Measuring reflectivity properties of a surface of a material

Abstract

A gonioreflectometer for measuring the reflectivity properties of a material surface under the incidence of electromagnetic radiation (130) is proposed, comprising a frame (100) and a first and a second arm (104, 106), both of which are mounted on the frame (100) so as to be independently rotatable. Both arms (104, 106) rotate about a common axis of rotation. The first arm (104) carries a transmitter (110) for the electromagnetic radiation, and the second arm (106) carries a receiver (114). The surface of the material to be measured is placed in the region of the frame (100). An angle is then specified at which the surface is to be irradiated with the electromagnetic radiation (130) by the transmitter (110). The second arm (106) is rotated such that the receiver (114) measures the intensity of the electromagnetic radiation (134) reflected by the surface at a plurality of angles.In this way, a reflectance distribution function is recorded using simple means.

Description

Field of the invention

[0001] In automotive automation, environmental sensors are used to capture the vehicle's surroundings using various measurement principles. In addition to cameras, radar and lidar sensors are also used. These emit signals in the form of electromagnetic waves, detect reflections of these signals, and calculate the distance of the reflecting object based on the signal's propagation time, for example. Using this position information and the knowledge of the intensity of the signal reflected from a point, a model of the vehicle's current environment is created.

[0002] In addition to automated vehicles in road traffic, such environmental sensors are also used in the automation of agricultural machinery, trains, drones and other robotics.

[0003] To develop such automated systems and test their safety and functionality, either real-world tests with prototypes or simulations can be used. Depending on the product, building prototypes can be very complex and expensive, hazardous situations can only be tested to a limited extent, and environmental influences such as weather cannot always be adjusted at will. These disadvantages do not exist when using realistic simulations.

[0004] A prerequisite for the meaningful simulation of automated systems is their holistic, realistic modeling, including environmental sensors. To ensure realism, the reflectivity properties of the objects and materials in the environment must also be modeled accordingly. State of the art

[0005] Gonioreflectometers are used to measure the reflectivity of a material. A gonioreflectometer consists of a light source that illuminates the object or material being measured and a sensor that records the light reflected from the material. The sensor should be mounted flexibly so that it can record measurements based on the angle. The word "gonio" comes from the Greek gonía, which means "angle."

[0006] A gonioreflectometer can be used to record a reflectance distribution function. This represents the reflection behavior of a material's surface at given angles of incidence. It provides the percentage of the reflected radiation intensity at the respective exit angle for a light beam incident on the material at a given angle of incidence.

[0007] Reflectance distribution functions are used, among other things, in realistic 3D computer graphics, where they represent part of the fundamental rendering equation and serve to represent surfaces as realistically and physically correctly as possible.

[0008] A well-known gonioreflectometer was developed by the Fraunhofer Society (accessed on April 16, 2024, at https: / / www.iosb.fraunhofer.de / de / projekte-produkte / brdfmessung-reflektanzverteilung-goniometrie / gonioreflektometer-messanlage.html). This gonioreflectometer uses a multi-jointed robotic arm for the receiver. The robotic arm allows the recording of reflected radiation at any angle, but is very costly and not mobile.

[0009] Another gonioreflectometer is described in the publication "Automotive Lidar Modeling Approach Based on Material Properties and Lidar Capabilities," Sensors 2020, 20(11), 3309. However, the transmitter and receiver cannot be rotated relative to each other, limiting the recording of reflectance distribution functions. The same applies to the reflectometer described in the publication "Angle-dependent spectral reflectance material dataset based on 945 nm time-of-flight camera measurements," Data in Brief, Volume 48, June 2023, 109031.

[0010] Another gonioreflectometer is known from the publication "Reflectometer for measuring the bidirectional reflectance of rough surfaces", Applied Optics, Vol. 37, 1998, No. 16. This gonioreflectometer has rotating arms for holding the optical components and is said to be less complex and significantly more cost-effective, partly due to the use of commercially available components.

