Method and system for calculating sea surface backscattering coefficient of large grazing angle based on sea tower platform

Abstract

The invention discloses a sea tower platform-based large-grazing-angle sea surface backscattering coefficient calculation method, which comprises the following steps of 1, sea clutter related information acquisition, 2, radar system calibration, 3, platform and sea surface distance estimation, 4, irradiation area calculation, 5, sea tower platform-based large-grazing-angle sea surface backscattering coefficient calculation, 6, sea tower platform-based large-grazing-angle sea surface backscattering coefficient calculation and 7, sea tower platform-based large-grazing-angle sea surface backscattering coefficient calculation. The calculation method and system disclosed by the invention are suitable for the calculation of the sea surface backscattering coefficient of a radar erected on a sea tower radar platform under the observation condition of a large grazing angle; and the sea surface backscattering characteristics of the sea tower radar platform can be analyzed under the condition of no elevation measurement facilities, tide and other environmental parameters.

Description

Technical Field

[0001] The invention belongs to the field of radar sea detection, and particularly relates to a method and system for calculating sea surface backscatter coefficients at a large ground-grazing angle based on a sea tower radar platform in the field. Background Art

[0002] The sea surface backscatter coefficient characterizes the intensity of electromagnetic wave backscattering per unit area of ​​the sea surface, which can be expressed as σ, with the unit of dB. The sea surface backscatter coefficient is the ratio of the sea surface radar cross section (RCS) to the irradiated area A, that is, σ = RCS / A. The sea surface backscatter coefficient can reflect the sea conditions and is an indispensable key parameter in radar sea detection and maritime target identification.

[0003] In order to obtain the measured results of the backscatter coefficient of the sea surface under large grazing angles, the common practice is to use airborne or sea tower radar platforms to build a measurement system for testing. However, airborne platforms are affected by weather and it is difficult to obtain measured data under high sea conditions. Therefore, the measurement of large grazing angles under high sea conditions is usually carried out based on sea tower radar platforms. For sea tower radar platforms, due to their close distance to the sea surface, affected by tides and waves, the height of the radar from the sea surface is always changing. This time-varying property will directly affect the accurate estimation of the radar irradiation area, and thus affect the accurate calculation of the backscatter coefficient of the sea surface. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for calculating the sea surface backscattering coefficient based on the sea tower radar platform based on the sea surface echo data received by the sea tower radar platform in the absence of environmental parameters such as tides, taking into account the interaction between electromagnetic waves and the sea surface, thereby solving the problem of inaccurate estimation of the irradiation area of ​​the sea tower radar platform.

[0005] The present invention adopts the following technical solution:

[0006] A method for calculating the backscatter coefficient of the sea surface at a large ground-grabbing angle based on a sea tower platform, the improvement of which is that it comprises the following steps:

[0007] Step 1: Obtain sea clutter related information:

[0008] Based on the sea clutter collection system of the large-angle sea tower radar platform, the sea clutter data is continuously collected for no less than 1 minute, and the radar system parameters are recorded at the same time, including the radar beam center angle α, polarization mode, and electromagnetic wave center frequency f c 、Radar half-power beamwidth θ 3dB , pulse width B w , sampling frequency S;

[0009] Step 2, radar system calibration:

[0010] Determine the radar transmission power P t , the known scattering cross-sectional area is σ c The standard scatterer is placed at a distance R, and the radar receiving power P is measured. r , calculate the loss coefficient L of the radar receiver:

[0011]

[0012] In the above formula, c is the speed of light, G t represents the gain of the transmitting antenna, G r represents the gain of the receiving antenna;

[0013] Step 3: Estimation of the distance between the platform and the sea surface:

[0014] The sea surface echo power received by the radar is averaged within one minute, and a sea surface echo power curve is drawn. The coordinate x of the midpoint of the rising edge of the curve is taken. i , calculate the height H of the sea tower radar platform from the average sea level according to the radar beam center rubbing angle α and the sampling frequency S:

