CN112098958B - Radar clutter prediction method based on digital map and meteorological hydrological information - Google Patents
Radar clutter prediction method based on digital map and meteorological hydrological information Download PDFInfo
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Abstract
The invention discloses a radar clutter prediction method based on a digital map and meteorological hydrological information, which comprises the following steps: (1) radar function and parameter determination: (2) determining the platform type and attitude parameters: (3) digital map data preparation: (4) preparing meteorological hydrological environment data: (5) selecting a scattering model: (6) and generating radar clutter data. The method disclosed by the invention can predict the three-dimensional dynamic clutter maps of different types of radars on different platforms under real, sea and meteorological conditions based on the actual digital map and the meteorological hydrological environment data. The existing domestic and foreign sea clutter models, gas image clutter models and statistical or real-time atmospheric refraction environment conditions are fully considered and selected, and different types or special scattering and atmospheric environments can be analyzed and predicted.
Description
Technical Field
The invention belongs to the field of target and environmental characteristics of radar detection, and particularly relates to a deterministic radar clutter calculation simulation or comprehensive prediction method based on working parameters of radar systems and platform carriers, land surface, low-level atmosphere and marine hydrological meteorological environment information in the field, which is applied to aspects of radar system development, test, training, verification, evaluation and the like and is used for relevant technical professional reference such as radar design, target detection and signal processing, propagation analysis, electronic countermeasure, microwave remote sensing and the like.
Background
The radar is a main means for acquiring target information, the radar clutter is an important factor influencing the detection performance of a radar system, and through theoretical analysis, experimental test, modeling technology and prediction method research on radar clutter characteristics, technical support can be provided for radar system design, signal analysis, algorithm optimization, performance evaluation, simulation, combat application and the like. The radar clutter is an echo generated by interaction of electric waves and media of surrounding environments such as the ground/sea surface, uneven atmosphere, meteorological water condensate and the like, and forms interference on target signal detection or identification. The radar platform has various modes such as land-based, shore-based, vehicle-mounted, ship-based, ball-borne, missile-borne, airborne and satellite-borne, and the like, and the types and the clutter characteristics of the radar platforms are different, so that the influence of the clutter characteristics of the ground/sea surface is particularly prominent for airborne or satellite-borne down-looking radars, ship-borne low-altitude and ultra-low-altitude small targets or low-detectability (stealth) target detection and other radar systems working in complex environments, and the system has serious influence on radar, fuze, guidance and the like. In the field of remote sensing, a radar environment becomes a remote sensing detection target, the environmental scattering characteristic is the basis for realizing qualitative analysis of remote sensing information, and the research of radar clutter can directly provide technical support for microwave remote sensing application. The effects and influences of complex terrain and landform environments and meteorological hydrological environments on information-based wars are explored and researched, and the real-time acquisition and integration integrated guarantee application capability of battlefield environment information including radar clutter can be improved.
A large number of radar clutter documents or monographs have been published at home and abroad, including radar system design and analysis methods, radar environments and modeling methods, radar clutter theories and numerical algorithms and experimental test technologies, radar clutter characteristic simulation and database technologies, and the like under various clutter backgrounds. The research works are mainly based on surface scattering and volume scattering models of electric wave propagation, dielectric parameters and geometric parameters of scattering surfaces and scattering bodies are reasonably set in a specific scene, and numerical operation is carried out to obtain scattering field space, frequency domain or time-varying characteristics; the experimental test is to carry out clutter measurement on a specific application environment classification scene, the obtained clutter characteristics correspond to actual parameters, and statistical analysis or empirical semi-empirical modeling is carried out on the basis; the radar environment modeling is mainly used for classifying land/ocean surface and meteorological information, obtaining a quantitative geometric mathematical model and physical characteristics and bringing the quantitative geometric mathematical model and the physical characteristics into a theoretical numerical simulation calculation process; the radar clutter simulation is to generate data under different parameters through a clutter statistical model, so as to provide support for a radar clutter suppression signal processing algorithm; the radar clutter database technology carries out classification management on clutter measurement data in a scene on the spot, and provides basic data support for radar clutter theoretical research, statistical modeling and numerical calculation verification. With the development of space remote sensing technology, numerical prediction technology, big data and cloud computing technology, the hydrological observation and prediction information of digital earth and meteorological phenomena is combined with radar clutter technology, and a new method is provided for radar clutter prediction.
