CN114280548A - Satellite-borne downward-looking ice-detection synthetic aperture radar transmission path calculation method - Google Patents
Satellite-borne downward-looking ice-detection synthetic aperture radar transmission path calculation method Download PDFInfo
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Abstract
The invention relates to the technical field of radar detection, in particular to a satellite-borne downward-looking ice-detection synthetic aperture radar transmission path calculation method, which comprises the following steps: acquiring earth model parameters, system parameters of a satellite-borne downward-looking ice-exploring synthetic aperture radar and echo simulation parameters; the echo simulation parameters comprise an orientation time sequence, an antenna position sequence and an in-ice target position under a rotating geocentric coordinate system; in south poles, north poles or other areas to be detected covered by ice, the air medium above the earth surface and the ice medium below the earth surface are used, and for each azimuth moment, the corresponding geocentric angle of the corresponding transmission path in the ice medium is solved, so that the lengths of the transmission path in the air medium and the ice medium are respectively determined; the transmission path connects the corresponding antenna position and the target position in the ice and is located within the beam range of the transmitting antenna. The invention can more accurately determine the transmission path and provide technical support for radar imaging, echo simulation and the like.
Description
Technical Field
The invention relates to the technical field of radar detection, in particular to a satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path calculation method, computer equipment and a computer readable storage medium.
Background
Since the last century, due to factors such as global warming, the melting of the ice cover in south and north poles is aggravated, the global sea level is directly increased, and great threat is brought to human survival. To fully understand the relationship between the polar regions and global climate changes, countries around the world begin scientific investigation of polar regions.
In the 60's of the 20 th century, ice radar systems were used in the detection of antarctic ice covers. Through the development of the last 60 years, the current ice radar plays a significant role in the ice cover detection research. At present, ice radars are mainly on-board and on-board. A Synthetic Aperture Radar (SAR) is an active remote sensing system carried on a satellite platform and working in a microwave band. The satellite-borne SAR is not limited by factors such as sunshine, weather, geography and the like, and can realize all-time and all-weather earth observation. The satellite-borne downward-looking ice-detecting synthetic aperture radar is expected to carry out more in-depth observation and research on scenes such as polar glaciers and the like.
The method is different from the conventional detection of ground targets, when the targets in the ice are detected, electromagnetic waves sent by a radar need to penetrate into the ice layer, the electromagnetic waves deflect on the ice surface due to the fact that the dielectric constants of an ice medium and an air medium are different, the ice radar transmission path is determined by means of subtracting the conventional satellite space position from the target space position, and accuracy of a measurement result is affected.
Disclosure of Invention
Technical problem to be solved
The invention aims to solve the technical problem that the accuracy of a radar detection result is poor due to inaccurate solving of an ice radar transmission path in the prior art.
(II) technical scheme
In order to solve the technical problem, the invention provides a satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path calculation method, which comprises the following steps:
acquiring earth model parameters, system parameters of a satellite-borne downward-looking ice-exploring synthetic aperture radar and echo simulation parameters; the echo simulation parameters comprise an orientation time sequence, an antenna position sequence and an in-ice target position under a rotating geocentric coordinate system;
in the area to be detected, the air medium above the earth surface and the ice medium below the earth surface are used, and for each azimuth moment, the corresponding geocentric angle of the corresponding transmission path in the ice medium is solved, so that the lengths of the transmission path in the air medium and the ice medium are respectively determined; the transmission path connects the corresponding antenna position and the target position in the ice and is located within the beam range of the transmitting antenna.
