CN107451957B - Imaging simulation method and device for satellite-borne TDI CMOS camera - Google Patents
Imaging simulation method and device for satellite-borne TDI CMOS camera Download PDFInfo
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Abstract
The invention provides a satellite-borne TDI CMOS camera imaging simulation method and equipment, wherein the method comprises the steps of obtaining a data source range of a CMOS instantaneous focal plane imaging area according to geometric parameters and satellite attitude and orbit data of a CMOS camera, obtaining earth surface reflectivity and atmospheric transmission simulation parameters of the imaging area, calculating an integration time interval according to image ground resolution, obtaining satellite orbit data and attitude data of each integration moment, uniformly dividing a CMOS pixel into a plurality of sub-pixels, obtaining a CMOS camera entrance pupil radiance image of each integration moment according to the parameters, filtering the CMOS camera entrance pupil radiance image to obtain a CMOS focal plane radiance image of each integration moment, converting the CMOS focal plane radiance image into a charge number image to obtain a charge number image of each integration moment, performing integration delay accumulation on the charge number image, and performing analog-to-digital conversion to obtain a gray value image. The invention solves the problems that the TDI CCD camera adopted by the existing surveying and mapping remote sensing satellite has many limitations and the imaging simulation research of the TDI CMOS camera is less.
Description
Technical Field
The invention relates to the technical field of satellite imaging simulation, in particular to a satellite-borne TDI CMOS camera imaging simulation method and equipment.
Background
With the development of the space remote sensing technology, people have higher and higher requirements on the updating frequency of remote sensing data. The time resolution of the remote sensing image needs to reach one day or even several hours. However, the satellite with a large platform like resource three is not only high in cost, but also limited in satellite maneuvering performance, and is difficult to meet the increasing image acquisition speed. The small satellite carrying the CMOS imaging sensor can form a satellite constellation due to low cost, and an image with hour-level time resolution is obtained, so that the small satellite is becoming a new trend in the field of space remote sensing.
Compared with the traditional CCD imaging sensor, the CMOS sensor has the advantages of low power consumption, high integration level, small size, strong anti-interference capability and the like, and the CMOS sensor can realize continuous-stage integral imaging, while the CCD imaging sensor can only meet the imaging requirements of a plurality of fixed integral stages. Therefore, the CMOS imaging sensor has great potential in the field of aerospace remote sensing and tends to gradually replace the CCD sensor.
Most of traditional mapping remote sensing satellites (such as resource III) adopt TDI CCD imaging sensors, and earth surface images are obtained in a linear array push-broom mode. While the new CMOS imaging sensors differ from CCDs in many ways. The CCD sensor transfers charges formed by incident photons in the photoelectric conversion unit (pixel) to be sequentially transferred and output, converted into an analog signal by a component outside the pixel array, and then converted into a digital signal. CMOS sensors integrate control and conversion components into the pixels, inside each of which incident photons are converted into digital signals. This makes CMOS sensors have different integration imaging modes than CCD sensors. In addition, unlike the CCD sensor which forms one line of image at a time, the satellite-borne CMOS sensor outputs one two-dimensional image at a time. Therefore, the images acquired by the satellite-borne CMOS sensor and the CCD linear array push-broom images have different characteristics.
Satellite imaging simulation has become an important link in modern satellite engineering. The success of the first civil transmission type three-dimensional mapping satellite resource III in China benefits from the detailed demonstration of various technical indexes of the satellite in the prior art to a great extent, and the satellite imaging simulation plays an important role in the technical index demonstration of the resource III and the construction of a ground application system. However, the conventional CCD sensor imaging simulation method cannot be directly applied to CMOS sensor imaging simulation and analysis. In order to analyze the imaging characteristics of the satellite-borne CMOS sensor and the influence of external influencing factors on the imaging quality and error positioning, the imaging characteristics and the influence are fed back to the optimization design of the satellite and the sensor so as to improve the accuracy and the use value of the image of the satellite and the sensor, and the imaging simulation technology of the satellite-borne TDI CMOS camera needs to be researched.
In the technical field of satellite imaging simulation, scholars at home and abroad put forward three technical approaches of physical simulation, semi-physical simulation and computer numerical simulation, wherein the engineering cost of the computer numerical simulation is the lowest. The method adopts the computer numerical value to simulate the whole link flow of the real current orbit dynamic imaging process, can compare the influence of the design technical index of the all-round simulated satellite on the on-orbit imaging quality of the satellite, and establishes the direct correlation between the satellite design parameters and the on-orbit imaging quality. Real satellite camera imaging is a process of acquiring and converting radiation information of a real ground physical scene, a numerical ground model is also needed for computer numerical simulation, and the numerical ground model needs to comprise geometric information and radiation information of each point on the ground. In other words, the ground model is composed of a geometric model that provides geometric information for each ground point and a radiation model that provides radiation information for each point on the ground.
Most of the existing simulation software and methods are directed at the traditional TDI CCD imaging sensor, so that the imaging simulation research of the satellite-borne TDICMOS camera is very urgent. The satellite image quality is the result of the combined action of a series of factors such as the performance of a sensor, the motion of a satellite platform, the working environment and the like. The imaging simulation of the satellite-borne TDI CMOS camera needs to comprehensively consider various influence factors, and the on-orbit time delay integral imaging simulation of the satellite-borne TDI CMOS camera can be realized only by designing reasonable technical indexes and working modes.
