Speckle-tracking vibration telesensor with dual optical receiver and method of correcting the vibrational noise of such a telesensor

Abstract

The present invention relates to a system and a method using a dual optical receiver ( CCD1 and CCD2 ) and an on line mathematical algorithm applied to an infrasonic speckle-tracking telesensor. In the measurement s with the infrasonic telesensor, said invention allows eliminating and / or reducing the vibrational noise present on two CCD s due to the vibration of the instrument it self and the disturbances caused by the air turbulence, in order to improve the accuracy of the measured rotational magnitude. For such a purpose, the two optical devices are arranged so that the CCD2 receives the vibrational signal of the target with the vibrational noise from the stand and the air fluctuations; the CCD1 is arranged to receive only the noise. The algorithm of speckle pattern acquisition and simultaneous mathematical proces sing of the two signals by the two receivers ef fectively eliminates / reduces noise. The signal proces sing mainly occurs through spatial correlation proces ses on the frames acquired by the two CCDs placed at the end of two independent optical configurations linked by some common parameters. It operates as a common-mode noise re j ection system.

Description

[0001] Speckle-tracking vibration telesensor with dual optical receiver and method of correcting the vibrational noise of such a telesensor

[0002] The present invention relates to a vibrational noise correction system— using two optical receivers which frame the target by means of two different lens arrangements, in speckle-tracking vibration telesensors. The first optical receiver receives the signal plus the noise (thereof and ambient) and projects it onto a first CCD (Charge Coupled Device, optical sensor) on the Fourier plane (or on the focal plane with an alternative optical configuration). The second optical receiver, placed on the focus of the optical system, receives only the noise and projects it— onto the conjugate plane of another CCD, to operate a sort of common-mode noise rejection.

[0003] Background art

[0004] Speckle-tracking vibration telesensors operate over a wide frequency band (0-12000 Hz), as described in various publications in the international literature [l]-[4] and in a filed patent [5]. Here we refer to those mainly operating in a frequency band up to 100 Hz, used in the detection of vibrations of buildings and structures which fall within the latter frequency range.

[0005] The speckle-tracking vibration telesensor is an optical receiver-transmitter system which transmits a 532 nm laser beam (or other wavelengths in the visible spectrum), a coherent light which is scattered by a vibrating or target surface, the irregularities of which produce small spots (or speckles). A receiving optical system ending with a photosensor (CCD) receives the granular image of the moving speckles. A mathematical algorithm then reconstructs the vibrations of the surface struck by the laser beam starting from the overall movement of the speckles (speckle pattern tracking).

[0006] The speckle-tracking infrasonic telesensor mainly measures angular velocity dOdl, where Q is the angular shift of the vibrational surface and t the time, fundamental frequencies and harmonics of the investigated surface. Angular shifts and accelerations can be inferred from these data with simple on-line operations. Moreover, other kinematic parameters can also be determined from the knowledge of the geometry of the vibrating surface. The telesensor can be used to measure vibrations of long distance L (up to 150 m) of buildings, infrastructures and natural structures.

[0007] Delving in greater detail into the working principle of the speckle-tracking telesensor, when a coherent light beam illuminates a rough surface, the light is scattered, resulting in a random (but time-stationary) diffraction pattern, commonly referred to as a speckle pattern. The speckle pattern is extremely sensitive to the microscopic detail of the reflective surface, which means that any deformation of the reflective surface gives rise to a change in the speckle pattern. For example, if the surface changes orientation by an angle 0, the resulting speckle pattern will be similar to the previous one but translated by 9L (where L is the observation distance). It is this kind of "optical lever" that makes it possible to determine changes in inclinations of very small angles. If the local orientation of a surface changes due to vibration, this can then be detected by an on-line correlation process between the various images acquired over time t . The telesensor TIS is based on the principle diagrammatically shown in figure 1: a) A laser beam 103, produced by a laser 101 through an optical system 102, strikes a distant L vibrating surface 104; b) the light scattered by the roughness of the surface 105 contains a speckle pattern varying over time (e.g., a vibrating surface stressed by an acoustic signal as depicted); c) the scattered light is received by an optical system 106 and a photodetector array (CCD) 107 which receives the speckle patterns at various times I(ti), I(t2),••• I(tn) 108, which contain the information of the angular variations Q of the surface (membrane) subjected to vibration; d) the (on-line) analysis of these images makes it possible, albeit with a slight time delay quantifiable in a fraction of tenths of a second, to reconstruct the nature of the vibration, i.e., the amplitude, frequency, and harmonic content (or timbre) of the vibrating surface. In particular, a speckle-tracking telesensor [5] capable of correcting the speckle pattern correlation centroid value in the presence of displacements due to vibrational noise is known. In fact, such a telesensor uses an accelerometric device which is capable of instantaneously highlighting the displacements of the CCD sensor with respect to an inertial reference, i.e., consisting of a mass which is immovable with respect to the fixed stars, installed in the optical axis of the sensor.