[0011] The publication "Gonioreflectometer for measuring 3D spectral BRDF of horizontally aligned samples with traceability to SI," Metrologia, Vol. 59, 2022, No. 2 (Art. No. 025006), describes a 3D gonioreflectometer developed at Aalto University. This gonioreflectometer features three driven arms and is specifically designed to determine spectral bidirectional reflectance distribution functions (sBRDF) of horizontally aligned powder samples, particularly sand.

[0012] Publication DE 101 34 458 A1 discloses a measuring system for measuring the optical properties of an object and a dedicated measuring head. Both the detector and the light source are mounted on the same measuring head, which is why this system also only allows limited reflectance distribution functions to be recorded.

[0013] Publication US 4,355,271 A describes a control unit for a vehicle's windshield wipers. Infrared radiation from a source inside the vehicle is reflected off the outside of the windshield and detected by a detector. Changes in the detected radiation intensity are used to determine the presence of dust and / or water on the windshield, and the windshield wiper or washer function is activated accordingly.

[0014] Publication CN 1 02 590 150 A presents a measurement system for hyperspectral reflectance distribution functions (BRDF) in indoor environments. This system is designed to reduce limitations on the angle at which light from a light source enters the room, thus eliminating shadowing that can occur when using only a single light source. Task

[0015] The object of the invention is to provide a cost-effective and mobile gonioreflectometer with which reflectance distribution functions can nevertheless be recorded. Solution

[0016] This problem is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0017] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0018] Individual method steps are described in more detail below. In a preferred variant of the invention, the steps are carried out in the order specified. However, the steps do not necessarily have to be carried out in the order specified, and the method to be described may also include additional, unmentioned steps.

[0019] To solve this problem, a method is proposed for measuring the reflectivity properties of a material surface under the incidence of electromagnetic radiation using a gonioreflectometer. The gonioreflectometer comprises a frame and a first and a second arm. The arms are rotatably mounted on the frame and can rotate independently of each other. The arms rotate around a common axis of rotation. To simplify the design, the arms have no joints other than the rotatable suspension.

[0020] The first arm carries a transmitter for the electromagnetic radiation, and the second arm carries a receiver for the electromagnetic radiation. Lasers, for example, are suitable as transmitters, and photodiodes, for receivers.

[0021] The transmitter is attached to the first arm in such a way that it is guided along a first circular arc by the rotation of the first arm. The same applies to the receiver on the second arm; it is also attached to the second arm in such a way that it can be guided along a second circular arc by the rotation of the second arm. The centers of these circular arcs lie on the common axis of rotation.

[0022] The receiver measures the intensity of the reflected electromagnetic radiation. The reflectance distribution function determines the proportion of the incident electromagnetic radiation that is reflected or scattered in the respective direction—in other words, the intensity distribution depends on the angle of reflection.

[0023] To receive the reflectance distribution function for multiple angles simultaneously and thus work particularly efficiently, a camera, such as a CCD camera, can be used as the receiver instead of a diode. While a diode lacks spatial resolution, the spatial resolution of a camera enables simultaneous acquisition from multiple angles.

[0024] Because the two arms can be rotated independently of each other, the reflectance distribution function of the reflected light can be measured as a function of the angle set for the receiver—that is, the angle at which the light is reflected or scattered by the surface. It is also possible to rotate the transmitter and thus change the angle of incidence of the light on the surface. The reflectance distribution function can be measured as a function of these two angles.

[0025] The procedure includes the following steps: The surface of the material to be measured is placed within the frame of the gonioreflectometer, along the rotation axis. It is advisable, but not mandatory, to place the surface exactly in a plane through which the rotation axis passes. In any case, the surface of the material is placed parallel to a plane spanned by the frame. This plane can also be referred to as the measurement plane.

