JP4481078B2 - Radar equipment - Google Patents

Description

  The present invention relates to the field of radar devices and signal processing, and more particularly to a radar device that detects a target existing on the sea surface or on the ground from a high elevation angle.

  In the radar equipment mounted on the aircraft, the irradiation area of the beam on the sea surface is calculated using information on the known radar altitude, beam pointing direction, and antenna pattern, and the magnitude of the gain in each range is calculated based on this calculation result. There is a method for improving the target visibility by suppressing the sea surface clutter by adjusting (see, for example, Patent Document 1).

  This method multiplies the received power by a coefficient determined by the known radar altitude, beam direction, and antenna pattern, and adjusts and displays the sea level clutter power as constant as possible on the screen. Visibility can be improved.

Japanese Patent Laying-Open No. 2003-107147 (first page, FIG. 1)

  However, the prior art has the following problems. As described above, the conventional technology does not essentially improve the power ratio between the signal and the clutter, so the clutter power on the sea surface or the ground surface is very high, as observed from a high elevation angle. If the signal to clutter power ratio (SCR) is low and the target detection probability is low, the target detection probability cannot be sufficiently improved.

  The present invention has been made to solve the above-described problems, and can improve the target detection performance even when the clutter power on the sea surface or the ground surface is very large and the signal-to-clutter power ratio is low. An object of the present invention is to obtain a radar device that can be used.

A radar apparatus according to the present invention is a radar apparatus that transmits a broadband pulse signal via a transmission / reception antenna, receives a reflected wave as a reception signal, and detects a target based on the reception signal. A radar altitude estimating means for estimating the radar altitude relative to the sea surface or the ground surface, a storage unit for storing the directivity angle of the transmission / reception antenna and the received signal in association with each other, and the directivity angle of the antenna pattern of the transmission / reception antenna in the elevation direction. A control device for controlling, and a range compression means for performing pulse compression processing on the received signal received via the transmission / reception antenna and storing the received signal after the pulse compression processing in the storage unit in association with the information on the directivity angle received from the control device Information on the estimated radar altitude, the pointing angle from the controller, and the antenna parameters of the transmitting and receiving antennas measured in advance. Based on the over emissions, each oriented angle at the estimated the radar altitude from the clutter range scanned and clutter radiation pattern calculation means for calculating the estimated clutter radiation pattern in the range was, the beam in the elevation direction the clutter radiation pattern calculated by the clutter radiation pattern calculation means, by least square fitting to the received signal after the pulse compression processing corresponding to the accumulated respective directivity angles were in the storage unit, per unit area with respect to Clutter scattering cross-section estimation means for estimating the clutter scattering cross-section, and a clutter in which the clutter power is suppressed for each received signal after pulse compression processing accumulated in the storage unit using the estimated clutter scattering cross-section. Clutter suppression means for calculating the suppression signal, and the calculated clutter suppression signal From those and a target detection means for detecting a target.

  According to the present invention, it is possible to detect a scattering point at a position higher than the sea level by separating the altitude of the scattering point by scanning the beam in the elevation direction, and further from the known radar altitude to the sea level. Targets can be detected based on signals that suppress the clutter component by estimating the clutter range, even when the clutter power on the sea surface or the ground surface is very large and the signal-to-clutter power ratio is low. A radar apparatus capable of improving the target detection performance can be obtained.

  A preferred embodiment of a radar apparatus according to the present invention will be described below with reference to the drawings. The present invention is particularly useful when a radar device mounted on an aircraft or the like is used to detect a ship existing on the sea surface by observing the sea surface from a high elevation angle. In the following embodiments, details of this case will be described. Explained. However, the platform is not limited to aircraft, and the observation area is not limited to the sea surface.

Embodiment 1 FIG.
First, an observation method and a basic principle when a ship on the sea is detected by a radar mounted on an aircraft or the like will be described with reference to FIGS. FIG. 1 is an explanatory diagram of an observation method and a basic principle of a radar apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, an aircraft 1 is equipped with a radar device 2 and flies over the sea surface 3. On the other hand, the ship 4 to be detected floats on the sea surface 3. The scattering point 5 exists on the ship 4 and is one of points that scatter radio waves from the radar device 2. A point 6 on the sea surface is a point on the sea surface where the distance from the radar device 2 is equal to the distance from the radar device 2 to the scattering point 5. A point 7 on the sea surface is a point on the sea surface immediately below the radar device 2 in the vertical direction. A point 8 on the sea surface is a point on the sea surface immediately below the scattering point 5 in the vertical direction. An antenna pattern 9 indicates an antenna pattern of a radio wave transmitted from the radar device 2.

