CN105093925A - Measured-landform-feature-based real-time adaptive adjusting method and apparatus for airborne laser radar parameters - Google Patents
Measured-landform-feature-based real-time adaptive adjusting method and apparatus for airborne laser radar parameters Download PDFInfo
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Abstract
The invention relates to a measured-landform-feature-based real-time adaptive adjusting method and apparatus for airborne laser radar parameters. A plane flies straightly at a constant speed with the altitude unchanged. When an elevation and a two-dimensional space frequency of a measured landform change, optimal computation is carried out to adjust setting values of a scanning field angle, a pulse repetition frequency, and a scanning frequency in real time, so that the laser scanning point cloud bandwidth is unchanged; meanwhile, the point cloud density meets the sampling theorem requirement all the time, thereby eliminating difficulty of distortion and data storage and processing for three-dimensional landform model reconstruction. Flight parameters and measured landform features are measured in real time by a laser scanner, a plane flight speed measurement instrument, and an aerial camera; with integrated computation, an elevation change and a two-dimensional space frequency of the landform are obtained; and then optimal computation is carried out to obtain optimal adjustment values of the three parameters including the pulse repetition frequency, the scanning frequency, and the scanning field angle of the laser scanner and real-time adjustment is carried out, thereby realizing real-time adaptive optimal measurement based on the measured-landform change.
Description
Technical field
The present invention relates to and be optimized design and real-time adaptive control method problem according to the running parameter of feature to airborne laser radar of tested landform.
Background technology
Airborne laser radar 3 Dimension Image Technique is the new technology in current topographic mapping field, and it can generate the digital surface model of tested landform, and object is the true tested landform of undistorted reproduction.
Tested landform can regard the elevation function on two dimensional surface as, and therefore the scanning survey process of airborne laser radar to tested ground is equivalent to two-dimensional discrete sampling process.
By list of references, (DigitalSignalandImageProcessing. translates version/(U.S.) Tamalbose. Wu Zhen and raises, Zhou Lin etc. translate. digital signal and image procossing. and Higher Education Publishing House, Beijing, 2006.7, p138) the two-dimentional sampling thheorem in is known, and two dimension sampling formula can be expressed as:
，
Wherein,
be respectively the sample frequency in x and y direction,
be respectively the sampling period in x and y direction.According to the sampling thheorem requirement that aliasing does not occur, that is:
, wherein,
be respectively tested landform highest frequency in the x and y direction.
Therefore, want the tested landform of undistorted recovery, basic premise meets above-mentioned two-dimentional sampling thheorem requirement to the laser point cloud Density Distribution of ground based scanning.But landform spatial frequency is very complicated usually, as document (Shi Wenzhong. spatial data and spatial analysis uncertainty principle. Science Press, Beijing, 2005.6, p144) sayed in, " landform of occurring in nature has two kinds of fundamental types, the landform (radio-frequency component enriches) of acute variation and the landform (low-frequency component enriches) of smooth variation.The complicated landform of any one all can regard as the synthesis of these two kinds of situations, and difference is that the ratio of this two type contained is different ".Therefore, different landform is made up of different frequencies, for different landform, should take different sample frequency.Airborne laser radar adopts different sample frequency to have following two advantages: on the one hand, from terrain reconstruction angle, can ensure undistorted reproduction real terrain; On the other hand, from the efficiency of whole laser scanning system, can make the service efficiency that system reaches the highest, as laser instrument, can to obtain maximum life, data acquisition and memory system data amount minimum, most effective etc.
In addition, airborne laser radar is in actual mechanical process, and airplane design is that absolute flying height (i.e. sea level elevation) is fixed, but changes along with the elevation of tested landform, and the relative flying height between aircraft and tested topographical surface can change.The change of airborne platform and topographical surface relative flying height causes the sweep bandwidth of ground laser point cloud to change, and the number of scan points of often going is constant, therefore the change of laser scanning bandwidth can cause a cloud density to change.When relative flying height increases, the sweep bandwidth of laser point cloud increases, and in making often to go, laser spots spacing increases, therefore some cloud density reduces, and the spatial resolution of laser sampling data is declined, causes the distortion of reconstruction of three-dimensional relief block to increase; Otherwise, when relative flying height reduces, the sweep bandwidth of laser point cloud reduces, although the laser spots spacing in often going reduces, some cloud density increases, the precision that can be conducive to follow-up three-dimensional imaging improves, but also causes the overlapping region between scanning strip to reduce, even occurs drain sweep region; Meanwhile, too high dot density can cause data to store and difficult treatment, and mass cloud data may make hard disk leave, and causes data redundancy, simultaneously data processing time length, inefficiency etc.Therefore, need to change according to the elevation of landform, in real time parameter is adjusted, stablize constant to keep analyzing spot cloud bandwidth sum dot density.
To sum up, according to tested lineament, i.e. landform altitude change and topographic space frequency change, the parameter setting values of real-time reconditioner bone laser radar, airborne laser radar can be made to reach optimum scanning mode, obtain optimum work efficiency and rebuild relief block precision, therefore having important practical significance.
