Surface Reflection Profiling Research Articles

Daily monitoring of marine mucilage using the MODIS products: a case study of 2021 mucilage bloom in the Sea of Marmara, Turkey.

Climate change and global warming along with human activities have caused abrupt changes in the atmosphere, marine, and terrestrial ecosystems. One of these changes is the rising number of mucilage events in marine ecosystems. During the recent two decades, mucilage blooms have begun to appear more frequently in the Sea of Marmara in Turkey, surrounded by seven densely populated cities with various anthropogenic activities including household pollution, heavy industrialization, agricultural pollution, commercial fishing, shipyards, and specialized marine terminals with high maritime traffic density. In Spring 2021, a massive mucilage event observed in the Sea of Marmara plagued the entire ecosystem and raised awareness among the government and the public to detect and monitor this phenomenon. In this research, daily monitoring and detection of mucilage formations from the coarse spatial resolution MODIS products were investigated during the 2021 bloom period. The results were validated with the reference mucilage datasets derived from Sentinel-2A imagery and in situ spectroradiometer measurements over mucilage formations. The results revealed that the MODIS surface reflectance profiles were highly correlated with the field spectral measurements and estimated mucilage formations were spatially overlapped with Sentinel-2A. Overall, the produced maps accurately depicted the mucilage-covered areas despite the limitations of unreliable estimates along the land-water transition lines, and no-data areas due to the low-quality observations and high cloud coverage.

Electromagnetically dual‐axis driven MEMS grating and its application to 3D profiling with near‐infrared low‐coherence interferometry

AbstractWe have investigated 3D profiling of the objects by a low‐coherence optical interferometer using MEMS grating. This system, constructed with optical fibers and MEMS devices, is a Fourier domain interferometer, which can discriminate distance to the object by wavelength analysis of the interference spectra. A MEMS mirror gives the object 2D optical scanning, and a MEMS grating permits spectroscopy of interference spectra. The MEMS grating can tilt to dual axis with electromagnetic force induced by planar coils and a permanent magnet. One axis tilting enables near‐infrared spectroscopy and another axis tilting functions as optical axis alignment in an interferometer. Fabricated MEMS grating could tilt ±3.5° (mech.)/less than ±10 mA in both directions at low frequency, which were equivalent to approximately 1400 to 1700 nm in wavelength. The interferometer, whose S/N was 50 dB and vertical standard deviation was 0.6 µm, could scan full wavelength width (1400 to 1700 nm) in 25 ms. Finally, we could realize 3D profiling which was not only surface reflection profiling of 1‐µm step, but also transparent profiling of IC process layer from the wafer backside. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(2): 9–15, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11452

電磁駆動型2軸可動MEMS グレーティングと近赤外低コヒーレンス干渉法を用いた3次元形状計測への応用

We have investigated 3D profiling of the objects by low coherence optical interferometer using MEMS grating. This system, constructed with optical fibers and MEMS devices, is Fourier domain interferometer, which can discriminate distance to the object by wavelength analysis of the interference spectra. A MEMS mirror gives the object 2D optical scanning, and a MEMS grating makes spectroscopy of interference spectra. The MEMS grating can tilt to dual-axis with electromagnetic force induced by planer coils and a permanent magnet. One axis tilting works as near infrared spectroscopy, and another axis tilting works as optical axis alignment in an interferometer. Fabricated MEMS grating could tilt ±3.5° (mech.) / less than ±10mA in both direction at low frequency, which were equivalent to approximately 1400-1700nm in wavelength. This interferometer, whose S/N was 50dB and vertical standard deviation was 0.6µm, could scan full wavelength width (1400-1700nm) in 25ms. Finally, we could realize 3D profiling which was not only surface reflection profiling of 1µm step, but also transparent profiling of IC process layer from backside of the wafer.

Seismic characterization of fracturing at the Äspö Hard Rock Laboratory, Sweden, from the kilometer scale to the meter scale

Abstract In 1986, the Swedish Nuclear Fuel and Waste Management Co. (SKB) decided to build an underground research laboratory, the Aspo Hard Rock Laboratory (HRL). The Aspo HRL offers the possibility to test and demonstrate a full site investigation sequence. As part of this work, various seismic techniques were tested and demonstrated, from the kilometer to the meter scale. The preliminary investigation stage comprised surface reflection profiling and VSP. The VSP measurements, though limited to one borehole, played an important role in defining the site model. Shallow reflection surveys in crystalline rock have been judged as basically feasible, but further development is required to reduce costs. During the construction of the laboratory, the objective of the seismic investigations was to check and refine the site model. Within the zone of excavation disturbance experiment project, seismic tomographic analyses were made for P- and S- wave velocity and attenuation, at 5–15 m scale. Crosshole reflection imaging was also performed. The tracer retention understanding experiments project also included transmission and reflection tomography but on a 100–300 m scale. For the experiments where both transmission and reflection measurements were processed, the seismic surveys also produced information regarding the intrinsic mechanical properties of the rock besides inferring a geometrical model of the rock structures.

