CN110221299B - Spaceborne dual-channel dual-beam InSAR current measurement system - Google Patents
Spaceborne dual-channel dual-beam InSAR current measurement system Download PDFInfo
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- CN110221299B CN110221299B CN201910598223.5A CN201910598223A CN110221299B CN 110221299 B CN110221299 B CN 110221299B CN 201910598223 A CN201910598223 A CN 201910598223A CN 110221299 B CN110221299 B CN 110221299B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
- G01S13/50—Systems of measurement based on relative movement of target
- G01S13/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
- G01S13/589—Velocity or trajectory determination systems; Sense-of-movement determination systems measuring the velocity vector
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9021—SAR image post-processing techniques
- G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9094—Theoretical aspects
Abstract
The invention discloses a satellite-borne dual-channel dual-beam InSAR current surveying system, which relates to the technical field of ocean remote sensing and comprises a phased array radar antenna and a broadband large squint dual-beam forming network module, wherein a plurality of phased array antenna radiation array elements are arranged on the phased array radar antenna; each phased array antenna radiation array element is respectively connected with a transmitting/receiving component; the broadband large squint double-beam forming network module is cascaded with the transmitting/receiving component in a series connection mode; when the radar transmits signals, a method of 'intra-pulse beam switching' is adopted; when receiving echo signals, the whole radar antenna aperture is divided into a front antenna sub-aperture and a rear antenna sub-aperture in the radar flying direction, each antenna sub-aperture forms a simultaneous dual-beam antenna directional diagram, and the radar echo signals of a forward beam and a backward beam are received at the same time. The effect of integrally realizing the wide swath measurement of the two-dimensional velocity vector of the ocean current is achieved on the premise of ensuring that the current measurement precision and the current measurement spatial resolution are not lost.
Description
Technical Field
The invention relates to the technical field of ocean remote sensing, in particular to a satellite-borne dual-channel dual-beam InSAR flow measurement system.
Background
The ocean covers about 70% of the earth's surface, and is an important space and an important resource bank for human survival and development, and ocean currents are one of the most important elements of the ocean. Firstly, mastering the law of ocean currents has important scientific significance for the research of ocean science and climate change. For example, sea currents have important effects and restrictions on the climate and the formation and changes of the weather above the sea: the ocean current flowing from low latitude to high latitude can cause the water vapor to be conveyed upwards, so that the air humidity is increased to generate precipitation; and the ocean current flowing from high latitude to low latitude can generate inverse temperature, so that water vapor is not easy to be transported upwards, and evaporation is weak and is not easy to become rain. Ocean currents also have influence and restriction on various physical, chemical, biological and geological processes in the ocean: in the sea area where the cold and warm currents are intersected, seawater is easy to disturb, and nutrients in the lower layer can be brought to the surface layer, so that mass propagation of fishes is facilitated; the ocean current can quickly diffuse the pollutants to accelerate the dilution and purification speed of the pollutants, and correspondingly expand the pollution range; ocean currents are an important factor in the formation of coastal topography, which can cause shoreline to migrate, affecting the transport of coastal sediments and the performance of sedimentation. Furthermore, the acquisition of ocean current information plays an important role in civil aspects, such as the selection of a trade ship route with reference to ocean current conditions and the like; for realizing the sustainable development of coastal zone resources, the law of ocean current needs to be researched; industries such as oil and gas exploration require reliable ocean current data to ensure safe working conditions.
In summary, ocean current detection methods are mainly divided into two categories, namely "on-site" observation and "remote sensing" observation. The instrument for on-site flow measurement mainly comprises an impeller current meter, an acoustic Doppler current profiler, a drifting buoy and the like. The field observation has the advantage of higher measurement accuracy, but has the disadvantages of limited space coverage, incapability of meeting the application requirements of large areas in the world and higher cost of each observation. The satellite-borne forward-orbit interferometric synthetic aperture radar (InSAR) is an advanced active microwave remote sensing detector and can realize effective measurement of a sea surface flow field. The satellite-borne down-track InSAR (interferometric synthetic aperture radar) remote sensing method is characterized in that two antennas are placed along a satellite orbit to obtain two Synthetic Aperture Radar (SAR) complex images, and radial ocean current information can be obtained by calculating interference phases of the two SAR complex images. Compared with the ocean current field observation method, the InSAR method has the advantages of high resolution, wide coverage (ocean current information in a global range can be observed), high revisitation rate in the same area, no limitation of meteorological conditions and the like.
Although the spaceborne orbit-compliant InSAR method has the advantages and potentials of the above aspects in the application of ocean current inversion, however, the existing satellite-borne InSAR systems (such as the TerrasAR-X radar system and the TanDEM-X system in Germany) can only measure the radial (namely the direction of the radar beam sight line) speed component of the current speed, and the complete two-dimensional speed vector of the current is difficult to acquire with high precision. Theoretically speaking, a direct method for acquiring a two-dimensional velocity vector of ocean current is to observe a sea surface scene from two different azimuth angles, measure two different radial velocity components of the ocean current vector, and then combine the two radial velocity components to obtain the two-dimensional vector of the ocean current velocity. Therefore, the key to ocean current vector measurement can be summarized as: how to generate two radar beams with different azimuth directions (or squint angles) to form a so-called "dual-beam InSAR" system.
