CN104462776B - A kind of low orbit earth observation satellite is to moon absolute radiation calibration method - Google Patents

A kind of low orbit earth observation satellite is to moon absolute radiation calibration method Download PDF

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CN104462776B
CN104462776B CN201410637920.4A CN201410637920A CN104462776B CN 104462776 B CN104462776 B CN 104462776B CN 201410637920 A CN201410637920 A CN 201410637920A CN 104462776 B CN104462776 B CN 104462776B
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moon
satellite
time
imaging
angle
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CN104462776A (en
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满益云
李海超
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中国空间技术研究院
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Abstract

A kind of low orbit earth observation satellite comprises the following steps to moon absolute radiation calibration method:Primarily determine that low orbit earth observation satellite can observe the time of the moon using Satellite Tool Kit;It is determined that between at the beginning of being imaged to the moon, the end time, the camera exposure time, imaging when attitude of satellite angle, rate of pitch etc.;Lunar map picture is obtained to moon imaging according to above-mentioned parameter;Lunar map picture is analyzed using ROLO absolute radiometric calibrations model, Absolute Radiometric Calibration Coefficients are obtained.The inventive method does not need onboard process device and travelling mechanism, without special ground calibration source is laid, and makes full use of the attitude maneuver ability of the long-time stability and satellite itself of the moon to obtain lunar map picture as reference source.

Description

A kind of low orbit earth observation satellite is to moon absolute radiation calibration method

Technical field

The present invention relates to a kind of Calibration Method, particularly a kind of low orbit earth observation satellite is to moon absolute radiation Calibrating method, belongs to remote sensing satellite calibration technology field.

Background technology

Larger degeneration can occur for the in-orbit radiance of Optical remote satellite, and quantification remote sensing application is fixed to absolute radiation Target precision and stability proposes strict demand.At present, the calibration based on onboard process device and ground calibration is conventional In-orbit absolute radiation calibration method.1) calibration of onboard process device is main includes the calibration of calibration lamp, the calibration of sun diffusing panel etc. Mode, but influenceed by outer space radiation environment, the own optical of scaling system, electronics and mechanical structure, performance is at any time Between can decay, influence calibration precision.2) ground calibration radiometric calibration site mainly lays target using ground, is the most frequently used at present Absolute radiation calibration method, but this method needs synchro measure atmospheric parameter, is influenceed seriously by weather, efficiency is low, cost is high, Complex operation.

The moon is as the celestial body nearest apart from the earth, and menology has fabulous reflectivity long-time stability, spectral response The exclusive advantages such as the unicity of the empty background of uniformity, surrounding deep cooling;Meanwhile, moon In-flight calibration can effectively avoid air and do Disturb, without developing special on-board equipment, have repeatedly similar geometry observation condition every month, have become in the world over the ground One of observation optical remote sensing satellite target Main Means, the stability for the in-orbit radiation quality of long term monitoring.Utilize the moon The advantage for carrying out Optical remote satellite In-flight calibration is:1. as the natural reflector of solar radiation, the stabilization of its reflectivity Property be better than 10-8/ year;2. moon brightness sharpness of border, is around deep cooling empty background and fixed star point target etc., red in visible ray shortwave Outer spectral coverage stray radiation very little;3. the moon itself reflectance spectrum is flat, without obvious reflection peak or absorption paddy, it is seen that spectrum segment Reflectivity it is similar to the reflection characteristic on land under the conditions of fair weather and ocean;4. the moon is without air, and calibration process is relatively simple Change, there is the observation airplane meeting of many days every month, and with similar observation geometrical property.

Because with above many advantages, to meet the demand of high stability quantification application, the moon has become the world One of main standard reference source of upper earth observation remote sensing satellite calibration, moon In-flight calibration is to solve current remote sensing image The important means of data quantitativeization application.Since 1997, United States Geological Survey (USGS) just carried out the moon from in-motion viewing Survey project (ROLO), establishes the ROLO absolute radiometric calibration models of moon brightness.It is existing a great deal of since ROLO models Satellite carry out radiation calibration and radiance monitoring using the moon, the MISR of such as low orbit satellite, MERIS, ASTER, MODIS, MSG/SEVIRI of SeaWIFS, VIIRS, ALI, HYPERION and Pleiades etc. and geostationary satellite etc., they are main Utilize the radiance difference between moon radiation calibration model monitoring different loads, the long-term decay of instrument radiance, spectral coverage The exhausted degree radiation information of radiation difference and instrument between spectral coverage, the calibration of effective guarantee satellite in orbit businessization should With.

The content of the invention

The technology of the present invention solves problem:The deficiencies in the prior art are overcome to be defended there is provided a kind of low orbit earth observation Star to moon absolute radiation calibration method, do not use onboard process equipment, have substantially no effect on imaging task, as far as possible without or On the premise of using ground calibration less, the attitude maneuver imaging capability of satellite itself is taken full advantage of, is the whole phase in orbit Between the radiation calibration lunar data of High-precision high-frequency time is provided, meet the leap of low orbit earth observation satellite quantification application Formula develops.