A stable method for linearized inversion of elastic parameters

An inversion method that stabilizes the multiparameter inverse problem for a constant background elastic isotropic medium is developed. The inverse problem is formulated in the wavenumber domain and the operators acting on the individual elastic parameters are displayed and analysed. From here it is noticed that for certain scattering angles some parameters produce no scattering. This scattering angle dependence is combined with the frequency dependence of the parameters to reduce the multiparameter inverse problem to a single parameter inversion problem, which is known to yield stable results. The method developed here is an extension of an acoustical medical imaging method by Norton (1983) to the elastic seismic imaging problem which inherits limited view constraints. This method is compared to the elastic extension of a multiparameter acoustic inversion method developed by Devaney (1985) and the resulting improvements in stability are demonstrated on synthetic examples. From the theory it is observed that a fixed 90° scattering angle can be used with multiple frequencies to achieve highly stable inversion results of all elastic parameters provided specific elastic parameters are extracted from specific scattering modes. The attempt to extract all elastic parameters from the P-to-P scattering mode using multiple scattering angles is seen to be very ill-conditioned and not recommended. For the 90° scattering angle we find that surface reflection profiling (SRP) and cross-hole geometries have the same wavenumber domain coverage and the multi-offset vertical seismic profiling (MVSP) geometries give a better coverage than only a SRP or cross-hole geometry.

A Processing Technique for Three Component Seismic Data: Use of Polarisation Characteristics

This paper presents a method that uses polarisation characteristics of three component seismic data (recorded by surface reflection profiling, VSP etc.) for discrimination and filtering of waves. Discrimination of waves in single (e.g., vertical) component data is based on frequency characteristics and apparent velocities, obtained from line-up observations. When three component records are used, discrimination based on polarisation characteristics is also possible. In this paper, we first describe the method by which polarisation characteristics are determined from three component records, and how these characteristics are used in polarisation filtering. Polarisation characteristics are estimated by eigenvector analysis of covariance matrices, which are obtained from three component data. The parameters thus obtained are then used in polarisation filtering. Following this is a discussion of the method. In this discussion, three component data, synthesized from waves having various polarisation characteristics, are used. Finally, we present an actual application of this method to data obtained in a surface observation. This example demonstrates that by the use of polarisation characteristics, it is possible to (1) discriminate linearly polarised waves (P or S waves) from elliptically polarised waves (Rayleigh type surface waves); and (2) distinguish between P waves and S waves, on the basis of differences in particle motion direction.

Diffraction tomography and multisource holography applied to seismic imaging

Seismic tomography is emerging as an imaging method for determining subsurface structure. When the view‐angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength, as is often true in geophysical applications, the performance of ordinary ray tomography becomes poor. Other tomographic methods are needed to improve the imaging process. Here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling (SRP), vertical seismic profiling (VSP), and cross‐hole measurements. Theoretical formulations are derived for two‐dimensional geometry in terms of line sources along a source line and line receivers along a receiver line. The theory for diffraction tomography is based on the Born or Rytov approximation. The performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples. Multisource holography, which is similar to Kirchhoff‐type migration, often gives distorted images of the object. This distortion causes long tails of the image in the case of SRP and a strong noise belt in the case of VSP and is due to incomplete and nonuniform coverage of the object spectrum. The filtering operation of diffraction tomography helps in correcting the nonuniform coverage (including duplication) of the object spectrum in the reconstruction process and therefore reduces the distortions. On the other hand, multisource holography is better suited for imaging sharp boundaries with large acoustic impedance contrasts since diffraction tomography is restricted, as presently formulated, to weak inhomogeneities. In addition, multisource holography has the flexibility to be used with an arbitrary number of sources (including a single source). Its sampling interval is not restricted by the Nyquist frequency. Numerical examples show that combined data sets (such as surface reflection data combined with VSP data, or cross‐hole data combined with surface data, etc.) improve the image quality.

Shallow seismic reflection investigations of coal in the Sydney Basin

Surface reflection profiling with the Mini‐SOSIE technique successfully mapped shallow coal seam structure in the western Sydney Basin, New South Wales. Several minor faults and zones of fracturing were detected. In regions of thick Triassic sandstone cover, data quality was poor and unsuitable for geologic interpretation. Synthetic seismograms based on nearby borehole and petrophysical control show excellent agreement with the Mini‐SOSIE sections and illustrate the deleterious filtering effects of coal seams and sequences. To establish a phenomenological basis for seismic wave propagation in shallow coal measures, two vertical seismic profiles (VSPs) which used small explosive charges were recorded with high spatial and temporal sampling. Numerous multiple reflections were observed in the downgoing wave display. The isolated upgoing waves were migrated to yield blurred images of the main coal seams. The subsurface velocity function, also deduced from the VSP, shows broad correlation with the geologic log. The VSP seismograms are not simple because of the combined effects of wave absorption, scattering, and interference. Such problems impede recovery of fine structural detail from seismic data in the shallow environment, particularly when a surface energy source is used.