A shipboard ground wave radar platform course optimization adjustment method under the condition of constant platform speed

Abstract

The present application relates to a kind of shipborne ground wave radar platform course optimization adjustment method under the condition of platform speed, the method comprises: the track of target and platform is predicted, the sea clutter blind area range under RD coordinate system and the effective detection area of radar under latitude and longitude coordinate system are estimated;The position state of target under two coordinate systems is classified, and whether the platform course needs corresponding adjustment is judged;Optimization objective function and constraint condition are constructed;Global solution is carried out to optimization problem under the condition of limited tracking time by using genetic algorithm, and the platform course adjustment process is fitted using different ways;Local solution is carried out to optimization problem under the condition of unlimited tracking time by using gradient descent method, and optimal heading is found every time, and the platform course is dynamically adjusted continuously.The present application makes full use of the characteristics of platform maneuvering flexibility, actively changes the doppler shift of target by course adjustment, and effectively improves the target detection performance of platform under the condition of movement.

Description

Technical Field

[0001] This invention relates to the field of shipborne ground wave radar target detection, and in particular to a method for optimizing the heading of a shipborne ground wave radar platform under the condition of constant platform speed. Background Technology

[0002] High-frequency ground-wave radar utilizes the characteristics of vertically polarized electromagnetic waves in the 3–30 MHz frequency band that diffract and propagate along the sea surface, enabling large-scale, over-the-horizon continuous detection of ship targets at sea. Compared to shore-based ground-wave radar with fixed sites and limited detection areas, shipborne ground-wave radar can leverage the mobility and flexibility of shipborne platforms to expand its detection area and improve the application range of high-frequency ground-wave radar. However, when the shipborne platform is in motion, it causes broadening of the first-order sea surface echo spectrum, resulting in a Doppler frequency shift of the target. The target signal falls into the sea clutter blind zone and is submerged, affecting target detection performance. Therefore, it is necessary to explore methods and approaches to avoid and reduce the impact of sea clutter broadening on target detection.

[0003] Currently, traditional methods for avoiding and reducing the impact of sea clutter broadening on target detection mainly fall into two categories: sea clutter suppression and motion compensation. Sea clutter suppression methods, due to the non-stationary characteristics of sea clutter caused by the motion of the shipborne platform, often result in false alarms and missed detections of weak targets due to residual clutter, making it difficult to fundamentally eliminate the impact of sea clutter on target detection. Compensation for platform motion, however, is limited by the size of the shipborne platform, resulting in a large beamwidth for ground wave radar, which simultaneously observes the sea surface in multiple directions. Therefore, the compensation effect on first-order sea clutter broadening caused by the platform's forward motion is limited. Thus, traditional methods cannot fundamentally solve the problem of sea clutter broadening affecting target detection. Existing research shows that reducing the shipborne platform's speed can effectively reduce the sea clutter blind zone, thereby effectively reducing the impact of the sea clutter blind zone on target signals and improving the target detection performance of shipborne HFSWRs. However, this method is not suitable for scenarios where the platform speed is constant and the sea clutter blind zone broadening cannot be reduced.

[0004] Therefore, in response to the situation where the blind zone of sea clutter cannot be reduced, this invention combines the advantages of shipborne ground wave radar and utilizes the characteristic that adjusting the platform's heading can also adjust the positional relationship between sea clutter and the target. It proposes a method for optimizing the heading of a shipborne ground wave radar platform under the condition of constant platform speed, thereby improving the performance of continuous target detection. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] The purpose of this invention is to provide a method for optimizing and adjusting the platform's heading to separate the target from the sea clutter when the sea clutter blind zone cannot be reduced, thereby enabling continuous tracking and detection of the target.

[0007] (II) Technical Solution

[0008] This invention includes the following steps:

[0009] Step 1: Track prediction and exploration area estimation.

[0010] The trajectory of the target and the shipborne platform is predicted, and the blind zone of sea clutter and the effective detection area of ​​the radar are estimated respectively. This includes: predicting the trajectory of the target and the shipborne platform in the future time period based on the initial position and motion state information of the target and the shipborne platform, using a uniform motion model; and estimating the blind zone of sea clutter caused by the platform motion in the RD coordinate system and the effective detection area of ​​the radar in the latitude and longitude coordinate system, using the initial position and motion state information of the shipborne platform.

[0011] Step 2: Target position status classification and platform heading adjustment judgment.