The present invention technical solution be:A kind of low orbit earth observation satellite to moon absolute radiation calibration method, Step is as follows:

(1) determine that low orbit earth observation satellite can observe the time of the moon using Satellite Tool Kit, using defending Star tool software, which is obtained, can observe the attitude of satellite angle corresponding to the time of the moon, and calculating can observe the time of the moon Corresponding moon phase angle, further according to the attitude maneuver ability of satellite, is selected to the moon from the time that can observe the moon Ball imaging time, performs step (2);

The attitude maneuver ability refers to satellite pitching angle theta, roll angle Φ and yaw angleMaximum maneuvering range, to the moon The pose adjustment size of satellite must be within the attitude maneuver limit of power of satellite when ball is imaged;The moon phase angle is met The moon phase angular region selected in ROLO moon absolute radiometric calibration models, the model is:[1.55 °, 97 °];

(2) it is selected to moon imaging time according to step (1), mould is imaged to the moon it is determined that being transferred to from imaging pattern over the ground To the moon between at the beginning of formula, from the end time of imaging pattern over the ground and satellite linear array CCD camera is transferred to moon imaging pattern The imaging frequency n of push-scanning image, and the Satellite Camera time for exposure t that determination is imaged every timem, imaging initial time, imaging terminate Time, attitude of satellite angle, satellite rate of pitch d θm;When the attitude of satellite angle being imaged every time includes imaging starting every time Carve attitude angle, intermediate time attitude angle and finish time attitude angle;The attitude angle includes the angle of pitch, roll angle and yaw angle, The satellite linear array CCD camera is equal to moon push-scanning image number of times, the imaging initial time being imaged every time and imaging end time It is previously given;

(3) when earth observation satellite, the time reaches being transferred to pair from imaging pattern over the ground of being determined in step (2) in orbit When between at the beginning of month imaging pattern, satellite enters attitude maneuver pattern, and satellite is according to the attitude of satellite angle of determination in step (2) It is adjusted, is transferred to by imaging pattern over the ground to moon imaging pattern;

(4) when the time reaches the first time imaging initial time determined in step (2) to earth observation satellite in orbit, The linear array CCD camera of earth observation satellite according in step (2) determine each imaging Satellite Camera time for exposure tmStart The moon is imaged, lunar map picture is obtained, if the imaging frequency n to moon push-scanning image is more than 1, step (5) is performed, otherwise holds Row step (6);

(5) according to the Satellite Camera time for exposure t of each imaging determined in step (2)m, imaging initial time, imaging End time and attitude of satellite angle, complete all to moon push-scanning image according to the method in step (4), obtain all moons Ball image, into step (6);

(6) complete to moon push-scanning image, earth observation satellite enters attitude maneuver pattern, is transferred to moon imaging pattern Imaging pattern over the ground;

(7) all lunar map pictures obtained in step (6) are handled using ROLO absolute radiometric calibrations model, obtained Absolute Radiometric Calibration Coefficients.

The Satellite Camera time for exposure t being imaged every time is determined in the step (2)m, specifically realized by following steps:

(2a) calculates projection linear velocity v of the satellite in moonscapem, specifically by formula:

Provide, wherein, μ is Gravitational coefficient of the Earth, ReFor earth radius, H is the orbit altitude of satellite transit;RemFor the earth Center is to the distance of moon ball center, RmFor the moon radius of a ball;

(2b) calculates projected size GIFOV of each pixel on the moon in satellite linear array CCD cameram, specifically by formula:

Provide, wherein, p is the size of each pixel in satellite linear array CCD camera, and f is the focal length of Satellite Camera;

The satellite linear array of (2c) using the satellite in step (2a) in the projection linear velocity and step (2b) of moonscape Each projected size of the pixel on the moon in CCD camera, calculates the Satellite Camera time for exposure being imaged every time, specifically by public affairs Formula:

Provide.

Intermediate time attitude angle in the step (2), is realized by following steps:

Imaging initial time and imaging end time that (3a) is imaged every time according to satellite previously given in step (2), Calculating obtains the imaging intermediate time that satellite is imaged every time, further determines what is be imaged every time according to satellite orbit and moon ephemeris It is imaged the position vector between intermediate time satellite and the moon

Position vector between the imaging intermediate time satellite and the moon of (3b) in step (3a), it is calculated as in Between the moment pitching angle thetamid, roll angle ΦmidAnd yaw angleIt is imaged the pitching angle theta of intermediate timemidSpecifically by formula:

It is imaged the roll angle Φ of intermediate timemidSpecifically by formula:

Provide, wherein, r1For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate system Bx Projected size on direction of principal axis, r3For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate system BzProjected size on direction of principal axis;r2For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate It is ByProjected size on direction of principal axis;Wherein, satellite orbit coordinate system Bo-BxByBzOrigin BoIn orbit, BxAxle is pointed to and defended Star direction of advance, BzAxle points to the earth's core, B by centroid of satelliteyAxle is perpendicular to by BxWith BzThe orbit plane that axle is constituted;

The yaw angleIt is constant in imaging process, and be 0.

Step (2) the Satellite posture rate of pitch d θm, detailed process is as follows:

If satellite linear array CCD camera realizes that square sample is imaged by adjusting posture rate of pitch, the attitude of satellite Rate of pitch d θmBy formula:

Provide, wherein, μ is Gravitational coefficient of the Earth, ReFor earth radius, H is the orbit altitude of satellite transit;RemFor the earth Center is to the distance of moon ball center, RmFor the moon radius of a ball;

Otherwise, attitude of satellite rate of pitch d θmIt is zero.

