Method and system for inspecting an object disposed in a fluid

Abstract

The present invention provides a method for inspecting an object placed in a turbid fluid, the method comprising the steps of: A) generating electromagnetic radiation by a radiation source; B) emitting the electromagnetic radiation; C) modulating the amplitude or frequency of the electromagnetic radiation; D) illuminating a surface of the object at a plurality of object points with the modulated electromagnetic radiation, the illumination of the object surface occurring along an illumination beam axis; and E) focusing the electromagnetic radiation reflected from the object points toward a light receiving portion of a detector by an optical system having a focal length, the detector having an aperture having an aperture shape in an aperture plane, the aperture plane being separated from the light receiving portion by a detector distance and the aperture plane being separated from the optical system by an aperture distance, the focusing occurring along the detection beam axis. and F) detecting electromagnetic radiation reflected from the surface of the object with the receiver; and for each of the plurality of object points, G) measuring an indication of a propagation time of the electromagnetic radiation from a reference point in a beam path of the electromagnetic radiation to each object point; and H) outputting the indication of the propagation time, wherein the illumination beam axis and the detection beam axis form a parallax angle, the aperture has an aperture position in a direction perpendicular to at least the illumination beam axis or the aperture beam axis, and the surface of the object is spaced a measurement distance from the receiver.

Description

[Technical Field]

[0001] The present invention provides a method for inspecting an object placed in a turbid fluid, the method comprising the steps of: A) generating electromagnetic radiation by a radiation source; B) emitting the electromagnetic radiation; C) modulating the amplitude or frequency of the electromagnetic radiation; D) illuminating a surface of the object with the modulated electromagnetic radiation at a plurality of frequencies of the object, the illumination of the surface of the object being along an illumination beam axis; and E) focusing the electromagnetic radiation reflected from an object point towards a light receiving portion of a detector by an optical system having a focal length, the detector having an aperture having an aperture shape in an aperture plane, the aperture plane being spaced apart from the light receiving portion by a detector distance; an aperture plane spaced an aperture distance from the optical system, the collecting is along a detection beam axis, the illumination beam axis and the detection beam axis form a parallax angle, the aperture has an aperture position in a direction perpendicular to at least the illumination beam axis or the aperture beam axis, and the surface of the object is spaced a measurement distance from the light receiving unit; F) detecting the electromagnetic radiation reflected from the surface of the object with the light receiving unit; and for each of the plurality of object points, G) measuring an indication of a propagation time of the electromagnetic radiation from a reference point in a beam path of the modulated electromagnetic radiation to each of the object points; and H) outputting the indication of the propagation time.

[0002] The present invention also provides a system for inspecting an object placed in a turbid fluid, the system comprising: a radiation source configured to generate and emit electromagnetic radiation during operation of the system; modulation means configured to modulate the amplitude or frequency of the electromagnetic radiation during operation of the system; an illumination device (4) configured and arranged to illuminate a surface (5) of the object (7) at a plurality of object points (16) with the modulated electromagnetic radiation (3) during operation of the system; and a detector with a light receiving portion, the detector comprising an aperture having an aperture shape in an aperture plane, the aperture plane being spaced apart from the light receiving portion by a detector distance. an optical system constructed and arranged to focus the electromagnetic radiation reflected from the object towards the light receiving section of the detector with a focal length, the aperture plane being spaced apart from the optical system by an aperture distance; and an evaluation device operatively connected to the light receiving section to receive detector signals from the light receiving section during operation of the system, the evaluation device configured to: determine, for each of the plurality of object points, an indication of a propagation time of the electromagnetic radiation from a reference point in a beam path of the modulated electromagnetic radiation to the respective object point, and output the indication of the propagation time during operation of the system. [Background technology]

[0003] Infrastructure structures such as bridges, dams, and jetty heads, as well as other objects such as ships, must be inspected periodically for their structural or constructional condition. Inspection of the geometry and / or surface of such objects is part of the assessment. Optical measurement methods are ideal for this type of inspection, allowing for high spatial resolution when recording the geometry and surface of the object. Furthermore, data acquired using optical measurement methods can also be reliably analyzed.

