scholarly journals An Improved Equivalent Squint Range Model and Imaging Approach for Sliding Spotlight SAR Based on Highly Elliptical Orbit

2021 ◽  
Vol 13 (23) ◽  
pp. 4883
Author(s):  
Xinchang Hu ◽  
Pengbo Wang ◽  
Hongcheng Zeng ◽  
Yanan Guo
Keyword(s):  
Fourth Order ◽  
Elliptical Orbit ◽  
Orbital System ◽  
Imaging Algorithm ◽  
Time Frequency ◽  
Doppler Parameter ◽  
History Of ◽  
Large Eccentricity ◽  
High Orbit ◽  
Orbit Period

As an emerging orbital system with flexibility and brand application prospects, the highly elliptical orbit synthetic aperture radar (HEO SAR) can achieve both a low orbit detailed survey and continuous earth surface observation in high orbit, which could be applied to marine reconnaissance and surveillance. However, due to its large eccentricity, two challenges have been faced in the signal processing of HEO SAR at present. The first challenge is that the traditional equivalent squint range model (ESRM) fails to accurately describe the entire range for the whole orbit period including the perigee, the apogee, and the squint subduction section. The second one is to exploit an efficient HEO SAR imaging algorithm in the squinted case which solves the problem that traditional imaging algorithm fails to achieve the focused imaging processing of HEO SAR during the entire orbit period. In this paper, a novel imaging algorithm for HEO SAR is presented. Firstly, the signal model based on the geometric configuration of the large elliptical orbit is established and the Doppler parameter characteristics of SAR are analyzed. Secondly, due to the particularity of Doppler parameters variation in the whole period of HEO, the equivalent velocity and equivalent squint angle used in MESRM can no longer be applied, a refined fourth-order equivalent squint range model(R4-ESRM) that is suitable for HEO SAR is developed by introducing fourth-order Doppler parameter into Modified ESRM (MESRM), which accurately reconstructs the range history of HEO SAR. Finally, a novel imaging algorithm combining azimuth resampling and time-frequency domain hybrid correlation based on R4-ESRM is derived. Simulation is performed to demonstrate the feasibility and validity of the presented algorithm and range model, showing that it achieves the precise phase compensation and well focusing.

Diagnose Method Based on Spectral Analysis of Measured Parameters

2014 ◽  
Vol 1036 ◽  
pp. 535-540 ◽  
Author(s):  
Radu Vilău ◽  
Marin Marinescu ◽  
Octavian Alexa ◽  
Marian Truta ◽  
Valentin Vinturis
Keyword(s):  
Frequency Analysis ◽  
Fourier Transforms ◽  
Power Spectra ◽  
Time History ◽  
Point Of View ◽  
Mechanical Parameter ◽  
Accurate Analysis ◽  
Frequency Spectra ◽  
Time Frequency ◽  
History Of

The paper presents a possible method to diagnose a mechanical fault of an automotive system. Starting from the point of view that every fault of a mechanical system should introduce an abnormal component within the signal that describes the time history of a mechanical parameter we tried to find a way to reveal it.We were performing some tests involving a military vehicle with respect to the performances of its braking system. The tests were aiming at identifying a way to bring up-to-date the old weapon system from the braking systems point of view. During these tests we observed some anomalies concerning the pressure evolution within the braking cylinders of the vehicle. Some unusual but also systematic noises occurred. As a main issue at this point, the source of the noise should have been identified and filtered if necessary. We had to decide whether the noisy component of the signal is just a noise that should be removed by filtering the signal or it is a physical component of the mechanical parameter itself (not noise but a useful information).These procedures take time and they also request accurate knowledge as well as fine expertise in automotive testing. Since our Dept. has a long and rich practice in this respect, we assumed to processing data and give them a thorough interpretation. So, the first thing we did was to perform a frequency analysis, using classical methods. Usually, a simple frequency analysis cant provide information about a time variation of the frequency spectra due to the Fourier Transforms behavior, since it freezes the signal in time. A much more accurate analysis is the time-frequency analysis. However, observing both the amplitude and power spectra can lead to a useful conclusion. We concluded that the noise we met within the signal is due to the brake drums loss of circular shape (they turned into an oval, the process being known as ovalization). Hence, we cant talk about a noise as it is usually defined.

