CN116559874A - Two-dimensional ocean current inversion method and system based on multi-azimuth angle synthetic aperture radar - Google Patents
Two-dimensional ocean current inversion method and system based on multi-azimuth angle synthetic aperture radar Download PDFInfo
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Abstract
The invention provides a two-dimensional ocean current inversion method and a two-dimensional ocean current inversion system based on a multi-azimuth angle synthetic aperture radar, wherein the two-dimensional ocean current inversion method comprises the following steps: acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method; the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising: if the observation azimuth angle is two nonparallel observation azimuth angles, the east and north components are calculated according to the observed one-dimensional sea surface flow velocity of the two nonparallel observation azimuth angles; the velocity and direction of the two-dimensional ocean current are calculated from the east and north components. According to the invention, the one-dimensional ocean current flow velocity is respectively inverted for the data observed by a plurality of synthetic aperture radar satellites on the same sea surface under different azimuth angles, and the two-dimensional ocean current is synthesized according to the radar observation azimuth angle vector.
Description
Technical Field
The invention belongs to the technical field of ocean remote sensing, and particularly relates to a two-dimensional ocean current inversion method and system based on a multi-azimuth angle synthetic aperture radar.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The global ocean circulation carries heat and salt transportation, influences local and even global climate change, and is one of key physical quantities of ocean power. The accurate measurement of the sea surface flow field has important significance for multi-scale ocean power phenomenon, ocean atmospheric interaction and ocean energy circulation.
With further exploration of the ocean, people put forward demands on large-scale and high-precision ocean surface flow field data, and the in-situ ocean current data provided by the existing navigation vessel, the anchor system buoy and the Lagrangian drifting buoy have the defects of limited observation range, short observation time, high cost and the like. The spaceborne altimeter obtains ground diversion by measuring the sea surface altitude change of the undersea point, but the ground diversion has lower spatial resolution, and is difficult to distinguish the marine dynamic phenomenon smaller than the sub-mesoscale. The typical spatial scale of the sea surface currents ranges from a few kilometers to thousands of kilometers with periods ranging from 1 day to years. The sea surface currents modulate the sea surface wave spectrum and are detected by the spaceborne synthetic aperture radar (Synthetic Aperture Radar, SAR). Compared with other observation means, the spaceborne synthetic aperture radar has the measuring capability of full-time, all-weather, large breadth (500 km) and high spatial resolution (several meters), and is one of important data sources for global sea surface flow field monitoring.
There are two common methods for inverting sea surface flow rates with synthetic aperture radar, namely Doppler centroid anomaly (Doppler Centroid Anomal, DCA) and in-orbit interferometry (Along-Track Interferometric, ATI). The DCA method uses echo Doppler centroid frequency shift of single-antenna synthetic aperture radar imaging data to invert the ocean current flow velocity, but the spatial resolution is lower (1-2 km). The ATI method uses double antennas to respectively acquire sea surface imaging data, utilizes the interference phase difference of two-scene imaging data to invert the sea surface flow velocity, and has high spatial resolution (10-100 m). The two methods have the common defects that only the flow velocity component of the two-dimensional ocean current in the radar view direction can be obtained, and the direction and the size of the real two-dimensional ocean current flow field cannot be obtained.
The application number 201510852862.1 of China discloses an angle diversity-based ocean flow field inversion spaceborne synthetic aperture radar system and a method thereof, wherein single-star double-antenna-based time-sharing observation of the same sea area under two azimuth angles is performed, and a DCA method is utilized to obtain sea current components under different two azimuth angles, so that two-dimensional sea currents are vector synthesized. The method has the defects that the DCA method can only be used for inverting the ocean current, the spatial resolution is limited, the same ocean area can only be irradiated in different time, and the dynamic ocean is required to change in real time in the time.
The Chinese patent with application number 201910840751.7 discloses a two-dimensional flow field inversion method and system of a single-channel synthetic aperture radar based on Doppler center shift, which adopts a sub-aperture segmentation technology to decompose sub-images of single-star synthetic aperture radar images in different azimuth angles, carries out ocean current inversion on each sub-image, and further synthesizes two-dimensional ocean currents by vectors. Secondly, the azimuth interval between the segmented sub-aperture images is smaller, and the vector synthesis result of different components in a small angle range can have larger error with the real ocean current within the range of less than 10 degrees. Thirdly, the same is only applicable to the DCA method of single-star synthetic aperture radar data, and the overall spatial resolution is limited.