According to the principle of work of airborne laser radar, affect in the factor of laser point cloud density, for aircraft, be mainly flying height and the flying speed on relative ground; For laser scanner, be mainly scanning field of view angle, sweep frequency and pulse repetition rate.Generally, in order to flight efficiency and security, the flying height of aircraft and speed determine that, with changeless, this depends on the performance of aircraft, then the settings of the changeable scanning field of view angle only had in laser scanner, sweep frequency and pulse repetition rate three parameters.
In current airborne laser radar, the operational parameter settings of laser scanner is generally fixing, after namely starting flight, only has a kind of single parameter mode of operation, cannot adaptively changing.
Therefore, the object of the application's patent proposes a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament, by arranging multiple airborne measurement load, obtain the various information about flight parameter and tested lineament, analyze elevation change and the spatial frequency feature of tested landform, adopt optimal design and adaptive control mode, according to fluctuating characteristic and the complexity of landform, three parameter setting values of real-time adjustment laser scanner, i.e. scanning field of view angle, sweep frequency and pulse repetition rate, to reach the object of adaptively changing point cloud bandwidth sum dot density, make terrain sampling meet sampling thheorem all the time and want ball, Simultaneous Sampling Data amount is not too large again, thus reach a kind of data acquisition state of Optimization Balancing.
Summary of the invention
The method and apparatus according to topography variation feature, airborne laser radar parameter being carried out to real-time adaptive adjustment is also lacked in existing airborne laser radar measuring technique, the invention provides a kind of method and apparatus carrying out the adjustment of airborne lidar parameter real-time adaptive based on tested lineament, its objective is, when tested lineament changes, three parameter values of real-time change airborne laser radar, as scanning field of view angle, sweep frequency and pulse repetition rate, laser scanning point cloud distribution and density is made to reach optimum state.
A kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament provided by the invention and device, is characterized in that comprising terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3), airborne platform (4).Described terrain feature and flight parameter measurement device (1) comprise laser scanner (11), aircraft flight speed measuring instrumentation (12), aerocamera (13).Described scanner parameter adjustment control (3) comprises pulse repetition rate regulating device (31), sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33).Described airborne platform (4) is the mounting platform of various load, and described terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3) are all fixed on described airborne platform (4).Described laser scanner parameter adaptive CONTROLLER DESIGN (2) obtains laser scanner (11), aircraft flight speed measuring instrumentation (12), the measurement data of aerocamera (13), by real-time calculating, obtain tested lineament, as two dimensional terrain spatial frequency and elevation information, calculate by optimizing, obtain three running parameters of laser scanner, i.e. pulse repetition rate, sweep frequency, the optimal adjustment value at scanning field of view angle, and export control signal, control described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33) realizes the real-time adjustment of three operational parameter settings.Described airborne platform (4) keeps sea level elevation constant and unaccelerated flight, when tested landform has elevation to change, relative flying height between described airborne platform (4) and tested topographical surface changes, cause the wide and dot density respective change of the analyzing spot cloud bar of airborne laser radar, by adjustment scanning field of view angle and pulse repetition rate, analyzing spot cloud bandwidth sum dot density can be kept constant.When tested topographic space frequency changes, by regulating sweep frequency and pulse repetition rate settings in real time, laser scanning sample frequency in the two-dimensional direction can be changed, make laser scanning point cloud density meet sampling thheorem requirement all the time, avoid the distortion of subsequent reconstruction three-dimensional terrain model.
Wherein, aircraft flight speed measuring instrumentation (12) adopts pitot tube air speed instrument to measure, and wherein pitot tube (121) horizontal positioned, then this current situation pressure is zero, then the air hydrodynamic that pitot tube is measured is that total head deducts static pressure.By differential pressure type pressure transducer (122) by dynamic pressure
be converted to voltage export, self-induction type displacement transducer as differential in differential capsule formula, then by
, wherein
be atmospheric density, thus can flying speed be obtained
v.Laser ranging value when adopting laser scanner to overlap with sky bottom line, laser ranging value when namely scan angle is zero, as the relative flying height value between airborne platform (4) and tested topographical surface.The laser ranging data adopting the former seconds times of laser scanner and the view data obtained by aerocamera, predict the two dimensional terrain spatial frequency of tested landform on heading and horizontal scanning direction as calculated, be designated as
with
.
Wherein, aircraft unaccelerated flight and flight time keep sea level elevation to immobilize, but when tested landform has elevation to change, the relative flying height between aircraft and tested topographical surface can be changed, cause that analyzing spot cloud bar is wide to change.Suppose that sweep frequency and the pulse repetition rate of laser scanner are constant, when tested landform is higher, then the relative height between aircraft and tested ground is less, and analyzing spot cloud bar is wide narrower, and the dot density of laser point cloud can uprise; Otherwise when tested landform is lower, relative flying height is larger, and analyzing spot cloud bar is wide, then dot density is lower.The degree of overlapping that can reduce between adjacent bandwidths that what analyzing spot cloud bar was wide narrow, serious meeting causes the drain sweep of tested landform, causes sampling unsuccessfully, tested landform partial reconstruction disappearance.Point cloud density too Gao Zehui causes data redundancy, be unfavorable for the raising of the Storage and Processing efficiency of data, and the too low distortion increase that can cause reconstruction topographical surface model of density, therefore, need to carry out real-time optimization adjustment according to lineament to Laser Scanning Parameters.
