Lidar autocalibration

Abstract

In accordance with an example embodiment, there is provided a lidar assembly for atmospheric measurements, the lidar assembly comprising: a primary lens assembly to collimate an emitter beam originating from a first focus within the lidar assembly to illuminate a target at a distance from the lidar assembly, the second focus is used for focusing backscattered light from the target to a second focus in the lidar assembly; a transmitter arranged in the first focal point; a receiver arranged in the second focus; a beam reflector arranged between the first focal point and the main lens assembly wherein the lidar assembly comprises a calibrator subsystem comprising: a beam sampler arranged between the beam reflector and the main lens assembly for reflecting a portion of the emitter beam as a calibrator beam; and an optical device for transmitting the calibrator beam toward a selected target of the plurality of targets in the calibrator subsystem.

Description

Technical Field

[0001] An exemplary and non-limiting embodiment of the present invention relates to a calibration apparatus for a LiDAR (Light Detection and Ranging) device. Background Art

[0002] The term LiDAR refers to a surveying technique that measures the distance to a target by illuminating the target with pulsed laser light and measuring the pulses reflected from the target using a receiver. The reflected pulses may also be referred to as backscattered light or backscattered light. The basic components of a LiDAR device include a transmitter for generating pulsed laser light, a receiver for recording the backscattered light, an optical system for shaping and directing the emitted and backscattered light within the LiDAR device, and a processing component for determining the distance to the target based on the backscattered light.

[0003] Lidar-based devices can be used in a variety of fields, including agriculture, archaeology, the automotive industry, geology, mining, astronomy, robotics, etc. One application area of ​​particular interest for lidar devices is meteorology, where ground-based lidar devices can be used for atmospheric measurements, such as measuring backscatter from clouds and / or aerosols or vapors in the atmosphere. Such devices may be referred to as atmospheric lidars, which can be used to provide functions such as cloud height estimates and estimates of meteorological variables such as temperature, humidity, and / or wind.

[0004] Atmospheric LiDARs are typically installed outdoors for continuous operation, and such LiDAR devices can even operate for decades. Environmental conditions may cause changes in the components of the LiDAR device, which in turn degrades the accuracy of the measurements obtained from the LiDAR device. As a specific example in this regard, temperature changes in the operating environment of the LiDAR device can change the laser power and receiver sensitivity, which may have a significant adverse effect on the accuracy of the measurements of the LiDAR device. Another factor that may affect the accuracy of the measurement is the replacement of any LiDAR component on site: the transmitter, receiver, and optical system of the LiDAR are carefully pre-calibrated and aligned with each other when the device is manufactured to optimize the measurement performance. Replacing any of these components with new components under field conditions may cause slight misalignment and / or signal loss, and therefore, the accuracy of subsequent measurements may be affected. In addition, atmospheric LiDARs operating under field conditions are susceptible to vibrations and / or external shocks, which may not be enough to cause actual damage, but may still have an adverse effect on the alignment between the transmitter, receiver, and optical system of the LiDAR device, which may result in impaired measurement performance. Summary of the invention

[0005] It is therefore an object of at least some embodiments of the present invention to provide a technique that enables the accuracy and reliability of measurements made by a lidar device to be improved.

[0006] According to an example embodiment, a laser radar assembly for atmospheric measurement is provided, the laser radar assembly comprising: a main lens assembly for collimating a transmitter beam originating from a first focal point within the laser radar assembly to illuminate a target at a certain distance from the laser radar assembly, and for focusing backscattered light from the target to a second focal point within the laser radar assembly; a transmitter, arranged in the first focal point, for generating the transmitter beam for emission toward the main lens assembly; a receiver, arranged in the second focal point, for capturing the backscattered light entering the laser radar assembly through the main lens assembly; a beam reflector, arranged between the first focal point and the main lens assembly, for allowing the beam reflector to reach the main lens assembly In the case of a laser radar component, the backscattered light is reflected toward the second focus, wherein the laser radar component includes a calibrator subsystem, which includes: a beam sampler, arranged between the beam reflector and the main lens assembly, for reflecting a portion of the transmitter beam as a calibrator beam; and an optical device, for transmitting the calibrator beam toward a selected target among a plurality of targets in the calibrator subsystem, wherein the plurality of targets include at least the following items: a first scattering plate, arranged to produce diffuse reflection of the calibrator beam encountering its surface, thereby causing the backscattered calibrator beam to be transmitted to the receiver via the optical device, via the beam sampler and via the beam reflector; and at least one element, arranged to prevent the provision of the backscattered calibrator beam.

[0007] The exemplary embodiments of the invention presented in this patent application should not be interpreted as limiting the applicability of the appended claims. The verb "comprise" and its derivatives are used as open limitations in this patent application, which do not exclude the existence of unlisted features. Unless otherwise explicitly stated, the features described below can be freely combined with each other.

[0008] Certain features of the invention are set forth in the appended claims. However, the invention both as to its construction and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of certain exemplary embodiments when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which

[0010] Figure 1 schematically illustrates some components of a lidar assembly according to one example;

[0011] Figure 2Aschematically illustrates some components of a lidar assembly according to one example;

[0012] Figure 2B schematically illustrates some components of a lidar assembly according to one example;

[0013] Figure 3A schematically illustrates some components of a lidar assembly according to one example;

[0014] Figure 3B schematically illustrates some components of a lidar assembly according to one example;

[0015] Figure 4 schematically illustrates some components of a lidar assembly according to one example; and

[0016] Figure 5 Some components of a lidar assembly according to one example are schematically illustrated. DETAILED DESCRIPTION

[0017] Figure 1 Some components of a laser radar assembly 100 of a laser radar device suitable for atmospheric measurement are schematically illustrated. The laser radar assembly 100 includes a transmitter 101 for generating a light beam for illuminating a target at a certain distance from the laser radar assembly 100 and a receiver 102 for capturing backscattered light from the target. The transmitter 101 is arranged in a first focus of a main lens assembly 103, and the receiver 102 is arranged in a second focus of the main lens assembly 103, wherein the backscattered light can be guided to the second focus by reflection from a reflector 104. The reflector 104 is arranged between the transmitter 101 and the main lens assembly 103, and it is provided with a hole, which enables light from the transmitter 101 to pass through the reflector 104 and pass through the main lens assembly 103 to leave the laser radar assembly 100, and the reflector area around the hole is used to reflect the backscattered light entering the laser radar assembly 100 through the main lens assembly 103 to the receiver 102. The reflector 104 serves as an example of a beam reflector. Additional examples of this are provided later in this article.