[0004] However, when using optical measurement methods, it is important to realize that the ambient conditions in the area of ​​the path of the electromagnetic radiation used will affect the measurement results. On land, rain may fall, and fog or smoke may limit visibility. In water, mainly fine particles can sometimes cause significant scattering of the electromagnetic radiation used. Such turbidity reduces the quality of the test. The greater the turbidity, the less light reaches the corresponding detector from the object, and the shorter the maximum usable measurement distance of the system at that turbidity.

[0005] From the prior art it is known to use time-of-flight measurement methods to inspect objects placed in a fluid. Such time-of-flight measurement methods are also known as time-of-flight methods (ToF methods for short). The best-known ToF methods are LIDAR ( L ight D etection a nd R ToF stands for Optical Sensing and Ranging. Methods and systems known from the prior art for inspecting objects using ToF methods use a fixed focal length. Changes in the turbidity of the fluid in which the object is placed reduce the measurement accuracy at the same measurement distance and also reduce the maximum available measurement distance. Summary of the Invention [Problem to be solved by the invention]

[0006] In contrast, it is an object of the present invention to provide a method and system for inspecting objects placed in a turbid fluid in which the measurement accuracy has reduced or no dependence on the turbidity of the fluid. [Means for solving the problem]

[0007] The above-mentioned object is achieved by a method for inspecting an object placed in a turbid fluid as set forth in the attached independent claim 1. To achieve such object, a method of the above-mentioned kind further comprises the steps of I) detecting an indication of turbidity of the fluid, and J) adjusting at least the focal length, the aperture distance, the parallax angle, the aperture position or the aperture shape depending on the indication of turbidity.

[0008] The basic idea of ​​the present invention is to modify at least one essential parameter of the measurement setup depending on the indication of the turbidity of the fluid.

[0009] If the turbidity index changes, one of these parameters is also changed, and in one embodiment, this change is automated.

[0010] In one embodiment, the fluid in which the object is placed is a liquid, particularly water. In one embodiment, the fluid is a gas, particularly air. Turbidity in a liquid is particularly caused by fine particles in the liquid. In a gas, such as air, turbidity can be due to, for example, smoke, steam or fog.

[0011] An aperture is a device that limits the cross-section of the electromagnetic radiation on the detection beam axis. In one embodiment of the invention, the aperture is a pinhole aperture. In one embodiment of the invention, the aperture is an effective aperture formed by the boundary of the receiver itself. In this case, the aperture plane is in the plane of the receiver. In such an embodiment, the detector distance as defined herein is zero.

[0012] In principle, it is possible to adjust the measurement geometry depending on the turbidity by adjusting either the focal length, the aperture distance, the parallax angle, the aperture position or the aperture shape, however it is also possible to set several of these parameters simultaneously.

[0013] In one embodiment, adjusting the aperture shape includes changing the dimensions of the aperture. If the aperture is a slit aperture, in one embodiment, the aperture shape is adjusted by changing the slit width of the slit aperture. If the aperture is an iris aperture, in one embodiment, the aperture shape is adjusted by changing the free opening diameter of the iris aperture.

[0014] In one embodiment, adjusting the aperture shape includes changing the geometry of the aperture, for example, the aperture is changed from a slit shape to a keyhole shape or from a circle to a triangle.

[0015] If the aperture position is adjusted, this is understood in the sense of the present application to mean that the position of the aperture is changed at least in the direction perpendicular to the illumination beam axis or the aperture beam axis.

[0016] In one embodiment of the present invention, the step of illuminating the surface of the object at multiple object points is performed sequentially, i.e., the surface of the object is scanned or rasterized object point by object point, however, embodiments are also contemplated in which multiple points are detected simultaneously.

[0017] In principle, it is possible to change the detector distance, i.e. the distance from the light receiving part to the aperture plane, but in one embodiment of the invention the detector distance is constant, ie the detector distance is not adjusted depending on the turbidity index.

[0018] In one embodiment of the invention, the reference point is an element of a detector in the beam path of the electromagnetic radiation, in particular a receiver, In one embodiment of the invention, the reference point is an optical system.

