Synthetic aperture radar(SAR)aboard SEASAT was first launched in 1978.At the beginning of the 21st century,the Chinese remote sensing community recognized the urgent need to develop domestic SAR capabilities.Unlike sc...Synthetic aperture radar(SAR)aboard SEASAT was first launched in 1978.At the beginning of the 21st century,the Chinese remote sensing community recognized the urgent need to develop domestic SAR capabilities.Unlike scatterometers and al-timeters,space-borne SAR offers high-resolution images of the ocean,regardless of weather conditions or time of day.SAR imagery provides rich information about the sea surface,capturing complicated dynamic processes in the upper layers of the ocean,particular-ly in relation to tropical cyclones.Over the past four decades,the advantages of SAR have been increasingly recognized,leading to notable marine applications,especially in the development of algorithms for retrieving wind and wave data from SAR images.This study reviews the history,progress,and future outlook of SAR-based monitoring of sea surface wind and waves.In particular,the ap-plicability of various SAR wind and wave algorithms is systematically investigated,with a particular focus on their performance un-der extreme sea conditions.展开更多
To realize effective co-phasing adjustment in large-aperture sparse-aperture telescopes,a multichannel stripe tracking approach is employed,allowing simultaneous interferometric measurements of multiple optical paths ...To realize effective co-phasing adjustment in large-aperture sparse-aperture telescopes,a multichannel stripe tracking approach is employed,allowing simultaneous interferometric measurements of multiple optical paths and circumventing the need for pairwise measurements along the mirror boundaries in traditional interferometric methods.This approach enhances detection efficiency and reduces system complexity.Here,the principles of the multibeam interference process and construction of a co-phasing detection module based on direct optical fiber connections were analyzed using wavefront optics theory.Error analysis was conducted on the system surface obtained through multipath interference.Potential applications of the interferometric method were explored.Finally,the principle was verified by experiment,an interferometric fringe contrast better than 0.4 is achieved through flat field calibration and incoherent digital synthesis.The dynamic range of the measurement exceeds 10 times of the center wavelength of the working band(1550 nm).Moreover,a resolution better than one-tenth of the working center wavelength(1550 nm)was achieved.Simultaneous three-beam interference can be achieved,leading to a 50%improvement in detection efficiency.This method can effectively enhance the efficiency of sparse aperture telescope co-phasing,meeting the requirements for observations of 8-10 m telescopes.This study provides a technological foundation for observing distant and faint celestial objects.展开更多
The purpose of this study is to analyze the impact of upper ocean dynamics on velocity bunching,represented by az-imuthal cutoff wavelength(i.e.,sea surface wind,wave,and current).In this study,over 1400 dual-polarize...The purpose of this study is to analyze the impact of upper ocean dynamics on velocity bunching,represented by az-imuthal cutoff wavelength(i.e.,sea surface wind,wave,and current).In this study,over 1400 dual-polarized(vertical-vertical(VV)and vertical-horizontal(VH))Sentinel-1(S-1)synthetic aperture radar(SAR)images collected in tropical cyclones(TC)are utilized.These images are combined with wind and rain observations from the stepped-frequency microwave radiometer(SFMR),wave simu-lations conducted using a third-generation numerical wave model,WAVEWATCH-III(WW3),and SAR-derived wind information collected from CyclObs winds.The WW3-simulated significant wave height(SWH)is validated against measurements from HY-2B altimeter taken in August and September 2021,yielding a root mean square error(RMSE)of 0.48 m and a correlation coefficient(COR)of 0.88.The SAR-based azimuthal cutoff wavelengths in VV polarization,which quantitatively represent the effect of velocity bunching,are compared with theoretical values calculated using WW3-simulated SWH.A notable relationship is observed between the difference in azimuthal cutoff wavelength and SAR-derived wind speed and WW3-simulated SWH.Analysis results show that the correlation between SAR-based azimuthal cutoff wavelength and SWH is stronger than that with wind and current.Finally,a machine learning algorithm is used to develop an algorithm aimed at simulating the azimuthal cutoff wavelength in TCs,including wind,wave,and incidence angle.This method yields an RMSE of 8.90 m,a COR of 0.91,and a scatter index of 0.04 for VV-polar-ization SAR.展开更多
Dome A,in Antarctica,offers an exceptional site for ground-based infrared astronomy,with its extremely low atmospheric infrared background noise and excellent seeing conditions.However,deploying near-infrared telescop...Dome A,in Antarctica,offers an exceptional site for ground-based infrared astronomy,with its extremely low atmospheric infrared background noise and excellent seeing conditions.However,deploying near-infrared telescopes in the harsh environment of Antarctica faces the critical challenge of frost accumulation on optical mirrors.While indium tin oxide heating films effectively defrost visible-band Antarctic astronomical telescopes,their thermal radiation at infrared wavelengths introduces significant stray light,severely degrading the signal-to-noise ratio for infrared observations.To address this limitation,we have designed a mechanical snow-removal system capable of efficiently clearing frost from sealing window surfaces at temperatures as low as–80°C.Aperture photometry of target sources,Canopus and HD 2151,revealed that after six days without intervention,floating snow extinction reduced target brightness by up to 3 magnitudes.Following mechanical defrosting,the source flux recovered to stable levels,with measured magnitudes showing rapid initial improvement followed by stabilization.Data analysis indicates that a frost removal strategy operating every 48 h,with each operation consisting of 4–6 cycles,enables efficient removal of frost and snow without introducing additional thermal noise.Future work will focus on optimizing the adaptive control algorithm and exploring novel low-temperature defrosting materials to extend the periods during which Antarctic infrared telescopes can operate unattended.展开更多