[0008] A telesensor is also known from patent document [7], which relates to a method and a system for monitoring at least one parameter of an object. An imaging system is provided for monitoring at least one movement parameter of a moving object, the system comprising at least one imaging unit comprising an optical transformer configured and usable to apply the spatial image space transformation of at least one movement parameter in geometric relation, translating different components of six degrees of freedom of movement in a three-dimensional space into a lateral translation; where the image acquisition unit is configured and usable to form the image of the moving object on an image plane and generate image data indicative of the object moving in a plane xy; the imaging system generates movement data indicative of the six degrees of freedom of movement.

[0009] Again, electron interferometry of the speckle pattern as published [8] is known. This technique combines the image of an object with a reference wave and is a base configuration for interferometric analysis. It analyses the dynamics of the speckle patterns and laser fringes formed in an imaging-speckle-pattern interferometer with the aim of detecting three-dimensional linear movement and out-of-plane components of the rotation in real time, using spatial filtering techniques. It is demonstrated that it is possible to determine both the values and the direction of all three linear displacement components of the movement of the object. At the same time, the out- of-plane rotation of the object and the directions thereof can be determined using the average function of the set and applied to the intensity distributions obtained at two successive positions of the object and to the spatial gradient of the fringe movement. The theory is confirmed by an experimental apparatus (see Fig. 7) with real measurements.

[0010] However, such telesensors have a high vibrational noise as well as some distortions due to air turbulence causing a wavefront distortion (containing the speckle pattern), such as angular variations due to the variation of the refractive index along the path of the optical beam .

[0011] Therefore, the need is felt for a speckle-tracking telesensor which can minimize the errors introduced by environmental factors and make a vibrational signal of the target more intelligible.

[0012] Purpose and object of the invention

[0013] It is the object of the present invention to provide a speckle-tracking telesensor using a dual optical receiver and a method of correcting the vibrational noise of such a telesensor which solve the problems and overcome the drawbacks of the prior art, in whole or in part.

[0014] The present invention relates to a speckle-tracking telesensor and a method of correcting the vibrational noise of such a telesensor, according to the appended claims.

[0015] Detailed description of embodiments of the invention

[0016] List of drawings

[0017] The invention will now be described by way of example, with particular reference to the figures of the accompanying drawings, in which:

[0018] — figure 1 shows a diagrammatic arrangement of a speckle-tracking infrasonic telesensor, according to the prior art;

[0019] — figure 2 shows a diagram of the speckle-tracking telesensor with two optical receivers, according to an embodiment of the invention;

[0020] — figure 3 shows an arrangement of the lenses in common configuration (CC) with the first CCD, "CCD1" placed on the focus (conjugate point) at distance li from the optical system represented only by the lens feq (feq is a lens equivalent to the group fi,f2and fs in Fig. 2), where L is the distance between the telesensor and the target; the magnitudes acquired by CCD1 form the common noise which will be subtracted from the signal+noise acquired by the second CCD "CCD2" (shown in Fig. 2 or in Figs. 4 and 5) in both a dependent "CD" and an independent "CI" configuration from the distance L;

[0021] — figure 4 shows a diagram of the speckle-tracking telesensor in detail regarding CCD2 in a so-called dependent configuration CD, according to an embodiment of the invention, where the magnitude measured on the CCD2 placed on the Fourier plane depends on L, which condition is achieved with specific values of fi , f2 and the distance thereof;

[0022] — figure 5, according to an embodiment of the invention, shows a detail of the CCD2 in a speckletracking telesensor configuration, placed on the focal plane in which the measurement on the CCD2 is independent of the distance L, which condition is achieved with values offiand ft different from those in figure 4. In such a configuration, the distance between fi and ft is also preset and independent of L;

[0023] — figure 6 conceptually shows the diagram of noise cancellation by the telesensor of the invention (within the optical group, the solid lines representing the beams related to the configuration CD, the dotted lines are related to the configuration CI);

[0024] — figure 7 shows a spectrum of the uncorrected vibrational signal (solid gray) compared with the corrected vibrational spectrum (dotted), obtained from a prototype of a telesensor according to an embodiment of the present invention with a distancedependent configuration CD. It is here specified that elements of different embodiments can be combined to provide further embodiments, without restrictions, by respecting the technical concept of the invention, as those skilled in the art will effortlessly understand from the description .

