CN112799056B - Spaceborne radar altimeter system and method - Google Patents
Spaceborne radar altimeter system and method Download PDFInfo
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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
- G01S13/882—Radar or analogous systems specially adapted for specific applications for altimeters
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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
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- 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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Abstract
The invention provides a method and a system for a satellite-borne radar altimeter, which comprise the following steps: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse is in an orthogonal relation; setting pulse repetition frequency on the zebra pattern, controlling the set pulse repetition frequency to enable the nadir echo and the interference side high-region echo to be received by the radar receiver at the same time, wherein waveforms of radar emission signals corresponding to the nadir echo and the interference side high-region echo are different; based on the setting of a coded signal pulse sequence and the setting of pulse repetition frequency, obtaining a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time, wherein the obtained bottom view radar altimeter echo and the obtained side view radar altimeter echo signal are orthogonal at the same time; based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted, and the functions of bottom view altimeter height measurement and side view altimeter height measurement are realized.
Description
Technical Field
The invention relates to the technical field of satellite-borne radars, in particular to a system and a method for a satellite-borne radar altimeter, and more particularly to a system and a method for integrating a side view altimeter and a bottom view altimeter of an interferometric synthetic aperture radar based on signal coding.
Background
The satellite height measurement technology is one of the important components of global marine observation systems, and currently, in-orbit height measurement satellites in China mainly comprise ocean No. 2 (HY-2) and the like. The traditional radar altimeter is a bottom view altimeter and can only generate a one-dimensional elevation profile. In recent years, interferometric synthetic aperture radar side-looking altimeters have been extensively studied at home and abroad, typical systems such as surface water and ocean altitude (SWOT) satellites in the united states.
However, it should be noted that The currently proposed designs of satellite-borne radar altimeters at home and abroad all use The method of independent design of interferometric synthetic aperture radar side view altimeter and radar bottom view altimeter, such as The united states SWOT satellite interferometric synthetic aperture radar side view altimeter (m. Dual et al, the surface water and ocean positioning transmission: operating terrestrial surface water and ocean positioning media, proceedings of IEEE,2010,98 (5)). This will increase the development cost of the satellite-borne radar system, and will also increase the power consumption and weight of the whole satellite, etc., which will bring some difficulties to the design of the satellite system.
How to further simplify the satellite-borne radar altimeter system and effectively reduce the power consumption, the weight and the development cost of the satellite is worthy of exploration.
Patent document CN105659862B (application number: 201218002637.6) discloses a system level test method for a radar altimeter, which adopts an echo simulator to form a closed loop test system, and tests the height measurement function, the wave height test function and the system AGC adaptive adjustment function of the radar altimeter, so as to comprehensively verify the system level measurement function of the radar altimeter and solve the system level verification problem of a satellite-borne radar altimeter under the satellite-adjusting condition. The method of the invention uses the echo simulator to form a closed-loop test system, changes the system input of the radar altimeter through the setting of the echo simulator and the adjustment of the attenuator, interprets the final test result of the radar altimeter, and the test result reflects the complete working logic of the radar altimeter, thereby achieving the purpose of system level verification of the radar altimeter.
The invention combines an interferometric synthetic aperture radar side-view altimeter and a radar bottom-view altimeter into a whole by utilizing a signal coding technology, and is the first time at home and abroad.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method and a system for a satellite-borne radar altimeter.
The invention provides a method for a satellite-borne radar altimeter, which comprises the following steps:
step M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
step M2: setting pulse repetition frequency on the zebra pattern, and controlling the radar working time sequence by the set pulse repetition frequency to enable the sky bottom echo and the interference side high area echo to be simultaneously received by a radar receiver, wherein the waveforms of radar emission signals corresponding to the sky bottom echo and the interference side high area echo are different;
step M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
step M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted through orthogonal signal processing, and the functions of bottom view altimeter height measurement and side view altimeter height measurement are achieved.
Preferably, the step M1 of setting the coded signal pulse sequence includes setting a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission form is that the pulse number of the pulse sequence is used as a period to carry out periodic repeated emission.
Preferably, the setting of the pulse repetition frequency in the step M2 includes: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that the transmitting signal corresponding to the sky bottom radar echo is different from the transmitting signal corresponding to the side-looking observation area radar echo.
