Scanning instrument for laser-based aerial survey comprising beam deflection device

Abstract

A scanning instrument for laser-based aerial survey includes a beam deflection device. The invention relates to a scanning instrument for laser-based aerial survey. The guide deflector is mounted in a fixed spatial relationship with the first wedge and has a cross-section smaller than that of the two wedges. The outgoing measuring beam first passes through the guide deflector and then passes through the two wedges. At most a small portion of the return radiation passes through the guide deflector, and a larger portion of the return radiation is deflected by the two wedges without interacting with the guide deflector. The guide deflector produces a guide of the outgoing measurement beam with respect to a direction of movement of the outgoing measurement beam associated with a helical scanning pattern generated by rotation of the two wedges. Due to the resulting guide and the specific arrangement of the two wedges and guide deflectors, the dot diagram of the helical scan pattern drawn on the receiver is compressed, while providing a compact deflection arrangement for generating different helical scan patterns.

Description

Technical Field

[0001] The present invention relates to a scanning instrument for laser-based airborne surveying, the scanning instrument comprising a beam deflection device for deflecting an outgoing measurement beam and radiation returned from the target area by the outgoing measurement beam. Background Art

[0002] In laser-based airborne surveying, beam deflection components (such as movable mirrors or refractive or diffractive optical devices) are used to direct the measurement beam towards the target surface according to a defined scanning pattern. As an example, the measurement beam provides a sequence of laser pulses, and the distance between the scanning instrument and the observed surface points of the target area is mapped by means of the pulse time-of-flight method. The measured distances are associated with the target angles given by the scanning pattern and the known position of the scanning instrument to determine the 3D point cloud of the observed target area.

[0003] Commonly used scanning patterns include the so-called zigzag pattern, also known as the whiskbroom pattern or cross-track pattern, in which the measurement beam sweeps back and forth from left to right perpendicular to the flight direction of the scanning instrument. For example, such a scanning pattern is achieved by using a scanning mirror.

[0004] Other commonly used scanning patterns include the spiral scanning pattern, in which the measurement beam is moved to map the spiral scanning pattern onto the target area to be observed. For example, in the so-called Palmer scan, the spiral scanning pattern is generated by a combination of a circular scan of the measurement beam provided, for example, by a rotating tilt-deflection mirror or a rotating refractive wedge and the forward flight movement of the scanning instrument.

[0005] Different scanning patterns are selected according to the required scanning requirements. For example, compared with spiral scanning, zigzag scanning can provide a larger field of view in the direction perpendicular to the flight direction. Therefore, a larger area can be observed in a shorter time. On the other hand, in spiral scanning, each surface point is scanned from different perspectives, so the shadow effect (e.g., the blocking of the measurement beam by trees or buildings) is minimized.

[0006] One problem with such airborne scanning instruments relates to the angular difference that occurs between the outgoing measurement beam and the returned radiation due to the finite round-trip time of the emitted measurement beam traveling at the speed of light and the rapidly changing deflection angles provided by the fast-steering optics. This problem is also known as the so-called lag angle effect, which causes the receiver to be displaced from the position where the measurement beam hits the ground. Due to the rapid movement of the deflection optics, the imaged measurement points move on the receiver surface, which requires the receiver surface to be larger than the imaged measurement points. However, such an overly large receiver surface usually results in increased noise, lower speed, and higher cost.

[0007] For example, the required field of view of the receiver can be 10 to 20 times the size of the measurement beam, which results in a strong increase in solar background noise that limits the detection threshold of weak return pulse signals. One option could be to increase the transmission power to achieve a sufficient signal-to-noise ratio (S / N). However, increasing the transmission power is typically limited by eye safety regulations, the availability of lasers, and results in increased costs.

[0008] Various measures are known to compensate for the lag angle. For example, the angular difference occurring between the outgoing and incoming laser pulses is compensated by compensation optics (e.g., additional tilting mirrors or rotating wedges) arranged in the transmitter beam path or the receiver beam path, where the tilting or rotating angle of the compensation optics can be set according to the measured distance and angular velocity of the measurement beam. Another possibility is to use an adaptive detector mask (e.g., by a movable blocking member on the receiver surface) to provide distance-dependent activation of different detection areas on the receiver surface. There are also available detectors that provide electronic activation of different domains on the receiver surface according to the measured distance (and angular scan speed).