scholarly journals Classification of persistent and long-standing persistent atrial fibrillation by means of surface electrocardiograms

2016 ◽  
Vol 61 (1) ◽  
pp. 19-27 ◽  
Author(s):  
Nuria Ortigosa ◽  
Carmen Fernández ◽  
Antonio Galbis ◽  
Óscar Cano
Keyword(s):  
Atrial Fibrillation ◽  
Population Sample ◽  
Structural Heart Disease ◽  
Persistent Atrial Fibrillation ◽  
Time Frequency ◽  
Tertiary Center ◽  
History Of ◽  
Novel Method ◽  
Antiarrhythmic Treatment

Abstract Atrial fibrillation, which is the most common cardiac arrhythmia, is typically classified into four clinical subtypes: paroxysmal, persistent, long-standing persistent and permanent. The ability to distinguish between them is of crucial significance in choosing the most suitable therapy for each patient. Nevertheless, classification is currently established once the natural history of the arrhythmia has been disclosed as it is not possible to make an early differentiation. This paper presents a novel method to discriminate persistent and long-standing atrial fibrillation patients by means of a time-frequency analysis of the surface electrocardiogram. Classification results provide approximately 75% accuracy when evaluating ECGs of consecutive unselected patients from a tertiary center and higher than 80% when patients are not under antiarrhythmic treatment or do not have structural heart disease (76% sensitivity and 88% specificity). Moreover, to our knowledge, this is the first study that discriminates between persistent and long-standing persistent subtypes in a heterogeneous population sample and without discontinuing antiarrhythmic therapy to patients. Thus, it can help clinicians to address the most suitable therapeutic approach for each patient.

Extracting of Micro Doppler Parameter of Helicopter Rotor Based on Time-Frequency Analysis

2011 ◽  
Vol 130-134 ◽  
pp. 2696-2700 ◽  
Author(s):  
Lei Zhang ◽  
Guo Qing Huang
Keyword(s):  
Frequency Domain ◽  
Frequency Analysis ◽  
Time Domain ◽  
Good Method ◽  
Helicopter Rotor ◽  
Echo Signal ◽  
Time Frequency Analysis ◽  
Time Frequency ◽  
Radar Echo ◽  
Doppler Parameter

The micro Doppler effect of the radar echo signal of helicopter rotor is studied, and the formula of helicopter rotor echo is obtained. Then the received echo signal of helicopter rotor simulated is analyzed in time domain, frequency domain and time-frequency domain respectively, the analysis results show that it is a good method to extract micro Doppler of helicopter rotor echo by time-frequency analysis. According to analysis results, obtained a method to determine parity of blades and velocity of helicopter rotor, these methods can be used to identify helicopter.

Reflections of a European on the Symposium on Land Registration and Data Banks

1969 ◽  
Vol 23 (1) ◽  
pp. 46-53
Author(s):  
K. Rinner
Keyword(s):  
Central Europe ◽  
Fourth Order ◽  
Large Scale ◽  
Control Points ◽  
Land Registration ◽  
Modern Times ◽  
History Of ◽  
Increasing Demand ◽  
Map Data ◽  
Data Banks