[0025] The present description also makes reference to the prior art for the implementation thereof in relation to the detail features not described, such as elements of minor importance usually used in the prior art in solutions of the same type.

[0026] When an element is introduced, it is always understood that there can be "at least one" or "one or more".

[0027] When elements or features are listed in this description, it is understood that the finding according to the invention "comprises" or alternatively "consists of" such elements.

[0028] Embodiments

[0029] According to an aspect of the invention, the vibrational signal acquired by a telesensor can be thought of as an angular shift Q of the surface-target plus a translation A thereof, the surface-target being the surface T in Fig. 2 et seq. or surface 104 in Fig. 1, to which the vibrations (especially angular microshifts) of the telesensor itself and, possibly, the air fluctuations are added.

[0030] The angular shift Q is defined with respect to a first reference axis X and a second reference axis Y (the axis Y being exiting the sheet in Fig. 2 and in Fig. 6, i.e., the vertical axis in Fig. 1) perpendicular to each other, a third reference axis Z being defined perpendicular to the first and second axes.

[0031] This composite vibrational signal received by the optical receiver by means of an image sequence on CCD2 is therefore the sum of at least 4 components (angular shift, translation, vibrations, air fluctuations) from only the angular shift Q is to be isolated, which in a particular lens arrangement (dependent configuration - see below) is also proportional to the distance L between the telesensor and the target surface.It can be shown from estimates and experimental evidence that the translation (A) of the target surface is negligible with respect to the angular shift since, in the first approximation, it is proportional to 1 / L [6].

[0032] Fig. 2 shows an example configuration of the telesensor according to the invention, in which two CCDs (in general optical "measuring sensors", CCD1 and CCD2) are arranged at 90° to independently receive the light beams after a beam splitter M. The laser LS sends a light beam onto the target surface T at a distance L which scatters it towards the telesensor. At this point, the scattered beam passes through an optical system consisting of a first lensfiwhich collects the scattered speckle pattern and a second lensfzwhich makes the beams parallel by projecting the speckle pattern onto CCD2 passing through M, a dependent configuration CD (a different configuration is possible, see below).

[0033] Between the second lens fz and CCD2, a 45° semi- reflective mirror M (beam splitter) is positioned and from here the returning light beam is split into a first beam R1 towards CCD1 through a focusing lens (common configuration CC) and a second beam R2 towards the second CCD2, without focusing lens. Thereby, the beam R1 projects an almost punctual image (however very small) on CCD1 placed on the lens focus fs.

[0034] The apparatus is completed by an electronic processing unit of the data detected by the two measuring sensors, configured to calculate a correlation of the speckle pattern (see figure 6) and provide a measurement of the angular shift with reduction of errors due to environmental causes.

[0035] Angular disturbances a and p form a source of noise to be reduced or eliminated. The first (a) is caused by the air turbulence (variations in the refractive index) which distorts the wavefront containing the speckle pattern, the second (p) is caused by the angular shift of the telesensor itself (micro-seismicity, traffic, wind, etc.). These perturbations are received by both optical sensors and thus also by the optical receiver CCD1, which is optically adjusted to receive only the last two components (a, p) (and not 0, which is seen only by CCD2). This condition is obtained with CCD1 on the focus of the optical system (figure 3) which in the common configuration DC is not sensitive to the rotations (0) of the vibrational signal of the target surface. Therefore, being shared by the two optical receivers, the two components a and p can be ideally eliminated or at least reduced.

[0036] In more detail, the processing of sequential frames on CCD1 and CCD2 returns the measurement of the angular shift over time d0 / dt(vibration), affected by the noise a and p. The optical system ending with CCD1 does not see the angular variations of the surface, but only a and p. For this reason, only the component 6 can be isolated from the signal of CCD2.

[0037] This effect can be quantitatively described under some assumptions, but it is clear that the present invention is not linked to a specific quantitative description, the principle of deletion being applied between the two CCDs due to the arrangement thereof.