During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomen...During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomenon,a numerical simulation framework of the finite volume method and transient embedded discrete fracture model is proposed to establish a new constitutive model that links poroelastoplastic deformation,adsorption-induced swelling,and aperture compression.From this model,anisotropic permeability tensors were derived to further achieve the simulation of coevolution.Meanwhile,our permeability model was verified against the measured permeability data,and the history match of the numerical model showed better results where the mismatch was less than 5%.The results indicate that(1)the long-term permeability evolution clearly showed the competitive effects of multiple deformation mechanisms,which involves three stages:compaction-dominated decline,adsorption-dominated rebound,and creep-controlled loss.(2)The increased number of compressible cleats/fractures accelerated the initial permeability decline,while the increased desorption-induced strain promoted faster rebound and enhancement and higher viscosity coefficients enhanced the creep effect,which led to significant long-term permeability loss.(3)Massive hydraulic fracturing created a larger drainage area,accelerating methane desorption and causing sharp permeability rebound with reduced residual gas,which shows that the permeability remained higher than the initial values even after the extensive extraction via the fractured horizontal wells.The permeability evolution mechanisms displayed varying properties,such as coal rank and burial depth,and distinct characteristics.A precise understanding of multiple competitive stress effects is crucial for optimizing coalbed methane extraction techniques and improving recovery efficiency.展开更多
Synthetic aperture radar(SAR)radio frequency identification(RFID)localization is widely used for automated guided vehicles(AGVs)in the industrial internet of things(IIoT).However,the AGV’s speeds are limited by the p...Synthetic aperture radar(SAR)radio frequency identification(RFID)localization is widely used for automated guided vehicles(AGVs)in the industrial internet of things(IIoT).However,the AGV’s speeds are limited by the phase difference(PD)of two neighboring readers.In this paper,an inertial navigation system(INS)based SAR RFID localization method(ISRL)where AGV moves nonlinearly.To relax the speed limitation,a new phase-unwrapping method based on the similarity of PDs(PU-SPD)is proposed to deal with the PD ambiguity when the AGV speed exceeds 60km/h.In localization,the gauss-newton algorithm(GN)is employed and an initial value estimation scheme based on variable substitution(IVE-VS)is proposed to improve its positioning accuracy and the convergence rate.Thus,ISRL is a combination of IVE-VS and GN.Moreover,the Cramer-Rao lower bound(CRLB)and the speed limitation is derived.Simulation results show that the ISRL can converge after two iterations,and the positioning accuracy can achieve 7.50cm at a phase noise levelσ=0.18,which is 35%better than the Hyperbolic unbiased estimation localization(HyUnb).展开更多
Amplitude stripes imposed by ionospheric scintillation have been frequently observed in many of the equatorial nighttime acquisitions of the Advanced Land Observing Satellite(ALOS)Phased Array-type L-band Synthetic Ap...Amplitude stripes imposed by ionospheric scintillation have been frequently observed in many of the equatorial nighttime acquisitions of the Advanced Land Observing Satellite(ALOS)Phased Array-type L-band Synthetic Aperture Radar(PALSAR).This type of ionospheric artifact impedes PALSAR interferometric and polarimetric applications,and its formation cause,morphology,and negative influence have been deeply investigated.However,this artifact can provide an alternative opportunity in a positive way for probing and measuring ionosphere scintillation.In this paper,a methodology for measuring ionospheric scintillation parameters from PALSAR images with amplitude stripes is proposed.Firstly,sublook processing is beneficial for recovering the scattered stripes from a single-look complex image;the amplitude stripe pattern is extracted via band-rejection filtering in the frequency domain of the sublook image.Secondly,the amplitude spectrum density function(SDF)is estimated from the amplitude stripe pattern.Thirdly,a fitting scheme for measuring the scintillation strength and spectrum index is conducted between the estimated and theoretical long-wavelength SDFs.In addition,another key parameter,the scintillation index,can be directly measured from the amplitude stripe pattern or indirectly derived from the scintillation strength and spectrum index.The proposed methodology is fully demonstrated on two groups of PALSAR acquisitions in the presence of amplitude stripes.Self-validation is conducted by comparing the measured and derived scintillation index and by comparing the measurements of range lines and azimuth lines.Cross-validation is performed by comparing the PALSAR measurements with in situ Global Position System(GPS)measurements.The processing results demonstrate a powerful capability to robustly measure ionospheric scintillation parameters from space with high spatial resolution.展开更多
The multifunctional integration system(MFIS)is based on a common hardware platform that controls and regulates the system’s configurable parameters through software to meet dif-ferent operational requirements.Dwell s...The multifunctional integration system(MFIS)is based on a common hardware platform that controls and regulates the system’s configurable parameters through software to meet dif-ferent operational requirements.Dwell scheduling is a key for the system to realize multifunction and maximize the resource uti-lization.In this paper,an adaptive dwell scheduling optimization model for MFIS which considers the aperture partition and joint radar communication(JRC)waveform is established.To solve the formulated optimization problem,JRC scheduling condi-tions are proposed,including time overlapping condition,beam direction condition and aperture condition.Meanwhile,an effec-tive mechanism to dynamically occupy and release the aperture resource is introduced,where the time-pointer will slide to the earliest ending time of all currently scheduled tasks so that the occupied aperture resource can be released timely.Based on them,an adaptive dwell scheduling algorithm for MFIS with aperture partition and JRC waveform is put forward.Simulation results demonstrate that the proposed algorithm has better com-prehensive scheduling performance than up-to-date algorithms in all considered metrics.展开更多