[0009] Optomechanical lag angle compensation generally results in the scanning instrument becoming heavy and bulky. For example, implementing multiple galvanometers in the receiver path, which leads to an increase in the total weight and size of the scanning instrument, which may cause the scanning instrument to be unusable for smaller airborne carriers because the scanning instrument is too large and heavy.

[0010] Furthermore, when using certain scanning patterns, large and rapid variations in the angular velocity of the measurement beam for different regions of the scanning pattern may occur. For example, in an elliptical scanning pattern generated by moving the measurement beam to follow an ellipse, the angular velocity of the measurement beam in the region of each of the two main vertices on the major axis of the ellipse is higher and varies much faster than in the region of each of the two minor vertices on the minor axis of the ellipse.

[0011] Another problem with airborne scanning instruments relates to so-called near-field noise, which is generated by the radiation returned from the outgoing measurement beam from nearby obstacles such as particles or clouds. Such return signals potentially lead to false measurements because the time-of-flight calculated with these reflected signals (e.g., pulses) does not represent the distance to the intended target area. Generally, the intensity of the light backscattered from near-field obstacles (e.g., due to little backscattering) is similar to the intensity of the signals regularly reflected from the target, making it difficult to distinguish between the actual measurement signal and the false measurement signal.

[0012] For example, the near-field noise problem can be solved by using a special type of receiver having a central detection area and an outer detection area. In the case where the receiver has a fixed focus that is essentially set to infinity, the actual measurement signal returning from a far target area impinges only on the central detection area, where the radiation returning from nearby objects impinges on both the central detection area and the outer detection area.

[0013] Typically, off-the-shelf receivers are within a limited size and dimension range. It may be difficult or impossible to find a receiver with an optimized overall size and an optimal size of its detection surface (e.g., to ensure that the actual measurement signal impinges only on the central detection area and the near-field return radiation impinges on both the central detection area and the outer detection area). Summary of the Invention

[0014] Accordingly, an object of the present invention is to provide a scanning instrument for laser-based aerial surveying, which overcomes the deficiencies of the prior art, and in particular provides a more compact scanning instrument that can be carried by a smaller aircraft such as a helicopter or a drone.

[0015] Another object is to provide a scanning instrument for laser-based aerial surveying that provides more efficient scanning when using a helical scan pattern.

[0016] Another object is to provide a scanning instrument for laser-based aerial surveying, especially for near-field noise, which is less error-prone while providing a compact overall setup.

[0017] The present invention relates to a scanning instrument configured to be mounted on an airborne vehicle and for acquiring point cloud data representing a target area. The scanning instrument includes beam deflection means for deflecting an outgoing measurement beam and the radiation returning from the target area of the outgoing measurement beam. The beam deflection means includes two wedges arranged one after another in the direction of the outgoing measurement beam, and the two wedges are mounted to be rotatable about a common axis of rotation. Each of the two wedges has an optical property for deflecting incident radiation, and the acquisition of the point cloud data includes emitting the outgoing measurement beam and receiving the radiation returning from the target area via the beam deflection means while rotating the two wedges about the axis of rotation.

[0018] The wedge through which the outgoing measurement radiation first passes among the two wedges is referred to herein as the "upstream" wedge, and the other of the two wedges is referred to herein as the "downstream" wedge. For example, each of the two wedges is mounted to be rotatable about a central axis of a part of the beam path of the outgoing measurement beam. The upstream wedge has optical properties that provide a beam deflection with a first deflection angle, and the downstream wedge has optical properties that provide a beam deflection with a second deflection angle. The first deflection angle and the second deflection angle may be the same or different. As an example, the second deflection angle is different from the first deflection angle, for example, where the difference between the first deflection angle and the second deflection angle falls within an interval of 3° to 15°.