Disclosure of Invention
The influence of natural and artificial environment on radar detection performance mainly includes reflection, scattering and diffraction of radar waves on the earth surface, radar wave bending or refraction caused by non-uniformity of atmospheric medium, absorption and scattering of radar waves by atmosphere and moisture condensate, and the like. The invention overcomes the limitation of the prior radar clutter calculation and simulation prediction technology based on ideal or assumed environmental conditions, aims at radar technical indexes with different functions and working modes such as different platforms such as land-based, shore-based, ship (ship) borne and airborne and the like and different functions and working modes such as air, sea and downward looking detection, search, early warning and the like, provides actual complex terrain, ground object and hydrological meteorological environment data such as terrain elevation data, ground object characteristic parameters, wind speed and wind direction, seawater temperature, dielectric constant, roughness, atmospheric refractive index, rainfall rate and the like based on digital maps and hydrological meteorological information, comprehensively analyzes and calculates the influence of the radar wave beam, scattering surface clutter, land clutter, atmospheric refraction and meteorological clutter according to a geometric model, a physical model and a statistical model, and truly reflects the clutter interference caused by the actual environmental surface scattering and the body scattering mechanism, and a data solution is provided for radar target detection algorithm, clutter suppression and signal processing, detection performance verification and evaluation and the like.
The invention aims to solve the technical problem of providing a radar clutter prediction method based on a digital map and meteorological hydrological information.
The invention adopts the following technical scheme:
the technical scheme of the invention is that a digital map and meteorological hydrological information (including model and data of terrain digital elevation, ground/sea surface dielectric property, ground object vegetation type and scattering characteristic, atmospheric refraction state, water condensate characteristic and the like) formed by various means such as remote sensing, monitoring and forecasting and the like are taken as a basis, different types and functions of radars and fixed or moving platforms are combined, and radar clutter characteristics are simulated and predicted according to radar wave beam irradiation and geometric intersection relation of scattering surfaces/bodies, radar and platform parameters and scattering cross sections or scattering coefficients of the scattering surfaces/bodies and a radar equation. Firstly, setting the type and function of a radar, platform parameters and a working environment, determining the geometrical and physical characteristics of a scattering surface/body in a radar beam resolution unit, and predicting or constructing an atmospheric refractive index profile by using a model; selecting a radar clutter model related to radar parameters, atmospheric environment, ground/sea surface environment and gas image water condensate; the incidence or grazing angle of radar beams at scattering surfaces/bodies at different detection distances of the radar when the radar beams are transmitted by atmospheric refraction is determined by an atmospheric refraction index profile and a ray tracking algorithm, and the transmission loss at different detection distances is determined by the atmospheric refraction index profile and a radio wave transmission numerical algorithm (such as a parabolic wave equation step algorithm). And calculating clutter data by adopting radar and platform parameters, electric wave propagation characteristics and a scattering model, and finally forming a three-dimensional space clutter map. The method comprises the following steps:
(1) radar function and parameter determination:
according to the actual radar clutter prediction requirement, the radars are classified according to land-based, vehicle-mounted, shore-based and shipborne air warning or searching or tracking radars, shore-based and shipborne sea warning or searching or tracking radars, airborne, missile-borne, ball-borne and satellite-borne downward warning or searching or tracking radars and the like, each type of radar adopts a corresponding clutter prediction method according to different functions and platforms, and the bistatic radar equation is expressed as follows:
in the formula: pt, Pr — Radar transmit and receive power; gt, Gr-gain of the transmitting and receiving antenna in the direction of the target or scattering surface, body; λ -radar operating wavelength; sigmaA-radar cross section of the target or scattering surface, volume; ft and Fr are propagation factors from a radar transmitting antenna to a target or a scattering surface, from a body to the target or the scattering surface and from the body to a radar receiving antenna respectively; rt, Rr-distance of transmitting and receiving antenna from target or scattering area; lt, Lr-loss factor of the transmitting and receiving system; lp-polarization loss factor; the single-base radar Gt and Gr, Rt and Rr, Ft and Fr with the same transmitting and receiving antenna and the same place are equal;
the radar parameters mainly comprise radar position, working frequency, transmitting power, polarization direction, antenna height, antenna gain, beam width of a vertical plane or a horizontal plane, detection distance, azimuth or elevation angle, pulse width and system sensitivity;
