GB2561258A

GB2561258A - System and method for measuring atmospheric attenuation

Info

Publication number: GB2561258A
Application number: GB1709107.5A
Authority: GB
Inventors: Banda Rueda Antonio; Joseph John Jim
Original assignee: Dubai Electricity and Water Authority
Current assignee: Dubai Electricity and Water Authority
Priority date: 2017-04-03
Filing date: 2017-06-08
Publication date: 2018-10-10
Anticipated expiration: 2037-06-08
Also published as: GB2561258B; GB201709107D0

Abstract

A system for measuring atmospheric attenuation of radiation comprises at least one vehicle, a radiation source and a radiation detector configured to measure the radiation from the source. The system further comprises means for precise positioning of the vehicle. The vehicle may be a drone (D) and/or a rover (R) and they may be autonomous or remotely controlled. The radiation detector is mounted on the drone and the radiation source is mounted on the rover (or vice versa), and the system is configured such that the atmospheric attenuation of the radiation can be measured over several distances and elevation angles. Such a system is optimally suited to performing all the measurements necessary for monitoring atmospheric attenuation at a central tower concentrated solar power plant.

Description

(54) Title of the Invention: System and method for measuring atmospheric attenuation Abstract Title: System and method for measuring atmospheric attenuation (57) A system for measuring atmospheric attenuation of radiation comprises at least one vehicle, a radiation source and a radiation detector configured to measure the radiation from the source. The system further comprises means for precise positioning of the vehicle. The vehicle may be a drone (D) and/or a rover (R) and they may be autonomous or remotely controlled. The radiation detector is mounted on the drone and the radiation source is mounted on the rover (or vice versa), and the system is configured such that the atmospheric attenuation of the radiation can be measured over several distances and elevation angles. Such a system is optimally suited to performing all the measurements necessary for monitoring atmospheric attenuation at a central tower concentrated solar power plant.

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-1 Applicant:

Dubai Electricity and Water Authority

System and method for measuring atmospheric attenuation

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to a system and method for measuring atmospheric attenuation. This is of relevance e.g. in solar thermal power plants, especially in those that use central tower (CT) concentrated solar power (CSP) technology, with receivers that may be positioned hundreds of meters distant from reflecting heliostat mirrors. Atmospheric attenuation due to scattering and extinction by aerosols and e.g. water vapor in the lower atmosphere will occur in such a situation, and must be monitored.

DESCRIPTION OF RELATED ART

Current methods used for evaluating atmospheric attenuation are laborious, inflexible and may have large errors. Typical setups are described by Ζ. M. Tahboub et al. (“Solar Beam Attenuation Experiments - Abu Dhabi, Conference Proceedings of 18^th SolarPACES Conference, January 2012). They involve a small number (usually four) of measuring stations, where pyrheliometers are mounted. The radiation source is either the sun or its reflection on a heliostat. Such a setup only allows for measurements over a very limited number of distances and elevation angles, and thus only a very coarse detemination of the attenuation at e.g. a solar thermal plant. Setting up a number of measuring stations also requires a lot of effort.

-2OBJECT OF THE INVENTION

It is, therefore, an object of the present invention to provide an improved system and method for measuring atmospheric attenuation of radiation.

BRIEF SUMMARY OF THE INVENTION

This aim is achieved by the inventions as claimed in the independent claims. Advantageous embodiments are described in the dependent claims.

Even if no multiple back-referenced claims are drawn, all reasonable combinations of the features in the claims shall be disclosed.

The present invention proposes a system for measuring atmospheric attenuation of radiation, comprising at least one aerial or ground vehicle, a radiation source and a radiation detector configured to detect and measure the radiation from the radiation source. The system further comprises a positioning system for positioning the at least one vehicle at a predetermined measuring position, preferably with an uncertainty of less than 10 cm. At least one of the radiation detector and the radiation source is mounted on the at least one vehicle, and the system is configured for aligning the radiation source and the radiation detector and calculating the atmospheric attenuation on the basis of the measured radiation between the radiation source and the radiation detector.