Disclosure of Invention
Aiming at the problem of insufficient space dimension of the existing SAR inversion sea surface flow field, the invention provides a two-dimensional ocean current inversion method and system based on a multi-azimuth angle synthetic aperture radar. According to the method, a plurality of SAR satellites are used for respectively inverting one-dimensional ocean current flow velocity for data observed by the same sea surface under different azimuth angles, and two-dimensional ocean currents are synthesized according to radar observation azimuth angle vectors. The invention can be applied to DCA method and also applied to multi-star ATI method with different heading.
To achieve the above object, one or more embodiments of the present invention provide the following technical solutions:
the invention provides a two-dimensional ocean current inversion method based on a multi-azimuth angle synthetic aperture radar, which comprises the following steps:
acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method;
the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising:
if the observation azimuth angle is two nonparallel observation azimuth angles, the eastern ocean current component and the northward ocean current component are calculated according to the observed one-dimensional ocean surface flow velocity of the two nonparallel observation azimuth angles;
the velocity and direction of the two-dimensional ocean current are calculated from the east and north ocean current components.
The second aspect of the invention provides a two-dimensional ocean current inversion system based on a multi-azimuth angle synthetic aperture radar, which comprises:
a one-dimensional sea surface flow rate calculation module configured to: acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method;
a two-dimensional ocean current synthesis module configured to: the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising:
if the observation azimuth angle is two nonparallel observation azimuth angles, the east and north components are calculated according to the observed one-dimensional sea surface flow velocity of the two nonparallel observation azimuth angles;
the velocity and direction of the two-dimensional ocean current are calculated from the east and north components.
The one or more of the above technical solutions have the following beneficial effects:
(1) The invention utilizes the ATI method to invert ocean currents aiming at single-satellite multi-beam interference or double-satellite accompanying interference data, has the method flexibility aiming at different data sources, and realizes the inversion of SAR remote sensing data on the global two-dimensional ocean surface flow field.
(2) According to the invention, the space resolution of ocean current inversion can be effectively improved by inverting ocean current by using the ATI method.
(3) The SAR operation system with multiple stars and multiple tasks can be designed, the same sea area observation with different heading cross tracks at the same time or short interval is realized, and the timeliness of ocean current inversion is improved.
Additional aspects of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
Fig. 1 is a flowchart of a two-dimensional ocean current inversion method based on a multi-azimuth synthetic aperture radar according to a first embodiment.
Figure 2 is a graph of doppler centroid shifts at different observation azimuths for the DCA method of the first embodiment.
Fig. 3 (a) and 3 (b) are doppler shift diagrams caused by the relative motion of the synthetic aperture radar satellite observation platform and the earth in the observation direction 1 and the observation direction 2 of the first embodiment, respectively.
Fig. 4 (a) and 4 (b) are electromagnetic pointing error diagrams of the observation direction 1 and the observation direction 2 of the first embodiment, respectively.
Fig. 5 is a schematic diagram of a first embodiment of a two-dimensional ocean current synthesized from one-dimensional flow velocity vectors observed at different azimuth angles.
Fig. 6 (a) and 6 (b) are two-dimensional ocean current flow velocity and direction scatter plots inverted by the DCA method of the first embodiment, respectively.
Fig. 7 (a) and 7 (b) are interference phase diagrams of the observation direction 1 and the observation direction 2 of the first embodiment, respectively.
Fig. 8 (a) and 8 (b) are scatter plots of inverted two-dimensional ocean current flow velocity and direction, respectively, for the first embodiment.
Detailed Description
Example 1
As shown in fig. 1, the embodiment discloses a two-dimensional ocean current inversion method based on a multi-azimuth angle synthetic aperture radar, which comprises the following steps:
step 1, obtaining one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or an along-track interferometry;
and 2, synthesizing the one-dimensional ocean currents into two-dimensional ocean currents according to the one-dimensional ocean current flow rates of different observation azimuth angles.