Currently, the manner in which dual beam InSAR systems generate "dual beams" can be summarized as follows. In the first mode, two sets of independent antennas, a radar signal transmitter and a radar receiver system are used for generating forward beams and backward beams respectively, so that a dual-beam InSAR system is formed; for the second dual-beam generation mode, the same InSAR system alternately transmits forward beams and backward beams in two adjacent pulses and alternately receives radar echo signals; for the third approach, the same InSAR system uses a "Burst of azimuth" mode to generate "forward" and "backward" beams, i.e.: the radar beam points in the "forward" direction for a certain number of "radar burst" times, and in the "backward" direction for the next same number of "radar burst" times. In 2004, massachusetts university in the united states developed an "airborne" dual-beam InSAR system, which belongs to the first dual-beam generation approach described above. This system has some disadvantages, such as: the system has a large "weight"; occupies a large "space"; consume more "electric power energy"; while generating a larger "radar data volume". These disadvantages make the system difficult to generalize from "on-board" to "on-board". For the second approach, to avoid the occurrence of "azimuth ambiguity", the Pulse Repetition Frequency (PRF) of the SAR needs to be doubled, which results in a reduction of the unambiguous range swath width to one-half of the original value (since the unambiguous range swath width is inversely proportional to the PRF). In other words, this dual beam formation is traded for "reduced swath width". For the third dual-beam generation mode, the direct consequence of using the "Burst" mode is the so-called "scallop effect" caused by the "missing SAR azimuth data", so that the amplitude of the SAR image changes periodically in azimuth direction, and the "non-uniformity" of the image not only causes spatial inconsistency of the "velocity measurement uncertainty" of the ocean current inversion, but also generates an "extra" velocity measurement "mean deviation. In addition, the Burst mode can also cause certain 'difference' to be generated in SAR data corresponding to the 'forward' beam and the 'backward' beam, thereby bringing negative influence on the inversion of the ocean current velocity vector. The second and third dual beam generation approaches are currently in the conceptual stage, and there is no practical in-orbit InSAR system.
In summary, there is no satellite-borne dual-beam InSAR current measurement system capable of being operated in a business manner, and a novel satellite-borne dual-beam InSAR system needs to be invented to solve the problem existing in the two-dimensional velocity vector inversion of the sea surface flow field.
Disclosure of Invention
The invention aims to provide a satellite-borne dual-channel dual-beam InSAR flow measurement system which can integrally (only one radar and two physical receiving channels are used) realize wide swath measurement of a two-dimensional velocity vector of ocean current on the premise of ensuring that the flow measurement precision and the flow measurement spatial resolution are not lost.
The technical purpose of the invention is realized by the following technical scheme:
a satellite-borne two-channel dual-beam InSAR current surveying system comprises a phased array radar antenna which is placed along the flight direction of a satellite and is observed towards the sea surface, wherein a plurality of phased array antenna radiation array elements for radiating and transmitting signals to the external space are arranged on the phased array radar antenna;
the broadband strabismus dual-beam forming network module is used for generating a forward beam and a backward beam;
the whole radar antenna aperture is divided into two groups in the radar flying direction, the two groups respectively comprise a front antenna sub-aperture and a rear antenna sub-aperture, and each antenna sub-aperture forms a 'simultaneous dual-beam' antenna directional diagram when receiving echo signals and simultaneously receives radar echo signals of a forward beam and a backward beam;
each phased array antenna radiation array element is respectively connected with a transmitting/receiving component; the transmitting/receiving component comprises a phase shifter used for correcting deviation between forward beam and backward beam swaths caused by earth rotation, and the broadband large squint dual-beam forming network module is cascaded with the transmitting/receiving component in a serial mode.
Furthermore, the number of antenna elements in the azimuth direction should be not less than N:
N＝L(1+sinθ sq )/λ
in the above formula, L is the total aperture length of the radar antenna in the azimuth direction, λ is the radar wavelength, and θ sq Is the forward beam squint angle.
Furthermore, each transmit/receive module comprises a transmit amplifier HPA for power amplification of the radar transmitted signals, and a receive amplifier LNA for low-noise power amplification of the received radio-frequency signals in the reception of echoes by the radar.
Furthermore, the broadband large squint dual-beam forming network module comprises two groups of delay lines connected in parallel, wherein the two groups of delay lines are a forward delay line group and a backward delay line group respectively corresponding to the forward beam and the backward beam.
Further, the lengths of the respective delay lines of the forward delay line group
The squint angle of the forward beam is determined, specifically:
length of each delay line of backward delay line group
Determined by the squint angle of the backward beam, namely:
in the above two formulas, d represents the interval between the radiation array elements of the phased array antenna,θ sq and K is the number of the radiation array elements of the phased array antenna, wherein the forward beam squint angle is obtained.
Further, each delay line is provided with a switch, the switch connected to the forward delay line is referred to as a forward delay line switch, and the switch connected to the backward delay line is referred to as a backward delay line switch.