Optionally, for one azimuth instant, the corresponding geocentric angle α of the respective transmission path in the ice medium is solved2The method comprises the following steps:
calculating the target P from the antenna S to the geocentric O and in the ice2To the earth' S center O and antenna S to the in-ice target P2And calculating the antenna S and the target P in the ice2The corresponding geocentric angle α;
calculating the local radius R of the sub-satellite point of the antenna S based on the earth model parameters and the corresponding antenna positionL；
Setting a transmission path passing through an ice surface incident point P1And ice surface incident point P1Distance to the earth center O and local radius R of the sub-satellite point of the antenna SLEquality, respectively calculating the incident point P on the ice surface1Incident angle on ice surface thetai1Sine sin theta ofi1And an in-ice target P2Angle of incidence thetai2Sine sin theta ofi2The expression of (1);
according to the law of refraction, based on sine sin thetai1And sin θi2Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (1);
target P in ice based on distance from antenna S to geocenter O2Distance to the earth center O, ice surface incident point P1The distance to the center of earth O and the center angle alpha according to the ratio n of the dielectric constants of the ice medium and the air medium1Calculating the corresponding geocentric angle alpha of the transmission path in the ice medium2。
Optionally, the distance from the antenna S to the geocenter O is calculated by the expression:
wherein R iss(ti)＝[Rsxi,Rsyi,Rszi]Denotes the ith (i ═ 1,2, …, Na) Individual azimuth time tiCorresponding to the position coordinates of the antenna S, NaRepresenting the number of azimuth sampling points;
the calculation of the in-ice target P2The distance to the geocenter O is expressed as:
wherein [ P ]2x,P2y,P2z]Representing an in-ice target P2The position coordinates of (a);
the computing antenna S to the in-ice target P2The expression is:
the calculated antenna S and the target P in the ice2The corresponding geocentric angle α is expressed as:
optionally, the local radius R of the sub-satellite point of the antenna S is calculatedLThe method comprises the following steps:
calculating latitude phi of antenna S subsatellite pointsThe expression is:
calculating longitude Ψ of antenna S subsatellite pointsThe expression is:
obtain the local radius R of the subsatellite pointL：
Wherein R iseIs the equatorial radius of the earth, RpThe polar radius of the earth ellipsoid.
Optionally, the point of incidence P on the ice surface is calculated1Incident angle on ice surface thetai1Sine sin theta ofi1Includes:
α1representing the corresponding centre of earth angle of the transmission path in the air medium, alpha ═ alpha1+α2；
Calculating in-ice target P2Angle of incidence thetai2Sine sin theta ofi2Includes:
obtaining the ratio n of the dielectric constants of the ice medium and the air medium1Includes:
angle of refraction theta in icet1And an in-ice target P2Angle of incidence thetai2The relationship between is thetat1＝θi2-α2Obtaining an ice internal refraction angle thetat1Sine sin theta oft1The expression is as follows:
the ratio n of the dielectric constants of the ice medium and the air medium according to the refraction theorem1The expression of (a) is:
optionally, the corresponding geocentric angle alpha of the transmission path in the ice medium is calculated2The method comprises the following steps:
setting the center angle of the earth alpha2Sufficiently small, thetat1＝θi2-α2≈θi2Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (a) is:
squaring the two sides of the expression, and setting x as sin alpha2Then, there are:
let x be small enough, have
When thickness d of ice layer2＝RL-RtgNot equal to zero, target P in ice2The distance to the earth center O is less than the local radius R of the sub-satellite pointLThen, there are:
solving for sin alpha2Further obtaining the corresponding geocentric angle alpha of the transmission path in the ice medium2。
Optionally, the length R of the transmission path in the air medium is determined separatelyTairAnd length R in ice mediumTiceThe method comprises the following steps:
optionally, if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a two-station radar including a transmitting antenna and a receiving antenna, for each azimuth moment, respectively solving transmission paths corresponding to the transmitting antenna and the receiving antenna, and adding to obtain a final transmission path;
if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a single-station radar and a transmitting and receiving common antenna is adopted, the final transmission path is a double one-way transmission path at each azimuth moment.
The invention also provides computer equipment which comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes the steps of the satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path calculation method when executing the computer program.
The invention also provides a computer readable storage medium, on which a computer program is stored, which when executed by a processor implements the steps of any of the above-mentioned method for computing a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar.
(III) advantageous effects
The technical scheme of the invention has the following advantages: the invention provides a satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path calculation method, computer equipment and a computer readable storage medium. The invention can more accurately determine the transmission path and provide technical support for radar imaging, echo simulation and the like.