(2) determining the platform type and attitude parameters:
the radar is arranged on a platform carrier, the platform is divided into a land-based fixed platform, a shore-based fixed platform, a vehicle-mounted fixed platform, a ship-mounted fixed platform, a shipborne mobile platform, an airborne mobile platform and a ball-mounted mobile platform according to functional purposes, the mobile platform can be divided into an empty platform and a downward-looking platform, parameters describing the platform comprise longitude and latitude, height, motion direction and speed, inclination angle, roll angle and drift angle, and the installation and working state of a radar antenna, the relative geometric relationship between an antenna beam and a scattering surface and a body and a signal synthesis and processing method can be determined according to the property and the motion attitude of the platform;
(3) digital map data preparation:
the digital map or the digital ground model DTM is in a sequential numerical value array form distributed in a plurality of information spaces of ground forms, and the digitized information of the earth surface can be represented by a two-dimensional function:
Imn＝fi(m,n)(i＝1,2,…,k)
in the formula: imn represents the value of ith type ground characteristic information on a ground two-dimensional coordinate point (m, n), and the coordinate (m, n) can be a plane coordinate projected by any map or a longitude and latitude and a matrix row number and represents a surface element represented by a certain point and a proper tiny neighborhood thereof; k is the number of types of ground characteristic information, including height and land feature types, including mountains, hills, forests and farmlands;
the digital elevation model DEM is a subset of DTM, and in order to simulate clutter contributions of relevant ground/sea surface units according to real terrain and surface features, specific ground geographic information is firstly extracted, including digital terrain elevation data DTED and surface feature analysis data DFAD, containing natural and artificial environments, DEM data expressed in square grids, when the scattering analysis of the ground surface is carried out, the ground surface is divided into the terrain surface which takes triangles as elements to achieve the best approximation of the uneven relief terrain in the nature, each pair of data in the ground triangles represents the ground altitude and the ground feature scattering characteristics which take grid nodes as the center and have certain terrain resolution, the digital map is used for extracting the digital terrain elevation data with different resolutions and different precisions required by the radar distance and the azimuth detection range and carrying out geometric surface modeling, the modeling comprises triangular grids, and the grid area and the incident angle are calculated according to the geometric relationship between radar beams and the ground grids; extracting the type and the characteristics of the ground objects at the position of the triangular grid from the digital map, and judging the type of the scattering unit and an applicable scattering model;
(4) preparing meteorological hydrological environment data:
the atmospheric environment parameters mainly comprise atmospheric temperature, humidity, pressure, wind speed and direction and sea surface temperature of a radar detection area, are used for predicting an atmospheric refractive index profile, and further judge the radio wave refraction type, ray path tracking and propagation angle calculation; the water condensate parameters mainly comprise the distance, the azimuth, the height, the rainfall rate and the like of a rainfall area, the scattering properties of other atmospheric sediments can be determined according to the requirements, and the ray tracking method is used for calculating the actual distance and the elevation angle of a scattering surface and a body or the atmospheric refraction influence is considered by adopting the mode that the equivalent earth replaces the actual earth;
the statistical parameters of the atmospheric structure of each region greatly vary with specific regions (such as coastal regions, mountain regions, deserts, plateaus and the like) and specific time (such as daily change, monthly change, seasonal change and the like). Description of the normal atmospheric refractive index as a function of height tropospheric index patterns (N units) may be selected:
in the formula: n (h) is the refractive index (N unit) at altitude h (km), C is the attenuation coefficient, Ns, hs (km) are the ground refractive index and altitude, respectively;
under the condition of a real-time environment, calculating or predicting an atmospheric refractive index profile based on meteorological observation data, tracking the direction of radar beam rays under different refraction conditions, and determining the incident or grazing wave angle of a scattering surface and a scattering body;
(5) selecting a scattering model:
scattering power of the target or environment is determined by the scattering cross section σACharacterization, which depends on wavelength, direction of incidence and scattering, polarization relationships, and geometrical and physical properties of the scattering surface, the volume itself. For ground clutter and sea clutter, assuming that a scattering surface and a body system are uniform in a radar resolution unit, and normalizing a scattering cross section by using an irradiation area A to obtain a radar clutter scattering coefficient:
σ0＝σA/A