Highlights from the history of surveying and mapping during medieval and modern times in Central Europe are cited to illustrate the ever increasing demand for better surveys and better maps for tax collection, land registration, civil engineering, military, scientific and other purposes. In Austria, which has an area of 75,000 square kilometers and a population of 7,000,000 people, there is complete triangulation, from first to fourth order, and further densification to 500 meters is planned. Control and boundary points are durably marked and described by coordinates. A cadastral resurvey has been completed for some 540 of 5,000 communities. Much of the work has been done by consulting engineers who are obliged to execute public orders during about 30 per cent of their working time. There are about 200 consultants and an equal number of state-employed survey engineers, with a ratio of three technicians per engineer. From a summary of the main features of the new Austrian survey act, some recommendations are made for Canada. Specifically, there should be a network of control points based on a single datum; authorities should issue regulations governing the coordination of all surveys and the recording of all data; accuracy should be related to land value; administration and revision of surveys should be attended to by regional offices and, for large-scale maps and plans, a projection, which permits observed data to be directly related to map data should be chosen. Several related problems, such as the development of a unified datum, are discussed.

A Near-Field Fast Time-Frequency Joint 3-D Imaging Algorithm Based on Aperture Linearization

2021 ◽  
Author(s):  
Xuan Zeng ◽  
Yuxin Ma ◽  
Zhongyu Li ◽  
Junjie Wu ◽  
Jianyu Yang
Keyword(s):  
Near Field ◽  
Fast Time ◽  
Imaging Algorithm ◽  
Time Frequency

Fractional Order Filter Discretization With Marine Predators Algorithm

2021 ◽  
Author(s):  
Abdullah Ates ◽  
YangQuan Chen
Keyword(s):  
Uniform Distribution ◽  
Fractional Order ◽  
Discrete Time ◽  
Fourth Order ◽  
Continuous Time ◽  
Heuristic Method ◽  
Hunting Behavior ◽  
Time Frequency ◽  
Frequency Responses ◽  
Marine Predators

Abstract In this study, discrete time models of continuous time fractional order filters are obtained by using the Marine Predators Algorithm (MPA). Marine Predators optimization algorithm is a population-based heuristic method. This method is inspired by the hunting behavior of marine predators. The algorithm works on three basic phases. These phases occur according to the difference or equality of the velocity of the prey and the predator. As it is known, uniform distribution is generally used in stochastic based optimization algorithms. However, in the MPA method, Brownian and Levy distributions are also used as well as uniform distribution. First, continuous time frequency responses of fractional order filters are generated. Then, fourth order discrete time filters are designed that can give similar responses with generated continues time filter frequency responses. Ten parameters were optimized for the design of fourth order discrete time filters numerator and denominator. The Marine Predators method’s results are compared with the results of the Fractional order Darwinian Particle Swarm Optimization (FODPSO) algorithm, from which discrete time filters are obtained for two fractional order continuous time filter models. In this way, it has been shown comparatively that the Marine Predators Algorithm can be used in real engineering problems and can do filter discretization better.

The life history of Pteronarcys dorsata (Say) (Plecoptera: Pteronarcyidae) in southwestern Virginia

1983 ◽  
Vol 61 (9) ◽  
pp. 1981-1985 ◽  
Author(s):  
Richard A. Lechleitner ◽  
Boris C. Kondratieff
Keyword(s):  
Life History ◽  
Life Cycle ◽  
Fourth Order ◽  
Maximum Size ◽  
Warm Water ◽  
Leaf Packs ◽  
History Of ◽  
Podostemum Ceratophyllum

The life history of the giant stonefly Pteronarcys dorsata was investigated in a warm water fourth order river in southwestern Virginia. The life cycle of P. dorsata was univoltine with emergence occurring mid-March to 1st week of April. Adults lived up to 42 days in the laboratory. Mean fecundity was 242 eggs with up to four separate egg batches produced. Eggs hatched in 23 to 38 days. Early nymphal instars were collected in the river in mid-June. Nymphs reached maximum size by late November or December. During the warm months nymphs were found in mats of Podostemum ceratophyllum (river weed) and through the winter months under large unembedded rocks or leaf packs. The diet consisted of diatoms and detritus. Higher water temperatures of longer duration in the Little River probably allowed this species to complete its life cycle in 1 year rather than the 2 to 4 years previously reported.

Sign in / Sign up

Export Citation Format

Share Document