Furthermore, the radar resource scheduling method comprises the following steps:
s10: when the radar is in a transmitting state, the radar transmits,
after digital/analog conversion and power amplification of an amplifier, the linear frequency modulation signal generated by the linear frequency modulation signal digital generator is mixed with a local oscillator signal and up-converted to radar carrier frequency;
s20: the signal is sent to the broadband large squint dual-beam forming network module through the feed network, the radar resource scheduling circuit system module sends an intra-pulse beam switching scheduling instruction to the broadband large squint dual-beam forming network module, and in the first half of the time of each pulse, the backward delay line switch is connected while the forward delay line switch is disconnected, so that a backward beam is generated; during the second half of the pulse, turning on the forward delay line switch and turning off the backward delay line switch, thereby generating a forward beam; it also produces orthogonality between the forward and backward beam transmit signals, thereby producing an orthogonally encoded chirp signal;
s30: after the signal is amplified by a high-power transmitting amplifier in the transmitting/receiving component, the radio-frequency signal is radiated to the space by the radiating array element to finish the transmission of the signal;
s40: when the radar echo signal is received, the radar echo signal is sent to the receiver,
for each antenna sub-aperture, namely a front antenna sub-aperture or a rear antenna sub-aperture, a forward delay line switch and a backward delay line switch in the broadband large squint dual-beam forming network module are communicated to form a simultaneous dual-beam antenna directional diagram and simultaneously receive radar echo signals of forward and backward beams;
s50: the received signals are subjected to down-conversion and analog/digital conversion to obtain front antenna sub-aperture SAR original signals and rear antenna sub-aperture SAR original signals;
s60: the influence of the earth rotation on the contact ratio of the forward and backward beam swaths is corrected by using beam scanning, so that the swaths of the forward and backward beams can be completely overlapped.
Further, the correction in step S60 specifically includes the steps of:
s61: determining the velocity vector V of the satellite flight from the position of the satellite in the earth-centered inertial frame sat Linear velocity vector V of rotation with the earth rot ；
S62: according to V sat And V rot The following tangent angle θ is calculated yaw ：
In the above formula, atan (. Cndot.) represents an arctan function;
s63: according to angle theta yaw Determining the phase applied by a phase shifter in each transmit/receive component in a phased array antenna
The following were used:
in the above formula, λ represents a radar wavelength;
s64: radar resource scheduling circuitry based on
Sending an instruction to the transmitting/receiving component to scan the azimuth beam, and simultaneously enabling the forward beam and the backward beam to scan the azimuth beam at an angle theta yaw Thus, the swaths of the two beams can be coincided.
Furthermore, the method for carrying out ocean current vector inversion by using the flow measurement system comprises the following steps:
s'10: extracting radar echo signals corresponding to forward and backward beams by using two window functions with different center distance frequencies;
s'20: and inverting the ocean current velocity vector according to the echo signals after the forward and backward wave beams are separated.
Furthermore, in step S'10, based on the signal orthogonality, the forward and backward beam echo signals in the echo data received by the dual-channel dual-beam InSAR flow measurement system are separated, and the specific steps are as follows:
s'11: front antenna sub-aperture radar echo signal s received by double-channel double-beam InSAR system 1 (t a ,t r ) And a post-antenna sub-aperture radar echo signal s 2 (t a ,t r ) Performing a two-dimensional Fourier transform, wherein t a And t r Respectively representing slow time and fast time, converting into two-dimensional frequency domain, i.e. Doppler frequency/distance frequency domain, and respectively obtaining signal S 1 (f d ,f r ) And S 2 (f d ,f r ). Wherein f is d And f r Respectively representing a doppler frequency and a range frequency;
s'12 in the two-dimensional frequency domain, two window functions W are used + (f d ,f r ) And W - (f d ,f r ) Respectively taking out front antenna sub-aperture radar echo signals S 1 (f d ,f r ) Respectively obtaining the forward wave beam echo signal of the front antenna sub-aperture
Echo signal with backward beam
The method comprises the following specific steps:
in the above two formulae, W + (f d ,f r ) And W - (f d ,f r ) The expression of (a) is:
wherein, F s And f PRF Respectively representing a distance sampling frequency and a pulse repetition frequency;
s'13: for post-antenna sub-aperture radar return signal S 2 (f d ,f r ) Repeating the above step S'12 to obtain the forward wave beam echo signal of the rear antenna sub-aperture
Echo signal with backward beam
S'14: will be provided with
Two-dimensional inverse Fourier transform is carried out to respectively obtain two-dimensional time domains, namely slow time domain echo signals/fast time domain echo signals
And
wherein
And
a forward beam echo signal and a backward beam echo signal representing the front antenna sub-aperture respectively,
and
a forward beam echo signal and a backward beam echo signal respectively representing a rear antenna sub-aperture;
in step S'20, four separated echo signals are used
And
inverting the ocean current velocity vector according to the following steps:
s'21: to pair
And
interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of the forward wave beam
S'22: to pair
And with
Interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of the backward beam
S'23: using two estimated radial velocity components
And with
And calculating the ocean current velocity vector v according to the geometrical relation of the dual-channel dual-beam InSAR and the following formula cur ：
In the above formula, the first and second carbon atoms are,
and
respectively representing the velocity vector v of the ocean current cur The azimuthal velocity component of (a) and the horizontal plane distance component of (b),
the expression of matrix H is:
in the above formula, θ inc Representing the central angle of incidence of the beam.
