Ship body attitude calculation method and application
阅读说明：本技术 一种船体姿态计算方法及应用 (Ship body attitude calculation method and application ) 是由 胡桐 仇志金 *** 王中秋 邹靖 漆随平 于 2020-07-21 设计创作，主要内容包括：本发明公开了一种船体姿态计算方法及应用,船体姿态计算方法包括如下步骤：(1)利用船载GNSS天线、GNSS接收机观测GNSS信号信噪比；(2)反演GNSS天线距水面高度；(3)拟合船体姿态平面,计算出横摇角度、纵摇角度和升沉位移。得到船体姿态后,将船体外部传感器安装点、船体最低点的设计坐标通过旋转和平移映射到船体姿态平面,得到坐标变换后的垂直高度,可以计算船体外部传感器距水面垂直高度或船体吃水深度。本发明的方法能够为外部传感器测量数据提供测量高度的元数据描述,提高数据质量,并且与船上安装的其他吃水深度测量设备互为补充,保障船舶航行安全。本发明无需安装其他外部光学、声学传感器。(The invention discloses a ship attitude calculation method and application, wherein the ship attitude calculation method comprises the following steps: (1) observing the signal-to-noise ratio of the GNSS signal by utilizing a ship-borne GNSS antenna and a GNSS receiver; (2) inverting the height of the GNSS antenna from the water surface; (3) and fitting a ship body attitude plane, and calculating a rolling angle, a pitching angle and heave displacement. After the attitude of the ship body is obtained, the design coordinates of the mounting point of the sensor outside the ship body and the lowest point of the ship body are mapped to the attitude plane of the ship body through rotation and translation, the vertical height after coordinate transformation is obtained, and the vertical height from the sensor outside the ship body to the water surface or the draught depth of the ship body can be calculated. The method can provide the metadata description of the measurement height for the measurement data of the external sensor, improve the data quality, supplement other draft measurement equipment installed on the ship and ensure the navigation safety of the ship. The invention does not need to install other external optical and acoustic sensors.)
1. A ship body attitude calculation method is characterized by comprising the following steps:
(1) utilizing a ship-borne GNSS antenna and a GNSS receiver to observe the signal-to-noise ratio of a GNSS signal: collecting and storing data sent by each GNSS receiver, and extracting the carrier-to-noise ratio C/N of the current visible satellite signal corresponding to each GNSS receiver0Then calculating the signal-to-noise ratio SNR of the signal;
(2) and (3) inverting the height of the GNSS antenna from the water surface: carrying out Lomb Scargle periodic spectrum analysis on fluctuation items of the signal-to-noise ratio of the GNSS signals to obtain coherent frequency, and calculating the vertical height from the phase center of the GNSS antenna to the water surface according to the coherent frequency;
(3) and (3) fitting a hull attitude plane: and (3) taking the difference value between the vertical height inversion value from the phase center of the GNSS antenna to the water surface and the height value between the GNSS antenna design installation point and the plane of the design waterline as a sample set, performing least square linear fitting on the three-dimensional plane describing the ship body attitude, fitting the ship body attitude plane, and calculating the roll angle, the pitch angle and the heave displacement.
2. The ship hull attitude calculation method according to claim 1, wherein in the step (1), the vertical heights of the GNSS antenna installation points are not required to be consistent, and the projections of the GNSS antenna installation points in the horizontal plane are not collinear.