Initial time attitude angle and finish time attitude angle in the step (2), specific calculating process are as follows:

Initial time pitching angle thetastartBy formula:

Provide, wherein, t is the difference between imaging end time in each imaging process and imaging initial time;

Initial time roll angle ΦstartBy formula:

Φstartmid

Provide,

Finish time pitching angle thetaendBy formula:

Provide,

Finish time roll angle ΦendBy formula:

Φendmid

Provide.

Determine in the step (2) to be transferred to being imaged between at the beginning of moon imaging pattern, to the moon from imaging pattern over the ground Pattern is transferred to the end time of imaging pattern over the ground, is specially:

From imaging pattern over the ground be transferred to between at the beginning of moon imaging pattern by formula:

tstart=tstart1-t′

Provide, wherein, tstartIt is transferred to for imaging pattern over the ground between at the beginning of moon imaging pattern, tstart1For for the first time The initial time being imaged to the moon, t ' is transferred to the attitude maneuver time to moon imaging pattern for imaging pattern over the ground, specifically by formula:

Provide, wherein twFor attitude stabilization time, θstart1The angle of pitch of initial time, θ are imaged to the moon for first time0To be right The angle of pitch of ground imaging, d θ are satellite rate of pitch, Φstart1The roll angle of initial time, Φ are imaged to the moon for first time0 For the roll angle being imaged over the ground, d Φ satellite rate of roll;

From the end time of imaging pattern over the ground is transferred to moon imaging pattern by formula:

tend=tendn+t″

Provide, wherein, tendTo be transferred to the end time of imaging pattern over the ground, t to moon imaging patternendnIt is n-th to the moon The end time of imaging, t " is the attitude maneuver time that imaging pattern over the ground is transferred to moon imaging pattern, specifically by formula:

Provide, wherein t 'wFor attitude stabilization time, θendnThe angle of pitch of finish time, θ are imaged to the moon for n-th1To be right The angle of pitch of ground imaging, d θ are satellite rate of pitch, ΦendnThe roll angle of finish time, Φ are imaged to the moon for n-th1To be right The roll angle of ground imaging, d Φ satellite rate of roll.

The present invention has the beneficial effect that compared with prior art:

(1) present invention is using absolute radiometric calibration source of the moon as remote sensing satellite, and the moon possesses the long-term steady of reference source It is qualitative, robot scaling equipment and travelling mechanism are not needed on star, is denoted as reference source, saving without special land-based target is laid Calibrate cost;

(2) present invention is directed to low orbit Optical remote satellite, on the premise of reliability and security is ensured, makes full use of The attitude maneuver ability of satellite realizes that satellite is to the moon high-quality and is scaled to picture, and to the moon imaging process when star sensor not When available, the required precision of other replacement sensors is given;

(3) present invention proposes on the one hand to can be achieved many repeatedly to moon push-scanning image in a satellite imagery task Piece CCD obtains lunar map picture respectively, and on the other hand the achievable multiple push-scanning image with a piece of CCD sets up camera as input Non-linear absolute radiometric calibration model.

Brief description of the drawings

Fig. 1 is a kind of flow chart of the low orbit earth observation satellite of the invention to moon absolute radiation calibration method;

Fig. 2 is the moon phase angle schematic diagram between the sun of the present invention, the moon, satellite;

Fig. 3 (a) is the schematic diagram of square sample grid, and Fig. 3 (b) is the rectangularly-sampled to the moon from common line array CCD As a result the schematic diagram of square sample is transformed to;

Fig. 4 is the position and posture relation schematic diagram that LEOS Low Earth Orbiting Satellite of the present invention is imaged to the moon;

Fig. 5 is multiple push-scanning image schematic diagram of the LEOS Low Earth Orbiting Satellite of the present invention to moon imaging task;

Fig. 6 is of the invention at 0.0035196 second time of integration, and MTF, which declines, is no more than 10% constraints, in difference Integration series under, to it is other replacement sensors attitude accuracies requirement;

Fig. 7 is of the invention at 0.00036259 second time of integration, and MTF, which declines, is no more than 10% constraints, not Under same integration series, the requirement to the attitude accuracies of other replacement sensors;

Embodiment

A kind of low orbit earth observation satellite is to moon absolute radiation calibration method, specific steps as shown in figure 1, this method Realized by following steps:

1st, determine that low orbit earth observation satellite can observe the time of the moon using Satellite Tool Kit STK, utilize Satellite Tool Kit, which is obtained, can observe the attitude of satellite angle corresponding to the time of the moon, calculate can observe the moon when Between corresponding moon phase angle, further according to the attitude maneuver ability of satellite, the selection pair from the time that can observe the moon Moon imaging time, performs step 2;

The attitude maneuver ability refers to satellite pitching angle theta, roll angle Φ and yaw angleMaximum maneuvering range, to the moon The pose adjustment size of satellite must be within the attitude maneuver limit of power of satellite when ball is imaged.

The moon is observed in Space Remote Sensors, the spoke brightness of the moon is continually changing, the earth, the sun, the track of moon three Be continually changing, cause life distance, the moon distance change, the radiant illumination that the moon is subject to changes, observed from satellite Spoke brightness value also in change, whole lunar surface when the phase angle variations of the moon and the optical libration of the moon are the influence observation moon The principal element of radiance.

It is exhausted that moon phase angle corresponding to the date and time of selected moon imaging plan should meet the ROLO moon To the demand of radiation calibration model, the moon phase angle range selected in ROLO databases is [1.55 °, 97 °].As shown in Fig. 2 the moon The definition at phase angle is the angle between the sun-moon-satellite.