[0026] Next, an angle is specified at which the surface is to be irradiated with electromagnetic radiation from the transmitter. The first arm is rotated so that the transmitter assumes a position at which the electromagnetic radiation irradiates the surface at the specified angle.

[0027] The second arm is rotated so that the receiver measures the intensity of the electromagnetic radiation reflected from the surface at a variety of angles. This can be done continuously or at multiple sampling points.

[0028] Alternatively, an angle is specified for the receiver at which the intensity of the electromagnetic radiation reflected from the surface is to be measured by the receiver. The second arm is then rotated so that the receiver assumes a position at which it can measure the intensity of the electromagnetic radiation reflected from the surface at the specified angle. Subsequently, the first arm with the transmitter is rotated so that the transmitter irradiates the surface with electromagnetic radiation at a plurality of angles. This can also be done either continuously or across multiple support points.

[0029] If the surface is positioned above or below the rotation axis, meaning the measurement plane is above or below the rotation axis, adjustments can be made to the alignment of the transmitter and / or receiver so that the transmitter and receiver are aligned to the point where the electromagnetic radiation emitted by the transmitter hits the surface. For example, if the measurement plane is above the rotation axis and the transmitter is rotated to the right, the point where the beam hits the surface also shifts to the right. The receiver then receives the reflected radiation not at the angle at which it was set in its rotation, but at an angle that is, for example, larger.

[0030] This effect can be accounted for mathematically by considering the actual reception angle when acquiring the data. Alternatively, the receiver can be rotated relative to the second arm so that it is again precisely aligned with the illuminated point. The relative alignment of the receiver to the second arm can be done manually using thumbscrews or automatically using stepper motors. The resulting reflection angle of the radiation can also be mathematically accounted for when acquiring the data.

[0031] Instead of correcting the alignment of the receiver to the second arm, the alignment of the transmitter to the first arm can just as easily be corrected in a completely analogous manner.

[0032] In this way, reflectance distribution functions for a wide variety of materials can be recorded using relatively simple means.

[0033] In order to achieve the most realistic representations, simulations, etc., the measurement of the reflectivity properties can be carried out at a plurality of different temperatures, a plurality of different relative humidities and at a plurality of different degrees of wetting and / or contamination and / or other manipulations of the surface.

[0034] The intensities of the reflected electromagnetic radiation measured by the receiver are preferably stored together with the corresponding transmission and reception angles.

[0035] A data storage device can then be created on which the obtained data is stored.

[0036] In this way, a data set of reflectivity properties of surfaces of materials under the incidence of electromagnetic radiation can be created.

[0037] The result is a data set of reflectivity properties obtained using the described procedure.

[0038] This dataset can be used to computationally calculate the reflection of electromagnetic radiation from surfaces.

[0039] Furthermore, the object is achieved by a computer program comprising instructions which cause the gonioreflectometer to carry out the method steps of the described method.

[0040] A computer-readable medium on which the computer program just described is stored also solves the problem.

[0041] Gonioreflectometers with components described below are particularly suitable for the described method.

[0042] To prevent measurement results from scattered light being distorted, the gonioreflectometer has a cover that is opaque to the electromagnetic radiation used for measurement. If light is used for measurement, the cover is opaque. If radar or lidar is used, the cover must be opaque to the respective wavelengths.

[0043] To further suppress interfering stray light, a bandpass filter can be placed in front of the receiver, selectively allowing only electromagnetic radiation with the same wavelength as the electromagnetic radiation emitted by the transmitter to pass through. Such a bandpass filter can be easily replaced when the transmitter's wavelength changes. Under appropriate circumstances, this can make it possible to use a single receiver for several different transmitters.

[0044] Even more stray light suppression can be achieved by placing a cylindrical shield in front of the receiver. Such a "tube" in front of the receiver can shield, in particular, stray light caused by scattering and multiple reflections—including from the test bench components.

[0045] In order to make the measurement results reproducible and automatable, the arms have at least one drive for rotating the arms.