the illuminated area a is related to the radar beam width and the waveform parameters. The irradiation area of the pulse radar is as follows:
A＝cτ/2×θ
in the formula: c is the speed of light, τ is the pulse width, and θ is the beam azimuth width;
the radar ground clutter is generated by the composite scattering of ground surface and ground features, the ground surface is described by dielectric constant and roughness, the ground features are divided into natural vegetation, crops and artificial objects or a mixture thereof, the natural vegetation types comprise forests, shrubs and the like, the crops comprise wheat, rice, corn, cotton and the like, and the artificial objects comprise buildings, bridges, cities, villages, factories and the like. Due to factors such as diversity, variability, randomness, etc., statistical models may be employed. The American Georgia technology research institute obtains a variation model of the average value of scattering coefficients of different frequency bands in a larger range ground wiping angle according to the actual measurement data of different ground objects:
in the formula: psi is the scrub angle (radian), sigmahGround standard deviation (cm), λ radar wavelength, A, B, C, D empirical constants fitted from the data;
t.ullaby nine geoenvironment classifications: for HH, VV, HV polarization of L, S, C, X, Ku frequency bands, statistical empirical models for soil and rock surfaces, forests, grasslands, shrubs, short vegetation, pavements, urban areas, dry snow, wet snow are:
in the formula: p1-P6As a statistical parameter, θ is the local angle of incidence (radian);
sea surface sea state corresponds to certain wave height, period, wavelength, wave velocity and wind speed, the relation of sea clutter with wind speed, wind direction, frequency and incident angle can be described by a relevant model, and in a flat area with a medium incident angle, the relation of sea surface scattering coefficient and incident angle can adopt an exponential function:
in the formula: theta1、θ2Related to wind speed, under a certain incident angle and wind speed condition, the relation between the scattering coefficient and the wind direction is as follows:
σ0(u,θ,φ)＝A+Bcosφ+Ccos(2φ)
in the formula, u is a wind speed (m/s), theta is an incident angle, phi is an azimuth included angle between the incident direction of radar waves and a wind vector, and a sea clutter model coefficient A, B, C is related to the incident angle, the wind speed and polarization;
precipitation and other sediments in the atmospheric environment are main meteorological clutter sources, and a rainfall clutter scattering cross section and rainfall frequency and frequency relation model:
η＝ARB(m2/m3)
in the formula: eta is a scattering cross section of unit volume, R is rainfall rate (millimeter/hour), and A and B are fitting parameters of different frequency bands;
(6) radar clutter data generation:
radar clutter prediction is carried out according to the type and the function of a radar and the relation with a platform carrier, and the working mode can be divided into platform fixing and radar beam scanning, such as a vehicle-mounted/shore-based/spherical-mounted space search radar; platform motion, radar beams only follow platform motion, such as airborne/spaceborne SAR; platform motion, autonomous scanning of radar beams, such as airborne/shipborne space/sea search radar; firstly, constructing a radar, a platform coordinate system and a ground coordinate system, establishing a geometric transformation equation between space coordinate systems according to a time variable and a space variable, calculating a space-time position point where the radar is located according to a platform motion track, calculating an irradiation area range (area or volume) and a scattering unit of a beam in the ground, the sea or the air according to the radar antenna beam azimuth and the lobe width and combining actual atmospheric refraction conditions, calculating a grid radar beam incident angle or a ground wiping angle according to digital ground elevation, selecting a ground and sea surface scattering model according to ground feature type information, selecting a rain scattering model according to meteorological rainfall parameters, calculating a corresponding distance of the radar and a scattering echo in an azimuth resolution unit by adopting a radio wave propagation numerical algorithm to obtain clutter characteristics of corresponding working parameters of the radar location, and corresponding to the scattering echoes of the radar location at different times, and obtaining a corresponding radar motion track three-dimensional dynamic clutter prediction map.
The invention has the beneficial effects that:
the method disclosed by the invention can predict the three-dimensional dynamic clutter maps of different types of radars on different platforms under real, sea and meteorological conditions based on the actual digital map and the meteorological hydrological environment data. The existing domestic and foreign sea clutter models, gas image clutter models and statistical or real-time atmospheric refraction environment conditions are fully considered and selected, and different types or special scattering and atmospheric environments can be analyzed and predicted. The method is applicable to fixed or mobile radar platforms and functional parameters, the geometrical relation between radar antenna beams and scattering surfaces and bodies caused by platform postures and motion tracks is fully considered, and clutter prediction data can further fuse target scattering data and reflect the composite scattering characteristics of environments and targets.