[0038] Consider the shift along X or Z of the correlation centroid in the two CCDs, bearing in mind that the same operations can be repeated along Y.

[0039] In the two CCDs we will have a pixel shift (linear) of the speckle pattern X or Z between two images at two successive arbitrary times (preferably as close as possible) which will contain the angular 6 and translational A signal information, the rotations and translations p due to the angular movement of the telesensor itself and the angular disturbances a due to air turbulence. In the following relationship this displacement of the speckle pattern is referred to as Xspeckie. The multiplicative constants of the signal containing the translations 6,A, p and a depend on the geometry and optics used. In short, these magnitudes 9, A, p and a are received with multiplication constants. They can be dependent on the distance L between the telesensor and the target surface and on the optical parameters of the lenses (lens focus) fi, f2, fs. From the theory known as Ray Transfer Matrix, RTM, the calculation shows that in the three optical configurations referred to in Table 1, the multiplication constants of the rotational and translational magnitudes are established as follows.

[0040] The three optical configurations are "common configuration" (CC, Fig. 3), "distance-dependent configuration L" (CD, Fig. 4) and "distance-independent configuration L” (CI, Fig. 5).

[0041] Table 1

[0042] The table above shows the translational and rotational values (column 1) of the signal in the respective lens configurations. The second column has the optical and geometric parameters on which the translations A depend with the rotations 0 relative to the common configuration (CC), i.e., with CCD1 focused. The third column shows the optical and geometric parameters on which A and 0 depend in the telesensor lens configuration CD dependent on the distance L, i.e., with CCD2 in the Fourier plane (the measured rotations 0 are equivalent to 0 / 2of the target due to Snell's law). The fourth column shows the parameters related to the telesensor lens configuration CI independent of the distance L, i.e., with CCD2 in the focal plane (even in this case the target rotations are equal to 0 / 2).

[0043] The peculiarity of a speckle-tracking vibration telesensor [1, 2, 3, 4 and 5] lies in the fact that the translations of the CCD pixels on the plane X or Z and Y of the latter are in relation to the rotations and translations of the target, i.e., the vibrations. Such a relationship arises essentially from a spatial correlation operation between the speckle patterns of the frames acquired sequentially over time (successive images acquired by the same apparatus described herein). This operation indicated with xspeckleand yspeckle, which is also quite complex computationally, relates the pixel displacements to the target movements.

[0044] This consideration is utilized by the invention. In fact, in the configuration CC, another relationship is also added, which concerns the calculation of the movement of the center of gravity of the spot, laser imprint on the target measured by CCD1. This operation Xspotand Yspothas never been described in the cited references and / or implemented in the speckle-tracking vibration telesensors reported. It is gainfully applied only to highlight and / or eliminate a particular type of noise superimposed on the signal from the target.

[0045] The two operations, which are carried out on CCD1, are the calculation of the center of gravity XccDispotto obtain the light intensity distribution center of the first granular image (made of speckles) and that of the correlation centroid of the speckle pattern XccDispeckle(speckle tracking), which is obtained by correlating two successive images, as described below.

[0046] The center of the spot is obtained by calculating the center of gravity of a brightness distribution. On the axis X the center is therefore: where / j are the light intensity values of the pixel i (with z’=l,...,NxM pixels) and Xj is the pixel position with respect to the axis X distributed in a plane XY. The operation is repeated for each acquired image and also for the axis Y, with a similar mathematical calculation.

[0047] The calculation of Xccoispeckleis referred to as a speckle tracking and is obtained by correlating sequences of images acquired over time by the camera CCD1 and such a process ends with the determination of the correlation centroid. The calculation is similar to the above formula but is applied to the calculated correlation curve with respect to X, where Q are the discrete values of the curve (with z’=l,..., NxM pixels) along the axis X: where Xj is the pixel position with respect to the axis X.

[0048] Such an operation is carried out by operating a two- dimensional Fast Fourier Transform (FFT) on the n sequential images, making the product FFTn*FFTn+iin the frequency domain, where the second term is conjugate complex, and then applying an inverse transform IFFT and returning to the time domain. The result of the correlation Q is generally bell-shaped with respect to the two axes of the related images. The coordinate X of the correlation bell centroid is denoted Xccoispeckle. The latter indicates the movement between two speckle patterns on the axis X, correlating the images acquired sequentially. This magnitude represents the entire curve in a single value with a much higher resolution than the intra-pixel distance. It is the most representative value of the correlation curve or, better said, of the correlation function since all the values of the curve are considered with the right weight.