Drawings
FIG. 1 is a geometrical diagram of a satellite-borne downward-looking ice-detecting synthetic aperture radar observation target;
FIG. 2 is a schematic diagram of a transmission path from a transmitting satellite to an in-ice target in an on-board look-down ice-seeking synthetic aperture radar;
FIG. 3 is a schematic diagram illustrating a step of a method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar according to an embodiment of the present invention;
FIG. 4 is a flowchart of another method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar according to an embodiment of the present invention;
FIG. 5 shows a method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar to solve a slant range error from a transmitting satellite to a target according to an embodiment of the present invention;
fig. 6 shows a method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar to solve a slant range error from a receiving satellite to a target in the embodiment of the invention.
Fig. 7 shows a method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar to solve a slant range error from a receiving satellite to a target in the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
FIG. 1 is a geometrical schematic diagram of a satellite-borne downward-looking ice-detecting synthetic aperture radar observation target. In order to obtain a more accurate ice radar transmission path, the surface of the earth is set as an air medium area by combining an earth model, and the dielectric constant of the air is epsilon1The region below the earth's surface is a region of ice medium having a dielectric constant of epsilon2. As shown in fig. 1, for the two-station radar, two satellites respectively carry a transmitting antenna and a receiving antenna (respectively identified by S and Q), the transmitting antenna is preferably a reflector antenna, and the receiving antenna is preferably a half-wavelength dipole antenna, so that it can be ensured that echo signals within the beam range of the transmitting antenna can be received by the receiving antenna, that is, the transmitting antenna beam is included in the receiving antenna beam.
FIG. 2 illustrates a transmission satellite (i.e., a satellite carrying a transmitting antenna) to an iced target P2A geometric transfer path for transfer in air and ice media. In practice, the same is true for the transmission relationship between the receiving satellite (i.e., the satellite carrying the receiving antenna) and the target, except that the transmission direction is reversed. As shown in FIG. 2, the earth' S center is marked by O, and the low-frequency microwave signal emitted by the transmitting antenna S carried by the transmitting satellite passes through P on the interface of air and ice1Point, the angle of incidence of ice in the air medium is θi1Angle of refraction in ice of theta in ice mediumt1Microwave signals are propagated in the ice medium and irradiated to a target P in the ice2The angle of incidence at the target point is thetai2. Antenna S, boundary P1The included angle of the earth center formed by the point and the earth center O is alpha1I.e. the corresponding centre of earth angle, P, of the transmission path in the air medium1Point, P2The included angle of the center of the earth formed by the three points of the point and the center of the earth O is alpha2I.e. the corresponding geocentric angle of the transmission path in the ice medium.
As shown in fig. 3, a method for calculating a transmission path of a satellite-borne downward-looking ice-detecting synthetic aperture radar according to an embodiment of the present invention includes:
and 300, acquiring earth model parameters, system parameters of the satellite-borne downward-looking ice-exploring synthetic aperture radar and echo simulation parameters. The echo simulation parameters comprise a position moment sequence, an antenna position sequence and an in-ice target position in a rotating geocentric coordinate system. The system parameters include the operating wavelength λ, the diameter of the transmitting antenna (or the azimuth length of the transmitting antenna)TaThe method can be used for determining the antenna beam range and performing echo simulation.
The earth model [ R ] can be obtained by the prior arte,Rp]Wherein R iseIs the equatorial radius of the earth, RpThe polar radius of the earth ellipsoid. Respectively setting the first azimuth moment and the last azimuth moment of the synthetic aperture radar echo as t1And
Nathe number of sampling points in the azimuth direction. All coordinates are in a rotating earth center coordinate system, and the coordinates of the earth center O are [0, 0%]，Rs(ti)＝[Rsxi,Rsyi,Rszi]Denotes the ith (i ═ 1,2, …, Na) Individual azimuth time tiThe coordinate position of the corresponding antenna S, i.e. the position of the satellite carrying the antenna S, { Rs(ti) The sequence of the antenna positions in a rotating earth center coordinate system is shown as an ice target P2Has the coordinate [ P ]2x,P2y,P2z]。
The method is characterized in that a double-medium model is established by considering the particularity of an ice radar detection target, and the transmission paths in the air medium and the ice medium are calculated and solved based on earth model parameters, system parameters of the satellite-borne downward-looking ice detection synthetic aperture radar and echo simulation parameters, so that the one-way transmission path closer to the actual condition is finally obtained. The method can improve the accuracy of calculating the ice radar transmission path and provide technical support for radar imaging, echo simulation and the like.