Since at least one of the radiation source and the radiation detector is mounted on a vehicle and thus mobile, the system allows measurements of the atmospheric attenuation over a virtually unlimited range of distances, and also - if the vehicle is an aerial vehicle - a virtually unlimited range of elevation angles. The attenuation at a large site can thus be determined with more or less any desired spatial resolution, since obtaining additional data points merely requires navigating the vehicle to the next desired measuring location and then performing the measurement.

In a preferred embodiment, the system comprises a first and a second vehicle, more preferably an aerial vehicle (e.g. a helicopter) and a ground vehicle. It is also preferred if at least one vehicle is an unmanned aerial or ground vehicle, and especially preferred if one of the vehicles is an unmanned aerial vehicle (e.g. a drone) and the other vehicle is an unmanned ground vehicle (rover). In all cases in which the system comprises two vehicles, the radiation detector is mounted on one vehicle and the radiation source is mounted on the oth-3er vehicle. Such a system is optimally suited to performing all the measurements necessary for monitoring atmospheric attenuation at a CT CSP plant.

In advantageous developments of the system, either at least one of the unmanned vehicles is remote controlled, or at least one of the unmanned vehicles is automatically controlled by software. Remote control allows the (human) operator to adapt to unforeseen circumstances, providing safer and more efficient operation. Automatic control via software allows the system to operate for longer periods of time without human intervention, which saves labor costs, potentially increases positioning accuracy and is especially advantageous in the event of long, tedious series of measurements, e.g. at a large site. If the unmanned ground vehicle is automatically controlled, the control software must include obstacle avoidance and pathfinding algorithms.

In further embodiments of the system, the positioning system comprises Real Time Kinematic satellite navigation, or Lidar, or image pattern positioning.

Real Time Kinematic satellite navigation supplements or enhances commonly used satellite navigation systems, e.g. GPS, whose accuracy (approximately 3 m) is insufficient for the purpose of this invention.

Alternatively, Lidar can be used - this is especially advantageous if the unmanned vehicles are already equipped with such a system for navigation and object avoidance purposes. Preferably, two systems may be used, one installed alongside the radiation source and one alongside the detector. Thus, a high-precision relative coordinate system can be established between the two.

Image pattern positioning is an alternative solution for achieving accurate relative positions of radiation source and detector, using image-recognition techniques. In this case the hardware required to be installed on the unmanned vehicles is less complex and costly.

Various embodiments are possible, wherein the radiation source comprises one or more of the following group: a wide spectrum LED, a laser source with a preferable wavelength of 470, 530, or 650 nm, an infrared source, an ultraviolet source, or a reflective or refractive solar radiation source. The choice of radiation source may depend on the expected atmospheric aerosol or water content, weather conditions, desired visibility measurements or other criteria. Typically, reflected or refracted solar radiation or a source that approximates solar radiation is used.

-4Accordingly, in various embodiments the radiation detector comprises one or more of the following group: a photodiode, a pyrheliometer, a spectral solar irradiance meter, a light detector configured for detecting visible light, infrared radiation or ultraviolet radiation, or a narrow-band detector for detecting light with a wavelength of 470, 530, or 650 nm. The choice of detector is usually dependent on the chosen radiation source. Preferably, a pyrheliometer is used.

The inventive system becomes especially useful and efficient if the unmanned aerial or ground vehicles are configured to autonomously assume coordinated measuring positions according to a predetermined pattern, wherein the predetermined pattern is configured such that the coordinated measuring positions allow the radiation from the radiation source to be measured with the radiation detector over several distances and/or elevation angles. The predetermined pattern could have any kind of geometrical shape (e.g. linear, symmetrical around any number of axes), or even be completely random. However, it is preferred that the shape correspond to the site layout, e.g. a series of concentric circles or ellipses for a typical CT CSP plant. If applicable, the pattern also determines the altitude or altitudes at which the unmanned aerial vehicle operates.