Wherein, described laser pulse transmitter (311) sends laser pulse, described rotating prism (332) is arrived after described catoptron (331) reflection, directive ground after described rotating prism (332) reflection, described rotating prism motor (321) drives described rotating prism (332) to rotate, and described rotating prism optical electric axial angle encoder (333) measures the real-time rotational angle of described rotating prism (332).Described pulse repetition rate regulating device (31) produces the square-wave signal of required frequency, is supplied to described laser pulse transmitter (311), can realizes the adjustment of laser pulse repetition frequency.The exportable control signal of described sweep frequency regulating device (32), can realize the adjustment of sweep frequency by the rotating speed changing described rotating prism motor (321).Described laser scanning visual field angle regulating apparatus (33) can measure the real-time rotational angle of described rotating prism (332) according to described rotating prism optical electric axial angle encoder (333), by adjusting the scan angle size of effective Emission Lasers pulse of described rotating prism (332), realize the adjustment at scanning field of view angle.
Wherein, when landform altitude changes, relative flying height between aircraft and tested topographical surface changes, and the adjustment object of laser scanning instrument parameter is by adjustment scanning field of view angle and pulse repetition rate, makes analyzing spot cloud bandwidth sum dot density on ground remain constant.If the desirable relative flying height between aircraft and tested ground is
, ideal scan field angle is
o (), when practical flight height is
time, scanning field of view angle becomes
o (), requires that sweep bandwidth is constant, has
, then
.In addition, if the rotating speed of described rotating prism (332) is
n(rev/min), then angular velocity is 60
n(o/s) number of scan points of every bar sweep trace while of,
mfor constant, in desirable relative flying height be then
, scanning field of view angle is
o, time (), the sweep time obtaining a laser scanning line is
, then the pulse repetition rate under desirable relative flying height is
(Hz).In like manner, when actual relative flying height is
, scanning field of view angle is
o, time (), pulse repetition rate is now
(Hz), then
.Therefore, when tested landform altitude changes, by formula
, the real-time regulated value at scanning field of view angle can be obtained; Again by formula
, the real-time regulated value of pulse repetition rate can be obtained, thus the adverse effect of landform altitude change to laser scanning bandwidth sum dot density can be eliminated.
Wherein, according to sampling thheorem, the 3-D view of the tested landform of undistorted reconstruction, first obtain the highest frequency of tested landform
, and the parameter designing value of airborne laser radar should be able to make ground sample frequency meet
, ground sample frequency then depends primarily on the density of a cloud.Because different terrain has different undulatory propertys and complicacy, namely there is different topographic space frequencies, different sample frequency should be adopted in Laser Radar Scanning mapping process, rebuild the three-dimensional model of tested landform with the sampling efficiency of optimum, be therefore necessary to carry out adaptive design airborne laser radar parameter value according to tested topographic space frequency feature.
Wherein, according to the spatial frequency feature of flying speed, relative flying height and tested landform, calculate and obtain laser scanner three parameters, be i.e. the real-time regulated value of scanning field of view angle, sweep frequency and pulse repetition rate.For rotating prism line sweep mode, if sweep frequency is
n, the flying speed of aircraft is
v, relative flying height is
h, laser pulse repetition frequency is
f r , field angle is fov(fieldofview), the number of scan points of laser scanning a line is
m(that is
f r /
n), then the dot spacing in a horizontal scanning line is
, line space is
.
Wherein, if relative flying height
hand flying speed
vconstant, variable parameter is field angle fov, scanning mirror sweep frequency is n and laser pulse repetition frequency
f r , now, some cloud density is:
.When the sample frequency of laser point cloud is greater than the twice of tested topographic space frequency, then meeting sampling thheorem, can not there is distortion in the landform three-dimensional model of reconstruction.If be two one dimension samplings by plane sub-sample resolution, when meeting sampling thheorem condition, have:
,
.Wherein,
with
be respectively the spatial frequency of tested ground in x direction and y direction, then
.Due to
,
, therefore:
,
, then
, and
.In reality, for improving sample frequency, general sample frequency is taken as 3 ~ 5 times of tested topographic space frequency, if get 3 times, then when desirable relative flying height is H
e, actual relative flying height is H
a, flying speed is v, ideal scan field angle is
time, then actual scanning field angle
, sweep frequency n, pulse repetition rate
calculating formula be respectively:
。
In addition, known when being changed by tested landform altitude required pulse repetition rate adjusted value be
, therefore, actual pulse repetition rate is desirable
with
in maximal value, then can meet simultaneously by landform altitude change and topographic space frequency change required by pulse repetition rate adjusted value.To sum up, if obtain flying height, the landform spatial frequency in the two-dimensional direction on flying speed, the relatively ground of aircraft
,
, then can to three of a laser scanner parameter value, namely scanning field of view angle, sweep frequency, pulse repetition rate carry out real-time adaptive optimization design.