3. The hull attitude calculation method according to claim 1, characterized in that the specific method of step (2) is as follows:
the upper computer collects and stores NMEA standard format data sent by each GNSS receiver, and according to the communication protocol of the GNSS receiver actually used, if the $ GPGSV statement in the NMEA standard format data contains the current carrier-to-noise ratio C/N of the visible satellite signal0Then converted to signal to noise ratio SNR using:
4. the hull attitude calculation method according to claim 1, characterized in that the specific method of step (3) is as follows:
(1) the signal-to-noise ratio SNR of GNSS signals is a function of the satellite elevation angle e (t), and can be decomposed into a trend term tSNR due to the direct signal and a fluctuation term dSNR due to the coherence of the direct signal and the reflected signal, and the formula is as follows:
SNR(e(t))＝tSNR(e(t))+dSNR(e(t)) (2)
wherein t is an observation time, e (t) is a satellite elevation angle at the time t, SNR (e (t)) is a signal-to-noise ratio time sequence corresponding to the satellite elevation angle at different times, tSNR (e (t)) is a trend item caused by a direct signal in the signal-to-noise ratio time sequence, and dSNR (e (t)) is a fluctuation item caused by coherence of the direct signal and a reflected signal in the signal-to-noise ratio time sequence;
(2) eliminating tSNR (e (t)) from the SNR of the signal-to-noise ratio observation time sequence, wherein the tSNR (e (t)) can be expressed by the following formula:
tSNR(e(t))＝c0+c1e(t)+c2e(t)2+… (3)
fitting second or third order polynomial to SNR and e (t) observation time series according to formula (3) to obtain coefficient c0，c1，c2.., obtaining tSNR (e (t)); eliminating tSNR (e (t)) from the formula (2) to obtain dSNR (e (t));
(3) lomb Scargle periodic spectrum analysis is carried out on the fluctuation term dSNR (e (t)), so as to obtain the coherent frequency f, and the dSNR (e (t)) can be expressed by the following formula:
dSNR(e(t))＝Am(e(t))cos(2πfsin(e(t))+Φ) (4)
wherein A ismF is the coherent frequency of the direct signal and the reflected signal, phi is the phase offset of the direct signal and the reflected signal;
(4) calculating the vertical height H from the phase center of the GNSS antenna to the water surface by using the following formulaantenna：
Hantenna＝f·λ/2 (5)
Wherein λ is the satellite signal carrier wavelength.
5. The hull attitude calculation method according to claim 1, characterized in that the specific method of step (4) is as follows:
(1) inverse value H of vertical height of each GNSS antenna from water surfaceantennaAnd taking the difference value of the height value between the GNSS antenna design installation point and the plane where the design waterline is located as a single sample, and performing least square linear fitting on a ship attitude plane describing the average rolling angle, the pitching angle and the heave displacement of the ship in a time window by utilizing the sample set of each GNSS receiver in the sliding time window, wherein the fitting formula is as follows:
wherein i is GNSS antenna serial number, j is sample serial number, xi、yiRespectively an abscissa and an ordinate, z, of the mounting position of the ith GNSS antenna in the horizontal planei，jFor the jth inversion value of the ith GNSS antennaThe height value between the GNSS antenna mounting point and the plane where the design waterline is locatedThe difference between:
(2) a, B, C, D four coefficients are obtained by using the formula (6), and a hull attitude plane, namely a three-dimensional plane passing through the center of gravity of the hull is obtained:
Ax+By+Cz+D＝0 (8)
the x-axis points to the stem, the y-axis points to the port, and the z-axis points to the zenith;
(3) describing the attitude of the ship body by an Euler angle, and expressing by a ship body attitude plane, the heave displacement delta z is as follows:
the normal vector N of the horizontal plane is (0, 0, 1) after the rotation and the rolling angleAfter the pitching angle theta and the translational heave displacement delta z are rotated, a standardized ship body attitude plane normal vector is obtainedSolving for roll angleThe method of the pitch angle θ is:
6. use of a method for calculating the attitude of a ship's hull, characterized in that the method according to any one of claims 1-5 is used for calculating the vertical height of a sensor outside the ship's hull from the water surface or the draught of the ship's hull.
7. The application of the ship body attitude calculation method according to claim 6, characterized in that the design coordinates of the installation point of the ship body external sensor and the lowest point of the ship body are mapped to a ship body attitude plane through rotation and translation, and the vertical height after coordinate transformation, namely the vertical height of the ship body external sensor from the water surface or the draught depth of the ship body, is obtained.