  When the off-nadir angle is small (that is, when the depression angle is large), the reflected wave from the ship 4 that is the detection target is buried in the sea surface clutter, making detection difficult. However, it is assumed that the scattering point 5 on the ship 4 is present at a position higher than the altitude of the sea surface 3. The basic principle of target detection in the present invention focuses on this point, and scans the transmission beam in the elevation direction and separates various scattering points according to altitude, so that the scattering at a position higher than the sea level is scattered. Detect points.

  The beam width in the elevation direction is a major factor that determines the performance of the target detection method in the first embodiment. That is, when the beam width in the elevation direction is sufficiently narrow, the target scattering point can be detected by separating from the sea surface clutter relatively easily by the elevation angle. However, if the beam width in the elevation direction is not sufficiently narrow, it becomes difficult to identify the target scattering point only by the elevation angle, and in order to detect the target scattering point more accurately, Repression is necessary.

  Therefore, in the first embodiment, when the range of the sea surface clutter is estimated from the known radar altitude, and the component of the sea surface clutter is suppressed based on the estimation result, the beam width in the elevation direction is insufficient. In addition, a method that enables detection of the target is given.

  The positional relationship among the radar device 2, the scattering point 5, and other points in FIG. 1 is defined as follows. The radar device 2 mounted on the aircraft 1 is assumed to be at an altitude H from the sea level 3, and the scattering point 5 existing on the ship 4 floating on the sea level 3 is at an altitude h from the sea level 3. The distance (slant range) from the radar device 2 to the scattering point 5 is r, and the distance from the point 7 on the sea surface immediately below the vertical direction of the radar device 2 to the point 8 on the sea surface directly below the scattering point 5 in the vertical direction. Let (ground range) be R.

Further, the point 6 on the sea surface is a point on the sea surface whose distance from the radar device 2 is equal to the distance r from the radar device 2 to the scattering point 5. Therefore, the reflected wave from the point 6 on the sea surface and the reflected wave from the scattering point 5 are both observed as signals in the same range. However, the arrival angles of the reflected waves are different, and this arrival angle difference is Δθ. A straight line connecting the point 8 and the radar unit 2 on the sea surface is a vertical line and angle theta, the direction of the center of the beam is vertical line and angle (off-nadir angle) and theta _O.

  When the beam width in the elevation direction of the radar is sufficiently narrower than Δθ, the incoming wave from the scattering point 5 on the ship 4 and the incoming wave from the point 6 on the sea surface are transmitted in the elevation direction. It is easily separated by operating to.

  Therefore, first, the magnitude of the arrival angle difference Δθ between the incoming wave from the scattering point 5 and the incoming wave from the point 6 on the sea surface is estimated. When the angle between the straight line connecting the point 8 on the sea surface immediately below the scattering point 5 on the sea surface and the radar device 2 is θ, the arrival angle difference Δθ is the height H of the radar device 2 and the height of the scattering point 5. It can be expressed as a function of h and angle θ, and satisfies the relationship of the following equation (1).

  FIG. 2 is a diagram showing the relationship between the arrival angle difference Δθ and the altitude h when the angle θ is a parameter in the first embodiment of the present invention, and is a graph showing the relationship of the above equation (1). is there. Specifically, the height h of the scattering point 5 is taken as the horizontal axis, and the arrival angle difference Δθ between the incoming wave from the scattering point 5 and the incoming wave from the point 6 on the sea surface is taken as the vertical axis. The function of the above formula (1) is graphed using the value as a parameter.

  The angle θ which is a parameter is four types of θ = 10 °, 15 °, 20 ° and 25 °, and is shown in FIG. 2 as a solid line, a dotted line, a one-dot chain line and a broken line, respectively. Further, the altitude H of the radar apparatus 2 indicates a case where H = 2000 m is fixed. In FIG. 2, the line at the angle θ = 10 ° is cut halfway. This is because when the target altitude h exceeds a certain value, a circle whose radius is the distance to the scattering point 5 around the radar position does not intersect the sea surface 3 (that is, “the distance from the radar device 2 is This means that there is no data because there is no point 6 ″ on the sea surface that is equidistant from the distance from the radar device 2 to the scattering point 5).

  From FIG. 2, when θ = 20 °, for example, when the altitude h of the scattering point 5 is 20 m, the arrival angle difference Δθ is about 2 °. Therefore, when the beam width in the elevation direction is sufficiently narrower than 2 °, the scattering point 5 and the sea surface clutter can be easily separated by the difference in the arrival angle in the elevation direction. However, when the beam width in the elevation direction is 2 ° or more, the scattering point 5 and the sea surface clutter cannot be separated due to the difference in the arrival angle in the elevation direction, and a clutter suppression process is required.

