CN112255606A - Method for calculating front side-view imaging attitude angle of Geo-SAR (synthetic aperture radar) satellite based on single reflector antenna - Google Patents

Abstract

The invention discloses a method for calculating a front side-looking imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna, which comprises the steps of firstly, establishing a model through a satellite-ground geometric relationship, determining a mechanism for generating SAR satellite squint angle formation and offset, carrying out simulation analysis on the squint angle characteristic of a geosynchronous orbit SAR under typical orbit parameters, and then calculating a pitch angle and a roll angle which need to be adjusted by a two-dimensional pitch and roll guidance method and a squint angle value after guidance based on an SAR satellite zero Doppler plane vector analysis algorithm; the pitch and roll two-dimensional attitude guidance algorithm provided by the method can accurately calculate the pitch angle and the roll angle of the satellite to be adjusted, the attitude angle to be adjusted is reduced by at least 1 magnitude compared with a two-dimensional yaw guidance method, and the maneuvering speed of the satellite is improved by at least 1 magnitude.

Description

Method for calculating front side-view imaging attitude angle of Geo-SAR (synthetic aperture radar) satellite based on single reflector antenna

Technical Field

The invention belongs to the technical field of total design of geosynchronous orbit microwave remote sensing satellites, and particularly relates to a method for calculating a front side view imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna.

Background

When the satellite runs in a geosynchronous orbit with six determined orbits, a yaw angle is generated under the influence of the rotation of the earth, a pitch angle is further generated under the action of the eccentricity of the orbit, and satellite beams generate an oblique angle with a constant period under the combined action of the two, wherein the angle can be periodically changed along with the difference of the orbital position of the satellite. In order to realize the forward and side view of the satellite, the radar beam center needs to be corrected to be constantly perpendicular to the heading of the satellite, the distance/azimuth coupling in the received data is reduced, and the data processing difficulty is reduced. The conventional method is to directly compensate the deviated yaw angle and pitch angle by a beam electric switching pointing or satellite attitude control method.

The satellite-borne SAR attitude guidance methods which can be found in the prior published documents are all based on a two-body motion model, and the yaw angle and pitch angle offset of a satellite are calculated through simultaneous vector equations, so that corresponding two-dimensional yaw guidance is carried out. If the SAR satellite is a phased array system SAR satellite, the beam pointing direction can be directly adjusted through a phased array antenna wave control system, and the yaw and pitch offset can be indirectly compensated; in the case of a reflector system SAR satellite, the yaw and pitch attitude of the satellite is adjusted by a satellite control system to directly compensate the yaw and pitch offset. The existing low-orbit SAR satellites in service in orbit adopt the method.

At present, the geosynchronous orbit SAR becomes a research hotspot at home and abroad due to the advantages of high mobility, large breadth and quick revisit. The satellite also faces the problem of yaw angle and pitch angle offset caused by earth rotation and orbital eccentricity, so that the forward and side view imaging control is also required to be completed through attitude guidance to achieve the purpose of forward and side view imaging. The conventional low-orbit SAR satellite two-dimensional yaw guidance technology can be also applied to geosynchronous orbit SAR and achieves the effect of front side view imaging. However, due to the orbital nature of geosynchronous orbit SAR, its yaw angle is typically at least 1 order of magnitude greater than that of low-orbit SAR satellites, and the rate of change of this angle is extremely fast, so new approaches need to be developed to address this problem.

Disclosure of Invention

In view of this, the invention provides a method for calculating a front side-view imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna, which can accurately calculate a pitch angle and a roll angle of the satellite, which need to be adjusted to achieve the front side view.

The technical scheme for realizing the invention is as follows:

a method for calculating a front side-view imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna is characterized in that the yaw angle, the pitch angle and the rolling angle of the satellite are 0, the pitch angle is theta_pitchThe roll angle to be adjusted is theta_roll；

Where H is the satellite altitude, P is the beam center ground landing point for squint, γ is the down-angle, θ is_dIs the ground bevel angle.

