Ship-based GNSS reflected signal marine oil spill monitoring method and system

Abstract

The invention provides a ship-based GNSS reflected signal marine oil spill monitoring method, and belongs to the technical field of marine environment monitoring. The method comprises the following steps: receiving a direct signal and a reflection signal of a satellite system; obtaining a time delay-Doppler graph of a sea surface scattering area based on a direct signal and a reflection signal of a satellite system; extracting time delay distribution characteristics and Doppler distribution characteristics of the time delay-Doppler graph of the sea surface scattering area; oil spill identification characteristics are obtained based on the time delay distribution characteristics and the Doppler distribution characteristics; judging the relationship between the oil spill identification feature and an oil spill threshold value to obtain an oil spill detection result; and obtaining a comprehensive oil spill detection result based on the oil spill detection result corresponding to the satellite system. The ship-based platform is used for sea surface oil spill detection, and then sea surface oil spill detection which is flexible in detection range and accurate in oil spill detection result is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of marine environment monitoring, and in particular to a ship-based GNSS reflection signal marine oil spill monitoring method and system. Background Art

[0002] Due to the substantial increase in offshore oil development and shipping activities, the risk of ship collisions and oil and gas leaks has also increased significantly. Marine oil spills have had a lasting negative impact on the ecological environment and marine resources. Among traditional oil spill monitoring methods, optical remote sensing is difficult to achieve all-day and all-weather monitoring due to the influence of natural conditions such as fog and rainstorms. Synthetic aperture radar in microwave remote sensing also has problems such as high equipment cost, complex data processing and timeliness.

[0003] Therefore, the existing technology uses satellite reflection signals in the GNSS system to detect the marine environment. GNSS-R technology has the characteristics of low cost, all-weather, and global coverage. It can use existing satellites as signal sources, avoiding the dependence of traditional active remote sensing on transmitting equipment. The current GNSS-R methods for detecting marine oil spills mainly include: satellite-borne, airborne, and shore-based platforms. However, the above methods cannot meet the requirements of high spatial resolution and high accuracy at the same time. In addition, the satellite-borne platform is limited by spatial resolution and it is difficult to meet the requirements of local details; the airborne platform has high operating costs and a limited monitoring cycle; the shore-based platform can accurately monitor specific areas, but is limited by the monitoring range and cannot cover large areas of sea.

[0004] Therefore, a sea surface oil spill detection method with flexible detection range and high accuracy is needed. Summary of the invention

[0005] In view of this, the present invention provides a ship-based GNSS reflection signal marine oil spill monitoring method and system, which converts the GNSS reflection signal into a Doppler map, and uses the time delay-Doppler map characteristics to detect oil spills, thereby solving the problems of low temporal and spatial resolution, insufficient flexibility and low accuracy in existing marine oil spill monitoring technologies.

[0006] To this end, the present invention provides the following technical solutions:

[0007] A ship-based GNSS reflection signal marine oil spill monitoring method, comprising:

[0008] Receive direct and reflected signals from satellite systems;

[0009] Obtain the time delay-Doppler map of the sea surface scattering area based on the direct signal and reflected signal of the satellite system;

[0010] Extract the delay distribution characteristics and Doppler distribution characteristics of the delay-Doppler map in the sea surface scattering area;

[0011] Obtain oil spill identification features based on time delay distribution characteristics and Doppler distribution characteristics;

[0012] Determine the relationship between the oil spill identification features and the oil spill threshold to obtain the oil spill detection results;

[0013] Based on the oil spill detection results corresponding to the satellite system, the comprehensive oil spill detection results are obtained.

[0014] Furthermore, the oil spill detection result corresponding to the satellite system is used to obtain a comprehensive oil spill detection result, including:

[0015] When a direct signal and a reflected signal of a satellite system are received, the oil spill detection result corresponding to the satellite system is used as the comprehensive oil spill detection result;

[0016] When direct signals and reflected signals from multiple satellite systems are received, the oil spill detection results corresponding to the multiple satellite systems are fused to obtain a comprehensive oil spill detection result.

[0017] Furthermore, the fusing of the oil spill detection results corresponding to the plurality of satellite systems to obtain a comprehensive oil spill detection result includes:

[0018] By assigning weights to each satellite system and fusing the oil spill detection results corresponding to multiple satellite systems, comprehensive oil spill detection results are obtained.

