CN105606128A - External-field calibration method of space-borne laser altimeter - Google Patents

Abstract

The invention discloses an external-field calibration method of a space-borne laser altimeter. The method basically includes the steps of firstly, laying light-emitting targets on the ground at night to serve as control points, laying a ground detecting array at a light spot prediction position, shooting near infrared high-resolution image data on an airborne platform when a satellite passes, and using a ground detector to capture a light spot and measure atmosphere data; secondly, according to the data of the ground detecting array, acquiring transmission waveforms, correcting satellite time determination errors and calibrating a laser receiver; thirdly, acquiring a light spot position according to the aviation image, and calibrating distance-measuring errors and the setting angle of a laser device and a footprint camera. The method has the advantages that the defect that a calibration method which relies on the ground detecting array alone is low in success rate is overcome, the distance-measuring and attitude-measuring errors of the space-borne laser altimeter can be calibrated, and high efficiency is achieved.

Description

A kind of satellite borne laser altimeter outfield calibration method

Technical field

The invention belongs to Global observation by remote sensing field, relate to a kind of satellite borne laser altimeter outfield calibration sideMethod.

Background technology

In order to improve the precision of stereoplotting satellite, need badly research and solve its range finding revise, location revise,Series of key techniques problem in waveform application process, wherein of paramount importance content is used outfield inspection exactlyThe means in school, after satellite is entered the orbit operation the position of ground survey/catch laser and form to range finding,A series of error terms of surveying in appearance process are carried out calibration.

The calibration work of satellite borne laser altimeter only has GLAS team of the U.S. to do particular study, employingIt is the mode that relies on merely lattice pattern receiver. The method once can only receive the signal of a hot spot, costHigh, bulky, laying is wasted time and energy. Be limited to the area of graticule mesh, if the prediction of laser footmark pointWhen error is larger, the method may occur that very greatly hot spot, not in the situation in graticule mesh district, wastes a large amount of manpower and materials.

Finally, complete the calibration work of instrument in 2-3 month that stereoplotting satellite generally need to be after entering the orbit,And adopt the laser spot test technology of the mode of lattice pattern receiver can only obtain 6 at most in 2-3 monthIndividual, can not meet calibration and the precision test demand of instrument far away. Therefore, provide a kind of efficient, Gao LuCan laser spot test technology rod, that limit without landform become stereoplotting laser satellite altimeter and throwThe necessary technology means that enter to use.

The present invention has designed a kind of outfield calibration method that high score image and ground location graticule mesh combine, the partyMethod only need to be used graticule mesh to obtain one or two secondary data can deadline error and the calibration of waveform. And by highDivide image can disposablely obtain more footmark point, and the calibration of finding range with it. The method can be shorterIn time, complete the high accuracy calibration of satellite borne laser altimeter, effectively repair laser instrument and cannot repair before transmittingMultiple range error, position error, waveform resolution error. For the survey of the laser altimeter of stereoplotting satelliteDistance, survey appearance data provide accurate correction parameter. This is for promoting satellite data geometric manipulations precision and productQuality has great importance.

Summary of the invention

Problem to be solved by this invention is: the domestic laser altimeter outfield that a kind of pattern of working at night is providedCalibration method.

Technical scheme provided by the invention adopts following steps:

1. satellite borne laser altimeter outfield precise calibration method, is characterized in that, comprises the following steps:

(1) ground preparation, lays target and gathers and survey district's terrain data, and detailed step is as follows:

(1-1) the general position of time, laser facula that 3-7 days prediction satellites pass by night before satellite passes byPut, select target area according to facula position and required topography and geomorphology;

(1-2) lay the luminous target of blue-green of particular design in target area;

(1-3) locus of employing high-precision GPS measurement target drone;

(1-4) adopt airborne LiDAR to obtain the terrain data of target area;

(2) night in the time that satellite is crossed top in airborne platform photographs near-infrared high score image data, ground finderCatch hot spot, measure atmospheric parameter; Concrete steps are as follows:

(2-1) before satellite passes by, each target in target area is lighted;

(2-2) high split-phase motor is equipped on special stabilized platform, goes up to the air to the height of design with carrierDegree. According to the design in target range, adjust the shooting angle of camera, can photograph territory, land-based target place;

(2-3) exposure of control camera. Camera 3s before satellite passes by starts exposure, and satellite passes by consuming time2.5s continues to take 3s after passing by, and 8.5s altogether exposes. The satellite time advance that passes by calculates, and exposes to the sunControl between the light time is independently controlled by high score camera control point.

