CN106124170A - A kind of camera optical axis based on high-precision attitude information points to computational methods - Google Patents

Abstract

The present invention provides a kind of camera optical axis based on high-precision attitude information to point to computational methods, according to scanning camera optical axis in the { sensing under b} of satellite body systemAnd satellite body coordinate system { b} relative orbit coordinate system { the transition matrix A of o}_bo, calculate the sensing under camera optical axis road coordinate system in-orbitBy{ o} is relative to geocentric inertial coordinate system { the transition matrix A of i} with satellite orbit coordinate system_oi, calculate camera optical axis in the geocentric inertial coordinate system { sensing of i}ByAnd geocentric inertial coordinate system { transition matrix (HG) that i} relative to ground is admittedly, calculating camera optical axis sensing under ground is admittedlyThe calculation of the present invention can be by the real-time calculating in ground and revise optical axis and point to, also can in advance by the track on ground, be admittedly information be stored on star by star in real time from host computer and revise optical axis and point to, by calculation briefly above, the imaging capability of satellite can be improved.

Description

Camera optical axis direction calculation method based on high-precision attitude information

Technical Field

The invention relates to a satellite optical axis pointing technology, in particular to a camera optical axis pointing calculation method based on high-precision attitude information.

Background

In order to make a remote sensing instrument have high ground resolution and a large observation range, a motion scanning mirror is often adopted to make a remote sensing camera capable of observing ground targets at different positions in detail.

IMAGER of a scanning IMAGER installed on the United states GOES-I/M satellite adopts a swing mirror east-west scanning mode. TM (subject mapper) on Landsat-4, 5 satellites in usa is a swept multispectral scanning radiometer. The HRG (high resolution geometry) camera on the SPOT-5 French satellite obtains the observation capability of an oblique viewing angle by using a directional mirror mechanism, and the maximum side viewing angle is 27 degrees. A scanning radiometer carried by a first generation polar orbit meteorological satellite FY-1 (Fengyun I) in China adopts a 45-degree rotating reflector scanning mode. An infrared multispectral scanner (IRMSS) carried by a Zhongba earth resource satellite (CBERS) also adopts a scanning mode of a swinging scanning mirror, so that the scanning efficiency is improved.

However, the use of the scanning mirror brings new influences to the imaging process of the remote sensing camera, and the high-precision optical axis pointing information of the camera is usually difficult to obtain accurately under the influence of factors such as earth orbit thermal deformation, platform control errors, scanning mechanism pointing deviation and the like, so that how to obtain the optical axis pointing efficiently by using the existing information is a problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a camera optical axis direction calculation method based on high-precision attitude information, which can simply and effectively acquire the optical axis direction of a camera and improve the imaging capability of a satellite.

In order to achieve the above object, the present invention provides a camera optical axis direction calculation method based on high-precision attitude information, which is implemented by the following steps, wherein the calculation time in each step takes the camera exposure time as a reference point:

1) calculating the pointing direction of the optical axis of the scanning camera under the system { b } of the satellite

During calculation, the direction of the optical axis of the camera is obtained according to the exposure time and the rotation angle measurement information of the camera in satellite downloading, and meanwhile, the initial installation deviation angle of the camera is considered in the calculation process.

2) Calculating a conversion matrix A of a satellite body coordinate system { b } relative to an orbit coordinate system { o }_bo；

And during calculation, the high-precision attitude measurement information is obtained by satellite time transmitted by a satellite and the high-precision attitude measurement information obtained by a control system. Therefore, a high-precision attitude angle and attitude angular velocity information are obtained by a combined high-precision attitude determination method of the star sensor and the gyroscope; and meanwhile, considering that the exposure time of the camera is deviated from the attitude time calculated by the onboard control system, the exposure time difference is compensated by recursion of the attitude angle and the angular speed.

3) Calculating the pointing direction of the optical axis of the camera in the orbital coordinate systemCalculated from 1) and 2)And A_boTo obtain

4) Calculating a conversion matrix A of a satellite orbit coordinate system (o) relative to a geocentric inertial coordinate system (i)_oi；

And obtaining the satellite position and the velocity vector of the camera at the exposure time according to the satellite orbit data information measured and controlled on the ground, and calculating the attitude transformation matrix between the orbit system and the geocentric inertial system.