In conclusion, the invention has the following beneficial effects:
1. on the premise of not losing the flow measurement precision and resolution, the spaceborne dual-channel dual-beam InSAR flow measurement system provided by the invention can provide a two-dimensional velocity vector flow field with a larger range width. Existing dual-beam generation schemes, the "adjacent pulse beam alternating" dual-beam generation approach, require doubling of the Pulse Repetition Frequency (PRF) of the radar to avoid the occurrence of "doppler ambiguity", which can shift the distance towards the unambiguous "swath width" to half of the single-beam case (since the unambiguous distance swath width is inversely proportional to the PRF). Compared with the prior art, the novel dual-channel dual-beam InSAR system provided by the invention can overcome the defects. The reason is that the new system adopts the technology of 'intra-pulse beam switching' (namely, 'backward' beams are generated in the first half time of each transmitted pulse, and 'forward' beams are generated in the second half time of the pulse), the PRF does not need to be doubled, and the aperture of the radar antenna in the azimuth direction is fully utilized, so that the large swath width in the range direction can be realized;
2. the novel satellite-borne dual-channel dual-beam InSAR flow measurement system provided by the invention has higher integration degree, namely: the receiving of the data of the front antenna sub-aperture/forward beam, the front antenna sub-aperture/backward beam, the rear antenna sub-aperture/forward beam and the rear antenna sub-aperture/backward beam can be realized by only using two (but not four) radar physical receiving channels. When the radar echo signals are received, the invention adopts a simultaneous double-beam receiving technology, and can realize that the two channels simultaneously receive the radar echo SAR data of the four beams. In addition, because the invention adopts the coding mode of orthogonal signals of ' forward ' and ' backward ' wave beams ' when the radar transmits pulse signals, the ' signal separation ' is easily realized from SAR echo data received by double channels, and the ' front antenna sub-aperture/forward wave beam ', ' front antenna sub-aperture/backward wave beam ', ' back antenna sub-aperture/forward wave beam ', ' back antenna sub-aperture/backward wave beam ' InSAR data are reconstructed. The 'simple' integrated radar system design is beneficial to placing radar loads on a satellite platform;
3. the novel satellite-borne dual-channel dual-beam InSAR flow measurement system provided by the invention has stronger system flexibility, and is specifically embodied as follows:
a) Through the adjustment of the radar resource scheduling scheme, the dual-channel dual-beam InSAR system can be conveniently converted into a traditional single-beam InSAR system;
b) The newly proposed dual-channel dual-beam InSAR system has stronger expansibility of working modes, for example, a pitching scanning mode, a dual-polarization mode and the like can be added to the system;
c) The newly proposed two-channel and two-beam InSAR system can realize 'multi-functionalization', for example, sea surface wind field measurement, sea wave spectrum measurement, other sea surface and land imaging functions and the like can be realized simultaneously.
Drawings
FIG. 1 is a geometrical diagram of a satellite-sea surface defined in a geocentric rotation coordinate system of a spaceborne dual-channel dual-beam InSAR flow measurement system provided by the invention;
FIG. 2 is a general structure diagram of a spaceborne dual-channel dual-beam InSAR current surveying system provided by the invention;
fig. 3 is an internal structural view of an active transmission/reception module;
FIG. 4 is a diagram of a "broadband strabismus dual beam forming network";
FIG. 5 is a schematic diagram of the working principle of a spaceborne dual-channel dual-beam InSAR current surveying system provided by the invention;
FIG. 6 is a schematic diagram of the "intra-pulse beam switching" technique;
FIG. 7 is a "time-frequency signature" of the "forward" and "backward" beam transmit signals;
figure 8 is the "orthogonality" of the "forward" beam receive echo signals with the "backward" beam receive signals.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings, and the present embodiment is not to be construed as limiting the invention.
The utility model provides a spaceborne binary channels dual beam InSAR current surveying system, is based on current "active phased array antenna" technique, as shown in figure 1, includes and places along satellite direction of flight and towards the phased array radar antenna of sea observation with the mode that looks sideways at, is equipped with a plurality of phased array antenna radiation array elements to outer space radiation emission signal on the phased array radar antenna. The system comprises two beams of a forward beam and a backward beam, wherein the central incident angles of the two beams are theta inc The squint angle of the forward beam is theta sq And the squint angle of the backward beam is-theta sq 。
1) For a phased array antenna radiating array element:
in this embodiment, a "waveguide slot" antenna is used as a radiation array element of a phased array antenna of a novel dual-channel dual-beam InSAR current measurement system. The waveguide slot antenna is characterized in that a slot is formed in a waveguide, and electromagnetic waves are radiated to an external space through the slot. Its advantages are light weight, good planar structure, high utilization rate of aperture surface, and low by-pass valve or extremely low by-pass valve. Meanwhile, the waveguide slot antenna also has the advantages of firm structure, simplicity, compactness, easiness in processing, convenience in feeding, simplicity in erection and the like.
In order to achieve a "two-dimensional" velocity vector measurement of ocean currents, it is necessary that the "forward" and "backward" beams have a large "squint angle" (see fig. 1). On the other hand, a larger squint angle requires that the number of the azimuth antenna array elements must meet certain requirements so as to avoid the occurrence of 'antenna gain reduction' and 'antenna grating lobe'. Under the condition of lower 'grating lobe' level, according to the correlation theory of antenna array, the oblique angle theta is realized sq The number of antenna elements in the azimuth direction is not less than N:
N＝L(1+sinθ sq )/λ
in the above formula, L is the total aperture length of the radar antenna in the azimuth direction, λ is the radar wavelength, and θ sq Is the forward beam squint angle.
2) For T/R components, i.e. transmit/receive components:
as shown in fig. 2 and fig. 3, each phased array antenna radiation array element is connected with an active transmitting/receiving component; the transmit/receive assembly (i.e., T/R assembly) includes phase shifters for correcting the divergence between the forward and backward beam swaths caused by earth rotation.