[0019] Furthermore, the determining the relationship between the oil spill identification feature and the oil spill threshold to obtain the oil spill detection result includes:

[0020] When the oil spill identification feature is greater than the preset oil spill threshold, it is determined that an oil spill is detected;

[0021] When the oil spill identification feature is less than or equal to the preset oil spill threshold, it is determined that no oil spill is detected.

[0022] Furthermore, the delay-Doppler diagram of the sea surface scattering area is obtained based on the direct signal and the reflected signal of the satellite system:

[0023]

[0024] Where: R t (r) and R r (r) are the distances from the satellite and the delayed receiver to the scattering point respectively; G(r) represents the effective gain of the antenna at the scattering point; Λ represents the code autocorrelation function; T i represents the coherent integration time; σ 0 (r) represents the scattering coefficient; δ τ (r) is the difference between the time delay of the reflected signal component at each point on the reflecting surface and the corresponding value; and δ f(r) is the difference between the Doppler value of the reflected signal component at each point on the reflecting surface and the corresponding value; the sea surface scattering area is divided by the delay and Doppler lines, forming a delay-Doppler diagram of the sea surface scattering area.

[0025] Further, the extracting of the delay distribution characteristics and Doppler distribution characteristics of the sea surface scattering region delay-Doppler map includes:

[0026] Normalize the delay-Doppler diagram of the sea surface scattering area:

[0027]

[0028] Where, p(τ,f) represents the original delay-Doppler value; p min and p max Indicates the minimum and maximum power values ​​in the current delay-Doppler graph.

[0029] Furthermore, the extracting of the delay distribution characteristics and Doppler distribution characteristics of the sea surface scattering region delay-Doppler map further includes:

[0030]

[0031] in, is the delay distribution characteristic; is the Doppler distribution characteristic; (τ peak ,f peak ) is the time delay and Doppler coordinates at the peak power; τ mean and f mean are the weighted means in the delay direction and Doppler direction respectively.

[0032] Furthermore, the oil spill identification feature is obtained based on the time delay distribution characteristic and the Doppler distribution characteristic, including:

[0033] The average values ​​of time delay distribution characteristics and Doppler distribution characteristics are used as oil spill identification features.

[0034] A ship-based GNSS reflection signal marine oil spill monitoring system, comprising:

[0035] GNS signal receiving module, signal processing module, oil spill identification feature extraction module, oil spill area judgment module;

[0036] The GNSS signal receiving module receives direct signals and reflected signals from the satellite system.

[0037] The signal processing module obtains a time delay-Doppler map of the sea surface scattering area based on the direct signal and the reflected signal of the satellite system.

[0038] The oil spill identification feature extraction module extracts the time delay distribution characteristics and Doppler distribution characteristics of the sea surface scattering area delay-Doppler map, and obtains the oil spill identification features based on the time delay distribution characteristics and Doppler distribution characteristics.

[0039] The oil spill area determination module determines the relationship between the oil spill identification feature and the oil spill threshold, obtains the oil spill detection result, and obtains the comprehensive oil spill detection result based on the oil spill detection result corresponding to the satellite system.

[0040] Advantages and positive effects of the present invention:

[0041] The present invention utilizes the abundant signal sources provided by the global satellite system, and the system design is modularized to improve the accuracy of oil spill identification, and can cope with oil spill monitoring tasks of different scales. The oil spill identification features based on the delay-Doppler map are combined with multi-system weights, and the results of multiple systems are integrated to gradually improve the accuracy of oil spill monitoring. The use of ship-borne platforms for sea surface oil spill detection enhances the flexibility of the system, can monitor the oil spill information of the navigation environment in real time, and achieve high-resolution monitoring. It is suitable for deployment in complex marine environments and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0043] Figure 1 This is a flow chart of the method for monitoring marine oil spills using ship-based GNSS reflection signals in this embodiment;

[0044] Figure 2 This is a structural diagram of the ship-based GNSS reflection signal marine oil spill monitoring system in this embodiment. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0047] The present invention provides a marine oil spill monitoring method based on ship-based GNSS reflection signals. As ships are conventional carriers of marine activities, they have good flexibility and maneuverability, and monitoring equipment can be flexibly deployed according to demand to achieve dynamic monitoring of key sea areas. Therefore, a monitoring system for a ship-based platform is proposed to achieve ship self-monitoring, and as an important node of the marine oil spill monitoring network, a regional or even global marine oil spill monitoring system is constructed. Time delay distribution characteristics and Doppler distribution characteristics are proposed as the basis for oil spill judgment, taking into account the requirements of high spatial resolution and high precision.