Based on this relationship, a specific procedure for target detection will be described next. The distance r _O between the point where the beam center direction intersects the sea surface and the radar apparatus 2 is expressed by the following equation (3) using the off-nadir angle θ _O and the altitude H.

Here, r _o corresponds to the range of the peak of clutter power of sea in off-nadir angle theta _O. When the altitude h of the scattering point 5 on the ship 4 is larger than 0, the peak range r of the reflected power from the scattering point 5 satisfies the following expression (4).

If altitude H and the off nadir angle theta _O of the radar device 2 is known, for each of the off-nadir angle theta _O, the range r _o the peak of the main lobe clutter sea occurs, using equation (3) Can be calculated in advance. Therefore, to detect the peak of the received signal at various off-nadir angle theta _O, range r of the peaks satisfies equation (4), it can be determined that the target signal.

Also, when the range r satisfying the out type of the received signal (4) is Motoma' for a plurality of off-nadir angle theta _O performs detection of peak among them, the detected peak target signal determination can do.

  However, if the beam width in the elevation direction cannot be made sufficiently narrow, it is difficult to separate the scattering point 5 from the sea surface clutter in the elevation direction, and the above equation (4) is used for the received signal as it is. The target cannot be judged. In such a case, it is necessary to estimate the sea clutter range from the known radar altitude and suppress the sea clutter.

  In the present invention, sea level clutter is suppressed by the following method. That is, if the antenna pattern, the radar altitude, and the off-nadir angle of the beam center are known, the beam irradiation pattern on the sea surface can be calculated. Therefore, the sea surface clutter component is suppressed by subtracting the calculated irradiation pattern from the observed value, which is a received signal, by least square fitting. Details of this clutter suppression method will be described next.

  FIG. 3 is an explanatory diagram showing the relationship among the antenna pattern, range resolution, and clutter irradiation area in Embodiment 1 of the present invention. In FIG. 3, a vertical antenna pattern 11 indicates a pattern obtained by viewing the antenna pattern 9 from the upper side in the vertical direction. The horizontal antenna pattern 12 shows the same antenna pattern 9 viewed from the horizontal side.

  Here, as an example, it is assumed that the pattern of the gain G (ψ, φ) of the transmission / reception antenna 16 is represented by a sinc function type of the following equation (5). However, this antenna pattern is not limited to the sinc function type, and it is obvious that the same processing can be performed with an arbitrary pattern.

Here, G ₀ represents the antenna gain in the beam center direction, and ψ and φ represent the angle in the elevation direction and the azimuth direction from the beam center direction of the antenna, respectively. Ψ and Φ are 4 dB beam widths in the elevation direction and the azimuth direction, respectively. The relationship between φ and Φ with respect to the vertical antenna pattern 11 and the relationship between ψ and ψ with respect to the horizontal antenna pattern 12 are shown in FIG.

Further, the irradiation range 13 is a beam at a certain off-nadir angle theta _O showed range (footprint) for irradiating the sea surface 3. By a variety of off-nadir angle theta _O, the position of the irradiation range 13 of the sea surface 3 are different. Therefore, the position on the sea surface 3 to cover the irradiation range 13 for the various off-nadir angle theta _O, and that you divide the range cell in advance 1 to N.

In this division, the sea surface 3 is virtually divided into N by changing the distance (slant range) from the radar apparatus 2 to the scattering point on the sea surface 3 by the range resolution Δr. it can be determined in advance from the nadir angle θ _O. The irradiation range 13 in FIG. 3 shows a state where the irradiation range 13 exists in the range cells from n−1 to n + 3.

Assume that an angle between a straight line connecting each point on the sea surface 3 divided into 1 to N range cells and the radar apparatus 2 and a vertical line is represented by θ _n . Furthermore, the slant range for each θ _n is expressed as r _n (n = 1, 2,..., N). In the following description, n = 1, 2,..., N is a range number, N is the number of range cells, and each divided range is represented by each range cell n (n = 1, 2,..., N). Call it.

The scattering cross section σ _n and the scattering coefficient σ ⁰ _n for each range cell n (n = 1, 2,..., N) obtained by dividing the irradiation range 13 are related by the following equation (6).

