• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.5
• /
• pp.69-76
• /
• 2020

The sound signal radiated from an underwater source is received by the hydrophone of the system, including multi-path time-delay and multi-path signal by sea surface and bottom reflection. The system using a time-delay between received signals for the source localization shows performance degradation due to incoherence by the multi-path propagation environment and the disturbance of a marine environment. Various types of array and signal processing have been used for robust source range and bearing estimation in this environment. In this paper, we use a line array composed of doublet array and an estimated time-delay correction method for robust localization performance in a multi-path propagation environment. Three doublet arrays are located on the same line, and the time-delay between signals received on each doublet array is estimated in a two-step procedure. The estimated time-delay value is obtained by the cross-correlation function and corrected by the interaction formula between the center-frequency of received signal and the geometry of the array with respect to aperture. By this proposed procedure, the range and bearing of source from array were calculated. In order to confirm the validity of the proposed method and array, we simulated localization and estimation using the Monte-Carlo method.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.4
• /
• pp.318-327
• /
• 2017

Synthetic Aperture Radars (SARs) that can be performed regardless of weather and day-and-night conditions have been developed for Earth remote sensing in recent decades. Korea Aerospace Research Institute (KARI) has developed and launched successfully the KOrea Multi-Purpose SATellit-5 (KOMPSAT-5) which is the first Korean SAR satellite in 2013, and is currently developing the KOMPSAT-6 which is the next generation series of the SAR satellite. This paper describes the development of the system performance analysis simulator which is necessary for spaceborne SAR payload design and analysis. The system performance analysis simulator consists of the antenna pattern generation simulator, the SAR performance analysis simulator, and the image quality analysis simulator. The simulation results of this research show that this simulator can be applicable as the design and analysis tool for the spaceborne SAR payload system during the design phase.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.28 no.3
• /
• pp.186-194
• /
• 2017

In this paper, we analyze the main performance of satellite's Synthetic Aperture Radar system for high resolution and wide swath. We have used the radiation pattern of reflector antenna with array feed and comparison between the conventional ScanSAR mode and SweepSAR mode has been carried out. The SweepSAR mode is a high-resolution wide-swath mode that transmits beams over a wide range and receives echo signals through sequential beamforming based on SCORE(SCan On REceive). In this paper, we analyzed the operating principle and characteristics of satellite's SweepSAR mode and simulate system performances. In addition, in order to increase the utilization of image, performances analysis for multiple frequency bands(C-band, X-band) has been considered.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.16 no.1 s.92
• /
• pp.9-18
• /
• 2005

This paper presents an antenna for US-PCS band indoor repeaters with enhancement of isolation. In common repeaters require an enough isolation to reduce the interferences between transmitted and received signals. Thus, it is investigated to improve front-to-back ratio of IBD(Integrated Balun Dipole) antenna which has a good linear polarization with a cavity or multi-cavity by using polarization diversity and aperture matching method. From the simulated and measured results, the antenna realized by using polarization diversity and aperture matching method has a VSWR below 1.5, gain over 8 dBi and enhanced isolation of 15$\~$24 dB in US-PCS band.

• The Bulletin of The Korean Astronomical Society
• /
• v.36 no.2
• /
• pp.129.1-129.1
• /
• 2011

We have applied an advanced multi-aperture indexing photometry and sophisticated de-trending method to existing Taiwanese-American Occultation Survey (TAOS) data sets. TAOS, a wide-field ($3^{\circ}{\times}3^{\circ}$) and rapid photometry (5Hz) survey, is designed to detect small objects in the Kuiper Belt. Since TAOS has fast and multiple exposures per zipper mode image, point spread function (PSF) varies in a given image. Selecting appropriate aperture among various size apertures allows us to reflect these variations in each light curve. The survey data turned out to contain various trends such as telescope vibration, CCD noise, and unstable local weather. We select multiple sets of stars using a hierarchical clustering algorithm in such a way that the light curves in each cluster show strong correlations between them. We then determine a primary trend (PT) per cluster using a weighted sum of the normalized light curves, and we use the constructed PTs to remove trends in individual light curves. After removing the trend, we can get each synthetic light curve of star that has much higher signal-to-noise ratio. We compare the efficiency of the synthetic light curves with the efficiency of light curves made by previous existing photometry pipelines. Our photometric method is able to restore subtle brightness variation that tends to be missed in conventional aperture photometric methods, and can be applied to other wide-field surveys suffering from PSF variations and trends. We are developing an analysis package for the next generation TAOS survey (TAOS II) based on the current experiments.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.2
• /
• pp.109-117
• /
• 2018

