An attitude error compensation method for shipborne weather radar

Abstract

The present invention provides an attitude error compensation method for a ship-borne weather radar. The method can calculate the angle of deviation of the radar beam caused by the change of the airship attitude angle, i.e., the angle that needs to be compensated, based on the transformation between different coordinate systems and utilizing a mathematical model of the airship attitude angle change and measured data. Then, a reasonable compensation strategy is formulated to compensate for the attitude error, so that the radar beam can still point to the ideal position when the airship attitude changes, thereby avoiding positioning errors.

Description

Technical Field

[0001] The present invention belongs to the technical field of weather radars, and in particular relates to an attitude error compensation method for a boat-borne weather radar. Background Art

[0002] Weather radar is the most effective means of monitoring and warning of sudden and disastrous weather events. It can quickly and accurately predict weather conditions and strengthen natural disaster prevention. Over the past 50 years, my country's weather radar monitoring network has made significant progress, playing a vital role in monitoring and warning of disastrous weather events and achieving significant social, economic, and ecological benefits.

[0003] To achieve more accurate high-altitude meteorological detection, weather radars can be carried on high-altitude platforms such as aircraft, airships, and satellites. Unlike aircraft and satellites, stratospheric airships rely on gas for lift and control and propulsion systems for flight. Their relatively large mass and significant inertial characteristics make their motion significantly affected by the environment; even small air currents can cause significant movement. Even when stationary, various non-ideal factors can cause the airship's attitude angle to shift, causing the radar beam to deviate from its ideal position and resulting in positioning errors. Therefore, the motion characteristics of aircraft and satellites differ significantly from those of airships. Therefore, compensation for the airship's attitude errors is necessary to ensure that the radar beam remains pointed at the ideal position despite changes in the airship's attitude. Summary of the Invention

[0004] To solve the above problems, the present invention provides an attitude error compensation method for a shipborne weather radar. The method establishes a conversion relationship between different coordinate systems based on the geometric relationship observed by the shipborne weather radar. The method uses a mathematical model of the airship attitude angle change and measured data to calculate the angle of deviation of the radar beam caused by the airship attitude angle change, that is, the angle that needs to be compensated. Then, a reasonable compensation strategy is formulated to complete the compensation of the attitude error.

[0005] The attitude error compensation method for a boat-borne weather radar of the present invention comprises:

[0006] S1, establish the observation geometry of the shipborne weather radar. Based on the conversion relationship between the ship coordinate system and the antenna coordinate system, calculate the coordinates of the target in the ship coordinate system before the attitude change according to the coordinates of the target pointed by the radar beam in the antenna coordinate system;

[0007] S2, based on the conversion relationship between the hull coordinate system before and after the airship attitude change, and the conversion relationship between the antenna coordinate system and the hull coordinate system, combined with the coordinates of the target in the hull coordinate system before the attitude change obtained in step S1, calculate the coordinates of the target pointed by the radar beam in the original antenna coordinate system after the airship attitude angle changes;

[0008] S3, based on the coordinates obtained in step S2 and the coordinates of the target in the antenna coordinate system when the airship attitude angle does not change, the difference between the two can be used to calculate the deviation of the radar beam pointing caused by the change in the airship attitude angle, which is used as the angle to be compensated;

[0009] S4, formulate compensation strategy to complete the compensation of posture error.

[0010] Furthermore, step S1 includes:

[0011] Establish the geometric relationship of the shipborne weather radar observation, define the geodetic coordinate system S-OXYZ and the ship body coordinate system S a -O a X a Y a Z a and antenna coordinate system S b -O b X b Y b Z b The three axes of the earth coordinate system are determined according to the airship route direction, the three axes of the hull coordinate system are determined according to the design axis of the hull, and the antenna coordinate system is determined according to the radar beam direction;

[0012] According to the observation geometry of the shipborne weather radar, the antenna coordinate system S is established. b To the hull coordinate system S a The conversion relationship:

[0013]

[0014] Among them, [x a y a z a ] T is the coordinate in the hull coordinate system, [x b y b z b ] T is the coordinate in the antenna coordinate system, a is the radar beam depression angle, θ=θ(t) is the beam azimuth that changes with time and is related to the antenna rotation speed and sampling time, R x 、R z is the transformation matrix between the antenna coordinate system and the hull coordinate system. The specific expression is as follows:

[0015]

[0016] Assuming that the attitude angle of the airship does not change, the target pointed by the radar beam is in the antenna coordinate system S b The coordinates below are P b0 (x b ,yb ,z b ), according to formula (1), P b0 Transform to the hull coordinate system S a Below is P a0 (t)(x a (t), y a (t), z a (t).

