Method for monitoring an environment using radar over an observation area and associated devices

Abstract

Method of monitoring an environment by a radar over an observation domain and associated devices The present invention relates to a method of monitoring an environment by a radar (16) over an observation domain, the method comprising successive transmissions and receptions of a waveform having a pattern formed by: - ​​a first Doppler pulse, - a second non-Doppler pulse, - a third non-Doppler pulse, the angle of the observation direction of the second and third pulses along a second scanning direction being modified after a first number of transmissions and receptions of the waveform at the same observation angle along the first scanning direction and the angle of the observation direction of the first pulse along both scanning directions being modified after a second number of transmissions and receptions of the waveform, the second number being strictly greater than the first number.Figure for the abbreviation: figure 1.

Description

Title of the invention: Method for monitoring an environment by radar over an observation area and associated devices

[0001] The present invention relates to a method of environmental monitoring using radar over an observation area. It also relates to a monitoring system adapted for implementing such a method.

[0002] In a marine environment, it is useful to know the sea clutter to improve target detection.

[0003] For this purpose, it is known to use a Doppler analysis mode dedicated to the characterization of sea clutter.

[0004] This Doppler analysis mode is carried out after implementation of a non-Doppler maritime surveillance detection mode.

[0005] The surveillance is therefore a succession of Doppler and non-Doppler modes corresponding to an interleaving strategy of tasks called "short time" at the scale of a radar processing block or called "long time" at the scale of a complete scan of the environment to be probed.

[0006] This imposes a limited refresh time because the overall refresh time of the two analysis and monitoring modes is equal to the sum of the two unit refresh times, which can be detrimental for target tracking for example, which is all the better when the overall refresh time is low.

[0007] There is therefore a need for a method allowing observation in Doppler and non-Doppler modes which has a lower refresh time.

[0008] To this end, the description relates to a method of monitoring an environment by radar over an observation domain, the observation domain comprising a set of possible observation directions, each observation direction being spatially identified by a first scanning direction and a second scanning direction,

[0009] the method comprising successive transmissions and receptions of a waveform having a pattern formed by:

[0010] - a first radar pulse, the first pulse being a Doppler pulse,

[0011] - a second radar pulse, the second pulse being a pulse non-Doppler observation of the environment over a domain encompassing observation directions where the observation angle along the first scanning direction is less than or equal to a first angle,

[0012] - a third radar pulse, the third pulse being a pulse non-Doppler observation of the environment over a domain encompassing observation directions where the observation angle along the first direction is greater than or equal to a second angle, the second angle being greater than or equal to the first angle, the second and third pulses presenting an observation direction with the same observation angle along the second scanning direction,

[0013] the angle of the observation direction of the second and third pulses along the second scanning direction being modified after a first number of emission-receptions of the waveform at the same observation angle along the first scanning direction and the angle of the observation direction of the first pulse along both scanning directions being modified after a second number of emission-receptions of the waveform, the second number being strictly greater than the first number.

[0014] 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:

[0015] - the two scanning directions are perpendicular.

[0016] - one of the scanning directions is in elevation.

[0017] - one of the scanning directions is in azimuth.

[0018] - for each waveform, the ratio between the second number of emissions- receptions and the first number of transmissions-receptions is between 5 and 20, preferably equal to 10.

[0019] - for each waveform, the ratio between the duration of the second pulse and the The duration of the third pulse is between 5 and 20.

[0020] - after the second number of transmissions-receptions, the frequency of the third The radar pulse is also modified.

[0021] - the time interval between the first two sub-pulses of two waveforms successive is between 0.5 seconds and 5 seconds, preferably equal to 1 second.

[0022] - the environment is a marine environment.

[0023] The description also relates to a radar suitable for monitoring an environment over an observation domain, the observation domain comprising a set of possible observation directions, each observation direction being spatially identified by a first scanning direction and a second scanning direction,

[0024] the radar being adapted to implement successive transmissions and receptions of a waveform having a pattern formed by:

[0025] - a first radar pulse, the first pulse being a Doppler pulse,

[0026] - a second radar pulse, the second pulse being a pulse non-Doppler observation of the environment over a domain encompassing observation directions where the observation angle along the first scanning direction is less than or equal to a first angle,

[0027] - a third radar pulse, the third pulse being a pulse non-Doppler observation of the environment over a domain encompassing observation directions where the observation angle along the first direction is greater than or equal to a second angle, the second angle being greater than or equal to the first angle, the second and third pulses presenting an observation direction with the same observation angle along the second scanning direction,

[0028] the angle of the observation direction of the second and third pulses along the second scanning direction being modified after a first number of emission-receptions of the waveform at the same observation angle along the first scanning direction and the angle of the observation direction of the first pulse along both scanning directions being modified after a second number of emission-receptions of the waveform, the second number being strictly greater than the first number.

