Fig 1
GE-1.6M, a typical three-blade wind turbine structure: it has rotor diameter of 82.5 m and hub height of 80 m. Vane on top of hub senses wind direction, based on which, yaw mechanism turns blade into wind for maximum efficiency. Blade position μ and aspect angle ' are defined as follows: μ is angle from yaw axis to reference leading edge, and ' is angle from radar LOS to rotor axis. Blade angle ® is angle formed by two edges of same blade.
Source publication
Wind turbines can cause interference to nearby radars due to strong backscattering. As a recently recognized type of radar interference, wind turbine radar signatures need to be fully studied. The scaled measurement of a wind turbine model has been proposed to characterize wind turbine radar signatures. The radar wind turbine testbed (RWT2) has bee...
Citations
... can cause the radar to show wind turbine images in places where they are not located. Additionally, due to their blade length, large wind turbines exhibit large blade tip speeds and significant Doppler spectrum contamination as a result [9]. These can often be above the minimum unambiguous velocity detectable by the radar, making them very difficult to filter, and causing the initiation of false tracks in the vicinity of the wind farm. ...
A novel, low cost, highly accurate, millimeter-wave RCS characterization method is developed and presented in this paper. In order to develop and verify the validity of the proposed method, full scale models and scale models of the horizontal-axis wind turbine (HAWT) and Crossflow turbines have been simulated and compared for a case study. The RCS of a scaled Crossflow turbine model was then experimentally verified using the novel method presented at frequencies of 76-81GHz. The proposed method utilizes the AWR1843BOOST evaluation board and DCA1000EVM real-time high-speed data capture card from Texas Instruments. To the best of the authors’ knowledge, this is the first RCS analysis of a scaled model performed at the mm-wave frequencies of 76-81GHz. This novel method is quick, simple, and fully automated, while maintaining high accuracy. Additionally, this has been achieved at a low cost using commercially available off the shelf parts. Good agreement was observed between the simulated and experimental results. Comparing the RCS data of the two turbines, it appears that the Crossflow turbine geometry offers a lower RCS and Doppler spectrum contamination as compared with a traditional horizontal axis wind turbine structure. These results are necessary and useful in allaying the increasing concerns regarding wind turbine radar interference, which have appeared as a result of the widespread adoption of wind power generation in recent years.
... In the past decade, radars have been used in many studies to measure wind turbines. Laboratory measurements of spectrograms for wind turbine scale models were reported in 2010 and 2013 [5][6][7][8]. From 2015 to 2017, studies have been conducted to directly measure the industrial wind turbine to obtain the spectrogram [9][10][11]. Many studies have examined the performance of structural health monitoring of wind blades using noncontact sensors. ...
In operating a wind turbine, both predictive and condition-based maintenances are required to minimize the downtime caused by maintenance. The imbalance of rotor rotational speed is an important factor for diagnosing wind turbine failures. The rotational speed imbalance can be caused by accumulated damage or the accumulation of ice, dust, and moisture. In this paper, we proposed a method for detecting the rotational speed imbalance of a wind turbine using a Doppler radar. We calculated the difference in the rotational speed for different times using spectrograms obtained by observing the wind turbine with a Doppler radar and determined the rotational speed imbalance using the fast Fourier transform. The performance of the proposed algorithm was verified using both synthetic and numerical data.
... One is to deal with the WTs by reducing their radar cross section (RCS) [5], for example to paint materials absorbing electromagnetic waves on WT blades [6]. The other one is to deal with radar by filtering WT clutters from radar echoes, which is based on acquiring the unique Doppler features of wind turbine radar echoes (WTRE) [7][8][9]. While it is difficult to apply the methods of reducing RCS effectively in real wind farms [7], current research has mainly focused on obtaining WTRE accurately [8][9][10][11][12][13]. * Correspondence: 916920262@qq.com ...
... The other one is to deal with radar by filtering WT clutters from radar echoes, which is based on acquiring the unique Doppler features of wind turbine radar echoes (WTRE) [7][8][9]. While it is difficult to apply the methods of reducing RCS effectively in real wind farms [7], current research has mainly focused on obtaining WTRE accurately [8][9][10][11][12][13]. * Correspondence: 916920262@qq.com ...
... The experimental measurements of WTRE were facing problems including high cost, complicated process, and inconvenient modification of model parameters [9,10]. As a result, people tended to develop numerical methods to simulate and obtain the Doppler features of WTRE [10][11][12], and then verify the results with experiments. ...
... Current methods to acquire wind turbine Doppler echoes could be classified into two categories, namely the experimental measurement and the numerical simulation [6][7][8][9]. Experimental measurement is the most reliable but it can hardly be widely performed due to their high cost and rather complicated procedures [7,8]. Therefore, more and more efforts have been put into the numerical simulation of wind turbine Doppler echoes. ...