[0019] For example, the acquisition of point cloud data includes the rotation of the upstream wedge about the rotation axis at a first rate in a first direction and the rotation of the downstream wedge about the rotation axis at a second rate in a second direction. This allows the scanning instrument to provide movement of the outgoing measurement beam according to different scanning patterns, for example, by setting the same rotation direction of the two wedges and by setting the opposite rotation directions of the two wedges.

[0020] As an example, the scanning instrument is configured to provide at least one of a circular scanning pattern, an elliptical scanning pattern, a flower scanning pattern, and a Lissajous scanning pattern.

[0021] The beam deflection device includes a guiding deflector that is mounted to be rotatable about the rotation axis and has optical properties for deflecting incident radiation. For example, the guiding deflector is embodied as another wedge. The guiding deflector has a maximum extent in a direction perpendicular to the rotation axis that is smaller than the extent of each of the two wedges. The guiding deflector is arranged such that the outgoing measurement beam passes through the guiding deflector, and the guiding deflector is mounted in a fixed spatial relationship with the wedge through which the outgoing measurement beam first passes among the two wedges (the upstream wedge).

[0022] In particular, the guiding deflector and the upstream wedge are configured and arranged such that for light rays incident from a direction parallel to the rotation axis, the projection of the light rays deflected by the guiding deflector onto a projection plane perpendicular to the rotation axis intersects the projection of the light rays deflected by the upstream wedge onto the projection plane. In other words, the guiding deflector and the upstream wedge have a phase shift in their orientations about the rotation axis such that the guiding deflector deflects the outgoing measurement beam at different azimuth angles in the projection plane.

[0023] In particular, the size of the guiding deflector is set to match the beam diameter or beam size (cross-section) of the outgoing measurement beam, but has a smaller cross-section than the cross-sections of the upstream wedge and the downstream wedge. Thus, at most a small fraction of the return radiation passes through the guiding deflector, while a larger fraction of the return radiation is deflected by the upstream wedge and the downstream wedge without interacting with the guiding deflector.

[0024] The beam deflection device according to the invention provides for a compact deflection arrangement for generating different helical scan patterns, such as circular scan patterns and elliptical scan patterns, while the guiding deflector is arranged to provide a deflection direction of the outgoing measurement beam that is different from the deflection direction of the upstream wedge, and (for a nominal measurement distance and a nominal range of the rotational speed of the two wedges) reduces the angular difference that occurs between the outgoing measurement beam and the return radiation due to the finite round-trip time of the outgoing measurement beam (so-called lag angle compensation).

[0025] In one embodiment, each of the two wedges has an inner region arranged around a rotational axis, for example, where the rotational axis is coaxial with the above-mentioned central axis of the section of the beam path of the outgoing measurement beam. In addition, each of the two wedges has an outer region arranged around the respective inner region, where the beam deflection device is configured such that the outgoing measurement beam only passes through the inner region, and the radiation returning from the target region of the outgoing measurement beam can pass through the outer region, where the size of the guiding deflector is set and arranged (e.g., completely) to cover the inner region of the upstream wedge. For example, the size of the guiding deflector is designed and arranged such that it completely covers the inner region of the upstream wedge but does not cover the outer region of the upstream wedge.

[0026] As an example, the guiding deflector is configured to provide a beam deflection with a third deflection angle and is arranged to be pierced by the above-mentioned central axis of the section of the beam path of the outgoing measurement beam.

[0027] In another embodiment, the guiding deflector is mounted on or in the upstream wedge, for example, where the guiding deflector is glued to the upstream wedge.

[0028] In another embodiment, the guiding deflector and the upstream wedge are configured and arranged such that the outgoing measurement beam is first deflected by the guiding deflector and then by the upstream wedge, where the projection of the outgoing measurement beam deflected by the guiding deflector onto a projection plane perpendicular to the rotational axis intersects the projection of the outgoing measurement beam deflected by the upstream wedge onto the projection plane at an angle ranging from 70 degrees to 110 degrees.

[0029] For example, in such an embodiment, the guiding deflector is configured to deflect the incident radiation at a deflection angle of less than 0.25°.

[0030] In another embodiment, the projection of the outgoing measurement beam deflected by the guiding deflector intersects the projection of the outgoing measurement beam deflected by the upstream wedge at an angle of 90 degrees.

