Reflection Tomography Imaging Research Articles

Tutorial: Real-time coherent terahertz imaging of objects moving in one direction with constant speed

Pulsed terahertz (THz) electric fields enable various coherent THz imaging modes, such as reflection tomography, spectral imaging, and computed tomography (CT) for nondestructive inspection, quality control, and material characterization. The extension of coherent THz imaging modes to moving objects has been regarded as key to their social implementation. This Tutorial focuses on two-dimensional spatiotemporal (2D-ST) THz imaging of objects moving in one direction with constant speed as a promising means of enabling real-time coherent THz imaging. In 2D-ST THz imaging, the temporal waveform and line image of the THz pulse are simultaneously acquired without the need for mechanical scanning of the time delay and sample position using a combination of non-collinear 2D free-space electro-optic sampling with THz line-imaging optics. This 2D-ST THz imaging boosts the imaging rates of THz reflection tomography, THz spectral imaging, and THz CT to levels that are applicable to moving objects. The advanced THz reflection tomography and THz spectral imaging that result from the assistance of 2D-ST THz imaging achieve real-time line imaging of cross sections and spectral signatures, respectively. Subsequently, this enables in-line total inspection of objects moving on a translation stage or a conveyor belt. A THz CT system using real-time line projection of a THz beam is effectively applied to a 2D spectral cross section of a continuously rotating object. 2D-ST THz imaging enables the functional THz imaging of moving objects in various practical applications.

Optimization Method for Laser Reflective Tomography Imaging Based on Waveform Decomposition

Optimization Method for Laser Reflective Tomography Imaging Based on Waveform Decomposition

3D velocity-depth model from multichannel seismic in the Dinaric foredeep of the Gulf of Trieste (Adriatic Sea), at the NE edge of Adria plate

The Gulf of Trieste (GT), northeastern Adriatic, sits at the rigid edge of the Adria microplate representing the foreland of the adjoining Meso-Cenozoic External Dinarides and Southeastern Alps. The Adria-Eurasia plate boundary extends along the GT eastern coastline, depicted by the Karst Thrust, outer ramp of the SW-verging Dinarides. This separates the Cretaceous-Paleogene carbonates outcropping hundreds of meters on the Karst Plateau (hanging-wall) from their counterparts buried in the eastern gulf. Although the thrust has no evidence of historical and instrumental seismicity, a detailed seismic velocity field is needed to quantify reliable geometries in the foredeep, embedded in a tectonically active area where Adria is moving NNW-ward. Availability of a newly acquired marine multichannel seismic dataset, allowed us to provide the first well-constrained 3D P-wave velocity and depth model in the footwall of the Karst Thrust. Two iterative techniques, traveltime reflection tomography and depth seismic imaging, were applied on the data surveying the Dinaric foredeep. Our findings provide mean velocity values of 1700 m/s for the Quaternary sediments, 2900 m/s for the upper Eocene flysch turbidites, 4500 m/s for the lower flysch, 5000 m/s for the upper carbonates. The maximum flysch unit thickness results in about 1500 m and the top carbonates depth reaches about 1600 m below sea level, 1.7 km offshore Trieste, revealing the thrust is responsible for a minimum 1600–1800 m vertical throw. This study provides benefits for Adria geodynamic models and give new constraints for the geological and tectonic setting assessment, in a region settled over a currently active continental margin.

Determining the limiting conditions of sampling interval and sampling angle for laser reflective tomography imaging in sensing targets with typical shapes

Laser reflective tomography imaging (LRTI) is unique in the remote sensing of space targets because the resolution is independent of the distance. As it is usually difficult to obtain the 360-degree of reflectance projections, the estimation of the proper sampling interval and sampling angle becomes a key problem. In this paper, we conducted an LRTI experiment with a distance of 0.98-km and a wavelength of 1064 nm, and constructed three targets with typical shapes, namely, planar target, plane combination target, and closed-surface target. By comparing the evaluation indexes of retrieved images, the following was found: (1) When the sampling interval exceeds the maximum sampling interval derived by the Nyquist sampling law, the quality of reconstructed images deteriorates rapidly; (2) When the sampling angle is greater than 70 degrees and 90 degrees, the image of planar and plane combination target can be reconstructed excellently, respectively. However, contour image reconstruction requires full angle projection for closed-surface target; (3) When the sampling angle is fixed, the quality of reconstructed image is best for the vertical detection. This paper determines the limiting conditions of the sampling interval and sampling angle, which are of great practical significance in guiding the space-borne LRTI in sensing the space target with a long distance.

