A method for estimating sea ice thickness based on GNSS reflected signal phase

Abstract

The present application relates to the field of sea ice detection, in particular to a sea ice thickness estimation method based on GNSS reflected signal phase. According to the oscillation frequency of the reflected signal phase with the satellite elevation angle, the thickness of the sea ice is estimated. The present application takes the navigation satellite as the signal source, receives and processes the GNSS direct signal and the signal reflected by the sea surface, extracts the frequency of the reflected signal phase oscillation with the satellite elevation angle, and estimates the thickness of the sea ice through the linear correspondence between the phase oscillation frequency and the sea ice thickness. The algorithm has low complexity, high detection accuracy, rich signal resources, global all-day, all-weather coverage, wide detection range, low cost, is not affected by the antenna pattern, is not limited by the receiver mode, does not need to select a specific satellite, has low algorithm complexity, high detection accuracy, and can effectively estimate the thickness of the sea ice.

Description

Technical Field

[0001] This invention relates to the field of sea ice detection, and in particular to a method for estimating sea ice thickness based on the phase of GNSS reflected signals. Background Technology

[0002] Currently, there are three main methods for detecting sea ice thickness:

[0003] The first method is direct measurement, which involves drilling in the field. Although this method is the most accurate, it is easily affected by environmental factors and cannot obtain sea ice thickness information on a larger scale.

[0004] The second method is indirect measurement, such as looking-up sonar and microwave remote sensing. Looking-up sonar involves a submarine or sonar moored on the seabed emitting sound waves upwards. The position of the ice bottom in the water is estimated by obtaining the time delay of the ice bottom echo, thereby estimating the thickness of the sea ice. This method is costly and cannot detect areas inaccessible to submarines.

[0005] The third method is the traditional microwave remote sensing method for detecting sea ice thickness, which mainly uses synthetic aperture radar. However, this method is costly and has certain blind spots in monitoring near-shore sea ice.

[0006] Ocean remote sensing using GNSS reflected signals is one of the new technologies in satellite remote sensing, which has advantages such as multiple signal sources, wide detection range, light weight, spread spectrum processing, and wide application.

[0007] GNSS-R (Global Navigation Satellite System-Reflected) technology uses specialized receiving equipment—shore-based, airborne, and airborne—to receive direct GNSS signals and echo signals scattered by reflectors. It then processes the direct and reflected signals to invert the characteristics of the target object. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for estimating sea ice thickness based on the phase of GNSS reflected signals.

[0009] This method can estimate the thickness of sea ice based on the oscillation frequency of the reflected signal phase as the satellite elevation angle changes. This invention uses a navigation satellite as the signal source, receives and processes both direct GNSS signals and signals reflected from the sea surface, extracts the frequency of the reflected signal phase oscillation as the satellite elevation angle changes, and estimates the sea ice thickness through the linear correspondence between the phase oscillation frequency and the sea ice thickness.

[0010] The technical solution is as follows:

[0011] A method for estimating sea ice thickness based on the phase of GNSS reflected signals, comprising an antenna assembly for receiving direct satellite signals and detecting sea surface reflected signals, including the following steps:

[0012] d: Acquire direct and reflected signals, and simultaneously perform positioning calculations on the direct signals to obtain satellite elevation angle information;

[0013] e: Calculate the phase of the reflected signal based on the reflected signal;

[0014] f: Calculate the observable based on the phase of the reflected signal;

[0015] g: Estimate the oscillation frequency of the observation as the satellite elevation angle changes;

[0016] h: Estimate sea ice thickness based on observed oscillation frequency.

[0017] Furthermore, the antenna assembly includes a right-hand circularly polarized direct-fire antenna, a left-hand circularly polarized reflective antenna, a right-hand circularly polarized reflective antenna, and an antenna support;

[0018] The right-hand circularly polarized direct-fire antenna is mounted on the top of the antenna support;

[0019] The left-hand circularly polarized reflective antenna and the right-hand circularly polarized reflective antenna are located on both sides below the right-hand circularly polarized direct antenna.

[0020] Furthermore, step d includes:

[0021] Right-hand circularly polarized direct signal is obtained through a right-hand circularly polarized direct antenna, and left-hand circularly polarized signal and right-hand circularly polarized signal are obtained through a left-hand circularly polarized reflective antenna and a right-hand circularly polarized reflective antenna.

[0022] Furthermore, step d also includes: synchronizing the direct signal and transmitting the code phase and carrier Doppler information to the reflection channel to achieve synchronization of the reflected signal.

[0023] Furthermore, step d also includes: outputting a direct-view channel sequence I and a left- or right-handed reflection channel sequence Q.

[0024] Furthermore, step e calculates the phase using the following formula:

[0025]

[0026]

[0027] in, and I represents the phase of the left-hand and right-hand reflected signals. maxL and Q maxLThese represent the maximum values ​​of the I and Q sequences output by the left-hand reflection channel, respectively. maxR and Q maxR These represent the maximum values ​​of the I and Q sequences output by the right-hand reflection channel, respectively.