Preferably, the step M4 includes:
step M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracking extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
step M4.2: the method comprises the steps of performing distance compression on a bottom-view radar altimeter echo and a side-view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to the bottom-view radar altimeter echo as a matched filtering function, removing a top-view radar echo signal from the signal, obtaining a radar signal from which the top-view radar echo signal is removed, performing anti-matched filtering processing on the radar signal from which the top-view radar echo signal is removed by taking the transmitting signal corresponding to the bottom-view radar altimeter echo as an anti-matched filtering function, performing distance compression by taking a transmitting signal corresponding to an observation area echo signal of the side-view altimeter as a matched filtering function, and then performing azimuth compression and interference processing to realize the side-view altimeter function of the interferometric synthetic aperture radar.
Preferably, the matched filtering function in the step M4.1 includes performing pulse compression on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter, which are received at each azimuth moment and are mixed together by time, by using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filtering function;
the tracking and extracting of the echo signals of the bottom vision radar altimeter comprises the steps of calculating an echo distance unit where a sky bottom echo is located according to the height of a satellite and preset elevation information, and detecting bright lines around the echo distance unit to achieve detection of the bottom vision echo signals.
Preferably, the removing of the nadir echo signals from the distance-compressed signals includes zeroing echo signals in a distance unit corresponding to the detected return signals of the bottom-view radar altimeter and a plurality of distance units around the distance unit in the distance-compressed return signals;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
According to the invention, the satellite-borne radar altimeter system comprises:
a module M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
a module M2: setting pulse repetition frequency on the zebra pattern, and controlling the radar working time sequence by the set pulse repetition frequency to enable the sky bottom echo and the interference side high area echo to be simultaneously received by a radar receiver, wherein the waveforms of radar emission signals corresponding to the sky bottom echo and the interference side high area echo are different;
a module M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
a module M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted through orthogonal signal processing, and the functions of bottom view altimeter height measurement and side view altimeter height measurement are achieved.
Preferably, the setting of the coded signal pulse sequence in the module M1 includes setting of a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission form is that the pulse number of the pulse sequence is taken as a period to carry out periodic repeated emission;
setting the pulse repetition frequency in the module M2 comprises: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that a transmitting signal corresponding to the sky bottom radar echo is different from a transmitting signal corresponding to the side-looking observation area radar echo.
Preferably, said module M4 comprises:
module M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracking extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
module M4.2: the method comprises the steps of performing distance compression on a bottom-view radar altimeter echo and a side-view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to the bottom-view radar altimeter echo as a matched filtering function, removing a top-view radar echo signal from the signal, obtaining a radar signal from which the top-view radar echo signal is removed, performing anti-matched filtering processing on the radar signal from which the top-view radar echo signal is removed by taking the transmitting signal corresponding to the bottom-view radar altimeter echo as an anti-matched filtering function, performing distance compression by taking a transmitting signal corresponding to an observation area echo signal of the side-view altimeter as a matched filtering function, and then performing azimuth compression and interference processing to realize the side-view altimeter function of the interferometric synthetic aperture radar.
Preferably, the matched filtering function in the module M4.1 includes pulse compression on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are received at each azimuth moment and are mixed together by using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filtering function;
the tracking and extracting echo signals of the bottom view radar altimeter comprise echo distance units where sky bottom echoes are calculated according to satellite heights and preset elevation information, and bright lines are detected around the echo distance units to realize detection of the bottom view echo signals;
removing the nadir echo signals from the distance-compressed signals comprises zeroing the echo signals in the distance units corresponding to the detected echo signals of the bottom-view radar altimeter and a plurality of distance units around the distance units in the distance-compressed echo signals;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
Compared with the prior art, the invention has the following beneficial effects:
1. the method effectively breaks through the limitation that the height gauge and the bottom view height of the traditional interferometric synthetic aperture radar need to be independently designed, simplifies the design difficulty of the load hardware of the satellite radar height gauge, reduces the requirements on the power consumption, weight and cost of the satellite, and can effectively improve the observation performance of the satellite of the radar height gauge;
2. according to the invention, through the technical characteristics of signal coding, PRF optimization design, bottom view altimeter signal extraction and processing and side view interferometric synthetic aperture radar altimeter signal extraction and processing, the problem that the bottom view altimeter and the side view interferometric synthetic aperture radar altimeter must be designed independently is solved, and the technical effects of two-in-one design of the side view interferometric synthetic aperture radar altimeter and the radar bottom view altimeter and the same frequency band work are realized;
3. the invention relates to a satellite-borne radar system which breaks through the limitation of independent design of a traditional radar bottom view altimeter and an interferometric synthetic aperture radar side view altimeter by utilizing a signal coding technology and simultaneously realizes the functions of the bottom view altimeter and the interferometric synthetic aperture radar side view altimeter.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of the system design and signal processing flow of the radar altimeter of the present invention;
FIG. 2 is a graph showing simulated point target and subsatellite point echo signals;
FIG. 3 is a graph showing an extracted echo signal of the bottom view altimeter;
fig. 4 is a diagram of extracted side view altimeter echo signal SAR imaging results.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
Aiming at the defects in the prior art, the invention aims to provide a two-in-one system of an interferometric synthetic aperture radar altimeter and a bottom view radar altimeter based on signal coding and a method thereof, which effectively simplify the hardware design of a satellite system and reduce the difficulty in satellite development.