Determining the Limiting Conditions of Sampling Interval and Sampling Angle for Laser Reflective Tomography Imaging in Sensing Targets with Typical Shapes

Determining the Limiting Conditions of Sampling Interval and Sampling Angle for Laser Reflective Tomography Imaging in Sensing Targets with Typical Shapes

Circular synthetic aperture acoustic imaging of spherical targets in cylindrical rod clutter

A model apparatus has been built to demonstrate acoustic imaging of several spherical targets in cylindrical clutter. Reflective ultrasonic tomography imaging was chosen because the medical community, using photo-acoustic tomography imaging, utilizes a similar back-projection imaging algorithm. The experiment involves suspending an ultrasonic transducer unit (resonant frequency 1.0 MHz) in an aquarium filled with water. The transducer (sender-receiver) generates a 5-cycle tone burst. The circular plane array transducer diameter is D = 1.27 cm. Its wavelength is 1.48 mm (using c = 1482 m/s). The target, located 15 cm from the source, consists of two 0.64 cm diameter metal spheres separated by 5 cm. A mechanical structure of thin perforated disks (10 cm diam) comprise a step-motor controlled rotational platform that supports the targets and slender stainless steel cylindrical vertical rods (2 mm diameter, 10 cm long) that serve as the clutter. Received echoes versus time (data sets) were measured at 10° rotation increments of the structure (from 0° to 360°) for back-projecting the 2-D image reflectance of the targets among the clutter (using Mathematica®). The original apparatus and supporting electronics were built by Madeline Bell for her USNA Capstone research (Fall 2020) involving scattering from cylindrical targets.

Effects of Typical Emission Waveform on Laser Reflective Tomography Imaging

Laser reflective tomography imaging is a new imaging method of long distance and high resolution. The echo could be expressed as the convolution of incident waveform and the reflectance projection distribution, so the deconvolution effect of the echo obtained by different emission waveforms is also different. In order to explore the reflectance projection distribution obtained by deconvolution of different emission waveforms under the same SNR, we simulated four kinds of emission pulses and from the comparison of the RMS of Euclidean distance between deconvolution results and reality results, we found that Gaussian pulse could be selected as the most suitable emission waveform when the SNR was less than 40, and when the SNR was larger, Sawtooth pulse was the best choice.

Typical influencing factors analysis of laser reflection tomography imaging

By transmitting narrow laser pulses the range-resolved laser reflective tomography imaging is promising for detecting space-based objects in the distance. Its advantage is that this kind of laser radar can obtain outlines of the object with single-pixel detector. This can be implemented by collecting the multi-view echoes of the object and utilizing image reconstruction algorithms. In this paper, the imaging model of laser reflection tomography is established. Combining 3-D modeling with OpenGL processing, the imaging process of the laser reflection tomography is simulated. In simulated experiments, three kinds of laser pulse widths and three kinds of surface materials are considered, and their influences on the reconstructed image quality are compared and analyzed. Moreover, four kinds of object models are built to investigate the effects of shape on reflection tomography imaging. The experimental results demonstrate that the pulse width, surface material and geometric appearance make different influences on the imaging results. Based on the conclusions, it is possible to realize target recognition in space by laser reflection tomography imaging.

激光反射层析成像相位恢复算法研究

激光反射层析成像相位恢复算法研究

基于距离分辨的激光雷达技术研究进展

Laser radar is an important technical way for high-accuracy detection, tracking and monitoring space-based target in the distance. Compared to the traditional imaging system, the range-resolved laser radar system has the advantages of simple structure and small atmospheric effect. At home and abroad the relative research institutes have done much work about this technology. The status and trend of two kinds of laser radar, which were called high resolution echoes detecting laser radar and reflective tomography imaging laser radar respectively, was introduced. The developments of the theoretical algorithms, modeling simulation, experimental verification and actual application were summarized and compared with each other. The technical characteristics of these two kinds of laser radar were analyzed, and the prospect of developments was expected.

