Disclosure of Invention
For navigation positioning of an underwater vehicle, in order to overcome the defects of an inertial navigation system, the invention provides an underwater synchronous positioning and mapping method based on polarized light/inertial/visual integrated navigation, and an underwater integrated navigation system is constructed by adopting a polarized light/inertial/visual integrated navigation mode. The polarized light compass is used as an orientation result, the image information of the polarized visual scene is utilized, the characteristics of the topological nodes are used as an identification and expression method, the self-positioning of underwater navigation is realized, and meanwhile, an environment map is constructed. And an AUKF data fusion model is provided and applied to synchronous positioning and mapping of the underwater vehicle, so that more accurate navigation orientation positioning precision is obtained.
The technical scheme is as follows: the invention provides an underwater synchronous positioning and mapping method based on polarized light/inertia/vision combined navigation, which comprises the following five steps:
step 1: selecting the attitude, the speed and the position of the underwater vehicle as a system state, and establishing a kinematic model of the underwater vehicle;
step 2: calculating a sun vector by adopting a least square method of a polarization state through an orientation algorithm of a polarization sensor, and determining the position of the sun;
and step 3: constructing a visual scene environment characteristic map by using image polarization information through a topological node identification algorithm;
and 4, step 4: according to the speed output of the inertial navigation system, establishing a speed inertial navigation measurement model and a polarized light nonlinear measurement model;
and 5: and integrating the steps, and establishing an integrated navigation system model through data fusion to construct an environment map.
Step 1: in SLAM research algorithm, the method is important for constructing a model for a vector. Selecting the attitude, the speed and the position of the underwater vehicle as a system state, and establishing a kinematic model of the underwater vehicle;
the nonlinear equation of the motion model is as follows:
in the formula above, the first and second groups of the compound,
and
the position abscissa, the position ordinate, the zenith coordinate and the course coordinate of the underwater vehicle are respectively, u is a control input vector, and w is a zero-mean Gaussian-distribution process noise vector;
step 2: calculating a sun vector by a least square method of a polarization state through an orientation algorithm of a polarization sensor;
in the formula above, the first and second groups of the compound,
a heading angle representing the direction of a probe on the vehicle,
representing an element angle difference;
is an estimate of the position of the sun;
the sun position is thus determined from the estimated values:
in the formula above, the first and second groups of the compound,
the position of the sun, t is the measurement time, and arcidist (-) is the arc length;
and step 3: the method comprises the steps that information is provided for autonomous navigation through a topological node as a carrier, positioning calculation is carried out, a scene and a detection target are identified through polarization information, and a visual scene environment characteristic map is constructed;
according to the position information of the identification image, determining a target sample (an image sample of a region corresponding to the center of each node), marking a mark, wherein in the navigation topological graph, n nodes contain m image samples, and the image target corresponding to each node is marked as:
the above formula IiIs the feature vector of the ith image sample, yi∈[1,2,…,n]Target labels for nodes;
then, training target samples in adjacent topological nodes according to a large-boundary neighbor algorithm in machine learning to obtain a new measurement matrix M, so that the target samples with the same label are more compact, and the target samples with different labels are looser;
the distance metric between any two target samples is defined as:
dM(Ii,Ii+j)=(Ii-Ii+j)TM(Ii-Ii+j)
above formula, dMIs the Euclidean distance of two nodes in the reconstructed topological node space, dM(Ii,Ii+j) In a linear relationship with the metric matrix, IiAnd Ii+jA target neighbor sample;
and finally, solving the optimal solution of the following objective function by using the measurement matrix M:
let yilE {0,1} represents whether the characteristic vectors of the samples belong to the same node, if the characteristic vectors belong to the same node, the characteristic vectors are 1, otherwise, the characteristic vectors are 0; λ denotes the weight parameter, εijlThe total number of non-target samples. Therefore, an optimal solution can be obtained, and the expression and measurement of the topological graph on the motion environment are obtained;
and 4, step 4: establishing a combined model of velocity inertial navigation measurement and nonlinear state polarized light measurement;
the state model of the integrated navigation system is as follows:
the measurement equation of the integrated navigation system is as follows:
and 5: navigation data fusion of the underwater autonomous underwater vehicle is carried out by adopting an AUKF algorithm through course information provided by polarized light navigation, speed information provided by inertial navigation and position information provided by visual navigation, SLAM is carried out, and the steps are as follows:
1) reading speed, position and course observation data of the underwater vehicle respectively provided by an inertial navigation sensor, a visual odometer and a polarized light sensor;
2) selecting weighting coefficients
3) Calculating adaptive factor coefficients
Coefficient of adaptive factor lambdaiExpressed as:
of the above formula, λ
0Tr (-) represents the matrix tracking for the initial value, S is the adjustable coefficient,
is a residual sequence;
4) attenuation memory time-varying noise statistic estimator
Recursive formula of attenuation memory time-varying noise statistic estimator
The expression is as follows:
in the formula above, the first and second groups of the compound,
in order to be the covariance of the system noise,
for observing noise covariance, K is Kalman gain, W
iAre the weights of the mean and covariance,
satisfies the UKF sequence;
5) through the noise reduction processing of the filter, the convergence condition of the filter is as follows:
6) performing data association on the acquired attitude, position, speed and course by adopting a nearest neighbor data association algorithm; if the nodes (target samples) in the navigation topological graph are adjacent, merging is carried out, namely association is successful, and the underwater vehicle carries out time updating and measurement updating once; otherwise, adding the new metric as a new feature to the current state vector, namely performing state augmentation, and then continuing to perform merging (namely data association) of adjacent target samples, as follows;
in the formula above, the first and second groups of the compound,
is a new feature vector.