Nonperiodic interrupted sampling repeater jamming(ISRJ)against inverse synthetic aperture radar(ISAR)can obtain two-dimensional blanket jamming performance by joint fast and slow time domain interrupted modulation,whi...Nonperiodic interrupted sampling repeater jamming(ISRJ)against inverse synthetic aperture radar(ISAR)can obtain two-dimensional blanket jamming performance by joint fast and slow time domain interrupted modulation,which is obviously dif-ferent from the conventional multi-false-target deception jam-ming.In this paper,a suppression method against this kind of novel jamming is proposed based on inter-pulse energy function and compressed sensing theory.By utilizing the discontinuous property of the jamming in slow time domain,the unjammed pulse is separated using the intra-pulse energy function diffe-rence.Based on this,the two-dimensional orthogonal matching pursuit(2D-OMP)algorithm is proposed.Further,it is proposed to reconstruct the ISAR image with the obtained unjammed pulse sequence.The validity of the proposed method is demon-strated via the Yake-42 plane data simulations.展开更多
As same as the conventional inverse synthetic aperture radar（ISAR）, the compressed ISAR also requires the echo signal based motion compensation, which consists of the range alignment and the phase autofoeusing. A ph...As same as the conventional inverse synthetic aperture radar（ISAR）, the compressed ISAR also requires the echo signal based motion compensation, which consists of the range alignment and the phase autofoeusing. A phase autofocusing algorithm for compressed ISAR imaging is presented. In the algorithm, phase autofocusing for the sparse ISAR echoes is accomplished using the eigenvector method. Experimental results validate the effectiveness of the algorithm.展开更多
We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equa...We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equal-radius penny-shaped crack inclusions in each layer. The P-wave velocity and amplitude were measured parallel and perpendicular to the layers of cracks at frequencies of 0.1 MHz to 1 MHz. The experiments show that as the crack aperture increases from 0.l mm to 0.34 mm, the amplitude of the P-waves parallel to the crack layers decreases linearly with increasing frequency and the P-wave velocity dispersion varies from 1.5% to 2.1%, whereas the amplitude of the P-wave perpendicular to the crack layers decreases quadratically with increasing frequency and the velocity dispersion varies from 1.9% to 4.7%. The variation in the velocity dispersion parallel and perpendicular to the cracks intensifies the anisotropy dispersion of the P-waves in the crack models （6.7% to 83%）. The P-wave dispersion strongly depends on the scattering characteristics of the crack apertures.展开更多
A windowed very small aperture laser (VSAL) source for use in high resolution near field optical data storage is fabricated.The windowed regions are introduced to avoid shorting the pn junction with metal coating a...A windowed very small aperture laser (VSAL) source for use in high resolution near field optical data storage is fabricated.The windowed regions are introduced to avoid shorting the pn junction with metal coating and suppress the COD effect.It facilitates producing VSAL by simplified technology and improves the laser performance.A VSAL with 400nm small aperture is demonstrated by focused ion beam (FIB) and the output power is 0 3mW at 31mA.展开更多
Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our ...Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our previous studies, it was shown that the wave retrieval algorithm, named the parameterized first-guess spectrum method(PFSM), works for C-band and X-band SAR at low to moderate sea states. In this work, we investigate the performance of the PFSM algorithm when it is applied for dual-polarization c-band sentinel-1(S-1) SAR acquired in extra wide-swath(EW) and interferometric wide-swath(IW) mode under cyclonic conditions.Strong winds are retrieved from six vertical-horizontal(VH) polarization S-1 SAR images using the c-band crosspolarization coupled-parameters ocean(C-3 PO) model and then wave parameters are obtained from the image at the vertical-vertical(VV) polarization channel. significant wave height(SWH) and mean wave period(MWP) are compared with simulations from the WAVEWATCH-III(WW3) model. The validation shows a 0.69 m root mean square error(RMSE) of SWH with a –0.01 m bias and a 0.62 s RMSE of MWP with a –0.17 s bias. Although the PFSM algorithm relies on a good quality SAR spectrum, this study confirms the applicability for wave retrieval from an S-1 SAR image. Moreover, it is found that the retrieved results have less accuracy on the right sector of cyclone eyes where swell directly affects strong wind-sea, while the PFSM algorithm works well on the left and rear sectors of cyclone eyes where the interaction of wind-sea and swell is relatively poor.展开更多
Radio frequency interference（RFI） is becoming more and more frequently, which makes it an important issue in SAR imaging.RFI presented in synthetic aperture radar either on purpose or inadvertent will distort the us...Radio frequency interference（RFI） is becoming more and more frequently, which makes it an important issue in SAR imaging.RFI presented in synthetic aperture radar either on purpose or inadvertent will distort the useful SAR echoes, thus degrade the SAR image quality.To resolve this issue, a long time study was carried out to study the characteristic of the RFI through the RFIaffected spaceborne and airborne SAR data.Based on the narrow band nature of RFI, this paper proposes a new process which contains both RFI detection and RFI suppression.A useful subband spectral kurtosis detector is first used to detect RFI, and then its results are used for RFI suppression.The proposed process has two advantages： one is the economization on the compute time for unnecessary interference suppression when no RFI existed; the other is improving the performance of the suppression method with knowing the exact position where RFI is.Moreover, the previous RFI suppression method––subband spectral cancelation（SSC） is supplemented and perfected.The subband division step is also elaborated detail in this paper.The experiment results show that the subband spectral kurtosis detector exhibits good performance in recognizing both weak and narrow-band RFI.In addition, the validity of the SSC method with subband spectral kurtosis detector is also validated on the real SAR echoes.展开更多