[0018] According to one example, the reflector 104 and the hole therethrough are both circular, wherein the hole is disposed in or near the center of the reflector 104. Thus, the area of ​​the main lens assembly 103 may be (conceptually) divided into a central portion and an edge portion surrounding the central portion, wherein the central portion is used to collimate the light beam originating from the transmitter 101, and the edge portion is used to focus the backscattered light entering the lidar assembly 100 at the receiver 102 via the reflector 104. The light beam originating from the transmitter 101 may be referred to as a transmitter beam, and the backscattered light entering the lidar assembly 100 through the main lens assembly 103 and reflected to the receiver 102 via the reflector 104 may be referred to as a receiver beam. Due to the hole in or near the center of the reflector 104, the receiver beam has a ring shape, and it surrounds the transmitter beam emitted through the hole in the reflector 104. The route of the transmitter light beam from the transmitter 101 through the hole in the reflector 104 and through the main lens assembly 103 can be referred to as the first optical path, while the route of the receiver light beam through the main lens assembly 103 and to the receiver 102 via the reflector 104 can be referred to as the second optical path.

[0019] The diameter and optical properties of the main lens assembly 103, as well as the distance between the main lens assembly 103 and other components of the lidar assembly 100, can be selected according to the requirements of the lidar device in which the lidar assembly 100 is used. In a non-limiting example, the main lens assembly 103 includes a doublet lens with a diameter of 150 mm, and the lens assembly 103 is arranged at a distance of about 500 mm from the transmitter 101.

[0020] The transmitter 101 may be provided as a laser transmitter arranged to generate laser pulses of desired characteristics under the control of a control entity (not shown). The receiver 102 is arranged to capture a measurement signal describing the backscattered light and provide the captured measurement signal for analysis by the control entity and / or an external processing entity. As an example, the receiver 102 may include a photodetector, which is typically followed by an amplifier, while in another example, the receiver 102 may include a photodiode arranged to act as a photon counter.

[0021] Apart from Figure 1 In addition to those elements shown in FIG. 1 , the laser radar assembly 100 may also include a plurality of additional elements, Figure 1Only the general operating principle of a known lidar assembly is illustrated, which is applicable to a lidar device suitable for atmospheric measurement and serves as an example framework for describing various aspects related to automatic calibration of a lidar assembly applied in a lidar device. As a non-limiting example in this regard, the lidar assembly 100 may also include a transmitter pre-optical device for shaping the transmitter beam before it travels through the hole in the reflector 104, and / or a receiver pre-optical device for shaping the beam entering the lidar assembly 100 via the main lens assembly 103 before encountering the receiver 102. For example, the lidar assembly 100 may be as described in U.S. Patent Publication No. 2005 / 0179888A1, with reference to Figures 3 and Figure 4 as described in detail.

[0022] In addition to the laser radar assembly 100, the laser radar device using the above-mentioned laser radar assembly 100 also includes a (tubular) housing, which is used to protect the components of the laser radar assembly 100 and other components of the laser radar device arranged therein. The laser radar device also includes a control entity, which is arranged to: control the operation of the transmitter 101, and control the capture of the measurement signal via the operation of the receiver 102, and the control entity can also be arranged to: implement analysis of the measurement results, and / or transmit the measurement signal to an external processing entity to implement analysis therein. The laser radar device may also include a user interface (UI), which includes a user input component (e.g., one or more keys, one or more buttons, a touch screen, a touch pad, etc.) for inputting control inputs for controlling the operation of the laser radar device, and includes an output component (e.g., a display or a touch screen) for providing information about the operating status of the laser radar device to the user and / or for displaying measurement results to the user. The control entity can be implemented through the operation of a computing device, which includes one or more processors and one or more memories for storing one or more computer programs, wherein the one or more computer programs are arranged to: when executed by the one or more processors, cause the computing device to operate as a control entity of the lidar device according to the present disclosure.

[0023] Figure 2A Schematically illustrates some components of a lidar assembly 200, which includes the components described above for the lidar assembly 100 and a conceptual example of a calibrator subsystem, the implementation of which is described below by reference to Figure 3A , Figure 3B , Figure 4 and Figure 5 In particular, Figure 2AThe example of is used to illustrate the concept of using the calibrator subsystem to create a model of the receiver beam, which enables automatic calibration of the lidar assembly 200 under the control of the control entity of the lidar assembly 200. However, Figure 2A The conceptual example illustrates an arrangement in which the calibrator subsystem is always active, which would interfere with the normal operation of the lidar assembly 200. Therefore, in an actual implementation, the calibrator subsystem is also provided with an activation mechanism that enables the calibrator subsystem to be selectively activated or deactivated (deactivating), as described in the non-limiting example provided below. In the present disclosure, the automatic calibration operation enabled by the calibrator subsystem is primarily referred to as calibration, however it may also be referred to as automatic calibration because the lidar assembly 200 is able to implement calibration during its operation without the involvement of external calibration tools and / or without the intervention of maintenance personnel.

[0024] It is worth noting that Figure 2A The illustrations and subsequent illustrations should be construed as highly schematic, as they are not intended to accurately depict the relative positions of the components appearing therein, their sizes relative to each other, the actual appearance of the corresponding elements of the illustrated lidar assembly, or the transmission of light through the optical components of the illustrated lidar assembly, but rather the illustrations serve as a framework for facilitating the description of certain functional and structural aspects associated with various examples of lidar assemblies according to the present disclosure.