[0049] These operations give the system a resolution which could not otherwise be had.

[0050] The operation is repeated for each pair of related images. As in the previous case, such an operation is repeated for the axis Y (and Z instead of X) and for the images acquired with CCD2, which also has NxM pixels, also as described below.

[0051] Noise reduction with lens arrangement in configuration CD

[0052] Referring to the diagram in Figure 4 (distancedependent configuration), the signal Xspeckle, received from CCD2 in the configuration CD placed on the Fourier plane, will be dependent on the distance L. The composite signal acquired from CCD2, from which the first equation of the system below is derived, contains the magnitudes Q, X, p and a with the related constants fi, f2 and L. Such magnitudes are measured with respect to a reference axis in the plane of the sensor (or horizontal axis X) and for the sake of simplicity, the time dependence is omitted.

[0053] The second and third equations of the system derive from the signal received from CCD1 of the optical configuration CC, as shown in particular in Fig. 3. The signal acquired by such a configuration, as it is made, will contain the magnitudes A, p and a with the combination of the related parameters fi,ft, and L but will not have the angular shift 0, as shown in table 1. The other two equations of the system arise from this signal, in which the variations of the speckle pattern on CCD1 xspeckleare related to the magnitude fi which also appears in the second equation. The last equation of the system still derives from the signal acquired from CCD1, from which the center of gravity of the received spot can be extracted, a center of gravity which we will call ultimately, with the obvious meaning of the symbols, we will have the system below:

[0054] This is an indeterminate system in that the number of unknowns 6, A, p, and a is greater than the number of equations. Some considerations and calculations based on the behavior of a minimally elastic body or structure (practically all constructions) subjected to micro- seismic and environmental stresses allow us to neglect the translations A with respect to the rotations Q and other magnitudes which appear in this system of equations. It can be shown that the translation A of the target surface is a negligible signal with respect to the angular shift 0 since, in the first approximation, it is proportional to 1 / L, which can also be obtained with a quantitative evaluation [5].

[0055] Therefore, we will have the following system:

[0056] The system can be solved with simple subtraction operations and it is possible to derive the rotational magnitude 9, which is what we actually want do determine, as follows:

[0057] Similar considerations also apply to the axis Y.

[0058] It should be noted that the formula constants for 0 depend on the particular modelling of the optical system of the invention above. That used to derive the specific expressions provided herein is not the only possible one and can be replaced by other possible ones without affecting the fundamental concept of the invention.

[0059] The speckle-tracking vibration telesensor, with such a static correction, was actually made into a prototype by the Applicant. The result of a measurement with illumination of an excited piezoelectric at 17 Hz is presented as shown in Figure 7. The low-frequency oscillations introduced by stressing the base on which the telesensor was placed, were actually eliminated.

[0060] Noise reduction with lens arrangement in configuration CI

[0061] The same noise reduction method can be applied considering a telesensor assembled for the detection of vibrations independent of the distance L between the telesensor and the target.

[0062] With reference to Fig. 5, the receiving optical group {fiand / ?) is diagrammed, as in the fourth column in Table 1, with a single lens feq, CCD2 is placed on the focal plane (plane where the beams from infinity converge at a point). In this configuration CI the semi-reflective mirror is still positioned after the lens / ?, where the beams converge on the focal plane, while the lens fs brings the image into focus on a plane at an appropriate distance (in focus) where CCD1 is placed.

[0063] In this case, the configurations CC (of CCD1) and CI (of CCD2) are taken into account with the related results in Table 1. This allows us to write the following system of equations:

[0064]

[0065] In this case, since there are no target translations, the noise cancellation is even more immediate: where where dis the distance between the lenses fi and fz.

[0066] Similar considerations also apply to the axis Y perpendicular to said plane and therefore to said horizontal axis X.

[0067] In any case, in all the above configurations, the angular shift 0 is always of the form:

[0068] In which from time to time jo, ji, jz are constants which depend on the optical parameters of the first focusing optic f3, the second receiver optic fi,f2, and possibly the distance L (only in the configuration CD), with specific values which vary depending on the chosen model and the assumptions made for the optical system described. References

[0069] [1] Bianchi Silvio, "Vibration detection by observation of speckle patterns," Appl. Optics 53, 931-936

[0070] (2014).