Wherein, adopt the number of scan points certificate of former seconds times of laser scanner, in conjunction with the front width view data of aerocamera, tested landform two dimensional spatial frequency can be obtained, namely
with
.
Wherein, predict that the method for landform spatial frequency is as follows by laser scanner past data: in the laser chopper along x direction or a laser scanning line along y direction, crust deformation dynamic frequency is embodied in following three indexs: (1) angle changing: from left to right, the line extended line of 2 was datum line in the past, calculate the angle rotating to down some lines, wherein corner is just set to counterclockwise, and clockwise corner is set to negative, article one, in sweep trace all positive and negative corner absolute values and average, namely
, this average is larger, then the frequency change of landform on this scan-line direction is larger.(2) the positive and negative sudden change number of times of corner (is designated as
w): namely corner is by just becoming negative and by the positive change number of times of negative change, can reflecting topographic space frequency size, add up by following program:
w=0
forj=1,n
if
w=
w+1
end
(3) in the two-dimensional direction, the maximal value of the absolute value of positive and negative corner
with
, it can reflect the fluctuation severe degree of landform, and this value is larger, then landform fluctuation Shaoxing opera is strong.
The topographic space coefficient of frequency then obtained by the past data of laser scanning point cloud can be expressed as:
;
, wherein,
with
empirical scalar coefficient,
with
be respectively the positive and negative sudden change number of times of each corner in x direction and y direction laser scanning line.
Wherein, the front width image of aerocamera collection is utilized to obtain terrain texture feature as follows to the method analyzing landform spatial frequency: the image obtained by aerocamera tries to achieve its gradient map, gradient reflects the steep of often some slope on image, and the Grad as object edge place is just larger.According to the size of gradient, the distribution situation of different objects in image can be judged.Obtain mean value after being added by the Grad at pixel places all in image, the large I of gradient mean value reflects the intensity of variation of image texture.Gradient mean value is larger, then image texture variation is larger, and the possible space frequency of landform is also larger.In image procossing, the gradient calculation of certain pixel can adopt following formula:
, namely the Grad at certain pixel place is the maximal value in the absolute value of this some absolute value of the difference of neighbor and the difference of vertical direction neighbor in the horizontal direction.
In a sub-picture, the average of the Grad of all pixels is:
.
Wherein, comprehensively by the view data of laser point cloud data and aerocamera, the topographic space coefficient of frequency of acquisition can be calculated as:
；
。
In practical application, before flight, carry out experience according to scanning area estimate, obtain the experience sweep frequency on two-dimensional directional and topographic space coefficient of frequency, namely
with
,
with
, then can obtain in practical flight process, in real time frequency values is estimated to landform on two-dimensional directional, be calculated as follows:
，
。
Wherein, based on the airborne laser radar parameter real-time adaptive Optimum Design System of tested lineament by ARM embedded system as described laser scanner parameter adaptive CONTROLLER DESIGN (2).By described laser scanner (11), flying speed measuring instrument (12) and aerocamera (13) obtain the flight parameter of aircraft and the laser scanning point cloud of tested landform and photographs, be sent to respectively in ARM controller through serial ports, obtain height value and the topographic space frequency characteristic parameter prediction value of tested landform as calculated, calculate the real-time optimization design load of three adjustment parameters of laser scanner further, the real-time optimization design load of these three parameters is exported by D/A delivery outlet, be supplied to described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32) and laser scanning visual field angle regulating apparatus (33), thus paired pulses repetition frequency can be realized, the real-time optimal adjustment at sweep frequency and scanning field of view angle.
Accompanying drawing explanation
Fig. 1 is the airborne laser radar parameter adaptive adjustment System composition diagram based on tested lineament.
Fig. 2 is the airborne laser radar parameter adaptive adjustment System measuring equipment mounting structure schematic diagram based on tested lineament.
Fig. 3 is that landform altitude change is to an effect diagram for cloud density.
Fig. 4 is that laser scanner principle of work and parameter regulate schematic diagram.
The method of adjustment schematic diagram of laser scanning instrument parameter when Fig. 5 is landform altitude change.
Fig. 6 is according to the method for adjustment analysis chart of tested topographic space frequency change to Laser Scanning Parameters.
Fig. 7 is the computing method schematic diagram by prior laser analyzing spot and the tested topographic space frequency of aerocamera image prediction.
Fig. 8 is the airborne laser radar parameter real-time adaptive adjustment System hardware configuration schematic diagram based on tested lineament.
Embodiment
Below in conjunction with accompanying drawing, patent Example of the present invention is described in further detail.