[0031] In another embodiment, the upstream wedge has a recess which is arranged such that the outgoing measurement beam is deflected by the guiding deflector and passes through the recess without being deflected by the upstream wedge. As an example, the guiding deflector is embodied as another wedge arranged in the recess of the upstream wedge.

[0032] Depending on the selected scan pattern generated by the beam deflection device (generated by setting defined values of the rotation rates of the two wedges and by setting defined rotation directions of the two wedges relative to each other), there may still be some remaining movement of the measurement spot on the receiver surface of the scanning instrument. However, the beam deflection device according to the invention provides a beneficial compromise between the simplicity of the hysteresis angle compensation (which, for example, enables a sufficiently small size and weight of the scanning instrument and low opto-mechanical complexity) and the small remaining spot movement on the receiver surface (which, for example, enables the use of a receiver providing a sufficiently small signal-to-noise ratio due to a sufficiently small ratio between the receiver surface size and the spot size).

[0033] In particular, the beam deflection device according to the invention can be beneficially combined with a so-called near-field noise detector which is configured to take into account near-field return radiation (radiation returning from the outgoing measurement beam from nearby obstacles such as particles or clouds) based on an evaluation of a central detection region and an outer detection region on the receiver surface. In combination with a fixed focus which is typically set essentially to infinity, these types of receivers utilize the fact that the actual measurement signal returning from a more distant target region only impinges on the central detection region, whereas the radiation returning from nearby objects impinges on both the central detection region and the outer detection region.

[0034] Using an elliptical scan pattern generally results in an increased movement of the spot on the receiver surface because the angular velocity of the measurement beam increases in the region of each of the two main vertices on the major axis of the ellipse. The beam deflection device according to the invention inherently provides a compression of the region of the dot pattern drawn on the receiver in the regions associated with the two main vertices on the major axis of the ellipse. Thus, the dot pattern drawn on the receiver by the radiation (returning from the target region) of the outgoing measurement beam can be contained within the central detection region of the available near-field noise detector. At the same time, the beam deflection device allows tuning of the optical layout and the available near-field noise detector such that the near-field return radiation impinges on both the central detection region and the outer detection region.

[0035] In another embodiment, the scanning instrument includes a receiver having a receiving surface with a central detection area and an outer detection area. The receiver is configured to image only the radiation returning from a distance equal to or longer than a threshold distance of the outgoing measurement beam onto the central detection area, and image the radiation returning from a distance shorter than the threshold distance of the outgoing measurement beam onto the central detection area and the outer detection area. The receiver is also configured to provide separate detection of the radiation impinging on the central detection area and the radiation impinging on the outer detection area. This separate detection allows for distinguishing the return distance measurement signal (e.g., light pulse) provided by the outgoing measurement beam that is detected only by the central detection area from the return distance measurement signal detected by the central detection area and the outer detection area, where this distinction provides separation of the near-field return radiation from the return radiation from distances farther than the threshold distance and is thus assumed to be associated with the target area.

[0036] In another embodiment, the scanning instrument is configured to provide adaptation of the field of view of at least one scanning pattern by providing a different relative adjustment of the rotation of the upstream wedge with respect to the rotation of the other of the two wedges.

[0037] In another embodiment, the scanning instrument is configured to provide an elliptical scanning pattern that has an elliptical shape about a reference axis passing through the deflection device (by setting opposite rotation directions of the two wedges), wherein the rotation of the major axis of the elliptical scanning pattern about the reference axis can be set by providing a different relative adjustment of the rotation of the upstream wedge with respect to the rotation of the other of the two wedges. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The scanning instrument according to different aspects of the present invention will be described or explained in more detail below only by way of example with reference to working examples schematically shown in the accompanying drawings. Identical elements are marked with the same reference numerals in the figures. Specifically,

[0039] Figure 1 : Typical aerial surface scanning using the scanning instrument according to the present invention;

[0040] Figure 2 : Schematically shows the optical emission and reception paths of the scanning instrument according to an embodiment of the present invention;

[0041] Figure 3 : Shows a top view of the upstream wedge and the guiding deflector fixedly mounted on the upstream wedge according to an embodiment of the deflection device;