In the step 1, a Doppler mass center anomaly method is used for obtaining one-dimensional sea surface flow velocity observed in different observation azimuth angles, and the method comprises the following steps:
101-1, obtaining Doppler mass center frequency shift of observation in different azimuth angles;
assuming that the actual motion trajectory of the satellite is a locally uniform linear motion, the earth is locally flat and not rotating, the Doppler centroid shift (f dc ) The method comprises the following steps:
where V denotes the radar speed, beta is the instantaneous angle of view of the radar, lambda is the radar wavelength,is the following viewing angle:
wherein H is the distance from the earth center to the synthetic aperture radar sensor, and R is the slant distance; r is R e Is the earth radius. Let R be 0 Is the tilt distance at a certain instant point, will be in (2)Taylor expansion, given by:
in the formula ,is corresponding to the inclination distance R 0 Lower viewing angle at that time. This can be achieved by:
in the formula ,f0 The expansion center of the view angle at a certain instantaneous point representing the Doppler centroid frequency shift can be approximated as a constant;
f dc not only can be obtained through a theoretical formula, but also f observed in different azimuth angles can be obtained respectively through a header file or an auxiliary file of imaging data dc The method comprises the steps of carrying out a first treatment on the surface of the The synthetic aperture radar data product is distributed with header files and auxiliary files, including required incident angle, imaging position, satellite attitude, product level, etc. parameters, depending on the distribution form of the data. By acquiring synthetic aperture radar data of different azimuth angles, f under the corresponding azimuth angles is calculated by using the header file and the auxiliary file dc Compared with a calculation method through a theoretical formula, the calculation method is more convenient.
Step 101-2, removing Doppler frequency shift caused by satellite-ground relative motion from Doppler mass center frequency shift, and obtaining Doppler frequency shift caused by ocean current flow velocity only by electromagnetic pointing error caused by synthetic aperture radar antenna fluctuation and Doppler frequency shift caused by ocean surface storms;
f of sea surface area dc Is caused by the relative motion of a synthetic aperture radar observation platform and a rough scattering surface modulated by ocean currents, and can be decomposed into the following parts:
f dc ＝f geo +f em +f wv +f c (6)
in the formula ,fgeo For Doppler shift caused by relative movement of the star and ground, f em For electromagnetic pointing error caused by fluctuation of synthetic aperture radar antenna, f wv For Doppler shift caused by sea surface wind wave, f c Is the doppler shift caused by the current flow rate. According to formula (6), f dc Removing f geo 、f em 、f wv After that, f is obtained c And inverting the sea surface flow rate.
f geo Theoretically, it is possible to operate by means of the attitude and velocity for a given satellite:
in the formula ,kr Is the wave number of radar, V SC Is the speed of the satellite along the orbital plane, gamma is the radar down view angle, alpha is the angle between the radial altitude plane and the satellite orbital plane,is the rotational angular velocity of the earth, < >>Is satellite velocity, ε represents radar left-view (ε= -1) and right-view (ε= +1), and β is the amplitude of latitude. Dividing the theoretical formula to calculate and obtain f geo The Doppler coefficient can be calculated by:
f geo ＝d 0 +d 1 (t SR -t 0 )+d 2 (t SR -t 0 ) 2 +d 3 (t SR -t 0 ) 3 +d 4 (t SR -t 0 ) 4 (8)
in the formula ,di Is the doppler coefficient (i=1, 2,3, 4), t SR Is the double-range skew time, t 0 Is the standard skew time. In practical application f geo But may also be provided by a header file or an auxiliary file of the imaging data.