[0012] The position of the target of interest in the RD coordinate system and latitude and longitude coordinate system at each time point is classified to determine whether it is in the sea clutter blind zone and within the effective detection range of the radar during the detection period. Based on this, the platform's course needs to be adjusted. This includes: classifying the position of the target of interest in the RD coordinate system and latitude and longitude coordinate system at each time point based on the trajectory prediction results of the target and the shipborne platform, combined with the estimation of the sea clutter blind zone and the effective detection area of ​​the radar; and based on the above classification results, determining whether the platform's course needs to be adjusted accordingly.

[0013] Step 3: Optimize the objective function and construct constraints.

[0014] To optimize the platform's heading and achieve optimal detection performance for the target in both the latitude / longitude coordinate system and the RD coordinate system, this invention models the platform's heading adjustment process as an optimization problem and constructs optimization objective functions and constraints, including: constructing the optimization objective function using the target's detection performance indicators in the RD coordinate system; and constructing constraints using the target's detection performance indicators in the latitude / longitude coordinate system.

[0015] Step 4: Platform heading optimization and adjustment strategy.

[0016] For both finite and infinite tracking durations, the platform's heading is optimized and adjusted accordingly. Specifically, for finite tracking duration, a genetic algorithm is used to globally solve the optimization problem, obtaining the optimal heading that maximizes the effective detection time of the target outside the sea clutter blind zone throughout the entire tracking period. Combined with the ship's actual heading maneuverability, two smooth adjustment methods, uniform straight line and S-curve, are used to achieve a gradual transition in heading. For infinite tracking duration, the gradient descent method is used to locally solve the optimization problem, finding the optimal heading time-by-time, and continuously dynamically adjusting the platform's heading as the tracking duration increases.

[0017] (III) Beneficial Effects

[0018] Compared with the prior art, the innovation of this invention is reflected in the following aspects:

[0019] This invention abandons the traditional approach of suppressing sea clutter or compensating for platform motion in target detection methods, instead viewing platform motion as a positive factor in improving target detection performance. When the sea clutter blind zone cannot be reduced, the invention fully utilizes the platform's maneuverability to actively alter the target's Doppler frequency shift through heading adjustments, thereby enhancing its detectability. For both finite-duration and infinite-duration tracking scenarios, genetic algorithms and gradient descent methods are employed to solve for the optimal heading, effectively improving the platform's target detection performance while in motion. Attached Figure Description

[0020] Figure 1 The flowchart illustrates the method for optimizing the heading of a shipborne ground wave radar platform under constant platform speed, as provided by this invention.

[0021] Figure 2 The measured results in the RD coordinate system at frame 61 before the platform heading adjustment provided by this invention.

[0022] Figure 3 The process of adjusting the platform heading in the RD coordinate system provided by this invention.

[0023] Figure 4 The present invention describes the changes in the heading of the shipborne platform during the adjustment process.

[0024] Figure 5 The measured results in the RD coordinate system at frame 111 before the platform heading adjustment provided by this invention. Detailed Implementation

[0025] The method of the present invention will be further described below with reference to the accompanying drawings.

[0026] A method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed, such as... Figure 1As shown, it includes the following steps:

[0027] Step 1: Track prediction and exploration area estimation.

[0028] Based on the initial position and motion state information of the target of interest and the shipborne platform, the trajectories of the target and the shipborne platform in the future are predicted using a uniform motion model.

[0029] Specifically, obtain the target's initial position information. and motion status information , and the initial position information of the shipborne platform. and motion status information , Using a uniform motion model, the flight paths of the target and platform over a future period are predicted, resulting in two flight paths composed of the latitude and longitude information of the target and platform at each moment, denoted as follows: and The latitude and longitude position information at each moment can be calculated from the latitude and longitude position information of the previous moment and the motion state, as shown in the following formula:

[0030]

[0031]

[0032] In the formula, Let k represent the target and the platform, respectively, and k represent the current time. This represents the time difference between two consecutive moments, where R is the Earth's radius. In this invention, R = 6371 km. Indicates the target or platform heading in radians, and .

[0033] Using the acquired initial position and motion state information of the shipborne platform, the blind zone range of sea clutter caused by the platform motion in the RD coordinate system and the effective detection area of ​​the radar in the latitude and longitude coordinate system are estimated respectively.

[0034] Specifically, utilizing the acquired initial position information of the shipborne platform and motion status information , Estimate the extent of the sea clutter blind zone:

[0035]

[0036] In the formula, It is a first-order Bragg velocity, and .

[0037] Next, the effective detection angle range of the radar is estimated using the following formula:

[0038]

[0039] In the formula, This represents half of the radar detection sector angle, which is taken in this invention. .