However, A _n is represents the clutter irradiated surface of the n-th range cells, the relationship is shown in the irradiation range 13 of FIG. Since the scattering cross section σ _n is obtained by multiplying the scattering coefficient σ ⁰ _n by an effective irradiation area, the relationship of the following equation (7) is established.

Here, A ′ _n is an effective irradiation area obtained by weighting with the antenna pattern, and in the following description, this is referred to as a beam irradiation pattern on the sea surface. A ′ _n is a function of the off-nadir angle θ _O and will be explicitly expressed as A ′ _n (θ _O ) in the following description. This A ′ _n (θ _O ) satisfies the relationship of the following equation (8).

  However, H is the altitude of the radar, and r satisfies the relationship of the following equation (9).

  The function Si (x) is defined by the following equation (10).

Therefore, if the altitude H of the radar device 2 and the off-nadir angle θ _{O at the} beam center are known from prior measurements, the irradiation pattern of the clutter can be obtained by the above equation (8).

The beam is scanned in the elevation direction, and pulses are transmitted and received at M off-nadir angles θ _Om (m = 1, 2,..., M). Here, a received signal in a range cell having an off-nadir angle θ _Om and a slant range r _n (n = 1, 2,..., N; N is the number of range cells) is represented as X _n (θ _Om ).

First, an irradiation pattern A ′ _n (θ _Om ) of the clutter is obtained from the known (or previously estimated) radar height H and off-nadir angle θ _{Om according} to the equation (8).

Next, to estimate the magnitude of the clutter scattering cross section s _n per unit area in the n-th range cell by the following equation (11).

Here, the symbol “^” above s _n on the left side of Equation (11) indicates that the value is an estimated value. Using the value of the clutter scattering cross section s _n per unit area estimated in this way, the clutter power is suppressed by the following equation (13), and the clutter suppression signal Y _n (θ _Om ) is obtained as a signal after the clutter suppression. Ask for.

Expression (13) is a process of removing the estimated clutter component from the received signal. In the clutter suppression signal Y _n (θ _Om ), the SCR is improved, and as a result, the target detection probability is improved.

  Based on the above principle, the configuration and operation of the radar apparatus according to the first embodiment will be described. FIG. 4 is a configuration diagram of the radar apparatus according to Embodiment 1 of the present invention.

  When the transmitter 14 generates a pulse signal as a wideband pulse, the transmitter 14 drives the transmission / reception antenna 16 via the transmission / reception switch 15 to radiate the pulse signal from the transmission / reception antenna 16 to space. At this time, the control device 17 controls the directivity direction of the antenna pattern of the transmission / reception antenna 16 so that the direction of the beam center is directed to a desired direction.

  For example, when the transmission / reception antenna 16 is an array antenna, the control device 17 controls the directivity direction of the antenna pattern by controlling the feeding phase of the element antenna. Alternatively, when the transmission / reception antenna 16 is fixed to a gimbal or the like and mechanically scans, the control device 17 controls the directivity direction of the antenna pattern by controlling the gimbal.

  The polarization of the transmission / reception antenna 16 is preferably a polarization with low clutter power such as sea surface clutter, and it is desirable to use horizontal polarization or circular polarization. However, the polarization of the transmission / reception antenna 16 is not limited to these polarizations.

  The pulse signal radiated from the transmitting / receiving antenna 16 to the space is scattered by the observation target. When the transmission / reception antenna 16 receives the pulse signal scattered by the observation target, the transmission / reception antenna 16 sends the reception pulse signal to the receiver 18 via the transmission / reception switch 15. The receiver 18 performs phase detection processing and A / D conversion processing on the reception pulse signal received by the transmission / reception antenna 16, outputs a digital reception signal indicating the amplitude and phase of each reception pulse signal, and performs range compression Send to means 19.

  The range compression means 19 performs pulse compression processing on the digital received signal from the receiver 18 to generate a high-resolution range profile. Furthermore, the range compression means 19 stores the generated range profile in the memory 20 that is a storage unit.

For example, at the M off-nadir angles θ _Om (m = 1, 2,..., M), the control device 17 scans the beam in the elevation direction by controlling the directivity direction of the antenna pattern. Pulse transmission and reception can be controlled. In the memory 20, for each of the M off-nadir angles θ _Om , the received signal X _n (θ _Om ) in the range cell of the slant range r _n (n = 1, 2,..., N; N is the number of range cells). Is accumulated.

The inertial navigation device 21 is mounted on the aircraft 1 and measures position information. The radar height estimation means 22 calculates the height H of the radar device 2 from the position information measured by the inertial navigation device 21. Alternatively, when the measurement accuracy of the altitude H of the radar apparatus 2 by the inertial navigation apparatus 21 is not sufficiently high, the radar altitude estimation means 22 uses the received signal X _n (θ _Om ) stored in the memory 20. The altitude H of the radar apparatus 2 is estimated as follows.