The synthetic aperture radar antenna or platform is affected by external factors, the antenna pointing away from the theoretical direction, resulting in f dc In presence of f em Causing errors in inverting the ocean current. To ensure thatThe resulting current velocity is relative to land and this part of the error needs to be removed. f (f) em While existing in both marine and land areas throughout the imaged scene. Land area in the synthetic aperture radar image is free of f ww and fc Thus, in acquiring f from synthetic aperture radar data dc And obtaining f by calculation geo On the premise of (1), f can be obtained according to the formula (6) em Distribution of land areas within an imaging scene and fitting f em Equation (d). The f of the ocean area can be obtained through the fitting equation em 。
The interaction of the sea surface wind field and waves jointly modulates sea surface capillary waves and long waves, so that f caused by the influence of wind waves exists in Doppler centroid frequency shift wv . F for C-band radar at 20-40 DEG incident angle wv Gradually decreasing with increasing angle of incidence. F under the condition of wind speed of 1-20 m/s wv And positive correlation is shown with wind speed. F generated by wind direction and radar at different azimuth angles wv Also different, the maximum (0 °) is the upwind, the minimum (180 °) is the downwind, and the near 0 is the crosswind. At present, f cannot be accurately obtained by theoretical calculation wv The f is typically obtained using an empirical geophysical model fitted to the observed data wv 。
Step 101-3, inverting the one-dimensional sea surface flow velocity of a certain observation azimuth according to Doppler frequency shift caused by the sea flow velocity.
By removing Doppler frequency shift caused by non-ocean current factors, the echo signal in the sea surface area only has f caused by ocean current velocity c The one-dimensional sea surface flow velocity of a certain observation azimuth angle can be obtained through the formula (9).
Where ke is the radar wavenumber and θ is the radar incident angle.
In the step 1, a one-dimensional sea surface flow velocity observed in different observation azimuth angles is obtained by using an along-track interferometry, and the method comprises the following steps:
102-1, respectively acquiring phases of observation data of a synthetic aperture radar on the sea surface of the same target under different azimuth angles;
the method comprises the steps of respectively obtaining single-view complex SLC (Single Look Complex) data of two antennas (a main star and an auxiliary star) of the synthetic aperture radar for observing the sea surface of the same target under different azimuth angles, wherein the phases of the corresponding data are as follows:
in the formula , and />Respectively representing the phases of the observation data of the main star and the auxiliary star, R 1 and R2 The tilt distances from the main and auxiliary antennas to the target are respectively, and Δt is the time difference between the imaging of the two antennas.
Step 102-2, calculating an interference phase difference between phases of the two observed data
102-3, removing a land leveling phase caused by a land leveling effect from the interference phase difference, and obtaining a phase difference caused by only a ocean current flow velocity from a phase difference caused by a topography change and a phase difference caused by sea surface wind wave influence;
specifically, as shown in fig. 2, the phase difference of echo signals in the sea surface area caused by the rough scattering surface displacement modulated by the factors such as ocean currents needs to be removed from the independent terms in order to obtain the phase difference caused by the one-dimensional ocean current velocity:
in the formula ,is of a level ground effectLevel ground phase which should be caused, +.>Phase differences caused by the response of the cross-track baselines to terrain variations. />For the phase difference caused by the influence of sea surface stormy waves, etc, ++>Is the phase difference caused by ocean currents.
When the flat ground interference phase is actually calculated, the slant range R of the pixel corresponding to SLC data of the main star and the auxiliary star is calculated according to the satellite orbit parameters of the synthetic aperture radar and the WGS84 reference ellipsoid 11 、R 22 . Corresponding can be obtained through the skew difference
The orbital baselines and the cross-track baselines between the main satellite and the auxiliary satellite may exist simultaneously. Topography variations and sea surface heights and the presence of the cross-track baseline can produce topography phase. The sea surface altitude phase difference is required to be obtained according to the altitude phase measurement principle:
in the formula ,B⊥ For the cross-track baseline, H is the sea elevation, and θ is the radar incident angle.
There is a contribution component of the phase velocity of the sea surface large scale wave and Bragg wave +.> And can also be obtained from empirically fitted geophysical models.
102-4, calculating one-dimensional sea surface flow velocity of a certain observation azimuth angle according to the phase difference caused by the sea current flow velocity
Wherein V represents radar speed, lambda is radar wavelength, theta is radar incident angle,b is the track base length, which is the phase difference caused by ocean currents.