As shown in fig. 3, each of the transmission/reception modules includes a transmission amplifier HPA that performs power amplification when a radar transmits a signal, and a reception amplifier LNA that performs low-noise power amplification on a received radio frequency signal when a radar receives an echo;
as shown in fig. 3, each transmit/receive module includes two circulator switches used as selection and switch of path, two channels respectively including transmit amplifier HPA and receive amplifier LNA are connected between the two circulator switches, and both channels are connected to the standard feedback circuit for aperture calibration and compensation through the directional coupler;
as shown in fig. 3, a phase shifter and a variable gain amplifier are connected between the circulator switch and the radar circuit, the phase shifter performs different 'phase shifts' on radar signals to realize the change and scanning of radar beam direction, and the variable gain amplifier performs weighting control on the signal amplitude of each path of transmitting/receiving component to realize the change of radar beam shape;
as shown in fig. 3, the phase shifter and the variable gain amplifier are respectively connected to a control logic circuit, and the control logic circuit controls the amplitude of the variable gain amplifier and the phase of the phase shifter, and the circulator switch; and the transmitting/receiving assembly is also connected with a power regulating circuit for regulating the voltage in the transmitting/receiving assembly.
3) For broadband large squint dual-beam forming networks:
as shown in fig. 2, the spaceborne dual-channel dual-beam InSAR flow measurement system includes a broadband large squint dual-beam forming network module for generating a forward beam and a backward beam, and the broadband large squint dual-beam forming network module is cascaded with a transmitting/receiving component in a serial manner.
For smaller scan angles, a phased array antenna including transmit/receive components may achieve a larger signal "bandwidth". However, for the present invention, a large squint angle is required in order to achieve the measurement of the "two-dimensional" velocity vector of the ocean current (fig. 1). For this case, if the radar beam scanning is still achieved using only the "phase shifters" in the transmit/receive components, the "bandwidth" of the phased array antenna is greatly limited due to the "frequency sweeping" phenomenon. In fact, according to the phased array antenna theory, the bandwidth Δ f of a phased array antenna is inversely proportional to L · sin (θ) sq ) (where L is the total aperture length of the radar antenna in the azimuth direction, θ) sq Beam scan squint angle), the larger the squint angle, the smaller the bandwidth of the phased array.
In view of the wide-band signal of "chirp" and the large squint angle, the present invention cannot satisfy the requirement of "wide-band large squint dual-beam formation" only by the "phase shifter" in the transmitting/receiving component. In order to solve the difficult problem, the invention adopts the technical scheme of a 'transmitting/receiving component cascade delay line network', namely, a broadband large squint dual-beam forming network (figure 2) is adopted. The structure of the broadband large squint dual-beam forming network module is shown in fig. 4, and specifically as follows:
a) The broadband large squint dual-beam forming network module comprises two groups of delay lines connected in parallel, wherein the two groups of delay lines are a forward delay line group and a backward delay line group which respectively correspond to a forward beam and a backward beam.
Length of each delay line of forward delay line group
The squint angle of the forward beam is determined, specifically:
length of each delay line of backward delay line group
Determined by the squint angle of the backward beam, namely:
in the above two formulas, d represents the distance between the radiation array elements of the phased array antenna, and theta sq And K is the number of the radiation array elements of the phased array antenna, wherein the forward beam squint angle is obtained.
b) Each delay line is provided with a switch, the switch connected with the forward delay line is called a forward delay line switch, and the switch connected with the backward delay line is called a backward delay line switch (figure 4);
c) The whole antenna aperture (including radiating array elements, transmitting/receiving components and delay lines) is equally divided into two parts in the radar flight direction, which are respectively called as a front antenna sub-aperture and a rear antenna sub-aperture (figure 4) and are respectively connected with other parts (a mixer and the like) of a radar system, each antenna sub-aperture forms a simultaneous dual-beam antenna directional diagram and simultaneously receives radar echo signals of a forward beam and a backward beam;
4) For other components in the system
The spaceborne dual-channel dual-beam InSAR flow measurement system also comprises a radar resource scheduling circuit system which sends an instruction of azimuth beam scanning to the transmitting/receiving component and sends an intra-pulse beam switching scheduling instruction or a simultaneous dual-beam receiving instruction to the broadband large squint dual-beam forming network module, and the radar resource scheduling circuit system comprehensively utilizes the 'intra-pulse beam switching' technology, the 'orthogonal coding' technology and the 'simultaneous dual-beam receiving' technology.
And the rest components, including the components such as the "chirp signal digital generator", "local oscillator signal generator", "down conversion mixer", "up conversion mixer", "digital/analog converter", etc., are the same as those of the conventional single beam active phased array antenna SAR system, and will not be described in detail herein.
The basic principle of the spaceborne dual-channel dual-beam InSAR flow measurement system provided by the invention is generally described as follows by combining FIG. 5:
1. for radar signal transmission, the novel satellite-borne dual-channel dual-beam InSAR system adopts a full-aperture antenna to transmit a linear frequency modulation pulse signal, and utilizes an intra-pulse beam switching technology to generate a forward beam and a backward beam, namely: a "backward" beam is generated during the "first half time" of a certain pulse, and a "forward" beam is generated during the "second half time" of the pulse (see fig. 6). Compared with the method of respectively generating forward beams and backward beams by utilizing the sub-apertures of the two antennas, the scheme of intra-pulse beam switching fully utilizes the aperture resources of the antenna in the direction of direction, thereby realizing larger swath width in the distance direction.
Another feature of the "intra-pulse beam switching" technique is that the transmission signals of the "forward" beam and the transmission signals of the "backward" beam are "separated" from each other in the "distance frequency" domain (see fig. 7), which means that the "forward" beam and the "backward" beam transmit signals using "orthogonal" coding.