The invention provides a method for a satellite-borne radar altimeter, which comprises the following steps:
step M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
step M2: setting pulse repetition frequency on the zebra diagram, and controlling the radar working time sequence by the set pulse repetition frequency to enable the nadir echo and the interference side high-area echo to be simultaneously received by a radar receiver, wherein the radar transmitting signal waveforms respectively corresponding to the nadir echo and the interference side high-area echo are different;
step M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
step M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted through orthogonal signal processing, and the functions of bottom view altimeter height measurement and side view altimeter height measurement are achieved.
Specifically, the setting of the coded signal pulse sequence in the step M1 includes setting of a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission mode is that the pulse number of the pulse sequence is used as the period to carry out periodic repeated emission.
Specifically, the setting of the pulse repetition frequency in the step M2 includes: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that the transmitting signal corresponding to the sky bottom radar echo is different from the transmitting signal corresponding to the side-looking observation area radar echo.
Specifically, the step M4 includes:
step M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracking extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
step M4.2: the method comprises the steps of performing distance compression on a bottom-view radar altimeter echo and a side-view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to the bottom-view radar altimeter echo as a matched filtering function, removing a top-view radar echo signal from the signal, obtaining a radar signal from which the top-view radar echo signal is removed, performing anti-matched filtering processing on the radar signal from which the top-view radar echo signal is removed by taking the transmitting signal corresponding to the bottom-view radar altimeter echo as an anti-matched filtering function, performing distance compression by taking a transmitting signal corresponding to an observation area echo signal of the side-view altimeter as a matched filtering function, and then performing azimuth compression and interference processing to realize the side-view altimeter function of the interferometric synthetic aperture radar.
Specifically, the matched filtering function in the step M4.1 includes performing pulse compression on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter, which are received at each azimuth moment and are mixed together by time, by using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filtering function;
the tracking and extracting of the echo signals of the bottom vision radar altimeter comprises the steps of calculating an echo distance unit where a sky bottom echo is located according to the height of a satellite and preset elevation information, and detecting bright lines around the echo distance unit to achieve detection of the bottom vision echo signals.
Specifically, the removing of the nadir echo signals from the distance-compressed signals includes zeroing echo signals in a distance unit corresponding to the detected return signals of the bottom-view radar altimeter and a plurality of distance units around the distance unit in the distance-compressed return signals;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
According to the invention, the satellite-borne radar altimeter system comprises:
a module M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
a module M2: setting pulse repetition frequency on the zebra diagram, and controlling the radar working time sequence by the set pulse repetition frequency to enable the nadir echo and the interference side high-area echo to be simultaneously received by a radar receiver, wherein the radar transmitting signal waveforms respectively corresponding to the nadir echo and the interference side high-area echo are different;
a module M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
a module M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted through orthogonal signal processing, and the functions of bottom view altimeter height measurement and side view altimeter height measurement are achieved.
Specifically, the setting of the coded signal pulse sequence in the module M1 includes setting of a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission mode is that the pulse number of the pulse sequence is used as the period to carry out periodic repeated emission.
Specifically, the setting of the pulse repetition frequency in the module M2 includes: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that the transmitting signal corresponding to the sky bottom radar echo is different from the transmitting signal corresponding to the side-looking observation area radar echo.