[0029] The description also relates to a surveillance system comprising a radar as previously described.

[0030] The description also relates to an aircraft comprising a radar as previously described or a surveillance system as previously described.

[0031] In this description, the expression "specific to" means interchangeably "suitable for", "adapted to" or "configured for".

[0032] 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:

[0033] - [Fig. 1] [Fig. 1] is a schematic representation of an aircraft exhibiting a an environmental monitoring system using a specific waveform pattern,

[0034] - [Fig.2] [Fig.2] is a schematic representation of an emission of a shape of a wave exhibiting the specific pattern,

[0035] - [Fig.3] [Fig.3] is a schematic representation of the emission bands / reception corresponding to the reception of [Fig.2], and

[0036] - [Fig.4] [Fig.4] is a schematic representation of an example of scanning the environment by using waveforms exhibiting the specific pattern.

[0037] An aircraft 10 is schematically represented in [Fig.1].

[0038] The aircraft 10 is used here to monitor the environment 12, which is a marine environment. The sea surface is illustrated as a line.

[0039] Aircraft 10 seeks, in particular, to detect the presence of potential targets.

[0040] The aircraft 10 is equipped with a monitoring system 14, the monitoring system 14 comprising a radar 16 interacting with a computer 18.

[0041] The radar 16 is suitable for observing the observation domain by implementing a monitoring method.

[0042] This observation domain brings together possible observation directions for radar 16.

[0043] The observation direction is the main direction of the main lobe emitted by the radar 16.

[0044] In this example, each observation direction is spatially located by a site angle and an azimuth angle.

[0045] The radar 16 is suitable for using a waveform pattern that allows simultaneous implementation of a "fast" non-Doppler mode with two elevation lines and a "slow" Doppler analysis mode with one elevation line.

[0046] The radar 16 is thus suitable for carrying out successive transmissions and receptions of this waveform whose pattern is specific.

[0047] Such a pattern is schematically presented in transmission on [Fig.2] and in reception on [Fig.3].

[0048] The pattern is formed by three radar pulses marked respectively II, 12 and 13.

[0049] These three impulses II, 12 and 13 share the same recurrence period and the same listening time.

[0050] The first pulse II is a Doppler pulse.

[0051] The space or domain which allows observation of the first pulse II is represented on [Fig.1] by a first domain extending between a minimum distance Dlmin and a maximum distance Dlmax (here at the intersection between the observation lobe and the surface of the sea).

[0052] The second pulse 12 is a non-Doppler observation pulse of the environment 12 on a second domain gathering observation directions whose observation angle in elevation is less than or equal to a first elevation angle.

[0053] This corresponds to the second distance domain visible on [Fig.1], namely the domain extending between a minimum distance D2min and a maximum distance D2max.

[0054] The third pulse 13 is a non-Doppler observation pulse of the environment on a third domain bringing together observation directions whose observation angle in elevation is greater than or equal to a second angle.

[0055] The second angle is greater than or equal to the first angle.

[0056] This corresponds to the third distance domain visible on [Fig. 1], namely the domain extending between a minimum distance D3min and a maximum distance D3max.

[0057] In this case, the minimum distance D3min of the third domain is equal to the maximum distance D2max of the second domain.

[0058] This means that the third pulse 13 is used to observe the environment 12 at a relatively long distance while the second pulse 12 is used to observe the environment 12 at a relatively short distance.

[0059] According to the example, this different spatial observation is obtained, for each waveform, by different pulse durations.

[0060] Typically, the ratio between the duration of the second pulse and the duration of the third pulse is between 5 and 20.

[0061] Furthermore, it appears that in this example, the minimum distance Dlmin of the first domain is relatively close to the minimum distance D3min and maximum distance D2max while the maximum distance Dlmax is located approximately in the middle of the third domain.