Preferably, in the method, the time t is determined for one azimuthiSolving the corresponding geocentric angle alpha of the corresponding transmission path in the ice medium2The method specifically comprises the following steps:
calculating the target P from the antenna S to the geocentric O and in the ice2To the earth' S center O, and an antenna S to an in-ice target P2And calculating the antenna S and the target P in the ice2The corresponding geocentric angle α; centre of earth angle alpha, i.e. antenna S, target P in ice2Angle of earth center SOP formed with earth center O2；
Calculating the local radius R of the subsatellite point of the antenna S at the azimuth moment based on the earth model parameters and the corresponding antenna positionL；
Setting a transmission path passing through an ice surface incident point P1And ice surface incident point P1Distance to the earth center O and local radius R of the sub-satellite point of the antenna SLEquality, respectively calculating the incident point P on the ice surface1Incident angle on ice surface thetai1Sine sin theta ofi1Expression of (2) and in-ice target P2Angle of incidence thetai2Sine sin theta ofi2The expression of (1); these two expressions and the parameter α to be solved2Correlation;
according to the law of refraction, based on sine sin thetai1And sin θi2Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (1); the parameter α still to be solved in the expression2；
Target P in ice based on distance from antenna S to geocenter O2Distance to the earth center O, ice surface incident point P1The distance to the center of earth O and the center angle alpha according to the ratio n of the dielectric constants of the ice medium and the air medium1Calculating the corresponding geocentric angle alpha of the transmission path in the ice medium2。
Further, at the ith azimuth time tiCalculating the distance from the antenna S to the geocenter O (or called the distance between the antenna S and the geocenter O), and the expression is:
calculating in-ice target P2Distance to the earth center O (or target P in ice)2And the earth center O), the expression:
RLis the local radius of the sub-satellite point of the antenna S, d2Thickness of the ice layer (i.e. depth of target in ice), d1Representing the distance of the antenna S from the surface of the earth.
Calculating the distance from the antenna S to the target P in the ice2Distance (or called antenna S and ice target P)2Distance between) expressed as:
calculating the transmitting antenna S and the target P in the ice according to the three distances and the cosine theorem of the triangle2And the geocentric angle alpha formed by the geocentric O, the expression is as follows:
further, the local radius R of the sub-satellite point of the antenna S is calculatedLThe method comprises the following steps:
calculating skyLatitude phi of the subsatellite point of line SsThe formula is as follows:
calculating the longitude Ψ of the Susbaster Point of the antenna SsThe formula is as follows:
further obtaining the local radius R of the subsatellite point of the antenna SLComprises the following steps:
as shown in FIG. 2, according to the earth ellipsoid model, it can be considered that the distances from the points near the subsatellite point to the geocenter are all equal to the local radius R of the subsatellite pointL. Therefore, the ice surface incident point P1And the earth center O can be approximated as:
further, the incident point P on the ice surface is calculated1Incident angle on ice surface thetai1Sine sin theta ofi1The expression (c) can be obtained according to the geometrical relationship:
Calculating in-ice target P2Angle of incidence thetai2Sine sin theta ofi2As shown in FIG. 2From the geometric relationships, we can see:
Center angle of earth alpha1The center angle of the earth alpha2And the geocentric angle α is:
α＝α1+α2 (11)
the geocentric angle alpha is known, and the ice surface incident angle theta is knowni1Sine sin theta ofi1Expression of (2) and in-ice target P2Angle of incidence thetai2Sine sin theta ofi2Are all related to the parameter theta to be solved2And (4) correlating.
Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1Includes:
angle of refraction theta in icet1And an in-ice target P2Angle of incidence thetai2The relationship between them is:
θt1＝θi2-α2 (12)
obtaining the ice internal refraction angle theta according to the formula (10) and the formula (12)t1Sine sin theta oft1The expression of (a) is:
according to the law of refraction, angle of incidence on ice θi1And angle of refraction theta in icet1The ratio of these two dielectric constants is equal to the second order root of the ratio of the two dielectric constants, namely:
substituting equations (9), (11) and (13) into equation (14) can obtain the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (a) is:
as can be seen from equation (15), the expression has only one unknown α2. In one embodiment, the parameter α may be solved using the solve function in Matlab software2This way is an exact solution.