[0019] In the ToF method, which forms the basis of the method and system according to the present invention, amplitude- or frequency-modulated electromagnetic radiation is generated and emitted by a radiation source, and the emission is performed so that an object is illuminated at one or more points by the modulated electromagnetic radiation. The electromagnetic radiation reflected or scattered from the surface of the object is detected by a detector, which allows a measure of the propagation time of the electromagnetic radiation from a reference point in the beam path to be measured. The distance between the reference point and the object point can be determined from the measure of the propagation time of the electromagnetic radiation.

[0020] For the purposes of this application, amplitude modulated electromagnetic radiation also includes optical pulses. If the electromagnetic radiation is frequency modulated, such ToF methods are also called FMCW-LIDAR (Frequency Modulated Continuous Wave Lidar).

[0021] To measure the measure of the propagation time of electromagnetic radiation, various methods known from the prior art can be considered.

[0022] In one embodiment, a reference signal phase-coupled at the modulation frequency to the modulation of the amplitude of the electromagnetic radiation is used and correlated with the amplitude of the modulated signal recorded by the receiver of the detector.

[0023] Alternatively, a portion of the electromagnetic radiation is applied to a reference detector as a reference signal, which acts as a start signal in determining the propagation time index, and a pulse of electromagnetic radiation reaching the receiver then acts as a stop signal. This embodiment is particularly useful for pulsed electromagnetic radiation as a special case of amplitude modulated electromagnetic radiation.

[0024] In an alternative embodiment, when the electromagnetic radiation is frequency modulated, the frequency of the electromagnetic radiation varies, preferably linearly, as a function of time during emission from the radiation source. A portion of the electromagnetic radiation does not pass through the fluid and is not reflected by the surface of the object, but is instead applied directly to the detector as a reference signal. A beat signal is then generated in the detector, the beat frequency of which is a measure of the propagation time.

[0025] In one embodiment of the present invention, in addition to a measure of the flight time, the intensity or mean amplitude is measured in step G. Both the flight time and the intensity information can be used to generate an image of the surface of the object.

[0026] Within the meaning of the present invention, maximum measurement distance is understood to be the measurement distance between an object point on the surface of the object and the receiving part, at which an analyzable indication of the propagation time of the electromagnetic radiation can still be measured by the receiving part of the detector.

[0027] Because the theoretically possible maximum measurement distance is very difficult to measure, one embodiment of the present invention is based on a measured maximum measurement distance, which is typically slightly smaller than the theoretical maximum measurement distance, but is a good approximation.

[0028] It is desirable to keep the light flux essentially constant over all measurement distances. In the prior art, optical systems and detectors are optimized for this purpose by optimized but fixed selection of focal length, aperture distance, parallax angle, aperture position, and aperture shape. The aperture distance is optimized so that the focal point is located in the aperture plane at a given nominal maximum measurement distance. The parallax angle and aperture shape are adapted to the nominal extinction. However, when turbidity changes, the actual maximum measurement distance can be significantly greater or less than the nominal or theoretical maximum measurement distance.

[0029] In one embodiment of the present invention, the criterion for setting one of the above parameters is defined such that, at the maximum measurement distance that the measurement geometry allows for a given turbidity, the focus generated in a certain plane by the optical system is always in the aperture plane. In other words, one of the above parameters is set such that, at the maximum measurement distance, in particular for each maximum measurement distance measured, the aperture distance coincides with the focus formed for that maximum measurement distance. This condition can be met by appropriately setting one of the above parameters.

[0030] In another embodiment of the invention, the criterion for setting one of the above parameters is defined such that the power of the radiation focused by the optical system towards the receiver of the detector is substantially constant for all maximum measurement distances over a turbidity range, thereby making optimal use of the dynamic range of the detector for each maximum measurement distance.

[0031] In one embodiment of the present invention, the adjustment in step J) comprises: a) increasing the aperture distance or decreasing the focal length if turbidity increases; and b) decreasing the aperture distance or increasing the focal length if turbidity decreases.

[0032] In one embodiment, the aperture distance or focal length is increased or decreased for each maximum measurement distance measured so that the aperture distance matches the focus formed for that maximum measurement distance.