[0048] A method for monitoring marine oil spills based on ship-based GNSS reflection signals comprises the following steps:

[0049] S1. Receive GNSS direct signals and reflected signals. An upward-looking antenna and a downward-looking antenna for receiving reflected signals are fixed on the ship-based platform at a certain height above the water surface. The dual antennas are connected to a delay receiver. The upward-looking antenna points to the zenith, and the received direct signal can be used for positioning. The downward-looking antenna faces the sea surface, where the downward-looking antenna faces a preset angle, which affects the position of the reflection area.

[0050] S2. Process multi-system GNSS direct signals and reflected signals. During navigation, the reflected signals of multiple navigation systems are collected simultaneously, including Beidou, GPS, and Galileo. The spatial domain is converted to the delay-Doppler domain to obtain the delay-Doppler map. The code phase and Doppler shift are determined in the time and frequency dimensions. Bandpass filters are used in signal filtering to filter out non-target frequency band signals and reduce interference and noise.

[0051] S3, extract the central peak and tail extension information of the delay-Doppler graph, analyze the changes in characteristic parameters, and extract the oil spill identification features of the delay-Doppler graph. The sea surface covered with oil spills has more significant GNSS reflected signal power. Therefore, the delay distribution characteristics and Doppler distribution characteristics of the delay-Doppler graph are extracted as oil spill identification features.

[0052] S4. According to the oil spill identification features of the time delay-Doppler map, the relationship between the oil spill identification features and the oil spill threshold is determined, and the oil spill detection results are obtained in combination with the time and space positions of the mirror reflection points; based on the oil spill detection results corresponding to the satellite system, the comprehensive oil spill detection results are obtained.

[0053] like Figure 2 As shown, the present application also provides a ship-based GNSS reflection signal marine oil spill monitoring system, including:

[0054] GNSS signal receiving module, signal processing module, oil spill identification feature extraction module, oil spill area judgment module;

[0055] GNSS signal receiving module, receives direct signals and reflected signals from the satellite system.

[0056] The signal processing module uses the GNSS direct signal and reflected signal to convert the spatial domain to the delay-Doppler domain to obtain the delay-Doppler map.

[0057] The oil spill identification feature extraction module calculates the differential delay-Doppler map and extracts the central power peak and tail information, and obtains the delay distribution characteristics and Doppler distribution characteristics of the delay-Doppler map as oil spill identification features.

[0058] The oil spill area judgment module judges the relationship between the oil spill identification features and the oil spill threshold, and obtains the oil spill detection results based on the spatiotemporal position of the mirror reflection point; based on the oil spill detection results corresponding to the satellite system, the comprehensive oil spill detection results are obtained.

[0059] The method of the present invention is further described with the following multi-satellite system embodiment:

[0060] S1. An upward-looking antenna and a downward-looking antenna for receiving reflected signals are fixed on the ship-based platform at a certain height above the water surface. Since the reflected signal from the sea surface is weak, the downward-looking antenna is a high-gain antenna and is installed at a height greater than 15 meters.

[0061] S2. During the navigation process, the reflected signals of multiple navigation system satellites are collected simultaneously, which are Beidou, GPS and Galileo in this embodiment; and the spatial domain is converted to the delay Doppler domain through the delay receiver, and displayed in different channels, including the satellite altitude angle, azimuth mirror reflection point longitude and latitude;

[0062] The delay resolution and Doppler resolution are set according to actual conditions; in this embodiment, the Doppler frequency is (-500 Hz, 500 Hz); the delay code chip is (-2, 2).

[0063] Based on the bistatic radar equation, the geometric optics method of Kirchhoff approximation is used to digitally process the GNSS reflected signal:

[0064]

[0065] Where: R t (r) and R r (r) are the distances from the satellite and the delayed receiver to the scattering point respectively; G(r) represents the effective gain of the antenna at the scattering point; Λ represents the code autocorrelation function; T i represents the coherent integration time; σ 0 (r) represents the scattering coefficient; δ τ (r) and δ f (r) are the delay and Doppler values ​​of the reflected signal components at each point on the reflection surface and the difference between the corresponding values. Specifically, the sea surface scattering area is divided by the delay and Doppler lines to achieve the conversion from the space domain to the delay Doppler domain.