Preferably, the invention also provides a method for rapidly solving the geocentric angle alpha2(approximate solution) embodiment, in which the corresponding geocentric angle α of the transmission path in the ice medium is solved2The method comprises the following steps:
local central angle alpha2Sufficiently small to obtain:
θt1＝θi2-α2≈θi2(16) thus, equation (15) can be rewritten as:
to obtain a univariate equation, the equation (17) is squared on the left and right sides, and x is sin α2Then, there are:
since x is a very small value, there are
When thickness d of ice layer2＝RL-RtgNot equal to zero, target P in ice2The distance to the earth center O is less than the local radius R of the sub-satellite pointLSorting equation (18) may result in a one-dimensional quintic equation for x:
with the quintic equation of formula (19), sin α can be directly solved2Further obtaining the corresponding geocentric angle alpha of the transmission path in the ice medium2。
By adopting the implementation mode, sin alpha can be obtained by solving the roots function of Matlab software2Compared with two implementation modes of accurate solution and approximate solution, the Matlab software has different function choices, and the operation speed is different by nearly 1000 times. The invention provides a method for rapidly solving the geocentric angle alpha2The implementation of (approximate solution) is more efficient and can effectively save computation time.
Further, the center angle of the earth alpha1The center angle of the earth alpha2And the cosine theorem of triangle, determining the length R of the transmission path in the air medium (namely the air transmission length)TairThe method comprises the following steps:
determining the length R of the transport path in the ice medium (i.e. the transport length in ice)TiceThe method comprises the following steps:
optionally, if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a two-station radar including a transmitting antenna and a receiving antenna, for each azimuth moment, respectively solving transmission paths corresponding to the transmitting antenna and the receiving antenna, and adding to obtain a final transmission path;
if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a single-station radar and a transmitting and receiving common antenna is adopted, the final transmission path is a double one-way transmission path at each azimuth moment.
As shown in FIG. 4, the invention also provides a satellite-borne downloadA method for calculating the transmission path of visual ice-exploring synthetic aperture radar for solving the two-way transmission path of satellite-borne downward-looking double-station ice-exploring synthetic aperture radar and the target P in ice2Can be simultaneously illuminated by the range beams of the transmitting antenna S and the receiving antenna Q, only considering whether the range beams of the transmitting antenna S and the receiving antenna Q can be simultaneously illuminated by the azimuth beams of the transmitting antenna S and the receiving antenna Q, the method comprising:
s1, obtaining earth model parameters, system parameters of the satellite-borne downward-looking ice-exploring synthetic aperture radar and echo simulation parameters;
step S2, at the i-th azimuth time tiCalculating the target P in the transmitting antenna S and the ice2The geocentric angle alpha formed with the geocentric O, and the local radius R of the subsatellite point of the transmitting antenna SL；
Step S3, setting the transmission path to pass through the ice surface incidence point P1Center of earth angle alpha of transmission path in air medium1＝∠SOP1Center of earth angle alpha of transmission path in ice medium2＝∠P1OP2Respectively deducing the ice surface incident angles thetai1Sine sin theta ofi1And an in-ice target P2Angle of incidence thetai2Sine sin theta ofi2；
Step S4, according to the refraction theorem, solving sin alpha by a quintic equation2And calculating alpha1And alpha2；
Step S5, alpha1、α2And the trigonometric cosine theorem, the length R of the transmission path in the air medium is obtainedTairAnd the length R of the transport path in the ice mediumTice；
Step S6, referring to steps S1 to S5, calculating to obtain the target P in ice2The length R of the transmission path in the air medium to the receiving antenna QTairAnd length R in ice mediumTice。
Step S7, at the i-th azimuth time tiJudging the target P in the ice2Whether simultaneously illuminated by the transmit antenna azimuth beam and the receive antenna azimuth beam.