[0033] In one embodiment, the aperture distance or focal length is increased or decreased so that the power of radiation focused by the optical system towards the receiver of the detector is substantially constant for all maximum measurement distances over a range of turbidity.

[0034] In one embodiment of the present invention, the detection of the indication of the turbidity of the fluid in step I) is carried out by a turbidity sensor distinct from the detector, such turbidity sensors being known from the prior art in various embodiments.

[0035] For example, in one embodiment, the indication of turbidity is detected using optical methods. In one embodiment of the present invention, the attenuation (transmittance) of electromagnetic radiation along a measurement path is detected by a turbidity sensor, and this attenuation forms the indication of turbidity. In one embodiment, the side scattering of electromagnetic radiation in the fluid is detected by a turbidity sensor, and this side scattering forms the indication of turbidity.

[0036] However, in one embodiment of the present invention, the indication of turbidity of the fluid is detected in step I) by a detector used in the ToF method. There are many ways in which this detector can also be used to detect indications of turbidity of the fluid.

[0037] According to one embodiment of the present invention, detecting the indication of turbidity includes determining the power of reflected electromagnetic radiation incident on the detector with a propagation time shorter than the measurement distance for the object point currently being measured.

[0038] This embodiment is based on the following idea: By using the ToF method, the detected power can be measured as a function of the propagation time of the electromagnetic radiation between the radiation source and the detector and plotted as needed. In the absence of turbidity, the signal is ideally zero for all propagation times shorter than the propagation time to the object point on the object's surface. In the presence of turbidity, particles causing turbidity also cause electromagnetic radiation that does not reach the object's surface to reach the receiver. This electromagnetic radiation is reflected or scattered by particles before reaching the surface, significantly shortening its propagation time. The power of this radiation scattered to the detector by the turbidity of the fluid is an indicator of turbidity. The greater the turbidity, the more power reaches the receiver at propagation times shorter than the propagation time corresponding to the distance from the object's surface to the receiver. The curve of the plot of power as a function of propagation time due to scattering by particles in the fluid, and thus turbidity, is also called the turbidity bulge.

[0039] To utilize this principle and record an index of turbidity, many evaluation techniques are available. These involve recording the power as a function of the propagation time of the electromagnetic radiation. For example, a number of power measurements as a function of propagation time can be used, a median value can be formed, and from this median value, an integral of the power over a section of propagation times can be formed, all of which are before the propagation time required for radiation to or from the object. This integral is the index of turbidity.

[0040] Alternatively, in one embodiment, image and pattern recognition techniques, for example based on artificial intelligence, are used to assess the change in power as a function of transit time and determine an index of turbidity.

[0041] In one embodiment of the present invention, the maximum measured distance forms an indication of turbidity.

[0042] An alternative approach for detecting an indicator of turbidity using a detector that is also used to measure the indicator of the propagation time therefore comprises the steps of measuring, for a plurality of object points having different measurement distances from each other, an indicator of the propagation time of the electromagnetic radiation from a reference point to each object point, in each case respectively, determining the maximum measured distance measured from the indicators of the propagation time, and using the maximum measured distance measured as an indicator of the turbidity of the fluid. Such a method may also be called a "distance histogram".

[0043] If the field of view of the system is large enough, there will usually always be object points within the field of view where the electromagnetic radiation reflected by these object points can be detected well, barely, or no longer. In this way, the maximum measurement distance can be measured or determined from the measurement results for many object points.

[0044] In one embodiment, if all object points in the field of view are detectable (transparent or slightly turbid fluids), at least the conventional settings for focal length, aperture distance, parallax angle, aperture position or aperture shape are maintained. In particular, in such cases, the focal point is behind the object as seen from the radiation source. This prevents saturation of the detector by electromagnetic radiation reflected by the object in the case of close objects.

[0045] Because turbidity rarely changes suddenly, even if it is not possible to measure the maximum measurement distance for a particular object point in the field of view, there is no problem in maintaining at least the focal length, aperture distance, parallax angle, aperture position or aperture shape.

[0046] The maximum measurement distance of the system measured in this way can be equated to determining the signal-to-noise ratio for the combination of measurement system and fluid.