[0042] Figure 4 : Shows a perspective view of the upstream wedge and the guiding deflector according to another embodiment of the deflection device, wherein the guiding deflector is arranged in a recess of the upstream wedge;

[0043] Figure 5 schematically depicts the principle of a near-field noise detector using a fixed-focus imaging optical device, where the detector includes a central detection region and an outer detection region;

[0044] Figure 6 schematically depicts the operating principle of the receiver surface of an exemplary near-field noise detector based on an optical fiber device;

[0045] Figure 7 schematically shows, as Figure 6 shown, the movement of the return radiation of an elliptical scan pattern on a near-field noise detector, where the elliptical scan pattern has been generated by a beam deflection device according to the present invention. DETAILED DESCRIPTION

[0046] Figure 1 shows a typical aerial surface scan using a scanning instrument 1 according to the present invention carried on an airborne vehicle 2 (such as a helicopter). The scanning instrument 1 is configured to provide a distance map based on the pulsed time-of-flight method by an outgoing measurement beam 3. For example, the distance is determined by emitting laser pulses towards the ground with a lidar unit and measuring the emission and return times of the laser pulses, and the emission and return times are used to determine the round-trip time of the laser pulses. A deflection device is used to direct the outgoing measurement beam 3 that provides the laser pulses towards the ground according to a defined helical scan pattern 4 using two rotatable wedges (not shown here, see Figure 2 ).

[0047] The helical scan pattern 4 is generated by the combination of the forward flight movement of the scanning instrument and the circular and / or elliptical movement of the measurement beam 3 relative to the scanning instrument 1.

[0048] Figure 2 schematically shows the optical emission and reception paths of a scanning instrument according to the present invention, where the enlarged part on the left includes a beam deflection device 5 according to the present invention.

[0049] In the illustrated embodiment, the emission path and the reception path include coaxial portions, where the outgoing measurement beam 3 is coupled into the coaxial portion by a fixed deflection mirror 6. Then, the outgoing measurement beam 3 passes through the beam deflection device 5, which variably deflects the measurement beam 3 towards the ground 11 according to a defined helical scan pattern. The beam deflection device 5 includes a so-called upstream wedge 7 and a so-called downstream wedge 8, and the downstream wedge 8 is rotatably mounted around the central axis 9 of the coaxial beam path.

[0050] For example, the deflection angle provided by the upstream wedge is in the range of 5° to 30°, and the deflection angle provided by the downstream wedge is in the range of 5° to 30°.

[0051] Different helical scan patterns can be set by adjusting the rotation of the upstream wedge 7 relative to the rotation of the downstream wedge 8, for example, by adjusting the rotation rate and rotation direction of the two wedges relative to each other. The beam deflection device 5 further includes a guiding deflector 10, which is specifically implemented as another wedge in this case, and the other wedge is mounted in a fixed spatial relationship with the upstream wedge 7. For example, the guiding deflector 10 is glued to the upstream wedge 7.

[0052] The guiding deflector 10 is arranged to provide the deflection direction of the outgoing measurement beam 3, such that the additional deflection of the guiding deflector 10 results in the guiding of the outgoing measurement beam 3 relative to the moving direction of the outgoing measurement beam 3 associated with the helical scan pattern. For the nominal measurement distance and nominal range (providing different scan patterns) of the rotational settings (rotation rate and rotation direction) of the upstream wedge 7 and the downstream wedge 8 relative to each other, the guiding of the outgoing measurement beam 3 generated by the guiding deflector 10 results in a reduction in the angular difference that occurs between the outgoing measurement beam 3 and the return radiation.

[0053] As an example, as Figure 3 shown, Figure 3 A top view of the upstream wedge 7 and the guiding deflector 10 mounted on the upstream wedge 7 according to an embodiment of the deflection device is shown. The guiding deflector 10 deflects light incident parallel to the central axis 9 (here, the rotation axis of the upstream wedge) using an azimuthal deflection component 28 that is offset by 90° from the azimuthal deflection component 29 provided by the upstream wedge 7. Since the guiding deflector 10 is mounted on the upstream wedge 7, both the upstream wedge 7 and the guiding deflector 10 rotate at the same rotation rate and in the same rotation direction 16.

