This research proposes a highly sensitive transformer fault detection method based on fluorescence spectral analysis to solve the problems of DGA (Dissolved Gases Analysis) technology, which is widely used for insulating oil condition detection: (1) the detection cycle is long and cannot respond in time; (2) the detection sensitivity is insufficient and fails when the amount of dissolved gas is small or there is no dissolved gas under low-energy fault. Fluorescence spectroscopy-based rapid detection technique. To master the fluorescence spectrum features of insulating oil and its ideal acquisition settings, the fluorescence spectral characteristics of commercially available new oil and insulating oil from real functioning transformers were gathered and evaluated. Perform a thermal aging fault simulation test, collect fluorescence spectra from defective oil samples to determine the ideal excitation wavelength, and link the fluorescence bimodal characteristic ratio with the duration of the thermal aging fault. The comparison results show that the fluorescence spectroscopy analysis method can detect the fault on the 30th day of thermal aging, which is approximately ten days earlier than the DGA method, shows how the test can assist fluorescence analysis approaches in detecting failures at an earlier stage. Meanwhile, fluorescence spectroscopic detection and analysis are quick, allowing for online real-time defect monitoring. The approach has the benefits of being quick and sensitive and not requiring sample treatment, and it has a promising future in the field of transformer failure identification.
The Off-axis Three-mirror Simultaneous Imaging Polarimeter (OTSIP) is a kind of polarimetric remote sensor with high spatial resolution. In OTSIP, simultaneous measurements were performed by means of prism dividing amplitude. Due to various equipped polarizers and complex polarimetric characteristics of OTSIP, its instrument matrix will deviate from the ideal value. In order to ensure the polarimetric accuracy of OTSIP, the development of an efficient polarimetric calibration is indispensable. In this paper, a calibration method using a standard linear polarization light source and circular polarization light source was proposed. The first three columns of the instrument matrix were firstly calibrated by a linear polarimetric calibration source to obtain the calibration coefficients via the least-squares fitting algorithm, and then the fourth column of the instrument matrix was calibrated by a circular polarimetric calibration source. Moreover, the nonideality of circular polarization state light was significantly improved by averaging measured results at 0 and 90° azimuths. As for the full field of view polarization calibration, a linear fitting method to each element of the instrument matrixes at multiple field of view angles was used. The resulting polarimetric measurement accuracy showed that the linear and circular polarization measurement accuracy was better than 1% (DOP<=0.3), validating the effectiveness and feasibility of this polarimetric calibration method. This method greatly improves the calibration efficiency of the OTSIP, making it possible to calibrate the polarimeter in flight.
The spatially modulated full polarization imaging system can acquire target images and polarization information by using spatial carrier fringes to encode full Stokes parameters in a single interference image. This polarization detecting technology uses a Savart Plate (SP) as a spatial modulation module encodes two-dimensional Stokes parameters S0~S3 and the information of four Stokes quantities can be obtained by a single detection. The principle and mathematical model of this system is analyzed in details, and the image reconstruction method is also presented. Two different frequency domain filtering algorithms for demodulation are applied to reconstruct images in numerical simulation and laboratory experiment. The frequency domain algorithm based on two-dimensional Gauss low-pass filter does not have ringing, it has obvious advantages in image reconstruction. The measured data of polarized light and depolarized light from spatially modulated full polarization imaging system is demodulated by optimal algorithm. Reconstruction results show the polarization degree of depolarization light is less than 5%, which the one of polarized light generated by a polarizer is approximate to 100%. These results are coincident with the theoretical prediction well, which verify the feasibility and validity of the algorithm.
KEYWORDS: Sensors, Control systems, Infrared detectors, Control systems design, Signal detection, Infrared sensors, Detection and tracking algorithms, Interference (communication), Signal processing, Indium gallium arsenide
The InGaAs Short-wave infrared detector is a temperature-sensitive device. Accurate temperature control can effectively reduce the background signal and improve detection accuracy, detection sensitivity, and the SNR of the detection system. Firstly, the relationship between temperature and detection background, NEP is analyzed, the principle of TEC and formula between cooling power, cooling current and hot-cold interface temperature difference are introduced. Then, the high precision constant current drive circuit based on triode voltage control current, and an incremental algorithm model based on deviation tracking compensation and PID control are proposed, which effectively suppresses the temperature overshoot, overcomes the temperature inertia, and has strong robustness. Finally, the detector and temperature control system are tested. Results show that: the lower of detector temperature, the smaller the temperature fluctuation, the higher the detection accuracy and the detection sensitivity. The temperature control system achieves the high temperature control with the temperature control rate is 7~8°C/min and the temperature fluctuation is better than ±0. 04°C.
According to the environmental requirement of detectors, we studied the characteristics of Si and InGaAs detectors irradiated by the Cobalt60-γray with the total dose of 5krad, 10 krad, 20 krad, 30krad respectively. We measured the dark current and relative spectral responsivity by the Relative Responsivity Measurement Apparatus before and after irradiation. The results suggest that the characteristics of Silicon and InGaAs detectors don't change obviously after different total dose irradiation, both detectors can work in the space irradiation environment due to its stability and reliability.