[0047] Such a distance histogram is advantageously based on a large number of measurements of the propagation times of object points, e.g., 50,000 object points. If one of the above parameters is set according to the maximum measurement distance, an optimized system for a given turbidity is obtained.

[0048] When a turbidity index is determined from such a distance histogram, the reflectivity of the object surface is included in the maximum measured distance and is therefore taken into account in addition to the turbidity when setting the above parameters: if the reflectivity of the object surface is low, the maximum measured distance between the surface and the receiver will be shorter than for a surface with ideal reflectivity.

[0049] In one embodiment of the present invention, the parallax angle is zero, ie the illumination and detection beam axes overlap.

[0050] In one embodiment of the present invention, the parallax angle between the illumination beam axis and the detection beam axis is different from zero degrees. Such parallax prevents radiation scattered from the near range of the optics from reaching the receiver, thereby preventing excess light from the near range of the optics from reaching the receiver and saturating the detector.

[0051] If the parallax angle is different from zero degrees, it is necessary that the focus is on the detection beam axis before and after adjusting the focal length in step J). Alternatively or additionally, if the aperture distance is set in step J), it must be ensured that the aperture is on the detection beam axis before and after the adjustment, as long as the parallax angle is different from zero degrees.

[0052] According to one embodiment of the present invention, where the parallax angle is different from zero degrees, when adjusting the aperture distance in step J), the aperture plane and the light receiving part are moved linearly relative to the optical system along the detection beam axis.

[0053] According to one embodiment of the present invention, when adjusting the aperture distance in step J), the parallax angle is additionally adjusted.

[0054] According to one embodiment of the present invention, the detector signal of the light receiving unit is amplified by an amplification factor according to the turbidity index.

[0055] At least one of the above-mentioned objects is also achieved by a system for inspecting an object placed in a turbid fluid, as set forth in the relevant independent claim. To this end, a system of the type mentioned in the introduction comprises, according to the invention, a turbidity detection device configured to detect an indication of turbidity during operation of the system and operatively connected to evaluation means, such that the evaluation means receives the indication of turbidity from the turbidity detection device during operation of the system, the evaluation means operatively connected to the at least one actuator, such that during operation of the system the at least one actuator receives a distance control signal from the evaluation device, and the evaluation device is arranged to determine the distance control signal in response to the indication of turbidity and output it to the at least one actuator during operation of the system, the at least one actuator configured and arranged to adjust at least a focal length, an aperture distance or an aperture shape in response to the distance control signal during operation of the system.

[0056] Insofar as aspects of the invention are described above with respect to methods, they also apply to corresponding systems for inspecting objects placed in a turbid fluid. Insofar as the methods are performed using a system according to the invention, the system comprises corresponding devices therefor. In particular, the system embodiments are suitable for carrying out the method embodiments described above.

[0057] In one embodiment of the invention, the evaluation device comprises a computer with a processor on which algorithms for data evaluation and control of the system are executed during operation of the system.

[0058] Further advantages, features and applicability of the present invention will become apparent from the following description of embodiments and the accompanying drawings, in which similar elements are provided with the same reference numerals. [Brief explanation of the drawings]

[0059] [Figure 1] 1 is a schematic diagram of a LIDAR system for inspecting underwater structures. [Figure 2] 2 is a schematic plot of normalized signal amplitude of electromagnetic radiation incident on a receiver of the system of FIG. 1 as a function of propagation time; [Figure 3] FIG. 1 is a schematic diagram of an embodiment of a method for adjusting opening distance depending on water turbidity. [Figure 4] FIG. 10 is a schematic diagram of another embodiment of a method for adjusting opening distance depending on water turbidity. DETAILED DESCRIPTION OF THE INVENTION

[0060] FIG. 1 shows an exemplary configuration of a LIDAR system 1 according to the present invention. A laser 2 as a radiation source generates and emits modulated electromagnetic radiation 3. A deflection unit 4 directs the radiation 3 onto the surface 5 of an object 7 placed in water 6. The deflection unit 4 enables the surface 5 of the object 7 to be scanned point by point, thereby generating a complete image of the surface 5. The radiation 8 reflected or scattered by the surface 5 of the object 7 is detected by a detector 9. The detector 9 essentially comprises an optical system 10 and a receiver 11. The optical system 10 focuses the reflected electromagnetic radiation 8 toward the receiver 11 via a focal length. In the illustrated embodiment, the illumination beam axis 12 and the detection beam axis 13 form a slight parallax angle α, i.e., the beam axes 12, 13 do not overlap each other.