[0025] exist Figure 2A In the conceptual example shown in , the etalon subsystem includes a beam sampler 215, an etalon lens assembly 213, and a scattering plate 216. The beam sampler 215 is arranged to intersect the first optical path and the second optical path in a position between the reflector 104 and the main lens assembly 103, and it is configured to reflect a portion of the transmitter beam toward the etalon lens assembly 213 and pass the remaining portion of the transmitter beam toward the main lens assembly 103. The beam sampler 215 also passes most of the beam in the receiver beam from the direction of the main lens assembly 103 toward the reflector 104 and further toward the receiver 102. The portion of the transmitter beam reflected from the beam sampler 215 toward the etalon lens assembly 213 (for transmission to the scattering plate 216) can be referred to as the etalon beam, and the remaining portion of the transmitter beam passed toward the main lens assembly 103 can be referred to as the main transmitter beam.

[0026] The beam sampler 215 can be arranged to reflect a predefined percentage of the transmitter beam, and therefore a predefined portion of the radiant flux of the transmitter beam, as a collimator beam. In a non-limiting example, the beam sampler 215 can be operated to reflect approximately 4% of the transmitter beam as a collimator beam, while the remaining approximately 96% of the transmitter beam can be passed to the main lens assembly 103 as the main transmitter beam. In one example, the beam sampler 215 includes a glass plate that is arranged in a position between the reflector 104 and the main lens assembly 103 so that it intersects the transmitter beam originating from the transmitter 101 (and the receiver beam arriving from the direction of the main lens assembly 103) at an oblique angle. The side of the glass plate facing the transmitter 101 is preferably uncoated or provided with a weakly reflective coating, while the opposite side of the glass plate can be provided with an anti-reflective coating to prevent unnecessary losses and multiple reflections in the transmitter beam and the receiver beam. Using uncoated glass as the side of the glass plate facing the transmitter results in approximately 4% of the transmitter beam being reflected as a collimator beam.

[0027] Generally speaking, the collimator subsystem includes one or more targets and includes an optical device for transmitting a collimator beam to one of the targets in the collimator subsystem. Figure 2A In the lidar assembly 200 of the conceptual example, the optical device includes an etalon lens assembly 213, and one or more targets include a scatter plate 216, wherein the etalon lens assembly 213 is arranged to focus the etalon beam at the surface of the scatter plate 216. In one example, the etalon lens assembly 213 includes one or more lenses sharing the same optical axis, and the one or more lenses are arranged to: collimate the light transmitted from the etalon beam reflected from the beam sampler 215, and focus the collimated light at the surface of the scatter plate 216. The diameter and optical properties of the etalon lens assembly 213 and the length of the optical path from the beam sampler 215 to the scatter plate 216 can be selected according to the requirements of the lidar device using the lidar assembly 200.

[0028] In a non-limiting example, the calibrator lens assembly 213 includes a pair of lenses sharing the same optical axis, wherein both lenses have an optical design similar to the optical design of the main lens applied in the main lens assembly 103, and both lenses have a diameter that is substantially half the diameter of the main lens applied in the main lens assembly 103. Thus, the pair of lenses of the calibrator lens assembly 213 may have optical properties substantially similar to the optical properties of the main lens of the main lens assembly 103, but each has a size that is substantially half the size of the main lens. In a non-limiting example in this regard, the pair of lenses of the calibrator lens assembly 213 and the main lens of the main lens assembly 103 may be provided as respective doublets. The use of such a lens arrangement in the calibrator lens assembly 213 and the main lens assembly 103 results in accurate modeling of the optical aberration characteristics of the main lens assembly 103 in the calibrator subsystem, thereby facilitating accurate (automatic) calibration of the lidar assembly 200 via operation of the calibrator subsystem.

[0029] The scatter plate 216 of the calibrator subsystem is arranged to provide diffuse reflection of the calibrator beam encountering the surface of the scatter plate 216. The diffuse reflection properties of the scatter plate 216 simulate the diffuse reflection properties of an atmospheric target such as a cloud, and the scatter plate 216 receives a scaled version of the image of the transmitter beam that would be formed on the surface of the atmospheric target when encountering the (primary) transmitter beam. Thus, in response to the calibrator beam encountering the scatter plate 216, the diffuse reflection from the scatter plate 216 provides a backscattered calibrator beam. The diffuse reflection surface of the scatter plate 216 may be made of, for example, a suitable ceramic material, such as (substantially white) aluminum oxide (Al2O3) or polytetrafluoroethylene (such as ).

[0030] The backscattered collimator beam generated by diffuse reflection from the scattering plate 216 is transmitted in the opposite direction through the optical device (which is at Figure 2A 104), and is reflected by beam sampler 215 toward reflector 104, which in turn reflects the backscattered collimator beam toward receiver 102. Thus, the backscattered collimator beam appears to receiver 102 as if it were a receiver beam backscattered from an atmospheric target such as a cloud.

[0031] Figure 2BSome components of the laser radar assembly 200' are schematically illustrated, and the laser radar assembly 200' is a variation of the laser radar assembly 200. The difference from the laser radar assembly 200 is that the optical device of the calibrator subsystem also includes a calibrator beam reflector 217, which is used to reflect the calibrator beam received via the calibrator lens assembly 213 toward the scattering plate 216, so that the reflected calibrator beam is focused on the surface of the scattering plate 216. The calibrator beam reflector 217 is also used to reflect the backscattered calibrator beam from the direction of the scattering plate 216, through the calibrator lens assembly 213 toward the beam sampler 215, and further reflected to the receiver 102 via the reflector 104. Figure 2A Similar to the laser radar assembly 200, Figure 2B The lidar assembly 200' also serves as a conceptual example of a calibrator subsystem in which the calibration function is continuously active, while in actual implementation, the calibrator subsystem is also provided with a mechanism for selectively activating or deactivating the calibrator subsystem.