With a target P2Whether or not to be transmitted by antennaThe bit-wise beam irradiation is explained as an example. The transmitting antenna azimuth beam width is the ratio of the wavelength to the transmitting antenna diameter:
the longitude and latitude of the S-shaped subsatellite point of the transmitting antenna are shown in a formula (5) and a formula (6). In the same way, target P2Latitude of
And longitude
The formulas are respectively as follows:
ice surface incident point P1Latitude of
And longitude
Respectively as follows:
therefore, the ice surface incident point P1The coordinates of (a) are:
transmitting antenna S to ice surface incident point P1Is vector of
Refer to "synthetic Aperture Radar satellite" book of Welch bolt
Is converted into an antenna coordinate system from a geocentric coordinate system, and the vector in the antenna coordinate system is
Then azimuth angle ζaThe calculation formula of (2) is as follows:
thus, at the i-th azimuth time tiTransmitting the antenna S to the target P2When the transmitting antenna is in the irradiation range of the azimuth beam, the following conditions are satisfied:
the simultaneous illumination indicates that an echo signal may be generated, otherwise no echo signal is generated.
Similarly, the reception antenna Q is calculated to the in-ice target P2Whether it is within the range of beam irradiation in the receiving antenna azimuth.
Then, whether i is smaller than the number N of azimuth sampling points is judgedaIf the condition is satisfied, i +1 continues to loop through steps S2 to S7, otherwise the loop end calculation is skipped.
The invention also verifies the validity of the proposed method, and in a particular embodiment the orbital parameters of the transmitting satellite carrying the transmitting antenna S and the receiving satellite carrying the receiving antenna Q are shown in table 1. According to orbit parameters, the transmitting antenna S and the receiving antenna Q can realize satellite-borne downward-looking double-station observation near polar regions. The transmitting antenna adopts a reflecting surface antenna, and the receiving antenna adopts a half-wavelength dipole antenna.
TABLE 1 orbital parameters of transmitting and receiving satellites
| Parameter name | Numerical value |
| Semi-major axis of track | 6806.137Km |
| Argument of |
0° |
| Ascending crossing point of the right ascension | 120° |
| Eccentricity of orbit of launching |
0 |
| Eccentricity of orbit of received satellite | 20e-6 |
| Launch satellite orbital inclination | 90° |
| Receiving satellite orbit inclination | 90.028° |
| Simulation starting time | 1380s |
The relevant parameters for calculating the satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path are shown in the following table 2:
TABLE 2 satellite-borne downward-looking ice-detection synthetic aperture radar transmission path calculation related parameters
| Parameter name | Numerical value |
| Diameter of transmitting antenna | 40m |
| Pulse repetition interval | 5.56e-04s |
| Number of sampling points in azimuth direction | 6096 |
| Equatorial radius of the earth | 6378137m |
| Polar radius of earth ellipsoid | 6356752.315m |
At the time of the simulation center, three targets in ice are arranged at 5000m (heading 5000m) below the satellite of the transmitting antenna S and perpendicular to the flight direction of the transmitting satellite, wherein the targets are respectively positioned in 3900m, 2000m and 100m in the ice, and the longitude, the latitude and the depth in the ice are respectively as follows:
(116.8567471479693°,89.011722494825293°,3900m)
(116.8567471479693°,89.011722494825293°,2000m)
(116.8567471479693°,89.011722494825293°,100m)。
as shown in fig. 5 to 7, the present invention compares the transmission path error (i.e. the slant range error) from the transmitting antenna to the target by using two calculation modes of an one-dimensional quintic equation approximate solution and a precise solution equation solution, respectively, fig. 5 shows the one-way slant range error from the transmitting satellite to the target obtained by the approximate solution relative to the precise solution, wherein 3900m of the target in ice corresponds to the slant range error closest to 0, 2000m of the target in ice corresponds to the slant range error, and the maximum error occurs in 100m of the target in ice, fig. 6 shows the one-way slant range error from the receiving satellite obtained by the approximate solution relative to the precise solution, wherein 3900m of the target in ice corresponds to the slant range error closest to 0, 2000m of the target in ice corresponds to the slant range error, and the maximum error occurs in 100m of the target in ice, fig. 7 shows the two-way slant range error from the transmitting satellite to the target obtained by the precise solution and the receiving satellite to the target by the approximate solution, wherein the corresponding slope error of 3900m of the target in the ice is closest to 0, the corresponding slope error of 2000m of the target in the ice is secondly, and the maximum error occurs in the corresponding slope error of 100m of the target in the ice. As can be seen from FIGS. 5 to 7, solving with a quintic equation results in a pitch error of 1.86e-4m maximum (target depth in ice of 100 m). The phase error due to the skew error must be less than pi/4, so that Δ R ≦ pi λ/8 — 0.125 m. It can be known that the slope distance error of 1.86e-4m is far less than 0.125m caused by solving the quintic equation with one element, so that the calculation accuracy of the two-way slope distance is ensured. Meanwhile, the roots function in the MATLAB software can be used for establishing the quintic equation, and compared with the method for accurately solving by using the solve function in the MATLAB software, the calculation efficiency is obviously improved.