The 12 May 2008 Wenchuan Ms8.0 earthquake produced surface displacements along the causative fault, the Yingxiu-Beichuan Fault, which are up to several meters near the fault. Because of the large gradient, satellite s...The 12 May 2008 Wenchuan Ms8.0 earthquake produced surface displacements along the causative fault, the Yingxiu-Beichuan Fault, which are up to several meters near the fault. Because of the large gradient, satellite synthetic aperture radar （SAR） interferometric data are strongly incoherent; the usual SAR interferometry method does not allow such displacements to be measured. In the present study, we employed another approach, the technique based on pixel offset tracking, to solve this problem. The used image data of six tracks are from the Advanced Land Observing Satellite, Phased Array type L-band Synthetic Aperture Radar （ALOS/PALSAR） dataset of Japan. The results show that the entire surface rupture belt is 238 km long, extending almost linearly in a direction of 42°north-east. It is offset left laterally by a north-west-striking fault at Xiaoyudong, and turns at Gaochuan, where the rupture belt shifts toward the south by 5 km, largely keeping the original trend. In terms of the features of the rupture traces, the rupture belt can be divided into five sections and three types. Among them, the Beichuan-Chaping and Hongkou-Yingxiu sections are relatively complex, with large widths and variable traces along the trend. The Pingtong-Nanba and Qingping-Jingtang sections appear uniform, characterized by straight traces and small widths. West of Yingxiu, the rupture traces are not clear. North of the rupture belt, surface displacements are 2.95 m on average, mostly 2-3.5 m, with 7-9 m the maximum near Beichuan. South of the rupture belt, the average displacement is 1.75 m, dominated by 1-2 m, with 3-4 m at a few sites. In the north, the displacements in the radar line of sight are of subsidence, and in the south, they are uplifted, in accordance with a right-slip motion that moves the northern wall of the fault to the east, and the southern wall to the west, respectively. Along the Guanxian-Jiangyou Fault, there is a uplift zone in the radar line of sight, which is 66 km long, 1.5-6 km wide, and has vertical displacements of approximately 2 m, but no observable rupture traces.展开更多
The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms...The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms a long dark wake on the SAR image due to the suppression of the Bragg wave by the oil fi lm. This study investigates key techniques for rapid detection of long ship wakes, thereby providing law enforcement agencies with candidate ships for possible discharge. This paper presents a rapid long ship wake detection method that uses satellite imaging parameters and the axial direction of the ship in images to determine the potential detection area of the wake. Then, the threshold of long ship wake detection is determined using statistical analysis, the area is binarized, and isolated points are removed using a morphological filter operator. The method was tested with ENVISAT Synthetic Aperture Radar and GF-3 SAR data, and results showed that the method was eff ective, and the overall accuracy of the decision reaches 71%. We present two innovations;one is a method that draws a Doppler shift curve, and uses the SAR imaging parameters to determine the detection area of the long wake to achieve rapid detection and reduce the image detection area. The other is where a classical linear fitting method is used to quickly and accurately determine whether the detected dark area is a long ship wake and realizes the twisted long ship wake detection caused by the sea surface flow field, which is otherwise diffi cult to detect by the traditional Radon and Hough transform methods. This method has good suppression performance for the dark spot false alarm formed by low speed wind region or upward flow. The method is developed for maritime ship monitoring system and will promote the operational application of maritime ship monitoring system.展开更多
Simultaneous multistage hydraulic fracturing of unconventional gas shale in parallel multilateral wells is an effective technique to raise the connectivity of the reservoir to the wellbore and improve reservoir permea...Simultaneous multistage hydraulic fracturing of unconventional gas shale in parallel multilateral wells is an effective technique to raise the connectivity of the reservoir to the wellbore and improve reservoir permeability for an economical production. However, this technique should be accompanied with some optimization procedures to obtain an efficiently fractured reservoir with the highest production and the lowest cost. In unconventional hydraulic fracturing, fracture deviation/collapse and trapping are familiar phenomena which occur when a non-optimized fracturing pattern is used. These problems occur respectively when stress shadow size has not been considered in optimization and fracturing pressure is higher than the available pressure in the sealed section. Therefore, in an optimized hydraulic fracturing,having straight fractures with no deviation or collapse needs consideration of stress shadow effect(SSE).Apart from that, having efficiently propagated fractures to the extent of the reservoir without any fracture trap requires consideration of stress intensity factor(SIF) and aperture. SSE was studied and published by the authors in 2014. For the case of SIF, investigating any change in mode I SIF and aperture with different influencing variables such as fracture geometry and pattern are studied in the current research work. Three different fracturing techniques are assumed as multistage fracturing, simultaneous single-stage fracturing, and simultaneous multistage fracturing techniques. Since obtaining SIF for threedimensional fractures is a challenging issue, a stress ratio technique is used for calculation of SIF ratios of different fracturing scenarios compared to the case of a single fracture. Therefore, changes of SIF for different fracturing schemes are estimated and analyzed to understand whether or not a fracturing scheme is efficient and all the spaced perforations are activated and change to hydraulic fractures.展开更多
基金supported by the National Nat-ural Science Foundation of China(No.42376174)the Natural Science Foundation of Shanghai(No.23ZR 1426900).