[0066] S3. Based on the time-delay-Doppler diagram generated by multiple systems, the central peak and tail extension information are extracted to explore the relationship between this information and the oil spill area, and then the relevant characteristics of the oil spill are identified.

[0067] Normalized delay-Doppler plot to eliminate the effect of absolute power differences between the device and the environment:

[0068]

[0069] The time delay and Doppler coordinates at the peak power are:

[0070] (τ peak ,f peak ) = argmaxp norm (τ,f)

[0071] Where p(τ,f) represents the original delay-Doppler projection power value; p min and p max Indicates the minimum and maximum power values ​​in the current delay-Doppler diagram. It also records the delay and Doppler shift coordinates of the power peak.

[0072] The presence of oil film on the sea surface reduces the surface tension of water, and the oil film will suppress surface waves. The scattering characteristics are different from those of seawater, resulting in more concentrated reflected signals. The delay-Doppler graph of the clean seawater surface shows a more significant tail. The central peak of the delay-Doppler graph is used as the reference point for the extension of the tail.

[0073] The delay distribution characteristics and Doppler distribution characteristics are described as:

[0074]

[0075] Among them, τ mean and f mean They are the weighted means in the delay direction and Doppler direction respectively:

[0076]

[0077] The changing trends of the delay and Doppler distribution characteristics in the differential delay-Doppler diagram on the time series are also used as features for monitoring the spread of oil spills. The changing trends of the characteristics in each system are processed independently to ensure that the processing results of different systems do not interfere with each other.

[0078] S4. Determine whether there is oil spill on the sea surface by combining the delay-Doppler diagrams, delay distribution characteristics and Doppler distribution characteristics obtained by multiple systems with the position of the mirror reflection point.

[0079] Oil spills reduce the roughness of the sea surface, shorten the tail length in the delay and Doppler directions, and the power distribution will show a shrinking trend; based on experimental data and experience with sea surface conditions, the oil spill identification feature threshold is set;

[0080] In this embodiment, the average values ​​of the time delay distribution characteristic and the Doppler distribution characteristic are calculated as the oil spill identification feature; the oil spill threshold is 0.5; that is, when the oil spill identification feature is greater than 0.5, it is judged that the oil spill is detected; when the oil spill identification feature is less than or equal to 0.5, it is judged that the oil spill is not detected.

[0081] The oil spill identification characteristic threshold can be optimized according to different system response characteristics during multiple monitoring processes.

[0082] Since different systems have different responses to reflected signals, they show different sensitivities to the same oil spill identification feature; therefore, a weight value is defined for each system to emphasize its contribution to the judgment of the oil spill area. The judgment formula after weight allocation is:

[0083] score=∑w sys ·s sys

[0084] In the formula, w sys represents the system weight, s sys It indicates the judgment result of the system on the oil spill area, and the value is 1 or 0 (1 means oil spill is detected, and 0 means no oil spill is detected).

[0085] In this embodiment, the initial weight ratio of each system is 1:1:1; the weight ratio is optimized during multiple monitoring processes to obtain an accurate weight ratio. The contribution of each system to oil spill judgment can be dynamically adjusted by analyzing the accuracy of oil spill area detection by different systems during multiple monitoring processes.

[0086] More accurate classification models, such as support vector machines, random forests, or deep learning models, can be used to achieve precise oil spill monitoring based on the time delay distribution characteristics and Doppler distribution characteristics.

[0087] Through the method of the present invention, the GNSS direct signal and the reflected signal are received by the ship-based platform and converted into a delay-Doppler map. The delay distribution characteristics and the average value of the Doppler distribution characteristics are extracted based on the delay-Doppler map as oil spill identification features. The method has the advantages of flexible monitoring range and high spatial resolution, thereby realizing accurate identification of sea surface oil spills.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A ship-based GNSS reflection signal marine oil spill monitoring method, characterized in that: include: Receive direct and reflected signals from satellite systems; Obtain the time delay-Doppler map of the sea surface scattering area based on the direct signal and reflected signal of the satellite system; Extract the delay distribution characteristics and Doppler distribution characteristics of the delay-Doppler map in the sea surface scattering area; Obtain oil spill identification features based on time delay distribution characteristics and Doppler distribution characteristics; Determine the relationship between the oil spill identification features and the oil spill threshold to obtain the oil spill detection results; Based on the oil spill detection results corresponding to the satellite system, the comprehensive oil spill detection results are obtained.