Seismic depth imaging of sequence boundaries beneath the New Jersey shelf

Numerical modelling of fluid flow and transport processes relies on a well-constrained geological model, which is usually provided by seismic reflection surveys. In the New Jersey shelf area a large number of 2D seismic profiles provide an extensive database for constructing a reliable geological model. However, for the purpose of modelling groundwater flow, the seismic data need to be depth-converted which is usually accomplished using complementary data from borehole logs. Due to the limited availability of such data in the New Jersey shelf, we propose a two-stage processing strategy with particular emphasis on reflection tomography and pre-stack depth imaging. We apply this workflow to a seismic section crossing the entire New Jersey shelf. Due to the tomography-based velocity modelling, the processing flow does not depend on the availability of borehole logging data. Nonetheless, we validate our results by comparing the migrated depths of selected geological horizons to borehole core data from the IODP expedition 313 drill sites, located at three positions along our seismic line. The comparison yields that in the top 450 m of the migrated section, most of the selected reflectors were positioned with an accuracy close to the seismic resolution limit (≈ 4 m) for that data. For deeper layers the accuracy still remains within one seismic wavelength for the majority of the tested horizons. These results demonstrate that the processed seismic data provide a reliable basis for constructing a hydrogeological model. Furthermore, the proposed workflow can be applied to other seismic profiles in the New Jersey shelf, which will lead to an even better constrained model.

Detection of barycenter of planar target based on laser reflective tomography

Reflective tomography imaging Lidar system has been proved a useful approach in remote high-resolution imaging. For space target such as debris, barycenter detection could help monitor their motion status and track. We proposed a barycenter location method based on laser reflection tomography, which could precisely determine the range information and location of barycenter of planar target, whether it is coincident with rotation center or not. Experiments on actual Lidar system was conducted and the results came out that calculated barycenter is about 5 cm away from the real barycenter in detection range of 50 m, which could initially confirm the efficiency of this method.

Multimodal ultrasound computer-assisted tomography: An approach to the recognition of breast lesions

The research here presented aims at developing a new, promising method for the imaging diagnostics of breast lesions – ultrasound tomography (UST). A currently implemented device enables the reconstruction three complementary images for each coronal breast section. Based on in vivo breast examination, the authors developed an approach to breast diagnostics which employs ultrasound transmission and reflection tomography imaging. The obtained transmission images of ultrasound speed distribution show good correlation of glandular tissue areas with their visualization on MRI images. The results also allow a prediction that the implemented UST device offering fusion of reconstructed images may contribute to achieving a new standard for breast cancer diagnostics through non-invasive, fast and cheap screening tests.

变分贝叶斯解卷积法在激光反射层析成像中的应用

变分贝叶斯解卷积法在激光反射层析成像中的应用

Inversion of the elliptical Radon transform arising in migration imaging using the regular Radon transform

In recent years, many types of elliptical Radon transforms that integrate functions over various sets of ellipses/ellipsoids have been considered, relating to studies in bistatic synthetic aperture radar, ultrasound reflection tomography, radio tomography, and migration imaging. In this article, we consider the transform that integrates a given function in Rn over a set of ellipses (when n=2) or ellipsoids of rotation (when n≥3) with foci restricted to a hyperplane. We show a relation between this elliptical Radon transform and the regular Radon transform, and provide the inversion formula for the elliptical Radon transform using this relation. Numerical simulations are performed to demonstrate the suggested algorithms in two dimensions, and these simulations are also provided in this article.

Imaging results of multi-modal ultrasound computerized tomography system designed for breast diagnosis

Nowadays, in the era of common computerization, transmission and reflection methods are intensively developed in addition to improving classical ultrasound methods (US) for imaging of tissue structure, in particular ultrasound transmission tomography UTT (analogous to computed tomography CT which uses X-rays) and reflection tomography URT (based on the synthetic aperture method used in radar imaging techniques). This paper presents and analyses the results of ultrasound transmission tomography imaging of the internal structure of the female breast biopsy phantom CIRS Model 052A and the results of the ultrasound reflection tomography imaging of a wire sample. Imaging was performed using a multi-modal ultrasound computerized tomography system developed with the participation of a private investor. The results were compared with the results of imaging obtained using dual energy CT, MR mammography and conventional US method. The obtained results indicate that the developed UTT and URT methods, after the acceleration of the scanning process, thus enabling in vivo examination, may be successfully used for detection and detailed characterization of breast lesions in women.