And (3) time updating:
measurement updating:
in the formula above, the first and second groups of the compound,
and
the previous state vector, covariance vector and measurement vector of state at time k-1, x, respectively, of the system
i,k∣k-1、z
i,k∣k-1Is the value obtained by sampling the Sigma points,
and
weight, Q, of the system mean and covariance, respectively
k-1Is the covariance of the system noise and,
and
are all observed covariances obtained in the system measurement update, R is the covariances of the observed noise, K
kIn order to be a matrix of the filter gains,
and
respectively, the current state vector and covariance vector of the system.
And finally, completing underwater synchronous positioning and mapping.
Compared with the prior art, the invention has the advantages that:
(1) the invention utilizes the polarized light bionic navigation principle, does not need the support of a geophysical field database, and can complete autonomous navigation in an underwater complex unstructured environment by researching the orientation algorithm of the underwater polarization sensor. The navigation mode is high in concealment and strong in robustness.
(2) Compared with the application scenario of the land SLAM, the underwater environment is dim and complex, and the visual sensor-based SLAM system has many limitations. Therefore, the invention fully utilizes the image information of the polarization vision, provides position data for the identification of the topology nodes of the visual scene, obviously improves the positioning and orientation precision of the integrated navigation and effectively inhibits the positioning accumulative error in the autonomous navigation process.
(3) At present, a Kalman filter is mostly adopted for navigation system data fusion, and the great disadvantage is that the accuracy of the established model is seriously depended on for the estimation precision of navigation error parameters. The typical UKF algorithm is a nonlinear filter which avoids the linearization of state or measurement equations, but the implementation principle has limitation and is not suitable for underwater SLAM. The invention provides the AUKF-SLAM algorithm, which can effectively inhibit the divergence of the filter and improve the quick tracking capability of the filter under the condition of unknown underwater and time-varying noise in deep sea areas and the like, thereby improving the performance of the integrated navigation system.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
Step 1: in SLAM research algorithm, the method is important for constructing a model for a vector. Selecting the attitude, the speed and the position of the underwater vehicle as a system state, and establishing a kinematic model of the underwater vehicle;
the motion rule of the underwater vehicle is very complex, the motion needs to be simplified, and only the plane motion of two degrees of freedom of a horizontal plane and a vertical plane is considered. The augmented state of the motion model is defined as follows:
of the above formula, XvA state vector matrix, { x, { for the current attitude in the spacecraftiI-0.. k-1} is a node of the state vector in the attitude map, where X isvIs defined as:
Xv=[x y z y]T
in the above formula, x, y and z are position coordinates, and y is the heading angle of the underwater vehicle in the horizontal reference coordinate system.
Since the corresponding error covariance matrix is extended, the augmented error covariance matrix can be expressed as:
of the above formula, Pv,vIs the covariance of the current attitude, Pv,jAnd Pi,jRespectively representing the covariance of the jth current state and the ith, jth previous state;
the system state equation is:
in the above formula, A is a transfer matrix, xvIs the estimated value of the system state at the moment v, B is an input weighting matrix, u is a control input vector, w is a zero mean Gaussian distributed process noise vector, and the covariance matrix is Qv。
Establishing a relational expression of the covariance of the current attitude error and the current attitude state vector, i.e.