First, the radar altitude estimation unit 22, for each off-nadir angle theta _Om, detects the range r _m where the reflected power is maximized. Then, the radar altitude estimating means 22, the distance from the radar device 2 when off-nadir angle of _Om theta to the point where the straight line of the central beam axis intersects the sea surface is considered to be r _m, the following equation (14) The estimated value of altitude H is calculated by

Equation (14) is a non-linear least-square equation, and the radar height estimation means 22 obtains an estimated value of the height H by an iterative solution using the radar height measurement by the inertial navigation device 21 as an initial value. . By having such an estimation function, the radar altitude estimating means 22 is based on the received signal X _n (θ _Om ) even when the altitude measurement accuracy of the radar apparatus 2 by the inertial navigation apparatus 21 is not sufficiently high. The altitude H of the radar apparatus 2 can be accurately estimated.

Next, the clutter irradiation pattern calculation means 23 is the off-nadir corresponding to the height H of the radar apparatus 2 estimated by the radar height estimation means 22 and the received signal X _n (θ _Om ) of the range profile stored in the memory 20. Based on the information of the angle θ _Om , the irradiation pattern A ′ _n (θ _Om ) of the clutter is obtained by the equation (8). Information on the off-nadir angle θ _Om can also be provided from the control device 17.

Next, the clutter scattering cross-sectional area estimation unit 24 receives the range profile received signal X _n (θ _Om ) stored in the memory 20 and the clutter irradiation pattern A ′ _n (θ calculated by the clutter irradiation pattern calculation unit 23. based _om) and to estimate the magnitude of the clutter scattering cross section s _n per unit area in the n-th range cell by the formula (11).

The clutter suppression means 25 uses the value of the clutter scattering cross section s _n per unit area estimated by the clutter scattering cross section estimation means 24 to suppress the clutter power by the equation (13), and the clutter suppression signal Y _n ( θ _Om ) is output.

Finally, the target detection unit 26 applies threshold processing or the like to the range satisfying the expression (4) in the clutter suppression signal Y _n (θ _Om ) calculated by the clutter suppression unit 25 to obtain a power peak. To detect. The target detection means 26 determines the peak detected in this way as a target signal. In addition, as the threshold value processing for target detection here, for example, a widely used CFAR (Constant False Alarm Rate) processing can be applied.

  According to the first embodiment, in a radar apparatus mounted on an aircraft or the like, a beam is scanned in the elevation direction, the target and clutter echoes are separated in the elevation direction, and the target is detected. And targets on the ground surface can be detected. In addition, it is possible to estimate sea level clutter signals from known antenna patterns and radar altitude measurements, and to detect targets based on clutter suppression signals that suppress sea level clutter components based on estimation results. The target detection performance can be improved even when the beam width in the elevation direction is insufficient.

Embodiment 2. FIG.
In the first embodiment, the radar apparatus using one transmission / reception antenna 16 has been described. In the second embodiment, a radar apparatus using a plurality of polarization transmitting / receiving antennas will be described. FIG. 5 is a configuration diagram of the radar apparatus according to Embodiment 2 of the present invention. Compared with the radar apparatus of FIG. 1, the radar apparatus of FIG. 5 includes a first polarization transmission / reception antenna 28, a second polarization transmission / reception antenna 29, and a polarization switching unit 27 instead of the transmission / reception antenna 16.

  In addition, the radar apparatus of FIG. 5 uses a plurality of polarization clutter scattering as a similar means corresponding to a plurality of polarizations instead of the clutter scattering cross section estimation means 24, the clutter suppression means 25, and the target detection means 26 in FIG. A cross-sectional area estimation unit 30, a multi-polarization clutter suppression unit 31, and a multi-polarization target detection unit 32 are provided.

  The first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29 have characteristics in which the polarization characteristics are orthogonal to each other. In addition, as a combination in which the polarization characteristics in the first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29 are orthogonal, for example, a combination of vertical polarization and horizontal polarization, or right-handed circular polarization and left-handed circular polarization A combination of waves can be considered.

  Next, the operation will be described. When the transmitter 14 generates a pulse signal as a wideband pulse, the transmitter 14 sends the pulse signal to the polarization switch 27 via the transmission / reception switch 15. The polarization switch 27 radiates the pulse signal from the first polarization transmission / reception antenna 28 to the space by driving the first polarization transmission / reception antenna 28. The pulse signal radiated into the space from the first polarization transmitting / receiving antenna 28 is scattered by the observation target.