Drawings
FIG. 1 is a geometric graph of ground and sea surface radar wave scattering;
FIG. 2(a) is a schematic diagram of a ground-based radar scattering environment;
FIG. 2(b) is a schematic diagram of a scattering environment of a radar on board a ship;
FIG. 2(c) is a schematic view of an airborne downward looking radar scattering environment;
FIG. 3 is a graph of the scattering coefficient of the earth and the sea surface as a function of the incident angle;
FIG. 4 is a schematic diagram of the atmospheric refraction path of a radar wave;
FIG. 5 is a digital map of China and surrounding areas;
FIG. 6(a) is a digital terrain elevation map of hilly terrain;
FIG. 6(b) is a digital terrain elevation diagram of mountainous terrain;
FIG. 7 is a plot of C-band VV polarization 40 incident angle scattering coefficients;
FIG. 8 is a schematic diagram of an airborne side view radar resolution unit;
FIG. 9(a) is a schematic diagram of a pulse Doppler radar clutter unit;
FIG. 9(b) is a schematic representation of Doppler clutter spectrum;
FIG. 10 is a digital terrain grid triangulation schematic;
FIG. 11(a) is a schematic diagram of a terrain shading relationship;
FIG. 11(b) is a schematic diagram of local incident angle calculation;
FIG. 12(a) is a digital topographic map in the airborne pulse Doppler radar clutter prediction process of example 1;
FIG. 12(b) is a ground Doppler frequency chart in the airborne pulse Doppler radar clutter prediction process according to the embodiment 1;
FIG. 12(c) is a schematic diagram of the ground antenna directivity factor in the airborne pulse Doppler radar clutter prediction process in the embodiment 1;
FIG. 12(d) is a topographic gray scale map in the clutter prediction process of the airborne pulse Doppler radar in the embodiment 1;
FIG. 12(e) is a schematic diagram of the ground shading and the visible region in the clutter prediction process of the airborne pulse Doppler radar in the embodiment 1;
FIG. 12(f) is a scattering coefficient gray scale map in the clutter prediction process of the airborne pulse Doppler radar in the embodiment 1;
fig. 12(g) is a radar range-doppler clutter map in the airborne pulse doppler radar clutter prediction process of example 1;
fig. 13 is a diagram of a composite scattered echo of a shore and ship-borne radar sea clutter and a target in embodiment 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
FIG. 1 is a geometric relationship diagram of radar wave scattering from the earth and sea surface, showing the interaction between radar waves and rough surface and the geometric relationship between reflected waves and scattered waves and incident waves; FIG. 2(a) is a schematic diagram of a ground-based radar scattering environment, FIG. 2(b) is a schematic diagram of a shipborne radar scattering environment, and FIG. 2(c) is a schematic diagram of an airborne downward-looking radar scattering environment, showing the correlation of the radar and platform with the surrounding environment and target; FIG. 3 is a graph of the variation of the scattering coefficient of the earth and the sea surface with the incidence angle, and the variation trend and the characteristics are obviously different in three typical angle areas; FIG. 4 is a schematic diagram of the atmospheric refraction path of radar waves, which shows the propagation path of radar wave rays under different meteorological conditions, and has a large influence on scattering on the ground and the sea; FIG. 5 is a digital map of China and surrounding areas from which radar wave scattering characteristic specific resolution terrain and feature data can be extracted and determined; fig. 6(a) is a digital terrain elevation map of hilly terrain, and fig. 6(b) is a digital terrain elevation map of mountainous terrain; the local incidence angle of radar waves can be determined by digital elevation, and the scattering echo intensity is further calculated by a model; FIG. 7 is a plot of C-band VV polarization 40 incident angle scattering coefficients, showing the geographical distribution of scattering intensity for a particular frequency band, polarization, and incident angle; FIG. 8 is a schematic diagram of an airborne side view radar resolution unit associated with the radar, platform position and operating parameters; FIG. 9(a) is a schematic diagram of a clutter unit of a pulse Doppler radar, and FIG. 9(b) is a schematic diagram of a Doppler clutter spectrum in which clutter unit echo powers at the same range and Doppler frequency are superimposed under the radar regime; FIG. 10 is a schematic diagram of the triangulation of digital terrain grids, which are subdivided into triangular meshes by the square grids of a digital map to more effectively simulate the coverage of undulating terrain; fig. 11(a) is a schematic diagram of a topographic shading relationship, and fig. 11(b) is a schematic diagram of a local incident angle calculation, and the scattering intensity of the scattering surface and the radar wave is determined according to a geometric relationship.
The method can be applied to design, development, test evaluation and actual use of various radars, particularly ultrashort wave, microwave and millimeter wave frequency band radars, and can be used for checking the signal processing method and the target detection performance of the radars under the environment conditions of typical sea clutter and meteorological clutter.
Example 1, airborne pulse doppler radar clutter prediction:
FIGS. 12(a) -12(g) reflect the actual prediction process and results of this embodiment.
The method comprises the steps of carrying out distance-Doppler clutter influence analysis on a Pulse Doppler (PD) radar under the conditions of any airborne attitude and three-dimensional real landform, and predicting radar clutter power according to radar parameters, airborne attitude, geometric relation, surface condition and other information.
Assuming that the radar pulse repetition frequency is fr and the pulse width is τ, the range resolution Δ R is c τ/2, the doppler filter bandwidth Δ f is fr/N (N represents the total filter count or the number of pulses processed by FFT at the same time), and the ambiguity range and the ambiguity frequency are represented as:
fu＝fr. The target and ground units that satisfy range ambiguity and frequency ambiguity within the same range gate and doppler bandwidth should satisfy the following range and doppler frequency conditions:
R0+mRu≤R≤(R0+ΔR)+mRu
f0+nfr≤f≤(f0+Δf)+nfr
in the formula: m, n is 0, ± 1, ± 2, …. R0，f0If R is selected for the range gate and Doppler shift corresponding to the scattered echo0＝(I-1)ΔR,f0When the value is (J-1) Δ f, I, J corresponds to the number of range gates and the number of doppler filters, respectively.
