequency and direction of the echoes received during the stage of receiving the N recurrences that the M additional recurrences follow, and - N additional recurrences following the M additional recurrences and comprising a stage of: - emission of pulses at the repetition period in the additional direction at the additional frequency, and - reception of the echoes emitted at the additional frequency in the additional direction, the sequence comprising (K-2) additional series for K directions observed by the radar (16), K being an integer greater than or equal to 3.

4. A method according to any one of claims 1 to 3, wherein, at each emission step, at least one emitted pulse includes a respective random phase introduced by the radar (16) and, wherein, each reception step of an echo received from the at least one emitted pulse with a random phase includes compensation for the phase shift related to the introduced random phase.

5. A method according to any one of claims 1 to 4, wherein the method includes a step of processing the received echoes to determine at least one of a distance to a target and a velocity of a target in the environment (12).

6. A method according to any one of claims 1 to 5, wherein the method comprises a step of analyzing the echoes listened to during a listening session to obtain an electromagnetic behavior in the direction and frequency of the echoes listened to.

7. A method according to claims 5 and 6, wherein the processing step takes into account the electromagnetic behavior obtained in the analysis step.

8. Radar (16) suitable for carrying out several recurrences of a signal transmission and reception step, at least one sequence of recurrences comprising, for two integers N and M: - N first recurrences during which the radar (16) is suitable - to emit pulses at a repetition rate in a first direction at a first frequency, and - to receive echoes emitted at the first frequency in the first direction, - M recurrences following the first N recurrences and during which the radar (16) is specific to: - emit pulses at the repetition period in a second direction at a second frequency, the second direction being different from the first direction and the second frequency being different from the first frequency, and - listen for echoes emitted at the first frequency in the first direction, and - N second recurrences following the M recurrences and during which the radar (16) is specific to: - emit pulses at a repetition rate in the second direction at the second frequency, and - to receive echoes emitted at the second frequency in the second direction.

9. Observation system (14) comprising a radar (16) according to claim 8.

10. Aircraft (10) comprising a radar (16) according to claim 8 or an observation system (14) according to claim 9.

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