scholarly journals Subsurface Detection of Shallow Targets by Undersampled Multifrequency Data and a Non-Cooperative Source

2019 ◽  
Vol 9 (24) ◽  
pp. 5383 ◽  
Author(s):  
Adriana Brancaccio ◽  
Angela Dell’Aversano ◽  
Giovanni Leone ◽  
Raffaele Solimene
Keyword(s):  
Spatial Data ◽  
Equivalence Theorem ◽  
Single Frequency ◽  
Acquisition Time ◽  
Frequency Diversity ◽  
Frequency Data ◽  
Buried Objects ◽  
Under Sampling ◽  
Data Acquisition Time ◽  
Soil Interface

Imaging buried objects embedded within electrically large investigation domains can require a large number of measurement points. This is impractical if long data acquisition time cannot be tolerated or the system is conceived to work at some stand-off distance from the air/soil interface; for example, if it is mounted over some flying platform. In order to reduce the number of spatial measurements, here, we propose a method for detecting and localizing shallowly buried scattering targets from under-sampled far-field data. The method is based on a scattering model derived from the equivalence theorem for electromagnetic radiation. It exploits multi-frequency data and does not require that the transmitter and receivers are synchronized, making the source non-cooperative. To provide a benchmark against which spatial data have to be reduced, first, the number of required spatial measurements is examined by analyzing the properties of the relevant scattering operator. Then, since under-sampling data produces aliasing artifacts, frequency diversity (i.e., multi-frequency data) is exploited to mitigate those artifacts. In particular, single-frequency reconstructions are properly fused and a criterion for selecting the frequencies to be used is provided. Numerical examples show that the method allows for satisfactory target transverse localization with a number of measurements that are much less than the ones required by other methods commonly used in subsurface imaging.

scholarly journals Experimental Validation of a Microwave Imaging Method for Shallow Buried Target Detection by Under-Sampled Data and a Non-Coperative Source

2021 ◽  
Author(s):  
Adriana Brancaccio ◽  
Giovanni Leone ◽  
Rocco Pierri ◽  
Raffaele Solimene
Keyword(s):  
Spatial Data ◽  
Horn Antenna ◽  
Test Site ◽  
Microwave Imaging ◽  
Single Frequency ◽  
Reference Plane ◽  
Imaging Method ◽  
Sampled Data ◽  
Working Frequency ◽  
Soil Interface

In microwave imaging it is often of interest to inspect electrically large spatial regions. In these cases, data must be collected over a great deal of measurement points which entails long measurement time and/or costly, and often unfeasible, measurement configurations. In order to counteract such drawbacks, we have recently introduced a microwave imaging algorithm which looks for the scattering targets in terms of equivalent surface currents supported over a given reference plane. While this method is suited to detect shallowly buried targets, it allows to independently process each frequency data, hence the source and the receivers do not need to be synchronized. Moreover, spatial data can be reduced at large extent, without incurring in aliasing artefacts, by properly combining single-frequency reconstructions. In this paper, we validate such an approach by experimental measurements. In particular, the experimental test site consists of a sand box in open air where metallic plate targets are shallowly buried (few cm) under the air/soil interface. The investigated region is illuminated by a fixed transmitting horn antenna whereas the scattered field is collected over a planar measurement aperture at a fixed height from the air-sand interface. The transmitter and the receiver share only the working frequency information. Experimental results confirm the feasibility of the method.

scholarly journals Experimental Validation of a Microwave Imaging Method for Shallow Buried Target Detection by Under-Sampled Data and a Non-Cooperative Source

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5148
Author(s):  
Adriana Brancaccio ◽  
Giovanni Leone ◽  
Rocco Pierri ◽  
Raffaele Solimene
Keyword(s):  
Spatial Data ◽  
Horn Antenna ◽  
Test Site ◽  
Microwave Imaging ◽  
Single Frequency ◽  
Reference Plane ◽  
Imaging Method ◽  
Sampled Data ◽  
Working Frequency ◽  
Soil Interface