[0062] The first pulse II therefore seeks to make an observation at medium distances. More generally, the first pulse II makes an observation in an area where it is relevant in terms of the overall assessment to measure the Clutter-to-Noise ratio.

[0063] On [Fig.2], two successive motifs M1 and M2 are shown, each comprising the series of three impulses II to 13.

[0064] The time interval between the first two sub-pulses of two successive pattern waveforms M1 and M2 is the pattern repetition period.

[0065] The refresh period of the non-Doppler pulses depends on the number of points to be made to cover the angular domain in the case of a two-dimensional AESA architecture or on the scanning speed in the case of a one-dimensional mechanically scanned AESA antenna.

[0066] The refresh time, that is to say the time between two pointings or sweeps towards the same azimuth, is then typically between 0.5 seconds and 5 seconds, preferably equal to 1 second.

[0067] The radar 16 is capable of emitting these three-pulse patterns II to 13 throughout the observation period.

[0068] The radar 16 is also capable of receiving these pulses II to 13 in the same reception frequency band as schematically represented in [Fig. 3]. The radar 16 is, in fact, capable of frequency-separating the emitted bands of each pulse II to 13.

[0069] In the example described, the observation direction of each pulse II to 13 has the same angle in azimuth, only the angle in elevation varies.

[0070] However, in a general case, only the impulses 12 and 13 have an observation direction whose observation angle is the same in azimuth.

[0071] Indeed, the azimuth angle of the observation direction of the second and third pulses 12 and 13 is modified after a first number of transmissions and receptions of the waveform at the same site angle.

[0072] This first number is denoted N.

[0073] The first number N is between 4 and 30.

[0074] This is schematically represented in [Fig.4].

[0075] Conversely, the angle of the observation direction of the first pulse II in elevation and azimuth is modified after a second number of transmissions and receptions of the waveform.

[0076] The second number is strictly greater than the first number N.

[0077] In the example described, the second number is equal to the product of the first number N by an integer M.

[0078] The integer M thus corresponds to the ratio between the second number and the first number.

[0079] The integer M is between 5 and 20, preferably equal to 10.

[0080] Preferably, after the implementation of M*N transmissions-receptions, the frequency of the first pulse II is also modified.

[0081] In operation, the first pulse II is used to conduct the Doppler analysis of a direction (azimuth, elevation), it is inserted into the pattern and is associated with a site line and an azimuth direction which may be different from those of the detection mode.

[0082] To do this, phase coherence is maintained on the first recurrence pulse (same emission frequency) unlike the other two pulses which are non-Doppler waveforms (variation of emission frequency to perform non-coherent processing).

[0083] Finally, to compensate for the reduced energy budget linked to the small pulse width and to operate with a suitable Clutter-to-noise ratio for the analysis, we choose to emit a band that is also smaller compared to the detection mode in order to average the clutter over distance squares of significant width: the analysis is then centered on the calculation and exploitation of the average power of the clutter by eliminating the impulsive character, a phenomenon appearing with higher emitted bands.

[0084] Thus, the minimum observation distance of each pulse depends on its position in the emission window: • The first pulse II is that of the analysis mode: we are not trying to have a good minimum distance for this mode, nor to have a good The maximum observed distance is measured. The aim is to probe general characteristics of sea clutter over a domain where the clutter-to-noise ratio is sufficient. The distance domain processed on a beam in the middle of the domain is sufficient for this purpose. • The second pulse 12 is the longest pulse, as it is adapted for detecting the most distant targets; it corresponds to the long-range line of sight. • the third pulse 13 is placed last to deal with the short range distance domain because it is the one that defines the minimum distance of the detection mode (we want it to have the lowest eclipse distance).

[0085] A frequency band is allocated to the Doppler mode during the entire acquisition of signals in one direction, while the frequency bands vary during the integration of the non-coherent signals of the non-Doppler mode.

[0086] A single receiving window is used to receive the echoes from the three pulses. At the receiver, the entire receiving band is sampled, and then digital filters separate the contributions from the three bands associated with a recurrence. Conventional beamforming at the transmitter positions the pulses in the desired directions, in conjunction with a second beamforming at the receiver that separates the channels and collects the information from each direction / colored pulse.