[0032] The collimator beam reflector 217 may be arranged to attenuate the collimator beam received from the beam sampler 215 so as to simulate the attenuation that normally occurs in the main transmitter beam and the receiver beam. The reflective surface of the collimator beam reflector 217 preferably has similar reflective properties as the beam sampler 215, in other words, the collimator beam reflector 217 is preferably arranged to reflect a predefined percentage of the collimator beam received from the beam sampler 215 via the collimator lens assembly 213 towards the scattering plate 216, for example, about 4% of the collimator beam. Therefore, the collimator beam reflector 217 may also include a glass plate having an uncoated glass surface for reflecting the collimator beam towards the scattering plate 216 and reflecting the backscattered collimator beam towards the beam sampler 215.

[0033] Preferably, the collimator beam reflector 217 is arranged relative to the beam sampler 215 and the scatter plate 216 so that the major axis of the collimator beam portion reflected from the collimator beam reflector 217 toward the scatter plate 216 is parallel or substantially parallel to the major axis of the transmitter beam (as well as the major axis of the main transmitter beam). In this arrangement, rays near the edge of the transmitter beam that are reflected at a relatively sharp angle from the beam sampler 215 are reflected at a relatively wide angle from the collimator beam reflector 217, and vice versa, thereby ensuring that substantially equal amounts of light from both edges of the transmitter beam are transmitted to the scatter plate 216 in the collimator beam.

[0034] In a variation of the lidar assembly 200', the order of the collimator lens assembly 213 and the collimator beam reflector 217 in the optical path from the beam sampler 215 to the scatter plate 216 is reversed so that the collimator beam reflector 217 is arranged to reflect the collimator beam received directly from the beam sampler 215 toward the scatter plate 216 via the collimator lens assembly 213, while the backscattered collimator beam is transmitted in the opposite direction via the same optical path. However, due to the divergence of the backscattered collimator beam, this change may result in an increase in the size of the collimator beam reflector 217 and the collimator lens assembly 213, and therefore may not be a feasible approach in those application scenarios where the small size of the lidar assembly 200' is an important design criterion.

[0035] In a variation of the lidar assembly 200 or 200', the spatial relationship between the optics of the calibrator subsystem and the scatter plate 216 is modified so that the calibrator beam is focused at a predefined distance behind the scatter plate 216. This can be achieved, for example, by positioning the scatter plate 216 closer to the final optical components of the optical subsystem in the optical path from the beam sampler 215 to the scatter plate 216. Thus, the calibrator beam encounters the surface of the scatter plate 216 off-focus, and the resulting backscattered calibrator beam is used to simulate a receiver beam backscattered from a target (such as the base of a cloud) at a certain distance from the lidar device, where the certain distance is shorter than the distance at which the main lens assembly 103 focuses the light transmitted in the transmitter beam. The certain distance can be appropriately selected during the manufacture of the lidar assembly 200, 200' and the predefined distance can be appropriately set.

[0036] The previously described lidar assemblies 200 and 200' serve as non-limiting examples to illustrate the operating principle of the calibrator subsystem. However, in lidar assemblies 200 and 200', the calibrator subsystem is continuously active, thereby resulting in a scenario in which the transmitter beam originating from the transmitter 101 will continuously cause the receiver 102 to obtain both a receiver beam backscattered from an atmospheric object at a certain distance from the lidar assemblies 200, 200' and a backscattered calibrator beam from the calibrator subsystem. Therefore, the measurement signal recorded at the receiver 102 will include both the actual measurement signal component generated by the receiver beam and the calibration signal component generated by the backscattered calibrator beam, which will not result in meaningful operation of the lidar assemblies 200, 200'.

[0037] In actual implementation, the calibrator subsystem of the laser radar assembly 200, 200' (or laser radar assembly in general) is provided with an activation mechanism, which enables the calibrator subsystem to be selectively activated or deactivated. Basically, the calibrator subsystem can be activated by allowing the calibrator beam to enter the calibrator system and allowing the backscattered calibrator beam to reach the receiver 102. Therefore, examples of implementing the activation mechanism include the following:

[0038] – a mechanism enabling adjustment of the position and / or orientation of the beam sampler 215 so that it allows selectively enabling or disabling the transmission of the collimator beam towards the scattering plate 216 .

[0039] - a mechanism (e.g. a movable opaque element) that enables selective blocking or unlocking of the optical path from the beam sampler 215 to the scattering plate 216;

[0040] - A mechanism that enables adjustment of the position and / or orientation of components within the optics of the collimator subsystem so that it can selectively enable or disable transmission of the collimator beam to the scatter plate 216.

[0041] While each of the above examples of implementing an activation mechanism is applicable to actual implementations of a lidar assembly utilizing the calibrator subsystem illustrated via the lidar assembly 200, 200', in the following, we describe a non-limiting example of a lidar assembly in which the activation mechanism is provided via a movable component of the calibrator subsystem. In this regard, the optical device of the calibrator subsystem may be provided with a selection mechanism that enables the calibrator beam to be directed toward a selected target of a plurality of targets in the calibrator subsystem, wherein the plurality of targets includes a scattering plate 216 for activating the calibrator subsystem and includes at least one other target for deactivating the calibrator subsystem. As a non-limiting example in this regard, the selection mechanism may include a movable reflector that can be selectively arranged into one of a plurality of predefined positions relative to the calibrator beam reflector 217, wherein each of the predefined positions is used to reflect the calibrator beam toward a corresponding target of a plurality of targets in the calibrator subsystem. A non-limiting example of a selection mechanism is provided below.