文摘Synthetic aperture radar(SAR)aboard SEASAT was first launched in 1978.At the beginning of the 21st century,the Chinese remote sensing community recognized the urgent need to develop domestic SAR capabilities.Unlike scatterometers and al-timeters,space-borne SAR offers high-resolution images of the ocean,regardless of weather conditions or time of day.SAR imagery provides rich information about the sea surface,capturing complicated dynamic processes in the upper layers of the ocean,particular-ly in relation to tropical cyclones.Over the past four decades,the advantages of SAR have been increasingly recognized,leading to notable marine applications,especially in the development of algorithms for retrieving wind and wave data from SAR images.This study reviews the history,progress,and future outlook of SAR-based monitoring of sea surface wind and waves.In particular,the ap-plicability of various SAR wind and wave algorithms is systematically investigated,with a particular focus on their performance un-der extreme sea conditions.
文摘To realize effective co-phasing adjustment in large-aperture sparse-aperture telescopes,a multichannel stripe tracking approach is employed,allowing simultaneous interferometric measurements of multiple optical paths and circumventing the need for pairwise measurements along the mirror boundaries in traditional interferometric methods.This approach enhances detection efficiency and reduces system complexity.Here,the principles of the multibeam interference process and construction of a co-phasing detection module based on direct optical fiber connections were analyzed using wavefront optics theory.Error analysis was conducted on the system surface obtained through multipath interference.Potential applications of the interferometric method were explored.Finally,the principle was verified by experiment,an interferometric fringe contrast better than 0.4 is achieved through flat field calibration and incoherent digital synthesis.The dynamic range of the measurement exceeds 10 times of the center wavelength of the working band(1550 nm).Moreover,a resolution better than one-tenth of the working center wavelength(1550 nm)was achieved.Simultaneous three-beam interference can be achieved,leading to a 50%improvement in detection efficiency.This method can effectively enhance the efficiency of sparse aperture telescope co-phasing,meeting the requirements for observations of 8-10 m telescopes.This study provides a technological foundation for observing distant and faint celestial objects.
基金supported by the National Natural Science Foundation of China(Nos.42076238,42376174)the Natural Science Foundation of Shanghai(No.23ZR1426900).
文摘The purpose of this study is to analyze the impact of upper ocean dynamics on velocity bunching,represented by az-imuthal cutoff wavelength(i.e.,sea surface wind,wave,and current).In this study,over 1400 dual-polarized(vertical-vertical(VV)and vertical-horizontal(VH))Sentinel-1(S-1)synthetic aperture radar(SAR)images collected in tropical cyclones(TC)are utilized.These images are combined with wind and rain observations from the stepped-frequency microwave radiometer(SFMR),wave simu-lations conducted using a third-generation numerical wave model,WAVEWATCH-III(WW3),and SAR-derived wind information collected from CyclObs winds.The WW3-simulated significant wave height(SWH)is validated against measurements from HY-2B altimeter taken in August and September 2021,yielding a root mean square error(RMSE)of 0.48 m and a correlation coefficient(COR)of 0.88.The SAR-based azimuthal cutoff wavelengths in VV polarization,which quantitatively represent the effect of velocity bunching,are compared with theoretical values calculated using WW3-simulated SWH.A notable relationship is observed between the difference in azimuthal cutoff wavelength and SAR-derived wind speed and WW3-simulated SWH.Analysis results show that the correlation between SAR-based azimuthal cutoff wavelength and SWH is stronger than that with wind and current.Finally,a machine learning algorithm is used to develop an algorithm aimed at simulating the azimuthal cutoff wavelength in TCs,including wind,wave,and incidence angle.This method yields an RMSE of 8.90 m,a COR of 0.91,and a scatter index of 0.04 for VV-polar-ization SAR.
基金supported by the Space Debris Research Project,China(KJSP2020010102)the National Key R&D Program of China(2022YFC2807300)the National Natural Science Foundation of China(12573081)。
文摘Dome A,in Antarctica,offers an exceptional site for ground-based infrared astronomy,with its extremely low atmospheric infrared background noise and excellent seeing conditions.However,deploying near-infrared telescopes in the harsh environment of Antarctica faces the critical challenge of frost accumulation on optical mirrors.While indium tin oxide heating films effectively defrost visible-band Antarctic astronomical telescopes,their thermal radiation at infrared wavelengths introduces significant stray light,severely degrading the signal-to-noise ratio for infrared observations.To address this limitation,we have designed a mechanical snow-removal system capable of efficiently clearing frost from sealing window surfaces at temperatures as low as–80°C.Aperture photometry of target sources,Canopus and HD 2151,revealed that after six days without intervention,floating snow extinction reduced target brightness by up to 3 magnitudes.Following mechanical defrosting,the source flux recovered to stable levels,with measured magnitudes showing rapid initial improvement followed by stabilization.Data analysis indicates that a frost removal strategy operating every 48 h,with each operation consisting of 4–6 cycles,enables efficient removal of frost and snow without introducing additional thermal noise.Future work will focus on optimizing the adaptive control algorithm and exploring novel low-temperature defrosting materials to extend the periods during which Antarctic infrared telescopes can operate unattended.
基金support of the National Natural Science Foundation of China(U23B6004 and 52404045)the CAST Young Talent Support Program,Doctoral Student Special Project.