Advantageously, the system additionally comprises a charging (if the vehicles are electrically powered) or refueling station (if the vehicles are fuel powered, e.g. gas or diesel) compatible with the at least one unmanned aerial or ground vehicle. Said at least one unmanned aerial or ground vehicle is configured to automatically navigate to the charging or refueling station when its charge or fuel level falls below a predetermined value, and subsequently to recharge or refuel, preferably automatically. This procedure can be simplified if the charging station operates according to the induction principle.

The object of the invention is also achieved by a method. In what follows, individual steps of a method will be described. The steps do not necessarily have to be performed in the order given in the text. Also, further steps not explicitly stated may be part of the method.

A method for measuring atmospheric attenuation of radiation is thus suggested, with the following steps:

providing a radiation source and a radiation detector;

wherein the radiation detector is configured to detect and measure radiation from the radiation source;

-5providing at least one vehicle; wherein said at least one vehicle comprises an aerial and/or a ground vehicle;

providing a positioning system for positioning the at least one vehicle at a predetermined measuring position, preferably with an uncertainty of less than 10 cm;

wherein at least one of the radiation detector and the radiation source is mounted on the at least one vehicle;

aligning the radiation source and the radiation detector;

measuring the radiation from the radiation source with the radiation detector; and calculating the atmospheric attenuation between the radiation source and the radiation detector based on the measured radiation.

Since at least one of the radiation source and the radiation detector is mounted on a vehicle and thus mobile, this method allows measurements of the atmospheric attenuation over a virtually unlimited range of distances, and also - if the vehicle is an aerial vehicle -a virtually unlimited range of elevation angles. The attenuation at a large site can thus be determined with more or less any desired spatial resolution, since obtaining additional data points merely requires navigating the vehicle to the next desired measuring location and then performing the measurement.

In a preferred embodiment, two vehicles are provided: an unmanned aerial vehicle (drone) and an unmanned ground vehicle (rover); wherein the radiation detector is mounted on one of the vehicles and the radiation source is mounted on the other vehicle.

It is advantageous to perform the additional step of calibrating the radiation detector.

A development of the method described above involves performing the steps of navigating the at least one vehicle to within 10 cm of a predetermined measuring position;

aligning the radiation source and the radiation detector;

measuring the radiation from the radiation source with the radiation detector; and calculating the atmospheric attenuation between the radiation source and the radiation detector;

multiple times, such that the measurements occur at several distances and/or elevation angles.

In such a way, all the measurements necessary for monitoring atmospheric attenuation at a CT CSP plant can be obtained.

-6BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects and advantages of the present invention may be ascertained from a reading of the specification and appended claims in conjunction with the drawings therein.

For a more complete understanding of the present invention, reference is established to the following description made in connection with accompanying drawings in which:

Fig. 1 shows a schematic cross section of a typical CT power plant;

Fig. 2 shows schematic top view of a typical CT power plant;

Fig. 3 shows the same view as Fig. 1, with a typical measurement pattern for a drone and a rover according to the invention; and

Fig. 4 shows the same view as Fig. 2, with a typical measurement pattern for a drone and a rover according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 show representative images of a central tower based power plant. The heliostats H1, H2, H3, HT, H2’, H3’ are positioned in a circular or elliptical manner to focus the solar radiation received on their reflective surfaces to the thermal receiver CT at the center. The dashed circles in Fig. 2 symbolize the positions of all the heliostats.

The measuring setup consists of four main components: A drone D, a rover R (which can be seen in Figs. 3 and 4), and a radiation source and a radiation detector, which are each mounted on one of the unmanned vehicles. In Fig. 3, the short-dashed lines represent possible movements of the drone D and rover R between measuring positions, which would usually coincide with the typical heliostat positions H1, H2, H3, HT, H2’, and H3’ for the rover R, and with the tower position for the drone D. The long-dashed lines correspond to the typical optical beam paths for the measurements. In Fig. 4, the dotted lines show rover positions for measurements according to a typical pattern.

