Wind Turbine Blade Radar Signatures in the Near Field:Modeling and Experimental Confirmation

This paper presents methods and results in modeling wind turbine dynamic radar signatures in the near field. The theoretical analysis begins with the simpler case of modeling 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 modeled. Theoretical modeling 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

Experimental analysis of multistatic wind turbine radar clutter statistics

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

WIND TURBINE CLUTTER IN WEATHER RADAR: CHARACTERIZATION AND MITIGATION

With the rapid growth of the wind power industry, many commercial utility-scale wind turbines have been built across the country. These extremely large man-made structures are reported to have negative impact on nearby radars due to their complex scattering mechanisms. Various forms of clutter effect caused by wind turbines in the radar vicinity are generally referred to as the Wind Turbine Clutter (WTC). Due to the lack of awareness on this newly recognized clutter, many wind farms have been built in the Line of Sight (LOS) coverage of operational radars, potentially affecting their performance. Weather radar is the one affected most by WTC because the target of interest is precipitation particles, which is spatially inseparable from the wind turbine within the clutter contaminated resolution volume. Our study thus focuses on analyzing the cause of different types of clutter effects by wind turbines, characterizing the radar signatures of such clutter and mitigating the clutter effect for weather radar. The Micro-Doppler signature of the WTC reveals interesting time-variant spectrum features which are closely related to the instantaneous motions of the wind turbine. The complex motions of a wind turbine can be mostly characterized by three rotations: roll, pitch and yaw. Electromagnetic (EM) characterization of such a dynamic electrical large target is challenging. Various scattering mechanisms are analyzed and the back scattered field and RCS of the wind turbine are computed using commercial EM solver and a hybrid high-frequency approximation approach developed from our study. Field measurements were carried out by deploying the mobile radar to wind farms. The measurements give us the first non-aliased Doppler spectrum of wind turbines. In order to synchronize the wind turbine motion with radar data acquisition, the Radar Wind Turbine Testbed (RWT$^2$) was developed for indoor scaled measurements, which includes the scaled wind turbine model and the scatterometer. Both frequency and time domain measurements were made to characterize the statistics of return signal from the wind turbine model. Several mitigation schemes developed from our study will be discussed, including the telemetry based method, the Adaptive Spectrum Processing (ASP) and the mitigation scheme for moment data based on the Maximum A Posterior (MAP) criteria. A thorough analysis of utilizing LOS avoidance to prevent WTC at the first place will be presented at the end

From Fauna to Flames : Remote Sensing with Scheimpflug Lidar

This thesis presents applications of the Scheimpflug Lidar (S-Lidar) method. The technique has been applied to combustion diagnostics on a scale of several meters as well as fauna detection and monitoring over distances of kilometers. Lidar or laser radar is a remote sensing technique where backscattering of laser light is detected with range resolution along the direction of the laser beam. It is an established method in e.g. atmospheric sensing where it is used to map and monitor gases and aerosols. In contrast to conventional Lidar, which uses a time-of-flight approach, Scheimpflug Lidar uses imaging to achieve range resolution. The laser beam transmitted from the Lidar system is sharply imaged onto a detector, resulting in range resolution along the sensor. This is done by placing the laser beam, the collection optics and the detector according to two trigonometrical conditions called the Scheimpflug and hinge rules. This kind of Lidar technique enables the use of small, continuous-wave diode lasers and line-array detectors with kHz sampling rates. A general description of the equations governing the achievable measurement range and resolution of S-Lidar are presented. The way the equations relate to the conventional Lidar equation is also discussed as well as the impact of the beam width. The instrumentation and experimental considerations for far range S-Lidar for aerial fauna monitoring are described and some temporally and spatially resolved data from field campaigns in Africa, China and Sweden are presented. A method used to reduce and analyze the large amount of collected data is also described. For the short-range applications, down-scaled versions of the system were developed. These systems are described as well as their applications. The short range system has mostly been used to investigate the potential of the technique to be applied for combustion diagnostics, and results from measurements in flames using both elastic and inelastic optical techniques, such as Rayleigh scattering and two-line atomic fluorescence are presented. A hyperspectral Lidar system aimed at aquatic applications is also presented

Investigation of non-cooperative target recognition of small and slow moving air targets in modern air defence surveillance radar

This thesis covers research in the field of non-cooperative target recognition given the limitations of modern air defence surveillance radars. The potential presence of low observable manned or unmanned targets within the vast surveillance volume demand highly sensitive systems. This may again introduce unwanted detections of single birds of comparable radar cross section, previously avoided by use of wide clutter rejection filters and sensitivity time control. The demand for methods effectively separating between birds and slow moving manmade targets is evident. The research questions addressed are connected to identification of characteristic features of birds and manmade targets of comparable size. Ultimately the goal has been to find methods that can utilize such features to effectively distinguish between the classes. In contrast to the vast majority of non-cooperative target recognition publications, this thesis includes non-rigid targets covering a range of dielectric properties and targets falling in the resonant and Rayleigh scattering regions. These factors combined with insufficient spatial resolution for classification require alternative approaches such as utilization of periodic RCS modulation, micro-Doppler- and polarimetric signatures. Signatures of birds and UAVs are investigated through electromagnetic prediction and radar measurements. A flexible and fully polarimetric radar capable of simultaneous operation in both L- and S-band is developed for collection of relevant signatures. Inspired by the use of polarimetric radar for classification of precipitation covered in the weather radar literature, focus has been on using similar methods to recognize signatures of rotors, propellers and bird wings. Novel micro-Doppler signatures combining polarimetric information from this sensor is found to hold information about the orientation of such target parts. This information combined with several other features is evaluated for classification. The benefit from involving polarimetric measurements is especially investigated, and is found to be highly valuable when information provided by other methods is limited

Aeronautical engineering: A continuing bibliography with indexes (supplement 319)

This report lists 349 reports, articles and other documents recently announced in the NASA STI Database. The coverage includes documents on the engineering and theoretical aspects of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems. It also includes research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles

Aeronautical Engineering: A Continuing Bibliography with Indexes

This report lists reports, articles and other documents recently announced in the NASA STI Database