Clutter power within the range gate-doppler bandwidth is a contribution of a large number of node units, and the radar equation expression is as follows:
in the formula: pt and Pr respectively represent radar transmitting power and receiving power;
respectively representing the sum of clutter satisfying distance ambiguity and frequency ambiguity;
representing the sum of clutter corresponding to each node in each range-doppler cell;
Rirespectively representing the antenna gain at a node and the distance from the node to the radar; sigmaiRepresenting the scattering cross-section at the node (isolated object) or
(either the scattering surface or the extended target),
is the scattering coefficient of the ground object, Δ AjDepending on the node area division.
Converting data with ground coordinates as reference into spherical coordinate system of airborne radar
In the method, the position vector of any node on the ground is set as:
in the formula: z is a radical ofi＝hi-H，hiIs the terrain height, H is the radar height; x is the number ofiYi is determined by the radar projection relative to the node position.
The included angle between the projection of the speed vector of the carrier on the xoy plane and the x axis is alpha, the included angle between the projection of the speed vector of the carrier and the horizontal plane is beta (dive), and the speed coordinate system of the carrier is xvyvzvThen the velocity vector and the node position vector are:
point (x)i,yi,zi) The Doppler shift of (d) is:
due to the influence of bias current and roll, corresponding coordinate transformation is required to be carried out and finally the coordinate transformation is consistent with an antenna coordinate system taking the machine body as a reference, and the antenna directivity factor of the terrain node is obtained. Setting the counterclockwise direction deflection alpha of the forward direction of the fuselage relative to the navigational speed directiondUpward-facing betadThe coordinate system x of the fuselage when the drift current is deriveddydzdAnd a speed coordinate system xvyvzvThe relation of (1):
setting the side roll angle delta around xdThe shaft rotates clockwise, ydThe axes being off the horizontal, with the coordinate system x rolled sidewaysryrzrI.e. co-antenna coordinate system xayazaSuperposing:
comprehensively considering navigational speed, drift current and roll, converting the radar coordinate taking the ground as a reference into an antenna coordinate taking the machine body as a reference, wherein the relationship is as follows:
[T]＝[Tr][Td][Tv]
the elevation value of each grid point of the terrain is obtained from the DTED, the neighborhood of each grid point is also known, a linear linked list of triangular nodes is directly established, and the actual area of a small triangular plane is calculated by three-dimensional coordinates of the three nodes. Due to the fact that the terrain is fluctuated and natural or artificial ground objects exist, each triangular ground unit is possibly shielded by other units or the triangular ground unit, the visibility judgment of the radar scattering unit is needed to be carried out by utilizing a ray tracing technology, a local or local incidence angle is introduced into a relevant scattering model, and a distinguishing unit in a shielding or shadow area is ignored.
The distance-Doppler clutter map is subjected to simulation calculation by adopting real digital terrain data, airborne machine and radar parameters, a relevant prediction map is given, and the parameters are used as shown in the following table 1.
TABLE 1 clutter prediction parameter table
Embodiment 2, prediction of over-horizon clutter of shore-based and ship (warship) radar:
FIG. 13 reflects the composite scatter prediction of the present embodiment for sea clutter and targets.
In the process of detecting sea surface or low-altitude targets by using shore-based and ship (ship) -borne microwave radars, the radar is possibly greatly influenced by marine meteorological hydrological environment and sea clutter. Especially under the condition of low-altitude atmospheric waveguide (such as a shore-based radar is mainly a surface waveguide, and a shipborne radar is mainly an evaporation waveguide), atmospheric hyper-refraction changes a radio wave propagation path, the radar can realize over-line-of-sight target detection, meanwhile, over-line-of-sight clutter can also interfere remote target detection, and the sea surface local incidence or glancing angle in a sea surface scattering model needs to be calculated according to an actual atmospheric refractive index profile and a ray tracking technology.