5) Calculating the direction of the optical axis of the camera in the geocentric inertial coordinate system (i)Calculated from 3) and 4)And A_oiTo obtain

6) Calculating a conversion matrix (HG) of the geocentric inertial coordinate system { i } relative to the earth-fixed system;

during calculation, the influences of nutation, precision and autorotation are considered according to the IAU2000 specification, and the J2000 coordinate system is converted into the earth fixed coordinate system WGS-84.

7) Calculating the orientation of the optical axis of the camera in the earth's fixation systemCalculated from 5) and 6)And (HG) to obtain

Compared with the prior art, its advantage and beneficial effect are:

1) the method comprises the steps that the optical axis direction of a camera is simply and effectively obtained through an algorithm by utilizing the existing exposure time, corner measurement information and high-precision attitude information of the camera on the satellite in combination with the track information and the ground fixation information of the ground;

2) the calculation method can calculate and correct the optical axis direction in real time on the ground, can also store the orbit and the earth fixation information of the ground on the satellite in advance, and can automatically calculate and correct the optical axis direction in real time on the satellite, and can improve the imaging capability of the satellite through a simple calculation mode.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings:

fig. 1 is a flowchart of a method for calculating an optical axis direction of a camera based on high-precision posture information according to an embodiment of the present invention.

Detailed Description

The present invention will be described in more detail below with reference to the accompanying drawings, which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

As shown in fig. 1, the method for calculating the direction of the optical axis of the camera based on the high-precision posture information provided by the present invention includes the following steps:

1. calculating the pointing direction of the optical axis of the scanning camera under the system { b } of the satellite

Using camera detector centre point r_smFor input of signals by deducing r_smThe output light ray r under the camera main body coordinate system (consistent with the measurement coordinate system) is obtained through scanning rotation_xjBy r_xjTo describe the relationship between the camera rotation angle measurement information and the optical axis orientation:

r_sm＝(0 0 1)^T

r_xj＝A_zd ^T·R_x(α_xj)^T·N_z·R_x(α_xj)·A_zd·r_sm

wherein A is_zdConversion matrix of the measurement coordinate system for camera imaging to the camera rotation axis coordinate system, α_xjFor an angle of rotation about an axis of rotation, R_xRepresenting a rotation matrix, N, around the x-axis_zA polarity matrix scanned by the camera.

During the satellite final assembly process, the reference value of the camera is inconsistent with the theoretical value due to the installation of the camera and the like, and the reference deviation matrix delta A is determined through installation measurement_smActual pointing under { b }Comprises the following steps:

$r_{xj}^b={\mathrm{\ΔA}}_{sm}{r}_{xj}$

2. calculating a conversion matrix A of a satellite body coordinate system { b } relative to an orbit coordinate system { o }_bo

The method comprises the following steps of obtaining high-precision attitude angle and attitude angular velocity information through a combined high-precision attitude determination method of a star sensor and a gyroscope, considering that the exposure time of a camera has deviation from the attitude time calculated by an on-satellite control system, compensating the exposure time difference in a mode of recursion of the attitude angle and the angular velocity, taking a rolling axis as an example:

wherein,represents t_kThe angle of the roll at the moment in time,represents t_kRoll angular velocity at a moment; k is a sequence.

In the above manner, it is possible to obtainRespectively represent a rolling angle, a pitching angle and a yawing angle, and then the direction cosine array of the satellite body under the orbit system can be represented as:

R_yrepresenting a rotation matrix, R, about the y-axis_zRepresenting a rotation matrix rotating about the z-axis.

3. Calculating the pointing direction of the optical axis of the camera in the orbital coordinate system

From step 1 and step 2, the optical axis orientation of the camera under the orbital system can be obtained:

$r_{xj}^o=A_{bo}^T{r}_{xj}^b$

4. calculating a conversion matrix A of a satellite orbit coordinate system (o) relative to a geocentric inertial coordinate system (i)_oi

Camera exposure time t_xjAt that time, the position of the satellite r ═ r (r)_x,r_y,r_z)^TAnd velocity v ═ v (v)_x,v_y,v_z)^TAnd calculating an attitude transformation matrix according to the position and speed vectors:

$A_{oi}\left(3\right)=-\frac{r}{\left|r\right|}$

$A_{oi}\left(2\right)=-\frac{r\×v}{|r\×v|}$

A_oi(1)＝A_oi(2)×A_oi(3)