文摘During gas extraction from deep coal,the rock endures high effective stress,with both the time-dependent deformation and anisotropic structure of the rock controlling the permeability evolution.To reveal this phenomenon,a numerical simulation framework of the finite volume method and transient embedded discrete fracture model is proposed to establish a new constitutive model that links poroelastoplastic deformation,adsorption-induced swelling,and aperture compression.From this model,anisotropic permeability tensors were derived to further achieve the simulation of coevolution.Meanwhile,our permeability model was verified against the measured permeability data,and the history match of the numerical model showed better results where the mismatch was less than 5%.The results indicate that(1)the long-term permeability evolution clearly showed the competitive effects of multiple deformation mechanisms,which involves three stages:compaction-dominated decline,adsorption-dominated rebound,and creep-controlled loss.(2)The increased number of compressible cleats/fractures accelerated the initial permeability decline,while the increased desorption-induced strain promoted faster rebound and enhancement and higher viscosity coefficients enhanced the creep effect,which led to significant long-term permeability loss.(3)Massive hydraulic fracturing created a larger drainage area,accelerating methane desorption and causing sharp permeability rebound with reduced residual gas,which shows that the permeability remained higher than the initial values even after the extensive extraction via the fractured horizontal wells.The permeability evolution mechanisms displayed varying properties,such as coal rank and burial depth,and distinct characteristics.A precise understanding of multiple competitive stress effects is crucial for optimizing coalbed methane extraction techniques and improving recovery efficiency.
基金supported by the National Natural Science Foundation of China under Grant U21A20449The Zhongguancun Project under Grant 23120035.
文摘Synthetic aperture radar(SAR)radio frequency identification(RFID)localization is widely used for automated guided vehicles(AGVs)in the industrial internet of things(IIoT).However,the AGV’s speeds are limited by the phase difference(PD)of two neighboring readers.In this paper,an inertial navigation system(INS)based SAR RFID localization method(ISRL)where AGV moves nonlinearly.To relax the speed limitation,a new phase-unwrapping method based on the similarity of PDs(PU-SPD)is proposed to deal with the PD ambiguity when the AGV speed exceeds 60km/h.In localization,the gauss-newton algorithm(GN)is employed and an initial value estimation scheme based on variable substitution(IVE-VS)is proposed to improve its positioning accuracy and the convergence rate.Thus,ISRL is a combination of IVE-VS and GN.Moreover,the Cramer-Rao lower bound(CRLB)and the speed limitation is derived.Simulation results show that the ISRL can converge after two iterations,and the positioning accuracy can achieve 7.50cm at a phase noise levelσ=0.18,which is 35%better than the Hyperbolic unbiased estimation localization(HyUnb).
基金supported partly by the National Natural Science Foundation of China(NSFC)(62101568 and 62371460)the Scientific Research Program of the National University of Defense Technology(ZK21-06)the Taishan Scholars of Shandong Province(ts20190968)。
文摘Amplitude stripes imposed by ionospheric scintillation have been frequently observed in many of the equatorial nighttime acquisitions of the Advanced Land Observing Satellite(ALOS)Phased Array-type L-band Synthetic Aperture Radar(PALSAR).This type of ionospheric artifact impedes PALSAR interferometric and polarimetric applications,and its formation cause,morphology,and negative influence have been deeply investigated.However,this artifact can provide an alternative opportunity in a positive way for probing and measuring ionosphere scintillation.In this paper,a methodology for measuring ionospheric scintillation parameters from PALSAR images with amplitude stripes is proposed.Firstly,sublook processing is beneficial for recovering the scattered stripes from a single-look complex image;the amplitude stripe pattern is extracted via band-rejection filtering in the frequency domain of the sublook image.Secondly,the amplitude spectrum density function(SDF)is estimated from the amplitude stripe pattern.Thirdly,a fitting scheme for measuring the scintillation strength and spectrum index is conducted between the estimated and theoretical long-wavelength SDFs.In addition,another key parameter,the scintillation index,can be directly measured from the amplitude stripe pattern or indirectly derived from the scintillation strength and spectrum index.The proposed methodology is fully demonstrated on two groups of PALSAR acquisitions in the presence of amplitude stripes.Self-validation is conducted by comparing the measured and derived scintillation index and by comparing the measurements of range lines and azimuth lines.Cross-validation is performed by comparing the PALSAR measurements with in situ Global Position System(GPS)measurements.The processing results demonstrate a powerful capability to robustly measure ionospheric scintillation parameters from space with high spatial resolution.
基金supported by the National Natural Science Foundation of China(6203100762371093).
文摘The multifunctional integration system(MFIS)is based on a common hardware platform that controls and regulates the system’s configurable parameters through software to meet dif-ferent operational requirements.Dwell scheduling is a key for the system to realize multifunction and maximize the resource uti-lization.In this paper,an adaptive dwell scheduling optimization model for MFIS which considers the aperture partition and joint radar communication(JRC)waveform is established.To solve the formulated optimization problem,JRC scheduling condi-tions are proposed,including time overlapping condition,beam direction condition and aperture condition.Meanwhile,an effec-tive mechanism to dynamically occupy and release the aperture resource is introduced,where the time-pointer will slide to the earliest ending time of all currently scheduled tasks so that the occupied aperture resource can be released timely.Based on them,an adaptive dwell scheduling algorithm for MFIS with aperture partition and JRC waveform is put forward.Simulation results demonstrate that the proposed algorithm has better com-prehensive scheduling performance than up-to-date algorithms in all considered metrics.
基金supported by the National Natural Science Foundation of China(62001481,61890542,62071475)the Natural Science Foundation of Hunan Province(2022JJ40561)the Research Program of National University of Defense Technology(ZK22-46).