2nd, it is selected to moon imaging time according to step 1, it is determined that being transferred to from imaging pattern over the ground to moon imaging pattern At the beginning of between, from being transferred to the end time of imaging pattern over the ground to moon imaging pattern and satellite linear array CCD camera is pushed away to the moon Sweep the imaging frequency n of imaging, and the Satellite Camera time for exposure t that determination is imaged every timem, imaging initial time, imaging at the end of Between, attitude of satellite angle, satellite rate of pitch d θm;The attitude of satellite angle being imaged every time includes imaging initial time every time Attitude angle, intermediate time attitude angle and finish time attitude angle;The attitude angle includes the angle of pitch, roll angle and yaw angle, institute State satellite linear array CCD camera pre- to moon push-scanning image number of times, the imaging initial time being imaged every time and imaging end time First give.

For linear TDI CCD, synchronism is imaged to meet it, the square sample imaging to the moon, Ke Yitong is realized The time of integration or adjustment measuring satellite angular velocities for crossing adjustment TDI cameras are realized to be imaged to the square sample of the moon.And for Common line array CCD, upon exposure between it is non-adjustable when, satellite can sweep speed the moon is imaged according to conventional push away, then using weight Sampling processing obtains the square sample to the moon, can also be by adjusting square of the measuring satellite angular velocities realization to the moon Sampling imaging;Between upon exposure can timing can also be realized by adjusting the time for exposure of linear array CCD camera to the pros of the moon Shape sampling imaging.

2.1st, the Satellite Camera time for exposure t being imaged every time is determinedm, specifically realized by following steps:

(1) projection linear velocity v of the satellite in moonscape is calculatedm

According to two-particle systems rule, satellite rings using the earth as barycenter around angular speed be:

Wherein μ is Gravitational coefficient of the Earth, ReFor earth radius, H is the orbit altitude of satellite transit

Projection linear velocity at the earth's surface is:

It is in the projection linear velocity of moonscape:

Wherein, RemFor earth center to the distance of moon ball center, RmFor the moon radius of a ball.

(2) projected size GIFOV of each pixel on the moon in satellite linear array CCD camera is calculatedm

Each the projected size of pixel on earth is:

Wherein, p is the size of each pixel in satellite linear array CCD camera, and f is the focal length of Satellite Camera.

Each projected size of the pixel on the moon is:

(3) the satellite line array CCD using the satellite in step (1) in the projection linear velocity and step (2) of moonscape Each projected size of the pixel on the moon in camera, calculates the Satellite Camera time for exposure being imaged every time.

It is imaged over the ground, generally is equal to this principle of projected size on earth to design according to pixel resolution over the ground, That is GSDe=GIFOVe, to ensure the square grid size of sampling.As Fig. 3 (a) show the signal of square sample grid Figure, i.e., it is consistent with the imaging resolution on velocity attitude in the horizontal direction.

Thus, time for exposure size is:

If be imaged the moon, still need to ensure to be equal to the projected size on the moon to the pixel resolution that the moon is imaged This principle, i.e. GSDm=GIFOVm, to ensure the square grid size of sampling, thus, time for exposure size is:

Drawn by formula (2) with formula (3):If retaining the square sample to the moon, the t of moon imagingmWith The t being imaged over the groundeBetween multiple proportion be

Therefore, for TDICCD, due to needing the synchronization between multistage, it is necessary to big with projection according to pixel resolution Small equal (GSD=GIFOV) this principle adjusts the time for exposure.

For common line array CCD, upon exposure between can timing, its time for exposure can be calculated according to above-mentioned steps;Work as exposure When non-adjustable between light time, rectangularly-sampled can be caused to moon imaging, in the resolution ratio and horizontal direction on velocity attitude now Resolution ratio it is inconsistent, the later stage needs resampling to be processed into square sample.As Fig. 3 (b) show common line array CCD to the moon Rectangularly-sampled result transform to the schematic diagram of square sample.

2.2nd, intermediate time attitude angle size is calculated according to the position relationship of intermediate time satellite and the moon

Satellite yaw angleIt is constant in moon imaging process, and be 0.Therefore, satellite passes through to moon imaging needs Adjust the angle of pitch and roll angle to realize, such as Fig. 4 (a) show the position that LEOS Low Earth Orbiting Satellite is imaged the moon and with posture relation shown It is intended to, Bo-BxByBzFor satellite orbit coordinate system, origin BoIn orbit, BxAxle points to satellite direction of advance, BzAxle is by satellite matter The heart points to the earth's core, ByAxle is perpendicular to by BxWith BzThe orbit plane that axle is constituted;SxSySzFor satellite body coordinate system.According to pushing away every time Sweep starting and the end time of imaging, calculate the position vector relation of intermediate time satellite and the moon, satellite is calculated accordingly to the moon The angle of pitch of ball push-scanning image intermediate time and roll angle size:

(1) the imaging initial time being imaged every time according to previously given satellite and imaging end time, calculating is defended The imaging intermediate time that star is imaged every time, when further determining the imaging centre being imaged every time according to satellite orbit and moon ephemeris Carve the position vector between satellite and the moon, the vector is in Bx,By,BzProjection on direction is respectively r1,r2,r3, it is expressed asThe S of satellite body coordinate system during imagingzDirection is vectorDirection, r1For imaging intermediate time satellite with Position vector between the moonIn satellite orbit coordinate system BxProjected size on direction of principal axis, r3For imaging intermediate time satellite Position vector between the moonIn satellite orbit coordinate system BzProjected size on direction of principal axis;r2Defended for imaging intermediate time Position vector between star and the moonIn satellite orbit coordinate system ByProjected size on direction of principal axis.