... Current methods to acquire wind turbine Doppler echoes could be classified into two categories, namely the experimental measurement and the numerical simulation [6][7][8][9]. Experimental measurement is the most reliable but it can hardly be widely performed due to their high cost and rather complicated procedures [7,8]. Therefore, more and more efforts have been put into the numerical simulation of wind turbine Doppler echoes. ...
Clutter filtering according to distinct Doppler echoes is a major measure to deal with the interference in radar signals caused by the rotating blades of nearby wind turbines. For the problem that the traditional simulation method of scattering point superposition model could not simulate the continuity of induced current on the blade's complex surface, the authors proposed a new simulation method of Doppler echoes based on scattered electric field calculation and expounded the basic principle and implementation steps of the method. First, they found the correspondence between the electric field's complex amplitude vector and the echo signal by deducing the equations of echo signal and scattering electric field; second, they used the quasi‐static technique, the hybrid algorithm of physical optics and method of moment to achieve an accurate solution of the scattered electric field sequence; finally, the authors used the short‐time Fourier transform to obtain the time–frequency domain data of blades Doppler echoes. The result was compared with data obtained from the scattering point superposition model and in‐field experiments, and the accuracy of the proposed method was verified.
... In order to obtain the Doppler characteristic of the radar echo of the wind turbines, the scholars at home and abroad have made a lot of research, mainly the field measurement [9,10], the shrinkage ratio model experiment [11,12], and the mathematical simulation [13][14][15][16] method. There are two kinds of methods involved in mathematical modelling of the wind turbine echo: one is to model the wind turbine echo based on the high-frequency approximation algorithm [16] which is used in the field of electromagnetic scattering to compute the radar cross section (RCS) of wind turbine blades; and the other is, under the far field condition, to use the approximate equivalent relation to equal the wind turbine blade to the scattering points, and then to model the echo of the scattering points [15]. ...
... Contrasting (9) and (11), it shows that the expression is basically the same except that the amplitude of the echo is quite different. The difference of amplitude is mainly due to the fact that (11) ignores the interval of scattering points when the integral is obtained. Since the echo amplitude does not affect the study of Doppler characteristics, the integral model of the blade is a special case of the scattering point model. ...
Wind turbines have serious electromagnetic interference to nearby radar stations. Accurately obtaining the Doppler characteristics of wind turbine's radar echo is the key technology and precondition to solve this problem. Based on the point scattering model of the wind turbines, the expression of the echo of the wind turbine blade scattering point model which is located at any point in the space is given, and the Doppler characteristic of the wind turbine blade echo is analysed by combining the existing integral model, which proves that the existing integral model is a special case of the scattering point model. Based on the radar resolution and Rayleigh resolution criteria, the scattering point spacing of the wind turbine blade is given. The simulation model is established according to the actual size of the wind turbines. After the analysis and comparison of the scattering point model and the integral wind turbine blade model, the simulation results of the wind turbine radar Doppler results are consistent with the theoretical analysis, which is of great significance to obtain the Doppler characteristics of the wind turbine blades.
... Many varied techniques have been suggested in the literature to address this problem and mitigate the aforementioned adverse effects, with a good summary of the main approaches in [6] and in the document issued by the UK Civil Aviation Authority (CAA) 'Policy and Guidelines on Wind Turbines' [7]. Some models of turbines in controlled setups to investigate the effect of different yaw angles and rotation speeds on the resulting radar signature [15][16]. The performance of realistic radar systems affected by wind farm clutter has also been characterised, for example for the effectiveness of Ground Moving Target Indication (GMTI) algorithms for targets within the wind farm area [17], for the behaviour of weather radar stations [18][19][20], for maritime radar systems [21][22], and for the detection and tracking of unauthorised aircraft entering restricted zones [23]. ...
... Far-field measurements appear to be therefore infeasible with the available radar systems. This issue was also mentioned in [15,43], arguing that it is not unlikely that wind farms, especially those with large and tall turbines, can be located in the near-field of practical radar systems and therefore the analysis of near-field data is still significant and reasonable. ...
The negative effects wind farm clutter has on the performance of radar systems for Air Traffic Control
and Air Surveillance is well-known in the radar research community and several mitigation techniques
have been proposed to address this problem. These include bistatic and multistatic radar systems
providing multiple views of the area under surveillance, and hence potential additional information that
can be used to improve the receiver performance. This paper presents the analysis of a set of
experimental data collected simultaneously by two radar systems, one operating at S-band and one at Xband,
of echoes from an operational wind farm in the UK near Oxford. This analysis presents several
parameters extracted from the time domain data and the Doppler spectra, such as Doppler centroid and
bandwidth of the micro-Doppler signature as well as amplitude statistics of the time domain returns.
These parameters are characterised using data recorded at monostatic and bistatic nodes, as well as at
different polarisation combinations.
... This last expression of the vector potential can also be obtained by setting | ( ) − ′ | = in (16). ...