The spatially modulated imaging polarimeter is a compact, static and simultaneous polarization imaging system which can collect the interferometric data in real time. By processing the interferometric data, the complete polarization information of the incident light can be demodulated to realize the polarization detection. Based on the device principle of the spatially modulated imaging polarimeter using Savart Plates, the interference pattern processing method in the frequency domain was analyzed. Then, the physical mechanism of the modulation was explained and its corresponding processing method in the spatial domain was analyzed. Finally, in order to evaluate and compare the two methods, the simulation was performed and a prototype of the polarimeter was developed to finish the field experiment. The experimental results show that the spatial processing method can effectively extract the polarization information from the interference pattern. It can identify the artificial targets more clearly from the natural background compared with the frequency-domain processing method.
With the polynomial fitting of source function in each order of scattering calculation and the effective process of aerosol forward scattering peak, a polarized radiative transfer (RT) model based on the improved successive order of scattering (SOS) method has been developed to solve the vector radiative transfer equation. By our RT model, not only the total Stokes parameters [I, Q, U] measured by the satellite (aircraft) and ground-based sensors with linear polarization could be approximately simulated, but also the results of parameters for each scattering order event could conveniently calculated, which are very helpful to study the polarization properties for the atmospheric aerosol multiple scattering. In this study, the synchronous measured aerosol results including aerosol optical depth, complex refractive index and particle size distribution from AERONET under different air conditions, are considered as the input parameters for the successive scattering simulations. With our polarized RT model and the Mie code combined, the Stokes parameters as well as the degree of polarization for each scattering order are simulated and presented; meanwhile, the polarization (depolarization) properties of multiply scattering are preliminary analyzed and compared with different air quality (clear and pollution). Those results could provide a significant support for the further research of polarized aerosol remote sensing and inversion. Polarization properties of aerosol, successive order of scattering, vector radiative transfer equation, polynomial fitting of source function , multiply scattering
For the along-track scanning mode, the same place along the ground track could be detected by the Advanced Multi-angular Polarized Radiometer (AMPR) with several different scanning angles from -55 to 55 degree, which provides a possible means to get the multi-angular detection for some nearby pixels. However, due to the ground sample spacing and spatial footprint of the detection, the different sizes of footprints cannot guarantee the spatial matching of some partly overlap pixels, which turn into a bottleneck for the effective use of the multi-angular detected information of AMPR to study the aerosol and surface polarized properties. Based on our definition and calculation of t he pixel coincidence rate for the multi-angular detection, an effective multi-angle observation’s pixel matching method is presented to solve the spatial matching problem for airborne AMPR. Assuming the shape of AMPR’s each pixel is an ellipse, and the major axis and minor axis depends on the flying attitude and each scanning angle. By the definition of coordinate system and origin of coordinate, the latitude and longitude could be transformed into the Euclidian distance, and the pixel coincidence rate of two nearby ellipses could be calculated. Via the traversal of each ground pixel, those pixels with high coincidence rate could be selected and merged, and with the further quality control of observation data, thus the ground pixels dataset with multi-angular detection could be obtained and analyzed, providing the support for the multi-angular and polarized retrieval algorithm research in t he next study.
It is important for scientific agriculture to observing soil moisture content using remote sensing technique. Optical
polarization remote sensing may be applied to soil moisture detection. There is a close relationship between soil surface
moisture and its polarization property. The information of soil moisture content can be retrieved quantitatively according
to the variation of polarization. In order to investigate the polarization properties of water-bearing soil, the yellow brown
soil samples were collected in Hefei, Anhui, and measured in different phase angles under laboratory conditions. The
incident angle of unpolarized beam was 40 degrees. The experiments of polarimetric imaging for the soil samples with
different moisture content were made. The polarization image data were obtained using the multi-band polarized CCD
camera. It was found that the degree of linear polarization (DOLP) of sample was inversely proportional to the viewing
waveband. The DOLP increased with an increase of the phase angle before the percent moisture content of the samples
reached 30% approximately. The DOLP reached the maximum with an increase of the phase angle when the soil samples
were near saturated, saturated and oversaturated in soil moisture content. But the DOLP decreased with a further increase
of the phase angle. The results indicate that the polarization properties of near saturated, saturated and oversaturated soil
samples present the similar characteristics of Fresnel reflection. Obviously, the multi-angle and multi-band polarimetric
imaging measurements for the water-bearing yellow brown soil provide an approach to monitor soil moisture using
polarimetric imaging in airborne or satellite remote sensing.
Multiband optical polarization measurement can provide the state of polarization and the intensity information of natural scenes. Gradually this technique is practically applied in remote sensing e.g. monitoring of the atmosphere land and environment. Recently an experimental multiband polarized CCD camera (EMPCC) has been built in our laboratory. It can obtain the polarimetric imaging information synchronously and the multispectral data subsequently. We analyze the characteristic of some polarimetric images which were acquired from aerial platform at 3000m high. These multiband polarization images of natural surfaces include soil vegetation water and a variety of man-made objects. We obtain the parameters of degree of linear polarization (DOLP) angle of polarization (AOP) and intensity of the targets by using Stokes parameters. The Stokes parameters can be derived from measured radiant images at three polarization directions. The results indicate that the characteristics of different targets can be discriminated on the basis of polarization images associated with intensity ones. The properties of targets could be enhanced to some extent when we use the DOLP of the aerial image to characterize the natural surfaces. Among these characteristics the shape edge texture and material could be emphasized. These afford a convenience in interpreting the polarization information.
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