Passive-source multitaper-spectral method based low-frequency data reconstruction for active seismic sources

Passive seismic data contain large amounts of low-frequency information. To effectively extract and compensate active seismic data that lack low frequencies, we propose a multitaper spectral reconstruction method based on multiple sinusoidal tapers and derive equations for multisource and multitrace conditions. Compared to conventional cross correlation and deconvolution reconstruction methods, the proposed method can more accurately reconstruct the relative amplitude of recordings. Multidomain iterative denoising improves the SNR of retrieved data. By analyzing the spectral characteristics of passive data before and after reconstruction, we found that the data are expressed more clearly after reconstruction and denoising. To compensate for the low-frequency information in active data using passive seismic data, we match the power spectrum, supplement it, and then smooth it in the frequency domain. Finally, we use numerical simulation to verify the proposed method and conduct prestack depth migration using data after low-frequency compensation. The proposed power-matching method adds the losing low frequency information in the active seismic data using the low-frequency information of passive- source seismic data. The imaging of compensated data gives a more detailed information of deep structures.

Diagnostic Value of Spectral CT Reconstruction Mode for Carotid Atherosclerotic Plaque Lesions

Objective:To investigate the diagnostic value of spectral CT reconstruction mode for carotid atherosclerotic plaque lesions.Methods:From January 2017 to January 2019,70 patients with carotid atherosclerotic plaque lesions in our hospita1 were selected as the research object.A11 patients were diagnosed with cervical vascular color Doppler ultrasound and spectral CT scan under spectral cr reconstruction mode.Taking the results of coronaryf angiography as the"gold standard",the clinical value of the two examination methods in the diagnosis of carotid atherosclerotic plaque lesions was compared and analyzed.Results:Coronary angiography diagnosis confirmed that 33 of 70 patients with suspected carotid atherosclerotic plaque lesions had vulnerable plaques and 37 had stable plaques.The accuracy of Spectral CT examination of carotid artery plaque was 87.14%(61/70),sensitivity was 90.91%(30/33),specificity was 83.78%(31/37),and the positive predictive value was 83.33%(30/36),the negative predictive value is 91.76%(31/34),which is higher than that of cervical vascular ultrasonography(61.43%,60.61%,56.76%,57.89%,65.63%),the difference is statistically significant(P<0.05).Conclusion:The application of Spectral CT in the clinical diagnosis and treatment of carotid atherosclerotic plaque lesions with higher accuracy,sensitivity and specificity,is more significant and can provide a more reliable and effective imaging basis.

An approach to gas sensors based on tunable diode laser incomplete saturated absorption spectra

A spectral profile reconstruction method that can be applied to incomplete saturated-absorption spectra is proposed and demonstrated. Through simulation and theoretical calculation, it is proved that compared with the traditional wholeprofile fitting method, this new method can increase the concentration detection upper limit of a single absorption line by about 8.7 times. High-concentration water vapor is measured using TDLAS technology, the total water vapor pressure and the self-broadened half-width coefficient of the spectrum were simultaneously measured from incomplete saturatedabsorption spectra and compared with high-precision pressure sensors and the HITRAN databases. Their maximum relative deviations were about 4.63% and 9.10%, respectively. These results show that the spectral profile reconstruction method has great application potential for expanding the dynamic range of single-line measurements to higher concentrations,especially for in-situ online measurements under complex conditions, such as over large temperature and concentration dynamic ranges.

Study on the key technology of spectral reflectivity reconstruction based on sparse prior by a single-pixel detector

By studying the traditional spectral reflectance reconstruction method, spectral reflectance and the relative spectral power distribution of a lighting source are sparsely decomposed, and the orthogonal property of the principal component orthogonal basis is used to eliminate basis; then spectral reflectance data are obtained by solving a sparse coefficient. After theoretical analysis, the spectral reflectance reconstruction based on sparse prior knowledge of the principal component orthogonal basis by a single-pixel detector is carried out by software simulation and experiment. It can reduce the complexity and cost of the system, and has certain significance for the improvement of multispectral image acquisition technology.

Iterative sparse reconstruction of spectral domain OCT signal

We propose and study an iterative sparse reconstruction for Fourier domain optical coherence tomography （FD OCT） image by solving a constrained optimization problem that minimizes L-1 norm. Our method takes the spectral shape of the OCT light source into consideration in the iterative image reconstruction procedure that allows deconvolution of the axial point spread function from the blurred image during reconstruction rather than after reconstruction. By minimizing the L-1 norm, the axial resolution and the signal to noise ratio of image can both be enhanced. The effectiveness of our method is validated using numerical simulation and experiment.