[0017] Furthermore, step S2 includes:

[0018] S21, when the attitude angle of the airship changes, the hull coordinate system and the antenna coordinate system also change. Let the hull coordinate system after the attitude angle changes be S a ′-O a 'X a 'Y a ′Z a ′, the antenna coordinate system after the attitude angle changes is S b ′-O b 'X b 'Y b ′Z b ';

[0019] When the attitude angle of the airship changes, the radar beam will point to the new target. Since the relative position of the airship's buoyancy center and the antenna does not change with the attitude angle, and the beam vector does not change, the new target is in the airship coordinate system S a ′ and antenna coordinate system S b The coordinates under ′ are

[0020]

[0021] Assume that the roll angle, pitch angle and heading angle of the airship are R, P, and Y respectively, and they change with time t according to the sinusoidal model, that is,

[0022]

[0023] Where T R 、T P 、T Y is the attitude angle change period;

[0024] According to the geometric relationship before and after the change of the attitude angle of the airship, the airship coordinate system S before and after the attitude angle change is established. a and S a ′The coordinate transformation relationship between them is:

[0025] P a ′(t)=M R M P M Y P a (t) (5)

[0026] Among them, P a (t) and P a ′(t) are the same target in S a Coordinate system and S a Coordinates in the ′ coordinate system, M R 、M P 、M Y are the conversion matrices of roll angle, pitch angle and heading angle respectively. The specific expressions are as follows:

[0027]

[0028] From formula (5), we can get

[0029] P a (t) = M -Y M -P M -R P a ′(t) (7)

[0030] Among them, M -R 、M -P 、M -Y M R 、M P 、M Y The inverse matrix of

[0031]

[0032] P a1 Substituting ′(t) into formula (7) we can get the new target pointed by the radar beam in the hull coordinate system S a The coordinate P a1 (t);

[0033] Step S22, obtain the coordinate system S from the hull by formula (1) a To the antenna coordinate system S b The conversion relationship is:

[0034]

[0035] Among them, R x (α) and R x (-α) are inverse matrices, R z (-θ) and R z (θ) are inverse matrices of each other;

[0036] P a1 Substituting (t) into formula (9) we can get the new target pointed by the radar beam in the antenna coordinate system S b The coordinate P b1 (t)=(x b1 (t),yb1 (t),z b1 (t)).

[0037] Furthermore, step S3 includes:

[0038] S31, the coordinate P obtained in step S2 b1 (t) and P b0 By subtraction, we can obtain the deviation vector caused by the change of the airship attitude angle in the antenna coordinate system S b Below

[0039] [Δx b (t),Δy b (t),Δz b (t)] T =P b1 (t)-P b0 =[x b1 (t)-x b ,y b1 (t)-y b ,z b1 (t)-z b ] T (10)

[0040] The angles of deviation of the radar beam in azimuth and elevation caused by the change of the airship attitude angle are:

[0041]

[0042] Where r represents the detection range of the radar;

[0043] By taking the difference of formula (11), we can find the angles that need to be compensated for the radar beam in azimuth and elevation within each CPI, that is,

[0044]

[0045] S32, set the initial compensation cycle to N, that is, perform angle compensation every N CPIs, and the angles to be compensated in the azimuth and pitch directions in each compensation cycle are respectively

[0046]

[0047]

[0048] Where n0 is the CPI number at the start of the compensation period.

