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- 实验方案
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A Novel High-Accuracy Phase-Derived Velocity Measurement Method for Wideband LFM Radar
摘要： A novel high-accuracy phase-derived velocity measurement (PDVM) method for fast-moving space targets is presented in this letter. First, a wideband linear frequency-modulated signal model that considers the effect of radial acceleration was developed. To obtain the unambiguous phase difference between two adjacent echo pulses, coarse velocity and acceleration measurements derived from range profile cross correlation were used to resolve the phase ambiguity. Then, the derived accurate and unambiguous phase difference and the phase error induced by the discrete Fourier transform were analyzed. The PDVM technique was applied after the phase error was compensated for, and all required parameters were calculated. Under low signal-to-noise ratio (SNR) conditions, a correction for the phase unwrapping error was developed. The simulation results showed that the proposed PDVM technique was highly accurate. The root-mean-square error of the PDVM results was less than 0.025 m/s when the SNR was greater than 15 dB.
关键词： space target,Low signal-to-noise ratio (SNR),wideband linear frequency-modulated (LFM) radar,phase-derived velocity measurement (PDVM)
更新于2025-09-19 17:15:36
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Accurate laser frequency locking to optical frequency combs under low-signal-to-noise-ratio conditions
摘要： We demonstrate a method for accurately locking the frequency of a continuous-wave laser to an optical frequency comb under conditions where the signal-to-noise ratio is low, too low to accommodate other methods. Our method is typically orders of magnitude more accurate than conventional wavemeters and can considerably extend the usable wavelength range of a given optical frequency comb. We illustrate our method by applying it to the frequency control of a dipole lattice trap for an optical lattice clock, a representative case where our method provides significantly better accuracy than other methods.
关键词： optical lattice clock,optical frequency combs,laser frequency locking,low-signal-to-noise-ratio
更新于2025-09-19 17:13:59
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Passive Detection of Small Low-Emission Sources: Two-Dimensional Numerical Case Studies
摘要： In Allmaras et al. [Inverse Prob. Imaging, Vol. 7, No. 1, p. 47 (2013)], we present the mathematical foundations for the passive detection of small low-emission radioactive sources buried in background noise using Compton gamma cameras. Here, we apply these techniques to the detection of small amounts of special nuclear material in various cargo container geometries. Simulated two-dimensional data are used. We demonstrate the feasibility of such an approach using various realistic cargo container loadings and assess the effect of angular detection errors in Compton cameras.
关键词： low signal-to-noise ratio,Passive detection,inverse problem
更新于2025-09-04 15:30:14
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Heterodyne phase measurement in low signal-to-noise ratios using genetic algorithm
摘要： The heterodyne phase measurement using radio frequency (RF) signal can only be performed in a sufficiently high signal-to-noise ratio (SNR). Because the strength of heterodyne signal is extremely sensitive to the phase front misalignment between the signal and the reference beams, the requirement of high SNR greatly limits its implementation. An innovative heterodyne phase measurement method using sequence shifting and genetic algorithm (GA) is reported in this paper. In the method, after being shifted with different steps, the digital sequences of the heterodyne signals containing the phases to be measured are added up. Taking the shifting steps of the sequences as variables, the GA searches the optimal shifting steps, with which the signal strength in the sum can reach the maximum. When the algorithm converges, the phase information can be derived by the optimal shifting steps. Numerical analysis indicates that the root mean square error (RMSE) of the phase measurement by our method can be less than ??/40 even when SNR is as low as ?10dB. With the excellent performance in low SNR, the new measurement method can be realized easily in practical applications.
关键词： Sequence shifting,Heterodyne phase measurement,Genetic algorithm,Low signal-to-noise ratio
更新于2025-09-04 15:30:14