2. obtain transmitted waveform, correct time determination error on star by ground location array data, and laser is connectReceiving device demarcates. Comprise the following steps:

(1) use ground location array to obtain waveform, concrete steps are as follows:

(1-1) find the strongest detector of energy receiving in ground location array, think this detectionDevice is the center of laser facula,

(1-2) waveform each detector in detection array being obtained carries out coordinate and returns 0 processing, to appointingThe Wave data that detector obtains of anticipating, moves to crest location the position of reference axis 0

(1-3) Wave data each detector after translation being obtained is weighted on average, and weight is by each spyThe distance of the position at Ce Qidao center is calculated, and obtains the transmitted waveform data of spaceborne laser.

(2) use ground location array to obtain the data that record on time of waveform and star, calibration time determination error,Concrete steps are as follows:

(2-1) calculate star with the coordinate in the Laser emission moment of GPS record on the geographical coordinate of central point and starGround distance L, calculates Laser Transmission time t_trans＝L/c；

(2-2) according to actual measurement atmospheric parameter, calculate laser t time delay_delay；

(2-3) with the actual T in reception waveform moment of ground location An arrayed recording, deduct t_transAnd t_delay,Correct time t during to satellite launch laser_real；

(2-4) deduct the time t of actual measurement with the crest x time recording on star_rea, system while obtaining surveying on starDelay;

(3) energy of laser pickoff is demarcated, concrete steps are as follows:

(3-1) the laser energy intensity and the distribution that record with each position sensor of ground location array, matchingGo out the laser dimensional energy distribution of gaussian-shape;

(3-2), to the less integration of the energy within the scope of whole hot spot, calculate the integral energy in laser facula;

(3-3), based on many groups land-based target mark measurement data, use atmospheric parameter to eliminate in the descending process of laser largeThe attenuation effect of gas to laser energy, the emitted energy DN value that obtains recording on laser emitting energy and star is intendedClose out the transformation ratio of emitted energy DN value and actual transmission energy;

(3-3) based on many groups land-based target mark measurement data, use atmospheric transmittance to be multiplied by ground return energy,Obtain laser entrance pupil energy, simulate projectile energy DN value with real with the projectile energy DN value recording on starThe transformation ratio of border entrance pupil energy;

3. the position of the multiple hot spots that obtain according to aerial image, calibration range error. Comprise the following steps:

(1) use the locus that obtains each laser spot center with DEM on aviation high score image,Concrete steps are as follows:

(1-1) position of each target on identification aviation high partial image, with and image coordinate, obtain many groupsPicture control point data;

(1-2), according to target control point, calculate the high partial image elements of exterior orientation of aviation;

(1-3), according to the inside and outside element of orientation of the high partial image of aviation, under dem data auxiliary, useFine positioning method is carried out geometric correction to the high partial image of aviation fast;

(1-5) use barycenter extraction algorithm, extract the pixel at the center of each laser facula on high score imagePosition;

(1-6), according to the geographical coordinate of high partial image, calculate the geographical coordinate position of each laser center<X, Y>, and on DEM, find corresponding elevation correction Z according to plan-position, the space obtaining is a little satMark<X, Y, Z>;

(2) position while using the position of ground light spot and laser satellite outgoing, calculates the distance between star groundFrom, concrete steps are as follows:

(2-1) by the eccentric vector of GPS on laser emitting point and star, the attitude of satellite, calculate laserLocus < the X of eye point₀,Y₀,Z₀>；

(2-2) locus < X of laser emitting point₀,Y₀,Z₀> and the topocentric space coordinates of laser facula<X, Y, Z>, the actual transmission paths L of calculating laser_real；

(3) use the atmosphere data of measuring, the distance measurement value of satellite record is carried out to atmospheric correction, and eliminate groundBall earth tide effect, obtains the actual distance measurement value L accurately correcting_record, concrete steps are as follows:

(3-1) use the parameters such as actual measurement atmospheric pressure, moisture content, calculate whole atmosphere retardation rootAccording to atmosphere delay amount, the distance measurement value of satellite borne laser altimeter is corrected;

(3-2) figure of the earth parameter in use Laser emission moment, surveys the Satellite-borne Radar Altimeter after atmospheric correctionCarry out earth tide correction apart from value;

(4) coefficient correlation between the distance measurement value that foundation (2) and (3) obtains, obtains satellite borne laser heightThe correction factor of meter distance measurement value.