[0071] [2] Bianchi Silvio, Giacomozzi Emanuele (2019), "Long- range detection of acoustic vibration by speckle tracking" - Applied Optics. Vol.58 (28) pp . 3397- 3406, Ed. Optical Society of America.

[0072] [3] Z. Zalevsky, Y. Beiderman, I. Margalit, S. Gingold, M. Teicher, V. Mico, and J. Garcia, "Simultaneous remote extraction of multiple speech sources and heart beats from secondary speckles pattern," Opt. express 17, 21566-21580 (2009).

[0073] [4] Giacomozzi Emanuele, Bianchi Cesidio,

[0074] "Telerilevamento di vibrazioni delle strutture tramite telesensore infrasonico" Quaderni di Geofisica N.169 INGV (2021).

[0075] [5] European Patent Application No. 21719961 with the related references.

[0076] [6] Pawel Sniady, Katarzyna Misiurek, Olga Szylko-Bigus,

[0077] Rafal Idzikowski, "Vibrations Of The Euler-Bernoulli Beam Under A Moving Force Based On Various Versions Of Gradient Nonlocal Elasticity Theory: Application In Nanomechanics" Studia Geotechnica et Mechanica, 2020; 42(4): 30 6-318https: / / doi.org / 10.2478 / sgem,

[0078] (2020).

[0079] [7] US10883818 B2.

[0080] [8] MICHAEL L. JAKOBSEN ET AL: "Speckle and fringe dynamics in imaging speckle-pattern interferometry for spatial-filtering velocimetry", APPLIED OPTICS, OPTICAL SOCIETY OF AMERICA, WASHINGTON, DC, US, vol. 50, no. 28, 1 October 2011 (2011-10-01), pages 5577- 5591, XP00 1570040, ISSN: 0003-6935, DOI: 10.1 364 / AO.50.005577 .

[0081] Preferred embodiments have been described above and variations of the present invention have been suggested, but it should be understood that those skilled in the art may make modifications and changes without departing from the related scope of protection, as defined by the appended claims.

Claims

CLAIMS1. A speckle-tracking vibration telesensor (TIS) for a surface subjected to an angular shift Q with respect to a first reference axis (X) and a second reference axis (Y) perpendicular to each other, a third reference axis (Z) being defined perpendicular to the first and second axes, the telesensor comprising the following components:— a laser (LS) configured to output a coherent light signal along an axis of a plane defined by said first reference axis (X) and said third reference axis (Z) and incident on the surface;— a first measuring sensor (CCD1) for measuring a return light signal from said surface along an optical axis on said plane, the first measuring sensor being arranged along said first reference axis (X) and said second reference axis (Y) and being configured to detect a first pair of images taken at successive times each with N x M pixels and containing a spot and a first speckle pattern of the return light signal;— first focusing receiver optics ( / j) for the focusing reception of the return light signal, positioned before the first measuring sensor (CCD1);— a second measuring sensor (CCD2) for measuring said return light signal along said optical axis, arranged along said second reference axis (Y) and said third reference axis (Z) and being configured to detect a second pair of images taken atsuccessive times each with N x M pixels and containing a second speckle pattern of the return light signal;— second receiver optics (firfz') for the reception of the return light signal, positioned before the second measuring sensor (CCD2) and at a distance L from said surface;— a beam splitter (M) positioned between said first focusing receiver optics ( / ?) and said second receiver opticsand configured to split said return light signal into a first beam Rl towards the first focusing receiver optics and a second beam R2 towards the second receiver optics; the second beam R2 being perpendicular to the first beam Rl; wherein:— the first measuring sensor (CCD1) is placed on the focus of the first focusing optics ( / j), configured so that the first beam (Rl) projects the spot and the first speckle pattern onto the first measuring sensor (CCD1); and— an electronic processing unit for the data detected by said first (CCD1) and said second (CCD2) measuring sensors is comprised and configured to:■ calculate a first correlation curve of the first speckle pattern and a second correlation curve of the second speckle pattern among the images of said first and said second pairs of images, respectively;■ calculate a center of gravity of the spot ofthe first image as jfror Jt_Thecomponent along the first reference axis (X) and for the component along the secondreference axis (Y) where It are the light intensity values of the pixel z, Xj and yi are the positions of the pixel z with respect to the first reference axis (X) and the second reference axis (Y), respectively, with i=l,.„,NxM, as well as a correlation centroid of the y■c "X‘ first speckle pattern Xccoispeckleas1for thecomponent with respect to said first reference axis (X) with respect to said secondreference axis (Y), wherein Q and c\ are the discrete values of the first correlation curve along the first (X) and second (Y) reference axes, respectively, with z’=l,...,NxM; calculate a correlation centroid of the second speckle pattern XccD2speckleas for thecomponent with respect to said first reference axis (X) and wrth respect to sard thrrdreference axis (Z), wherein Xj and Zj are the positions of the pixel z with respect to the first reference axis (X) and the third reference axis (Z), and Q and c"i are the discrete values of the second correlation curve along the first (X) and third (Z) reference axes, respectively, with z’=l,...,NxM,;■ calculate the angular shift 0 based on XccDispot, XccDispeckle, and XCCD2speckle.