  When the polarization switching device 27 drives both the first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29, the first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29 are scattered by the observation target. Each scattered wave is received.

  The first polarization transmission / reception antenna 28 and the second polarization transmission / reception antenna 29 send respective reception signals to the receiver 18. The receiver 18 performs a phase detection process and an A / D conversion process on each of the reception signals received by the first polarization transmission / reception antenna 28 and the second polarization transmission / reception antenna 29, and determines the amplitude of each reception signal. A digital reception signal indicating the phase is output and sent to the range compression means 19.

  The range compression means 19 performs pulse compression processing on the digital received signal from the receiver 18 to generate a high-resolution range profile. Furthermore, the range compression means 19 stores the generated range profile in the memory 20 that is a storage unit.

  Similarly, the broadband pulse generated by the transmitter 14 is sent to the polarization switch 27 via the transmission / reception switch 15, radiated from the second polarization transmission / reception antenna 28, and scattered by the observation target. Are received by the first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29.

  The first polarization transmission / reception antenna 28 and the second polarization transmission / reception antenna 29 send respective reception signals to the receiver 18. The receiver 18 performs a phase detection process and an A / D conversion process on each of the reception signals received by the first polarization transmission / reception antenna 28 and the second polarization transmission / reception antenna 29, and determines the amplitude of each reception signal. A digital reception signal indicating the phase is output and sent to the range compression means 19.

  The range compression means 19 performs pulse compression processing on the digital received signal from the receiver 18 to generate a high-resolution range profile. Furthermore, the range compression means 19 stores the generated range profile in the memory 20 that is a storage unit.

  In the above pulse transmission / reception, the control device 17 controls the first polarization transmission / reception antenna 28 and the second polarization transmission / reception antenna 29 so that the direction of the beam center is directed to a desired direction. The control method of the directivity direction of the antenna pattern here is the same as in Embodiment 1, but the directivity directions of the antenna patterns of the first polarization transmitting / receiving antenna 28 and the second polarization transmitting / receiving antenna 29 are the same. It is desirable to control.

  In the following description, “a signal transmitted by the first polarization transmission / reception antenna 28 and received by the first polarization transmission / reception antenna 28” is referred to as “a reception signal of the first polarization channel”, “a first polarization transmission / reception antenna”. The signal transmitted by the second polarization transmitting / receiving antenna 29 and received by the second polarization transmitting / receiving antenna 29 is transmitted by the second polarization transmitting / receiving antenna 29 and received by the first polarization transmitting / receiving antenna 28. "The received signal of the third polarization channel" and "the signal transmitted by the second polarization transmitting / receiving antenna 29 and received by the second polarization transmitting / receiving antenna 29" are "the received signal of the fourth polarization channel". Is defined.

The operations of the inertial navigation device 21, the radar height estimation means 22, and the clutter irradiation pattern calculation means 23 are the same as those in the first embodiment, and a description thereof is omitted. Next, the operation of the multi-polarization clutter scattering cross section estimation means 30 will be described. Similar to the first embodiment, the control device 17 can control the directivity direction of the antenna pattern and scan the beam in the elevation direction. For example, M off-nadir angles θ _Om (m = 1, 2). ,..., M), pulse transmission / reception is controlled.

At this time, the memory 20 stores the first polarization channel in the range cell of the slant range r _n (n = 1, 2,..., N; N is the number of range cells) for each of the M off-nadir angles θ _Om. -Received signals of the fourth polarization channel are accumulated. In these received signals ^{_{below, X k n (θ Om)}} ; expressed by (k = 1, 2, 3, 4 k are polarized channel number).

  The received signal in each range cell is expressed in a vector format such as the following equation (15).

Here, the norm of the vector _{k n} (θ _Om), the off nadir angle theta _Om, represents the intensity of the scattered to be observed in the range cell slant range _{r n,} the direction of vector _{k n} (θ _Om), scattered Represents the polarization characteristics.

The multi-polarization clutter scattering cross-section estimation means 30 is similar to the clutter scattering cross-section estimation means 24 in the first embodiment, and the range profile received signal X ^k _n (θ _Om ) (k = 1, 2, 3, 4; k is the polarization channel number) and the irradiation pattern A ′ _n (θ _Om ) of the clutter calculated by the clutter irradiation pattern calculation means 23, according to the following equation (16): It estimates the n-th vector s _n obtained by arranging clutter scattering cross section per unit area of the first polarization channel to the fourth polarization channel in range cells.