Brief description of the drawings

Fig. 1 is the laser altimeter outfield calibration method schematic diagram of high score image and the combination of graticule mesh detector.

Fig. 2 is the flow chart that uses ground location array calibration laser waveform, time determination error, energy scaling.

Fig. 3 is the flow chart that obtains laser spot position from high score image.

Fig. 4 is the flow chart that on laser star, distance measurement value and actual distance measurement value carry out range error associating calibration.

Detailed description of the invention

For setting forth better technical scheme of the present invention and advantage, below in conjunction with accompanying drawing to enforcement of the present inventionProcess is further described. Fig. 1 is the flow chart of whole calibration method, by ground measured data, pointNot right

The first step of the present invention need to be obtained the ground observation data of satellite borne laser altimeter. First pass by satelliteThe general position of time, laser facula that front 3-7 days prediction satellites pass by night, according to facula position and instituteNeed topography and geomorphology to select target area. Lay the luminous target of blue-green of particular design in target area, and adopt high accuracyThe locus of GPS measurement target drone, adopt airborne LiDAR to obtain the terrain data of target area.

Then in the time that crossing top, before satellite passes by, each target in target area is being lighted on satellite night. By high scoreCamera is equipped on special stabilized platform, goes up to the air to the height of design with carrier. According to establishing of target rangeMeter, the shooting angle of adjustment camera, can photograph territory, land-based target place. Control the exposure of camera.Camera 3s before satellite passes by starts exposure, and the satellite 2.5s consuming time that passes by continues to take 3s after passing by,8.5s altogether exposes. The satellite time advance that passes by calculates, and the control of time for exposure is by high score camera controlPoint is independently controlled.

Second step of the present invention is for obtaining transmitted waveform, correcting on star and survey mistiming by ground location array dataPoor, and laser pickoff is demarcated, Figure 2 shows that the demarcation flow process of waveform and energy.

First use ground location array to obtain waveform, by the strongest the energy receiving in ground location array by oneIndividual detector thinks that this detector is the center of laser facula, and each detector in detection array is obtainedThe waveform of getting carries out coordinate and returns 0 processing, and the Wave data any one detector being obtained, by crest positionHorizontalization moves on to the position of reference axis 0. Be weighted with the Wave data that each detector after translation obtains againOn average, weight is calculated to the distance of the position at center by each detector, obtains the transmitted waveform of spaceborne laserData, formula is as follows:

$W=\frac{\underset{i=1}{\overset{n}{\&Sigma;}}\frac{1}{d}\&CenterDot;W_i}{\underset{i=1}{\overset{n}{\&Sigma;}}\frac{1}{d}}$

In formula, n represents the number of detector within the scope of hot spot, W_iFor the waveform that detector receives, d representsDetector is to the distance of spot center.

Then use ground location array to obtain the reality recording on time of waveform and star, calibration time determination error.Calculate star ground distance L with the coordinate in the Laser emission moment of GPS record on the geographical coordinate of central point and star,Calculate Laser Transmission time t_trans=L/c. According to actual measurement atmospheric parameter, calculate laser t time delay_delay. WithThe actual T in the reception waveform moment of ground location An arrayed recording, deducts t_transAnd t_delay, obtain satellite launchCorrect time t when laser_real；

t_real＝T-t_trans-t_dela

With the crest x time t recording on star_outDeduct the time t of actual measurement_real, obtain prolonging of system while survey on starSlow:

△t＝t_out-t_real

Energy to laser pickoff is demarcated, and concrete steps are as follows:

The laser energy intensity and the distribution that record with each position sensor of ground location array, simulate GaussThe laser dimensional energy distribution of shape. To the less integration of the energy within the scope of whole hot spot, calculate in laser faculaIntegral energy. Based on many groups land-based target mark measurement data R_↓, use atmospheric parameter to eliminate the descending process of laserThe attenuation effect of middle atmosphere to laser energy, obtains laser emitting energy:

R_out＝R_↓/τ

In formula, τ represents atmospheric transmittance. Simulate emitted energy with the emitted energy DN value recording on starThe calibration coefficient of DN value and actual transmission energy.