Disclosure of Invention
In view of this, the embodiment of the invention provides an imaging simulation method and device for a satellite-borne TDI CMOS camera, so as to solve the problems that the existing surveying and mapping remote sensing satellite has many limitations due to the adoption of the TDI CCD camera and few imaging simulation researches are performed on the TDI CMOS camera.
Therefore, the embodiment of the invention provides the following technical scheme:
the embodiment of the invention provides a satellite-borne TDI CMOS camera imaging simulation method, which comprises the following steps: simulating satellite orbit data and satellite attitude data, acquiring a data source range of a CMOS instantaneous focal plane imaging area according to geometric parameters of a CMOS camera, the satellite orbit data and the satellite attitude data, acquiring earth surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging area, calculating an integration time interval according to image ground resolution, acquiring satellite orbit data and attitude data at each integration moment, acquiring a CMOS camera entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, the satellite orbit data and the attitude data at each integration moment, filtering the CMOS camera entrance pupil radiance image to acquire the CMOS focal plane radiance image at each integration moment, converting the CMOS focal plane radiance image at each integration moment into a charge number image to acquire the charge number image at each integration moment, and integrating, delaying and accumulating the charge number image at each integration moment, and performing analog-to-digital conversion to obtain a gray value image.
Optionally, acquiring a data source range of a CMOS instantaneous focal plane imaging region according to geometric parameters of a CMOS camera, the satellite orbit data, and the satellite attitude data, includes: interpolating the satellite orbit data and the satellite attitude data to obtain the satellite orbit data and the satellite attitude data at the imaging moment; acquiring coordinates of ground points in an earth reference coordinate system through a frame type strict geometric imaging model according to the satellite orbit data of the imaging moment and the geometric parameters of the CMOS camera; acquiring longitude and latitude of the ground point corresponding to the image point according to the coordinates of the ground point in the earth reference coordinate system; and extending the longitude and latitude of the ground point corresponding to the image point by a preset distance to obtain the data source range of the CMOS instantaneous focal plane imaging area.
Optionally, obtaining coordinates of the ground point in the earth reference coordinate system through a framed rigorous geometric imaging model according to the satellite orbit data at the imaging time and the geometric parameters of the CMOS camera, including:
in the formula (X)P,YP,ZP)TIs the coordinate of the ground point in the earth reference coordinate system, t is the imaging time, (X (t), Y (t), Z (t))TIs the coordinate of the projection center of the imaging moment sensor under the earth reference coordinate system, lambda is the denominator of the imaging scale at the imaging moment,
is a rotation matrix between a celestial sphere reference coordinate system and an earth reference coordinate system at the imaging moment,
is a rotation matrix between the satellite body and the celestial sphere reference coordinate system at the imaging moment,
for the mounting bias matrix of the CMOS camera, f is the focal length of the CMOS camera and (x, y) is the image plane coordinates.
Optionally, acquiring surface reflectivity and atmospheric transmission simulation parameters according to a data source range of the CMOS instantaneous focal plane imaging area, including: selecting multiple types of ground objects with known reflectivity, counting the gray level mean value of the multiple types of ground objects on a high-resolution ortho-image, and determining the gray level mean value and reflectivity combination of the multiple types of ground objects, wherein the high-resolution ortho-image is one of basic data for simulation; performing interpolation on the gray average value and the reflectivity combination of the multiple types of ground objects to calculate the earth surface reflectivity; acquiring a radiation transmission lookup table according to the atmospheric radiation transmission model and atmospheric parameters; and calculating the atmospheric transmission simulation parameters through linear interpolation according to the observation angle at the imaging moment, the optical thickness of the aerosol and the radiation transmission lookup table.
Optionally, a plurality of types of ground objects with known reflectivity are selected, the gray level mean value of the plurality of types of ground objects on the high-resolution ortho image is counted, and the combination of the gray level mean value and the reflectivity of the plurality of types of ground objects is determined, wherein the expression is as follows:
wherein n is the total number of selected ground object classes of known reflectivity, v is the brightness value of the high resolution image,
surface reflectance of v is given by a value of [0, 1]]In the range, vi、vjBrightness values, w, corresponding to the i, j-th class of ground objectsiThe reflectivity corresponding to the i-th class of land objects.
Optionally, the calculating an integration time interval according to the image ground resolution to obtain satellite orbit data and attitude data at each integration time includes: acquiring the ground resolution of an image and the ground speed of a satellite along the track direction according to the size of the CMOS camera probe element, the focal length of the CMOS camera and the satellite track data; acquiring an integration time interval according to the image ground resolution and the ground speed of the satellite along the orbital direction; and respectively acquiring satellite orbit data and attitude data of each integration moment by Lagrange interpolation and quaternion spherical interpolation according to the integration time interval and the satellite orbit data and the satellite attitude data.
Optionally, acquiring a CMOS camera entrance pupil radiance image according to the surface reflectivity, the atmospheric transmission simulation parameter, the satellite orbit data at each integration time, and the attitude data, includes: uniformly dividing each CMOS pixel into a plurality of sub-pixels, calculating an image plane coordinate corresponding to each CMOS sub-pixel, calculating a ground point coordinate corresponding to each sub-pixel through a frame-type strict geometric imaging model and a Digital Surface Model (DSM) according to the image plane coordinate and satellite orbit data and attitude data at each integration moment, interpolating and obtaining the reflectivity of each sub-pixel through the ground surface reflectivity according to the ground point coordinate corresponding to each sub-pixel, calculating the entrance pupil radiance of each sub-pixel according to the atmospheric transmission simulation parameters, calculating the entrance pupil radiance of each CMOS pixel according to the entrance pupil radiance image of the sub-pixel corresponding to the CMOS pixel, and obtaining the entrance pupil radiance image of the CMOS camera.