[0049] Furthermore, step S4 includes:

[0050] Assume that the servo's response capability (maximum rotation speed) is V max, then the maximum adjustable angle of the servo within one compensation cycle is

[0051] AZ max =V max ×N×CPI (14)

[0052] The compensation strategy is formulated as follows:

[0053] S41, determine d AZ_N and d AZ max If d AZ_N>d AZ max , first d AZ max Transmitted to the servo control component to compensate for the beam pointing, the residual error d AZ N -d AZ max Compensation needs to be made in subsequent compensation cycles;

[0054] S42, determine the tracking accuracy b of dAZ_N and dEL_N and the beam pointing angle min (the minimum angle that the beam can change each time) size relationship, if d AZ_N and d EL_N are less than b min , then no compensation is required in this cycle, and the value of N is appropriately increased to directly calculate the compensation angle for the next cycle;

[0055] S43, if d AZ_N and d EL_N do not belong to the above two cases, transmit d AZ_N and d EL_N to the radar control component to compensate the beam pointing;

[0056] S44, judging whether the compensation has been completed. If not, repeat S41, S42, and S43.

[0057] The beneficial effects of the present invention are:

[0058] The present invention provides an attitude error compensation method for a ship-borne weather radar. The method can calculate the angle of deviation of the radar beam caused by the change of the airship attitude angle, i.e., the angle that needs to be compensated, based on the transformation between different coordinate systems and utilizing a mathematical model of the airship attitude angle change and measured data. Then, a reasonable compensation strategy is formulated to compensate for the attitude error, so that the radar beam can still point to the ideal position when the airship attitude changes, thereby avoiding positioning errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 1 is an overall flow chart of the attitude error compensation method for a boat-borne weather radar according to the present invention;

[0060] Figure 2 Schematic diagram of the observation geometry of a boat-borne typhoon radar for the attitude error compensation method of the boat-borne weather radar of the present invention;

[0061] Figure 3 A schematic diagram of the change in radar beam pointing before and after the attitude angle of an airship changes in the attitude error compensation method for an airship-borne weather radar of the present invention;

[0062] Figure 4 The angle of the radar beam that needs to be compensated is obtained by using the model data of the attitude angle in the attitude error compensation method for the boat-borne weather radar of the present invention;

[0063] Figure 5 The angle of the radar beam that needs to be compensated is obtained by using the measured data of the attitude angle in the attitude error compensation method for the boat-borne weather radar of the present invention;

[0064] Figure 6 The angle to be compensated in each CPI is obtained by using the attitude angle model data in the attitude error compensation method for the shipborne weather radar of the present invention;

[0065] Figure 7 It is the angle that needs to be compensated in each CPI obtained by using the measured data of the attitude angle in the attitude error compensation method for the shipborne weather radar of the present invention. DETAILED DESCRIPTION

[0066] The present invention is described in detail below with reference to the accompanying drawings. In this example, radar-related parameters are shown in Table 1:

[0067] Table 1

[0068] parameter Numerical Radar rotation speed (° / s) 6 / 24 Maximum servo speed (° / s) 24 Beam pointing angle tracking accuracy (° / s) 0.2 Radar beam azimuth range (°) 0～360 Radar beam depression angle (°) 6 / 85 PRF(Hz) 1933 Number of pulse accumulation 64 Radar detection range (km) 10～100 Attitude angle variation range (°) ±10, sinusoidal variation Attitude angle change period (s) 40 Attitude angle change interval (s) One CPI (0.033s) Simulation time (s) 60

[0069] The present invention provides a method for compensating attitude error of a shipborne weather radar. The overall process is as follows: Figure 1 As shown, the specific steps include:

[0070] Step S1: Establishing the observation geometry of the airship-borne weather radar. Based on the conversion relationship between the airship coordinate system and the antenna coordinate system, calculate the coordinates of the target pointed by the radar beam in the airship coordinate system when the airship attitude does not change.

[0071] Establish the geometric relationship of shipborne weather radar observations such as Figure 2 As shown, the geodetic coordinate system S-OXYZ is defined: the origin O is a fixed point on the ground, the OY axis points to the direction of the airship route in the ground plane, the OZ axis is perpendicular to the ground and upward, and the OX axis is determined by the right-hand rule.

[0072] Define the hull coordinate system S a -O a X a Y a Z a : Origin O a Coincident with the airship's buoyancy center, Oa Y a The axis is in the longitudinal section of the airship and is parallel to the design axis of the hull, pointing to the bow. a X a The axis is perpendicular to the longitudinal section of the airship and points to the right. a Z a The axis is in the longitudinal section of the airship and perpendicular to O a X a The axis points upward.