Wide Spectrum Terahertz-Wave Generation From Nonlinear Waveguides

We have obtained efficient terahertz (THz)-wave generation from surface-emitting or waveguide propagation using Cherenkov-type radiation with nonlinear optical (NLO) crystals. This approach presented the following advantages: 1) many crystals can be used as THz-wave emitters; 2) it is not necessary to satisfy the phase-matching condition inside the crystal; and 3) THz-wave generation is not suppressed by the absorption in the crystal. We demonstrated that the THz-wave generation was enhanced 50× by suppressing the phase mismatch with a surfing configuration for bulk lithium niobate (LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) crystals. Using the prism-coupled Cherenkov phase-matching method with organic crystal 4-dimethylamino-N-metyl-4-stilbazolium tosylate, we produced tunable THz radiation within ~0.1-10 THz. There was no evidence of significant absorption in the crystal. To show the advantages of the waveguide emitter, we demonstrated THz generation using a ridge-type LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> waveguide with a thickness of 3.8 μm. We obtained THz-wave generation with an ideal temporal half-cycle pulse and a wide tuning range, which is applied to reflection tomography imaging.

Structural architecture of oceanic plateau subduction offshore Eastern Java and the potential implications for geohazards

The region offshore Eastern Java represents one of the few places where the early stage of oceanic plateau subduction is occurring. We study the little investigated Roo Rise oceanic plateau on the Indian plate, subducting beneath Eurasia. The presence of the abnormal bathymetric features entering the trench has a strong effect on the evolution of the subduction system, and causes additional challenges on the assessment of geohazard risks. We present integrated results of a refraction/wide-angle reflection tomography, gravity modelling, and multichannel reflection seismic imaging using data acquired in 2006 south of Java near 113°E. The composite structural model reveals the previously unresolved deep geometry of the oceanic plateau and the subduction zone. The oceanic plateau crust is on average 15 km thick and covers an area of about 100 000 km2. Within our profile the Roo Rise crustal thickness ranges between 18 and 12 km. The upper oceanic crust shows high degree of fracturing, suggesting heavy faulting. The forearc crust has an average thickness of 14 km, with a sharp increase to 33 km towards Java, as revealed by gravity modelling. The complex geometry of the backstop suggests two possible models for the structural formation within this segment of the margin: either accumulation of the Roo Rise crustal fragments above the backstop or alternatively uplift of the backstop caused by basal accumulation of crustal fragments. The subducting plateau is affecting the stress field within the accretionary complex and the backstop edge, which favours the initiation of large, potentially tsunamogenic earthquakes such as the 1994 Mw= 7.8 tsunamogenic event.

Sunda‐Banda arc transition: Incipient continent‐island arc collision (northwest Australia)

The eastern Sunda arc represents one of the few regions globally where the early stages of continent‐arc collision can be studied. We studied along the western limit of the collision zone at the Sunda‐Banda arc transition, where the Australian margin collides with the Banda island arc, causing widespread back arc thrusting. We present integrated results of a refraction/wide‐angle reflection tomography, gravity modeling, and multichannel reflection seismic imaging using data acquired in 2006 southeast of Sumba Island. The composite structural model reveals the previously unresolved deep geometry of the collision zone. Changes in crustal structure encompass the 10–12 km thick Australian basement in the south and the 22–24 km thick Sumba ridge in the north, where backthrusting of the 130 km wide accretionary prism is documented. The structural diversity along this transect could be characteristic of young collisional systems at the transition from oceanic subduction to continent‐arc collision.

Processing techniques applied to underwater target echoes and their relationships.

Interest in acoustic scattering from underwater unexploded ordnance (UXO) has been increasing because of the growing need for sonar technology able to detect submerged UXO and to efficiently separate these detections from those due to natural and man-made clutter. Recent efforts range from laboratory and numerical studies seeking to understand the basic structural acoustic echo formation processes and the environmental effects on them to field exercises determining how well a particular detection/identification technology performs. This paper discusses several important scattering-based constructs, which have been utilized in both the basic UXO studies and the technology exercises as well. They include: (1) σ(ω, θ), the frequency/angle-dependent scattering cross section; (2) standard imagery, oftentimes implemented with synthetic aperture arrays; (3) reflection tomography imaging; and (4) supersonic imaging using holographic techniques. Without a clear appreciation for the differences among the constructs, it is difficult to properly relate the results of the various studies. We have measured the broadband scattering from several underwater UXO targets using laboratory, rail-based, and AUV systems and processed the data using the above constructs. The use of a common, high quality UXO scattering data base in this process helps clarify the differences and relationships among the constructs. [Work supported by SERDP and ONR.]