A feature-based phase retrieval wavefront sensing approach using machine learning is proposed in contrast to the conventional intensity-based approaches. Specifically, Tchebichef moments which are orthogonal discrete domain of image coordinate space introduced represent features point spread functions (PSFs) at in-focus and defocus planes. The back-propagation artificial neural network, one most wide applied tool, utilized establish nonlinear mapping between moment corresponding aberration...

Long exposure time and wide field can effectively improve the ability of a space surveillance telescope to detect faint targets. However, complicated situations pose challenges for target detection. Background star images usually manifest rotated streak, trajectories be crossed, discontinuous, or nonlinear. This paper presents an accurate robust detection method, namely, spatiotemporal pipeline multistage hypothesis testing (SPMHT), overcome issues. Specifically, method includes following...

The performance of a staring infrared imaging system can be characterized based on estimating the modulation transfer function (MTF). slant edge method is widely used MTF estimation method, which effectively solve aliasing problem caused by discrete undersampling focal plane array. However, traditional has some limitations such as low precision angle extraction and using approximate to fit spread (ESF), affects accuracy estimation. In this paper, we propose modified including an that improve...

Barrier-function-based adaptive fast-terminal sliding-mode control approaches have been devised to enhance the precision of speed regulation permanent magnet synchronous motors (PMSMs). Firstly, loop utilizes control, which contributes a faster convergence rate and enhances robustness system. By adopting this technique, system can quickly reach desired setpoint effectively handle disturbances. Secondly, an law based on barrier function is employed adjust gain adaptively. The proposed...

Sandy deserts and desertified lands (SDDL) cover most of north‐western China, desertification is a severe environmental issue in this region. In study, we classify SDDL into mobile, semi‐mobile, semi‐anchored, anchored classes, divide the corresponding severity four levels: extremely severe, moderate, slight. Using databases derived from Landsat TM ETM images 1986 2000, discuss evolution processes causes desertification. The area increased by 16 101 km2 between land was classified as...

Considering that large quantities of soil hyperspectral data include the redundancy and overlap spectral information, technology selecting feature wavelength can effectively solve these problems, improve accuracy stability organic matter (SOM) content retrieval model. Traditional methods selection mainly attempt to establish empirical relationship between reflectance SOM contents, performance is directly related quality representativeness "training data". This study first distinguished...

The positioning accuracy and speed stability of the brushless DC motor (BLDC motor), as drive element optomechanically scanned system (OMSS), are closely interrelated to final imaging quality system. Active disturbance rejection control (ADRC) with strong anti-interference ability, fast response good robustness is one extensively used strategies. However, performance ADRC working in a complicated environment will be limited due controller structure, parameter tuning influence multi-source...

The simplified compliance matrix for right elliptical hinges is presented in this paper by nonlinear curve fitting on the basis of equations derived Chen et al. [Rev. Sci. Instrum. 79, 095103 (2008)]. rotation stiffness are then confirmed comparison with results from finite element analysis and experimental measurements. Percentage errors between theoretical predictions both testing within 5% a range geometries ratio s (b/t) 1 14. geometric parameter optimization purposes maximizing one...

The wide-field surveillance camera plays a critical role in space debris detection and the visible light situational awareness required for early warning. However, stray such system has always been serious problem. Current methods cannot effectively eliminate interference of light, which directly lead to inability accurately segment target background, greatly reduce accuracy recognition. To solve this problem, we proposed an accurate elimination method based on recursion multi-scale...

In the design of two-degree-of-freedom (2-DOF) fast steering mirror (FSM) system, in order to improve control bandwidth low-order natural frequency working direction should be reduced as much possible, and high-order non-working increased. this paper, a deep-cut flexure hinge system was studied. Firstly, motion first third vibration mode analyzed. Next, stiffness deduced solve problem that traditional calculation method is not suitable for direction. Then, energy Castigliano's second theorem...

Wide field and a long exposure time can effectively improve the ability of space surveillance telescope to detect faint targets. However, such systems are very susceptible stray light. A light nonuniform background will cause great interference subsequent target recognition, resulting in large number false alarms. This study presents an accurate robust correction algorithm, called improved new top-hat transformation (INTHT), for background. First, we analyzed formation mechanism influence...

Marine oil spills accidents has caused a large amount of crude to leak into the marine environment and threaten ecological environment. Hyperspectral remote sensing images (HRSI) technology can quickly accurately identify film different thickness on surface. In order overcome traditional spectrum analysis method space extraction long time sampling, calculation, other shortcomings. On account advantages spectral spatial information in field HRSI classification, spectral-spatial features...

Due to their similar color and material variability, some ground objects have characteristics overlap in bands. This leads a drop the classification accuracy of hyperspectral images. To address this problem, we simulated images vegetation with colors by mixed pixel calculation test performance dimensionality reduction method for samples close spectra. In addition, proposed novel wavelength selection algorithm called LBI-BPSO (Binary Particle Swarm Optimization Local Band Index), which...

In tunable diode laser absorption spectroscopy (TDLAS), the wavelength modulation (WMS) is widely employed. However, when measuring gas concentration with second harmonic signal, errors will occur and inversion accuracy be reduced, because change of depth lead to peak value, value cannot calculated directly in absence component. To improve WMS technology, we calibrate take it as a parameter model. this article, relationship between valley spacing first derived, used measurement; then, an...

Triangular planar ring resonant cavities are widely used in cavity ring-down spectroscopes (CRDS) because of the unique optical path advantage. Hermite-Gaussian theory is classical method to describe beam cavity. Since this can express transverse electromagnetic mode (TEM) meridian plane and sagittal surface separately an astigmatic triangular cavity, it has a advantage analysis cavities. However, among many analyses cavities, existing theories modes have not been able reasonably explain...