[0040] Step 2: Target position status classification and heading adjustment judgment.

[0041] Based on the trajectory prediction results of the target and the shipborne platform, and combined with the estimation of the sea clutter blind zone and the effective radar detection area, the position status of the target of interest in the RD coordinate system and the latitude and longitude coordinate system at each moment is classified.

[0042] Specifically, the position of the target in the RD coordinate system can be represented by the target's Doppler velocity, calculated as follows:

[0043]

[0044] In the formula, It is the Doppler velocity of the moving target. It is the angle between the direction of motion of the shipborne platform and the direction of the target echo. It is the angle between the direction of the target's movement and the direction of the target's echo.

[0045] Based on the extent of the sea clutter blind zone, the position state of the target in the RD coordinate system at each time step in the target track is classified, and the classification criteria are as follows:

[0046]

[0047] The position of a target in a latitude and longitude coordinate system can be represented by the target's azimuth angle, and the calculation formula is as follows:

[0048]

[0049] In the formula, It is the azimuth angle of the target relative to the platform.

[0050] Based on the effective detection angle range of the reference radar, the position of the target in the latitude and longitude coordinate system at each moment of the target trajectory is classified, and the classification criteria are as follows:

[0051]

[0052] This yields the classification results of the positional status of the target at each time point in the RD coordinate system and the latitude and longitude coordinate system.

[0053] Based on the above classification results, it is determined whether the platform's heading needs to be adjusted accordingly.

[0054] Specifically, if the target's position status at any given time meets the following conditions, the platform's heading needs to be adjusted; otherwise, the platform's heading does not need to be adjusted. The conditions are:

[0055]

[0056] Step 3: Optimize the objective function and construct constraints.

[0057] To obtain the optimal detection effect of the target in the RD coordinate system, an optimization objective function is constructed using the target detection performance index in the RD coordinate system.

[0058] Specifically, this invention defines the distance (in meters per second) between the target's Doppler velocity and the velocity at the boundary of its nearest sea clutter blind zone at each moment as the detection performance index in the RD coordinate system. ,and The larger the value of , the better the target detection effect in the RD coordinate system. Therefore, the optimization objective function is constructed as follows:

[0059]

[0060] right The specific modeling is performed, and its computational model consists of the Doppler velocity of the target and the boundary velocity of the sea clutter blind zone closest to the target:

[0061]

[0062] in, This represents the Doppler velocity of the target under any platform's heading.

[0063] To achieve optimal detection results for the target in the latitude and longitude coordinate system, constraints are constructed using the target's detection performance indicators in the latitude and longitude coordinate system.

[0064] Specifically, the azimuth angle of the target relative to the radar's main axis is defined as a detection performance index in the latitude and longitude coordinate system. and constrain it in Within the range, that is .

[0065] By organizing the above optimization functions and constraints, and considering the limitations of the platform's heading itself, the optimization problem of the platform heading adjustment process can be modeled as follows:

[0066] Optimization goal:

[0067]

[0068] Constraints:

[0069]

[0070]

[0071] Step 4: Platform heading optimization and adjustment strategy.

[0072] For situations with limited tracking time, a genetic algorithm is used to solve the optimization problem globally, obtaining the optimal course that maximizes the effective detection time of the target outside the sea clutter blind zone throughout the entire tracking period. Combined with the ship's actual course maneuvering capability, two smooth adjustment methods, uniform straight line and S-curve, are used to achieve a slow course transition.

[0073] Specifically, since the target's trajectory can be predicted throughout the entire tracking period under limited tracking time, a genetic algorithm can be used to solve the optimization problem and calculate the optimal platform heading that achieves the best detection effect for the target in the RD coordinate system. Subsequently, the platform's heading will be adjusted to this optimal value. The direction of the platform's heading adjustment can be determined by the following formula.

[0074]

[0075] In the formula, This indicates the platform's initial heading.

[0076] In addition, to avoid platform instability issues caused by drastic changes in course during the adjustment process, the platform's course adjustment process is fitted with an S-curve adjustment method if the target is initially located within sea clutter, so that the target can be quickly moved out of the sea clutter. If the target is initially located outside the sea clutter, a uniform linear adjustment method is used to fit the platform's course adjustment process, so as to avoid drastic changes in the target track during the adjustment process, which could lead to a break in track correlation.

[0077] For cases with infinite tracking time, the gradient descent method is used to locally solve the optimization problem, find the optimal heading time by time, and continuously adjust the platform heading dynamically as the tracking time increases.