Moon ephemeris uses JPL ephemeris, and JPL ephemeris are the day according to newest determination by U.S. jet propulsion laboratory The relative position of each major planet, the sun, the earth and the moon that literary constant and celestial motion theory are calculated, speed, nutation of longitude and The numerical value of physical libration of the moon and its variability.

(2) as shown in Fig. 4 (b), around ByAxle, which rotates to an angle, causes B new after rotationz' axle and vectorIn BxBzPlane On projection overlap, the angle be imaged intermediate time pitching angle thetamid, BxAxle rotates to Bx', obtained according to projection relation:

(3) around Bx' axle rotates to an angle so that Bz' axle rotates to and vectorThe direction of coincidence, i.e. SzDirection, this angle Degree is the roll angle Φ for being imaged intermediate timemid

2.3rd, the attitude of satellite rate of pitch d θ of push-scanning image are calculatedmSize

When line array CCD realizes that square sample is imaged by adjusting attitude angular velocity, then need calculating to push away and sweep The attitude of satellite rate of pitch d θ of imagingmSize.

(1) the projection line velocity magnitude on the moon is calculated

Set the rate of pitch d θ to moon imaging process Satellitem, then the caused projection linear velocity in moonscape Size is:

vm'=d θm×(Rem-Rm-H-Re)

It is again the v in formula (1) by projection linear velocity of the satellite rings caused by earth rotation on moonscapem, Therefore, with rate of pitch d θmProjection line velocity magnitude V of the satellite on moonscapemV can be usedmWith vm' sum comes near Like expression:

(2) the rate of pitch d θ of satellite are calculatedmSize

In the case where the time for exposure is constant, i.e., the time for exposure being imaged to the earth and the time for exposure phase being imaged to the moon Deng to ensure to be equal to the pixel resolution that the moon is imaged projected size this principle on the moon, i.e. GSDm=GIFOVm, with Ensure the square grid size of sampling, can be obtained by formula (3) and (4):

Combine the time for exposure being imaged to the earth, i.e. formula (2), according to tm=te, then rate of pitch d θmFor:

In the present embodiment, according to the above-mentioned R providede、Rem、Rm, H numerical value, and Kepler's constant μ, according to formula (6) Obtain rate of pitch d θm

Otherwise, attitude of satellite rate of pitch d θmIt is zero.

2.4th, push-scanning image initial time attitude angle and finish time attitude angle size are calculated

When line array CCD realizes that square sample is imaged by adjusting attitude angular velocity, according to bowing for calculating Elevation angle velocity magnitude d θm, and the pitching angle theta and roll angle Φ calculated, starting and end time further according to push-scanning image Show that to the duration that the moon is imaged be t, then t=end times-initial time, initial time pitching angle thetastartBy public affairs Formula:

Provide, wherein, t is the difference between imaging end time in each imaging process and imaging initial time;

Initial time roll angle ΦstartBy formula:

Φstartmid

Provide,

Finish time pitching angle thetaendBy formula:

Provide,

Finish time roll angle ΦendBy formula:

Φendmid

Provide.

For be not realized by adjusting attitude angular velocity square sample imaging in the case of, then to moon push-scanning image The pitching and roll angle with intermediate time of initial time, finish time it is equal, that is, be expressed as θstartend=θ, Φstart= Φend=Φ;

2.5th, determine to be transferred to between at the beginning of moon imaging pattern, from being transferred to moon imaging pattern pair from imaging pattern over the ground The end time of ground imaging pattern.

From imaging pattern over the ground be transferred to between at the beginning of moon imaging pattern by formula:

tstart=tstart1-t′

Provide, wherein, tstartIt is transferred to for imaging pattern over the ground between at the beginning of moon imaging pattern, tstart1For for the first time The initial time being imaged to the moon, t ' is transferred to the attitude maneuver time to moon imaging pattern for imaging pattern over the ground, specifically by formula:

Provide, wherein twFor attitude stabilization time, θstart1The angle of pitch of initial time, θ are imaged to the moon for first time0To be right The angle of pitch of ground imaging, d θ are satellite rate of pitch, Φstart1The roll angle of initial time, Φ are imaged to the moon for first time0 For the roll angle being imaged over the ground, d Φ satellite rate of roll;

From the end time of imaging pattern over the ground is transferred to moon imaging pattern by formula:

tend=tendn+t″

Provide, wherein, tendTo be transferred to the end time of imaging pattern over the ground, t to moon imaging patternendnIt is n-th to the moon The end time of imaging, t " is the attitude maneuver time that imaging pattern over the ground is transferred to moon imaging pattern, specifically by formula:

Provide, wherein t 'wFor attitude stabilization time, θendnThe angle of pitch of finish time, θ are imaged to the moon for n-th1To be right The angle of pitch of ground imaging, d θ are satellite rate of pitch, ΦendnThe roll angle of finish time, Φ are imaged to the moon for n-th1To be right The roll angle of ground imaging, d Φ satellite rate of roll.