[0054] In other words, the guiding deflector 10 and the upstream wedge 7 are configured and arranged such that for light rays incident in a direction parallel to the central axis 9, the projection of the light rays deflected by the guiding deflector 10 onto the projection plane 30 perpendicular to the central axis 9 intersects the projection of the light rays deflected by the upstream wedge 7 onto the projection plane 30 at an angle of 90°. Thus, for light rays coaxial with the central axis 9, the deflection plane 17 of the guiding deflector 10 and the deflection plane 18 of the upstream wedge 7 intersect at an angle of 90°. The deflection plane 17 of the guiding deflector 10 includes the central axis 9 and a deflection axis that indicates the beam direction after deflecting an incident beam coaxial with the central axis 9 through the guiding deflector 10. The deflection plane 18 of the upstream wedge 7 includes the central axis 9 and the beam axis of the beam after the beam has been deflected by the upstream wedge 7 but before being deflected by the downstream wedge. Since the deflection angle provided by the guiding deflector 10 is typically small, e.g., less than 0.25°, the deflection plane 18 of the upstream wedge 7 is substantially a plane including the central axis 9 and a deflection axis that indicates the beam direction after deflecting an incident beam coaxial with the central axis 9 through the upstream wedge 7.

[0055] Figure 4 A perspective view depicting another embodiment of the upstream wedge 7 and the guiding deflector 10 is shown, where the guiding deflector 10 is arranged in a recess in the center of the upstream wedge 7. Thus, the guiding deflector forms a central transmission region 31 of the upstream wedge 7, which has deflection characteristics regarding the deflection angle similar to the rest of the upstream wedge 7, but is slightly rotated about the central axis relative to the rest of the upstream wedge 7. Thus, the central transmission region 31 of the upstream wedge deflects light rays incident parallel to the rotation axis of the upstream wedge using an azimuthal deflection component that is slightly rotated compared to the azimuthal deflection component provided by the rest of the upstream wedge 7. This is also referred to as the central transmission region 31, and the rest of the upstream wedge has a phase shift in the rotation direction of the upstream wedge.

[0056] Referring again to Figure 2 , the radiation returning from the target region 11 of the outgoing measurement beam again passes through the two wedges 7 and 8 and the imaging optics 12, such that the radiation 13 is only imaged onto the central detection region 14 of a so-called near-field noise detector. Due to the fixed focus of the receiving path, the radiation 15 returning from an object closer to the threshold distance of the outgoing measurement beam is imaged onto the central detection region 14 and the outer detection region 15 of the near-field noise detector.

[0057] This principle is depicted in further detail by Figure 5 Figure 5 ​Schematically shows the focusing effect of a fixed-focus imaging optical device 12 that images radiation associated with different measurement distances onto the receiver surface of a near-field noise detector. Radiation returning from three different measurement distances is shown, namely return radiation 19 from the target area to be measured, return radiation 20 from an object located at a threshold distance 21, and return radiation 22 from an object located closer to the threshold distance 21.

[0058] The receiver surface includes a central detection area 14 and an outer detection area 15, where radiation 19 returning from a distance farther than the threshold distance 21 is only imaged onto the central detection area 14. As the measurement distance becomes shorter and approaches the threshold distance 21, the imaging beam spot on the receiver surface becomes larger (the beam spot becomes increasingly blurred). For radiation 20 returning from the threshold distance 21, the imaging beam spot completely covers the central detection area 14. When the measurement distance is even further shortened, the imaging beam spot becomes larger than the central detection area 14 and thus impinges on both the central detection area 14 and the outer detection area 15 of the near-field noise detector.