Based on the invention, firstly, based on marine meteorological hydrological environment measurement or prediction data, an atmospheric refractive index profile and sea condition conditions (sea temperature, wind speed and wind direction and wave height and wave direction) are determined, radar functions and platform parameters are combined, the antenna beam direction and the relative angle between the antenna beam direction and the sea surface wave motion direction are calculated in real time under the working states of platform static, platform motion and radar antenna scanning, the ray propagation direction is tracked to obtain the local grazing and ground wiping angles of sea surface scattering units, a sea surface scattering coefficient and a scattering cross section of a corresponding resolution unit under the working parameters of radar frequency, polarization and the like are obtained by selecting a suitable sea clutter model such as a Georgia Institute of Technology (GIT) model, and the echo intensity and a clutter map at the corresponding distance are calculated. Meanwhile, a meteorological clutter and a simulation target are arranged in the specific distance gate, and a composite scattering echo map of a sea surface target, the meteorological clutter and the sea clutter can be further predicted.
Claims (1)
1. A radar clutter prediction method based on a digital map and meteorological hydrological information is characterized by comprising the following steps:
(1) radar function and parameter determination:
according to the actual radar clutter prediction requirement, classifying the radars according to land-based, vehicle-mounted, shore-based and shipborne air warning or searching or tracking radars, shore-based and shipborne sea warning or searching or tracking radars, airborne, missile-borne, ball-borne and satellite-borne downward warning or searching or tracking radars, adopting corresponding clutter prediction methods according to functions and platforms, and expressing the bistatic radar equation as follows:
in the formula: pt, Pr — Radar transmit and receive power; gt, Gr-gain of the transmitting and receiving antenna in the direction of the target or scattering surface, body; λ -radar operating wavelength; sigmaA-radar cross section of the target or scattering surface, volume; ft and Fr are propagation factors from a radar transmitting antenna to a target or a scattering surface, from a body to the target or the scattering surface and from the body to a radar receiving antenna respectively; rt, Rr-distance of transmitting and receiving antenna from target or scattering area; lt, Lr-loss factor of the transmitting and receiving system; lp-polarization loss factor; the single-base radar Gt and Gr, Rt and Rr, Ft and Fr with the same transmitting and receiving antenna and the same place are equal;
the radar parameters include: radar position, working frequency, transmitting power, polarization direction, antenna height, antenna gain, beam width in a vertical plane or a horizontal plane, detection distance, azimuth or elevation angle, pulse width, and system sensitivity;
(2) determining the platform type and attitude parameters:
the radar is arranged on a platform carrier, the platform is divided into a land-based fixed platform, a shore-based fixed platform, a vehicle-mounted fixed platform, a ship-mounted fixed platform, a shipborne fixed platform, an airborne mobile platform and a ball-mounted mobile platform according to functional purposes, the mobile platform is divided into an empty platform and a downward-looking platform, parameters describing the platform comprise longitude and latitude, height, motion direction and speed, an inclination angle, a roll angle and a drift angle, and the installation and working state of a radar antenna, the relative geometric relationship between an antenna beam and a scattering surface and a body and a signal synthesis and processing method can be determined according to the property and the motion attitude of the platform;
(3) digital map data preparation:
the digital map or the digital ground model DTM is in a sequential numerical value array form distributed in a plurality of information spaces of ground forms, and the digitized information of the earth surface can be represented by a two-dimensional function:
Imn＝fi(m,n),i＝1,2,…,k
in the formula: imn represents the value of ith type ground characteristic information on a ground two-dimensional coordinate point (m, n), wherein the coordinate (m, n) is a plane coordinate or longitude and latitude and a matrix row number projected by any map and represents a surface element represented by a certain point and a proper tiny neighborhood thereof; k is the number of types of ground characteristic information, including height and land feature types, including mountains, hills, forests and farmlands;
the digital elevation model DEM is a subset of DTM, firstly, specific ground geographic information is extracted, including digital terrain elevation data DTED and terrain feature analysis data DFAD, including natural and man-made environments, DEM data expressed by square grids is divided into terrain surfaces taking triangles as elements when ground surface scattering analysis is carried out, so as to achieve the best approximation of uneven relief terrain in nature, each pair of data in the ground triangles represents ground altitude and terrain scattering features which take grid nodes as centers and have certain terrain resolution, digital terrain elevation data with different resolutions and different accuracies required by radar distance and azimuth detection ranges are extracted by a digital map, and geometric surface modeling is carried out, wherein the modeling comprises triangular grids, and grid area and incident angle are calculated according to the geometric relationship between radar beams and the ground grids; extracting the type and the characteristics of the ground objects at the position of the triangular grid from the digital map, and judging the type of the scattering unit and an applicable scattering model;
(4) preparing meteorological hydrological environment data:
the atmospheric environment parameters comprise atmospheric temperature, humidity, pressure, wind speed and direction and sea surface temperature of a radar detection area, are used for predicting an atmospheric refractive index profile, and further judge the radio wave refraction type, ray path tracking and propagation angle calculation; the water condensate parameters comprise the distance, the azimuth, the altitude and the rainfall rate of a rainfall area, the scattering characteristics of other atmospheric sediments are determined according to the requirements, and the ray tracking method is used for calculating the actual distance and the elevation angle of a scattering surface and a body or the atmospheric refraction influence is considered by adopting the mode that the equivalent earth replaces the actual earth;
describing the normal atmospheric refractive index as a function of height tropospheric index patterns can be selected:
in the formula: n (h) is the refractive index at altitude h, C is the attenuation coefficient, Ns, hs are the ground refractive index and altitude respectively;
under the condition of a real-time environment, calculating or predicting an atmospheric refractive index profile based on meteorological observation data, tracking the direction of radar beam rays under different refraction conditions, and determining the incident or grazing wave angle of a scattering surface and a scattering body;
(5) selecting a scattering model:
for ground clutter and sea clutter, assuming that a scattering surface and a body system are uniform in a radar resolution unit, and normalizing a scattering cross section by using an irradiation area A to obtain a radar clutter scattering coefficient:
σ0＝σA/A
the irradiation area of the pulse radar is as follows:
A＝cτ/2×θ
in the formula: c is the speed of light, τ is the pulse width, and θ is the beam azimuth width;
the radar ground clutter is generated by the composite scattering of the ground surface and ground objects, the ground surface is described by dielectric constant and roughness, and the ground objects are divided into natural vegetation, crops and artificial objects or a mixture of the natural vegetation, the crops and the artificial objects; natural vegetation types include forests, forests and shrubs, crops include wheat, rice, corn and cotton, and man-made objects include buildings, bridges, cities, villages and factories; the statistical model used was: the American Georgia technology research institute obtains a variation model of the average value of scattering coefficients of different frequency bands in a larger range ground wiping angle according to the actual measurement data of different ground objects:
in the formula: psi is the angle of scrub, sigmahIs the ground standard deviation, λ is the radar operating wavelength, A, B, C, D is the empirical constant fitted from the data;
t.ullaby nine geoenvironment classifications: for HH, VV, HV polarization of L, S, C, X, Ku frequency bands, statistical empirical models for soil and rock surfaces, forests, grasslands, shrubs, short vegetation, pavements, urban areas, dry snow, wet snow are:
in the formula: p1-P6As a statistical parameter, theta is a local incident angle;
sea surface sea state corresponds to certain wave height, period, wavelength, wave velocity and wind speed, the relation of sea clutter with wind speed, wind direction, frequency and incident angle can be described by a relevant model, and in a flat area with a medium incident angle, the relation of sea surface scattering coefficient and incident angle can adopt an exponential function:
in the formula: theta1、θ2Related to wind speed, under a certain incident angle and wind speed condition, the relation between the scattering coefficient and the wind direction is as follows:
σ0(u,θ,φ)＝A+Bcosφ+Ccos(2φ)
in the formula, u is a wind speed, theta is an incident angle, phi is an azimuth included angle between the incident direction of radar waves and a wind vector, and a sea clutter model coefficient A, B, C is related to the incident angle, the wind speed and polarization;
the sediment in the atmospheric environment is a meteorological clutter source, and a rain clutter body scattering cross section and rainfall frequency and frequency relation model:
η＝ARB(m2/m3)
in the formula: eta is a scattering cross section of a unit volume, R is a rainfall rate, and A and B are fitting parameters of different frequency bands of meteorological clutters;
(6) radar clutter data generation:
radar clutter prediction is carried out according to the type and the function of a radar and the relation with a platform carrier, and the working mode can be divided into platform fixing and radar beam scanning; the platform moves, and the radar wave beam only moves along with the platform; platform motion and radar beam autonomous scanning; firstly, a radar, a platform coordinate system and a ground coordinate system are constructed, a geometric transformation equation between space coordinate systems is established according to a time variable and a space variable, calculating the space-time position point of the radar according to the platform motion track, calculating the irradiation area range and the scattering unit of the wave beam on the ground, the sea surface or the air according to the wave beam direction and the lobe width of the radar antenna and combining the actual atmospheric refraction condition, calculating the incidence angle or ground rubbing angle of the grid radar wave beam according to the digital ground elevation, selecting a ground and sea surface scattering model according to the ground object type information, selecting a rain scattering model according to weather rainfall parameters, calculating scattering echoes in the corresponding distance and direction distinguishing units of the radar by adopting a radio wave propagation numerical algorithm to obtain clutter characteristics of corresponding working parameters of the position of the radar, and obtaining a three-dimensional dynamic clutter prediction map of the corresponding radar motion track corresponding to the scattering echoes of the radar positions at different times.
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