The embodiment of the invention also provides electronic equipment which comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to realize the method for calculating the transmission path of the satellite-borne downward-looking ice-detecting synthetic aperture radar in any embodiment of the invention.
An embodiment of the present invention further provides a computer-readable storage medium, where a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the processor is caused to execute a method for calculating a transmission path of an ice-sounding synthetic aperture radar under satellite loading according to any embodiment of the present invention.
Specifically, a system or an apparatus equipped with a storage medium on which software program codes that realize the functions of any of the above-described embodiments are stored may be provided, and a computer (or a CPU or MPU) of the system or the apparatus is caused to read out and execute the program codes stored in the storage medium.
In this case, the program code itself read from the storage medium can realize the functions of any of the above-described embodiments, and thus the program code and the storage medium storing the program code constitute a part of the present invention.
Examples of the storage medium for supplying the program code include a floppy disk, a hard disk, a magneto-optical disk, an optical disk (e.g., CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW), a magnetic tape, a nonvolatile memory card, and a ROM. Alternatively, the program code may be downloaded from a server computer via a communications network.
Further, it should be clear that the functions of any one of the above-described embodiments may be implemented not only by executing the program code read out by the computer, but also by causing an operating system or the like operating on the computer to perform a part or all of the actual operations based on instructions of the program code.
Further, it is to be understood that the program code read out from the storage medium is written to a memory provided in an expansion board inserted into the computer or to a memory provided in an expansion module connected to the computer, and then causes a CPU or the like mounted on the expansion board or the expansion module to perform part or all of the actual operations based on instructions of the program code, thereby realizing the functions of any of the above-described embodiments.
In summary, the present invention provides a satellite-borne downward-looking ice-detecting synthetic aperture radar transmission path calculation method, a computer device and a computer-readable storage medium; the method is based on observing the target in the ice under the low-orbit satellite, considering the correlation among the parameters such as the actual orbit height, the distance beam width, the maximum ice penetration depth and the like, the refraction angle from the air to the ice is approximate to the incidence angle of the target in the ice, and a univariate quintic equation is established by utilizing the Snell refraction theorem. And finally, directly and quickly solving by utilizing roots of the Matlab function library. Through comparison, the quintic equation approximation solving is about 1000 times faster than the solution function direct solving, the skew distance error is very small, and the accuracy of transmission path calculation is guaranteed.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A satellite-borne downward-looking ice-detection synthetic aperture radar transmission path calculation method is characterized by comprising the following steps:
acquiring earth model parameters, system parameters of a satellite-borne downward-looking ice-exploring synthetic aperture radar and echo simulation parameters; the echo simulation parameters comprise an orientation time sequence, an antenna position sequence and an in-ice target position under a rotating geocentric coordinate system;
in the area to be detected, the air medium above the earth surface and the ice medium below the earth surface are used, and for each azimuth moment, the corresponding geocentric angle of the corresponding transmission path in the ice medium is solved, so that the lengths of the transmission path in the air medium and the ice medium are respectively determined; the transmission path connects the corresponding antenna position and the target position in the ice and is located within the beam range of the transmitting antenna.