Fig. 1 is the airborne laser radar parameter adaptive adjustment System composition diagram based on tested lineament.A kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament provided by the invention and device, is characterized in that comprising terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3), airborne platform (4), described terrain feature and flight parameter measurement device (1) comprise laser scanner (11), aircraft flight speed measuring instrumentation (12), aerocamera (13), described scanner parameter adjustment control (3) comprises pulse repetition rate regulating device (31), sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33), described airborne platform (4) is the mounting platform of various load, and described terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3) are all fixed on described airborne platform (4), described laser scanner parameter adaptive CONTROLLER DESIGN (2) obtains laser scanner (11), aircraft flight speed measuring instrumentation (12), the measurement data of aerocamera (13), by real-time calculating, obtain tested lineament, i.e. two dimensional terrain spatial frequency and elevation information, calculate by optimizing, obtain three running parameters of laser scanner, i.e. pulse repetition rate, sweep frequency, the optimal adjustment value at scanning field of view angle, and export control signal, control described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33) realizes the real-time adjustment of three operating parameter values, described airborne platform (4) keeps sea level elevation constant and unaccelerated flight, when tested landform has elevation to change, relative flying height between described airborne platform (4) and tested topographical surface changes, cause the wide and dot density respective change of airborne laser radar analyzing spot cloud bar, by adjusting scanning field of view angle and pulse repetition rate in real time, maintenance analyzing spot cloud bar is wide and dot density is constant, when tested topographic space frequency changes, by regulating sweep frequency and pulse repetition frequency values in real time, change laser scanning sample frequency in the two-dimensional direction, make a cloud density meet sampling thheorem requirement all the time, avoid the distortion of subsequent reconstruction three-dimensional terrain model.
Fig. 2 is the airborne laser radar parameter adaptive adjustment System measuring equipment mounting structure schematic diagram based on tested lineament.Aircraft flight speed measuring instrumentation (12) adopts pitot tube air speed instrument to measure, and wherein pitot tube (121) horizontal positioned, then this current situation pressure is zero, then the air hydrodynamic that pitot tube is measured is that total head deducts static pressure.By differential pressure type pressure transducer (122) by air hydrodynamic
be converted to voltage export, self-induction type displacement transducer as differential in differential capsule formula, then by
, wherein
be atmospheric density, thus can flying speed be obtained
v; Adopt the laser ranging value of laser scanner when overlapping with sky bottom line, distance measurement value when namely scan angle is zero, as the relative flying height value between described airborne platform (4) and tested topographical surface; Adopt laser point cloud data and the width view data before being obtained by aerocamera of former seconds time of laser scanner, predict the two dimensional terrain spatial frequency of tested landform on heading and horizontal scanning direction through COMPREHENSIVE CALCULATING, be designated as
with
.
Fig. 3 is that landform altitude change is to an effect diagram for cloud density.Aircraft unaccelerated flight also keeps sea level elevation to immobilize, but when tested landform has elevation to change, can change the relative flying height of aircraft and tested topographical surface, causes that analyzing spot cloud bar is wide to change.Suppose that sweep frequency and the pulse repetition rate of laser scanner are constant, when tested landform is higher, then the relative height between aircraft and tested ground is less, and analyzing spot cloud bar is wide narrower, and the dot density of laser footpoint can uprise; Otherwise when tested landform is lower, relative flying height is larger, then analyzing spot cloud bar is wide, then dot density is lower.What analyzing spot cloud bar was wide narrow can reduce the wide degree of overlapping of adjacent analyzing spot cloud bar, and serious meeting causes scanning vacancy, causes the drain sweep of tested landform, causes sampling unsuccessfully, tested landform partial reconstruction disappearance.Point cloud density is too high, causes data redundancy, be unfavorable for that data store and data-handling efficiency, and the too low distortion increase that can cause reconstruction landform digital model of density, therefore, need to carry out real-time optimization adjustment according to the elevation change of landform to Laser Scanning Parameters.
Fig. 4 is that laser scanner principle of work and parameter regulate schematic diagram.Described laser pulse transmitter (311) sends laser pulse, described rotating prism (332) is arrived after described catoptron (331) reflection, directive ground after reflection, described rotating prism motor (321) drives described rotating prism (332) to rotate, and described rotating prism optical electric axial angle encoder (333) measures the real-time rotational angle of described rotating prism (332).Described pulse repetition rate regulating device (31) produces the square-wave signal of required frequency, is supplied to described laser pulse transmitter (311), realizes the adjustment to laser pulse repetition frequency.Described sweep frequency regulating device (32) exports control signal, changes the adjustment of rotating speed realization to sweep frequency of described rotating prism motor (321).Described laser scanning visual field angle regulating apparatus (33) measures the real-time rotational angle of described rotating prism (332) according to described rotating prism optical electric axial angle encoder (333), adjust the scan angle size of effective Emission Lasers pulse of described rotating prism (332), realize the adjustment to scanning field of view angle.