[0042] Figure 3A and Figure 3BSome components of a laser radar assembly 300 are schematically illustrated, and the laser radar assembly 300 is basically a variation of the laser radar assembly 200', supplemented with an activation mechanism. Therein, the difference from the laser radar assembly 200' is that the calibrator subsystem of the laser radar assembly 300 includes two targets: a scattering plate 216 and an absorber element 219, and the absorber element 219 is used to prevent the backscattered calibrator beam from being provided to the movable reflector 218, and further prevent the backscattered calibrator beam from being provided to the receiver 102. In this regard, the absorber element 219 can be arranged to absorb and / or redirect the light energy transmitted by the calibrator beam. In this regard, redirecting the light energy can involve, for example, reflecting the calibrator beam in a direction away from the movable reflector 218. Another difference from the laser radar assembly 200' is that the optical device of the calibrator subsystem in the laser radar assembly 300 also includes a movable reflector 218 as a selection mechanism, and the movable reflector 218 can be selectively arranged to one of at least two predefined positions relative to the calibrator beam reflector 217: in the first predefined position, the movable reflector 218 reflects the calibrator beam from the calibrator beam reflector 217 toward the scattering plate 216 so that the calibrator beam is focused at the surface of the scattering plate 216, and in the second predefined position, the movable reflector 218 reflects the calibrator beam toward the absorber element 219.

[0043] The surface of the absorber element 219 may include or be made of a substantially non-reflective (and non-scattering) material, whereby the absorber element 219 absorbs light energy transmitted by the collimator beam by reducing or even completely eliminating reflections and / or scattering of the collimator beam from the absorber element 219 when it is directed to the absorber element 219. Non-limiting examples of such materials include anti-reflective coated black filter glass and any commercially available optical black material. In some examples, additionally or alternatively, the absorber element 219 may be positioned relative to other components of the collimator subsystem so that the optical devices therein are arranged to focus the collimator beam away from the surface of the absorber element 219 (when directed to the absorber element 219 via operation of the selection mechanism), thereby reducing the amount of light reflected and / or scattered from the surface of the absorber element 219 toward the receiver 102. In some examples, additionally or alternatively, the surface of the absorber element 219 may be provided at an inclined angle relative to the main axis of the collimator beam to direct any reflections from the surface away from the movable reflector 218.

[0044] Thus, in the lidar assembly 300, when the movable reflector 218 is in a first predefined position, the calibrator subsystem is active (i.e., operable), and when the movable reflector 218 is in a second predefined position, the calibrator subsystem is inactive (i.e., inoperable or "off") . Figure 3A A scenario is depicted in which movable mirror 218 is in a first position, thereby reflecting the etalon beam towards scatter plate 216 and thereby providing a backscattered etalon beam to etalon beam reflector 217 through the optics of the etalon subsystem. Figure 3B A scenario is depicted wherein the movable mirror 218 is in a second position, thereby reflecting the etalon beam towards the absorber element 219 , which does not result in providing a backscattered etalon beam via reflection or scattering of the etalon beam towards the movable mirror 218 .

[0045] The calibrator subsystem may be applied to improve the accuracy of measurements obtainable by an atmospheric lidar device that employs the lidar assembly 300 via a control entity operating the calibrator subsystem to derive a calibrator system signal that is a description of the light transmitted in the backscattered calibrator beam and is suitable for implementing (automatic) calibration of the lidar assembly 300. In this regard, the control entity may operate the lidar assembly 300 to implement one or more calibration measurements when the calibrator subsystem is activated, and to implement one or more normal measurements when the calibrator subsystem is deactivated. The one or more calibration measurements and the one or more normal measurements are preferably implemented within a relatively short time window (e.g., within a time period shorter than one second) to facilitate implementation of these measurements under conditions substantially similar to atmospheric conditions. The corresponding measurements from both the calibration measurement and the normal measurement include signals from the atmosphere received through the main lens assembly 103, while the measurements from the calibration measurement also include the effects of the backscattered calibrator beam. Thus, the control entity may obtain the calibrator system signal based on the difference between the two types of measurements, for example, by subtracting the measurements obtained from the normal measurement from the measurements obtained from the calibration measurement.

[0046] In a non-limiting example, substantially at time t0, the control entity may implement the following operations:

[0047] - operating the lidar assembly 300 to perform a first calibration measurement and record a first calibration measurement signal C0,

[0048] - Operate the lidar assembly 300 to perform a first normal measurement and record a first normal measurement signal N0.

[0049] The control entity may derive a first calibrator system signal P0 as a difference between the first calibration measurement signal C0 and the first normal measurement signal N0, for example, P0=C0-N0. Subsequently, substantially at time t1, the control entity may perform the following operations:

[0050] - operating the lidar assembly 300 to perform a second calibration measurement and record a second calibration measurement signal C1,

[0051] - Operate the lidar assembly 300 to perform a second normal measurement and record a second normal measurement signal N1.

[0052] The control entity may derive the second calibrator system signal P1 as a difference between the second calibration measurement signal C1 and the second normal measurement signal N1 , eg P1 = C1 - N1 .

[0053] The control entity may apply the first calibrator system signal P0 and the second calibrator system signal P1 to implement automatic calibration of the laser radar assembly 300. As an example in this regard, the control entity may derive the first calibrator system signal P0 based on one or more calibration measurements and one or more normal measurements implemented close to time t0, and derive the second calibrator system signal P1 based on one or more calibration measurements and one or more normal measurements implemented close to time t1. Therefore, based on the first calibrator system signal P0 and the second calibrator system signal P1, the control entity may observe a change in the optical sensitivity of the laser radar assembly 300 from time t0 to time t1 (change P1 / P0). Therefore, if the initial calibration of the laser radar assembly 300 is implemented at or near time t0 (for example, at the factory when it is manufactured), the measurement signal obtained via normal measurements (such as atmospheric signals) implemented at or after this time t1 may be multiplied by the calibration factor P0 / P1 to obtain a corresponding calibration measurement signal to ensure that the correct calibration of the laser radar assembly 300 is maintained. During subsequent operation of the laser radar assembly 300 (after time t1), the control entity may, at the corresponding time t k The corresponding additional calibrator system signal P is derived at or near k , apply the above process to observe further changes in the optical sensitivity of the laser radar assembly 300 (e.g., change P k / P0), and apply the corresponding calibration factor P0 / P k At the corresponding time t k The atmospheric signal received at and after is multiplied to ensure that the correct calibration of the lidar assembly 300 is maintained.