文摘Nonperiodic interrupted sampling repeater jamming(ISRJ)against inverse synthetic aperture radar(ISAR)can obtain two-dimensional blanket jamming performance by joint fast and slow time domain interrupted modulation,which is obviously dif-ferent from the conventional multi-false-target deception jam-ming.In this paper,a suppression method against this kind of novel jamming is proposed based on inter-pulse energy function and compressed sensing theory.By utilizing the discontinuous property of the jamming in slow time domain,the unjammed pulse is separated using the intra-pulse energy function diffe-rence.Based on this,the two-dimensional orthogonal matching pursuit(2D-OMP)algorithm is proposed.Further,it is proposed to reconstruct the ISAR image with the obtained unjammed pulse sequence.The validity of the proposed method is demon-strated via the Yake-42 plane data simulations.
基金Supported by the National Natural Science Foundation of China(61071165)the Program for NewCentury Excellent Talents in University(NCET-09-0069)the Defense Industrial Technology Development Program(B2520110008)~~
文摘As same as the conventional inverse synthetic aperture radar（ISAR）, the compressed ISAR also requires the echo signal based motion compensation, which consists of the range alignment and the phase autofoeusing. A phase autofocusing algorithm for compressed ISAR imaging is presented. In the algorithm, phase autofocusing for the sparse ISAR echoes is accomplished using the eigenvector method. Experimental results validate the effectiveness of the algorithm.
基金supported by the Major National Project Program (No.2011ZX05007-006)
文摘We experimentally studied the effect of crack aperture on P-wave velocity, amplitude, anisotropy and dispersion. Experimental models were constructed based on Hudson＇s theory. Six crack models were embedded with equal-radius penny-shaped crack inclusions in each layer. The P-wave velocity and amplitude were measured parallel and perpendicular to the layers of cracks at frequencies of 0.1 MHz to 1 MHz. The experiments show that as the crack aperture increases from 0.l mm to 0.34 mm, the amplitude of the P-waves parallel to the crack layers decreases linearly with increasing frequency and the P-wave velocity dispersion varies from 1.5% to 2.1%, whereas the amplitude of the P-wave perpendicular to the crack layers decreases quadratically with increasing frequency and the velocity dispersion varies from 1.9% to 4.7%. The variation in the velocity dispersion parallel and perpendicular to the cracks intensifies the anisotropy dispersion of the P-waves in the crack models （6.7% to 83%）. The P-wave dispersion strongly depends on the scattering characteristics of the crack apertures.
文摘A windowed very small aperture laser (VSAL) source for use in high resolution near field optical data storage is fabricated.The windowed regions are introduced to avoid shorting the pn junction with metal coating and suppress the COD effect.It facilitates producing VSAL by simplified technology and improves the laser performance.A VSAL with 400nm small aperture is demonstrated by focused ion beam (FIB) and the output power is 0 3mW at 31mA.
基金The National Key Research and Development Program of China under contract No.2017YFA0604901the National Natural Science Foundation of China under contract Nos 41806005 and 41776183the Public Welfare Technical Applied Research Project of Zhejiang Province of China under contract No.LGF19D060003
文摘Theoretical-based ocean wave retrieval algorithms are applied by inverting a synthetic aperture radar(SAR)intensity spectrum into a wave spectrum, that has been developed based on a SAR wave mapping mechanism. In our previous studies, it was shown that the wave retrieval algorithm, named the parameterized first-guess spectrum method(PFSM), works for C-band and X-band SAR at low to moderate sea states. In this work, we investigate the performance of the PFSM algorithm when it is applied for dual-polarization c-band sentinel-1(S-1) SAR acquired in extra wide-swath(EW) and interferometric wide-swath(IW) mode under cyclonic conditions.Strong winds are retrieved from six vertical-horizontal(VH) polarization S-1 SAR images using the c-band crosspolarization coupled-parameters ocean(C-3 PO) model and then wave parameters are obtained from the image at the vertical-vertical(VV) polarization channel. significant wave height(SWH) and mean wave period(MWP) are compared with simulations from the WAVEWATCH-III(WW3) model. The validation shows a 0.69 m root mean square error(RMSE) of SWH with a –0.01 m bias and a 0.62 s RMSE of MWP with a –0.17 s bias. Although the PFSM algorithm relies on a good quality SAR spectrum, this study confirms the applicability for wave retrieval from an S-1 SAR image. Moreover, it is found that the retrieved results have less accuracy on the right sector of cyclone eyes where swell directly affects strong wind-sea, while the PFSM algorithm works well on the left and rear sectors of cyclone eyes where the interaction of wind-sea and swell is relatively poor.
基金co-supported by the China Postdoctoral Science Foundation (No.2013M541035)the National Natural Science Foundation of China (No.61301025)
文摘Radio frequency interference（RFI） is becoming more and more frequently, which makes it an important issue in SAR imaging.RFI presented in synthetic aperture radar either on purpose or inadvertent will distort the useful SAR echoes, thus degrade the SAR image quality.To resolve this issue, a long time study was carried out to study the characteristic of the RFI through the RFIaffected spaceborne and airborne SAR data.Based on the narrow band nature of RFI, this paper proposes a new process which contains both RFI detection and RFI suppression.A useful subband spectral kurtosis detector is first used to detect RFI, and then its results are used for RFI suppression.The proposed process has two advantages： one is the economization on the compute time for unnecessary interference suppression when no RFI existed; the other is improving the performance of the suppression method with knowing the exact position where RFI is.Moreover, the previous RFI suppression method––subband spectral cancelation（SSC） is supplemented and perfected.The subband division step is also elaborated detail in this paper.The experiment results show that the subband spectral kurtosis detector exhibits good performance in recognizing both weak and narrow-band RFI.In addition, the validity of the SSC method with subband spectral kurtosis detector is also validated on the real SAR echoes.