[0046] The control of the rotation of the arms becomes particularly precise when each arm has an individual drive, in the form of a stepper motor.

[0047] To ensure reproducible angle adjustments, the frame features stops that limit the rotation of the arms. These stops can be used to calibrate the rotation angles of the arms. The stops limit the range of motion of the rotatably movable arms, for example, within a range of -90° to +90°, or -86° to +86°, etc.

[0048] The design is modular. The transmitters and receivers are interchangeable. Depending on whether radar, lidar, or visible light is used, sources of electromagnetic radiation with wavelengths from 1 mm to 400 cm, 780 nm to 2000 nm, or 400 nm to 780 nm can be used as transmitters. The receivers can be interchanged accordingly to ensure they are suitable for the respective wavelengths, i.e., to ensure sufficient sensitivity.

[0049] The gonioreflectometer should preferably be portable to allow for on-site measurement of certain surfaces, such as roads. For this reason, the external dimensions of the gonioreflectometer should not exceed a width of 150 cm, a height of 100 cm, and a depth of 100 cm. Smaller versions, approximately half the specified dimensions or a width of 120 cm, a height of 60 cm, and a depth of 60 cm, are also conceivable. Furthermore, the weight of the gonioreflectometer should not exceed 80 kg, and preferably even 50 kg or 30 kg. These objectives can be achieved, for example, by using aluminum profiles.

[0050] To compensate for any unevenness in the surface being measured, the frame of the gonioreflectometer features height-adjustable feet. This allows for precise alignment of the test stand relative to the surface being measured, ensuring that the surface is parallel to the frame, even on uneven ground.

[0051] To ensure reproducible measurements of uneven, rough, or textured surfaces, a combination of lenses is mounted in front of the transmitter to expand the beam of electromagnetic radiation. For example, shining a laser beam with a relatively small diameter or focus onto a rough surface would result in poorly reproducible reflections in a wide variety of directions.

[0052] Further details and features will become apparent from the following description of a preferred embodiment in conjunction with the figures. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiment. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable subintervals.

[0053] An exemplary embodiment is shown schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally equivalent elements, or elements that correspond to one another in terms of their functions. In detail: Fig. 1 a schematic representation of the test bench; Fig. 2 an explanatory diagram for calculating the correction angle when the rotation axis of the two arms is not in the plane of the material surface to be measured; and Fig. 3 a representation of the measurement results of an exemplary material.

[0054] Fig. 1 shows a preferred embodiment of the test bench with a frame 100, on which four height-adjustable feet 102, as well as a transmitter arm 104 and a receiver arm 106, are preferably mounted. The transmitter arm 104 preferably carries a transmitter mount 108 with a transmitter 110, and the receiver arm 106 preferably carries a receiver mount 112 with a receiver 114. The transmitter mount 108 and receiver mount 112 can have knurled screws 116 or an automated adjustment mechanism for adjusting the alignment of the transmitter 110 or receiver. Drives 118, preferably stepper motors, are mounted on the transmitter arm 104 and the receiver arm 106, which can change the position of the transmitter arm 104 and receiver arm 106 using gears 120. A control unit 122, four stops 124, a plurality of pivot bolts 126 and calibrated limit switches 128 are preferably also mounted on the frame 100.

[0055] The test bench consists of a frame 100, preferably made of aluminum profiles, to which all other elements can be mounted directly or indirectly. The material to be measured can be placed horizontally as a material sample in the center of the frame. If a material sample cannot be placed within the frame due to its size (e.g., real road asphalt), the entire frame is placed on the material surface whose reflectivity properties are to be measured. The frame preferably has four height-adjustable feet 102, by means of which the frame can be aligned parallel to the material surface to be measured.

[0056] The test bench has a transmitting arm 104 and a receiving arm 106, each of which can be rotated independently of each other.

[0057] A transmitter mount 108 is preferably mounted on the transmitter arm 104, which supports a transmitter 110 that serves as a source of electromagnetic radiation. This can be, for example, a laser module.