The method of adjustment schematic diagram of laser scanning instrument parameter when Fig. 5 is landform altitude change, its adjustment object is that relative flying height between aircraft and tested topographical surface is when changing, by adjustment laser scanning field angle and pulse repetition rate, analyzing spot cloud bandwidth sum dot density on ground is made to remain constant.If the desirable relative flying height between aircraft and tested ground is
, ideal scan field angle is
o (), then when practical flight height is
time, require that sweep bandwidth is constant, have
, scanning field of view angle can be obtained thus and become
, namely the adjusted value at scanning field of view angle is
.In addition, if the rotating speed of described rotating prism (332) is
n(rev/min), then angular velocity is 60
n(o/s) constant all the time, meanwhile, the number of scan points of every bar sweep trace is set to constant
m, then in desirable relative flying height be
, scanning field of view angle is
o, time (), the sweep time obtaining a laser scanning line is
, then the laser scanning pulsed frequency under desirable relative flying height is
(Hz).In like manner, when actual relative flying height is
, scanning field of view angle is
o, time (), laser scanning pulsed frequency is now
(Hz), then
.Therefore, when landform altitude changes, by formula
, the real-time regulated value at scanning field of view angle can be obtained; Again by formula
, the real-time regulated value of pulse repetition rate can be obtained, thus the adverse effect of landform altitude change to laser scanning bandwidth sum dot density can be eliminated, make the bandwidth sum dot density of ground laser point cloud remain constant.
Fig. 6 is according to the method for adjustment analysis chart of tested topographic space frequency change to Laser Scanning Parameters.According to sampling thheorem, the tested landform 3-D view of undistorted reconstruction, first obtain the highest frequency of tested landform
, and the parameter designing value of airborne laser radar should be able to make ground sample frequency meet
, ground sample frequency then depends primarily on a cloud density.In addition, because different terrain has different undulatory propertys and complicacy, namely there is different topographic space frequencies, Laser Radar Scanning mapping process should adopt different sample frequency, rebuild tested landform three-dimensional model with the sampling efficiency of optimum, be therefore necessary the design airborne laser radar parameter value carrying out real-time adaptive according to landform vibration frequency feature.According to the topographic space frequency of flying speed, relative flying height and tested landform, calculate and obtain laser scanner three parameters, be i.e. the real-time regulated value of scanning field of view angle, sweep frequency and pulse repetition rate.For rotating prism line sweep mode, if scanning mirror sweep frequency is
n, the flying speed of aircraft is
v, relative flying height is
h, laser pulse repetition frequency is
f r , field angle is fov(fieldofview), the number of scan points of laser scanning a line is
m(that is
f r /
n), then the dot spacing in a horizontal scanning line is:
, line space is:
.If flying height
hand speed
vconstant, variable parameter comprises field angle fov, scanning mirror sweep frequency is n and laser pulse repetition frequency
f r , then putting cloud density is:
.When the sample frequency of laser point cloud is greater than the twice of tested topographic space frequency, then meeting sampling thheorem, can not there is distortion in the landform three-dimensional model of reconstruction.If flat scanning to be decomposed into two one-dimensional scannings, to meet under sampling thheorem condition, having:
，
，
Wherein,
with
be respectively the spatial frequency of tested landform on x direction and y direction.Then:
.Due to:
,
, therefore:
,
.Then:
，
。
In reality, in order to improve image quality, general sample frequency is taken as 3 ~ 5 times of tested topographic space frequency, if get 3 times, then when desirable relative flying height is H
e, actual relative flying height is H
a, flying speed is v, ideal scan field angle is
time, then actual scanning field angle
, sweep frequency n, pulse repetition rate
be calculated as follows:
，
，
。
In addition, known when being changed by landform altitude required pulse repetition rate method of adjustment obtain:
, therefore, actual pulse repetition rate settings are desirable
with
in maximal value, then can meet simultaneously by landform altitude change and topographic space frequency change required by pulse repetition rate adjusted value.Therefore, calculate formula according to the above, if obtain flying height, the landform two dimensional spatial frequency on flying speed, the relatively ground of aircraft
,
, then can to three of a laser scanner parameter, namely the settings of scanning field of view angle, sweep frequency, pulse repetition rate are optimized design.