According to the definition of the system state vector, establishing a motion model nonlinear equation:
in the formula above, the first and second groups of the compound,
and
the position abscissa, the position ordinate, the zenith coordinate and the course coordinate of the underwater vehicle are respectively, u is a control input vector, and w is a zero-mean Gaussian-distribution process noise vector;
step 2: the underwater mode in the E-vector angle of the underwater polarization mode is less sensitive to disturbances (including surface waves) and therefore can rely on the position of the sun and from this determine the heading and pitch angles of the sun to accurately estimate the position of the observer. Therefore, the sun vector is calculated by adopting a least square method of the polarization state through the orientation algorithm of the polarization sensor;
using the Mueller-Stokes form of polarized light, a beam of polarized light consisting of wave vectors
(representing wave number and propagation direction of polarized light) and Stokes vector
(representing the intensity and polarization state of polarized light) indicates that sunlight (k)
i,x
i,S
i) Refraction in water, air-water interface from surface normal n and actual refractive index η of air and water
i,η
tDefinition, S, assuming too much sunlight is unpolarized
i=(1,0,0,0)
TThus transmitting light (k) according to snell's law of refraction
t,x
t,S
t) Is represented as follows:
xt=xi=n×ki/||n×ki||
St=MRSi
above formula, SiAnd StStokes vectors of the incident angle and the emergence angle, respectively, where Si=(1 0 0 0)T. Using the above formula, matrix M is transformed by coordinatesR→STo obtain StIn the underwater transmission sunlight model, the scattering matrix is expressed as MSWave vector k of scattered lightsAnd k istThe size is the same, and the pointing detector is specifically expressed as follows:
Ss=MSMR→SSt
then the Stokes vector is:
Sd=MS→DMSMR→SMRSi
extracting a polarization angle by using Stokes vectors, and calculating an initial estimation value of the position of the sun in the sky angle as
L of the above formula
1The norm effect is to eliminate outliers caused by measurement noise, which, in the underwater scattering model,
a course angle representing the direction of the probe on the vehicle, then:
denotes the element angle difference, τ denotes the polarization angle:
to eliminate the minimization of model errors, the sun position is estimated using the least squares method:
the sun position is thus finally determined from the estimated values:
in the above formula, t is the measurement time, and arcidist (-) is the arc length;
and step 3: after the solar altitude angle and the solar azimuth angle are determined through the polarization mode of the scattering model, the step provides information for autonomous navigation through the topological nodes as a carrier, positioning calculation is carried out, and the problem of building a visual scene environment feature map is analyzed by utilizing polarization information to identify a scene and a detection target;
a schematic diagram of identifying characteristics of topology nodes, as shown in fig. 3, is a comparison diagram before and after training of a target sample, when a navigation topology map of an underwater environment is constructed, identification of the topology nodes is critical, and in a complex underwater environment, the environmental characteristics of some adjacent nodes may show high similarity, so that if a frame in a current node has too much similarity with a frame in a previous node, two adjacent nodes are merged, so that a memory of map can be saved;
the specific method comprises the following steps: according to the position information of the identification image, determining a target sample (an image sample of a region corresponding to the center of each node), marking a label, wherein in the navigation topological graph, n nodes contain m image samples, and the image target corresponding to each node is marked as:
the above formula IiIs the feature vector of the ith image sample, yi∈[1,2,…,n]The destination label of the node.
And then training target samples in adjacent topological nodes according to a large-boundary neighbor algorithm in machine learning to obtain a new measurement matrix M, so that the target samples with the same label are more compact, and the target samples with different labels are looser. The distance metric between any two target samples is defined as:
dM(Ii,Ii+j)=(Ii-Ii+j)TM(Ii-Ii+j)
above formula, dMIs the Euclidean distance of two nodes in the reconstructed topological node space, dM(Ii,Ii+j) In a linear relationship with the metric matrix, IiAnd Ii+jA target neighbor sample;
and finally, solving the optimal solution of the following objective function by using the measurement matrix M:
let yilE {0,1} represents whether the characteristic vectors of the samples belong to the same node, if the characteristic vectors belong to the same node, the characteristic vectors are 1, otherwise, the characteristic vectors are 0; λ represents a weight parameter, εijlThe total number of non-target samples. Therefore, the optimal solution can be obtained, and the expression and degree of the topological graph to the motion environment can be obtainedAn amount;
and 4, step 4: establishing a combined model of velocity inertial navigation measurement and nonlinear state polarized light measurement;
in the integrated navigation, attitude angle error, speed error, position error and gyro random drift in an inertial navigation system are taken as state variables of the system, namely:
in the formula above, the first and second groups of the compound,
for inertial navigation attitude angle error, δ v
E,δv
N,δv
uFor velocity error, δ L, δ λ, δ h are position errors, ε
bx,ε
by,ε
bzIs a constant error of the gyro random drift, epsilon
rx,ε
ry,ε
nA first order markov process for gyroscopic random drift,
random error for the accelerometer;
establishing state equations of each subsystem of inertial navigation and polarized light, wherein the state equations respectively comprise:
above formula, FIMU(t)、Fpolar(t) represents a state coefficient matrix, GIMU(t)、Gpolar(t) denotes the system noise drive matrix, WIMU(t)、Wpolar(t) represents a system noise matrix;
in summary, the state model of the integrated navigation system is:
the measurement model of the system is established as follows:
YIMU(t)=HIMU(t)+UIMU(t)
Ypolar(t)=Hpolar(t)+Upolar(t)
of the above formula, HIMU(t)、Hpolar(t) a non-linear function, U, representing the measurement equationIMU(t)、Upolar(t) represents the measurement noise of the inertial sensor and the polarized light sensor, respectively, wherein:
in summary, the measurement equation of the integrated navigation system is:
and 5: and integrating the steps, establishing a combined navigation system model through data fusion, and constructing an environment map.