Optionally, the integrating, delaying and accumulating the charge number image at each integration time, and performing analog-to-digital conversion to obtain a gray value image, including: and according to the charge number image at each integration time, performing delay accumulation on the obtained charge number images at a plurality of integration times according to the following formula:
wherein I is the final integral image, IiThe number of charges at the ith integration time is the image, M is the number of integration times, and (M, n) represents the mth row and nth column of the image; and performing analog-to-digital conversion on the image after the delayed accumulation is finished to obtain a final analog image with a gray value.
An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the imaging simulation method of the satellite-borne TDI CMOS camera as described above.
The embodiment of the invention also provides computer equipment, which comprises at least one processor and a memory which is in communication connection with the at least one processor; wherein the memory stores a computer program executable by the at least one processor to cause the at least one processor to perform the on-board TDI CMOS camera imaging simulation method as described above.
The embodiment of the invention has the following advantages:
the embodiment of the invention provides a satellite-borne TDI CMOS camera imaging simulation method and equipment, wherein the method comprises the steps of obtaining a data source range of a CMOS instantaneous focal plane imaging area according to geometric parameters, satellite orbit data and satellite attitude data of a CMOS camera, obtaining earth surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging area, calculating an integration time interval according to image ground resolution, obtaining satellite orbit data and attitude data at each integration moment, obtaining a CMOS entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, the satellite orbit data and the attitude data at each integration moment, filtering the CMOS entrance pupil radiance image, and obtaining the CMOS focal plane radiance image at each integration moment; and converting the CMOS focal plane radiance image at each integration moment into a charge number image to obtain the charge number image at each integration moment, accumulating the charge number image, and performing analog-to-digital conversion to obtain a gray value image. According to the invention, through orbit simulation, attitude simulation, atmospheric transmission simulation and CMOS digital domain delay integral imaging simulation, high-precision simulation of a strict geometric conversion and radiation conversion process is integrated by satellite orbit and attitude data, atmospheric transmission, camera geometric parameters and TDI CMOS multistage dynamic integral, and the accuracy of an imaging simulation result is ensured.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a flow chart of a method for imaging simulation of a satellite-borne TDI CMOS camera according to an embodiment of the invention;
FIG. 2 is a CMOS digital domain time delay integration scheme according to an embodiment of the present invention;
fig. 3 is a schematic hardware structure diagram of a computer device of the imaging simulation method of the satellite-borne TDI CMOS camera according to the embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it should be noted that the terms "first", "second", and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
In this embodiment, a method for imaging simulation of a satellite-borne TDI CMOS camera is provided, and fig. 1 is a flowchart of a method for imaging simulation of a satellite-borne TDI CMOS camera according to an embodiment of the present invention, as shown in fig. 1, the flowchart includes the following steps:
s101: simulating satellite orbit data and satellite attitude data; the satellite orbit data comprises scanning time, position and speed data of a satellite under an earth reference coordinate, and the satellite orbit is described by orbit six parameters in a celestial sphere reference coordinate system: the system comprises a satellite platform, a satellite attitude data acquisition system and a satellite attitude data acquisition system, wherein the satellite attitude data acquisition system comprises an orbit height, an orbit inclination angle, an orbit eccentricity ratio, an perigee amplitude angle, a true perigee angle and a rising intersection declination, and the satellite attitude data comprises a pitch angle, a roll angle and a yaw angle of the satellite platform.
S102: acquiring a data source range of a CMOS instantaneous focal plane imaging area according to the geometric parameters, the satellite orbit data and the satellite attitude data of the CMOS camera; specifically, a strict geometric imaging model is established to obtain a geometric relationship between a two-dimensional image point and a three-dimensional ground point of the CMOS camera, in this embodiment, an approximate longitude and latitude of the ground point corresponding to the image point is calculated by taking a Digital Surface Model (DSM) average elevation as an initial elevation H, a more accurate elevation H' is obtained by interpolation on the DSM and is calculated again, and iterative calculation is performed until an elevation change | Δ H | obtained by calculation twice before and after satisfies a set threshold value, so that a three-dimensional coordinate of the ground point corresponding to the image point is obtained. And sequentially resolving geodetic coordinates corresponding to four corners of the CMOS focal plane and extending a certain distance outwards to obtain the geographic range of the simulation reference data source corresponding to the CMOS instantaneous focal plane imaging area.
S103: acquiring earth surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging area; the earth surface reflectivity and the atmospheric transmission simulation parameters are obtained and used for imaging simulation of the CMOS camera, and the simulation precision can be improved.
S104: calculating an integration time interval according to the image ground resolution, and acquiring satellite orbit data and attitude data at each integration moment; in the satellite flight process, the TDI CMOS camera is formed by accumulating images at a plurality of integration moments into one image in the imaging process, so that the simulation is carried out on the image at each integration moment, and satellite orbit and attitude data at each integration moment are acquired firstly.
S105: acquiring a CMOS camera entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, and the satellite orbit data and the attitude data at each integration moment; and uniformly dividing each CMOS pixel into a plurality of sub-pixels, acquiring the entrance pupil radiance of each sub-pixel, and calculating the focal plane radiance of each pixel according to the entrance pupil radiance of the corresponding sub-pixel of each CMOS pixel to obtain the entrance pupil radiance image of the CMOS camera.