3. The squint angles of the forward beams and the backward beams are adjusted simultaneously by utilizing the scanning function of the phased array antenna, and the deviation between a zero Doppler line and the central lines of the forward beams and the backward beams caused by the rotation of the earth is corrected, so that the squint angles of the forward beams and the backward beams in the geocentric rotation coordinate system are equal in size, opposite in direction and the same in incident angle, and the swaths of the forward beams and the backward beams can be completely overlapped (refer to fig. 1).
4. When the novel dual-channel dual-beam InSAR system receives radar echo signals, the aperture of the whole radar antenna is divided into two sub-apertures in the radar flight direction to obtain a front antenna sub-aperture and a rear antenna sub-aperture; for each antenna sub-aperture, a "simultaneous dual beam" antenna pattern is formed using a "simultaneous dual beam" reception technique, while simultaneously receiving radar return signals for both the "forward" and "backward" beams (see fig. 5).
5. By utilizing the orthogonality between the radar echo signals received by the forward and backward beams (refer to fig. 8), the signals are separated in the distance frequency domain, and InSAR data of front antenna sub-aperture/forward beam, front antenna sub-aperture/backward beam, rear antenna sub-aperture/forward beam and rear antenna sub-aperture/backward beam are reconstructed.
Referring to fig. 2, fig. 3 and fig. 4, the invention also discloses a radar resource scheduling method of the satellite-borne dual-channel dual-beam InSAR flow measurement system, which comprises the following steps:
s10: when the radar is in a transmitting state, the radar transmits,
the linear frequency modulation signal generated by the linear frequency modulation signal digital generator is subjected to digital/analog conversion and amplifier power amplification, and then is subjected to frequency mixing and up-conversion with a local oscillator signal to a radar carrier frequency (refer to fig. 2);
s20: the signal is sent to the broadband large squint dual-beam forming network module through the feed network, the radar resource scheduling circuit system module sends an intra-pulse beam switching scheduling instruction to the broadband large squint dual-beam forming network module (refer to fig. 2), and in the first half time of each pulse, the backward delay line switch is connected while the forward delay line switch is disconnected, so that a backward beam is generated; in the latter half of the pulse, the forward delay line switch is turned on and the backward delay line switch is turned off, thereby generating a forward beam (see fig. 4); the radar resource scheduling mode of "intra-pulse beam switching" also generates orthogonality between forward and backward beam transmitting signals, thereby generating orthogonal coding chirp signals (fig. 7);
s30: after the signal is amplified by a high-power transmission amplifier HPA (figure 3) in the transmitting/receiving component, the radio-frequency signal is radiated to the space by the radiation array element to finish the transmission of the signal;
s40: when the radar echo signal is received, the radar echo signal is sent to the receiver,
equally dividing the whole radar antenna aperture into two sub-apertures in the radar flight direction to obtain a front antenna sub-aperture and a rear antenna sub-aperture, wherein for each antenna sub-aperture, namely the front antenna sub-aperture or the rear antenna sub-aperture, a forward delay line switch and a backward delay line switch in a broadband large squint dual-beam forming network module are communicated (refer to fig. 4), so that a simultaneous dual-beam antenna directional diagram is formed, and radar echo signals of forward and backward beams are received simultaneously;
s50: the received signals are subjected to down-conversion and analog/digital conversion to obtain front antenna sub-aperture SAR original signals and rear antenna sub-aperture SAR original signals (refer to fig. 2);
s60: the influence of the earth rotation on the contact ratio of the forward and backward beam swaths is corrected by using beam scanning, so that the swaths of the forward and backward beams can be completely overlapped;
due to the effects of earth rotation, the "zero doppler line" of the radar system can deviate from the "forward and backward" beam centerlines (see fig. 1), so that the swath of the "forward" beam does not coincide with the swath of the "backward" beam. In order to solve the problem, the invention utilizes the scanning function of the phased array antenna to simultaneously adjust the squint angles of the forward and backward beams and correct the influence of the autorotation of the earth, so that the swaths of the forward and backward beams can be completely overlapped, wherein the correction specifically comprises the following steps:
s61: determining the velocity vector V of the satellite flight from the position of the satellite in the earth-centered inertial frame sat Linear velocity vector V of rotation with the earth rot ；
S62: according to V sat And V rot The following tangent angle θ is calculated yaw ：
In the above formula, atan (-) represents an arctangent function;
s63: according to angle theta yaw Determining the phase applied by a phase shifter in each transmit/receive component in a phased array antenna
(see fig. 3), as follows:
in the above formula, λ represents a radar wavelength;
s64: radar resource scheduling circuitry based on
The transmit/receive module is instructed to scan the azimuth beam (see fig. 2) while the forward and backward beams are scanned at an azimuth scanning angle θ yaw Thereby enabling the swaths of the two beams to coincide.
The method for carrying out ocean current vector inversion by using the satellite-borne dual-channel dual-beam InSAR flow measurement system provided by the invention is described as follows, specifically comprising the following steps:
s'10: extracting radar echo signals corresponding to forward and backward beams by using two window functions with different center distance frequencies;
the novel satellite-borne dual-channel dual-beam InS' AR flow measurement system provided by the invention only has two physical receiving channels, namely a front antenna sub-aperture receiving channel and a rear antenna sub-aperture receiving channel. For each channel, the "forward" and "backward" beam echo signals are mixed together, and therefore, there is a problem of separation of the "forward" and "backward" beam signals (refer to fig. 2).