8. The application of the ship body attitude calculation method according to claim 7, wherein the method for calculating the vertical height of the sensor outside the ship body from the water surface is as follows:
the design coordinates of the hull external sensor are mapped to a hull attitude plane through rotation and translation, and the vertical height after coordinate transformation is obtained, namely the vertical height of the hull external sensor from the water surface:
wherein the content of the first and second substances,for the design coordinates of the hull external sensor mounting points, [ x y z ] z]sensorThe point is subjected to rotation and translation and then is subjected to mapping coordinates on a ship body attitude plane; wherein z issensorThe vertical height of the sensor outside the ship body from the water surface.
9. The application of the ship hull attitude calculation method according to claim 7, characterized in that the method for calculating the ship hull draft is as follows:
and mapping the design coordinate of the lowest point of the ship body to a ship body attitude plane through rotation and translation to obtain the vertical height after coordinate transformation, namely the ship body draft:
wherein the content of the first and second substances,
Technical Field
The invention relates to a ship body attitude calculation method and application.
Background
When the ship sails, the ship body is influenced by factors such as load weight, sea condition, navigational speed and course, and changes in postures such as pitching, rolling, heaving and the like are generated under the comprehensive action of wind, waves and currents. The instantaneous change of the posture of the ship body changes the vertical height between the ship body and a sensor arranged outside the superstructure and the water surface. The vertical height of the sensor from the water surface can be acquired in real time by adopting a direct measurement mode or an indirect calculation mode. The direct measurement mode usually adopts a laser ranging or ultrasonic ranging principle, and special optical and acoustic sensors need to be installed, so that the sensors need to be cleaned regularly, and the installation and maintenance costs of equipment are high. The indirect calculation method usually adopts an Inertial Measurement Unit (IMU) to measure the attitude of the hull in real time, or adopts a GNSS to measure the elevation of multiple antennas to calculate the attitude of the hull in real time, and then converts the vertical height of the sensor from the water surface.
Some shipborne systems need to obtain the average value of the vertical height of a certain sensor from the water surface within a certain time range, and the value is related to the average change of the posture of a ship body within the same time period, and is reflected as the average change of a pitch angle, a roll angle and a heave displacement. Taking the application of the height prediction of the marine evaporation waveguide as an example, the average value of the vertical height from the water surface of the shipborne meteorological element sensor in a certain time range (the window duration can be selected from ten minutes to one hour) is one of necessary input parameters, and the system deviation of the vertical height from the water surface of the meteorological element sensor directly influences the accuracy of the height prediction result of the evaporation waveguide.
In addition, in a certain time range, the average change of the posture of the ship body also influences the change of the dynamic draft of the ship in the same time period, and the accurate measurement of the draft of the ship also relates to the navigation safety of the ship. Such applications all have a need to obtain an average change in the attitude of the hull.
At present, a ship is generally provided with GNSS positioning navigation equipment, the water surface is a good GNSS signal reflecting surface, a ship-borne GNSS antenna receives a superposed signal of a direct satellite signal and a water surface reflected signal, and the coherence of the direct satellite signal and the reflected satellite signal is reflected as signal-to-noise ratio fluctuation of the received signal, so that the method can be used for inverting the vertical distance between the GNSS antenna and the water surface.
Disclosure of Invention
In order to solve the technical problems, the invention provides a hull attitude calculation method and application, a conventional shipborne GNSS antenna and a GNSS receiver are used for observing a signal-to-noise ratio time sequence of satellite signals, IMU is not relied on, other external optical and acoustic sensors are not required to be installed, and a plurality of problems caused by regular cleaning and maintenance of a specific sensor are avoided.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a ship body attitude calculation method comprises the following steps:
(1) utilizing a ship-borne GNSS antenna and a GNSS receiver to observe the signal-to-noise ratio of a GNSS signal: collecting and storing data sent by each GNSS receiver, and extracting the carrier-to-noise ratio C/N of the current visible satellite signal corresponding to each GNSS receiver0Then calculating the signal-to-noise ratio SNR of the signal;
(2) and (3) inverting the height of the GNSS antenna from the water surface: carrying out Lomb Scargle periodic spectrum analysis on fluctuation items of the signal-to-noise ratio of the GNSS signals to obtain coherent frequency, and calculating the vertical height from the phase center of the GNSS antenna to the water surface according to the coherent frequency;
(3) and (3) fitting a hull attitude plane: and (3) taking the difference value between the vertical height inversion value from the phase center of the GNSS antenna to the water surface and the height value between the GNSS antenna design installation point and the plane of the design waterline as a sample set, performing least square linear fitting on the three-dimensional plane describing the ship body attitude, fitting the ship body attitude plane, and calculating the roll angle, the pitch angle and the heave displacement.