In step 2, the one-dimensional ocean current velocity according to different observation azimuth angles is synthesized into two-dimensional ocean currents, which comprises the following steps:
if the observation azimuth angle is two nonparallel observation azimuth angles, the eastern ocean current component and the northward ocean current component are calculated according to the observed one-dimensional ocean surface flow velocity of the two nonparallel observation azimuth angles;
calculating the flow velocity and direction of the two-dimensional ocean current according to the east ocean current component and the north ocean current component;
if the observed azimuth angle is greater than two, vector synthesis is respectively carried out through the arrangement and combination of the two observed azimuth angles, and average east and north components are obtained;
specifically, the magnitude (V) of the two-dimensional ocean current is obtained by the ocean current components U and V in the east (x) and north (y) curr ) And direction (alpha) curr ). As long as the actual observation direction is not perpendicular to the two-dimensional ocean current direction, a component of the two-dimensional ocean current in that direction can be observed, which is also the sum of the projections of U and V in that direction, respectively. Based on the above principle, at least two ocean current flow rates of non-parallel observation azimuth angles are required to acquire U and V. When more than two observation azimuth angles are obtained, U and V can be calculated through the alignment of the combined azimuth angles, so that average U and V can be obtained, and finally, vector synthesis is carried out to obtain the two-dimensional ocean current. The azimuth angle of observation is increased,the synthesis accuracy of the two-dimensional ocean current flow field can be improved.
As can be seen in conjunction with fig. 5, the one-dimensional ocean current velocity V obtained at two observation azimuth angles 1 and V2 With two-dimensional ocean current V curr The relationship of (2) is shown in the formula (15):
after unfolding and finishing, the relation between the U and V is further shown in the following formula, and the U and V can be obtained by simultaneous solving.
in the formula ,α1 ，α 2 Two non-parallel observation azimuth angles, respectively.
The vector synthesized two-dimensional ocean currents are as follows:
in the formula , and />The U and V averages obtained by the combination of the plurality of sets of vectors are represented, respectively.
The reliability of the method is verified by two examples:
example 1:
the implementation of inversion of two-dimensional ocean currents by the DCA method is described by adopting a single synthetic aperture radar satellite to observe the ascending and descending orbit of the same sea area.
1. Taking Sentinel-1A (S1A) as an example, two observation azimuth data of ascending (observation direction 1) and descending (observation direction 2) are taken. f (f) dc Can be obtained from the data of stage 2 of S1A with a spatial resolution of about 1.5km, as shown in fig. 2.
f geo Can be obtained from the data of 2 steps of S1A, the f of the observation direction 1 and the observation direction 2 geo As shown in fig. 3 (a) and 3 (b), respectively;
wherein, S1A synthetic aperture radar data is issued according to the level. Level 0 raw echo data, level 1 imaging focus data, and 2 marine physical parameter data. Wherein the level 1 data is generated from level 0 data and the level 2 data is generated from level 1 data. This embodiment uses 2-level data.
Selecting the value of f dc Removing f geo The land imaging region doppler shift fits a first order linear equation with range pixels as arguments. Using this equation to obtain f throughout the imaged scene (including the ocean region) em As shown in fig. 4 (a) and 4 (b).
Inputting the S1A radar wavelength, the incident angle, the azimuth angle between the acquired wind speed and wind direction and the radar view direction and the polarization mode into a geophysical model CDOP to obtain a contribution component f of sea surface wind wave factors in echo signals wv 。
f dc Removing f geo ，f em and fwv Obtaining Doppler frequency shift f caused by sea surface flow in radar view direction c . The flow velocity components of the two-dimensional ocean currents in the two radar directions are obtained according to equation (9), respectively.
2. According to fig. 5 and the calculation methods of equations (17), (18), and (19), the two-dimensional ocean currents are vector synthesized. And (3) adopting a high-frequency (HF) radar to verify the matching of the actually measured two-dimensional ocean currents in the imaging area and the inversion of the multi-azimuth angle observation result. As shown in fig. 6 (a) and 6 (b), the deviation and root mean square of the inverted two-dimensional ocean current flow rates were 0.07m/s and 0.1m/s, respectively, and the deviation and root mean square error of the flow directions were-8.54 ° and 20 °, respectively.