Fig. 7 is the computing method schematic diagram by prior laser analyzing spot and the tested landform two dimensional spatial frequency of aerocamera image prediction.Adopt the number of scan points certificate of former seconds times of laser scanner, in conjunction with the front width view data of aerocamera, obtain the topographic space frequency on tested landform two-dimensional directional, namely
with
.First, predict that the method for landform spatial frequency is as described below by laser scanner past data: describe (a), (b) two laser scanning lines (comprising the laser chopper along x direction and the laser chopper along y direction two kinds) in Fig. 7, predict the spatial frequency of following tested landform according to nearer history scan-data.As can be seen from Fig. 7, the variation frequency of (b) figure is obviously higher than (a) figure, is mainly reflected in following three indexs:
(1) angle changing: from left to right, the line extended line of former 2 is datum line, calculates the angle rotating to down some lines, wherein corner is just set to counterclockwise, clockwise corner is set to negative, in a sweep trace all positive and negative corner absolute values and average, that is:
, visible, this average is larger, then landform is larger in the frequency change that this side up.(2) the positive and negative sudden change number of times of corner (is designated as
w): namely corner is by just becoming negative and by the positive variation number of times of negative change, reflect the spatial frequency of landform, available following program is added up:
w=0
forj=1,n
if
w=
w+1
end
(3) in the two-dimensional direction, the maximal value of the absolute value of positive and negative corner
with
, it can reflect the fluctuation severe degree of landform, and this value is larger, then landform fluctuation Shaoxing opera is strong.Then by the past data of laser scanning point cloud, can obtain topographic space coefficient of frequency is:
，
，
Wherein,
with
for empirical scalar coefficient,
with
be respectively the positive and negative sudden change number of times of each corner in x direction and y direction laser scanning line.
Secondly, the image of aerocamera is utilized to obtain terrain texture feature as follows to the method analyzing landform spatial frequency: the image obtained by aerocamera tries to achieve its gradient map, gradient reflects the steep of often some slope on image, and the Grad as object edge place is just larger.According to the size of gradient, the distribution situation of different objects in image can be judged.Obtain mean value after being added by the Grad at pixel places all in image, the large I of gradient mean value reflects the situation of change of image texture.Gradient mean value is larger, then image texture variation is larger, then the possible space frequency of landform is also larger.In image procossing, the gradient calculation of certain pixel can adopt following formula:
, namely the Grad at certain pixel place is the maximal value in the absolute value of this some absolute value of the difference of neighbor and the difference of vertical direction neighbor in the horizontal direction.In a sub-picture, the average of the Grad of all pixels is:
。
Finally, comprehensively by the view data of laser point cloud data and aerocamera, the topographic space coefficient of frequency of acquisition can be calculated as:
，
。
In practical application, before flight, carry out experience according to tested scanning landform estimate, obtain the experience sweep frequency on two-dimensional directional and topographic space coefficient of frequency, namely
with
,
with
, then can obtain in practical flight process, to the real-time spatial predictor frequency of landform on two-dimensional directional, be calculated as follows:
，
。
Fig. 8 is the airborne laser radar parameter real-time adaptive adjustment System hardware configuration schematic diagram based on tested lineament.Based on the airborne laser radar parameter real-time adaptive Optimum Design System of tested lineament by ARM (LPC2138) embedded system as described laser scanner parameter adaptive CONTROLLER DESIGN (2).By described laser scanner (11), flying speed measuring instrument (12) and aerocamera (13) obtain the flight parameter of aircraft and the laser scanning point cloud of tested landform and photographs, be sent in ARM (LPC2138) controller respectively through serial ports, obtain height value and the topographic space frequency characteristic parameter prediction value of tested landform as calculated, calculate the real-time optimization design load of three adjustment parameters of laser scanner further, the real-time optimization design load of these three parameters is exported by D/A delivery outlet, be supplied to described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32) and laser scanning visual field angle regulating apparatus (33), thus paired pulses repetition frequency can be realized, the real-time optimal adjustment at sweep frequency and scanning field of view angle.
Above to the description of the present invention and embodiment thereof, being not limited thereto, is only one of embodiments of the present invention shown in accompanying drawing.When not departing from the invention aim, designing the structure similar with this technical scheme or embodiment without creation, all belonging to scope.
Claims (6)
1., based on airborne laser radar parameter real-time adaptive method of adjustment and the device of tested lineament, it is characterized in that comprising terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3), airborne platform (4), described terrain feature and flight parameter measurement device (1) comprise laser scanner (11), aircraft flight speed measuring instrumentation (12), aerocamera (13), described scanner parameter adjustment control (3) comprises pulse repetition rate regulating device (31), sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33), described airborne platform (4) is the mounting platform of various load, and described terrain feature and flight parameter measurement device (1), laser scanner parameter adaptive CONTROLLER DESIGN (2), scanner parameter adjustment control (3) are all fixed on described airborne platform (4), described laser scanner parameter adaptive CONTROLLER DESIGN (2) obtains laser scanner (11), aircraft flight speed measuring instrumentation (12), the measurement data of aerocamera (13), by real-time calculating, obtain tested topographical surface feature, i.e. two dimensional spatial frequency and elevation information, calculate by optimizing, obtain laser scanner pulse repetition rate, sweep frequency, the optimal adjustment value at scanning field of view angle, and export control signal, control described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32), laser scanning visual field angle regulating apparatus (33) realizes the real-time adjustment of three operating parameter values, described airborne platform (4) keeps sea level elevation constant and unaccelerated flight, when tested landform has elevation to change, relative flying height between described airborne platform (4) and tested topographical surface changes, cause laser scanning point cloud bandwidth and dot density respective change, by adjusting the value at scanning field of view angle and pulse repetition rate in real time, maintenance analyzing spot cloud bar is wide and dot density is constant, when tested topographic space frequency changes, by regulating sweep frequency and pulse repetition frequency values in real time, change laser scanning sample frequency in the two-dimensional direction, make a cloud density meet sampling thheorem requirement all the time, avoid the distortion of subsequent reconstruction three-dimensional terrain model.