[0087] The non-Doppler mode pulses sweep the azimuth space during the integration of the Doppler pulse.

[0088] In the proposed digital application case, the non-Doppler pulses pointed to 10 azimuth positions while the Doppler pulse pointed to only one.

[0089] The signal processing collects and processes in parallel the signals of the non-Doppler mode and the Doppler mode signals associated with each direction.

[0090] The present method thus makes it possible to optimize at two scales the time budget allocated to a maritime target detection function.

[0091] The first optimization lever comes from the combination of the second and third impulses 12 and 13: saving approximately 10 to 15% of the budget by communalizing the short and long range reception time.

[0092] In such a case, this non-Doppler waveform used alone is not compatible with a spectral analysis of the sea clutter.

[0093] The second optimization lever comes from the addition of the first pulse II for the purpose of analyzing the Doppler spectrum of the sea clutter, instead of employing a short-time or long-time interleaving technique.

[0094] This allows for simple scheduling since the two functions performed simultaneously can be pre-constructed without the use of a complex scheduling algorithm aimed at integrating the two functions into the same frame.

[0095] Furthermore, the process allows the two functions to be decoupled by a uncorrelated refresh time.

[0096] To give an order of magnitude, this allows a refresh time of the non-Doppler mode of one second and a refresh rate of the Doppler mode of the order of 10 seconds.

[0097] The proposed method also allows the two functions to be performed simultaneously without degrading the performance of the detection mode (very minimal reduction in the budget at the margin due to the choice of a small pulse width of the analysis mode) while maintaining an optimal refresh time for the detection mode.

[0098] The emission band of the analysis mode is adapted accordingly and is chosen to be small in order to maintain a suitable clutter-to-noise ratio for analyzing the clutter. At low resolution, sea clutter exhibits a less impulsive character than the detection mode; this is not what we seek to characterize: on the contrary, the analysis mode seeks to characterize the Doppler spectrum, allowing us to deduce a wind direction and wind speed with greater precision and confidence than a non-Doppler mode can.

[0099] The present method therefore exploits a tripulse waveform in order to make a Doppler analysis waveform simultaneous with a bipulse non-Doppler detection waveform in the context of a maritime application in order to optimize the radar time budget and perform both modes simultaneously without loss of performance (range) of the detection mode or compromise on the refresh time.

[0100] Other embodiments are possible.

[0101] In particular, the method has been described for a scan in elevation and azimuth, but any other type of two-dimensional scan could be considered, including scans with non-perpendicular directions.

[0102] It could also be envisaged that embodiments with more non-Doppler pulses could be envisaged. For example, three non-Doppler pulses corresponding respectively to short-range, medium-range and long-range observations.

[0103] Furthermore, it is also possible to obtain better isolation of the echoes corresponding to the different radar modes during their reception.

[0104] Thus, different slopes of chirps are implemented to emit the different pulses.

[0105] In other words, the radar 16 emits the pulses using either an ascending or a descending slope depending on the type of pulses. The same slope is then used for all pulses of this type in all recurrences.

[0106] For example, for all recurrences, an upward slope is chosen for the pulses associated with the Doppler mode and a downward slope is chosen for the pulses associated with the non-Doppler mode.

[0107] Then, the radar 16 is capable of separating the signals associated with the different slopes received and of sufficiently isolating the echoes corresponding to the different modes.

[0108] For this purpose, radar 16 uses filters adapted to the corresponding chirp slopes.

[0109] According to another technique allowing also better isolation of echoes corresponding to different radar modes during their reception, radar 16 implements different polarizations of the waves used to emit the pulses associated with Doppler and non-Doppler modes.

[0110] In other words, the radar 16 emits the wave carrying each pulse with a polarization chosen according to the radar mode associated with that pulse. This same polarization is chosen for this type of pulse for all recurrences.

[0111] For example, two polarizations, namely a vertical polarization and a horizontal polarization, can be chosen for the emitted pulses.

[0112] According to other examples, 45° or circular polarization may be used. For example, left-hand circular polarization may be associated with the first configuration and right-hand circular polarization may be associated with the second configuration.

[0113] Then, radar 16 receives echoes having different polarizations. Radar 16 therefore determines the received polarizations in order to isolate the echoes corresponding to the different configurations.

