Coherent backscatter enhancement in bistatic Ku-/X-band radar observations of dry snow

The coherent backscatter opposition effect (CBOE) enhances the backscatter intensity of electromagnetic waves by up to a factor of two in a very narrow cone around the direct return direction when multiple scattering occurs in a weakly absorbing, disordered medium. So far, this effect has not been investigated in terrestrial snow in the microwave spectrum. It has also received little attention in scattering models. We present the first characterization of the CBOE in dry snow using ground-based and space-borne bistatic radar systems. For a seasonal snow pack in Ku-band (17.2 GHz), we found backscatter enhancement of 50–60 % (+1.8–2.0 dB) at zero bistatic angle and a peak half-width-at-half-maximum (HWHM) of 0.25°. In X-band (9.65 GHz), we found backscatter enhancement of at least 35 % (+1.3 dB) and an estimated HWHM of 0.12° in the accumulation areas of glaciers in the Jungfrau-Aletsch region, Switzerland. Sampling of the peak shape at different bistatic angles allows estimating the scattering and absorption mean free paths, ΛT and ΛA. In the VV polarization, we obtained ΛT = 0.4 ± 0.1 m and ΛA = 19 ± 12 m at Ku-band, and ΛT = 2.1 ± 0.4 m, ΛA = 21.8 ± 2.7 m at X-band. The HH polarization yielded similar results. The observed backscatter enhancement is thus significant enough to require consideration in backscatter models describing monostatic and bistatic radar experiments. Enhanced backscattering beyond the Earth, on the surface of solar system bodies, has been interpreted as being caused by the presence of water ice. In agreement with this interpretation, our results confirm the presence of the CBOE at X- and Ku-band frequencies in terrestrial snow.

Generalized Kerker effect in dielectric antennas for enhanced backscattering modulation

Enhancement of electromagnetic signal modulation is one of the key problems for modern contactless communication systems. Using resonance effects allows to achieve significant interaction between an electromagnetic wave and matter of an antenna, providing opportunity to control scattering. This work demonstrates efficiency of multipole engineering based on Mie theory for dielectric core-shell antennas, particularly we show that generalized Kerker effect is a useful tool for backscattering modulation magnification. Our approach allows to manipulate scattering properties of devices without increasing their size by using all-dieletric concept.

Numerical Modelling of a Distributed Acoustic Sensor Based on Ultra-Low Loss-Enhanced Backscattering Fibers

In this study, a distributed acoustic sensor (DAS) was numerically modeled based on the non-ideal optical components with their noises and imperfections. This model is used to compare the response of DAS systems to standard single-mode fibers and ultra-low loss-enhanced backscattering (ULEB) fibers, a fiber with an array of high reflective points equally spaced along its length. It is shown that using ULEB fibers with highly reflective points improves the signal-to-noise ratio and linearity of the measurement, compared with the measurement based on standard single-mode fibers.

Multiwell 3D distributed acoustic sensing vertical seismic profile imaging with engineered fibers: CO2CRC Otway Project case study

The 4D surface seismic monitoring is a standard method for reservoir surveillance during the production of hydrocarbons or CO2 injection. However, land 4D seismic acquisition campaigns are often associated with high cost and disruptions to industrial operation or agricultural activities in the area of acquisition. An alternative technique for time-lapse monitoring of the subsurface is the 3D vertical seismic profiling (VSP), which becomes particularly attractive when used with distributed acoustic fiber-optic sensors (DAS) installed in wells. The advantages of 3D DAS VSP include its relatively low cost, minimal footprint on the local area during acquisition, and superior spatial resolution compared to the resolution of geophones. The potential of this technique is explored by processing and analyzing multiwell 3D DAS VSP data acquired at the CO2CRC Otway Project site in Victoria, Australia. The DAS data were recorded using an engineered fiber with enhanced backscattering cemented behind the casing of five wells. The data from each well are processed individually using the same processing flow and then migrated using a 3D migration code tailored to DAS data. Having DAS along the full extent of multiple wells ensures adequate seismic coverage of the area of CO2 injection. The migrated images provide detailed information about the subsurface up to 700 m away from a well and up to 2 km depth. The images are consistent with previously acquired geophone VSP and surface seismic data. The quality of the 3D DAS VSP imaging is comparable or superior to the quality of conventional imaging using geophone data. Therefore, 3D DAS VSP is a demonstrably optimal solution for reservoir monitoring.

Backscattering cross-section from a metamaterial coated sphere covered with a metasurface

An analysis about the backscattering characteristics of a metamaterial coated magnetodielectric sphere covered with a metasurface has been presented. The effects of various types of metamaterial coatings and surface reactances of lossless metasurface upon the backscattering cross-section of a metamaterial coated magnetodielectric sphere covered with a metasurface have been studied. It is shown that the negligible backscattering cross-section from a double near-zero metamaterial coated magnetodielectric sphere can be enhanced significantly by using specific types of lossless metasurfaces. These types of enhanced backscattering cross-section find applications in the radar detection problems. The proposed theory is also extended to the lossy double negative metamaterial coated magnetodielectric sphere covered with a lossless metasurface. During the study, it is found that for a specific part of the lossy double negative metamaterial bandwidth, two specific types of lossless metasurfaces can be used to reduce the backscattering cross-section as compared to the backscattering cross-section of a lossy double negative metamaterial coated magnetodielectric sphere without metasurface.