S106: filtering the CMOS camera entrance pupil radiance image to obtain a CMOS focal plane radiance image at each integration moment; and according to the performance of the CMOS sensor, selecting a point spread function to filter the CMOS camera entrance pupil radiance image to obtain a CMOS focal plane radiance image at an integration moment, and performing the operations of the steps S105 and S106 on each integration moment to finally obtain the CMOS focal plane radiance image at each integration moment.
S107: converting the CMOS focal plane radiance image at each integration moment into a charge number image to obtain the charge number image at each integration moment;
s108: integrating, delaying and accumulating the charge number image at each integration moment, and performing analog-to-digital conversion to obtain a gray value image; different from a CCD sensor which forms a line of images at a time, the satellite-borne CMOS sensor outputs a two-dimensional image at a time, and the image contrast is improved and the imaging quality is ensured by accumulating the charge number images at each integration moment.
According to the imaging simulation method of the satellite-borne TDI CMOS camera, provided by the embodiment of the invention, the imaging simulation of the satellite-borne TDI CMOS camera based on a high-resolution digital ortho-image and a corresponding area digital surface model DSM is realized, and the high-precision simulation of the satellite orbit and attitude data, the atmospheric transmission, the camera geometric parameters and the CMOS TDI multistage dynamic integration which are combined with the strict geometric conversion and the radiation conversion process is realized through orbit simulation, attitude simulation, atmospheric transmission simulation and CMOS digital domain delay integral imaging simulation, so that the accuracy of a simulation result is ensured.
The above step S101 involves simulating satellite orbit data and satellite attitude data, and in one embodiment, simulating satellite orbit data and satellite attitude data according to the following steps:
(1) the simulated satellite orbit data comprises: the satellite orbit data includes the time, position, velocity data of the scanning of the satellites under the earth reference coordinate system WGS 84. The invention describes the satellite orbit by adopting the orbit six parameters in the celestial sphere reference coordinate system, and establishes a satellite orbit mathematical model through the two-body motion law. The method specifically comprises the following steps:
a. calculating satellite orbit parameters:
determining basic parameters of a satellite orbit, such as an orbit height H, an orbit inclination angle i, an orbit eccentricity e and an argument omega of a near place;
and (3) calculating coordinates of a WGS84 coordinate system corresponding to the position of the satellite:
wherein
RearthIs the long radius of the earth, eearthThe eccentricity of the earth, the semi-major axis of the satellite orbit
e is the orbital eccentricity, (X, Y, Z) is WGSAnd (6) satellite position coordinates (lon, lat) in an 84 coordinate system are longitude and latitude of the center of the ground scene.
According to the moment when the satellite passes through the scene center, the coordinates in the WGS84 when the satellite passes through the scene center are converted into a celestial sphere reference coordinate system J2000:
wherein the content of the first and second substances,
is a rotation matrix between the J2000 coordinate system and the WGS84 coordinate system.
Assuming that the right ascension of the ascending intersection point in the satellite orbit parameters is Ω and the true paraxial angle of the satellite at the moment of passing through the scene center is f, the position of the satellite in the celestial sphere reference coordinate system J2000 can be calculated by the following formula:
wherein r is the radial direction of the satellite,
R*the calculation method is that phi is a rotation matrix of the satellite around a coordinate axis and phi is an angle of the satellite rotating around a reference coordinate axis, and the calculation method comprises the following steps:
the true approach angle f and the ascension crossing right ascension Ω are calculated by simultaneous equations (1), (2) and (3). Thus, six parameters a, i, e, omega, f and omega of the satellite orbit in the J2000 coordinate system are determined, and the position of the satellite in the celestial sphere reference coordinate system at each moment can be calculated.
b. Calculating the position and speed data of the satellite at each moment:
and calculating the mean anomaly angle of the satellite according to the current time:
wherein G is a gravitational constant of 6.67 × 10-11m3/(kg·s2)，MearthThe value of 5.98 × 10 is the earth mass24kg, omega is the amplitude angle of the near place of the track, t is the current time, t0At the initial moment, a is the semi-major axis of the satellite orbit.
Solving a Kepler equation to obtain an approximate point angle E of the satellite platform:
M＝E-e sin(E) (5)
the solution can be iteratively solved by adopting a gradient descent method or a Newton method, and for the remote sensing satellite orbit (with small eccentricity), the initial value is suitable when taking E as M, wherein M is the mean anomaly angle of the satellite, E is the partial anomaly angle of the satellite, and E is the orbit eccentricity.
Calculating the position and the speed of the satellite in the orbital plane at a certain moment:
in the formula, f is a true near point angle of the satellite at the moment of passing through the scene center, E is an orbital eccentricity, and E is a deviation near point angle of the satellite.
r＝a(1-ecos(E)) (7)
In the formula, r is the radial direction of the satellite, a is the semi-major axis of the satellite orbit, E is the eccentric point angle of the satellite, and E is the orbit eccentricity.
Wherein V is the velocity of the satellite, G is the gravitational constant, MearthAnd (b) taking the earth mass as a, the semi-major axis of the satellite orbit and the radial direction of the satellite as r.
In the formula (x y z)TThe position vector of the satellite in the orbital plane is shown, r is the radial direction of the satellite, and f is the true approximate point angle of the satellite at the moment when the satellite passes through the scene center.