[0059] Figure 6 Schematically depicts the operating principle of the receiver surface of an exemplary near-field noise detector. Here, the near-field noise detector is based on an optical fiber device for splitting the returned light into a central detection area and an outer detection area, where the optical fiber device includes a central fiber input 23 arranged at the center of the receiver surface and a plurality of outer fiber inputs 24 symmetrically arranged around the central fiber input 23. The central fiber input 23 and the outer fiber inputs 24 are each configured to collect the radiation impinging on the area covered by the corresponding fiber input and forward the collected radiation to the corresponding detection unit. This allows for the separate detection of the radiation impinging on the central detection area given by the central fiber input 23 and the radiation impinging on the outer detection area given by the outer fiber inputs 24, in order to use the separate detection to distinguish between the radiation returning from a distance farther than the threshold distance and the radiation returning within the threshold distance.

[0060] Figure 7 Schematically depicts the movement of the returned radiation on the near-field noise detector in an elliptical scan pattern as Figure 6 depicted, where the elliptical scan pattern has been generated by a beam deflection device according to the present invention.

[0061] Due to the guiding deflector of the beam deflection device, the signal spot trace 25 of the radiation returning from the target area (an area farther than the threshold distance, see above) on the receiver is compressed in the area of the two main vertices on the major axis of the ellipse projected onto the receiver. The dashed line 26 schematically indicates the projected ellipse without the guiding deflector. On the other hand, the signal spot trace 27 of the near-field return radiation (returning from a distance closer than the threshold distance, see above) is substantially circular and moves on the transition between the central detection area and the outer detection area.

[0062] As a result, the radiation associated with the signal spot trace 25 (the spot pattern drawn on the receiver) of the outgoing measurement beam returning from the target area is included in the central detection area, while the near-field return radiation impinges on the central detection area and the outer detection area.

[0063] Therefore, the guiding deflector and the near-field noise detector are selected such that the center of the imaging spot of the near-field return radiation on the receiving surface lies on the edge of the central optical fiber. This ensures that half of the near-field return radiation falls on the central optical fiber and half on the outer fiber bundle. Thus, no near-field return radiation is missed, and no near-field return radiation that does not reach the central optical fiber is detected. In particular, the setup is optimized such that at the lowest flight altitude, the true return radiation only reaches the central optical fiber. Therefore, the center of the image of the true return radiation remains in the area of the central optical fiber, and the resulting spot caused by a fixed focus set to infinity only covers the central optical fiber and does not reach the outer fiber bundle.

[0064] Although the above part has illustrated the present invention with reference to some preferred embodiments, it must be understood that many modifications and combinations can be made to the different features of the embodiments. All such modifications are within the scope of the appended claims.

Claims

1. A scanning device (1) configured to be mounted on an aerial vehicle (2) and used to acquire point cloud data representing a target area (11), wherein: The scanning device (1) comprises a beam deflection device (5) for deflecting an outgoing measuring beam (3) and radiation of the outgoing measuring beam (3) returning from the target area (11), wherein The beam deflection device (5) comprises two wedges (7, 8) arranged one behind the other in the direction of the outgoing measuring beam (3), the two wedges (7, 8) being mounted so as to be rotatable about a common axis of rotation (9) and having optical properties for deflecting incident radiation, and The acquisition of the point cloud data comprises: emitting the outgoing measurement beam (3) and receiving radiation of the outgoing measurement beam (3) returning from the target area (11) via the beam deflection device (5) while rotating the two wedges (7, 8) around the rotation axis (9), Features The beam deflection device (5) comprises a guide deflector (10), in particular the guide deflector is embodied as a further wedge, the guide deflector is mounted so as to be rotatable about the rotation axis (9) and has optical properties for deflecting incident radiation, wherein the guide deflector: having a maximum extent in a direction perpendicular to the axis of rotation (9) which is smaller than the extent of each of the two wedges (7, 8), is arranged so that the outgoing measurement beam (3) passes through the guide deflector, and The upstream wedge (7) is mounted in a fixed spatial relationship with the wedge through which the outgoing measuring beam (3) passes first of the two wedges.

2. The scanning device (1) according to claim 1, wherein: The two wedges (7, 8) each have an inner region arranged around the rotation axis (9) and an outer region arranged around the inner region, wherein the beam deflection device (5) is configured so that the outgoing measurement beam (3) only passes through the inner region and the radiation of the outgoing measurement beam (3) returning from the target area (11) can pass through the outer region, wherein the guide deflector (10) is sized and arranged to cover the inner region of the upstream wedge (7), in particular, wherein the guide deflector (10) is arranged and sized so that the guide deflector completely covers the inner region of the upstream wedge (7) but does not cover the outer region.