[0058] A receiver mount 112 with a receiver 114 is preferably mounted on the receiver arm 106. The receiver receives the beam reflected from the material surface in the direction of the current receiver position and measures its intensity. The receiver 114 can be a photodiode, for example. A bandpass filter is preferably mounted in front of the receiver 114 so that only the relevant wavelengths reach the receiver 114. Furthermore, a preferably cylindrical shield can be mounted in front of the receiver 114 to minimize the influence of stray light, e.g., due to multiple reflections on the test bench.

[0059] The alignment of the transmitter 110 and the receiver 114 can be finely adjusted using knurled screws 116. Actuators such as stepper motors are preferably used as an automated alternative to the manually operated knurled screws 116.

[0060] The transmitter arm 104 and receiver arm 106 can be rotated independently of each other around a common rotation axis by drives 118. Preferably, stepper motors and a motion transmission via gears 120 are used for this purpose.

[0061] A control unit 122, preferably mounted on the frame 100, is used to control or regulate all actuators in the test bench, as well as to read out all sensors in the test bench. In addition, a wireless (e.g., WLAN) or wired communication interface, for example, to a PC or microcontroller can be provided. The PC can be used to control the test bench using a graphical user interface, e.g., to start the calibration of the drives 118 on the two arms, to start a measurement, or to set the desired measurement profile with a predetermined number of support points and other measurement parameters. In this way, any reflectivity maps of combinations of transmission and reception angles within the available movement range of the arms can be measured automatically. The control unit 122 can, via the above-mentioned communication interface, receive the current motor or arm positions and the status of the test bench (e.g.,Calibration status, motor movement status, measurement status) also send the recorded measurement data.

[0062] Stops 124 can limit the maximum rotation angles of the two arms 104 and 106 in both directions. The known angular position of the arms at these end stops allows calibration of the drives 118. By using pivoting locks 126, the arms can be securely held at the stops 124 even when the test stand is switched off, which can serve as a transport safety feature. The drives 118 can also be calibrated using calibrated limit switches 128.

[0063] The transmitter 110, mounted on the transmitter mount 108, transmits a signal 130 to the material surface to be measured. The transmitted beam 130 is preferably directed so that it intersects the rotation axis of the two arms. From the reflection point 132 on the material surface, the reflected beam 134 radiates in different spatial directions with varying intensity, depending on the properties of the material surface to be measured.

[0064] Fig. Figure 2 shows a sketch with a material surface 236 to be measured, located below the rotation axis 238 of the transmitter and receiver arms. Transmitter 210 and receiver 214 can rotate on a semicircular path 240 around the rotation axis 238.

[0065] If the material surface 236 to be measured is located in or below the test stand in such a way that the rotation axis 238 of the two arms is not in the plane of the material surface 236, the transmission angle relative to the material surface is not affected, but the receiver angle is.

[0066] In the illustration, a transmitter 210 and a receiver 214 can move around the common rotation axis 238 on the semicircular path 240.

[0067] In the example shown, the transmitter 210 is at an angle α to the vertical axis and is aligned so that the transmission beam 230 passes through the rotation axis 238 of the two arms.

[0068] If the rotation axis 238 lies on the leveled material surface 236, i.e., Δh = 0, the reception angle of the reflected beam 233 detected by the receiver 214 corresponds exactly to β. If the material surface 236 lies below the rotation axis 238 by Δh, the reflection point 232 of the beam on the material surface also shifts in the x-direction by Δx = Δh · tan (α). From this reflection point 232, the actually measured reception angle at the receiver 214 would be smaller than the desired reception angle β.

[0069] In order to measure the desired reception angle β with the receiver 214, the receiver 214 must be shifted by the correction angle γ. With the length r of the receiver arm and the length k=Δh2+Δx2 The correction angle is calculated using the sine theorem as γ=sin−1(kr⋅sin(α+β)).