[0114] For this purpose, the radar uses filters adapted to the corresponding polarization slopes.

[0115] In the example described, horizontal polarization could be used in transmission and reception for non-Doppler modes and vertical polarization for the non-Doppler mode.

[0116] Vertical polarization analysis for clutter analysis in non-Doppler mode facilitates the detection of average power (which is what we seek to characterize) and reduces impulsiveness (which is already achieved with bandwidth reduction). The method can also be implemented on board systems other than aircraft, particularly ships, submarines, or satellites, in applications involving the detection or identification of targets in the presence of sea clutter.

[0117] 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.

[0118] 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).

[0119] 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.

Claims

1.

2.

3. Demands Method for monitoring an environment by means of radar (16) over an observation domain, the observation domain comprising a set of possible observation directions, each observation direction being spatially identified by a first scanning direction and a second scanning direction, the method comprising successive transmissions and receptions of a waveform having a pattern formed by: - a first radar pulse (II), the first pulse (II) being a Doppler pulse, - a second radar pulse (12), the second pulse (12) being a non-Doppler observation pulse of the environment over a domain encompassing observation directions whose observation angle along the first scanning direction is less than or equal to a first angle,- a third radar pulse (13), the third pulse (13) being a non-Doppler observation pulse of the environment over a domain combining observation directions whose observation angle along the first direction is greater than or equal to a second angle, the second angle being greater than or equal to the first angle, the second pulse (12) and third pulse (13) having an observation direction having the same observation angle along the second scanning direction, the angle of the observation direction of the second and third pulses (12,13) ​​along the second scanning direction being modified after a first number of transmit-receive cycles of the waveform at the same observation angle along the first scanning direction and the angle of the observation direction of the first pulse (II) along both scanning directions being modified after a second number of transmit-receive cycles of the waveform,the second number being strictly greater than the first number. A monitoring method according to claim 1, wherein the two scanning directions are perpendicular. A monitoring method according to claim 1 or 2, wherein one of the scanning directions is in elevation.

4. A monitoring method according to any one of claims 1 to 3, wherein one of the scanning directions is in azimuth.

5. A monitoring method according to any one of claims 1 to 4, wherein, for each waveform, the ratio between the second number of transmissions and receptions and the first number of transmissions and receptions is between 5 and 20, preferably equal to 10

6. IV. A monitoring method according to any one of claims 1 to 5, wherein, for each waveform, the ratio between the duration of the second pulse and the duration of the third pulse is between 5 and 20.

7. A monitoring method according to any one of claims 1 to 6, wherein after the second number of transmit-receive cycles, the frequency of the third radar pulse is also changed.

8. A monitoring method according to any one of claims 1 to 7, wherein the time interval between the first two subpulses of two successive waveforms is between 0.5 seconds and 5 seconds, preferably equal to 1 second.

9. A monitoring method according to any one of claims 1 to 8, wherein the environment is a marine environment.

10. Radar (16) adapted to monitor an environment over an observation domain, the observation domain comprising a set of possible observation directions, each observation direction being spatially located by a first scanning direction and a second scanning direction, the radar (16) being adapted to implement successive transmissions and receptions of a waveform having a pattern formed by: - ​​a first radar pulse (II), the first pulse (II) being a Doppler pulse, - a second radar pulse (12), the second pulse (12) being a non-Doppler observation pulse of the environment over a domain comprising observation directions whose observation angle along the first scanning direction is less than or equal to a first angle, - a third radar pulse (13),the third impulse (13) being a non-Doppler observation impulse of the environment over a domain combining observation directions whose observation angle along the first direction is greater than or equal to,

11.

12. a second angle, the second angle being greater than or equal to the first angle, the second pulse (12) and third pulse (13) having an observation direction having the same observation angle along the second scanning direction, the angle of the observation direction of the second and third pulses (12,13) ​​along the second scanning direction being modified after a first number of emission-receptions of the waveform at the same observation angle along the first scanning direction and the angle of the observation direction of the first pulse (II) along both scanning directions being modified after a second number of emission-receptions of the waveform, the second number being strictly greater than the first number. Surveillance system (14) comprising a radar (16) according to claim 10. Aircraft (10) comprising a radar (16) according to claim 10 or a surveillance system (14) according to claim 11.

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