In particular, said module M4 comprises:
module M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracking extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
module M4.2: the method comprises the steps of removing a sky radar echo signal from a signal obtained after distance compression is carried out on a bottom view radar altimeter echo and a side view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to a bottom view radar altimeter echo as a matched filtering function, obtaining a radar signal after the sky radar echo signal is removed, carrying out anti-matched filtering processing on the radar signal after the sky radar echo signal is removed from the radar signal obtained after the sky radar echo signal is removed by taking the transmitting signal corresponding to the bottom view radar altimeter echo as an anti-matched filtering function, carrying out distance compression by taking a transmitting signal corresponding to a side view altimeter observation area echo signal as a matched filtering function, then carrying out azimuth compression and interference processing, and realizing the side view altimeter function of the interferometric synthetic aperture radar.
Specifically, the matched filtering function in the module M4.1 includes pulse compression performed on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter, which are received at each azimuth moment and are mixed together, by using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filtering function;
the tracking and extracting of the echo signals of the bottom vision radar altimeter comprises the steps of calculating an echo distance unit where a sky bottom echo is located according to the height of a satellite and preset elevation information, and detecting bright lines around the echo distance unit to achieve detection of the bottom vision echo signals.
Specifically, the step of removing the nadir echo signal from the distance-compressed signal includes zeroing echo signals in a distance unit corresponding to the detected echo signal of the bottom view radar altimeter and a plurality of distance units around the distance unit in the distance-compressed echo signal;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
Example 2
Example 2 is a modification of example 1
The invention is further described below with reference to the accompanying drawings.
The theoretical analytical basis for the present invention is summarized as follows, with reference to FIG. 1:
a two-in-one system of an interferometric synthetic aperture radar altimeter and a bottom view radar altimeter based on signal coding and a method thereof are characterized by comprising the steps of radar orthogonal coding signal sequence design, pulse repetition frequency design, bottom view altimeter signal extraction and processing and interferometric radar altimeter signal extraction and processing. Wherein:
1) Radar encoded signal sequence design
The coded signal pulse sequence is transmitted periodically, any pulse in the pulse signal sequence is in an orthogonal relation, and a mathematical model of the coded signal pulse sequence is as follows;
s k (t r )＝s k+N (t r )
in the formula, s k (t r ) For the kth transmitted pulse of azimuth, t r Distance-wise time, N pulse sequence length (repetition period), T p Is the pulse width. Typical signal forms are signals.
2) Pulse repetition frequency design
On the zebra pattern, a Pulse Repetition Frequency (PRF) with different radar emission signal waveforms is adopted, wherein the Pulse Repetition Frequency (PRF) is received by a nadir echo and an interference height measurement area echo at the same time, and the mathematical model is as follows:
wherein PRF is the pulse repetition period, R near And R far The shortest and longest slant distances of the observation region in a synthetic aperture time, c is the speed of light, T proc For the guard time, H is the satellite orbit height,
to round down the operator, mod (-) is the remainder operator.
3) Bottom view altimeter signal extraction and processing
Performing distance compression on the received echo signals by taking the transmitting signals corresponding to the nadir echo signals as a matched filtering function, and performing inversion on nadir elevations by tracking and extracting nadir signals to realize a function of an underflow altimeter;
the echo signal received by the radar can be expressed as
s(t a ,t r )＝s nadir (t a ,t r )+s obs (t a ,t r )
In the formula, s (t) a ,t r ) As radar returns, s nadir (t a ,t r ) As the nadir radar echo, s obs (t a ,t r ) For observing the echo of the region, t a Is the azimuth time. Suppose a radar nadir echo s (t) a ,t r ) Corresponding to a transmission signal s k (t r ) Using the signal pair s (t) a ,t r ) Pulse compression is performed.
In the formula, s nadir,comp (t a ,t r ) Is a signal s 'after compression of a satellite point echo pulse' obs,comp (t a ,t r ) Is a compressed signal of the echo of the observation region.
After pulse compression, radar nadir echoes are represented as bright lines in an image, signals in an observation area are still in a defocused state due to mismatching of matched filters, an echo distance unit where the nadir echoes are located can be calculated according to satellite height and reference elevation information, and bright lines are detected around the unit to realize detection and extraction of bottom view echo signals. Subsequently, the existing mature processing method of the bottom view altimeter can be used for realizing the height measurement of the point under the satellite, and the function of the bottom view altimeter is completed.