2. according to a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament according to claim 1 and device, it is characterized in that, aircraft flight speed measuring instrumentation (12) adopts pitot tube air speed instrument to measure, by differential pressure type pressure transducer (122), air hydrodynamic is converted to voltage to export, and then obtains flying speed as calculated; Adopt the laser ranging value of laser scanner when sky bottom line, distance measurement value when namely scan angle is zero, as the relative flying height value between airborne platform (4) and tested topographical surface; Adopt laser ranging data and the width view data before being obtained by aerocamera of former seconds time of laser scanner, predict the two dimensional terrain spatial frequency of tested landform on heading and horizontal scanning direction through COMPREHENSIVE CALCULATING, be designated as
with
.
3. according to a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament according to claim 1 and device, it is characterized in that, when landform altitude changes, relative flying height between aircraft and tested topographical surface changes, adjustment laser scanning field angle and pulse repetition rate, make analyzing spot cloud bandwidth sum dot density remain constant; If the desirable relative flying height between aircraft and tested ground is
, ideal scan field angle is
, when practical flight height is
time, require that sweep bandwidth is constant, scanning field of view angle becomes
, have
, then the regulated value at scanning field of view angle is
; If the rotating speed of described rotating prism (332) is
n(rev/min), the number of scan points of every bar sweep trace
mfor constant, when desirable relative flying height is
, scanning field of view angle is
time, ideal laser scanning impulse frequency is
; When actual relative flying height is
, scanning field of view angle is
time, real time laser scanning impulse frequency is
; Therefore
, this is the real-time regulated value of pulse repetition rate.
4., according to claim 1 and a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament according to claim 4 and device, it is characterized in that, when desirable relative flying height is H
e, actual relative flying height is H
a, flying speed is
v, ideal scan field angle is
time, then actual scanning field angle
, sweep frequency
n, pulse repetition rate
computing formula be respectively
,
,
; Pulse repetition rate method of adjustment in addition needed for landform altitude changes obtains
, actual pulse repetition rate is desirable
with
in maximal value, can meet simultaneously by landform altitude change and topographic space frequency change required by pulse repetition rate adjustment; Therefore, when obtaining the flying speed of aircraft, flying height, the landform spatial frequency in the two-dimensional direction on relative ground
,
, then can to three of a laser scanner parameter setting values, namely scanning field of view angle, sweep frequency, pulse repetition rate carry out real-time adaptive optimization design.
5. according to a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament according to claim 1 and device, it is characterized in that, adopt the number of scan points certificate of former seconds times of laser scanner, in conjunction with the view data of aerocamera, obtain tested landform two dimensional spatial frequency
with
; By the previous cloud data of laser scanner, according to three indexs, namely in a sweep trace all positive and negative corner absolute values and average
, corner positive and negative sudden change number of times
w, positive and negative corner absolute value in the two-dimensional direction maximal value
with
, obtain two dimensional terrain spatial frequency predictive coefficient, calculating formula is
with
, wherein
with
for empirical scalar coefficient,
with
be respectively the positive and negative sudden change number of times of each corner in laser scanning line on x direction and y direction; The image of aerocamera is utilized to obtain terrain texture feature, its method is that the image obtained by aerocamera tries to achieve its gradient map, gradient mean value is larger, then image texture variation is larger, the possible space frequency of tested landform is also larger, in a sub-picture, the average of the Grad of all pixels is designated as
; The two dimensional terrain spatial frequency predictive coefficient of comprehensive Point Cloud of Laser Scanner and aerial camera view data can be calculated as and; In practical application, before flight, carry out experience according to scanning area estimate, obtain the experience sweep frequency on two-dimensional directional and two dimensional terrain spatial frequency predictive coefficient, be designated as and and, then the topographic space frequency meter formula of estimating in real time on tested landform two-dimensional directional is
with
.
6., according to a kind of airborne laser radar parameter real-time adaptive method of adjustment based on tested lineament according to claim 1 and device, it is characterized in that, by ARM embedded system as described laser scanner parameter adaptive CONTROLLER DESIGN (2), described laser scanner (11), flying speed measuring instrument (12) and aerocamera (13) obtain laser scanning point cloud and the photographs of tested landform, be sent to respectively in ARM controller through serial ports, obtain flying speed and the relative flying height of aircraft as calculated, and the two dimensional spatial frequency discreet value of tested landform, and then calculate the pulse repetition rate of laser scanner, the real-time optimization design load of sweep frequency and scanning field of view angle three parameters, the real-time optimization design load of these three parameters is exported by D/A delivery outlet, be supplied to described pulse repetition rate regulating device (31) respectively, sweep frequency regulating device (32) and laser scanning visual field angle regulating apparatus (33), thus can realize regulating the real-time adaptive of three parameter values.
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