2. The method of claim 1, whereinAt one azimuth moment, the corresponding geocentric angle alpha of the corresponding transmission path in the ice medium is solved2The method comprises the following steps:
calculating the target P from the antenna S to the geocentric O and in the ice2To the earth' S center O and antenna S to the in-ice target P2And calculating the antenna S and the target P in the ice2The corresponding geocentric angle α;
calculating the local radius R of the sub-satellite point of the antenna S based on the earth model parameters and the corresponding antenna positionL；
Setting a transmission path passing through an ice surface incident point P1And ice surface incident point P1Distance to the earth center O and local radius R of the sub-satellite point of the antenna SLEquality, respectively calculating the incident point P on the ice surface1Incident angle on ice surface thetai1Sine sin theta ofi1And an in-ice target P2Angle of incidence thetai2Sine sin theta ofi2The expression of (1);
according to the law of refraction, based on sine sin thetai1And sin θi2Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (1);
target P in ice based on distance from antenna S to geocenter O2Distance to the earth center O, ice surface incident point P1The distance to the center of earth O and the center angle alpha according to the ratio n of the dielectric constants of the ice medium and the air medium1Calculating the corresponding geocentric angle alpha of the transmission path in the ice medium2。
3. The method of claim 2, wherein the distance from the antenna S to the geocenter O is calculated as:
wherein R iss(ti)＝[Rsxi,Rsyi,Rszi]Denotes the ith (i ═ 1,2, …, Na) Individual azimuth time tiCorresponding to the position coordinates of the antenna S, NaRepresenting azimuthal samplesCounting;
the calculation of the in-ice target P2The distance to the geocenter O is expressed as:
wherein [ P ]2x,P2y,P2z]Representing an in-ice target P2The position coordinates of (a);
the computing antenna S to the in-ice target P2The expression is:
the calculated antenna S and the target P in the ice2The corresponding geocentric angle α is expressed as:
4. method according to claim 3, characterized in that said calculation of the local radius R of the subsatellite point of the antenna S is carried outLThe method comprises the following steps:
calculating latitude phi of antenna S subsatellite pointsThe expression is:
calculating longitude Ψ of antenna S subsatellite pointsThe expression is:
obtain the local radius R of the subsatellite pointL：
Wherein R iseIs the equatorial radius of the earth, RpThe polar radius of the earth ellipsoid.
5. A method according to claim 4, characterized by calculating the point of incidence P on the ice surface1Incident angle on ice surface thetai1Sine sin theta ofi1Includes:
α1representing the corresponding centre of earth angle of the transmission path in the air medium, alpha ═ alpha1+α2；
Calculating in-ice target P2Angle of incidence thetai2Sine sin theta ofi2Includes:
obtaining the ratio n of the dielectric constants of the ice medium and the air medium1Includes:
angle of refraction theta in icet1And an in-ice target P2Angle of incidence thetai2The relationship between is thetat1＝θi2-α2Obtaining an ice internal refraction angle thetat1Sine sin theta oft1The expression is as follows:
the ratio n of the dielectric constants of the ice medium and the air medium according to the refraction theorem1The expression of (a) is:
6. the method of claim 5, wherein the calculated geocentric angle α of the transmission path in the ice medium is calculated2The method comprises the following steps:
setting the center angle of the earth alpha2Sufficiently small, thetat1＝θi2-α2≈θi2Obtaining the ratio n of the dielectric constants of the ice medium and the air medium1The expression of (a) is:
squaring the two sides of the expression, and setting x as sin alpha2Then, there are:
let x be small enough, have
When thickness d of ice layer2＝RL-RtgNot equal to zero, target P in ice2The distance to the earth center O is less than the local radius R of the sub-satellite pointLThen, there are:
solving for sin alpha2Further obtaining the corresponding geocentric angle alpha of the transmission path in the ice medium2。
7. Method according to claim 6, characterized in that the length R of the transmission path in the air medium is determined separatelyTairAnd in the ice mediumLength in matter RTiceThe method comprises the following steps:
8. the method of claim 1,
if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a double-station radar and comprises a transmitting antenna and a receiving antenna, solving transmission paths corresponding to the transmitting antenna and the receiving antenna respectively for each azimuth moment, and adding to obtain a final transmission path;
if the satellite-borne downward-looking ice-detecting synthetic aperture radar is a single-station radar and a transmitting and receiving common antenna is adopted, the final transmission path is a double one-way transmission path at each azimuth moment.
9. A computer device comprising a memory and a processor, the memory storing a computer program, wherein the processor when executing the computer program performs the steps of the method for on-board look-down ice synthetic aperture radar transmission path computation according to any one of claims 1 to 8.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method for computing a transmission path for an on-board look-down ice synthetic aperture radar according to any one of claims 1 to 8.
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