4) Interferometric synthetic aperture radar side-looking altimeter signal extraction and processing
And removing the sky bottom radar echo signals from the echo signals subjected to distance compression by taking the transmitting signals corresponding to the sky bottom echo signals as matching functions, performing anti-matching filtering processing on the echo signals by taking the transmitting signals corresponding to the sky bottom echo signals as anti-matching filtering functions, performing distance compression by taking the transmitting signals corresponding to the echo signals in an observation area as matching filtering functions, and performing subsequent azimuth compression and subsequent interference processing to realize the side view altimeter function of the interferometric synthetic aperture radar.
The echo signal from which the nadir echo is removed may be represented as
s' obs,comp (t a ,t r )＝s comp (t a ,t r )-s nadir,comp (t a ,t r )
And performing inverse matched filtering processing on the transmission signal corresponding to the nadir echo signal by using the transmission signal as an inverse matched filtering function, so as to obtain the echo signal of the observation area.
s' obs (t a ,t r )＝s' obs,comp (t a ,t r )*s k (t r )
Assuming that a transmitting signal corresponding to the echo of the radar observation area at the moment is s j (t r ) Subjecting it to distance compressionAnd then, acquiring the elevation information of the observation area by utilizing mature synthetic aperture radar imaging and interferometric synthetic aperture radar processing technology, and completing the functions of the interferometric synthetic aperture radar side-looking altimeter.
The validity of the invention is verified here using simulation data. The simulation parameters are shown in table 1.
TABLE 1 simulation parameters of satellite borne altimeter system
Assume that the encoded signal takes the following short offset quadrature waveform:
in the formula, K r In order to adjust the frequency of the transmitted signal,
the Pulse Repetition Frequency (PRF) designed by the patent is 4264Hz. As can be seen from figures 2, 3 and 4, the functions of the bottom view altimeter and the side view altimeter can be simultaneously realized, and the integrated design of the bottom view altimeter and the side view altimeter is realized.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description has described specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (8)
1. A method for a satellite-borne radar altimeter, comprising:
step M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
step M2: setting pulse repetition frequency on the zebra pattern, and controlling the radar working time sequence by the set pulse repetition frequency to enable the sky bottom echo and the interference side high area echo to be simultaneously received by a radar receiver, wherein the waveforms of radar emission signals corresponding to the sky bottom echo and the interference side high area echo are different;
step M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
step M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together in time, the bottom view radar altimeter echo and the side view radar altimeter echo signal are respectively extracted through orthogonal signal processing, and the height measuring functions of the bottom view altimeter and the side view altimeter are realized;
the step M4 comprises the following steps:
step M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracked and extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
step M4.2: the method comprises the steps of performing distance compression on a bottom-view radar altimeter echo and a side-view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to the bottom-view radar altimeter echo as a matched filtering function, removing a top-view radar echo signal from the signal, obtaining a radar signal from which the top-view radar echo signal is removed, performing anti-matched filtering processing on the radar signal from which the top-view radar echo signal is removed by taking the transmitting signal corresponding to the bottom-view radar altimeter echo as an anti-matched filtering function, performing distance compression by taking a transmitting signal corresponding to an observation area echo signal of the side-view altimeter as a matched filtering function, and then performing azimuth compression and interference processing to realize the side-view altimeter function of the interferometric synthetic aperture radar.
2. The method according to claim 1, wherein the step M1 of setting the pulse sequence of the coded signal comprises setting a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission mode is that the pulse number of the pulse sequence is used as the period to carry out periodic repeated emission.
3. The method of claim 1, wherein the setting of the pulse repetition frequency in step M2 comprises: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that the transmitting signal corresponding to the sky bottom radar echo is different from the transmitting signal corresponding to the side-looking observation area radar echo.
4. The method of claim 1, wherein the matched filtering function in step M4.1 comprises performing pulse compression on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are received at each azimuth moment and are mixed together by time by respectively using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filtering function;
the tracking and extracting of the echo signals of the bottom vision radar altimeter comprises the steps of calculating an echo distance unit where a sky bottom echo is located according to the height of a satellite and preset elevation information, and detecting bright lines around the echo distance unit to achieve detection of the bottom vision echo signals.