Further, the multi-polarization clutter scattering cross-sectional area estimation means 30 uses the clutter scattering cross-section estimated values per unit area of the first polarization channel to the fourth polarization channel in the nth range cell as the multi-polarization clutter suppression means. Send to 31. The multi-polarization clutter suppression means 31 uses the values of the clutter scattering cross-sections per unit area of the first polarization channel to the fourth polarization channel estimated by the multi-polarization clutter scattering cross-section estimation means 30 to The clutter component is suppressed by Expression (18). The clutter suppression signal after the clutter suppression is expressed as χ _n (θ _Om ).

  According to Equation (18), in order to suppress the component that matches the estimated value of the polarization characteristic of the sea surface clutter, if the target polarization characteristic is different from the polarization characteristic of the sea surface, the polarization information is The detection probability can be improved as compared with the case where it is not used.

Multiple polarization target detection unit 32, the clutter suppressing signal after clutter has been suppressed by a plurality polarization clutter suppression means 31 chi _n norm _{p n} (theta _Om) of (theta _Om), calculated by the following equation (19) To do.

The multi-polarization target detection unit 32 detects the peak of _pn (θ _Om ) by applying threshold processing or the like to the range satisfying the equation (4). The multi-polarization target detection means 32 determines the peak detected here as a target signal. Note that, as threshold processing for target detection here, CFAR (Constant False Alarm Rate) processing is applied as in the first embodiment.

  According to the second embodiment, pulses are transmitted / received by two antennas whose polarization characteristics are orthogonal to each other, and the polarization characteristics of the observation target are observed. Since the matched components are suppressed, the detection probability can be improved when the target polarization characteristic is different from the polarization characteristic of the sea surface as compared with the case where the polarization information is not used.

Embodiment 3 FIG.
In the third embodiment, a case where a display function is further added to the radar apparatus of the first embodiment will be described. FIG. 6 is a configuration diagram of the radar apparatus according to Embodiment 3 of the present invention. Compared with the radar apparatus of FIG. 1, the radar apparatus of FIG. 6 further includes a horizontal / vertical image generation means 33 and a display means 34. Since the clutter scattering cross section s _n per unit area is estimated by the clutter scattering cross section estimation unit 24 and the clutter suppression signal is calculated by the clutter suppression unit 25, the description is omitted.

Point of the off-nadir angle theta _Om and slant range r _n of the beam center, when expressed by the horizontal distance x and the vertical distance y from the radar device, the following relationship (20) holds.

Horizontal Vertical image generating unit 33 on the basis of the clutter suppression signal calculated by the clutter suppression means 25 calculates a two-dimensional array of off-nadir angle theta _Om and slant range r _m. Furthermore, horizontal vertical image generating unit 33, a clutter suppression signal calculated as a two-dimensional array of off-nadir angle theta _Om and slant range r _m, the distance of the distance x and the vertical direction in the horizontal direction in accordance with equation (20) y To a two-dimensional array of

  In this conversion process, an interpolation process such as a bilinear method or a bicubic method is used in combination. The display unit 34 displays a horizontal / vertical image based on the two-dimensional array output from the horizontal / vertical image generation unit 33. Further, the target detection result in the target detection means 26 may be displayed together. It should be noted that modifications such as switching the received power before clutter suppression and the power after clutter suppression to display are easy.

  According to the third embodiment, the clutter suppression signal can be displayed so that the horizontal axis and the vertical axis of the image are in the horizontal and vertical directions, respectively, and the visibility of the operator can be improved.

It is explanatory drawing of the observation method and basic principle of the radar apparatus in Embodiment 1 of this invention. It is the figure which showed the relationship between the arrival angle difference (DELTA) (theta) and the height h when angle (theta) is made into the parameter in Embodiment 1 of this invention. It is explanatory drawing which showed the relationship between the antenna pattern in Embodiment 1 of this invention, range resolution, and the clutter irradiation area. It is a block diagram of the radar apparatus in Embodiment 1 of this invention. It is a block diagram of the radar apparatus in Embodiment 2 of this invention. It is a block diagram of the radar apparatus in Embodiment 3 of this invention.

Explanation of symbols

  2 radar apparatus, 14 transmitter, 15 transmission / reception switch, 16 transmission / reception antenna, 17 control apparatus, 18 receiver, 19 range compression means, 20 memory (storage unit), 21 inertial navigation apparatus, 22 radar height estimation means, 23 clutter Irradiation pattern calculation means, 24 clutter scattering cross section estimation means, 25 clutter suppression means, 26 target detection means, 27 polarization switch, 28 first polarization transmission / reception antenna, 29 second polarization transmission / reception antenna, 30 multiple polarization clutter Scattering cross section estimation means (clutter scattering cross section estimation means), 31 Multiple polarization clutter suppression means (clutter suppression means), 32 Multiple polarization target detection means (target detection means), 33 Horizontal vertical image generation means, 34 Display means .