In the formula (vx vy vz)TThe velocity vector of the satellite in the orbital plane, V the velocity of the satellite, E the angle of approach point of the satellite, and E the orbital eccentricity.
Converting the position and the velocity vector of the satellite in the orbital plane into the celestial sphere reference coordinate system:
obtaining a rotation matrix between a celestial coordinate system and a terrestrial coordinate system at the current moment
And converting the position and posture data in the J2000 coordinate system into a WGS84 coordinate system.
c. According to the track precision requirement, random noise is added:
in order to make the random number sequence obey normal distribution, a group of pseudo-random numbers approximately in accordance with [0, 1] distribution are generated by utilizing Polar Method, Polar Method is an improved Method of Box-Muller algorithm in Gaussian distribution random number generation Method, the idea of Box-Muller algorithm is to obtain random numbers obeying uniform distribution first and then convert the random numbers into normal distribution, Polar Method replaces trigonometric function in the Box-Muller Method in circulation, and therefore algorithm efficiency is improved.
Using the property of a normal distribution, it can be converted to a mean value
A random number sequence with variance σ. Three groups of independent random number sequences [ n ] of three axial directions to be generatedXinYinZi]Adding into the position coordinates of each time:
and therefore, the position vector of the satellite in the earth reference coordinate system at each moment meeting the requirement of the preset orbit precision is obtained.
(2) The simulated satellite attitude data comprises:
according to the index value requirements of satellite attitude stability, attitude measurement accuracy and the like, the frequency and amplitude of low attitude error and high-frequency components are set, and different combinations are realized. The low frequency component is simulated by a trigonometric function, and the high frequency component is simulated by random noise.
Setting the low frequency period of attitude error as Troll，Tpitch，TyawAmplitude of Aroll，Apitch，AyawMean value of high frequency component is Eroll,Epitch,EyawVariance is σroll,σpitch,σyawThen, the attitude angles of the satellite in the three-axis directions are:
wherein, omega,
Kappa is attitude angle of the satellite in roll, pitch and yaw directions, namely the roll angle, pitch angle and yaw angle of the satellite, t' is phase difference and can be set according to requirements, N (E)*,σ*) Pseudo-random numbers generated by Polar Method were used.
The step S102 mentioned above relates to acquiring a data source range of the CMOS instantaneous focal plane image according to the geometric parameters of the CMOS camera, the satellite orbit data and the satellite attitude data, and in an alternative embodiment, the step S102 further includes the following steps:
(1) carrying out interpolation on the satellite orbit data and the satellite attitude data to obtain the satellite orbit data and the satellite attitude data at the imaging moment:
determining an imaging time t, and calculating the orbit parameters and the attitude parameters of the imaging time t satellite under a WGS84 coordinate system by adopting Lagrange interpolation through adjacent n groups of attitude data and orbit data:
and obtaining attitude quaternion q at any moment by adopting spherical linear interpolation for attitude data:
wherein X (t), Y (t), Z (t), VX(t)、VY(t)、VZ(t) is the position and velocity of the satellite in the WGS84 coordinate system at time t,
are each t0、t1(t0≤t<t1) The attitude quaternion of the satellite at the moment, i, j, is the code (0, 1.., n-1) of the group of n groups of data adjacent to the imaging moment t, ti、tjIs the imaging time of the ith and jth group of data.
(2) According to the satellite orbit data, the satellite attitude data and the geometric parameters of the CMOS camera at the imaging moment, the coordinates of the ground point under the earth reference coordinate system are obtained through a frame type strict geometric imaging model:
in global shutter mode, the relationship between the image point (x, y) on the image and the coordinates of the corresponding ground point in the WGS84 coordinate system can be described by a strict geometric imaging model, as follows:
in the formula (X)P,YP,ZP)TIs the coordinate of the ground point in the earth reference coordinate system, t is the imaging time, (X (t), Y (t), Z (t))TIs the coordinate of the projection center of the imaging time t sensor under the WGS84 coordinate system, lambda is the imaging scale denominator of the imaging time t,
is a rotation matrix between a J2000 coordinate system and a WGS84 coordinate system corresponding to the imaging time t,
is a rotation matrix between the satellite body corresponding to the imaging time t and the J2000 coordinate system,
is the mounting offset matrix of the CMOS imaging sensor and f is the focal length of the CMOS camera.
(3) Acquiring the longitude and latitude of the ground point corresponding to the image point according to the coordinates of the ground point in the earth reference coordinate system, and extending the longitude and latitude of the ground point corresponding to the image point by a preset distance to obtain the data source range of the CMOS instantaneous focal plane imaging area:
generally, the average elevation of a Digital Surface Model (DSM) is taken as the initial elevation H to calculate the approximate longitude and latitude (L, B) of the ground point corresponding to the image point, more accurate elevation H' is obtained by interpolation on the DSM and is calculated again, the three-dimensional coordinates of the ground point corresponding to the image point are obtained by iterative calculation until the elevation change | Delta H | calculated twice before and after meets the set threshold value, the geodetic coordinates corresponding to the four corners of the CMOS focal plane are calculated in sequence, and the geodetic coordinates corresponding to the CMOS focal plane imaging area are extended outwards by a certain distance to obtain the geographical range of the simulation reference data source corresponding to the CMOS instantaneous focal plane imaging area.