A_oi＝[A_oi(1) A_oi(2) A_oi(3)]^T

5. calculating the direction of the optical axis of the camera in the geocentric inertial coordinate system (i)

From step 3 and step 4, the optical axis orientation of the camera in the geocentric inertial system can be obtained:

$r_{xj}^i=A_{oi}^T{r}_{xj}^o=A_{oi}^T{A}_{bo}^T{r}_{xj}^b$

6. calculating a transformation matrix (HG) of the centroid inertial frame { i } relative to the earth-fixed frame

From the definition of the earth-fixed system, the earth-fixed system is related to the equatorial plateau, while the epoch J2000 inertial system is related to the equatorial plateau and the ecliptic plateau only. When considering the relationship between the earth fixed system and the inertial system, the following aspects need to be considered:

1. a change in instantaneous polar relative to the inertial system (J2000);

2. and (4) instantaneous pole rotation.

1) Variation of instantaneous polar of sky relative to the inertial system (J2000)

Due to the gravitational effect of the sun and the moon on the non-spherical part of the earth, the earth rotation shaft swings in space, so that the instantaneous poles of the earth have changes relative to an inertia system, mainly, the moments are time-dependent and nutation.

Three equatorial age parameters ζ converted between the equatorial coordinate systems of standard epoch J2000.0 to the computational epoch_A,z_A,θ_AThe derived age matrix is represented as:

(PR)＝R_z(-z_A)R_y(θ_A)R_z(-ζ_A)

the yellow meridian nutation delta phi, the intersection angle nutation delta and the intersection angle of an instantaneous flat equatorial plane and a ecliptic plane of an IAU2000 nutation model_AA nutation matrix is obtained:

(NR)＝R_x(-Δ)R_y(Δθ)R_z(-Δμ)

wherein Δ μ ═ Δ ψ cos_A,Δθ＝Δψsin_AIt is the declination and the right ascension nutation.

2) Autorotation of instantaneous celestial pole

The calculation of the earth rotation matrix ER (t) involves Greenwich mean time of constancy GAST at time t, i.e.

(ER)＝R_z(GAST)

In summary, the transformation relationship between the earth-centered inertial coordinate system (J2000) and the earth-fixed system (WGS84) coordinate system can be expressed as follows:

(HG)＝(ER)(NR)(PR)

7. calculating the orientation of the optical axis of the camera in the earth's fixation system

From step 5 and step 6, the optical axis orientation of the camera in the earth fixation system can be obtained:

$r_{xj}^e=\left(HG\right)r_{xj}^i=\left(HG\right)A_{oi}^T{r}_{xj}^o=\left(HG\right)A_{oi}^T{A}_{bo}^T{r}_{xj}^b$

according to the camera optical axis direction calculation method based on the high-precision attitude information, the optical axis direction of the camera is simply and effectively obtained through an algorithm by utilizing the existing camera exposure time, the rotation angle measurement information and the high-precision attitude information on the satellite in combination with the track information and the ground fixation information on the ground under the condition that redundant information and redundant working conditions are not increased. The calculation method can calculate and correct the optical axis direction in real time on the ground, can also store the orbit and the earth fixation information of the ground on the satellite in advance, and can automatically calculate and correct the optical axis direction in real time on the satellite, and can improve the imaging capability of the satellite through a simple calculation mode.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof.

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.

Claims (5)

1. A camera optical axis direction calculation method based on high-precision attitude information is characterized in that,

according to the orientation of the optical axis of the scanning camera under the system { b } of the satelliteAnd a transformation matrix A of the satellite body coordinate system b relative to the orbit coordinate system o_boTo calculate the pointing direction of the optical axis of the camera in the orbital coordinate system

$r_{xj}^o=A_{bo}^T{r}_{xj}^b$

According to the obtained directionAnd a transformation matrix A of the satellite orbit coordinate system { o } relative to the earth center inertial coordinate system { i }_oiTo calculate the direction of the optical axis of the camera in the centroid inertial coordinate system { i }

$r_{xj}^i=A_{oi}^T{r}_{xj}^o=A_{oi}^T{A}_{bo}^T{r}_{xj}^b$

According to the obtained directionAnd a conversion matrix (HG) of the centroid inertial coordinate system { i } relative to the earth-fixed system, and calculating the orientation of the camera optical axis in the earth-fixed system