Claims (5)

A radar device that transmits a broadband pulse signal via a transmission / reception antenna, receives a reflected wave as a reception signal, and detects a target based on the reception signal,
Radar height estimation means for estimating the radar height relative to the sea surface or the ground surface based on the input of position information;
A storage unit for storing the directivity angle of the transmitting / receiving antenna and the received signal in association with each other;
A control device for controlling the directivity angle of the antenna pattern of the transmission / reception antenna in the elevation direction;
Range compression means for performing pulse compression processing on the received signal received via the transmission / reception antenna, and storing the received signal after pulse compression processing in the storage unit in association with information on the directivity angle received from the control device; ,
Based on the estimated radar altitude, the information on the directivity angle from the control device, and the antenna pattern of the transmitting / receiving antenna measured in advance, the range of the clutter is estimated from the radar altitude, and the estimated range A clutter irradiation pattern calculating means for calculating a clutter irradiation pattern in
Pulse compression processing corresponding to each directivity angle stored in the storage unit, with the clutter irradiation pattern calculated by the clutter irradiation pattern calculation means for each directivity angle when the beam is scanned in the elevation direction Clutter scattering cross section estimation means for estimating the clutter scattering cross section per unit area by performing a least square fitting to the received signal after,
Clutter suppression means for calculating a clutter suppression signal that suppresses clutter power for each received signal after pulse compression processing accumulated in the storage unit, using the estimated clutter scattering cross section;
A radar apparatus comprising: target detection means for detecting a target from the calculated clutter suppression signal. The radar apparatus according to claim 1, wherein
The radar apparatus according to claim 1, wherein the transmitting / receiving antenna is a circularly polarized antenna. The radar apparatus according to claim 1 or 2,
The transmission / reception antennas are a first polarization transmission / reception antenna and a second polarization transmission / reception antenna having orthogonal polarization characteristics,
A polarization switch for switching between the first polarization transmitting / receiving antenna and the second polarization transmitting / receiving antenna;
The control device controls the directivity angles of the first polarization transmission / reception antenna and the second polarization transmission / reception antenna in the elevation direction,
The range compression means receives the reception of the respective polarizations transmitted from the first polarization transmission / reception antenna and the second polarization transmission / reception antenna via the first polarization transmission / reception antenna and the polarization switch. The signal is subjected to pulse compression processing, and the received signal after the pulse compression processing is stored in the storage unit in association with the directivity angle information of the first polarization transmission / reception antenna received from the control device, and the first polarization transmission / reception is performed. For each polarization transmitted from the antenna and the second polarization transmitting / receiving antenna, the received signal received via the second polarization transmitting / receiving antenna and the polarization switching unit is subjected to pulse compression processing, and after pulse compression processing The received signal is stored in the storage unit in association with the information on the directivity angle of the second polarization transmitting / receiving antenna received from the control device,
The clutter scattering cross-sectional area estimation means corresponds to the calculated clutter irradiation pattern, the directivity angle of the first polarization transmission / reception antenna and the directivity angle of the second polarization transmission / reception antenna accumulated in the storage unit, respectively. From the received signal after pulse compression, the clutter scattering cross section in each received signal is estimated, and the polarization characteristics are further estimated,
The clutter suppression means calculates a clutter suppression signal in which clutter power is suppressed for each received signal stored in the storage unit, using the estimated clutter scattering cross section and the polarization characteristics. A radar device characterized by the above. The radar apparatus according to any one of claims 1 to 3,
The radar altitude estimation means uses an input of position information as an initial value of the radar altitude, and estimates the radar altitude based on each received signal corresponding to each directivity angle accumulated in the storage unit. Radar device. The radar apparatus according to any one of claims 1 to 4,
The clutter suppression signal calculated by the clutter suppression means is calculated as a two-dimensional array of the directivity angle of the received signal and the distance from the transmission / reception antenna to the target, and further, based on the two-dimensional array, a horizontal distance and Horizontal / vertical image generation means for converting to a two-dimensional array of vertical distances;
A radar apparatus, further comprising: a display unit that displays a two-dimensional array of the horizontal distance and the vertical distance converted by the horizontal and vertical image generating unit.

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