In microwave imaging, it is often of interest to inspect electrically large spatial regions. In these cases, data must be collected over a great deal of measurement points which entails long measurement time and/or costly, and often unfeasible, measurement configurations. In order to counteract such drawbacks, we have recently introduced a microwave imaging algorithm that looks for the scattering targets in terms of equivalent surface currents supported over a given reference plane. While this method is suited to detect shallowly buried targets, it allows one to independently process all frequency data, and hence the source and the receivers do not need to be synchronized. Moreover, spatial data can be reduced to a large extent, without any aliasing artifacts, by properly combining single-frequency reconstructions. In this paper, we validate such an approach by experimental measurements. In particular, the experimental test site consists of a sand box in open air where metallic plate targets are shallowly buried a (few cm) under the air/soil interface. The investigated region is illuminated by a fixed transmitting horn antenna, whereas the scattered field is collected over a planar measurement aperture at a fixed height from the air-sand interface. The transmitter and the receiver share only the working frequency information. Experimental results confirm the feasibility of the method.

scholarly journals Kinematic PPP Using Mixed GPS/Glonass Single-Frequency Observations

2019 ◽  
Vol 54 (3) ◽  
pp. 97-112
Author(s):  
Mostafa Hamed ◽  
Ashraf Abdallah ◽  
Ashraf Farah
Keyword(s):  
Low Cost ◽  
Satellite System ◽  
Single Frequency ◽  
Future Research ◽  
Frequency Data ◽  
Dual Frequency ◽  
Trajectory Data ◽  
Average Improvement ◽  
Kinematic Ppp ◽  
Global Navigation Satellite

Abstract Nowadays, Precise Point Positioning (PPP) is a very popular technique for Global Navigation Satellite System (GNSS) positioning. The advantage of PPP is its low cost as well as no distance limitation when compared with the differential technique. Single-frequency receivers have the advantage of cost effectiveness when compared with the expensive dual-frequency receivers, but the ionosphere error makes a difficulty to be completely mitigated. This research aims to assess the effect of using observations from both GPS and GLONASS constellations in comparison with GPS only for kinematic purposes using single-frequency observations. Six days of the year 2018 with single-frequency data for the Ethiopian IGS station named “ADIS” were processed epoch by epoch for 24 hours once with GPS-only observations and another with GPS/GLONASS observations. In addition to “ADIS” station, a kinematic track in the New Aswan City, Aswan, Egypt, has been observed using Leica GS15, geodetic type, dual-frequency, GPS/GLONASS GNSS receiver and single-frequency data have been processed. Net_Diff software was used for processing all the data. The results have been compared with a reference solution. Adding GLONASS satellites significantly improved the satellite number and Position Dilution Of Precision (PDOP) value and accordingly improved the accuracy of positioning. In the case of “ADIS” data, the 3D Root Mean Square Error (RMSE) ranged between 0.273 and 0.816 m for GPS only and improved to a range from 0.256 to 0.550 m for GPS/GLONASS for the 6 processed days. An average improvement ratio of 24%, 29%, 30%, and 29% in the east, north, height, and 3D position components, respectively, was achieved. For the kinematic trajectory, the 3D position RMSE improved from 0.733 m for GPS only to 0.638 m for GPS/GLONASS. The improvement ratios were 7%, 5%, 28%, and 13% in the east, north, height, and 3D position components, respectively, for the kinematic trajectory data. This opens the way to add observations from the other two constellations (Galileo and BeiDou) for more accuracy in future research.

scholarly journals Rough surface reconstruction from phaseless single frequency data at grazing angles

2018 ◽  
Vol 34 (12) ◽  
pp. 124002 ◽  
Author(s):  
Yuxuan Chen ◽  
Orsola Rath Spivack ◽  
Mark Spivack
Keyword(s):  
Rough Surface ◽  
Surface Reconstruction ◽  
Single Frequency ◽  
Frequency Data ◽  
Grazing Angles

scholarly journals Signal Design to Suppress Coupling in the Polarimetric Phased Array Radar

2014 ◽  
Vol 31 (5) ◽  
pp. 1063-1077 ◽  
Author(s):  
D. S. Zrnić ◽  
R. J. Doviak ◽  
V. M. Melnikov ◽  
I. R. Ivić
Keyword(s):  
Time Series Data ◽  
Signal Transmission ◽  
Cross Coupling ◽  
Series Data ◽  
Acquisition Time ◽  
Signal Design ◽  
Doppler Data ◽  
Orthogonal Components ◽  
Data Acquisition Time ◽  
Predicted Values

AbstractExamined are two related modes of polarimetric signal transmission that reduce coupling between the orthogonal components of received signals. For the surveillance scan with large unambiguous range and the simultaneous mode of horizontal (H) and vertical (V) transmission, pulse-to-pulse coding is suggested. It relaxes conditions on cross-coupling isolation from about 45 to about 25 dB while preserving the unambiguous range of over 460 km. For application to systematic codes during Doppler data acquisition, time-multiplexed (back to back) H and V pulses are proposed. This approach also relaxes the cross-coupling isolation to about 25 dB. These theoretically predicted values agree with those obtained by emulating the two schemes using oversampled time series data.