[0028] Furthermore, step f calculates the observation M(θ) using the following formula:

[0029]

[0030] Where θ represents the satellite elevation angle.

[0031] Furthermore, step g includes:

[0032] Estimate the oscillation frequency of the observation M(θ) as a function of the satellite elevation angle θ, and fit the observation sequence with a cosine function, i.e.:

[0033]

[0034] Where a, b, and c are fitting parameters, representing the amplitude a, frequency b, and initial phase c of the observed oscillation, respectively.

[0035] Furthermore, step h estimates the sea ice thickness using the following formula:

[0036]

[0037] in, This is an estimate of the oscillation frequency of the observed quantity M(θ) as a function of the satellite elevation angle θ. This is the final estimated value for sea ice thickness.

[0038] Furthermore, the antenna assembly is deployed on a shore-based platform or a carrier for detecting the sea surface.

[0039] The beneficial effects of this invention are:

[0040] I. This invention enables the application of GNSS reflection signal technology to sea ice detection. Based on the linear correspondence between the oscillation frequency of the reflected signal phase as a function of elevation angle and the sea ice thickness, sea ice thickness can be estimated. The algorithm has low complexity and high detection accuracy.

[0041] Second, the GNSS reflection signal technology used in this invention has the advantages of abundant signal resources, global all-day and all-weather coverage, wide detection range, and low cost;

[0042] Third, this invention is based on the phase oscillation frequency of the reflected signal, which is not affected by the antenna pattern, is not limited by the receiver mode, and does not require the selection of specific satellites. It has low algorithm complexity, high detection accuracy, and can effectively estimate the thickness of sea ice. Attached Figure Description

[0043] Figure 1 A schematic diagram of sea ice thickness observation mode based on GNSS reflected signal phase.

[0044] Figure 2 Flowchart of GNSS direct and reflected signal reception and processing.

[0045] Figure 3 Flowchart of sea ice detection based on GNSS reflected signal phase. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0047] See Figure 1 A schematic diagram of a sea ice thickness observation mode based on the phase of GNSS reflected signals. The GNSS right-hand circularly polarized direct-fire antenna is fixed at the top of the antenna support on the shore-based platform to receive direct signals from navigation satellites;

[0048] The GNSS reflector antennas with two polarization characteristics, left-hand circular polarization and right-hand circular polarization, are fixed on both sides below the direct antenna to receive the echo signal reflected from the sea surface.

[0049] See Figure 2 Flowchart of GNSS direct and reflected signal reception and processing.

[0050] Step 1: Use a GNSS direct antenna to receive the right-hand circularly polarized direct signal, and use a GNSS reflector antenna to receive the reflected left-hand circularly polarized signal and right-hand circularly polarized signal. Then, use a GNSS data acquisition unit to down-convert and quantize the signals into digital intermediate frequency signals.

[0051] The second step is to synchronize the direct signal and transmit the code phase and carrier Doppler information to the reflection channel to achieve synchronization of the reflected signal.

[0052] The direct signal and the reflected signal are separated from the digital intermediate frequency signal, and the direct signal is captured and tracked. The time delay and Doppler value obtained by tracking the direct signal are used to generate a local signal. The digital intermediate frequency reflected signal and the generated local signal are correlated in the reflection channel to achieve synchronization of the direct and reflected signals.

[0053] Step 3: Output the direct signal channel sequence I and the left and right rotation reflection channel sequences Q, and simultaneously perform positioning calculations on the direct signal.

[0054] After the direct reflection signal is correlated with the local signal in its respective channel, the corresponding in-phase and quadrature correlation value sequences I and Q are output; at the same time, the direct signal is used to perform positioning calculation to obtain the receiver position and navigation satellite position information.

[0055] Direct output will output the direct I and Q sequences, and reflection will also output the reflection I and Q sequences. That is, each channel will output its own I and Q sequences, where I: in phase and Q: quadrature.

[0056] See Figure 3 The flowchart for sea ice detection based on GNSS reflected signal phase is as follows:

[0057] Step 1: From Figure 2 The output left-handed complex correlation value sequence I and right-handed complex correlation value sequence Q are used as inputs to calculate the phase using the following formula:

[0058] Step 1: From Figure 2 The output sequence of left-handed reflection complex correlation values ​​(both I and Q are present, i.e., I...) L Q L ) and the right-handed reflection complex correlation value sequence (here both I and Q are present, i.e. I R Q R Using this as input, calculate the phase using the following formula:

[0059]

[0060]

[0061] in, and I represents the phase of the left-hand and right-hand reflected signals. maxL and Q maxL They represent Figure 2 The maximum values ​​of the I and Q sequences output by the left-handed reflection channel, I maxR and Q maxR They represent Figure 2 The maximum values ​​of the I and Q sequences output by the right-handed reflection channel.