[0015]

[0016] Step 4, irradiation area calculation:

[0017] After obtaining the height H of the Haita radar platform from the mean sea level, according to the radar system parameters recorded in step 1, the radar footprint area is approximated as an ellipse, and each resolution unit is approximated as a rectangle. The radar footprint area A and the resolution unit area A unit Respectively expressed as:

[0018]

[0019] The smaller value of the two [A,A unit ] min The area that needs to be normalized for calculating the sea surface backscatter coefficient in step 5;

[0020] Step 5, calculation of sea surface backscatter coefficient:

[0021] Find the maximum value P of the sea surface echo power curve by peak search r and the position x of the corresponding sampling point j , then the radar sea surface backscatter coefficient σ 0 It is expressed as:

[0022]

[0023] A system for calculating sea surface backscatter coefficients at a large ground-grabbing angle based on a sea tower platform, the improvement of which is as follows:

[0024] The acquisition unit is used for acquiring sea clutter related information; the calibration unit is used for calibrating the radar system; the estimation unit is used for estimating the distance between the platform and the sea surface; the first calculation unit is used for calculating the irradiated area; and the second calculation unit is used for calculating the sea surface backscatter coefficient.

[0025] The beneficial effects of the present invention are:

[0026] The calculation method and system disclosed in the present invention are suitable for calculating the sea surface backscattering coefficient of a radar mounted on a sea tower radar platform under large ground-grazing angle observation conditions, and can analyze the sea surface backscattering characteristics of the sea tower radar platform in the absence of elevation measurement facilities and environmental parameters such as tides. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the flow chart of the calculation method disclosed in the present invention;

[0028] Figure 2 This is a curve of the sea surface echo power received by the measured Dachadi Cape Haita radar platform. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Embodiment 1, based on the interaction process between electromagnetic waves and the sea surface, this embodiment uses the sea surface echo received by the radar to disclose a method for calculating the backscattering coefficient of the sea surface at the Great Cape of the Sea Tower platform. Based on the sea surface echo data received by the Great Cape of the Sea Tower radar platform, the interaction mechanism between the electromagnetic waves emitted by the radar and the sea surface is considered, the distance of the Sea Tower radar platform from the average sea level and the irradiated area are estimated, and combined with the radar calibration constant, the accurate calculation of the sea surface scattering coefficient under the Sea Tower radar platform is realized. Figure 1 As shown, the following steps are included:

[0031] Step 1: Obtain sea clutter related information:

[0032] Based on the sea clutter collection system of the large-angle sea tower radar platform, a radar observation plan is set to continuously collect sea clutter data for no less than 1 minute, and the radar system parameters are recorded at the same time, including the radar beam center angle α, polarization mode (horizontal polarization or vertical polarization), and electromagnetic wave center frequency f c 、Radar half-power beamwidth θ 3dB , pulse width B w , sampling frequency S, etc.;

[0033] Step 2, radar system calibration:

[0034] Determine the radar transmission power P t , the gain of the transmitting antenna G t and the gain of the receiving antenna G r , the known scattering cross-sectional area is σ c The standard scatterer is placed at a distance R, and the radar receiving power P is measured. r , calculate the loss coefficient L of the radar receiver:

[0035]

[0036] In the above formula, c is the speed of light, G t represents the gain of the transmitting antenna, G r represents the gain of the receiving antenna;

[0037] Step 3: Estimation of the distance between the platform and the sea surface:

[0038] The sea surface echo power received by the radar is averaged within one minute, and the sea surface echo power curve is drawn, such as Figure 2 As shown in the figure, it can be found that the sea surface backscattered signal received by the radar has an obvious rising process in the process of contacting the sea surface. According to the mutual process between the radar electromagnetic wave and the sea surface, when the electromagnetic wave reaches the average sea level, the echo power reaches the midpoint position of the rising edge. Therefore, the coordinate x of the midpoint position of the rising edge of the curve is taken i , calculate the height H of the sea tower radar platform from the average sea level according to the radar beam center rubbing angle α and the sampling frequency S:

[0039]

[0040] Step 4, irradiation area calculation:

[0041] After obtaining the height H of the sea tower radar platform from the mean sea level, according to the radar system parameters recorded in step 1, the radar footprint area (radar beam irradiation area) is approximated as an ellipse, and each resolution unit is approximated as a rectangle. The radar footprint area A and the resolution unit area A unit Respectively expressed as:

[0042]

[0043] The smaller value of the two [A,A unit ] min The area that needs to be normalized for calculating the sea surface backscatter coefficient in step 5;

[0044] Step 5, calculation of sea surface backscatter coefficient:

[0045] The sea surface backscatter coefficient is defined as the ratio of the sea surface echo power to the area. Considering the interaction between electromagnetic waves and the sea surface, when the sea surface radar echo is the strongest, it can be considered that the radar irradiation area is almost entirely filled with the sea surface. Therefore, the peak search is used to find Figure 2 The maximum value P of the sea surface echo power curve r and the position x of the corresponding sampling point j , then the radar sea surface backscatter coefficient σ 0 It is expressed as:

[0046]

[0047] The present embodiment also discloses a system for calculating the sea surface backscatter coefficient at a large ground-grabbing angle based on a sea tower platform, comprising: an acquisition unit for acquiring sea clutter related information; a calibration unit for calibrating a radar system; an estimation unit for estimating the distance between the platform and the sea surface; a first calculation unit for calculating the irradiated area; and a second calculation unit for calculating the sea surface backscatter coefficient.

Claims

1. A method for calculating the backscatter coefficient of the sea surface based on the large ground-grabbing angle of the sea tower platform. It is characterized in that The steps include: Step 1: Obtain sea clutter related information: Based on the sea clutter collection system of the large-angle sea tower radar platform, the sea clutter data is continuously collected for no less than 1 minute, and the radar system parameters are recorded at the same time, including the radar beam center angle α, polarization mode, and electromagnetic wave center frequency f c 、Radar half-power beamwidth θ 3dB , pulse width B w , sampling frequency S; Step 2, radar system calibration: Determine the radar transmission power P t , the known scattering cross-sectional area is σ c The standard scatterer is placed at a distance R, and the radar receiving power P is measured. r , calculate the loss coefficient L of the radar receiver: In the above formula, c is the speed of light, G t represents the gain of the transmitting antenna, G r represents the gain of the receiving antenna; Step 3: Estimation of the distance between the platform and the sea surface: The sea surface echo power received by the radar is averaged within one minute, and a sea surface echo power curve is drawn. The coordinate x of the midpoint of the rising edge of the curve is taken. i , calculate the height H of the sea tower radar platform from the average sea level according to the radar beam center rubbing angle α and the sampling frequency S: Step 4, irradiation area calculation: After obtaining the height H of the Haita radar platform from the mean sea level, according to the radar system parameters recorded in step 1, the radar footprint area is approximated as an ellipse, and each resolution unit is approximated as a rectangle. The radar footprint area A and the resolution unit area A unit Respectively expressed as: The smaller value of the two [A,A unit ] min The area that needs to be normalized for calculating the sea surface backscatter coefficient in step 5; Step 5, calculation of sea surface backscatter coefficient: Find the maximum value P of the sea surface echo power curve by peak search r and the position x of the corresponding sampling point j , then the radar sea surface backscatter coefficient σ 0 It is expressed as:

2. A system for calculating the backscatter coefficient of the sea surface based on the large ground-grabbing angle of the sea tower platform. It is characterized in that include: An acquisition unit, used for acquiring sea clutter related information; Calibration unit, used for radar system calibration; An estimation unit, used for estimating the distance between the platform and the sea surface; A first calculation unit, used for calculating the irradiation area; The second calculation unit is used for calculating the sea surface backscatter coefficient.

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