[0070] The receiver 214 is accordingly shifted downward by γ, as indicated by the dashed arrow. The direction of the reflected signal 234 received at this new receiver position 215 corresponds exactly to β relative to the vertical axis or the material surface normal.

[0071] In order for the receiver 214 to be precisely aligned with the reflection point 232, the receiver 214 is additionally rotated by the correction angle γ relative to the receiver arm.

[0072] Fig. Figure 3 shows how the reflectivity measurement results can be visualized. These are preferably displayed as the intensity of the signal received by the receiver as a function of the corresponding transmission and reception angles. Glossary Gonioreflectometer

[0073] A gonioreflectometer consists of a light source that illuminates the object or material to be measured and a sensor that records the light reflected from the material. The sensor should be mounted flexibly so that it can record measurements depending on the angle. Lidar

[0074] Lidar (also LIDAR or LiDAR, abbreviation for light detection and ranging) is a radar-related method for optical distance and speed measurement, as well as for remote measurement of atmospheric parameters. Lidar systems emit directed light beams and detect the returned light. The distance to the scattered point is calculated from the time of flight of the light signals. With appropriate modulation, such as in FMCW lidar, speed can also be measured via frequency shifts. Typical wavelengths of the electromagnetic radiation used for lidar are in the range of 850 nm to 1600 nm; infrared radiation of 905 nm is used in particular. radar

[0075] Radar (short for radio detection and ranging) is the term for various detection and positioning methods and devices based on electromagnetic waves in the radio frequency range (radio waves). A radar device emits a so-called primary signal as a focused electromagnetic wave, receives the echoes reflected from objects as a secondary signal, and evaluates them according to various criteria, particularly for determining distance. Typical wavelengths for radar measurements range from 1 mm to 400 cm. Reference symbol 100 frames 102 Height-adjustable feet 104 Transmitter arm 106 Receiver arm 108 Transmitter mount 110 channels 112 Receiver mount 114 recipients 116 knurled screws 118 Drive 120 gear 122 Control unit 124 characters 126 swivel bolts 128 calibrated limit switches 130 transmit beam 132 Reflection point on the material surface 134 Reflected beam 210 channels 214 recipients 215 Receiver at a position shifted by the correction angle 230 transmission beam 232 Reflection point on the material surface 233 Hypothetically reflected ray in rotation axis 234 Beam reflected from material surface 236 Material surface 238 Rotation axis of transmitter and receiver arm 240 semicircular track on which transmitter and receiver can move cited literature cited patent literature DE 101 34 458 A1 CN 1 02 590 150 A US 4 355 271 A cited non-patent literature Gonioreflektometer der Fraunhofer Gesellschaft, aufgerufen am 16.4.2024 unter https: / / www.iosb.fraunhofer.de / de / projekte-produkte / brdf-messung-reflektanzverteilunggoniometrie / gonioreflektometer-messanlage.html Stefan Muckenhuber, Hannes Holzer, Zrinka Bockaj: „Automotive Lidar Modelling Approach Based on Material Properties and Lidar Capabilities“, Sensors 2020, 20(11), 3309; https: / / doi.org / 10.3390 / s20113309 David J. Ritter, Relindis Rott, Birgit Schlager, Stefan Muckenhuber, Simon Genser, Martin Kirchengast, Marcus Hennecke: „Angle-dependent spectral reflectance material dataset based on 945 nm time-of-flight camera measurements“, Data in Brief, Volume 48, June 2023, 109031, https: / / www.sciencedirect.com / science / article / pii / S235234092300149X?via%3Dihub Rod D. White et al.: „Reflectometer for measuring the bidirectional reflectance of rough surfaces“, Applied Optics, Vol. 37, 1998, No. 16; https: / / doi.org / 10.1364 / AO.37.003450 Dmitri Lanevski, Farshid Manoocheri, Erkki Ikonen: „Gonioreflectometer for measuring 3D spectral BRDF of horizontally aligned samples with traceability to SI“, Metrologia, Vol. 59, 2022, No. 2 (Art. No. 025006); https: / / doi.org / 10.1088 / 1681-7575 / ac55a7