R_out＝k_out*DN_out+b_out

Based on many groups land-based target mark measurement data, use atmospheric transmittance to be multiplied by ground return energy, swashedLight entrance pupil energy R_in＝R_↓* τ, then simulates projectile energy DN by the projectile energy DN value recording on starThe calibration coefficient R of value and actual entrance pupil energy_in＝k_in*DN_in+b_in。

The 3rd step of the present invention is according to aerial image actual range, as shown in Figure 3. First use aviation high scoreThe locus that obtains each laser spot center with DEM on image, then from the high partial image of identification aviationThe position of upper each target, with and image coordinate, obtain many groups as control point data. According to target controlPoint, calculates the high partial image elements of exterior orientation of aviation. According to the inside and outside element of orientation of the high partial image of aviation,Under dem data auxiliary, use quick fine positioning method to carry out geometric correction to the high partial image of aviation. UseBarycenter extraction algorithm, extracts the pixel position at the center of each laser facula on high score image. According to high scoreThe geographical coordinate of image, calculates the geographical coordinate position<X of each laser center, Y>, and according to plane positionPut and on DEM, find corresponding elevation correction Z, obtain space coordinates<X a little, Y, Z>;

Figure 4 shows that the flow chart that uses physical location calibration distance measurement value. First by the position of GPS<X_GPS,Y_GPS,Z_GPS>the eccentric vector of GPS on laser emitting point and star<u, v, w>, satellite attitude obtainSpin matrix M, calculate the locus < X of laser emitting point₀,Y₀,Z₀>, computing formula is:

$\left[\begin{array}{c}{X}_0\\ Y_0\\ Z_0\end{array}\right]=M\left[\begin{array}{c}u\\ v\\ w\end{array}\right]+\left[\begin{array}{c}{X}_{GPS}\\ Y_{GPS}\\ Z_{GPS}\end{array}\right]$

Then locus < the X being put by laser emitting₀,Y₀,Z₀> and the topocentric space coordinates of laser facula<X, Y, Z>, the actual transmission paths L of calculating laser_real；

$L_{real}=\sqrt{{(X_0-X)}^2+{(Y_0-Y)}^2+{(Z_0-Z)}^2}$

Use the parameters such as actual measurement atmospheric pressure, moisture content, calculate whole atmosphere retardation, and according to atmosphereRetardation corrects the distance measurement value of satellite borne laser altimeter. Use the figure of the earth ginseng in Laser emission momentNumber, carries out earth tide correction to the Satellite-borne Radar Altimeter distance measurement value after atmospheric correction. On true distance measurement value and star, surveyThere is following empirical relation apart from value:

L_real＝k*L_watch+b

By organizing true distance measurement value L more_realWith distance measurement value L on star_watchCoefficient correlation, adopts least square fitting to obtainTo empirical coefficient k, b.

Claims (1)

1. a satellite borne laser altimeter outfield calibration method, is characterized in that comprising the following steps:

[1] ground preparation, lays target and gathers and survey district's terrain data, and detailed step is as follows:

(1) the general position of time, laser facula that 3-7 days prediction satellites pass by night before satellite passes by,Select target area according to facula position and required topography and geomorphology;

(2) lay the luminous target of blue-green of particular design in target area;

(3) locus of employing high-precision GPS measurement target drone;

(4) adopt airborne LiDAR to obtain the terrain data of target area;

[2] night in the time that satellite is crossed top in airborne platform photographs near-infrared high score image data, ground finderCatch hot spot, measure atmospheric parameter; Concrete steps are as follows:

(1) before satellite passes by, each target in target area is lighted;

(2) high split-phase motor is equipped on special stabilized platform, goes up to the air to the height of design with carrier.According to the design in target range, adjust the shooting angle of camera, can photograph territory, land-based target place;

(3) exposure of control camera. Camera 3s before satellite passes by starts exposure, the satellite 2.5s consuming time that passes by,After passing by, continue to take 3s, 8.5s altogether exposes; The satellite time advance that passes by calculates, the time for exposureControl independently controlled by high score camera control point;

[3] obtain transmitted waveform, correct time determination error on star by ground location array data, and laser is connectReceiving device demarcates; Comprise the following steps:

(1) use ground location array to obtain waveform, concrete steps are as follows:

(1-1) find the strongest detector of energy receiving in ground location array, think this detectionDevice is the center of laser facula,

(1-2) waveform each detector in detection array being obtained carries out coordinate and returns 0 processing, to appointingThe Wave data that detector obtains of anticipating, moves to crest location the position of reference axis 0;

(1-3) Wave data each detector after translation being obtained is weighted on average, and weight is by each spyThe distance of the position at Ce Qidao center is calculated, and obtains the transmitted waveform data of spaceborne laser.