Towards real-time monitoring with a seismic antenna at Merapi volcano

2020 ◽  
Author(s):  
Jean-Philippe Metaxian ◽  
Agus Budi Santoso ◽  
François Beauducel ◽  
Nabil Dahamna ◽  
Vadim Monteiller ◽  
...  
Keyword(s):  
Real Time ◽  
Frequency Band ◽  
Time Delays ◽  
Time Windows ◽  
Single Frequency ◽  
Acquisition Time ◽  
Density Currents ◽  
Slowness Vector ◽  
Back Azimuth ◽  
Real Time Application

<p>Seismic antennas are often used on volcanoes to analyse emergent signals as LP events or tremor.  In fact, they can be used for any kind of seismicity whether the signal is impulsive or emergent. In this work we are using a seismic antenna as an instrument for monitoring the continuous seismic signal, with the objective of a real-time application.</p><p>A seismic antenna composed of 5 broadband stations equipped with Guralp CMG-6TD stations was installed in November 2013 close to the summit of Merapi, on the site called Pasar Bubar. Sensors have a flat response characteristic from 30 s to the Nyquist frequency (50 Hz). This network has an aperture of 280 m. The shortest distance between sensors is 100 m.</p><p> </p><p>In the perspective of a real-time application, the main analysis, which consists of estimating the slowness vector, requires a shorter computation time than the data acquisition time. We thus focused on a signal processing technique based on the calculation of time delays on the vertical component only and in a single frequency band. Given a set of time delays and associated errors calculated between each couple of sensors in the frequency domain, the corresponding slowness vectors can be recovered by inversion. Slowness vectors are estimated for successive time-windows in the frequency band 0.5-3 Hz. Temporal series of back-azimuth and apparent slowness are deduced with respect to time.</p><p>The analysis strategy for monitoring is then the following: A weight function expressed as a function of the derivatives of the time delays is calculated for successive moving time-windows. This function was designed in order to identify areas of stability of the back-azimuth values as function of time. A PDF of the back-azimuth and apparent slowness is then estimated for time series of 1 hour. This gives information on the dominant activity by time unit.</p><p>We will show the results obtained with the analysis of several months of continuous signal which are including different types of events generated by the on-going eruptive activity of Merapi: 1) volcano-tectonic events, 2) Multi-Phase (MP) events related with magma ascent in the conduit, 3) low-frequency events, 4) Rock-falls and 5) Pyroclastic density currents.</p>

Alternating Dual-Pulse, Dual-Frequency Techniques for Range and Velocity Ambiguity Mitigation on Weather Radars

2010 ◽  
Vol 27 (9) ◽  
pp. 1461-1475 ◽  
Author(s):  
Sebastián Torres ◽  
Richard Passarelli ◽  
Alan Siggia ◽  
Pentti Karhunen
Keyword(s):  
Pulse Repetition ◽  
Single Frequency ◽  
Weather Data ◽  
Frequency Diversity ◽  
Sampled Data ◽  
Dual Frequency ◽  
Multiple Pulse ◽  
Uniform Sampling ◽  
Weather Radars ◽  
Repetition Time

Abstract This paper introduces a family of alternating dual-pulse, dual-frequency (ADPDF) techniques. These are based on frequency diversity and are proposed as a means to mitigate range and velocity ambiguities on Doppler weather radars. ADPDF techniques are analyzed theoretically and through simulated and real weather data collected with a prototype C-band radar. Analogous to single-frequency, multiple-pulse-repetition-time (mPRT) techniques, such as staggered or triple PRT, it is demonstrated that ADPDF techniques can extend the maximum unambiguous velocity beyond what is achievable with uniform sampling. However, unlike mPRT techniques, ADPDF techniques exhibit better statistical performance and, more importantly, may be designed to preserve uniform sampling on one of the frequency channels, thus avoiding some of the difficulties associated with processing nonuniformly sampled data.

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