[0062] Step 2: Solve for the observable M(θ) using the following formula:

[0063]

[0064] Where θ represents the satellite elevation angle.

[0065] Step 3: Estimate the oscillation frequency of the observation M(θ) as a function of the satellite elevation angle θ. Fit the observation sequence with a cosine function, i.e.:

[0066]

[0067] Where a, b, and c are fitting parameters, representing the amplitude a, frequency b, and initial phase c of the observed oscillation, respectively.

[0068] Step 4: Estimate sea ice thickness from the observed oscillation frequency. Through theoretical analysis and experimental data verification, sea ice thickness exhibits an approximately linear relationship with the observed frequency. Sea ice thickness can be estimated using the following formula:

[0069]

[0070] in, This is an estimate of the oscillation frequency of the observed quantity M(θ) as a function of the satellite elevation angle θ. This is the final estimated value for sea ice thickness.

[0071] Taking the measurement of sea ice thickness in Bohai Bay as an example: Figure 2 After the corresponding steps one, two, and three, the I and Q complex correlation value sequences of the direct and inverse channels were obtained. Figure 3 The first step corresponds to calculating the phase of the left and right rotational reflection signals during the observation process. phase These are all the phase values ​​observed during the observation process, forming a sequence. The observed quantity M(θ) is calculated in the second step, and the amplitude of M(θ) is obtained after fitting in the third step. Approximately 1, oscillation frequency If the value is approximately 0.2, then the estimated value of the sea ice thickness is obtained from step four: That is, the sea ice thickness in the detection area at this time is about 0.57m.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims.

Claims

1. A method for estimating sea ice thickness based on the phase of GNSS reflected signals, comprising an antenna assembly for receiving direct satellite signals and detecting sea surface reflected signals, characterized in that, The steps include: d: acquiring direct and reflected signals, and simultaneously performing positioning calculations on the direct signal to obtain satellite elevation angle information; e: Calculate the phase of the reflected signal based on the reflected signal; f: Calculate the observation based on the phase of the reflected signal; g: Estimate the oscillation frequency of the observation as the satellite elevation angle changes; h: Estimate sea ice thickness based on the observed oscillation frequency; step f calculates the observed values ​​using the following formula. : in, Indicates the satellite's elevation angle. The phases of the left-hand and right-hand circular reflected signals are represented; step g includes: estimating the observed quantity. With satellite elevation angle The varying oscillation frequency is fitted to the observed sequence using a cosine function, i.e.: Where a, b, and c are fitting parameters, representing the amplitude a, frequency b, and initial phase c of the observed oscillation, respectively; Step h estimates the sea ice thickness using the following formula: in, For observation With satellite elevation angle The estimated value of the changing oscillation frequency. This is the final estimated value for sea ice thickness.

2. The sea ice thickness estimation method based on GNSS reflected signal phase according to claim 1, characterized in that, The antenna assembly includes a right-hand circularly polarized direct antenna, a left-hand circularly polarized reflective antenna, a right-hand circularly polarized reflective antenna, and an antenna support; the right-hand circularly polarized direct antenna is disposed at the top of the antenna support; the left-hand circularly polarized reflective antenna and the right-hand circularly polarized reflective antenna are disposed on both sides below the right-hand circularly polarized direct antenna.

3. The sea ice thickness estimation method based on GNSS reflected signal phase according to claim 2, characterized in that, Step d includes: acquiring a right-hand circularly polarized direct signal through a right-hand circularly polarized direct antenna, and acquiring a left-hand circularly polarized signal and a right-hand circularly polarized signal through a left-hand circularly polarized reflective antenna and a right-hand circularly polarized reflective antenna.

4. The sea ice thickness estimation method based on GNSS reflected signal phase according to claim 3, characterized in that, Step d further includes: synchronizing the direct signal and transmitting the code phase and carrier Doppler information to the reflection channel to achieve synchronization of the reflected signal.

5. The sea ice thickness estimation method based on GNSS reflected signal phase according to claim 4, characterized in that, Step d further includes: outputting the direct-view channel sequence I and the left-right rotation reflection channel sequence Q.

6. The sea ice thickness estimation method based on GNSS reflected signal phase according to claim 5, characterized in that, Step e calculates the phase using the following formula: in, This indicates the phase of the left-hand and right-hand reflected signals. These represent the maximum values ​​of the I and Q sequences output by the left-hand reflection channel, respectively. These represent the maximum values ​​of the I and Q sequences output by the right-hand reflection channel, respectively.

7. A method for estimating sea ice thickness based on the phase of GNSS reflected signals according to any one of claims 1-6, characterized in that, The antenna assembly is deployed on a shore-based platform or a carrier for detecting the sea surface.

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