2. According to claim 1, a ship-based GNSS reflection signal marine oil spill monitoring method is characterized in that: The oil spill detection result corresponding to the satellite system is used to obtain a comprehensive oil spill detection result, including: When a direct signal and a reflected signal of a satellite system are received, the oil spill detection result corresponding to the satellite system is used as the comprehensive oil spill detection result; When direct signals and reflected signals from multiple satellite systems are received, the oil spill detection results corresponding to the multiple satellite systems are fused to obtain a comprehensive oil spill detection result.

3. According to claim 2, a ship-based GNSS reflection signal marine oil spill monitoring method is characterized in that: The step of fusing the oil spill detection results corresponding to the plurality of satellite systems to obtain a comprehensive oil spill detection result includes: By assigning weights to each satellite system and fusing the oil spill detection results corresponding to multiple satellite systems, comprehensive oil spill detection results are obtained.

4. The method for monitoring marine oil spills using ship-based GNSS reflection signals according to claim 1, characterized in that: The determining the relationship between the oil spill identification feature and the oil spill threshold to obtain the oil spill detection result includes: When the oil spill identification feature is greater than the preset oil spill threshold, it is determined that an oil spill is detected; When the oil spill identification feature is less than or equal to the preset oil spill threshold, it is determined that no oil spill is detected.

5. The method for monitoring marine oil spills using ship-based GNSS reflection signals according to claim 1, characterized in that: The time delay-Doppler diagram of the sea surface scattering area is obtained based on the direct signal and the reflected signal of the satellite system: Where: R t (r) and R r (r) are the distances from the satellite and the delayed receiver to the scattering point respectively; G(r) represents the effective gain of the antenna at the scattering point; Λ represents the code autocorrelation function; T i represents the coherent integration time; σ0(r) represents the scattering coefficient; δ τ (r) is the difference between the time delay of the reflected signal component at each point on the reflecting surface and the corresponding value; and δ f (r) is the difference between the Doppler value of the reflected signal component at each point on the reflecting surface and the corresponding value; the sea surface scattering area is divided by the delay and Doppler lines, forming a delay-Doppler diagram of the sea surface scattering area.

6. A ship-based GNSS reflection signal marine oil spill monitoring method according to claim 5, characterized in that: The extracting of the delay distribution characteristics and Doppler distribution characteristics of the delay-Doppler map of the sea surface scattering region includes: Normalize the delay-Doppler diagram of the sea surface scattering area: Where, p(τ,f) represents the original delay-Doppler value; p min and p max Indicates the minimum and maximum power values ​​in the current delay-Doppler graph.

7. A ship-based GNSS reflection signal marine oil spill monitoring method according to claim 6, characterized in that: The extracting of the delay distribution characteristics and Doppler distribution characteristics of the sea surface scattering region delay-Doppler map also includes: in, is the delay distribution characteristic; is the Doppler distribution characteristic; (τ peak ,f peak ) is the time delay and Doppler coordinates at the peak power; τ mean and f mean are the weighted means in the delay direction and Doppler direction respectively.

8. A ship-based GNSS reflection signal marine oil spill monitoring method according to claim 7, characterized in that: The oil spill identification feature is obtained based on the time delay distribution characteristic and the Doppler distribution characteristic, including: The average values ​​of time delay distribution characteristics and Doppler distribution characteristics are used as oil spill identification features.

9. A ship-based GNSS reflection signal marine oil spill monitoring system, characterized in that: include: GNS signal receiving module, signal processing module, oil spill identification feature extraction module, oil spill area judgment module; The GNSS signal receiving module receives direct signals and reflected signals from the satellite system. The signal processing module obtains a time delay-Doppler map of the sea surface scattering area based on the direct signal and the reflected signal of the satellite system. The oil spill identification feature extraction module extracts the time delay distribution characteristics and Doppler distribution characteristics of the sea surface scattering area delay-Doppler map, and obtains the oil spill identification features based on the time delay distribution characteristics and Doppler distribution characteristics. The oil spill area determination module determines the relationship between the oil spill identification feature and the oil spill threshold, obtains the oil spill detection result, and obtains the comprehensive oil spill detection result based on the oil spill detection result corresponding to the satellite system.

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