基金supported by the State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration(CEA) (no. LED2010A02,LED2008A06)
文摘The 12 May 2008 Wenchuan Ms8.0 earthquake produced surface displacements along the causative fault, the Yingxiu-Beichuan Fault, which are up to several meters near the fault. Because of the large gradient, satellite synthetic aperture radar （SAR） interferometric data are strongly incoherent; the usual SAR interferometry method does not allow such displacements to be measured. In the present study, we employed another approach, the technique based on pixel offset tracking, to solve this problem. The used image data of six tracks are from the Advanced Land Observing Satellite, Phased Array type L-band Synthetic Aperture Radar （ALOS/PALSAR） dataset of Japan. The results show that the entire surface rupture belt is 238 km long, extending almost linearly in a direction of 42°north-east. It is offset left laterally by a north-west-striking fault at Xiaoyudong, and turns at Gaochuan, where the rupture belt shifts toward the south by 5 km, largely keeping the original trend. In terms of the features of the rupture traces, the rupture belt can be divided into five sections and three types. Among them, the Beichuan-Chaping and Hongkou-Yingxiu sections are relatively complex, with large widths and variable traces along the trend. The Pingtong-Nanba and Qingping-Jingtang sections appear uniform, characterized by straight traces and small widths. West of Yingxiu, the rupture traces are not clear. North of the rupture belt, surface displacements are 2.95 m on average, mostly 2-3.5 m, with 7-9 m the maximum near Beichuan. South of the rupture belt, the average displacement is 1.75 m, dominated by 1-2 m, with 3-4 m at a few sites. In the north, the displacements in the radar line of sight are of subsidence, and in the south, they are uplifted, in accordance with a right-slip motion that moves the northern wall of the fault to the east, and the southern wall to the west, respectively. Along the Guanxian-Jiangyou Fault, there is a uplift zone in the radar line of sight, which is 66 km long, 1.5-6 km wide, and has vertical displacements of approximately 2 m, but no observable rupture traces.
基金Supported by the National Natural Science Foundation of China(No.41476088)the National High Resolution Project of China(No.41Y30B12-9001-14/16)+1 种基金the 2016 Key Projects for Marine Environmental Security(No.2016YFC14032)the research grants of the Second Institute of Oceanography,MNR(No.JT1307)
文摘The maritime administrative department employs synthetic aperture radar (SAR) satellite remote sensing technology to obtain evidence of illegal discharge of ships. If the ship is discharged during navigation, it forms a long dark wake on the SAR image due to the suppression of the Bragg wave by the oil fi lm. This study investigates key techniques for rapid detection of long ship wakes, thereby providing law enforcement agencies with candidate ships for possible discharge. This paper presents a rapid long ship wake detection method that uses satellite imaging parameters and the axial direction of the ship in images to determine the potential detection area of the wake. Then, the threshold of long ship wake detection is determined using statistical analysis, the area is binarized, and isolated points are removed using a morphological filter operator. The method was tested with ENVISAT Synthetic Aperture Radar and GF-3 SAR data, and results showed that the method was eff ective, and the overall accuracy of the decision reaches 71%. We present two innovations;one is a method that draws a Doppler shift curve, and uses the SAR imaging parameters to determine the detection area of the long wake to achieve rapid detection and reduce the image detection area. The other is where a classical linear fitting method is used to quickly and accurately determine whether the detected dark area is a long ship wake and realizes the twisted long ship wake detection caused by the sea surface flow field, which is otherwise diffi cult to detect by the traditional Radon and Hough transform methods. This method has good suppression performance for the dark spot false alarm formed by low speed wind region or upward flow. The method is developed for maritime ship monitoring system and will promote the operational application of maritime ship monitoring system.
基金Oklahoma Department of Transportation (ODOT)Oklahoma Transportation Center for their financial support during the course of this study
文摘Simultaneous multistage hydraulic fracturing of unconventional gas shale in parallel multilateral wells is an effective technique to raise the connectivity of the reservoir to the wellbore and improve reservoir permeability for an economical production. However, this technique should be accompanied with some optimization procedures to obtain an efficiently fractured reservoir with the highest production and the lowest cost. In unconventional hydraulic fracturing, fracture deviation/collapse and trapping are familiar phenomena which occur when a non-optimized fracturing pattern is used. These problems occur respectively when stress shadow size has not been considered in optimization and fracturing pressure is higher than the available pressure in the sealed section. Therefore, in an optimized hydraulic fracturing,having straight fractures with no deviation or collapse needs consideration of stress shadow effect(SSE).Apart from that, having efficiently propagated fractures to the extent of the reservoir without any fracture trap requires consideration of stress intensity factor(SIF) and aperture. SSE was studied and published by the authors in 2014. For the case of SIF, investigating any change in mode I SIF and aperture with different influencing variables such as fracture geometry and pattern are studied in the current research work. Three different fracturing techniques are assumed as multistage fracturing, simultaneous single-stage fracturing, and simultaneous multistage fracturing techniques. Since obtaining SIF for threedimensional fractures is a challenging issue, a stress ratio technique is used for calculation of SIF ratios of different fracturing scenarios compared to the case of a single fracture. Therefore, changes of SIF for different fracturing schemes are estimated and analyzed to understand whether or not a fracturing scheme is efficient and all the spaced perforations are activated and change to hydraulic fractures.