In the above scheme, in step (1), the vertical heights of the GNSS antenna mounting points do not need to be consistent, and the projections of the mounting points in the horizontal plane are not collinear.
In the scheme, the specific method of the step (2) is as follows:
the upper computer collects and stores NMEA standard format data sent by each GNSS receiver, and according to the communication protocol of the GNSS receiver actually used, if the NMEA standard format data are in the NMEA standard format dataThe $ GPGSV statement in (1) contains the current visible satellite signal carrier-to-noise ratio C/N0Then converted to signal to noise ratio SNR using:
in the above scheme, the specific method of step (3) is as follows:
(1) the signal-to-noise ratio SNR of GNSS signals is a function of the satellite elevation angle e (t), and can be decomposed into a trend term tSNR due to the direct signal and a fluctuation term dSNR due to the coherence of the direct signal and the reflected signal, and the formula is as follows:
SNR(e(t))＝tSNR(e(t))+dSNR(e(t)) (2)
wherein t is an observation time, e (t) is a satellite elevation angle at the time t, SNR (e (t)) is a signal-to-noise ratio time sequence corresponding to the satellite elevation angle at different times, tSNR (e (t)) is a trend item caused by a direct signal in the signal-to-noise ratio time sequence, and dSNR (e (t)) is a fluctuation item caused by coherence of the direct signal and a reflected signal in the signal-to-noise ratio time sequence;
(2) eliminating tSNR (e (t)) from the SNR of the signal-to-noise ratio observation time sequence, wherein the tSNR (e (t)) can be expressed by the following formula:
tSNR(e(t))＝c0+c1e(t)+c2e(t)2+… (3)
fitting second or third order polynomial to SNR and e (t) observation time series according to formula (3) to obtain coefficient c0，c1，c2.., obtaining tSNR (e (t)); eliminating tSNR (e (t)) from the formula (2) to obtain dSNR (e (t));
(3) lomb Scargle periodic spectrum analysis is carried out on the fluctuation term dSNR (e (t)), so as to obtain the coherent frequency f, and the dSNR (e (t)) can be expressed by the following formula:
dSNR(e(t))＝Am(e(t))cos(2πf sin(e(t))+Φ) (4)
wherein A ismF is the coherent frequency of the direct signal and the reflected signal, phi is the phase offset of the direct signal and the reflected signal;
(4) calculating the phase center of the GNSS antenna to the water surface by using the following formulaVertical height H ofantenna：
Hantenna＝f·λ/2 (5)
Wherein λ is the satellite signal carrier wavelength.
In the scheme, the specific method of the step (4) is as follows:
(1) inverse value H of vertical height of each GNSS antenna from water surfaceantennaAnd taking the difference value of the height value between the GNSS antenna design installation point and the plane where the design waterline is located as a single sample, and performing least square linear fitting on a ship attitude plane describing the average rolling angle, the pitching angle and the heave displacement of the ship in a time window by utilizing the sample set of each GNSS receiver in the sliding time window, wherein the fitting formula is as follows:
wherein i is GNSS antenna serial number, j is sample serial number, xi、yiRespectively an abscissa and an ordinate, z, of the mounting position of the ith GNSS antenna in the horizontal planei，jFor the jth inversion value of the ith GNSS antenna
(2) a, B, C, D four coefficients are obtained by using the formula (6), and a hull attitude plane, namely a three-dimensional plane passing through the center of gravity of the hull is obtained:
Ax+By+Cz+D＝0 (8)
the x-axis points to the stem, the y-axis points to the port, and the z-axis points to the zenith;
(3) describing the attitude of the ship body by an Euler angle, and expressing by a ship body attitude plane, the heave displacement delta z is as follows:
the normal vector N of the horizontal plane is (0, 0, 1) after the rotation and the rolling angle
the application of the hull attitude calculation method is to calculate the vertical height of a sensor outside a hull from the water surface or the draught depth of the hull.