Has the advantages that:

the algorithm based on pitching and rolling two-dimensional attitude angle guidance can reduce the attitude adjustment angle of the geosynchronous orbit SAR by 1 order of magnitude, greatly shorten the satellite attitude adjustment time, improve the quick response capability of the satellite, reduce the development difficulty of a satellite control system, save the development cost of the satellite and further bring good social and economic benefits and military benefits.

Drawings

Fig. 1 is a schematic view of the geometrical relationship between yaw and pitch angles and the angle of squint.

Fig. 2 shows squint angle values of geosynchronous orbit SAR without attitude control under 3 typical orbit parameters.

Fig. 3 shows the calculated yaw and pitch angles of the geosynchronous orbit SAR under 3 typical orbit parameters, where (a) is the yaw angle and (b) is the pitch angle.

Fig. 4 shows squint angle values of geosynchronous orbit SAR after two-dimensional yaw steering under 3 typical orbit parameters.

Fig. 5 shows the pitch angle and roll angle of the two-dimensional pitch-roll guidance to be adjusted under 3 typical track parameters, where (a) is the pitch angle and (b) is the roll angle.

Fig. 6 shows squint angle values of geosynchronous orbit SAR after two-dimensional pitch-roll navigation under 3 typical orbit parameters.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

The invention provides a method for calculating a front side view imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna, which can effectively solve the problem of constant front side view imaging of a geosynchronous orbit SAR with a certain orbital eccentricity. According to the method, firstly, a mechanism for generating SAR satellite squint angle formation and offset is determined through satellite-ground geometric relation modeling, squint angle characteristics of a geosynchronous orbit SAR under typical orbit parameters are subjected to simulation analysis, secondly, the simulation analysis is performed on the basis of a traditional two-dimensional yaw guidance algorithm, a calculated yaw angle and pitch angle and a compensated squint angle, and finally, on the basis of an SAR satellite zero Doppler plane vector analysis algorithm, a pitch angle and a roll angle which need to be adjusted by a two-dimensional pitch rolling guidance method and a squint angle value after guidance are calculated. The pitch and roll two-dimensional attitude guidance algorithm provided by the method can accurately calculate the pitch angle and the roll angle of the satellite to be adjusted, the attitude angle to be adjusted is reduced by at least 1 magnitude compared with a two-dimensional yaw guidance method, and the maneuvering speed of the satellite is improved by at least 1 magnitude.

1) Squint angle change rule under condition of geosynchronous orbit SAR no-attitude control

The squint angle of the geosynchronous orbit SAR refers to an included angle between a slant range vector and a zero Doppler plane, is an important parameter for describing beam pointing, is measured in the slant range plane, and is consistent with a yaw angle if projected to the ground surface. In fact, the yaw and pitch angles of the satellite are factors that produce the squint angle, as shown in fig. 1, where S in fig. 1 denotes the satellite position, H is the satellite altitude, and R is the satellite altitude₀Is zero Doppler in-plane slope distance, R_sRepresenting the pitch, P₀Is the beam center ground landing point in the zero Doppler plane, P is the beam center ground landing point under squint condition, θ_yIs the yaw angle, θ_pIs the pitch angle, gamma is the down view angle, theta_rIs a squint angle, θ_drIs a ground bevel angle; it can be seen that the yaw angle causes the beam centerline to rotate about the X-axis, and thus deviate from the zero doppler plane; the elevation angle causes the beam centerline to rotate about the Z axis and thus deviate from the zero doppler plane, both of which together result in an oblique view. Without gesture guidance, there is a periodic inherent squint angle. The squint angle can be expressed as follows from the geometrical relationship shown in fig. 1:

in the formula, Y₀Is P₀And the linear distance between the two points P. Can be obtained by finding P₀And the space coordinates of the two points P, further obtaining Y₀，R₀Is the center slope of the radar, R_sIs the distance between the satellite and the earth's center.