The invention provides an AUKF algorithm for SLAM research (AUKF-SLAM), namely, the steps are integrated, navigation data fusion of an underwater autonomous underwater vehicle is carried out through course information provided by polarized light navigation, speed information provided by inertial navigation and position information provided by visual navigation, the algorithm solves the problems of precision reduction and divergence of the traditional UKF under the unknown and time-varying conditions, and introduces adaptive fading factors to correct prediction error covariance and adjust a filter gain matrix K, so that the divergence of a filter can be inhibited, and the rapid tracking capability is improved. The basic principle of the AUKF-SLAM algorithm is shown in FIG. 4, and the specific steps are as follows:
old data is gradually forgotten when the time-varying noise statistic is estimated, but the UKF algorithm does not have the change of the noise statistic, so the algorithm can be improved to design a time-varying noise statistic estimator by using an attenuation memory weighted index method under the condition of unknown and time-varying noise statistic parameters. Selecting a weighting coefficient:
can be written as:
thus, the recursive formula of the decaying memory time-varying noise statistic estimator
The expression is as follows:
in the formula above, the first and second groups of the compound,
in order to be the covariance of the system noise,
for observing noise covariance, K is Kalman gain, W
iAre the weights of the mean and the covariance,
satisfies the UKF sequence;
the AUKF algorithm calculates the self-adaptive factor coefficient lambda by introducing an attenuation factor formulaiThen using the coefficient to correct the covariance P of the predictable termk|k-1Thereby, divergence of the filter is suppressed and convergence of the filter is ensured. The convergence conditions are as follows:
calculating adaptive factor coefficient lambda for attenuation factor formulai:
Of the above formula, λ
0Tr (-) represents the matrix tracking for the initial value, S is the adjustable coefficient,
is a residual sequence;
factor lambda in the algorithmiThe larger the value, the smaller the proportion of information produced, resulting in a residual vector effect vkThe more pronounced. Therefore, the algorithm not only inhibits the divergence of the filter and improves the noise reduction capability of the filter, but also has strong tracking capability on the condition of sudden change of state;
after noise reduction, performing data association on the acquired attitude, position, speed, course and the like by adopting a nearest neighbor data association algorithm; if the nodes (target samples) in the navigation topological graph are adjacent, merging is carried out, namely association is successful, and the underwater vehicle carries out time updating and measurement updating once; otherwise, adding the new metric as a new feature to the current state vector, i.e. performing state augmentation, and then continuing to perform merging (i.e. data correlation) of adjacent target samples. The operation is as follows:
in the formula above, the first and second groups of the compound,
is a new feature vector.
Through the improvement, the time updating and the measurement updating are carried out on the filter:
and (3) time updating:
measurement updating:
in the formula above, the first and second groups of the compound,
and
the previous state vector, covariance vector and measurement vector of state at time k-1, x, respectively, of the system
i,k∣k-1、z
i,k∣k-1Values obtained for Sigma point sampling, W
i (m)And W
i (c)Weight, Q, of the system mean and covariance, respectively
k-1Is the covariance of the system noise and,
and
are all observed covariances obtained in the system measurement update, R is the covariances of the observed noise, K
kIn order to be a matrix of the filter gains,
and
respectively, the current state vector and covariance vector of the system.
In conclusion, the AUKF-SLAM algorithm provides a feasible and novel method for simultaneously positioning and mapping underwater under unknown environment.