The above step S103 involves acquiring surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging area, and in one embodiment, S103 further includes the following steps:
(1) selecting multiple types of ground objects with known reflectivity, counting the gray level mean value of the multiple types of ground objects on the high-resolution ortho-image, and determining the gray level mean value and the reflectivity combination (v) of the multiple types of ground objectsi,wi) The expression is shown as the following formula:
wherein n is the total number of selected ground object classes of known reflectivity, v is the brightness value of the high resolution image,
surface reflectance of v is given by a value of [0, 1]]In the range, vi、vjBrightness values, w, corresponding to the i, j-th class of ground objectsiThe reflectivity corresponding to the i-th class of land objects.
(2) Performing interpolation on the gray average value and the reflectivity combination of the multiple types of ground objects to calculate the earth surface reflectivity; lagrange interpolation should meet the requirement of monotonic increase to meet the practical situation that the higher the brightness value, the larger the surface reflectivity.
(3) Specifically, according to the requirement of the 6S radiation transmission model for parameters, the circulation step size of each parameter is designed to obtain a series of parameter combinations, the 6S radiation transmission code is operated to obtain the atmospheric transmission model parameters corresponding to different parameter combinations, and a radiation transmission look-up table (L ook UpTable, &lTtTtransmission = L "&gTt L &/T &gTt UT) is generated.
(4) Selecting corresponding parameters of aerosol optical thickness, zenith angle, azimuth angle and the like according to the imaging time, inquiring in L UT, and calculating the atmospheric transmission simulation parameter x by linear interpolationa、xb、xcFor use in subsequent steps.
In the above step S104, the integration time interval is calculated according to the ground resolution of the image, and the satellite orbit data and the attitude data at each integration time are acquired, in an embodiment, the step S104 further includes the following steps:
(1) acquiring the ground resolution of an image and the ground speed of a satellite along the track direction according to the size of a probe element of a CMOS camera, the focal length of the CMOS camera and the satellite track data;
calculating the ground resolution of the image, setting the size of the CMOS probe as l, the focal length of the camera as f, and the height of the track as HobtThen the image ground resolution s is:
calculating the ground speed v of the satellite along the orbit direction:
in the formula (V)X、VY、VZ) For the position and velocity of the satellite at time t in the WGS84 coordinate system, RearthThe long radius of the earth.
(2) Acquiring an integration time interval according to the image ground resolution and the ground speed of the satellite along the orbital direction;
the time interval dt at each integration instant is then:
so the time t of the i-th stage integration timeiIs composed of
ti＝t0+i·dt (34)
(3) Acquiring satellite orbit data and attitude data of each integration moment by interpolation according to the integration time interval and the satellite orbit data and the satellite attitude data; in particular according to tiAnd respectively acquiring the attitude and the orbit data of the current integration moment at the moment through Lagrange interpolation and quaternion spherical interpolation.
The above step S105 involves acquiring a CMOS camera entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, the satellite orbit data at each integration time, and the attitude data, and in one embodiment, S105 acquires the CMOS camera entrance pupil radiance image according to the following steps:
(1) each CMOS pixel element is evenly divided into a number of sub-pixel elements, and in a specific embodiment, each CMOS pixel element is evenly divided into k × k sub-pixel elements.
(2) Calculating the image plane coordinate corresponding to each CMOS sub-pixel; for each sub-pixel element, its corresponding image plane coordinates (x, y) are calculated.
(3) And calculating the ground point coordinates (L, B) corresponding to each sub-pixel through a frame type strict geometric imaging model and a Digital Surface Model (DSM) according to the image plane coordinates corresponding to each CMOS pixel and the satellite orbit data and attitude data at each integration moment.
(4) According to the ground point coordinates corresponding to each sub-pixel, the reflectivity of each sub-pixel is obtained through surface reflectivity interpolation; the reflectivity w of the sub-pixel is obtained by interpolating the surface reflectivity obtained in step S103.
(5) Calculating the entrance pupil radiance of each sub-pixel according to the atmospheric transmission simulation parameters; specifically, the atmospheric transmission simulation parameter x obtained in the step S103 is used as the basisa、xb、xcAnd calculating the entrance pupil radiance s of the sub-pixel:
(6) and calculating the entrance pupil radiance of each CMOS pixel according to the entrance pupil radiance image of the sub-pixel corresponding to the CMOS pixel to obtain the entrance pupil radiance image of the CMOS camera, specifically, repeating the step S105 to obtain the entrance pupil radiance image of each pixel, and thus obtaining the entrance pupil radiance image of the CMOS camera.
In one embodiment, a suitable point spread function is selected according to the performance of the CMOS sensor, and the instantaneous focal plane irradiance image is filtered to obtain the CMOS focal plane irradiance image at the current integration time.
The point spread function enables the radiation energy of any point of the image square to include the radiation energy from the 'target' point and the radiation energy from the points around the 'target point', so that the optical imaging characteristics of the camera can be well simulated.
Adopting a point spread function of Gaussian distribution, wherein the expression is as follows:
in the formula, exp is an exponential function, σ is a function descent parameter, and represents a speed at which the point spread function value changes with (x, y), and (x, y) is a two-dimensional plane coordinate of a point (FSP (x, y) >0) in the point spread function action range with respect to the point spread function origin, and represents an image plane position where the action pixel center is the origin.
In the present embodiment, the CMOS focal plane radiance image at the current integration time is converted into a charge number image, and noise charges are added according to a generation mechanism of shot noise to generate the charge number image at the integration time, and the CMOS focal plane radiance image at each integration time is converted to obtain the charge number image at each integration time.