In the scheme, the design coordinates of the mounting point of the sensor outside the ship body and the lowest point of the ship body are mapped to the attitude plane of the ship body through rotation and translation, and the vertical height after coordinate transformation, namely the vertical height of the sensor outside the ship body from the water surface or the draught depth of the ship body is obtained.
In a further technical scheme, the method for calculating the vertical height from the sensor outside the ship body to the water surface comprises the following steps:
the design coordinates of the hull external sensor are mapped to a hull attitude plane through rotation and translation, and the vertical height after coordinate transformation is obtained, namely the vertical height of the hull external sensor from the water surface:
wherein the content of the first and second substances,for the design coordinates of the hull external sensor mounting points, [ x y z ] z]sensorThe point is subjected to rotation and translation and then is subjected to mapping coordinates on a ship body attitude plane; wherein z issensorThe vertical height of the sensor outside the ship body from the water surface.
In a further technical scheme, the method for calculating the draught depth of the ship body comprises the following steps:
and mapping the design coordinate of the lowest point of the ship body to a ship body attitude plane through rotation and translation to obtain the vertical height after coordinate transformation, namely the ship body draft:
wherein the content of the first and second substances,
Through the technical scheme, the ship body attitude calculation method and the application provided by the invention can provide the metadata description of the measurement height for the measurement data of the external sensor, improve the data quality, supplement other draft measurement equipment installed on a ship and ensure the navigation safety of the ship. The invention does not need to install other external optical and acoustic sensors, and saves the equipment installation and maintenance cost compared with other direct measurement methods.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
Fig. 1 is a schematic application flow diagram of the hull attitude calculation method of the present invention.
FIG. 2 is a schematic diagram of a GNSS antenna on a ship for receiving signals.
Fig. 3 is a schematic plan view of the attitude of the hull of the present invention.
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.
The invention provides a method for calculating the attitude of a ship body, which comprises the following steps of:
(1) utilizing a ship-borne GNSS antenna and a GNSS receiver to observe the signal-to-noise ratio of a GNSS signal:
as shown in fig. 2, the on-board GNSS antenna receives signals superimposed by direct satellite signals and reflected signals from the water surface, and the coherence between the direct signals and the reflected signals is represented as fluctuation of signal-to-noise ratio of the signals. The upper computer receives and stores NMEA standard format data sent by each GNSS receiver, and the $ GPGSV statement extracts the carrier-to-noise ratio C/N of the current visible satellite signal of each GNSS receiver0Calculating the signal-to-noise ratio SNR:
(2) and (3) inverting the height of the GNSS antenna from the water surface:
a. the signal-to-noise ratio SNR of GNSS signals is a function of the satellite elevation angle e (t), and can be decomposed into a trend term tSNR due to the direct signal and a fluctuation term dSNR due to the coherence of the direct signal and the reflected signal, and the formula is as follows:
SNR(e(t))＝tSNR(e(t))+dSNR(e(t)) (2)
wherein t is an observation time, e (t) is a satellite elevation angle at the time t, SNR (e (t)) is a signal-to-noise ratio time sequence corresponding to the satellite elevation angle at different times, tSNR (e (t)) is a trend item caused by a direct signal in the signal-to-noise ratio time sequence, and dSNR (e (t)) is a fluctuation item caused by coherence of the direct signal and a reflected signal in the signal-to-noise ratio time sequence;
b. eliminating tSNR (e (t)) from the SNR of the signal-to-noise ratio observation time sequence, wherein the tSNR (e (t)) can be expressed by the following formula:
tSNR(e(t))＝c0+c1e(t)+c2e(t)2+… (3)
fitting second or third order polynomial to SNR and e (t) observation time series according to formula (3) to obtain coefficient c0，c1，c2.., obtaining tSNR (e (t)), and removing the fitted tSNR (e (t)) from the formula (2) to obtain dSNR (e (t));
c. lomb Scargle periodic spectrum analysis is carried out on the fluctuation term dSNR (e (t)), so as to obtain the coherent frequency f, and the dSNR (e (t)) can be expressed by the following formula:
dSNR(e(t))＝Am(e(t))cos(2πf sin(e(t))+Φ) (4)
wherein A ismF is the coherent frequency of the direct signal and the reflected signal, phi is the phase offset of the direct signal and the reflected signal;
d. calculating the vertical height H from the phase center of the GNSS antenna to the water surface by using the following formulaantenna：
Hantenna＝f·λ/2 (5)
Wherein λ is the satellite signal carrier wavelength.