Because the new system adopts orthogonal coding of the forward beam signals and the backward beam signals in the pulse signal transmitting stage, the forward beam signals and the backward beam signals are also orthogonal for radar echo signals. This means that the "forward" and "backward" beam echo signals are separated from each other in the "range frequency" domain (see fig. 8). Accordingly, two window functions with different center distance frequencies can be used for extracting radar echo signals corresponding to the forward beams and the backward beams,
the method comprises the following specific steps:
s'11: front antenna sub-aperture radar echo signal s received by two-channel dual-beam InS' AR system 1 (t a ,t r ) (where t is a And t r Respectively representing slow time and fast time) and a post-antenna sub-aperture radar echo signal s 2 (t a ,t r ) A two-dimensional fourier transform is performed, transforming into the two-dimensional frequency domain (i.e.: doppler frequency/range frequency domain), respectively, to obtain a signal S 1 (f d ,f r ) And S 2 (f d ,f r ) (wherein f d And f r Respectively representing doppler frequency and range frequency);
s'12 in the two-dimensional frequency domain, two window functions W are used + (f d ,f r ) And W - (f d ,f r ) Respectively taking out front antenna sub-aperture radar echo signals S 1 (f d ,f r ) Respectively obtaining the forward wave beam echo signal of the front antenna sub-aperture
Echo signal with backward beam
The method specifically comprises the following steps:
in the above two formulae, W + (f d ,f r ) And W - (f d ,f r ) The expression of (a) is:
wherein, F s And f PRF Respectively representing a distance sampling frequency and a pulse repetition frequency;
s'13: for post-antenna sub-aperture radar return signal S 2 (f d ,f r ) Repeating the above step S'12 to obtain the forward wave beam echo signal of the rear antenna sub-aperture
Echo signal of backward wave beam
S'14: will be provided with
Two-dimensional inverse Fourier transform is carried out to respectively obtain two-dimensional time domain (slow time/fast time domain) echo signals
And
wherein
And
a forward beam echo signal and a backward beam echo signal representing the front antenna sub-aperture respectively,
and
representing the forward and backward beam echo signals of the rear antenna sub-aperture, respectively (see fig. 5).
S'20: and inverting the ocean current velocity vector according to the echo signals after the forward and backward wave beams are separated.
Wherein, based on the four separated echo signals
And
inverting the ocean current velocity vector according to the following steps:
s'21: to pair
And
interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of the forward beam (figure 1)
S'22: to pair
And with
Interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of backward beam (figure 1)
S'23: using two estimated radial velocity components
And
and calculating the velocity vector v of the ocean current according to the following formula according to the geometrical relation (figure 1) of the double-channel double-beam InS' AR cur ：
In the above formula, the first and second carbon atoms are,
and
respectively representing the velocity vector v of the ocean current cur The azimuthal velocity component of (a) and the horizontal plane distance component of (b),
the expression of matrix H is:
in the above formula, θ inc Representation waveThe central angle of incidence of the beam.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention.
Claims (7)
1. A spaceborne dual-channel dual-beam InSAR flow measurement system is characterized in that: the system comprises a phased array radar antenna which is placed along the flight direction of a satellite and is observed towards the sea surface, wherein a plurality of phased array antenna radiation array elements for radiating and transmitting signals to the external space are arranged on the phased array radar antenna;
the broadband strabismus dual-beam forming network module is used for generating a forward beam and a backward beam; the broadband large squint dual-beam forming network module comprises two groups of delay lines connected in parallel, wherein the two groups of delay lines are a forward delay line group and a backward delay line group which respectively correspond to a forward beam and a backward beam; each delay line is provided with a switch, the switch connected with the forward delay line is called a forward delay line switch, and the switch connected with the backward delay line is called a backward delay line switch;
the whole radar antenna aperture is divided into two groups in the radar flying direction, the two groups respectively comprise a front antenna sub-aperture and a rear antenna sub-aperture, and each antenna sub-aperture forms a 'simultaneous dual-beam' antenna directional diagram when receiving echo signals and simultaneously receives radar echo signals of a forward beam and a backward beam;
each phased array antenna radiation array element is respectively connected with a transmitting/receiving component; the transmitting/receiving component comprises a phase shifter used for correcting deviation between forward beams and backward beams caused by earth rotation, and the broadband large squint dual-beam forming network module is cascaded with the transmitting/receiving component in a serial connection mode;
the radar resource scheduling method comprises the following steps:
s10: when the radar is in a transmitting state, the radar transmits,
after digital/analog conversion and amplifier power amplification, the linear frequency modulation signal generated by the linear frequency modulation signal digital generator is mixed with a local oscillator signal and up-converted to radar carrier frequency;
s20: the signal is sent to the broadband large squint dual-beam forming network module through the feed network, the radar resource scheduling circuit system module sends an intra-pulse beam switching scheduling instruction to the broadband large squint dual-beam forming network module, and in the first half of the time of each pulse, the backward delay line switch is connected while the forward delay line switch is disconnected, so that a backward beam is generated; during the second half of the pulse, turning on the forward delay line switch and turning off the backward delay line switch, thereby generating a forward beam; it also produces orthogonality between the forward and backward beam transmit signals, thereby producing an orthogonally encoded chirp signal;
s30: after the signal is amplified by a high-power transmitting amplifier in the transmitting/receiving component, the radio-frequency signal is radiated to the space by the radiating array element to finish the transmission of the signal;
s40: when the radar echo signal is received,
for each antenna sub-aperture, namely a front antenna sub-aperture or a rear antenna sub-aperture, a forward delay line switch and a backward delay line switch in the broadband large squint dual-beam forming network module are communicated to form a simultaneous dual-beam antenna directional diagram and simultaneously receive radar echo signals of forward and backward beams;
s50: the received signals are subjected to down-conversion and analog/digital conversion to obtain front antenna sub-aperture SAR original signals and rear antenna sub-aperture SAR original signals;
s60: the influence of the earth rotation on the contact ratio of the forward and backward beam swaths is corrected by using beam scanning, so that the swaths of the forward and backward beams can be completely overlapped.