In step S108, the charge number image at each integration time is accumulated and analog-to-digital converted to obtain a gray value image, and in one embodiment, the charge number images at a plurality of integration times are accumulated in a delayed manner according to the following formula:
wherein I is the final integral image, IiIs the image of the number of charges at the ith integration time, M is the number of integration times, and (M, n) represents the image's ithm rows and n columns;
and performing analog-to-digital conversion on the image after the delay accumulation is completed to obtain a finally simulated gray value image. For example, in one embodiment, M is 8, and specifically, the charge number images at M integration times are accumulated according to actual needs. FIG. 2 is a CMOS digital domain time delay integration scheme according to an embodiment of the present invention, as shown in FIG. 2, for t0、t1、t2The images at the 3 integration moments are accumulated according to a formula (37) to obtain a final gray value image.
The invention realizes that a digital orthoimage with a geometric resolution not less than 3 times of a simulation result image and a Digital Surface Model (DSM) or a Digital Elevation Model (DEM) of a corresponding area are used as a reference data source for simulation, imaging simulation can be carried out on a satellite-borne TDI CMOS image with a resolution of 1-5m, platform parameters and camera parameters are organically connected in series in a simulation link, and the combination of geometric simulation and radiation simulation is realized.
The imaging simulation method of the satellite-borne TDI CMOS camera provided by the embodiment of the invention realizes imaging simulation of the satellite-borne TDI CMOS camera based on an orthoimage with higher resolution and a DSM (digital system) corresponding to a region, realizes high-precision simulation of a satellite orbit and attitude data, atmosphere transmission, camera geometry and TDI CMOS multistage dynamic integration integrating rigorous geometry conversion and radiation conversion process, and ensures the accuracy of a simulation result.
Example 2
Fig. 3 is a schematic hardware structure diagram of a computer device of an imaging simulation method of a satellite-borne TDI CMOS camera according to an embodiment of the present invention, as shown in fig. 3, the device includes one or more processors 310 and a memory 320, where one processor 310 is taken as an example in fig. 3.
The device for executing the imaging simulation method of the satellite-borne TDI CMOS camera can further comprise: an input device 330 and an output device 340.
The processor 310, the memory 320, the input device 330, and the output device 340 may be connected by a bus or other means, such as the bus connection in fig. 3.
The memory 320 is a non-transitory computer readable storage medium, and can be used to store non-transitory software programs, non-transitory computer executable programs, and modules, such as program instructions/modules corresponding to the imaging simulation method of the on-board TDI CMOS camera in the embodiment of the present application. The processor 310 executes various functional applications and data processing of the server by running non-transitory software programs, instructions and modules stored in the memory 320, namely, implements the imaging simulation method of the satellite-borne TDICMOS camera in the above method embodiment.
The memory 320 may include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required for at least one function; the storage data area may store data created by use of the on-board TDI CMOS camera imaging simulation device, and the like. Further, the memory 320 may include high speed random access memory, and may also include non-transitory memory, such as at least one magnetic disk storage device, flash memory device, or other non-transitory solid state storage device. In some embodiments, memory 320 optionally includes memory remotely located from processor 310, which may be connected to a processing device of the on-board TDI CMOS camera imaging simulation via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The input device 330 may receive input digital or character information and generate key signal inputs related to user settings and function control of the on-board TDI CMOS camera imaging simulation processing device. The output device 340 may include a display device such as a display screen.
The one or more modules are stored in the memory 320 and, when executed by the one or more processors 310, perform the method shown in fig. 1.
The above-mentioned product can execute the method provided by the embodiment of the present invention, and has corresponding functional modules and beneficial effects of the execution method and technical details that are not described in detail in the embodiment, which can be specifically referred to the related descriptions in the embodiments shown in fig. 1 to fig. 2.
Example 3
The embodiment of the invention also provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions can execute the imaging simulation method of the satellite-borne TDI CMOS camera in any method embodiment. The storage medium may be a magnetic Disk, an optical Disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a Flash Memory (Flash Memory), a Hard Disk (Hard Disk Drive, abbreviated as HDD), a Solid State Drive (SSD), or the like; the storage medium may also comprise a combination of memories of the kind described above.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. A satellite-borne TDI CMOS camera imaging simulation method is characterized by comprising the following steps:
simulating satellite orbit data and satellite attitude data;
acquiring a data source range of a CMOS instantaneous focal plane imaging area according to the geometric parameters of the CMOS camera, the satellite orbit data and the satellite attitude data;
acquiring earth surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging area;
calculating an integration time interval according to the image ground resolution, and acquiring satellite orbit data and attitude data at each integration moment;
acquiring a CMOS camera entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, and the satellite orbit data and attitude data at each integration moment;
filtering the CMOS camera entrance pupil radiance image to obtain a CMOS focal plane radiance image at each integration moment;
converting the CMOS focal plane radiance image at each integration moment into a charge number image to obtain the charge number image at each integration moment;
and integrating, delaying and accumulating the charge number image at each integration moment, and performing analog-to-digital conversion to obtain a gray value image.