Example 2:
the present example illustrates the implementation of the ATI ocean current inversion method of the present invention using simulation data. The simulation parameters are shown in table 1:
TABLE 1
1. Based on the simulation parameters of table 1, the simulation data of the main star and the auxiliary star under two observation angles are respectively obtained, the resolution is about 100m after spatial averaging, and the interference phase difference is obtained after conjugate interferenceAs shown in fig. 7 (a) and 7 (b).
2. Calculating the slant distance of each pixel corresponding to the main image and the auxiliary image one by one according to the satellite orbit parameters of the synthetic aperture radar and (11) and obtaining the corresponding slant distanceSince the cross track baseline is set to 0, +.>＝0。
Inputting radar observation azimuth angle, wind speed of wind field and wind direction as parameters into a geophysical model CDOP to obtain Doppler frequency caused by sea surface wind wave influence, and converting the Doppler frequency into Doppler frequency
Remove-> and />Obtaining phase difference caused by sea surface flow velocity in radar view directionObtaining velocity components V of the ocean current velocity at two radar observation azimuth angles according to the formula (14) 1 and V2 。
3. The sea surface flow rates obtained under different azimuth angles are synthesized into two-dimensional sea currents according to vectors of formulas (15), (16), (17) and (18). The invention provides an ATI two-dimensional ocean current inversion method and a set two-dimensional ocean current parameter comparison verification method. As shown in fig. 8 (a) and 8 (b), the two-dimensional current flow rate deviation and root mean square of the inversion were 0.03m/s and 0.1m/s, respectively, and the deviation and root mean square error of the flow direction were 0.17 ° and 11.28 °, respectively.
In summary, the invention provides the two-dimensional ocean current inverted by adopting the DCA and ATI methods based on the multi-star multi-azimuth angle synthetic aperture radar, which is basically consistent with the HF actually measured and simulated two-dimensional ocean current in terms of flow velocity and flow direction, and the reliability of the method is verified.
Example two
The embodiment discloses two-dimensional ocean current inversion system based on diversified angle synthetic aperture radar, includes:
a one-dimensional sea surface flow rate calculation module configured to: acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method;
a two-dimensional ocean current synthesis module configured to: the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising:
if the observation azimuth angle is two nonparallel observation azimuth angles, the eastern ocean current component and the northward ocean current component are calculated according to the observed one-dimensional ocean surface flow velocity of the two nonparallel observation azimuth angles;
the velocity and direction of the two-dimensional ocean current are calculated from the east and north ocean current components.
It will be appreciated by those skilled in the art that the modules or steps of the invention described above may be implemented by general-purpose computer means, alternatively they may be implemented by program code executable by computing means, whereby they may be stored in storage means for execution by computing means, or they may be made into individual integrated circuit modules separately, or a plurality of modules or steps in them may be made into a single integrated circuit module. The present invention is not limited to any specific combination of hardware and software.
While the foregoing description of the embodiments of the present invention has been presented in conjunction with the drawings, it should be understood that it is not intended to limit the scope of the invention, but rather, it is intended to cover all modifications or variations within the scope of the invention as defined by the claims of the present invention.
Claims (10)
1. A two-dimensional ocean current inversion method based on a multi-azimuth angle synthetic aperture radar is characterized by comprising the following steps:
acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method;
the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising:
if the observation azimuth angle is two nonparallel observation azimuth angles, the eastern ocean current component and the northward ocean current component are calculated according to the observed one-dimensional ocean surface flow velocity of the two nonparallel observation azimuth angles;
the velocity and direction of the two-dimensional ocean current are calculated from the east and north ocean current components.
2. The two-dimensional ocean current inversion method based on the multi-azimuth angle synthetic aperture radar according to claim 1, wherein if the observed azimuth angle is greater than two, vector synthesis is respectively carried out through the arrangement and combination of the two observed azimuth angles, and average east and north ocean current components are obtained;
the velocity and direction of the two-dimensional ocean current are calculated from the averaged east and north ocean current components.