[0073] Define the antenna coordinate system S b -O b X b Y b Z b : Origin O b Located at the radar position, O b Y b Passing through the beam center, O b Z b Along O b Y b Counterclockwise elevation beam direction, O b X b Along O b Z b Azimuth beam direction in counterclockwise direction.

[0074] Based on the antenna coordinate system S b To the hull coordinate system S a Assuming that the attitude angle of the airship does not change, the target pointed by the radar beam is in the antenna coordinate system S b The coordinates below are P b0 [0 r 0] T According to formula (1), P b0 Transform to the hull coordinate system S a Below

[0075]

[0076] Step S2, based on the conversion relationship between the hull coordinate system before and after the airship attitude changes and the conversion relationship between the antenna coordinate system and the hull coordinate system, combined with the coordinates obtained in step S1, calculate the target pointed by the radar beam in the original antenna coordinate system S after the airship attitude changes. b The coordinates below.

[0077] Step S21: When the attitude angle of the airship changes, the hull coordinate system and the antenna coordinate system also change. Let the hull coordinate system after the attitude angle changes be S a ′-O a 'X a 'Y a ′Z a, the antenna coordinate system is S b ′-O b 'X b 'Y b ′Z b ,like Figure 3 shown.

[0078] Depend on Figure 3 It can be seen that when the attitude angle of the airship changes, the target pointed by the radar beam will also change. P is the target pointed by the radar beam before the attitude angle of the airship changes, and P′ is the target pointed by the radar beam after the attitude angle of the airship changes. Since the relative position of the airship's buoyancy center and the antenna does not change with the change of attitude, and the beam vector does not change, the target P′ is in the airship coordinate system S a ′ and antenna coordinate system S b The coordinates under ′ are

[0079]

[0080] Based on the transformation relationship between the airship coordinate system before and after the airship attitude changes, P a1 Substituting ′(t) into formula (7) we can get the target P′ in the coordinate system S a The coordinate P a1 (t) is

[0081]

[0082] Step S22: P a1 Substituting (t) into formula (9) we can get the target P′ at the original antenna coordinate S b The coordinates below are

[0083]

[0084] Step S3, according to the coordinates P obtained in step 2 b1 (t), combined with the target's coordinates P in the antenna coordinate system when the airship attitude angle does not change b0 The difference between the two can be used to obtain the deviation in radar beam pointing caused by the change in the airship attitude angle, that is, the angle that needs to be compensated.

[0085] Step S31: The error vector caused by the airship attitude angle in the antenna coordinate system is

[0086] [Δx b (t),Δy b (t),Δz b (t)] T =P b1 (t)-P b0 =[x b1 (t),y b1 (t)-r,zb1 (t)] T (19)

[0087] Formula (11) is used to calculate the angles of deviation of the radar beam in azimuth and elevation caused by the change of the airship attitude angle, that is, the angles that need to be compensated are

[0088]

[0089] Using the model data and measured data of attitude angle, when the radar beam pitch angle is 6° and 85° and the rotation speed is 6° / s and 24° / s respectively, the obtained beam angle that needs to be compensated is as follows: Figure 4 、 Figure 5 shown.

[0090] Formula (12) is used to calculate the angles that the radar beam needs to compensate for each CPI in azimuth and elevation directions:

[0091]

[0092] Using the model data and measured data of the attitude angle, when the radar beam pitch angle is 6° and 85° and the rotation speed is 6° / s and 24° / s respectively, the angle that needs to be compensated for each CPI is obtained as follows: Figure 6 、 Figure 7 shown.

[0093] Depend on Figure 5 、 Figure 6 It can be seen that when the airship model data is used for simulation, the compensation angle of each CPI is basically within 0.1°. When the airship measured data is used for simulation, except for the first CPI which requires a larger angle of compensation, the compensation angles of the remaining CPIs are all within 0.05°, which is a small compensation angle. This shows that in actual operation, it is not necessary to compensate for each CPI, and multiple CPIs can be compensated at once.