For example, the drone D can be equipped with the detector or the light source for the spectral measurements. The light source could either be a wide spectrum LED or a combination of a number of laser sources of wavelengths in the range of 470, 530 or 650 nm (for visibility measurement) and/or other wavelength ranges (based on the expected local aerosol content of the atmosphere). The detector would be accordingly mounted on the rover R and

-7may accordingly comprise photodiodes or other sensors that can identify the light beam from the source. Based on e.g. the weather conditions, either the drone D or the rover R can be mounted with the light source or the detector assembly.

The drone D can be mounted with a pyroheliometer or a solar spectral irradiance meter (e.g. from Spectrafry) to detect the beam radiation or direct normal irradiance (DNI) at various altitudes from the ground to find the attenuation in the DNI. A light detector adapted to the emitter is also considered.

Accurate localization is needed for the rover to follow accurate paths and adjust sensor angles and the drone altitude. In fact, global navigation satellite systems such as GPS alone could be used, but they suffer from considerable inaccuracy (3 m error range), which is too high for the desired measurements. However, there are several ways to improve. One way is to use Real Time Kinematic (RTK) satellite navigation. Another way to achieve accurate localization is by using Lidar, which measures the distance to a target by illuminating that target with a laser light. Two Lidar systems can be installed (if they are not already provided by design), one on the drone D and one on the rover R, to create a relative coordinate system between them, which can be used to adjust drone altitude, rover paths and sensor angles accordingly. Image pattern positioning for sensor and emitter aiming is the simplest option.

The system is intended to reduce the labor cost and increase measurement accuracy. Therefore, additional autonomous functionalities that enable the system to run for long time period without human intervention are also provided:

Autonomous navigation

The drone should fly autonomously in coordination with the rover location and sensor angles. In certain situations, the rover should take a detour to avoid certain obstacles and then continue on its predefined path. The rover should navigate autonomously and obtain optimal paths over different terrains (e.g., sand dunes).

Automatic drone/rover charging

The drone should land on a charging station whenever needed. An Inductive charging station can be used to simplify the charging process. Similarly, the rover should navigate autonomously to a charging dock as required. Gas (or other fuel) operated drones/rovers in combination with autonomous fuel stations are considered as an alternative.

System planning

The system should automatically test different measurement patterns, i.e. layouts, drone heights and e.g. circles/ellipses for the rover, in order to find an optimal set-up. Different layouts should be tested at different time slots and consolidated in a detailed report that illustrates optimal layouts for any time during a day or a year.

-8While the present invention has been described and illustrated in conjunction with a number of specific embodiments, those skilled in the art will appreciate that variations and modifications may be made without departing from the principles of the invention as herein illustrated, as described and claimed. The present invention may be embodied in other spe5 cific forms without departing from its spirit or essential characteristics. The described embodiments are considered in all respects to be illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalence of the claims are to be embraced within this scope.

Glossary

-9Atmospheric attenuation or extinction

As it passes through the atmosphere, sunlight is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Atmospheric attenuation varies with location and altitude. Astronomical observatories generally are able to characterize the local extinction curve very accurately, to allow observations to be corrected for the effect. Atmospheric extinction has three main components: Rayleigh scattering by air molecules, scattering by aerosols, and molecular absorption. The most important sources of absorption are molecular oxygen and ozone, which absorb strongly in the near-ultraviolet, and water, which absorbs strongly in the infrared. The amount of atmospheric extinction depends on the elevation angle (astronomical altitude) of an object, being lowest at the zenith and at a maximum near the horizon. It is calculated by multiplying the standard atmospheric extinction curve by the mean airmass calculated over the duration of the observation.