2. The imaging simulation method of the on-board TDI CMOS camera according to claim 1, wherein the acquiring a data source range of a CMOS instantaneous focal plane imaging region according to the geometric parameters of the CMOS camera, the satellite orbit data and the satellite attitude data comprises:
interpolating the satellite orbit data and the satellite attitude data to obtain the satellite orbit data and the satellite attitude data at the imaging moment;
acquiring coordinates of ground points under an earth reference coordinate system through a frame type strict geometric imaging model according to the satellite orbit data, the satellite attitude data and the geometric parameters of the CMOS camera at the imaging moment;
acquiring longitude and latitude of the ground point corresponding to the image point according to the coordinates of the ground point in the earth reference coordinate system;
and extending the longitude and latitude of the ground point corresponding to the image point by a preset distance to obtain the data source range of the CMOS instantaneous focal plane imaging area.
3. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 2, wherein the step of obtaining coordinates of a ground point in an earth reference coordinate system through a frame-type rigorous geometric imaging model according to the satellite orbit data of the imaging time and the geometric parameters of the CMOS camera comprises the following steps:
in the formula (X)P,YP,ZP)TIs the coordinate of the ground point in the earth reference coordinate system, t is the imaging time, (X (t), Y (t), Z (t))TIs the coordinate of the projection center of the imaging moment sensor under the earth reference coordinate system, lambda is the denominator of the imaging scale at the imaging moment,
is a rotation matrix between a celestial sphere reference coordinate system and an earth reference coordinate system at the imaging moment,
is a rotation matrix between the satellite body and the celestial sphere reference coordinate system at the imaging moment,
for the mounting bias matrix of the CMOS camera, f is the focal length of the CMOS camera and (x, y) is the image plane coordinates.
4. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 1, wherein the obtaining of surface reflectivity and atmospheric transmission simulation parameters according to the data source range of the CMOS instantaneous focal plane imaging region comprises:
selecting multiple types of ground objects with known reflectivity, counting the gray level mean value of the multiple types of ground objects on a high-resolution ortho-image, and determining the gray level mean value and reflectivity combination of the multiple types of ground objects, wherein the high-resolution ortho-image is one of basic data for simulation;
performing interpolation on the gray average value and the reflectivity combination of the multiple types of ground objects to calculate the earth surface reflectivity;
acquiring a radiation transmission lookup table according to the atmospheric radiation transmission model and atmospheric parameters;
and calculating the atmospheric transmission simulation parameters through linear interpolation according to the observation angle at the imaging moment, the optical thickness of the aerosol and the radiation transmission lookup table.
5. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 4, wherein a plurality of types of ground objects with known reflectivity are selected, the gray level mean value of the plurality of types of ground objects on the high-resolution ortho image is counted, the combination of the gray level mean value and the reflectivity of the plurality of types of ground objects is determined, and the expression is as follows:
wherein n is the total number of selected ground object classes of known reflectivity, v is the brightness value of the high resolution image,
surface reflectance of v is given by a value of [0, 1]]In the range, vi、vjBrightness values, w, corresponding to the i, j-th class of ground objectsiThe reflectivity corresponding to the i-th class of land objects.
6. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 1, wherein the step of calculating an integration time interval according to the image ground resolution to obtain satellite orbit data and attitude data of each integration moment comprises the following steps:
acquiring the ground resolution of an image and the ground speed of a satellite along the track direction according to the size of the CMOS camera probe element, the focal length of the CMOS camera and the satellite track data;
acquiring an integration time interval according to the image ground resolution and the ground speed of the satellite along the orbital direction;
and respectively acquiring satellite orbit data and attitude data of each integration moment by Lagrange interpolation and quaternion spherical interpolation according to the integration time interval and the satellite orbit data and the satellite attitude data.
7. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 4, wherein the step of obtaining a CMOS camera entrance pupil radiance image according to the earth surface reflectivity, the atmospheric transmission simulation parameters, the satellite orbit data and the attitude data at each integration moment comprises the following steps:
uniformly dividing each CMOS pixel into a plurality of sub-pixels;
calculating the image plane coordinate corresponding to each CMOS sub-pixel;
calculating the ground point coordinate corresponding to each sub-pixel through a frame-type strict geometric imaging model and a Digital Surface Model (DSM) according to the image plane coordinate and the satellite orbit data and the attitude data at each integration moment;
according to the ground point coordinate corresponding to each sub-pixel, the reflectivity of each sub-pixel is obtained through the surface reflectivity interpolation;
calculating the entrance pupil radiance of each sub-pixel according to the atmospheric transmission simulation parameters;
and calculating the entrance pupil radiance of each CMOS pixel according to the entrance pupil radiance image of the sub-pixel corresponding to the CMOS pixel to obtain the entrance pupil radiance image of the CMOS camera.
8. The imaging simulation method of the satellite-borne TDI CMOS camera according to claim 1, wherein the integrating, delaying and accumulating the charge number image at each integration time, and performing analog-to-digital conversion to obtain a gray value image comprises:
and according to the charge number image at each integration time, performing delay accumulation on the obtained charge number images at a plurality of integration times according to the following formula:
wherein I is the final integral image, IiThe number of charges is the image of the ith integration time, M is the number of integration stages, namely the number of integration times, and (M, n) represents the nth row of the image;
and performing analog-to-digital conversion on the image after the delay accumulation is completed to obtain a finally simulated gray value image.
9. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, implements the on-board TDI CMOS camera imaging simulation method according to any one of claims 1 to 8.
10. A computer device, comprising:
at least one processor; and
a memory communicatively coupled to the at least one processor; wherein the memory stores a computer program executable by the at least one processor to cause the at least one processor to perform the on-board TDI CMOS camera imaging simulation method of any one of claims 1 to 8.
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