[0094] Step S32, set the initial compensation period to N = 1, and the angles to be compensated in the azimuth and elevation directions in each compensation period are the calculation results of formula (21), that is,

[0095] d AZ_N=d AZ(t)(t=1,2,3...)

[0096] d EL_N=d EL(t) (t=1,2,3...) (22)

[0097] The servo's response capability (maximum rotation speed) is V max =24° / s, the maximum compensable angle of the servo in one compensation cycle is

[0098] AZ max=V max ×N×CPI=24°×0.033=0.792° (23)

[0099] Step S4: Formulate a compensation strategy as follows:

[0100] S41, determine d AZ_N and d AZ max If d AZ_N>d AZ max , first d AZ max Transmitted to the servo control component to compensate for the beam pointing, the residual error d AZ N -d AZ max Compensation needs to be made in subsequent compensation cycles;

[0101] S42, determine the tracking accuracy of dAZ_N and dEL_N and the beam pointing angle b min =0.2° (the minimum angle that the beam can change each time), if dAZ_N and dEL_N are less than b min (the minimum angle that the beam can change each time), then no compensation is required in this cycle, and the value of N is appropriately increased, and the compensation angle calculation for the next cycle is directly performed;

[0102] S43, if dAZ_N and dEL_N do not belong to the above two cases, that is, greater than or equal to b min , and less than or equal to dAZ max , d AZ_N and d EL_N are transmitted to the radar control component to compensate for the beam pointing.

[0103] S44, judging whether the compensation has been completed. If not, repeat S41 to S43.

[0104] This attitude error compensation method for shipborne weather radar can calculate the angle that needs to be compensated for the radar beam in azimuth and pitch within each CPI after the airship attitude angle changes, and also provides a reasonable compensation strategy.

[0105] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the present invention.

Claims

1. A method for compensating attitude errors of a shipborne weather radar, characterized in that: include: S1, establish the observation geometry of the shipborne weather radar. Based on the conversion relationship between the ship coordinate system and the antenna coordinate system, calculate the coordinates of the target in the ship coordinate system before the attitude change according to the coordinates of the target pointed by the radar beam in the antenna coordinate system; S2, based on the conversion relationship between the hull coordinate system before and after the airship attitude change, and the conversion relationship between the antenna coordinate system and the hull coordinate system, combined with the coordinates of the target in the hull coordinate system before the attitude change obtained in step S1, calculate the coordinates of the target pointed by the radar beam in the original antenna coordinate system after the airship attitude angle changes; S3, calculating the difference between the coordinates obtained in step S2 and the coordinates of the target in the antenna coordinate system when the airship attitude angle does not change, and obtaining the deviation of the radar beam pointing caused by the change in the airship attitude angle as the angle to be compensated; S4, formulate compensation strategy to complete the compensation of posture error.

2. The attitude error compensation method for a shipborne weather radar according to claim 1, wherein: Step S1 includes: Establish the geometric relationship of the shipborne weather radar observation, define the geodetic coordinate system S-OXYZ and the ship body coordinate system S a -O a X a Y a Z a and antenna coordinate system S b -O b X b Y b Z b The three axes of the earth coordinate system are determined according to the airship route direction, the three axes of the hull coordinate system are determined according to the design axis of the hull, and the antenna coordinate system is determined according to the radar beam direction; According to the observation geometry of the shipborne weather radar, the antenna coordinate system S is established. b To the hull coordinate system S a The conversion relationship: Among them, [x a y a z a ] T is the coordinate in the hull coordinate system, [x b y b z b ] T is the coordinate in the antenna coordinate system, α is the radar beam depression angle, θ=θ(t) is the beam azimuth angle that changes with time and is related to the antenna rotation speed and sampling time, R x 、R z is the transformation matrix between the antenna coordinate system and the hull coordinate system. The specific expression is as follows: Assuming that the attitude angle of the airship does not change, the target pointed by the radar beam is in the antenna coordinate system S b The coordinates below are P b0 (x b ,y b ,z b ), according to formula (1), P b0 Transform to the hull coordinate system S a Below is P a0 (t)(x a (t),y a (t),z a (t)).