[0054] Calibration factor P0 / P1 (or the corresponding calibration factor P0 / P k) improves the reliability and accuracy of the measurements obtained by the respective lidar device and also makes it easier to compare (calibrated) measurement signals obtained after prolonged use of the respective lidar device under field conditions with past (calibrated) measurement signals obtained via operation of the respective lidar device. As a non-limiting example in this regard, calibration may be used to compensate for measurement errors caused by changes in the respective operation of components of lidar assembly 300 and / or slight changes in the relative positions of components of lidar assembly 300 that may occur over time, such as one or more of the following changes:

[0055] - a change in the operation of the transmitter 101, such as a change in the transmission power (eg laser power);

[0056] - a change in the operation of the receiver 102, such as a change in the responsivity of a photodetector (e.g., a photodiode such as an avalanche photodiode);

[0057] - a change in the respective focus of the transmitter 101 and / or the receiver 102;

[0058] - A change in the optical alignment between the transmitter 101 and the receiver 102 .

[0059] Figure 4 Some components of a laser radar assembly 300' are schematically illustrated, and the laser radar assembly 300' is a variation of the laser radar assembly 300. Therein, the difference from the laser radar assembly 300 is that the calibrator subsystem includes a light detector element 220 instead of an absorber element 219, wherein the light detector element 220 is arranged in such a position (relative to the movable reflector 218 and other components of the calibrator subsystem) that the movable reflector 218 in the second position reflects the calibrator beam toward the light detector element 220. The light detector element 220 may include, for example, a photodetector, such as a photodiode. Similar to the absorber element 219, the light detector element 220 may also be used to prevent the backscattered calibrator beam from being provided to the movable reflector 218 and further to the receiver 102. In this regard, the light detector element 220 may be arranged to absorb and / or redirect (at least a majority of) the light energy transmitted by the calibrator beam so as not to reflect or scatter the light directed thereback back to the movable reflector 218. In this regard, for example, one or more of the following methods may be applied:

[0060] - the surface of the photodetector element 220 may be substantially non-reflective (e.g. provided with an anti-reflective coating, such as an anti-reflective coated black filter glass attenuator),

[0061] - the surface of the light detector element 220 may be provided at an inclined angle relative to the main axis of the collimator beam to direct any reflections from the surface away from the movable mirror 218,

[0062] The collimator beam may be arranged to meet the surface of the photodetector element 220 off-focus (but preferably such that the collimator beam meets the photosensitive area of ​​the photodetector element 220 in its entirety).

[0063] Figure 4 The schematic example of FIG. 3 illustrates a scenario in which the movable mirror 218 is in the second position, thereby reflecting the calibrator beam toward the surface of the light detector element 220. In the scenario in which the movable mirror 218 of the lidar assembly 300' is in the first position, the calibrator beam is reflected toward the scattering plate 216 (with Figure 3A 101). Although in this example, the second position of the movable reflector 218 is also used to place the calibrator subsystem in an inactive (i.e., non-operating) state, the light detector element 220 provides a detector signal describing the optical power of the calibrator beam. The detector signal can be provided to a control entity of the laser radar assembly 300', thereby enabling the control entity to measure and / or analyze the optical power of the transmitter beam originating from the transmitter 101. This in turn enables, for example, monitoring and / or fine-tuning of the transmit power of the transmitter 101.

[0064] Figure 5 Some components of a laser radar assembly 300 ″ are schematically illustrated. The laser radar assembly 300 ″ is another variation of the laser radar assembly 200 ′ supplemented with an activation mechanism. The difference between the laser radar components 300 and 300' is that the calibrator subsystem of the laser radar component 300" includes three targets: a scattering plate 216, an absorber element 219 and a light detector element 220 arranged relative to the other elements of the calibrator subsystem as described above. In addition, relative to the calibrator beam reflector 217, the movable reflector 218 can be selectively arranged in one of at least three predefined positions so as to guide the calibrator beam to the corresponding target in the calibrator subsystem: in the first predefined position, the movable reflector 218 reflects the calibrator beam from the calibrator beam reflector 217 toward the scattering plate 216 so that the calibrator beam is focused at the surface of the scattering plate 216 (and reflects the backscattered calibrator beam from the scattering plate 216 toward the calibrator beam reflector 217); in the second predefined position, the movable reflector 218 reflects the calibrator beam toward the absorber element 219; and in the third predefined position, the movable reflector 218 reflects the calibrator beam toward the light detector element 220.

[0065] Figure 5 The schematic example of FIG. 3 illustrates a scenario in which the movable reflector 218 is in the third position, thereby reflecting the calibrator beam toward the surface of the light detector element 220. In the scenario in which the movable reflector 218 of the lidar assembly 300″ is in the first position, the calibrator beam is reflected toward the scattering plate 216 (with Figure 3A In the example of the laser radar assembly 300 in the frame, and in the scenario where the movable reflector 218 of the laser radar assembly 300 is in the second position, the collimator beam is reflected toward the absorber element 219 (in a manner shown in FIG. Figure 4 ) in the manner shown in the framework of the lidar assembly 300' in the example.

[0066] In a further variation, any of the lidar assemblies 300, 300' and 300" may be provided with a second scatter plate arranged such that the calibrator beam is focused at a predefined distance behind the surface of the second scatter plate (when directed to the second scatter plate), the resulting backscattered calibrator beam thus simulating a receiver beam backscattered from a target (such as the base of a cloud) that is a distance from the lidar device in the atmosphere, but closer to the lidar device than the distance at which the main lens assembly 103 focuses the light transmitted in the transmitter beam. Thus, the second scatter plate can be used as a further target in the calibrator subsystem, and the movable reflector 218 can be selectively arranged to one of a plurality of predefined positions relative to the calibrator beam reflector 217 so as to direct the calibrator beam to a corresponding one of the targets.