In order to form focused inverse synthetic aperture radar(ISAR) images of a non-uniformly rotating target, rotational motion compensation(RMC) should be performed. Prominent point processing(PPP), one of the most representative RMC methods, is used to compensate nonlinear rotation motion by exploiting the phase signals of scatterers. In this paper, we propose a new RMC method based on the integrated cubic phase function(ICPF). The ICPF requires only one-dimensional(1-D) maximization to estimate the phases of multi-component signals. Simulation results using a point scatterers model in the absence of dominant scatterers validate that PPP based on ICPF can achieve well-focused ISAR images in real time.

• Korean Journal of Remote Sensing
• /
• v.27 no.3
• /
• pp.225-234
• /
• 2011

This study proposes an inversion algorithm to extract the surface parameters, such as surface roughness and soil moisture contents, using multi-frequency SAR data. The study areas include the tidal flats of Jebu Island and the reclaimed lands of Hwaong district on the western coasts of the Korean peninsula. SAR data of three frequencies were accordingly calibrated to provide precise backscattering coefficients through absolute radiometric calibration. The root mean square (RMS) height and the correlation length, which can describe the surface roughness, were extracted from the backscattering coefficients using the inversion of the Integral Equation Method (IEM). The IEM model was appropriately modified to accommodate the environmental conditions of tidal flats. Volumetric soil moisture was also simultaneously extracted from the dielectric constant using the empirical model, which define the relations between volumetric soil moistures and dielectric constants. The results obtained from the proposed algorithm were verified with the in-situ measurements, and we confirmed that multi-frequency SAR observations combined with the surface scattering model for tidal flats can be used to quantitatively retrieve the geophysical surface parameters in tidal flats.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.10A
• /
• pp.1215-1222
• /
• 2004

In this paper, we proposed the directional coupler using two layer microstrip substrate which is improved coupling and isolation. Modified two-layer directional coupler is the structure which is added to the one-layer on the signal line and located the floating conductor on the added layer. Also, we applied the aperture on the ground plane in order to enhancing the coupling value, and located the conductor in order to enhancing the isolation and VSWR according to S$_{11}$. As a result, proposed two-layer directional coupler has about 2 dB more higher coupling and 20 dB more higher isolation than conventional couplerer

• Geomechanics and Engineering
• /
• v.24 no.1
• /
• pp.1-14
• /
• 2021

In this study, a new approach using electrical resistivity measurement was proposed to detect grout penetration and to evaluate the grouting performance for such as waterproof efficiency in single rock fracture. For this purpose, an electrical resistivity monitoring system was designed to collect multi-channel data in real time. This was applied to a system for grout injection/penetration using a transparent fracture replica with various aperture sizes and water-cement mix ratio. The electrical resistivity was measured under various grout penetration conditions in real time, which results were directly compared to the visual observation images of grout penetration/distribution. Moreover, the grouting success status after the curing process was evaluated by measuring the electrical resistivity in relation to changes in frequency in fracture cells where grout injection and penetration were completed. Consequently, it was determined that the electrical resistivity monitoring system could be applied effectively to the detection of successful penetration of grouting into a target area and to actual field evaluation of the grouting performance and long-term stability of underground rock structures.

• Korean Journal of Remote Sensing
• /
• v.30 no.6
• /
• pp.719-730
• /
• 2014

Small BAseline Subset (SBAS) technique using multi master interferograms can be effective to detect surface deformation in forest area. In this paper, The analysis reveals area of 2-dimension surface deformation at Seguam Island in Aleutian Arc., Alaska. We acquired ERS-1/2 data from track 201 and 473 datasets on Seguam Island from 1992 to 2008. This study analyze surface deformation applying Differential Interferometry Synthetic Aperture Radar (DInSAR) and SBAS time series method using two adjacent tracks. As a results, it was calculated that subsidence -1~2 cm in LOS direction and - 2~3 cm in vertical direction. The horizontal direction was repeated contraction and expansion. The observation of 2-dimension displacements explained the volcanic activity on Seguam island. Also, it is believed to be used for basic data to estimate movements of magma source.