2) Traditional two-dimensional yaw guiding method

According to the geometric relation between the star and the ground, the vector analysis method is utilized for the satellite-borne SAR running in the elliptical orbit, and the yaw angle theta for realizing the front side view in the full orbit period and the full surveying and mapping zone can be calculated and obtained through the derivation of a complex formula_yAnd a pitch angle theta_p. The calculation analysis expression is as follows:

in the formula:

wherein, mu is 3.98696 multiplied by 10¹⁴m³/s²Is the constant of the earth's gravity, [ theta ]_iIs the orbit inclination angle, f is the true paraxial angle, ω is the argument of the perigee_eIs the rotational angular velocity of the earth, a is the orbital semimajor axis, and e is the orbital eccentricity.

The calculation result of the method is also suitable for the geosynchronous orbit SAR, the squint angle value of the geosynchronous orbit SAR under the attitude-free control is simulated in the attached figure 2 under 3 typical orbit parameters, and the orbit parameters are shown in the table 1. And the corresponding yaw angle and pitch angle are compensated by utilizing a two-dimensional yaw guidance technology, so that the oblique angle of the satellite can be zero. Fig. 3(a) and (b) simulate the yaw and pitch angles of geosynchronous orbit SAR that need to be compensated for 3 typical orbital parameters, which are shown in table 1. Fig. 4 simulates squint angle values of geosynchronous orbit SAR after two-dimensional yaw steering under 3 typical orbit parameters, which are shown in table 1.

TABLE 1 geosynchronous orbit SAR satellite orbit parameters

3) Rapid two-dimensional pitching rolling guiding method

According to the satellite-borne SAR imaging mechanism, the fact that the Doppler center value is not zero necessarily means that the beam direction is not in a zero Doppler plane, namely that the radar has a certain squint angle. The squint angle of the SAR satellite refers to an included angle between a slant range vector and a zero Doppler plane, and is defined and measured in the slant range plane. Squint angle if projected onto the earth's surface, the resulting angle is defined as the ground bevel angle. The yaw angle and the pitch angle of the satellite are factors for generating an oblique angle, and the attached figure 1 shows the geometric relationship between the yaw angle and the pitch angle and the oblique angle, so that the oblique angle can be calculated according to the geometric relationship and the offset of the yaw angle and the pitch angle. Meanwhile, if only the pitch angle and the roll angle are adjusted, the method can replace the accurate compensation of the oblique angle caused by the offset of the yaw angle and the pitch angle, so that the oblique angle returns to zero, and the front side view is achieved. This is the core idea of two-dimensional pitch-roll attitude guidance.

By using the method, the angles of the three axes of the satellite to be adjusted are respectively as follows:

1. the yaw angle is always 0 and no adjustment is made.

2. The pitch guide angle calculation method comprises the following steps:

3. the rolling guide angle calculation method comprises the following steps:

where γ is the down viewing angle, θ_dIs the declination angle, H is the satellite altitude, and P is the beam center ground landing point under squint.

Based on the two-dimensional pitch and roll guidance algorithm provided by the invention, the pitch angle and the roll angle of the two-dimensional pitch and roll guidance which need to be adjusted under 3 typical track parameters are calculated, the track parameters are shown in table 1, and the results are shown in fig. 5(a) and (b). Further, the squint angle value of the geosynchronous orbit SAR after the two-dimensional pitching rolling guidance is calculated, the orbit parameters are shown in the table 1, and the result is shown in the figure 6.

In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (1)

1. A method for calculating a front side-view imaging attitude angle of a Geo-SAR satellite based on a single reflector antenna is characterized in that the yaw angle of the satellite, the pitch angle of the satellite and the roll angle of the satellite which need to be adjusted are 0 and theta_pitchThe roll angle to be adjusted is theta_roll；

Where H is the satellite altitude, P is the beam center ground landing point for squint, γ is the down-angle, θ is_dIs the ground bevel angle.

Images