Central tower

The solar power tower, also known as 'central tower' (CT) power plants or 'heliostat' power plants or power towers, is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target) (from https://en.wikipedia.org/wiki/Solar_power_tower).

Concentrated solar power

Concentrated solar power (CSP) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electricity is generated when the concentrated light is converted to heat, which drives a heat engine (usually a steam turbine) connected to an electrical power generator or powers a thermochemical reaction (from https://en.wikipedia.org/wiki/Concentrated_solar_power).

Heliostat

A heliostat (from helios, the Greek word for sun, and stat, as in stationary) is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space. To do this, the reflective surface of the mirror is kept perpendicular to the bisector of the angle between the directions of the sun and the target as seen from the mirror. In almost every case, the

-10target is stationary relative to the heliostat, so the light is reflected in a fixed direction (from https://en.wikipedia.org/wiki/Heliostat).

Lidar

Lidar (also called LIDAR, LiDAR, and LADAR) is a surveying method that measures distance to a target by illuminating that target with a laser light. The name Lidar, sometimes considered an acronym of Light Detection And Ranging, was originally a portmanteau of light and radar. Lidar is popularly used to make high-resolution maps, with applications in geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. Lidar sometimes is called laser scanning and 3D scanning, with terrestrial, airborne, and mobile applications.

Autonomous vehicles use Lidar for obstacle detection and avoidance to navigate safely through environments, using rotating laser beams. Cost map or point cloud outputs from the Lidar sensor provide the necessary data for robot software to determine where potential obstacles exist in the environment and where the robot is in relation to those potential obstacles (from https://en.wikipedia.org/wiki/Lidar).

Pyrheliometer

A pyrheliometer is an instrument for measurement of direct beam solar irradiance. Sunlight enters the instrument through a window and is directed onto a thermopile which converts heat to an electrical signal that can be recorded. The signal voltage is converted via a formula to measure watts per square meter. It is generally used with a solar tracking system to keep the instrument aimed at the sun (from https://en.wikipedia.org/wiki/Pyrheliometer).

Real Time Kinematic satellite navigation

Real Time Kinematic (RTK) satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems such as GPS, GLONASS, Galileo, and BeiDou. It uses measurements of the phase of the signal's carrier wave, rather than the information content of the signal, and relies on a single reference station or interpolated virtual station to provide real-time corrections, providing up to centimeterlevel accuracy. With reference to GPS in particular, the system is commonly referred to as Carrier-Phase Enhancement, or CPGPS (from https://en.wikipedia.org/wiki/Real_Time_Kinematic).

-11 Unmanned aerial vehicle

An unmanned aerial vehicle (UAV), commonly known as a drone, unmanned aircraft system (UAS), or by several other names, is an aircraft without a human pilot aboard. The flight of UAVs may operate with various degrees of autonomy: either under remote control by a human operator, or fully or intermittently autonomously, by onboard computers. UAVs are often preferred for missions too dull, dirty or dangerous for humans (from https://en.wikipedia.org/wiki/Unmanned_aerial_vehicle).

Unmanned ground vehicle

An unmanned ground vehicle (UGV) is a vehicle that operates while in contact with the ground and without an onboard human presence. UGVs can be used for many applications where it may be inconvenient, dangerous, or impossible to have a human operator present. Generally, the vehicle will have a set of sensors to observe the environment, and will either autonomously make decisions about its behavior or pass the information to a human opera15 tor at a different location who will control the vehicle through teleoperation (from https://en.wikipedia.org/wiki/Unmanned_ground_vehicle). In the context of the present invention, a UGV is also referred to as “rover”.