[0061] The distance between the surface 5 of the object 7 and the receiver 11 of the detector 9 is referred to as the measurement distance M. In the illustrated system 1, the modulation frequency of the modulation of the amplitude of the electromagnetic radiation is used as a reference signal 14 and is correlated in an evaluation device 15 with the modulation signal amplitude recorded by the receiver 11 of the detector 12. From this correlation, it is possible to determine a measure of the propagation time of the electromagnetic radiation 8 between the surface 5 of the object 7 and a reference point in the beam path of the system 1. In the illustrated embodiment, the receiver 11 is the reference point. Therefore, the measure of the propagation time of the electromagnetic radiation 8 in the illustrated embodiment directly corresponds to the measurement distance M.

[0062] Figure 2 shows a typical normalized signal amplitude of radiation 8 detected by receiver 11 as a function of propagation time in nanoseconds for a single object point 16 on surface 5. In the plot of Figure 2, reference numeral 17 denotes a reflection from surface 5. Additionally, a reflection from a disk 19 in front of deflection unit 4, indicated by reference numeral 18, can be seen in the signal. Furthermore, a large signal component 20 can be seen between reflection 18 from disk 19 and reflection from surface 5. This signal component 20 is due to scattering of electromagnetic radiation 3 by particles in water 6 and is therefore also called the turbidity belly.

[0063] Depending on the turbidity of the water 6, the size of the turbidity berries 20 increases or decreases. As the turbidity increases, the amount of radiation reaching the object surface and from there to the receiver gradually decreases. In the worst case scenario, the signal 17 from the surface 5 of the object 7 that should actually be detected is lost in the noise. In this case, the object 7 is outside the maximum measurement distance M.

[0064] The system 1 is provided with an arrangement that allows it to adjust according to, and thus adapt to, the turbidity of the water 6. For this purpose, the system 1 comprises a turbidity sensor 21, which is also arranged in the water. The turbidity sensor 21 detects the backscattering that the electromagnetic radiation 22 experiences as it passes through the water 6. This backscattering forms an indication of the turbidity of the water 6. A measurement signal 25 from the turbidity sensor 21, which contains the indication of the turbidity, is transmitted to the evaluation device 21.

[0065] The evaluation device 15 uses the turbidity indicator to calculate the optimum setting of the aperture distance B between the collection optics 10 and the aperture plane 26, which will now be explained with reference to the schematic diagram of Figure 3. As the turbidity increases, the maximum measurement distance M at which the propagation time from the surface 5 of the object 7 can be barely detected by the system increases. max In the example shown, the maximum measurement distance M max M max The maximum measurement distance M has been reduced to max In order to optimize the system for the ', the system shown is configured such that the aperture distance B between the collection optics 10 and the aperture plane 26 of the aperture in the form of a pinhole aperture 27 is adjustable. In the embodiment shown, the focal length of the optics 10 and the detector distance between the pinhole 27 and the light receiving unit 11 are constant. Therefore, the maximum measurement distance M max ,M max As ' decreases, the focus produced by optical system 10 moves away from optical system 10. In the illustrated embodiment, the maximum measurement distance M max ,M maxIt is required that the focal point generated by the optical system 10 for B, B' always lies in the aperture plane 26. In this way, the flux of radiation reflected from the surface 5 of the object 7 is maximized, while the pinhole aperture 27 provides a high degree of shielding against radiation scattered by particles in the water. To this end, the evaluation device 15 increases the aperture distance B, B' via an actuator (not shown) that it controls itself if the turbidity increases, and decreases it if the turbidity decreases. To ensure that the detector distance between the aperture plane 26 and the receiver 11 nevertheless remains constant, the actuator moves the receiver 11 by the same distance as the pinhole 27.