3rd, when earth observation satellite in orbit the time reach step 2 in determine from imaging pattern over the ground be transferred to the moon into When between at the beginning of picture pattern, satellite carries out attitude maneuver pattern, and satellite is adjusted according to the attitude of satellite angle determined in step 2 It is whole, it is transferred to by imaging pattern over the ground to moon imaging pattern.

During the entire process of satellite is imaged to the moon, in the case of not effective star chart is available, attitude measurement needs From star sensor measurement based on be transferred to based on inertial sensor or other metering systems for reaching required precision.

The inertial sensor or other metering systems for reaching required precision, mainly cause without effective star chart , it is necessary to meet the inertial sensor or other sensors of certain attitude accuracy requirement to substitute in the case of star sensor is disabled Star sensor, pointing accuracy and attitude stability requirement to inertia or other sensors are that caused MTF declines percentage No more than 5~10%;

Improper picture caused by attitude of satellite precision move computational methods (referring to《Attitude of satellite precision is to TDI CCD cameras Influence》, Harbin Institute of Technology's journal, 34 (3), 2002):Pointed to according to the focal length f, pixel dimension τ, posture of CCD camera Precision δ degree and attitude stability δ ' degrees seconds, then the time for exposure t being imaged to the moonmInterior generation along TDI, vertical TDI side To improper picture move dx, dy be respectively:

Moving caused MTF by improper picture is:

4th, when the time reaches the first time imaging initial time determined in step 2 to earth observation satellite in orbit, ground The linear array CCD camera of ball observation satellite is according to the Satellite Camera time for exposure t of each imaging determined in step 2mStart to the moon Ball is imaged, and obtains lunar map picture, if the imaging frequency n to moon push-scanning image is more than 1, is performed step 5, is otherwise performed step 6。

5th, according to the Satellite Camera time for exposure t of each imaging determined in step 2m, imaging initial time, imaging terminate Time and attitude of satellite angle, complete all to moon push-scanning image according to the method in step 4, obtain all lunar maps Picture, into step 6.

6th, complete to moon push-scanning image, earth observation satellite enters attitude maneuver pattern, is transferred to moon imaging pattern Imaging pattern over the ground.

7th, all lunar map pictures obtained in step 6 are handled using ROLO absolute radiometric calibrations model, obtains exhausted To radiation calibration coefficient.

Empirical equation using the ROLO moon disk equivalent reflectivity A provided is as follows:

In formula, g is moon phase angle, longitudes of the φ for observation camera in moon spherical coordinates, and θ is observation camera in moon spherical coordinates Latitude, Φ is longitude of the sun in moon spherical coordinates, a, b, c, and d, p is coefficient entry.

Section 1 in above formula is the elementary item of moon brightness, closely related with moon phase angle, is selected in ROLO databases Month phase angle range is 1.55 °<g<97°;The expression of Section 2 approximately is by the asymmetry according to moonscape, mainly by moon table Face dark area and the influence on highland;Section 3 four to Section 6 and containing c and libration and shine upon related;Last three Be nonlinear empirical term, represent respectively full moon liquidate effect influence and residual error.

Embodiment

In the present embodiment, satellite orbital altitude H=645km, earth radius R are givene=6378km, moon radius of a ball Rm= 1737km, the moon centre distance take Rem=384400km, camera focus f=2.6m, Kepler constant μ=3.986 × 105km3/ s2, in satellite linear array CCD camera each pixel p=10 μm of size.

1st, the Satellite Camera time for exposure t being imaged every time is determinedm

The time for exposure t for obtaining being imaged the earth according to formula (2)eFor:

The time for exposure t for obtaining being imaged the moon according to formula (3)mFor:

Therefore, if be imaged using square sample, the time for exposure t that satellite is imaged to the moonmAbout the earth is exposed T between light timee9.7 times.

2nd, the attitude of satellite rate of pitch d θ of push-scanning image are calculatedmSize

Available, the rate of pitch by formula (6):

3rd, during the entire process of satellite is imaged to the moon, in the case of not effective star chart is available, attitude measurement is needed It is transferred to based on being measured from star sensor based on inertial sensor or other metering systems for reaching required precision.

The integration series N of camera is set in the present inventionTDI=6,12,24,48,72,96 is adjustable, under integration series at different levels, To meet the decline of mtf value no more than 10%.

(1) when needing the adjustment time for exposure to realize to moon square sample, then the exposure being imaged to the moon Time tm=3.5196 × 10-3S, according to formula (7) and formula (8) calculate posture pointing accuracy δ degree and attitude stability δ ' degree/ Second:

1) by formula (7) obtain corresponding dx, dy be no more than 0.846,0.4187,0.2088,0.1043,0.0695, 0.0521 (unit:μm).

2) constraints, and formula (7) construction critical equation are used as further according to the scope of dx, dy no more than:

Qualified posture pointing accuracy δ and attitude stability δ ' is obtained by heuristic as shown in figure 5, figure bend Bottom-left quadrant be the condition that meets region, Fig. 6 (a) gives 6, corresponding oblique line, Fig. 6 (b) under 12,24 grades of integration series Gone out 48, corresponding oblique line under 72,96 grades of integration series, it can be seen that with the increase of integration series, attitude accuracy is wanted Ask increasingly stricter, suitable δ and δ ' can be selected according to the precision of sensor in actual applications.