$r_{xj}^e=\left(HG\right)r_{xj}^i=\left(HG\right)A_{oi}^T{r}_{xj}^o=\left(HG\right)A_{oi}^T{A}_{bo}^T{r}_{xj}^b.$

2. The method as claimed in claim 1, wherein the camera optical axis direction is obtained from the exposure time and rotation angle measurement information of the camera in the satellite download, and the initial installation deviation of the camera is used as the basisCorrecting the angle to obtain the direction

r_sm＝(0 0 1)^T

r_xj＝A_zd ^T·R_x(α_xj)^T·N_z·R_x(α_xj)·A_zd·r_sm

$r_{xj}^b={\mathrm{\ΔA}}_{sm}{r}_{xj}$

Wherein r is_smThe central point of the camera detector is used as signal input; by deducing the center point r of the camera detector_smObtaining the output light r under the camera main body coordinate system through scanning rotation_xjDescribing the relationship between the camera rotation angle measurement information and the optical axis direction;

A_zdconversion matrix, R, for the camera imaging measurement coordinate system to the camera rotation axis coordinate system_xRepresenting a rotation matrix rotating about the x-axis, α_xjFor an angle of rotation about an axis of rotation, N_zA polarity matrix scanned for the camera; delta A_smThe reference deviation matrix for the camera installation is measured at the time of satellite final assembly.

3. The method as claimed in claim 1, wherein the conversion matrix a is obtained by compensating the exposure time difference by recursion of the attitude angle and the attitude angular velocity for the deviation between the camera exposure time and the attitude time calculated by the satellite control system according to the satellite time downloaded from the satellite and the attitude measurement information obtained by the satellite control system_bo：

$\mathrm{\θ}\left(t_{xj}\right)=\mathrm{\θ}\left(t_k\right)+\stackrel{\·}{\mathrm{\θ}}\left(t_k\right)(t_{xj}-t_k)$

$\mathrm{\ψ}\left(t_{xj}\right)=\mathrm{\ψ}\left(t_k\right)+\stackrel{\·}{\mathrm{\ψ}}\left(t_k\right)(t_{xj}-t_k)$

Wherein, t_xjIs the camera exposure time, t_k-1＜t_xj≤t_k；

θ(t_k)、ψ(t_k) Respectively represent t_kThe roll angle, pitch angle, yaw angle at the moment,respectively represent t_kRoll angular velocity, pitch angular velocity, yaw angular velocity at that moment; r_yRepresenting a rotation matrix, R, about the y-axis_zRepresenting a rotation matrix rotating about the z-axis.

4. The method as claimed in claim 1, wherein the position r of the satellite is obtained from the satellite orbit data information measured and controlled on the ground at the exposure time of the camera (r ═ r)_x,r_y,r_z)^TAnd velocity v ═ v (v)_x,v_y,v_z)^TCalculating a transformation matrix A from the position vector and the velocity vector_oi：

$A_{oi}\left(3\right)=-\frac{r}{\left|r\right|}$

$A_{oi}\left(2\right)=-\frac{r\×v}{|r\×v|}$

A_oi(1)＝A_oi(2)×A_oi(3)

A_oi＝[A_oi(1) A_oi(2) A_oi(3)]^T。

5. The method for calculating the pointing direction of the optical axis of the camera based on the high-precision attitude information as claimed in claim 1, wherein the geocentric inertial coordinate system J2000 is converted into the earth fixed coordinate system WGS84 based on the time offset, nutation and rotation matrix of the IAU2000 specification:

the age matrix is represented as:

(PR)＝R_z(-z_A)R_y(θ_A)R_z(-ζ_A)

therein, ζ_A,z_A,θ_AThree equatorial age parameters converted from the geocentric inertial coordinate system J2000.0 of the standard epoch to the equatorial coordinate system of the calculation epoch;

the nutation matrix is represented as:

(NR)＝R_x(-Δ)R_y(Δθ)R_z(-Δμ)

wherein, Δ μ ═ Δ ψ cos_A,Δθ＝Δψsin_ANutation of right ascension and declination, respectively; the yellow meridian nutation delta phi, the intersection angle nutation delta and the intersection angle of an instantaneous flat equatorial plane and a ecliptic plane of an IAU2000 nutation model_A；

The earth rotation matrix er (t) is represented as:

(ER)＝R_z(GAST)

GAST is Greenwich mean time of constancy at time t;

determining a transformation matrix (HG):

(HG)＝(ER)(NR)(PR)。