[0067] As an example in this regard, the calibrator subsystem of the lidar assembly 300 or 300' may also be provided with a third target involving a second scatter plate, and the movable reflector 218 may be selectively arranged in one of three predefined positions relative to the calibrator beam reflector 217 to direct the calibrator beam to a corresponding one of the targets. In another example in this regard, the calibrator subsystem of the lidar assembly 300" may also be provided with a fourth target involving a second scatter plate, and the movable reflector 218 may be selectively arranged in one of four predefined positions relative to the calibrator beam reflector 217 to direct the calibrator beam to a corresponding one of the targets.

[0068] With the lidar assemblies 300, 300' and 300" and variations thereof, a movable mirror 218 serving as a selection mechanism within the optical device may be rotated about a pivot point so that it enters one of a plurality of predefined tilt angles relative to a principal axis of the calibrator beam so as to direct the calibrator beam toward one of a plurality of targets in the calibrator subsystem (and direct the backscattered calibrator beam toward the receiver 102), respectively. In one example, the rotational motion may be provided via an actuator coupled to the movable mirror 218 and arranged to rotate the movable mirror 218 to one of the predefined tilt angles under control of a control entity of the lidar assemblies 300, 300', 300".

[0069] In another example, the selection mechanism may enable the movable mirror 218 to be translationally moved in the direction of the main axis of the etalon beam to one of a plurality of predefined distances from the etalon beam reflector 217 so as to direct the etalon beam toward one of a plurality of targets in the etalon subsystem (and direct the backscattered etalon beam toward the receiver 102), respectively. In this example, the tilt angle of the movable mirror 218 may remain constant regardless of the distance from the etalon beam reflector 217.

[0070] The selection mechanism may operate under the control of a control entity. As one example in this regard, the control entity may be arranged to periodically operate the selection mechanism to set the calibrator subsystem to an active (i.e., operational) state, for example, by directing a calibrator beam toward scatter plate 216 (or toward an additional scatter plate if available), to implement a calibration procedure and to set the calibrator subsystem back to an inactive (i.e., non-operational) state, for example, by directing a calibrator beam toward absorber element 219 or photodetector element 220. In another example, the control component may implement activation of the calibrator subsystem, a calibration procedure, and deactivation of the calibrator subsystem in response to user commands received via a user interface of a lidar device (which employs lidar assembly 300, 300', 300" or one of their variations).

[0071] In the examples related to the previously described lidar assemblies 200, 200', 300, 300', 300" and their variations, the reflector 104 arranged between the transmitter 101 and the main lens assembly 103 is used as an example of a beam reflector, which is arranged between the transmitter 101 and the main lens assembly 103 and is arranged to reflect backscattered light toward the receiver 102 while allowing light originating from the transmitter 101 to pass through and exit the lidar assemblies 200, 200', 300, 300', 300" through the main lens assembly 103. In another example, the beam reflector may include a beam splitter (e.g., a 50:50 beam splitter), and in this example, the conceptual division of the main lens assembly 103 into a center portion and an edge portion is not applicable, but light originating from the transmitter 101 is able to leave the lidar assembly 200, 200', 300, 300', 300" throughout the area of ​​the main lens assembly 103, and backscattered light entering the lidar assembly 200, 200', 300, 300', 300" throughout the area of ​​the main lens assembly 103 can be directed toward the receiver 102. In another example, the beam reflector may include a reflector that only partially blocks the transmission path from the emitter 101 to the main lens assembly 103 (in a manner other than providing a hole in a central portion thereof), and in such an example, the area of ​​the main lens assembly 103 is (conceptually) divided into a first portion, through which light originating from the emitter 101 leaves the lidar assembly 200, 200', 300, 300', 300", and a second portion, through which backscattered light enters the lidar assembly 200, 200', 300, 300', 300". In one example, such a partially blocking reflector may have a semicircular shape, and it may be positioned so that it substantially allows a first half of the light beam originating from the emitter 101 to pass toward the main lens assembly 103 (while blocking a second half of the light beam), and so that it reflects a second half of the backscattered light that arrives through the main lens assembly 103 toward the receiver 102.

[0072] The lidar components 300, 300', 300" (and their variations) described above can be applied, for example, to atmospheric research, and a lidar device utilizing such a lidar component can be referred to as an atmospheric lidar. In a non-limiting example, an atmospheric lidar employing the lidar components 300, 300', 300" (or their variations) can be applied to functions such as cloud height estimation and / or estimation of one or more meteorological variables (such as temperature, humidity, wind, etc.). In addition, such an atmospheric lidar can be additionally or alternatively applied to other functions, such as measurement of vapor (such as water vapor) and / or certain gases (such as carbon dioxide) in the atmosphere.

[0073] Although some functions of the laser radar assembly 300, 300', 300" have been described above with reference to certain features of the laser radar assembly 300, 300', 300", these functions may be performed by other features, whether described or not. Although some features have been described with reference to certain embodiments, these features may also exist in other embodiments, whether described or not.

Claims

1. A laser radar assembly (300, 300', 300") for atmospheric measurement, the laser radar assembly (300, 300', 300") comprising: a main lens assembly (103) for collimating a transmitter beam originating from a first focal point within the laser radar assembly (300, 300', 300") to illuminate a target at a distance from the laser radar assembly (300, 300', 300"), and for focusing backscattered light from the target to a second focal point within the laser radar assembly (300, 300', 300"); an emitter (101) arranged in the first focus for generating the emitter beam for emission towards the main lens assembly (103); a receiver (102) arranged in the second focal point for capturing the backscattered light entering the laser radar assembly (300, 300', 300") through the main lens assembly (103); a beam reflector (104) disposed between the first focal point and the main lens assembly (103) for reflecting the backscattered light toward the second focal point in a manner such that the beam reflector (104) allows the transmitter beam to reach the main lens assembly (103), Characterized in that the laser radar assembly (300, 300', 300") includes a calibrator subsystem, and the calibrator subsystem includes: a beam sampler (215) disposed between the beam reflector (104) and the main lens assembly (103) for reflecting a portion of the transmitter beam as a collimator beam; and an optical device for transmitting the etalon beam toward a selected one of a plurality of targets in the etalon subsystem, wherein the plurality of targets includes at least the following: a first scattering plate (216) arranged to diffusely reflect the collimator beam encountering a surface of the first scattering plate, thereby causing a backscattered collimator beam for transmission via the optical device, via the beam sampler (215) and via the beam reflector (104) to the receiver (102), and At least one element (219, 220) is arranged to prevent providing said backscattered collimator beam.