[0078] Specifically, since it is impossible to calculate the optimal heading for the entire tracking period when the tracking time is infinite, the gradient descent method is used to locally solve the optimization problem, finding the optimal heading at each moment, and dynamically adjusting the platform heading as the tracking time increases. To ensure that the target's track projection in the RD coordinate system always maintains a monotonically decreasing trend away from sea clutter, further constraints are added to the optimization problem, and the optimization problem model is modified as follows:

[0079] Optimization goal:

[0080]

[0081] Constraints:

[0082]

[0083]

[0084]

[0085] In the formula, This represents the Doppler velocity of the target at time t. This represents the platform's heading at time t. Furthermore, to prevent excessive changes in heading at any given time from causing stability issues, the maximum heading adjustment at any given time is limited to no more than [a certain value]. (This invention incorporates actual navigation experience) =2°), the actual platform heading adjustment effect is that at each moment the platform heading is adjusted to approach the optimal heading value at that moment until the tracking ends, and finally the continuous detection and tracking of the target is achieved in the case of unlimited tracking time.

[0086] Example

[0087] The effects of the present invention will be further illustrated by the following data:

[0088] The proposed method was validated using experimental data from shipborne ground-wave radar obtained in the waters surrounding Qingdao in December 2021. Specifically, the position, velocity, and heading information of the shipborne platform at the corresponding time were obtained from the attitude data synchronously acquired from the shipborne ground-wave radar signal using an inertial navigation system. To evaluate the performance of the method, synchronously acquired Automatic Identification System (AIS) data was used as a reference for real vessel target data.

[0089] The vessel with MMSI number 636092840 was selected as the target of interest and continuously detected and tracked. Figure 2 The radar detection situation in the RD coordinate system at frame 61 is presented. At this time, the shipborne platform's speed is approximately 1.2 knots, and its heading is approximately 43.49°. It can be seen that the shipborne platform's motion causes sea clutter to broaden. Combined with the synchronized AIS data, the target's position in the RD spectrum falls within the sea clutter blind zone, severely affecting target detection performance. The target's track needs to be moved out of the blind zone as quickly as possible. The proposed method is used to adjust the shipborne platform's heading using an S-curve. The adjustment process is as follows: Figure 3 As shown. For ease of observation, Figure 3 The adjustment process was semi-simulated. From... Figure 3 It can be seen that by adjusting the platform's heading, the target track was successfully moved outside the blind zone of sea clutter and was no longer affected by sea clutter during subsequent tracking, maintaining an easily detectable state in the RD coordinate system. Figure 4 The changes in the shipborne platform's heading during the adjustment process are presented. Figure 5 The radar detection results in the RD coordinate system at frame 111 are given. At this time, the speed of the shipborne platform is still about 1.2 knots, and the heading of the shipborne platform is adjusted to 22.15°. It can be seen that the position of the target of interest in the RD coordinate system has been completely away from the sea clutter.

[0090] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed, characterized in that, Includes the following steps: (1) Track prediction and detection area estimation: predict the tracks of the target and the shipborne platform, and estimate the sea clutter blind zone and the effective detection area of ​​the radar, including: based on the initial position and motion state information of the target and the shipborne platform, using a uniform motion model to predict the tracks of the target and the shipborne platform in the future; using the initial position and motion state information of the shipborne platform, estimating the blind zone of the sea clutter caused by the platform motion in the RD coordinate system and the effective detection area of ​​the radar in the latitude and longitude coordinate system. (2) Target position status classification and platform heading adjustment judgment: The position status of the target of interest in the RD coordinate system and latitude and longitude coordinate system at each time is classified to determine whether it is in the sea clutter blind zone and whether it is within the effective detection range of the radar during the detection period. Based on this, the platform heading needs to be adjusted. This includes: classifying the position status of the target of interest in the RD coordinate system and latitude and longitude coordinate system at each time based on the trajectory prediction results of the target and the shipborne platform, combined with the estimation of the sea clutter blind zone and the effective detection area of ​​the radar; and judging whether the platform heading needs to be adjusted accordingly based on the above classification results. (3) Optimize the objective function and constraint conditions. In order to optimize the platform heading and achieve the best detection effect for the target in both the latitude and longitude coordinate system and the RD coordinate system, the platform heading adjustment process is modeled as an optimization problem, and optimization objective functions and constraints are constructed respectively, including: constructing the optimization objective function using the target detection performance index in the RD coordinate system; and constructing the constraint conditions using the target detection performance index in the latitude and longitude coordinate system. (4) Platform heading optimization and adjustment strategy: For the two cases of finite and infinite tracking time, the platform heading is optimized and adjusted respectively. For the case of finite tracking time, a genetic algorithm is used to solve the optimization problem globally to obtain the optimal heading that maximizes the effective detection time of the target outside the sea clutter blind zone during the entire tracking period. Combined with the actual heading maneuvering capability of the ship, two smooth adjustment methods, uniform straight line and S-curve, are used to achieve a slow transition of the heading. For the case of infinite tracking time, the gradient descent method is used to solve the optimization problem locally, find the optimal heading at each time step, and continuously adjust the platform heading dynamically as the tracking time increases.