Claims

[1] Method for measuring reflectivity properties of a surface of a material (236) under incidence of electromagnetic radiation (130, 230) by means of a gonioreflectometer, wherein 1.1.1 the gonioreflectometer has a frame (100); 1.1.2 the gonioreflectometer has a first and a second arm (104, 106); 1.1.3 the arms (104, 106) are rotatably attached to the frame (100); 1.1.4 the arms (104, 106) are rotatable independently of each other; 1.1.5 the arms (104, 106) are rotatable about a common axis of rotation (238); 1.1.6 the first arm (104) carries a transmitter (110) for the electromagnetic radiation; 1.1.7 the second arm (106) carries a receiver (114) for the electromagnetic radiation; 1.1.8 the transmitter (110) is attached to the first arm (104) in such a way that it can be guided on a first circular arc by the rotation of the first arm (104); and 1.1.9 the receiver (114) is attached to the second arm (106) in such a way that it can be guided on a second circular arc by the rotation of the second arm (106); the method comprising the following steps: 1.2 the surface of the material (236) is placed in the area of ​​the frame (100) of the gonioreflectometer on the rotation axis (238); 1.2.1 wherein the surface of the material (236) is placed parallel to a plane spanned by the frame (100); 1.3 an angle is specified at which the surface (236) is to be irradiated by the transmitter (110) with the electromagnetic radiation (130); 1.3.1 the first arm (104) is rotated such that the transmitter (110) assumes a position under which the electromagnetic radiation (130) irradiates the surface (236) at the predetermined angle; 1.3.2 the second arm (106) is rotated such that the receiver (114) measures the intensity of the electromagnetic radiation (134) reflected from the surface (236) at a plurality of angles; and / or 1.4 an angle is specified at which the intensity of the electromagnetic radiation (134) reflected by the surface (236) is to be measured by the receiver (114); 1.4.1 the second arm (106) is rotated such that the receiver (114) assumes a position in which it measures the intensity of the electromagnetic radiation (134) reflected from the surface (236) at the predetermined angle; 1.4.2 the first arm (104) is rotated such that the transmitter (110) irradiates the surface (236) with electromagnetic radiation (130) at a plurality of angles; 1.5 in the event that the surface (236) is placed above or below the rotation axis (238), corrections are made to the alignment of the transmitter (110) and / or receiver (114) so ​​that the transmitter (110) and receiver (114) are aligned with the point at which the electromagnetic radiation (130) emitted by the transmitter (110) strikes the surface (236). [2] Method according to the preceding method claim, characterized by that the measurement of reflectivity properties at 2.1 a plurality of different temperatures, 2.2 a variety of different relative humidities and 2.3 a plurality of different degrees of wetting and / or contamination of the surface (236) is carried out. [3] Method according to one of the preceding method claims, characterized bythat the intensities of the reflected electromagnetic radiation (134) measured by the receiver (114) are stored together with the associated transmission and reception angles. [4] Method according to the immediately preceding claim with the further step of creating a data carrier on which the obtained data are stored. [5] Method for producing a data set on reflectivity properties of surfaces of materials (236) under incidence of electromagnetic radiation (130), wherein the data are obtained by means of the method according to one of claims 1 to 4. [6] Data set of reflectivity properties obtained by the method according to the immediately preceding method claim. [7] Use of the data set according to the immediately preceding claim for computer-aided calculation of the reflection of electromagnetic radiation from surfaces. [8] Computer program comprising instructions which cause the gonioreflectometer to carry out the method steps according to one of the method claims 1 to 5. [9] A computer-readable medium on which the computer program according to the immediately preceding claim is stored.

Images