2. The laser radar assembly (300, 300', 300") according to claim 1, wherein The beam reflector comprises a reflector (104) provided with an aperture enabling at least a portion of the transmitter beam to pass through the reflector towards the main lens assembly (103).

3. A laser radar assembly (300, 300', 300") according to claim 1 or 2, wherein the optical device is arranged to focus the calibrator beam on the surface of the first scattering plate (216) when the calibrator beam is transmitted towards the first scattering plate (216).

4. The laser radar assembly (300, 300', 300") according to claim 3, wherein The plurality of targets include a second scattering plate for generating diffuse reflection of the collimator beam encountering a surface thereof, and The optical arrangement is arranged to focus the etalon beam behind a surface of the second scatter plate when the etalon beam is transmitted towards the second scatter plate.

5. The laser radar assembly (300, 300', 300") according to claim 1 or 2, wherein the optical device is arranged to focus the calibrator beam behind the surface of the first scattering plate (216) when the calibrator beam is transmitted toward the first scattering plate (216).

6. The lidar assembly (300', 300") according to any one of claims 1 to 5, wherein the at least one element arranged to prevent providing the backscattered collimator beam comprises a photodetector element (220) for facilitating an estimation of the light energy transmitted by the collimator beam, and wherein at least one of the following applies: The optical device is arranged to focus the etalon beam away from a surface of the photodetector element (220) when the etalon beam is transmitted towards the photodetector element (220), The light detector element (220) includes a substantially non-reflective surface, and The surface of the light detector element (220) is arranged at an oblique angle relative to the main axis of the etalon beam.

7. The lidar assembly (300, 300', 300") according to any one of claims 1 to 6, wherein the at least one element arranged to prevent providing the backscattered collimator beam comprises an absorber element (219), and wherein at least one of the following applies: The absorber element (219) comprises a substantially non-reflective surface, The surface of the absorber element (219) is arranged at an oblique angle relative to the main axis of the collimator beam, and The optical device is arranged to focus the etalon beam away from a surface of the absorber element (219) when the etalon beam is transmitted towards the absorber element (219).

8. The laser radar assembly (300, 300', 300") according to any one of claims 1 to 7, wherein the beam sampler (215) comprises a glass surface for reflecting the portion of the transmitter beam as the calibrator beam.

9. A laser radar assembly (300, 300', 300") according to any one of claims 1 to 8, wherein the optical device comprises a collimator lens assembly (213), which is used to focus the collimator beam at the scattering plate (216) when the collimator beam is transmitted toward the scattering plate (216).

10. The laser radar assembly (300, 300', 300") according to claim 9, wherein the calibrator lens assembly (213) includes two lenses arranged on the same optical axis, and each of the two lenses has optical properties substantially similar to the optical properties of the single lens in the main lens assembly (103), and has a diameter substantially half the diameter of the single lens of the main lens assembly (103).

11. A laser radar assembly (300, 300', 300") according to any one of claims 1 to 10, wherein the optical device comprises a collimator beam reflector (217), which is used to reflect the collimator beam so that the main axis of the collimator beam is basically parallel to the main axis of the transmitter beam.

12. The laser radar assembly (300, 300', 300") according to any one of claims 1 to 11, wherein the calibrator subsystem includes a selection mechanism, which is used to selectively transmit the calibrator beam toward one of the multiple targets in the calibrator subsystem.

13. A laser radar assembly (300, 300', 300") according to any one of claims 1 to 12, wherein the selection mechanism includes a movable reflector (218), which can be selectively arranged into one of a plurality of predefined positions, wherein each predefined position causes the movable reflector (218) to reflect the calibrator beam toward a corresponding target among the plurality of targets.

14. The laser radar assembly (300, 300', 300") of claim 13, wherein the movable reflector is rotatable about a pivot point into a selected one of the plurality of predefined positions.

15. The laser radar assembly (300, 300', 300") according to any one of claims 1 to 14, comprising a control entity arranged to: operating the transmitter (101), the receiver (102), and the etalon subsystem to derive a first etalon system signal describing a backscattered etalon beam at a first time; operating the transmitter (102), the receiver (102), and the etalon subsystem to derive a second etalon system signal describing a backscattered etalon beam at a second time occurring later than the first time; deriving a calibration factor based on the first calibrator system signal and the second calibrator system signal; At and / or after the second time instant, the calibration factor is applied to adjust a measurement signal recorded based on backscattered light captured at the receiver (102).

16. The laser radar assembly (300, 300', 300") according to claim 15, wherein the control entity is arranged to: substantially at the first time, operating the etalon subsystem to transmit the etalon beam to the first scatter plate (216) to obtain a first calibration measurement signal; substantially at the first time, operating the etalon subsystem to transmit the etalon beam to the at least one element arranged to prevent providing the backscattered etalon beam to obtain a first normal measurement signal; substantially at the second time, operating the etalon subsystem to transmit the etalon beam to the first scatter plate (216) to obtain a second calibration measurement signal; substantially at the second time, operating the etalon subsystem to transmit the etalon beam to the at least one element arranged to prevent providing the backscattered etalon beam to obtain a second normal measurement signal; deriving the first calibrator system signal as a difference between the first calibration measurement signal and the first normal measurement signal; as well as The second calibrator system signal is derived as a difference between the second calibration measurement signal and the second normal measurement signal.

17. A lidar assembly (300, 300', 300") according to claim 15 or 16, wherein the control entity is arranged to derive the calibration factor as a ratio of the first calibrator system signal to the second calibrator system signal.

18. A lidar assembly (300, 300', 300") according to any one of claims 15 to 17, wherein the control entity is arranged to: at and / or after the second moment, adjust the recorded measurement signal by multiplying the recorded measurement signal by the calibration factor.

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