(2) for the time for exposure need not be adjusted, then the time for exposure t being imaged to the moonmWith the exposure being imaged to the moon Time teIt is equal, tm=te=0.36259 × 10-3S, posture pointing accuracy δ degree and posture are calculated according to formula (7) and formula (8) Stability δ ' degrees seconds:

1) by formula (7) obtain corresponding dx, dy be no more than 0.846,0.4187,0.2088,0.1043,0.0695, 0.0521 (unit:μm).

2) constraints, and formula (7) construction critical equation are used as further according to the scope of dx, dy no more than:

Qualified posture pointing accuracy δ and attitude stability δ ' is obtained by heuristic as shown in figure 5, figure bend Bottom-left quadrant be the condition that meets region, Fig. 7 (a) gives 6, corresponding oblique line, Fig. 7 (b) under 12,24 grades of integration series Gone out 48, corresponding oblique line under 72,96 grades of integration series, it can be seen that with the increase of integration series, attitude accuracy is wanted Ask increasingly stricter, suitable δ and δ ' can be selected according to the precision of sensor in actual applications.

Unspecified part of the present invention belongs to general knowledge as well known to those skilled in the art.

Claims (6)

1. a kind of low orbit earth observation satellite is to moon absolute radiation calibration method, it is characterised in that step is as follows:
(1) determine that low orbit earth observation satellite can observe the time of the moon using Satellite Tool Kit, utilize satellite work Tool software, which is obtained, can observe the attitude of satellite angle corresponding to the time of the moon, and calculating can observe that the time institute of the moon is right The moon phase angle answered, further according to the attitude maneuver ability of satellite, selected from the time that can observe the moon to the moon into As the time, step (2) is performed;
The attitude maneuver ability refers to satellite pitching angle theta, roll angle Φ and yaw angleMaximum maneuvering range, to the moon into The pose adjustment size of satellite must be within the attitude maneuver limit of power of satellite during picture;The moon phase angle meets ROLO The moon phase angular region selected in moon absolute radiometric calibration model, the model is:[1.55 °, 97 °];
(2) it is selected to moon imaging time according to step (1), it is determined that being transferred to from imaging pattern over the ground to moon imaging pattern Time started, from being transferred to the end time of imaging pattern over the ground to moon imaging pattern and satellite linear array CCD camera is pushed away to the moon and swept The imaging frequency n of imaging, and the Satellite Camera time for exposure t that determination is imaged every timem, imaging initial time, imaging the end time, Attitude of satellite angle, satellite rate of pitch d θm;The attitude of satellite angle being imaged every time includes imaging initial time posture every time Angle, intermediate time attitude angle and finish time attitude angle;The attitude angle includes the angle of pitch, roll angle and yaw angle, described to defend Star linear array CCD camera to moon push-scanning image number of times, the imaging initial time being imaged every time and imaging the end time in advance to It is fixed;
(3) when earth observation satellite in orbit the time reach determined in step (2) from imaging pattern over the ground be transferred to the moon into When between at the beginning of picture pattern, satellite enters attitude maneuver pattern, and satellite is carried out according to the attitude of satellite angle determined in step (2) Adjustment, is transferred to moon imaging pattern by imaging pattern over the ground;
(4) when the time reaches the first time imaging initial time determined in step (2) to earth observation satellite in orbit, the earth The linear array CCD camera of observation satellite according in step (2) determine each imaging Satellite Camera time for exposure tmStart to the moon Ball is imaged, and obtains lunar map picture, if to imaging number of times j≤n of moon push-scanning image, performing step (5), otherwise, performs step (6);
(5) according to the Satellite Camera time for exposure t of each imaging determined in step (2)m, imaging initial time, imaging at the end of Between and attitude of satellite angle, complete all to moon push-scanning image according to the method in step (4), obtain all lunar maps Picture, into step (6);
(6) complete to moon push-scanning image, earth observation satellite enters attitude maneuver pattern, is transferred to over the ground to moon imaging pattern Imaging pattern;
(7) all lunar map pictures obtained in step (6) are handled using ROLO absolute radiometric calibrations model, obtains absolute Radiation calibration coefficient.
2. a kind of low orbit earth observation satellite according to claim 1 is to moon absolute radiation calibration method, its feature It is:The Satellite Camera time for exposure t being imaged every time is determined in the step (2)m, specifically realized by following steps:
(2a) calculates projection linear velocity v of the satellite in moonscapem, specifically by formula:
v m = &mu; ( R e + H ) &times; ( R e m - R m ) R e + H
Provide, wherein, μ is Gravitational coefficient of the Earth, ReFor earth radius, H is the orbit altitude of satellite transit;RemFor earth center To the distance of moon ball center, RmFor the moon radius of a ball;
(2b) calculates projected size GIFOV of each pixel on the moon in satellite linear array CCD cameram, specifically by formula:
GIFOV m = p &times; ( R e m - R m e - H - R e ) f
Provide, wherein, p is the size of each pixel in satellite linear array CCD camera, and f is the focal length of Satellite Camera;