2. The spaceborne dual-channel dual-beam InSAR flow measurement system of claim 1, characterized in that: the number of antenna elements in the azimuth direction is not less than N:
N＝L(1+sinθ sq )/λ
in the above formula, L is the total aperture length of the radar antenna in the azimuth direction, and λ is the radarUp to wavelength, theta sq Is the forward beam squint angle.
3. The spaceborne dual-channel dual-beam InSAR flow measurement system of claim 1, characterized in that: each transmit/receive module comprises a transmit amplifier HPA for power amplification when the radar is transmitting signals, and a receive amplifier LNA for low-noise power amplification of received radio-frequency signals when the radar is receiving echoes.
4. The spaceborne dual-channel dual-beam InSAR flow measurement system of claim 1, characterized in that: length of each delay line of forward delay line group
The squint angle of the forward beam is determined, specifically:
length of each delay line of backward delay line group
Determined by the squint angle of the backward beam, namely:
in the above two formulas, d represents the distance between the radiation array elements of the phased array antenna, and theta sq And K is the number of the radiation array elements of the phased array antenna, wherein the forward beam squint angle is obtained.
5. The spaceborne dual-channel dual-beam InSAR current surveying system of claim 4, wherein:
the correction in step S60 specifically includes the following steps:
s61: is used to the earth's centerDetermining the velocity vector V of the satellite flight from the position of the satellite in a linear coordinate system sat Linear velocity vector V of rotation with the earth rot ；
S62: according to V sat And V rot The following tangent angle theta is calculated yaw ：
In the above formula, atan (. Cndot.) represents an arctan function;
s63: according to angle theta yaw Determining the phase applied by a phase shifter in each transmit/receive component in a phased array antenna
The following were used:
in the above formula, λ represents a radar wavelength;
s64: radar resource scheduling circuitry based on
Sending an instruction to the transmitting/receiving component to scan the azimuth beam, and simultaneously enabling the forward beam and the backward beam to scan the azimuth beam at an angle theta yaw Thus, the swaths of the two beams can be coincided.
6. The on-board dual-pass dual-beam InSAR flow measurement system of claim 4, characterized in that: the method for carrying out ocean current vector inversion by using the current measuring system comprises the following steps:
s'10: extracting radar echo signals corresponding to forward and backward beams by using two window functions with different center distance frequencies;
s'20: and inverting the ocean current velocity vector according to the echo signals after the forward and backward wave beams are separated.
7. The spaceborne dual-channel dual-beam InSAR current surveying system of claim 6, wherein:
in step S'10, based on signal orthogonality, forward and backward wave beam echo signals in the echo data received by the dual-channel dual-wave beam InSAR flow measurement system are separated, and the method specifically comprises the following steps:
s'11: front antenna sub-aperture radar echo signal s received by double-channel double-beam InSAR system 1 (t a ,t r ) And a post-antenna sub-aperture radar echo signal s 2 (t a ,t r ) Performing a two-dimensional Fourier transform, wherein t a And t r Respectively representing slow time and fast time, converting to two-dimensional frequency domain, i.e. Doppler frequency/distance frequency domain, to respectively obtain signals S 1 (f d ,f r ) And S 2 (f d ,f r ) Wherein f is d And f r Respectively representing a doppler frequency and a range frequency;
s'12 in the two-dimensional frequency domain, two window functions W are utilized + (f d ,f r ) And W - (f d ,f r ) Respectively taking out front antenna sub-aperture radar echo signals S 1 (f d ,f r ) Respectively obtaining the forward wave beam echo signal of the front antenna sub-aperture
Echo signal with backward beam
The method specifically comprises the following steps:
in the above two formulae, W + (f d ,f r ) And W - (f d ,f r ) The expression of (c) is:
wherein, F s And f PRF Respectively representing a distance sampling frequency and a pulse repetition frequency;
s'13: for post-antenna sub-aperture radar return signal S 2 (f d ,f r ) Repeating the above step S'12 to obtain the forward wave beam echo signal of the rear antenna sub-aperture
Echo signal with backward beam
S'14: will be provided with
Two-dimensional inverse Fourier transform is carried out to respectively obtain two-dimensional time domains, namely slow time domain echo signals/fast time domain echo signals
And
wherein
And
a forward beam echo signal and a backward beam echo signal representing the front antenna sub-aperture respectively,
and
a forward beam echo signal and a backward beam echo signal respectively representing a rear antenna sub-aperture;
in step S'20, four separated echo signals are used
And
inverting the ocean current velocity vector according to the following steps:
s'21: to pair
And
interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of the forward wave beam
S'22: for is to
And
interference processing is carried out to obtain the radial velocity component of the ocean current velocity vector projected to the direction of the backward beam
S'23: using two estimated radial velocity components
And with
And calculating the ocean current velocity vector v according to the geometrical relation of the dual-channel dual-beam InSAR and the following formula cur ：
In the above formula, the first and second carbon atoms are,
and
respectively representing the velocity vector v of the ocean current cur The azimuthal velocity component of (a) and the horizontal plane distance component of (b),
the expression of matrix H is:
in the above formula, θ inc Representing the central angle of incidence of the beam.
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