(2) use ground location array to obtain the data that record on time of waveform and star, calibration time determination error,Concrete steps are as follows:

(2-1) calculate star with the coordinate in the Laser emission moment of GPS record on the geographical coordinate of central point and starGround distance L, calculates Laser Transmission time t_trans＝L/c；

(2-2) according to actual measurement atmospheric parameter, calculate laser t time delay_delay；

(2-3) with the actual T in reception waveform moment of ground location An arrayed recording, deduct t_transAnd t_delay,Correct time t during to satellite launch laser_real；

(2-4) deduct the time t of actual measurement with the crest x time recording on star_rea, system while obtaining surveying on starDelay;

(3) energy of laser pickoff is demarcated, concrete steps are as follows:

(3-1) the laser energy intensity and the distribution that record with each position sensor of ground location array, matchingGo out the laser dimensional energy distribution of gaussian-shape;

(3-2), to the less integration of the energy within the scope of whole hot spot, calculate the integral energy in laser facula;

(3-3), based on many groups land-based target mark measurement data, use atmospheric parameter to eliminate in the descending process of laser largeThe attenuation effect of gas to laser energy, the emitted energy DN value that obtains recording on laser emitting energy and star is intendedClose out the transformation ratio of emitted energy DN value and actual transmission energy;

(3-3) based on many groups land-based target mark measurement data, use atmospheric transmittance to be multiplied by ground return energy,Obtain laser entrance pupil energy, simulate projectile energy DN value with real with the projectile energy DN value recording on starThe transformation ratio of border entrance pupil energy;

[4]. the position of the multiple hot spots that obtain according to aerial image, calibration range error. Comprise the following steps:

(1) use the locus that obtains each laser spot center with DEM on aviation high score image,Concrete steps are as follows:

(1-1) position of each target on identification aviation high partial image, with and image coordinate, obtain many groupsPicture control point data;

(1-2), according to target control point, calculate the high partial image elements of exterior orientation of aviation;

(1-3), according to the inside and outside element of orientation of the high partial image of aviation, under dem data auxiliary, useFine positioning method is carried out geometric correction to the high partial image of aviation fast;

(1-4) use barycenter extraction algorithm, extract the pixel at the center of each laser facula on high score imagePosition;

(1-5), according to the geographical coordinate of high partial image, calculate the geographical coordinate position of each laser center<X, Y>, and on DEM, find corresponding elevation correction Z according to plan-position, the space obtaining is a little satMark<X, Y, Z>;

(2) position while using the position of ground light spot and laser satellite outgoing, calculates the distance between star groundFrom, concrete steps are as follows:

(2-1) by the eccentric vector of GPS on laser emitting point and star, the attitude of satellite, calculate laserLocus < the X of eye point₀,Y₀,Z₀>；

(2-2) locus < X of laser emitting point₀,Y₀,Z₀> and the topocentric space coordinates of laser facula<X, Y, Z>, the actual transmission paths L of calculating laser_real；

(3) use the atmosphere data of measuring, the distance measurement value of satellite record is carried out to atmospheric correction, and eliminate groundBall earth tide effect, obtains the actual distance measurement value L accurately correcting_record, concrete steps are as follows:

(3-1) use the parameters such as actual measurement atmospheric pressure, moisture content, calculate whole atmosphere retardation rootAccording to atmosphere delay amount, the distance measurement value of satellite borne laser altimeter is corrected;

(3-2) figure of the earth parameter in use Laser emission moment, surveys the Satellite-borne Radar Altimeter after atmospheric correctionCarry out earth tide correction apart from value;

(4) coefficient correlation between the distance measurement value that establishment step (2) and (3) obtain, obtains spaceborne sharpThe correction factor of light altimeter distance measurement value.