In order to solve problems of output chattering, difficulty in tuning and poor noise suppression ability of tracking differentiators (TDs), a TD based on the Gaussian error function (ERFTD) is designed. The ERFTD has a simple form and applies the Gaussian error function to construct the acceleration function, and introduces a terminal attractor function. The application of Gaussian error function reduces chattering caused by high-frequency signals of TD, and the terminal attractor function enhances noise suppression capability of the TD. The stability of ERFTD is proved by theoretical derivation. The parameter tuning rules were summarized through frequency sweep testing. Numerical simulations show that ERFTD has good tracking capability for signals contaminated by noise, with fast response speed and high tracking accuracy; The differential ability of ERFTD is strong, which effectively suppresses the noise. The tracking differentiator based on the Gaussian error function has excellent performance.
Near space usually refers to the earth space with a height of about 20-100 km. It is a highly interdisciplinary field involving atmospheric physics, space physics, plasma physics, photochemistry, solar and geosciences, Geosciences and life sciences. The development and utilization of near space is far less than that of traditional airspace and satellite orbital space. Near space usually corresponds to areas where traditional airplanes are difficult to fly and satellites are not easy to detect. Compared with the middle and lower atmosphere and higher ionosphere and outer space, there has been a lack of systematic and efficient observers in the near space for a long time. Objectively, near space has become a weak point of human's understanding of the whole earth's space.
With the development of high-speed digital system, high-speed serial data transmission is widely used and the FPGA containing high-speed serial transceiver is also widely used. The high-speed serial interface of Xilinx's FPGA includes GTP, GTX, GTH and other high-speed transceivers with different transmission rate. The physical transmission speed of these transceivers can reach tens of Gbps. These low-level high-speed transceivers can support a variety of top-level transmission protocols, such as SRIO, PCIE, SATA, optical fiber and so on. Among these top-level transmission protocols, optical fiber transmission has the longest transmission distance and is widely used in various scenarios. Optical fiber transmission has three advantages. Firstly, its transmission capacity is very large and it can support ultralong distance transmission, one line optical fiber transmission rate can easily reach several Gbps. Secondly, optical fiber communication has strong anti-electromagnetic interference characteristics, which can ensure the quality of data transmission. Thirdly, optical fiber transmission uses light wave for data transmission and the light wave transmitted in the optical fiber cannot run out, so there is no radiation and it is difficult to eavesdrop.
With the rapid development of image sensor research, mobile industry processor interface (MIPI) was used to meet the massive data throughput capacity since the higher frame rate and more pixels on the smaller sensors. This paper realized the image processing of MIPI based on FPGA. The image sensor used here is OS08A10, which has 8Mega Pixels and contains up to 4-lane MIPI serial output interface. The resolution of image sensor is 3840*2160 at frame rate of 25fps and each pixel is 10 bit, so the data throughput is 2Gbps. Since the FPGA used in this project is Spartan 6 series and it cannot deal with MIPI data directly, it is necessary to change these MIPI data into LVDS data beforehand. After receiving the processed sensor data, FPGA stores these data into DDR3 and output them through HDMI for display. The result shows that the data transmission and process of MIPI is stable and reliable which can be widely used in other MIPI sensor control.
Fourier transform infrared spectroscopy is an important technique in studying molecular energy levels, analyzing material compositions, and environmental pollutants detection. A novel rotational motion Fourier transform infrared spectrometer with high stability and ultra-rapid scanning characteristics is proposed in this paper. The basic principle, the optical path difference (OPD) calculations, and some tolerance analysis are elaborated. The OPD of this spectrometer is obtained by the continuously rotational motion of a pair of parallel mirrors instead of the translational motion in traditional Michelson interferometer. Because of the rotational motion, it avoids the tilt problems occurred in the translational motion Michelson interferometer. There is a cosine function relationship between the OPD and the rotating angle of the parallel mirrors. An optical model is setup in non-sequential mode of the ZEMAX software, and the interferogram of a monochromatic light is simulated using ray tracing method. The simulated interferogram is consistent with the theoretically calculated interferogram. As the rotating mirrors are the only moving elements in this spectrometer, the parallelism of the rotating mirrors and the vibration during the scan are analyzed. The vibration of the parallel mirrors is the main error during the rotation. This high stability and ultra-rapid scanning Fourier transform infrared spectrometer is a suitable candidate for airborne and space-borne remote sensing spectrometer.
In the field of Fourier-transform spectroscopy, tilt and shearing problems caused by the moving components in a translational type of spectrometer reduce the quality of the interferogram dramatically. While, the spectrometer based on rotational motion can avoid these problems. In this paper, a novel rotational type of interferometer, called rotating parallel-mirror-pair interferometer (RPMPI), is presented. Its principle and properties are studied. This interferometer consists of one beam splitter, two fixed flat mirrors, and one rotating wedged parallel-mirror-pair (PMP). The optical path difference (OPD) is obtained by the rotational motion of the PMP. Factors that affect the maximum OPD include the wedged angle of the rotating PMP, the distance between the two parallel mirrors, the direction of the incident ray, and the range of rotating angle. This interferometer can operate either in swinging mode or continuous rotary mode depending on the range of the rotating angle. In swinging mode, the OPD function is linear. In continuous rotary mode, the sampling efficiency is higher and it can operate as an ultra rapid scanning interferometer.
This paper presents an approach to enhance the resolution of refocused images by super resolution
methods. In plenoptic imaging, we demonstrate that the raw sensor image can be divided to a number
of low-resolution angular images with sub-pixel shifts between each other. The sub-pixel shift, which
defines the super-resolving ability, is mathematically derived by considering the plenoptic camera as
equivalent camera arrays. We implement simulation to demonstrate the imaging process of a plenoptic
camera. A high-resolution image is then reconstructed using maximum a posteriori (MAP) super
resolution algorithms. Without other degradation effects in simulation, the super resolved image
achieves a resolution as high as predicted by the proposed model. We also build an experimental setup
to acquire light fields. With traditional refocusing methods, the image is rendered at a rather low
resolution. In contrast, we implement the super-resolved refocusing methods and recover an image with
more spatial details. To evaluate the performance of the proposed method, we finally compare the
reconstructed images using image quality metrics like peak signal to noise ratio (PSNR).
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