-12 References

CT	thermal receiver
5 H1, H2, H3, HT,	, H2’, H3’ heliostat
D	drone
R	rover

-13References Cited

Non-patent literature

Z. M. Tahboub et al.: “Solar Beam Attenuation Experiments - Abu Dhabi”, Conference Pro ceedings of 18^th SolarPACES Conference, January 2012

Claims

1. System for measuring atmospheric attenuation of radiation, comprising:

at least one vehicle (R, D); wherein the at least one vehicle comprises an aerial and/or a ground vehicle;

a radiation source and a radiation detector;

wherein the radiation detector is configured to detect and measure radiation from the radiation source; and a positioning system for positioning the at least one vehicle at a predetermined measuring position, preferably with an uncertainty of less than 10 cm;

wherein the system is configured for aligning the radiation source and the radiation detector; and wherein the system is configured for calculating the atmospheric attenuation on the basis of the measured radiation between the radiation source and the radiation detector.

2. System according to claim 1, comprising a first and a second vehicle, wherein the radiation detector is mounted on the first vehicle and the radiation source is mounted on the second vehicle.

3. System according to claim 2, wherein one of the vehicles is an aerial vehicle (D) and the other vehicle is a ground vehicle (R).

4. System according to claim 1, wherein the at least one vehicle is an unmanned aerial or ground vehicle.

5. System according to claim 2 or 3, wherein at least one of the vehicles is an unmanned aerial or ground vehicle.

6. System according to one of claims 2, 3 or 5, wherein one of the vehicles is an unmanned aerial vehicle (D) and the other vehicle is an unmanned ground vehicle (R).

7. System according to one of claims 4 to 6, wherein at least one of the unmanned vehicles (R, D) is remote controlled.

-158. System according to one of claims 4 to 7, wherein at least one of the unmanned vehicles (R, D) is automatically controlled by software.

9. System according to one of claims 1 to 8, wherein the positioning system comprises a Real Time Kinematic satellite navigation system.

10. System according to one of claims 1 to 8, wherein the positioning system comprises a Lidar system.

11. System according to one of claims 1 to 8, wherein the positioning system comprises an image pattern positioning system.

12. System according to one of claims 1 to 11, wherein the radiation source comprises one or more of the following group: a wide spectrum LED, a laser source with a preferable wavelength of 470, 530, or 650 nm, an infrared source, an ultraviolet source, or a reflective or refractive solar radiation source.

13. Method according to one of claims 11-12, wherein the steps of navigating the at least one of the vehicles to a predetermined measuring position; aligning the radiation source and the radiation detector;

are performed multiple times, such that the measurements occur at several distances and/or elevation angles.

Simon Colcombe

21 November 2017

13. System according to one of claims 1 to 12, wherein the radiation detector comprises one or more of the following group: a photodiode, a pyrheliometer, a spectral solar irradiance meter, a light detector configured for detecting visible light, infrared radiation or ultraviolet radiation, or a narrow-band detector for detecting light with a wavelength of 470, 530, or 650 nm.

14. System according to one of claims 4 to 13, wherein the at least one unmanned aerial or ground vehicle is configured to autonomously assume coordinated measuring positions according to a predetermined pattern;

wherein the predetermined pattern is configured such that the coordinated measuring positions allow the radiation from the radiation source to be measured with the radiation detector over several distances and/or elevation angles.

15. System according to one of claims 4 to 14, wherein the at least one unmanned aerial or ground vehicle is electrically powered;

additionally comprising a charging station;

wherein the at least one unmanned aerial or ground vehicle is configured to automatically navigate to the charging station when a charge level of the unmanned aerial or ground vehicle falls below a predetermined value, and subsequently to recharge automatically.

-1616. System according to one of claims 4 to 14, wherein the at least one unmanned aerial or ground vehicle is fuel powered;

additionally comprising a refueling station for the type of fuel used;

wherein the at least one unmanned aerial or ground vehicle is configured to automatically navigate to the refueling station when a fuel level of the unmanned aerial or ground vehicle falls below a predetermined value, and subsequently to refuel automatically.