5. The method of claim 1, wherein the distance-compressed signal removing nadir echo signals comprises zeroing echo signals in a range cell corresponding to the detected bottom view radar altimeter echo signal and a plurality of range cells around the range cell in the distance-compressed echo signals;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
6. A satellite-borne radar altimeter system, comprising:
a module M1: setting a coded signal pulse sequence as a periodic emission sequence, wherein any pulse in the coded signal pulse sequence is in an orthogonal relation;
a module M2: setting pulse repetition frequency on the zebra pattern, and controlling the radar working time sequence by the set pulse repetition frequency to enable the sky bottom echo and the interference side high area echo to be simultaneously received by a radar receiver, wherein the waveforms of radar emission signals corresponding to the sky bottom echo and the interference side high area echo are different;
a module M3: acquiring a bottom view radar altimeter echo and a side view radar altimeter echo which are mixed together in time based on the setting of a coded signal pulse sequence and the setting of a pulse repetition frequency on a zebra diagram, wherein the bottom view radar altimeter echo and the side view radar altimeter echo signals acquired at the same time are orthogonal;
a module M4: based on the obtained bottom view radar altimeter echo and the side view radar altimeter echo which are mixed together in time, respectively extracting bottom view radar altimeter echo and side view radar altimeter echo signals through orthogonal signal processing, and realizing the height measuring functions of the bottom view altimeter and the side view altimeter;
the module M4 comprises:
module M4.1: taking a transmitting signal corresponding to the echo of the bottom view radar altimeter as a matched filtering function, performing distance compression tracking on the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are mixed together in time, extracting an echo signal of the bottom view radar altimeter, and performing inversion on the sky bottom elevation through the tracking extracted echo signal of the bottom view radar altimeter to realize the function of the bottom view altimeter;
module M4.2: the method comprises the steps of removing a sky radar echo signal from a signal obtained after distance compression is carried out on a bottom view radar altimeter echo and a side view radar altimeter echo which are overlapped in a time-mixing mode by taking a transmitting signal corresponding to a bottom view radar altimeter echo as a matched filtering function, obtaining a radar signal after the sky radar echo signal is removed, carrying out anti-matched filtering processing on the radar signal after the sky radar echo signal is removed from the radar signal obtained after the sky radar echo signal is removed by taking the transmitting signal corresponding to the bottom view radar altimeter echo as an anti-matched filtering function, carrying out distance compression by taking a transmitting signal corresponding to a side view altimeter observation area echo signal as a matched filtering function, then carrying out azimuth compression and interference processing, and realizing the side view altimeter function of the interferometric synthetic aperture radar.
7. The system according to claim 6, wherein the setting of the pulse sequence of the coded signal in the module M1 comprises setting of a signal coding form and a pulse sequence transmission form;
the signal coding form is an orthogonal coding pulse sequence, and any two pulses in the sequence are in a time domain orthogonal relation;
the pulse sequence emission form is that the pulse number of the pulse sequence is taken as a period to carry out periodic repeated emission;
setting the pulse repetition frequency in the module M2 comprises: setting an echo receiving window design constraint and an echo receiving orthogonality design constraint;
the design constraint of the echo receiving window is that the radar echo receiving window can simultaneously receive complete sky bottom radar echo and echo signals of a side-looking radar observation area;
and the design constraint of the echo receiving orthogonality is that the transmitting signal corresponding to the sky bottom radar echo is different from the transmitting signal corresponding to the side-looking observation area radar echo.
8. The system of claim 6, wherein the matched filter function in the module M4.1 comprises pulse compression of the echo of the bottom view radar altimeter and the echo of the side view radar altimeter which are received at each azimuth moment and are mixed together by time by respectively using a transmission signal corresponding to the echo of the bottom view radar altimeter as the matched filter function;
the tracking and extracting of the echo signal of the bottom vision radar altimeter comprises the steps of calculating an echo distance unit where a sky bottom echo is located according to the height of a satellite and preset elevation information, and detecting a bright line around the echo distance unit to realize the detection of the bottom vision echo signal;
removing the nadir echo signals from the distance-compressed signals comprises zeroing the echo signals in the distance units corresponding to the detected echo signals of the bottom-view radar altimeter and a plurality of distance units around the distance units in the distance-compressed echo signals;
the anti-matching filtering function comprises pulse decompression is carried out on radar signals with sky bottom radar echo signals removed at each azimuth moment by respectively using transmitting signals corresponding to the echoes of the bottom view radar altimeter as anti-matching functions to obtain echo signals of the side view radar altimeter;
the distance compression by taking the transmitting signal corresponding to the echo signal of the observation area of the side-looking altimeter as a matched filtering function comprises the following steps: and respectively performing pulse compression on the echo signals of the side-looking radar altimeter at each azimuth moment by using the transmitted signals corresponding to the echoes of the side-looking radar altimeter as matching functions.
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