[0066] 4 shows a schematic diagram of system 1 having a parallax between illumination beam axis 12 and detection beam axis 13. Illumination beam axis 12 and detection beam axis 13 form a parallax angle α that is greater than zero. Due to this parallax, radiation scattered from the near range of optical system 10 in water 6 does not reach receiver 11. Due to the parallax, when the aperture distance is changed, the combination of receiver 11 and pinhole 27 must be moved together by an actuator along a line that coincides with detection beam axis 13.

[0067] In the spirit of the original disclosure, it is pointed out that all features that are obvious to a person skilled in the art from the description, drawings and claims, even if specifically described only in connection with certain further features, can be combined individually or in any combination with other features or feature groups, unless such combination is expressly excluded or is impossible or meaningless due to technical conditions, and a comprehensive and explicit description of all possible feature combinations has been omitted for the sake of brevity and readability of the description.

[0068] While the invention has been illustrated and described in detail in the drawings and foregoing specification, this illustration and description are by way of example only and are not intended to limit the scope of protection defined by the claims. The invention is not limited to the disclosed embodiments.

[0069] Variations of the disclosed embodiments will be apparent to those skilled in the art from the drawings, the description and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "one" or "a" does not exclude a plurality. The mere fact that certain features are recited in different claims does not exclude their combination. Reference numerals in the claims are not intended to limit the scope of protection. [Explanation of symbols]

[0070] 1 System 2 Laser 3 Modulated radiation 4 Deflection Unit 5 surface 6 water 7 Object 8 Reflected / Scattered Radiation 9 Detector 10 Optical system 11 Light receiving part 12 Irradiation beam axis 13 Detection beam axis 14 Reference Signal 15 Evaluation equipment 16 object point 17 Signal components from object points 18 Signal components from the disc 19 discs 20 Turbidity Berry 21 Turbidity sensor 22 Electromagnetic radiation of turbidity sensors 25 Signals containing turbidity indicators 26 Opening surface 27 Pinhole Aperture α parallax angle M Measurement distance Mmax, Mmax' Maximum measurement distance B,B' opening distance

Claims

1. A method for inspecting an object (7) placed in a turbid fluid (6), comprising: A) generating electromagnetic radiation (3) by a radiation source (2); B) emitting said electromagnetic radiation (3); C) modulating the amplitude or frequency of said electromagnetic radiation (3); D) illuminating the surface (5) of the object (7) at a plurality of object points (16) with the modulated electromagnetic radiation (3), said step of illuminating said surface (5) of said object (7) along an illumination beam axis (12); E) focusing the electromagnetic radiation (8) reflected from the object point (16) towards the receiving part (11) of the detector (9) by an optical system (10) having a focal length, The detector (9) has an aperture (27) having an aperture shape in an aperture plane (26), The opening surface (26) is spaced apart from the light receiving unit (11) by a detector distance, The aperture plane (26) is spaced apart from the optical system (10) by an aperture distance (B, B'); The collection is along the detection beam axis (13), the illumination beam axis (12) and the detection beam axis (13) form a parallax angle (α); The aperture (27) has an aperture position in a direction perpendicular to at least the illumination beam axis (12) or the aperture beam axis (13); the step in which the surface (5) of the object (7) is spaced a measurement distance (M) from the light receiving unit (11); F) detecting the electromagnetic radiation (8) reflected from the surface (5) of the object (7) by the receiver (11); For each of said plurality of object points (16), G) measuring a measure of the propagation time of said electromagnetic radiation (3, 8) from a reference point (11) in the beam path of said electromagnetic radiation (3, 8) to each of said object points (16); H) outputting said indication of said propagation time, I) detecting an indication of the turbidity of said fluid (6); J) adjusting at least the focal length, the aperture distance (B, B'), the parallax angle, the aperture position or the aperture shape in response to the turbidity index.

2. 2. The method of claim 1, wherein in addition to the propagation time indicator, intensity is measured in step G).

3. The adjustment in step J) is a) increasing the aperture distance (B, B') or decreasing the focal length if turbidity increases; and 3. The method according to claim 1, further comprising the step of: b) decreasing the aperture distance (B, B') or increasing the focal length if the turbidity decreases.