In the step, the current visible satellite list of each GNSS receiver, the satellite elevation angle and the signal-to-noise ratio time sequence are updated in real time. And when the elevation angle of a certain visible satellite reaches the maximum value or the satellite exits the visible list, triggering Lomb Scargle periodic spectrum analysis, and calculating the vertical height between the phase center of the corresponding GNSS antenna and the water surface.
(3) And (3) fitting a hull attitude plane:
a. the inversion value H of the vertical height between the phase center of each GNSS antenna and the water surfaceantennaAnd taking the difference value of the height value between the GNSS antenna design installation point and the plane where the design waterline is located as a single sample, and performing least square linear fitting on a ship attitude plane describing the average rolling angle, the pitching angle and the heave displacement of the ship in a time window by utilizing the sample set of each GNSS receiver in the sliding time window, wherein the fitting formula is as follows:
wherein i is GNSS antenna serial number, j is sample serial number, xi、yiRespectively an abscissa and an ordinate, z, of the mounting position of the ith GNSS antenna in the horizontal planei，jFor the jth inversion value of the ith GNSS antenna
b. the four coefficients A, B, C, D are found by equation (6) to obtain the hull attitude plane, which is shown in fig. 3, i.e. the three-dimensional plane passing through the center of gravity of the hull:
Ax+By+Cz+D＝0 (8)
the x-axis points to the stem, the y-axis points to the port, and the z-axis points to the zenith;
c. describing the attitude of the ship body by an Euler angle, and expressing by a ship body attitude plane, the heave displacement delta z is as follows:
the normal vector N of the horizontal plane is (0, 0, 1) after the rotation and the rolling angleAfter the pitching angle theta and the translational heave displacement delta z are rotated, a standardized ship body attitude plane normal vector is obtained
the application of the hull attitude calculation method is to calculate the vertical height of a sensor outside a hull from the water surface or the draught depth of the hull. Meanwhile, the method can also calculate the average height of any instrument arranged on the ship body from the water surface.
(1) The method for calculating the height of the sensor outside the ship body comprises the following steps:
the design coordinates of the ship external sensor are mapped to a ship attitude plane through rotation and translation, and the vertical height after coordinate transformation is obtained, namely the height of the ship external sensor:
wherein the content of the first and second substances,
(2) The method for calculating the draught of the ship body comprises the following steps:
and mapping the design coordinate of the lowest point of the ship body to a ship body attitude plane through rotation and translation to obtain a vertical height difference value after coordinate transformation, namely the ship body draft:
wherein the content of the first and second substances,for the design coordinates of the lowest point of the hull, [ x y z [ ]]draftMapping coordinates for the hull attitude plane; wherein z isdraftThe draught of the ship body.
For a ship only provided with a set of shipborne GNSS antenna and GNSS receiver, neglecting hull pitching and rolling, taking an inversion value of the vertical height between the GNSS antenna phase center and the water surface in a sliding time window and the height difference value between the GNSS antenna design installation point and the plane of the design waterline as constant difference, and approximately calculating the heave displacement of the ship attitude plane; for a ship provided with two sets of shipborne GNSS antennas and GNSS receivers, and the shipborne GNSS antennas are arranged on the left side and the right side of a main mast, the ship body pitching is ignored, and the rolling angle and the heave displacement of the ship body attitude plane are approximately calculated by taking the vertical distance inversion values from the left side GNSS antenna and the right side GNSS antenna to the water surface in a sliding time window and the height difference value between the designed installation point of the GNSS antennas and the plane where the designed waterline is located as constant difference.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.