3. A scanning device (1) according to any one of the preceding claims, wherein: The guide deflector (10) is mounted on or in the upstream wedge (7), in particular wherein the guide deflector (10) is glued to the upstream wedge (7).

4. A scanning device (1) according to any one of the preceding claims, wherein: The guide deflector (10) and the upstream wedge (7) are configured and arranged with respect to each other so that, for a light ray incident from a direction parallel to the rotation axis (9), a projection of the light ray deflected by the guide deflector (10) onto a projection plane (30) perpendicular to the rotation axis (9) intersects with a projection of the light ray deflected by the upstream wedge (7) onto the projection plane (30).

5. The scanning device (1) according to claim 4, wherein: The guide deflector (10) and the upstream wedge (7) are configured and arranged so that the outgoing measurement beam (3) is first deflected by the guide deflector (10) and then deflected by the upstream wedge (7), wherein the projection of the outgoing measurement beam (3) deflected by the guide deflector (10) onto the projection plane (30) intersects the projection of the outgoing measurement beam (3) deflected by the upstream wedge (7) onto the projection plane (30) at an angle ranging from 70 degrees to 110 degrees.

6. The scanning device (1) according to claim 5, wherein: The projection of the outgoing measurement beam (3) deflected by the guide deflector (10) intersects the projection of the outgoing measurement beam (3) deflected by the upstream wedge (7) at an angle of 90 degrees.

7. The scanning device (1) according to any one of claims 4 to 6, wherein: The guide deflector (10) is configured to deflect the incident radiation at a deflection angle of less than 0.25°.

8. The scanning device (1) according to any one of claims 1 to 4, wherein: The upstream wedge (7) has a recess which is arranged such that the outgoing measurement beam (3) is deflected by the guide deflector (10) and passes through the recess without being deflected by the upstream wedge (7).

9. The scanning device (1) according to claim 8, wherein: The guide deflector (10) is embodied as a further wedge arranged in the recess of the upstream wedge (7).

10. A scanning device (1) according to any one of the preceding claims, comprising a receiver having a receiving surface with a central detection area (14) and an outer detection area (15), wherein: The receiver is configured to The radiation (19, 20) of the outgoing measurement beam (3) returning from a distance equal to or longer than a threshold distance (21) is imaged only onto the central detection area (14), and the outgoing measurement beam (3) is imaged imaging radiation (22) returning from a distance shorter than the threshold distance (21) onto the central detection region (14) and the outer detection region (15), providing separate detection of radiation impinging on said central detection area (14) and radiation impinging on said outer detection area (15), and The separate detection is used to distinguish between return distance measurement signals, in particular light pulses, provided by the outgoing measurement beam (3) and detected only by the central detection area (14) and return distance measurement signals detected by both the central detection area (14) and the outer detection area (15).

11. A scanning device (1) according to any one of the preceding claims, wherein: The two wedges (7, 8) are configured to deflect incident radiation at different deflection angles, in particular wherein the difference between the deflection angles of the two wedges (7, 8) falls within an interval of 3° to 15°.

12. The scanning instrument (1) according to any one of the preceding claims, configured to provide a movement of the outgoing measurement beam (3) according to different scanning patterns (4) by: Setting the same rotation direction of the two wedges (7, 8), and Opposite rotation directions of the two wedges (7, 8) are provided.

13. A scanning instrument (1) according to claim 12, wherein the scanning instrument is configured to provide adaptation of the field of view of at least one of the scanning patterns by providing different relative adjustments of the rotation of the upstream wedge (7) relative to the rotation of the other of the two wedges (8).

14. The scanning device (1) according to claim 12 or 13, the scanning device being configured to provide an elliptical scanning pattern having an elliptical shape with respect to a reference axis passing through the deflection device (5), wherein: The rotation of the major axis of the elliptical scanning pattern about the reference axis can be set by providing different relative adjustments of the rotation of the upstream wedge (7) with respect to the rotation of the other of the two wedges (8).

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