4. 4. The method according to any one of claims 1 to 3, wherein the detection of the indication of turbidity of the fluid (6) in step I) is performed using a turbidity sensor (21) different from the detector (9).

5. 4. The method according to any one of claims 1 to 3, wherein the detection of the indication of turbidity of the fluid (6) in step I) is carried out by means of the detector (9).

6. 6. The method according to claim 1, wherein detecting the indication of turbidity comprises determining the power of the reflected electromagnetic radiation incident on the detector (9) with a propagation time shorter than the measurement distance (M) of the object point (16).

7. Detecting the indicator of turbidity includes: - measuring, for a plurality of object points (16) having different measurement distances (M), in each case a respective measure of the propagation time of the electromagnetic radiation (3, 8) from the reference point (11) to each of the object points (16); The maximum measured distance (M ｍａｘ , M ｍａｘ ') and The measured maximum measurement distance (M ｍａｘ , M ｍａｘ and using the turbidity of said fluid as an indicator of said turbidity of said fluid.

8. the illumination beam axis (12) and the detection beam axis (13) form a parallax angle (α) different from zero degrees; When adjusting the focal length at least in step J), the focal point is on the detection beam axis (13) before and after the adjustment, or 8. The method according to claim 1, wherein when adjusting the aperture distance (B, B'), the aperture (27) is on the detection beam axis (13) before and after the adjustment.

9. 9. The method according to claim 1, wherein when adjusting the aperture distance (13) in step J), the aperture plane (26) and the light receiving unit (11) are moved linearly relative to the optical system along the detection beam axis (13).

10. 10. The method according to claim 8 or 9, wherein when adjusting the aperture distance (B, B') in step J), the parallax angle (α) is additionally adjusted.

11. 11. The method according to any one of claims 1 to 10, further comprising the step of: M) amplifying the detection signal of the light receiving unit (11) with a gain factor that depends at least on turbidity or reflectance.

12. A system for inspecting an object (7) placed in a turbid fluid (6), comprising: A radiation source (2), the radiation source (2) configured to generate and emit electromagnetic radiation during operation of the system; A modulation means, said modulation means being configured to modulate the amplitude or frequency of said electromagnetic radiation during operation of said system (1); An irradiation device (4), an illumination device (4) configured and arranged to illuminate a surface (5) of the object (7) at a plurality of object points (16) with the modulated electromagnetic radiation (3) during operation of the system (1); A detector (9) having a light receiving unit (11), An opening (11) having an opening shape in an opening surface (26), the detector (9) in which the aperture surface (26) is spaced from the light receiving portion (11) by a detector distance; An optical system (10), comprising: a detector (9) configured and arranged to focus the electromagnetic radiation (8) reflected from the object (10) towards the light receiving portion (11) of the detector (9) with a focal length; the optical system (10), wherein the aperture plane (26) is spaced apart from the optical system (10) by an aperture distance (B, B'); An evaluation device (15), operatively connected to the light receiving unit (11) to receive a detector signal from the light receiving unit (11) during operation of the system (1); During operation of the system (1), for each of the plurality of object points (16): determining a measure of the propagation time of the electromagnetic radiation (8) from a reference point (11) in a beam path of the modulated electromagnetic radiation (8) to each of the object points (16); and outputting an indication of the propagation time, Further comprising a turbidity detection device (21) and at least one actuator, The turbidity detection device (21) configured to detect an indication of turbidity during operation of the system (1); operatively connected to the evaluation device (15) such that during operation of the system (1), the evaluation device (15) receives an indication of the turbidity from the turbidity detection device (21); The evaluation device (15) operatively connected to the at least one actuator, wherein during operation of the system (1), the at least one actuator receives a distance control signal from the evaluation device (15); and During operation of the system (1), the evaluation device is configured to determine the distance control signal depending on the turbidity indicator and to output it to the at least one actuator, The at least one actuator 10. The system of claim 9, wherein during operation of the system (1), the at least one actuator is constructed and arranged to adjust at least a focal length, an aperture distance (B, B') or an aperture shape in response to the distance control signal.

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