2. The method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed as described in claim 1, characterized in that, The trajectory prediction and detection area estimation described in step (1) are as follows: the trajectory of the target and platform over a future period is predicted using a uniform motion model, and the formula is: , In the formula, Let k represent the target and the platform, respectively, and k represent the current time. This represents the time difference between two consecutive moments, where R is the Earth's radius and R = 6371 km. Indicates the target or platform heading in radians, and ; In the estimation method of the sea clutter blind zone range in the RD coordinate system, the blind zone range of sea clutter caused by platform motion can be estimated as follows: In the formula, It is a first-order Bragg velocity, and In the estimation method of the effective detection area of ​​radar in the latitude and longitude coordinate system, the effective detection angle range of radar can be estimated as follows: In the formula, This represents half of the radar detection sector angle, and .

3. The method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed as described in claim 1, characterized in that, The target position status classification and platform heading adjustment judgment mentioned in step (2): The target's position status in the RD coordinate system can be represented by the target's Doppler velocity, and the calculation formula is: In the formula, It is the Doppler velocity of the moving target. It is the angle between the direction of motion of the shipborne platform and the direction of the target echo. It is the angle between the target's direction of motion and the target's echo direction. The position of the target in the RD coordinate system at each moment in the target's trajectory is classified with reference to the width of the sea clutter blind zone. The classification criteria are as follows: The position of a target in a latitude and longitude coordinate system can be represented by the target's azimuth angle, calculated using the following formula: In the formula, It is the target's azimuth angle relative to the platform. Referring to the effective detection angle range of the radar, the target's position in the latitude and longitude coordinate system at each moment of its trajectory is classified. The classification criteria are as follows: The method for determining whether the platform's heading needs adjustment is based on the following criteria: If this condition is met, the platform's heading needs to be adjusted; otherwise, the platform's heading does not need to be adjusted.

4. The method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed as described in claim 1, characterized in that, The optimization objective function and constraint conditions described in step (3) are constructed using the target's detection performance indicators in the RD coordinate system. The objective function for optimization is constructed as follows: ,in It can be modeled as: In the formula, This represents the Doppler velocity of the target under any platform's heading; it utilizes the target's detection performance indicators in a latitude and longitude coordinate system. The constraints are as follows: By organizing the above optimization functions and constraints, and considering the limitations of the platform's heading itself, the optimization problem of the platform heading adjustment process is modeled as follows: Optimization goal: ； Constraints: ； 。 5. The method for optimizing the heading of a shipborne ground-wave radar platform under constant platform speed as described in claim 1, characterized in that, The platform heading optimization and adjustment strategy described in step (4) involves using a genetic algorithm to globally solve the optimization problem under the condition of finite tracking time, and calculating the optimal heading of the platform. The platform's heading is adjusted to this optimal value, with the following adjustment direction: In the formula, This represents the platform's initial heading. To avoid instability issues caused by drastic heading changes during the adjustment process, different methods are used to fit the platform's heading adjustment process to the optimal heading, taking into account the ship's actual heading maneuverability: The gradient descent method is used to locally solve the optimization problem under the case of infinite tracking time, finding the optimal heading time by time, and continuously adjusting the platform heading dynamically as the tracking time increases. In order to ensure that the target's trajectory projection in the RD coordinate system always maintains a monotonically decreasing trend away from sea clutter, further constraints are added to the optimization problem, and the optimization problem model is modified as follows: Optimization goal: ； Constraints: ； ； ； In the formula, This represents the Doppler velocity of the target at time t. This represents the platform's heading at time t. Furthermore, to prevent excessive changes in heading at any given time from causing stability issues, the maximum heading adjustment at any given time is limited to no more than [a certain value]. Based on actual navigation experience, =2°, the actual platform heading adjustment effect is that the platform heading is adjusted to approach the optimal heading value at each moment until the tracking ends, and finally the continuous detection and tracking of the target is achieved in the case of unlimited tracking time.

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