The satellite line array CCD phase of (2c) using the satellite in step (2a) in the projection linear velocity and step (2b) of moonscape Each projected size of the pixel on the moon in machine, calculates the Satellite Camera time for exposure being imaged every time, specifically by formula:
t m = GIFOV m v m = p f &times; &mu; ( R e + H ) 3 &times; R e m - R m - H - R e R e m - R m
Provide.
3. a kind of low orbit earth observation satellite according to claim 1 is to moon absolute radiation calibration method, its feature It is:Intermediate time attitude angle in the step (2), is realized by following steps:
Imaging initial time and imaging end time that (3a) is imaged every time according to satellite previously given in step (2), are calculated The imaging intermediate time that satellite is imaged every time is obtained, the imaging being imaged every time is further determined according to satellite orbit and moon ephemeris Position vector between intermediate time satellite and the moon
Position vector between the imaging intermediate time satellite and the moon of (3b) in step (3a)When being calculated as centre The pitching angle theta at quartermid, roll angle ΦmidAnd yaw angleIt is imaged the pitching angle theta of intermediate timemidSpecifically by formula:
It is imaged the roll angle Φ of intermediate timemidSpecifically by formula:
&Phi; m i d = a r c s i n &lsqb; | r 2 | r 1 2 + r 2 2 + r 3 2 &rsqb;
Provide, wherein, r1For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate system BxAxle side Upward projected size, r3For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate system BzAxle Projected size on direction;r2For the position vector between imaging intermediate time satellite and the moonIn satellite orbit coordinate system By Projected size on direction of principal axis;Wherein, satellite orbit coordinate system Bo-BxByBzOrigin BoIn orbit, BxAxle is pointed to before satellite Enter direction, BzAxle points to the earth's core, B by centroid of satelliteyAxle is perpendicular to by BxWith BzThe orbit plane that axle is constituted;
The yaw angleIt is constant in imaging process, and be 0.
4. a kind of low orbit earth observation satellite according to claim 1 is to moon absolute radiation calibration method, its feature It is:Step (2) the Satellite posture rate of pitch d θm, detailed process is as follows:
If satellite linear array CCD camera realizes that square sample is imaged by adjusting posture rate of pitch, attitude of satellite pitching Angular speed d θmBy formula:
d&theta; m = &mu; ( R e + H ) 3 &lsqb; R e H - ( R e m - R m ) ( R e m - R m - H - R e ) &rsqb;
Provide, wherein, μ is Gravitational coefficient of the Earth, ReFor earth radius, H is the orbit altitude of satellite transit;RemFor earth center To the distance of moon ball center, RmFor the moon radius of a ball;
Otherwise, attitude of satellite rate of pitch d θmIt is zero.
5. a kind of low orbit earth observation satellite according to claim 1 is to moon absolute radiation calibration method, its feature It is:Initial time attitude angle and finish time attitude angle in the step (2), specific calculating process are as follows:
Initial time pitching angle thetastartBy formula:
&theta; s t a r t = &theta; m i d - d&theta; m &CenterDot; t 2
Provide, wherein, t is the difference between imaging end time in each imaging process and imaging initial time;
Initial time roll angle ΦstartBy formula:
Φstartmid
Provide,
Finish time pitching angle thetaendBy formula:
&theta; e n d = &theta; m i d + d&theta; m &CenterDot; t 2
Provide,
Finish time roll angle ΦendBy formula:
Φendmid
Provide.
6. a kind of low orbit earth observation satellite according to claim 1 is to moon absolute radiation calibration method, its feature It is:Determine in the step (2) to be transferred to between at the beginning of moon imaging pattern, to moon imaging pattern from imaging pattern over the ground The end time of imaging pattern over the ground is transferred to, is specially:
From imaging pattern over the ground be transferred to between at the beginning of moon imaging pattern by formula:
tstart=tstart1-t′
Provide, wherein, tstartIt is transferred to for imaging pattern over the ground between at the beginning of moon imaging pattern, tstart1It it is first time to the moon The initial time of imaging, t ' is transferred to the attitude maneuver time to moon imaging pattern for imaging pattern over the ground, specifically by formula:
t &prime; = m a x { &theta; s t a r t 1 - &theta; 0 d &theta; , &Phi; s t a r t 1 - &Phi; 0 d &Phi; } + t w
Provide, wherein twFor attitude stabilization time, θstart1The angle of pitch of initial time, θ are imaged to the moon for first time0For over the ground into The angle of pitch of picture, d θ are satellite rate of pitch, Φstart1The roll angle of initial time, Φ are imaged to the moon for first time0To be right The roll angle of ground imaging, d Φ satellite rate of roll;
From the end time of imaging pattern over the ground is transferred to moon imaging pattern by formula:
tend=tendn+t″
Provide, wherein, tendTo be transferred to the end time of imaging pattern over the ground, t to moon imaging patternendnThe moon is imaged for n-th End time, t " is the attitude maneuver time of imaging pattern over the ground of being transferred to moon imaging pattern, specifically by formula:
t &prime; &prime; = m a x { &theta; e n d n - &theta; 1 d &theta; , &Phi; e n d n - &Phi; 1 d &Phi; } + t w &prime;
Provide, wherein t 'wFor attitude stabilization time, θendnThe angle of pitch of finish time, θ are imaged to the moon for n-th1For over the ground into The angle of pitch of picture, d θ are satellite rate of pitch, ΦendnThe roll angle of finish time, Φ are imaged to the moon for n-th1For over the ground into The roll angle of picture, d Φ satellite rate of roll.
CN201410637920.4A 2014-11-06 2014-11-06 A kind of low orbit earth observation satellite is to moon absolute radiation calibration method CN104462776B (en)

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