17. Method for measuring atmospheric attenuation of radiation, with the following steps:

providing a radiation source and a radiation detector;

providing at least one vehicle; wherein said at least one vehicle comprises an aerial and/or a ground vehicle;

aligning the radiation source and the radiation detector;

18. Method according to claim 17, wherein an unmanned aerial vehicle (D) and an unmanned ground vehicle (R) are provided; and wherein the radiation detector is mounted on one of the unmanned vehicles, and the radiation source is mounted on the other unmanned vehicle.

19. Method according to claim 17 or 18, with the additional step of calibrating the radiation detector.

tion:

20. Method according to one of claims 17 to 19, wherein the steps of navigating the at least one vehicle to within 10 cm of a predetermined measuring posi-17 aligning the radiation source and the radiation detector;

Amendments to the claims have been filed as follows;

05 06 18

1. System for measuring atmospheric attenuation of radiation in a CT (central tower) CSP (concentrated solar power) plant, comprising:

an unmanned aerial vehicle (D) and an unmanned ground vehicle (R); a radiation source and a radiation detector;

wherein the radiation detector is configured to detect and measure radiation from the radiation source; and a positioning system for positioning at least one of the vehicles at a predetermined measuring position;

wherein the radiation source is mounted on one of the vehicles and the radiation detector is mounted on the other of the vehicles;

wherein the system is configured for aligning the radiation source and the radiation detector;

wherein the system is configured for calculating the atmospheric attenuation on the basis of the measured radiation between the radiation source and the radiation detector;

wherein at least one of the vehicles is configured to autonomously assume coordinated measuring positions according to a predetermined pattern;

wherein the predetermined pattern is configured such that the coordinated measuring positions allow the radiation from the radiation source to be measured with the radiation detector over several distances and/or elevation angles; and, wherein the predetermined pattern has the geometrical shape of the CT CSP plant.

2. System according to claim 1, wherein at least one of the vehicles (R, D) is remote controlled.

3. System according to claim 1, wherein at least one of the vehicles (R, D) is automatically controlled by software.

4. System according to one of claims 1 to 3, wherein the positioning system comprises a Real Time Kinematic satellite navigation system.

5. System according to one of claims 1 to 3, wherein the positioning system comprises a Lidar system.

6. System according to one of claims 1 to 3, wherein the positioning system comprises an image pattern positioning system.

7. System according to one of claims 1 to 6, wherein the radiation source comprises one or more of the following group: a wide spectrum LED, a laser source with a preferable wavelength of 470, 530, or 650 nm, an infrared source, an ultraviolet source, or a reflective or refractive solar radiation source.

8. System according to one of claims 1 to 7, wherein the radiation detector comprises one or more of the following group: a photodiode, a pyrheliometer, a spectral solar irradiance meter, a light detector configured for detecting visible light, infrared radiation or ultraviolet radiation, or a narrow-band detector for detecting light with a wavelength of 470, 530, or 650 nm.

05 06 18

9. System according to one of claims 1 to 8, wherein at least one of the vehicles is electrically powered;

additionally comprising a charging station;

wherein the at least one of the vehicles is configured to automatically navigate to the charging station when a charge level of said vehicle falls below a predetermined value, and subsequently to recharge automatically.

10. System according to one of claims 1 to 8, wherein at least one of the vehicles is fuel powered;

additionally comprising a refueling station for the type of fuel used;

wherein the at least one of the vehicles is configured to automatically navigate to the refueling station when a fuel level of said vehicles falls below a predetermined value, and subsequently to refuel automatically.

11. Method for measuring atmospheric attenuation of radiation in a CT (central tower) CSP (concentrated solar power) plant, with the following steps:

providing a radiation source and a radiation detector;

05 06 18 providing an unmanned aerial vehicle (D) and an unmanned ground vehicle (R); providing a positioning system for positioning at least one of the vehicles at a predetermined measuring position;

aligning the radiation source and the radiation detector;

measuring the radiation from the radiation source with the radiation detector; and calculating the atmospheric attenuation between the radiation source and the radiation detector based on the measured radiation;

12. Method according to claim 11, with the additional step of calibrating the radiation detector.