3. The two-dimensional ocean current inversion method based on the multi-azimuth angle synthetic aperture radar as claimed in claim 1, wherein the method for obtaining the one-dimensional ocean surface flow velocity observed in different observation azimuth angles by using the Doppler centroid anomaly method comprises the following steps:
acquiring Doppler mass center frequency shifts of observations of different azimuth angles;
removing Doppler frequency shift caused by satellite-ground relative motion from Doppler mass center frequency shift, and obtaining Doppler frequency shift caused by only ocean current flow velocity by electromagnetic pointing error caused by synthetic aperture radar antenna fluctuation and Doppler frequency shift caused by ocean surface wind wave;
and inverting the one-dimensional sea surface flow velocity of a certain observation azimuth angle according to Doppler frequency shift caused by the sea current flow velocity.
4. The two-dimensional ocean current inversion method based on the multi-azimuth angle synthetic aperture radar as claimed in claim 1, wherein the method for obtaining the one-dimensional ocean surface flow velocity observed by different observation azimuth angles by using the cis-orbit interferometry comprises the following steps:
respectively acquiring phases of observation data of two antennas of the synthetic aperture radar on the same target sea surface under different observation azimuth angles;
calculating an interference phase difference between phases of the two observed data;
removing the land leveling phase caused by the land leveling effect, the phase difference caused by the topography change and the phase difference caused by the sea surface wind wave influence from the interference phase difference to obtain a phase difference caused by the ocean current flow velocity only;
and calculating the one-dimensional ocean current flow velocity of a certain observation azimuth angle according to the phase difference caused by the ocean current flow velocity.
5. The two-dimensional ocean current inversion method based on the multi-azimuth angle synthetic aperture radar according to claim 1, wherein the tilt distances of pixels corresponding to the main image and the auxiliary image are calculated according to the satellite orbit parameters of the synthetic aperture radar and the reference ellipsoid, and the land leveling phase caused by the land leveling effect is obtained through the tilt distance difference of the main image and the auxiliary image.
6. A two-dimensional ocean current inversion method based on a multi-azimuth angle synthetic aperture radar as defined in claim 1, wherein the phase difference caused by the change of the terrain is calculated according to the principle of elevation phase measurement.
7. The two-dimensional ocean current inversion method based on the multi-azimuth angle synthetic aperture radar according to claim 1, wherein the phase difference caused by the influence of ocean surface wind waves is obtained according to an empirically fitted geophysical model.
8. A two-dimensional ocean current inversion method based on a synthetic aperture radar with multiple azimuth angles as claimed in claim 1, wherein the one-dimensional ocean current velocity V is obtained under two non-parallel observation azimuth angles 1 and V2 With two-dimensional ocean current V curr The relation of (2) is:
one-dimensional ocean current velocity V acquired under two observation azimuth angles 1 and V2 The relationship with the east and north ocean current components U and V is:
in the formula ,α1 ，α 2 Respectively two nonparallel observation azimuth angles alpha curr Is the direction of two-dimensional ocean currents;
and solving a simultaneous equation system to obtain the two-dimensional ocean current.
9. The two-dimensional ocean current inversion method based on multi-azimuth angle synthetic aperture radar as claimed in claim 8, wherein the velocity V of the synthesized two-dimensional ocean current curr And direction alpha curr The method comprises the following steps of:
wherein , and />The average values of the east and north ocean current components U and V obtained by the combination of a plurality of groups of vectors are respectively represented.
10. A two-dimensional ocean current inversion system based on a multi-azimuth angle synthetic aperture radar, comprising:
a one-dimensional sea surface flow rate calculation module configured to: acquiring one-dimensional sea surface flow velocity observed by different observation azimuth angles by using a Doppler centroid anomaly method or a forward rail interferometry method;
a two-dimensional ocean current synthesis module configured to: the one-dimensional ocean current velocity synthesis according to different observation azimuth angles is two-dimensional ocean current, comprising:
if the observation azimuth angle is two nonparallel observation azimuth angles, the eastern ocean current component and the northward ocean current component are calculated according to the observed one-dimensional ocean surface flow velocity of the two nonparallel observation azimuth angles;
the velocity and direction of the two-dimensional ocean current are calculated from the east and north ocean current components.
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