This paper presents methods and results in modelling wind turbine dynamic radar signatures in the near-field. The theoretical analysis begins with the simpler case of modelling wind turbine blades as rectangular plates. The theoretical radar signature for the wind turbine in the near-field is formulated and its main peculiarities are investigated. Subsequently, the complex shape of the blades is considered and the corresponding radar signatures are modelled. Theoretical modelling is confirmed for both cases via experimental testing in laboratory conditions. It is shown that the experimental results are in good accordance with the theoretically predicted signatures.
... Significant research has been carried out to model accurately and with computationally efficient processing the RCS and Doppler signatures of wind turbines [8][9][10]. The use of scaled models of realistic turbines for controlled measurements in laboratory has also been reported [11][12], showing the effect of different rotation speeds and yaw angles on the micro-Doppler signatures and analysing the statistics of such signatures as they fluctuate. The impact of wind farm clutter on real radar systems and their performance has been also investigated, for instance on Ground Moving Target Indication (GMTI) for targets within the wind turbine area [13], on weather radar stations [14], on maritime radar systems [15], and on the detection and tracking capabilities of unauthorized aircraft entering a restricted zone [16]. ...
... The far-field distance is actually even longer if the calculation is repeated for Xband (approximately 64 km) or if the whole tower height is considered and not only the blade, making far-field measurements infeasible in practice with any research radar at microwave frequencies. In [11] and [31] this issue is also discussed and it is argued that it is not unlikely that wind farms, especially those with the largest turbines, are located in the near-field of radar systems and hence the experimental analysis of near field data is still very valuable. ...
This paper presents the analysis of recent experimental data acquired using two radar systems at S-band and X-band to measure simultaneous monostatic and bistatic signatures of operational wind turbines near Shrivenham, UK. Bistatic and multistatic radars are a potential approach to mitigate the adverse effects of wind farm clutter on the performance of radar systems, which is a well-known problem for Air Traffic Control and Air Defence radar. This analysis compares the simultaneous monostatic and bistatic micro-Doppler signatures of two operational turbines and investigates the key differences at bistatic angles up to 23°. The variations of the signature with different polarisations, namely VV and HH, are also discussed.
... Different mitigation techniques have been proposed in the literature, such as partial reshaping of the turbine with integration of radar absorbing material [3], radically novel wind turbine design [4], and improved digital signal processing algorithms [5] among others. Numerical simulations [6] and controlled laboratory measurements with scaled models of turbines [7] have also been widely investigated to characterize wind turbine clutter in different conditions. A comprehensive campaign to record monostatic Radar Cross Section (RCS) and Doppler signatures at different radar frequency bands was reported in [8][9], but in general there is little information published on actual radar experiments with operational wind farms, especially involving bistatic and multistatic radar. ...
... It is shown that there exists combinations of bistatic angles and polarization where the clutter statistics appear more favourable for bistatic data than for the simultaneous monostatic data, i.e. the bistatic distributions have shorter tails which are more beneficial for target detection against the clutter background. It is believed that these data and results are significant, as there is a limited amount of papers that discuss statistical models of wind turbine clutter [7,12], and only using monostatic data rather than bistatic/multistatic. ...
... Data analysis: The resolution for the S-band data is sufficient to discriminate in range the return from different turbines, hence the amplitude values at range bins containing the radar echoes from the TUT1 and TUT 2 are analysed separately. These values are related to the RCS of the turbines, but RCS can be properly defined only in the far-field of the turbines, whereas these measurements were performed in the near-field as the far-field distance at S-band would be in the range of 15 km, infeasible in practice for any research radar [7]. ...
This Letter presents preliminary results of the analysis of amplitude statistics of wind turbine clutter as extracted from multistatic radar data. It is shown that the T-location-scale distribution provides good fitting of the experimental data, and that there are combinations of bistatic angle and polarisations where the bistatic clutter has more favourable statistics for target detection than the simultaneous monostatic clutter.
... For the ILS case the initial approach of scaling and including the actual navigation information is presented in [8]. Investigations on scaled wind turbines are presented in [9], [10] but they are performed under the mentioned plane wave restriction that does not resemble realistic scenarios. The actual navigation information that provides a spatially differential signal is not included. ...
The performance of navigation systems is always reduced by unwanted multipath propagation. This is especially of practical importance for airborne navigation systems like the instrument landing system (ILS) or the VHF omni directional radio range (VOR). Nevertheless, the quantitative analysis of corresponding, potentially harmful multipath propagation disturbances is very difficult due to the large parameter space. Experimentally difficulties arise due to very expensive, real scale measurement campaigns and numerical simulation techniques still have shortcomings which are briefly discussed. In this contribution a new universal approach is introduced on how to measure very flexibly multipath propagation effects for arbitrary navigation systems using a channel sounder architecture in a scaled measurement environment. Two relevant scenarios of multipath propagation and the impact on navigation signals are presented. The first describes disturbances of the ILS due to large taxiing aircraft. The other example shows the influence of rotating wind turbines on the VOR.