3. The attitude error compensation method for a shipborne weather radar according to claim 2, wherein: Step S2 includes: S21, when the attitude angle of the airship changes, the hull coordinate system and the antenna coordinate system also change. Let the hull coordinate system after the attitude angle changes be S a ′-O a 'X a 'Y a ′Z a ′, the antenna coordinate system after the attitude angle changes is S b ′-O b 'X b 'Y b ′Z b '; When the attitude angle of the airship changes, the radar beam will point to the new target. Since the relative position of the airship's buoyancy center and the antenna does not change with the attitude angle, and the beam vector does not change, the new target is in the airship coordinate system S a ′ and antenna coordinate system S b The coordinates under ′ are Assume that the roll angle, pitch angle and heading angle of the airship are R, P, and Y respectively, and they change with time t according to the sinusoidal model, that is, Where T R 、T P 、T Y is the attitude angle change period; According to the geometric relationship before and after the change of the attitude angle of the airship, the airship coordinate system S before and after the attitude angle change is established. a and S a ′The coordinate transformation relationship between them is: P a ′(t)=M R M P M Y P a (t) (5) Among them, P a (t) and P a ′(t) are the same target in S a Coordinate system and S a Coordinates in the ′ coordinate system, M R 、M P 、M Y are the conversion matrices of roll angle, pitch angle and heading angle respectively. The specific expressions are as follows: From formula (5), we can get P a (t)=M -Y M -P M -R P a ′(t) (7) Among them, M -R 、M -P 、M -Y M R 、M P 、M Y The inverse matrix of P a1 Substitute ′(t) into formula (7) to obtain the new target pointed by the radar beam in the hull coordinate system S a The coordinate P a1 (t); Step S22, obtain the coordinate system S from the hull by formula (1) a To the antenna coordinate system S b The conversion relationship is: Among them, R x (α) and R x (-α) are inverse matrices, R z (-θ) and R z (θ) are inverse matrices of each other; P a1 Substituting (t) into formula (9) we can get the new target pointed by the radar beam in the antenna coordinate system S b The coordinate P b1 (t)=(x b1 (t),y b1 (t),z b1 (t)).

4. The attitude error compensation method for a shipborne weather radar according to claim 3, wherein: Step S3 includes: S31, the coordinate P obtained in step S2 b1 (t) and P b0 By subtraction, we can obtain the deviation vector caused by the change of the airship attitude angle in the antenna coordinate system S b Below [Δx b (t),Δy b (t),Δz b (t)] T =P b1 (t)-P b0 =[x b1 (t)-x b ,y b1 (t)-y b ,z b1 (t)-z b ] T (10) The angles of deviation of the radar beam in azimuth and elevation caused by the change of the airship attitude angle are: Where r represents the detection range of the radar; By taking the difference of formula (11), we can find the angles that need to be compensated for the radar beam in azimuth and elevation within each CPI, that is, S32, set the initial compensation cycle to N, that is, perform angle compensation every N CPIs, and the angles to be compensated in the azimuth and pitch directions in each compensation cycle are respectively Where n0 is the CPI number at the start of the compensation period.

5. The attitude error compensation method for a shipborne weather radar according to claim 4, wherein: Step S4 includes: Assume that the servo response capability is V max , the V max is the maximum rotation speed, then the maximum adjustable angle of the servo within one compensation cycle is δAZ max =V max ×N×CPI (14) The compensation strategy is formulated as follows: S41, determine δAZ_N and δAZ max The size relationship is, if δAZ_N>δAZ max , first δAZ max Transmitted to the servo control component to compensate for the beam pointing, the residual error δAZ_N-δAZ max Compensation needs to be made in subsequent compensation cycles; S42, determine the tracking accuracy β of δAZ_N and δEL_N and the beam pointing angle min The size relationship of the degree β min is the minimum angle of each beam change, if δAZ_N and δEL_N are less than b min , then no compensation is required in this cycle, and the value of N is appropriately increased to directly calculate the compensation angle for the next cycle; S43, if δAZ_N and δEL_N do not belong to the above two cases, transmit δAZ_N and δEL_N to the radar control component to compensate the beam pointing; S44, judging whether the compensation has been completed. If not, repeat S41, S42, and S43.

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