2. A telesensor according to claim 1, wherein the second measuring sensor (CCD2) is placed on the Fourier plane of said second receiver optics (jj,j2)•3. A telesensor according to claim 2, wherein the processing unit is configured to calculate the angular shift 0 according to the following formula: n> ■vspeckle> ■ySpeckle> .ySpot V— JOACCIll J1ACCD1 J2ACCD1 where jo, ji, j2 are constants depending on the optical parameters of the first focusing optics ( / j), of the second receiver optics ( / ;, / ?), and on the distance L.

4. A telesensor according to claim 1, wherein the second measuring sensor (CCD2) is placed on the focal plane of said second receiver optics {fi,f2)•5. A telesensor according to claim 4, wherein the processing unit is configured to calculate the angular shift 0 according to the following formula: n> ■ yspeckle> ■ySpeckle> .yspot V— JOACCI)1 J1ACCD1 J2ACCD1 where jo, ji, j2 are constants depending on the optical parameters of the first focusing receiver optics ( / j), ofthe second receiver optics (fi, ft) only.

6. A method for correcting the vibrational noise of a speckle-tracking telesensor, comprising the following steps:— providing a speckle-tracking telesensor (TIS) according to one of claims 1 to 5;— sending a coherent light signal along an axis incident on a surface subjected to an angular shift 0;— detecting the first and second images from the first (CCD1) and second (CCD2) measuring sensors;— calculating a first correlation curve of the first speckle pattern and a second correlation curve of the second speckle pattern;— calculating a center of gravity of the spot of thefirst image XccDispotas for the component alongthe first reference axis (X) and for thecomponent along the second reference axis (Y) where / j are the light intensity values of the pixel z,and yi are the positions of the pixel z with respect to the first reference axis (X) and the second reference axis (Y) and a correlation centroid ofV.Q “X' the first speckle pattern XccDispeckleas *1 1for the Lici component with respect to said first reference axis (X) andwith respect to said second reference Lic'i axis (Y), wherein Q and c\ are the discrete values of the first correlation curve along the first (X)and second (Y) reference axes, respectively;— calculating a correlation centroid of the second speckle pattern for the componentwith respect to said first reference axis (X) and wrth respect to sard second reference axis(Y), wherein Q and c"i are the discrete values of the second correlation curve along the first (X) and third (Z) reference axes, respectively;- calculating the angular shift 0 based on XccDispot,7. A method according to claim 6, wherein the calculation of the angular shift 0 is carried out according to the following formula if the second measuring sensor (CCD2) is placed on the Fourier plane:where jo, ji, j2 are constants depending on the optical parameters of the first focusing receiver optics ( / j), of the second receiver optics ( / ;, / ?), and on the distance L.

8. A method according to claim 7, wherein— f3is the value of the focus of the first focusing receiver optics ( / ?);- fi and fi are the values of the foci of a first (fi) and a second Iff) lens placed in line, which form the second receiver optics (fi,fi), wherein the first lens collects the return light signal and the second lens makes the beams of the return light signal parallel; and— L is the distance between the first lens and the surface .

9. A method according to claim 6, wherein the calculation of the angular shift 0 is carried out according to the following formula if the second measuring sensor (CCD2) is placed on the focal plane:where jo, ji, ji are constants depending on the optical parameters of the first focusing optics (f3) and of the second receiver optics (fl, f2) only.

10. A method according to claim 9, wherein:— fi is the value of the focus of the first focusing receiver optics (fi);— fi and fi are the values of the foci of a first ( / ;) and a second (fi) lens placed in line, which formthe second receiver optics (fi,ft), wherein the first lens collects the return light signal and the second lens converges it on the focal plane; and— d is the distance between the first lens and the second lens.

Images