• Proceedings of the KSRS Conference
• /
• 2002.10a
• /
• pp.429-434
• /
• 2002

The Synthetic Aperture Radar (SAR) data are considered to contain the greatest amount of information among various microwave techniques developed for measuring ocean variables from aircraft or satellites. They have the potential of measuring wavelength, wave direction and wave height of the ocean waves. But, it is difficult to retrieve significant ocean wave heights and surface current from conventional SAR data, since the imaging mechanism of ocean waves by a SAR is determined by the three basic modulation processes arise through the tilt modulation, hydrodynamic modulation and velocity bunching which are poorly known functions. Along-Track Interferometric (ATI) SAR systems can directly detect the Doppler shift associated with each pixel of a SAR image and have been used to estimate wave fields and surface currents. However, the Doppler shift is not simply proportional to the component of the mean surface current. It includes also contributions associated with the phase velocity of the Brags waves and orbital motions of all ocean waves that are longer than Brags waves. In this paper, we have developed a new method for extracting the surface current vector using multiple-frequency (L- & C-band) ATI SAR data, and have generated surface wave height information.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.37.2-37.2
• /
• 2017

The gravitational radiation capture between unequal mass black holes without spins is investigated with numerical relativistic simulations, and compared with the Post-Newtonian approximations. The parabolic approximation which assumes that the gravitational radiation from a weakly hyperbolic orbit is the same as that from the parabolic orbit is adopted. Using the radiated energies from the parabolic orbit simulations, we have obtained the impact parameters (b) of the gravitational radiation captures for weakly hyperbolic orbits with respect to the initial energy. The most energetic encounters occur around the boundary between the direct merging and the fly-by orbits, and we find that several percent of the total ADM initial energy can be emitted at the peak. The equal mass BHs emit more energies than unequal mass BHs at the same initial orbital angular momentum in the case of the fly-by orbits. The impact parameters obtained with numerical relativity deviate from those in Post-Newtonian when the encounter is very strong ($b{\leq}100M$), and the deviations are more conspicuous at the high mass ratio.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.2 no.2
• /
• pp.259-266
• /
• 1998

406MHz and INMARSAT-E EPIRB facility transmits the distress alerts by the relay of the polar-satellites and INTELSAT, but may cause the probability of delayed transmission because of the orbital period and not compliance with the implementation of GMDSS rules for small ships in A1 area.. Digital Selective Calling forms a critical part of the terrestrial elements of the GMDSS system and ensures the reliability and the efficiency in the system. In this paper, we suggests that new DSC EPIRB in the VHF band to overcome this defect for small ships in A1 area, and analyze the ITU-R recommendations and technical characteristics, design and implement the algorithm of calling sequences, frequency synthesizer for the RF signal and FSK moulation signals.

• Journal of the Korea Society of Computer and Information
• /
• v.23 no.11
• /
• pp.193-201
• /
• 2018

In this paper, we extracted relevant patent data and conducted statistical analysis to understand the technical development trend related to Wireless Power Transfer (WPT) for Light Rail Transit (LRT). Recently, with the development of WPT technologies, the Light Rail Transit (LRT) industry is concentrating on applying WPT to the power supply system of trains because of their advantages compared wired counterpart, such as low maintenance cost and high stability. This technology is divided into three areas: wireless feeding and collecting technology, high-frequency power converter technology and orbital and infrastructure technology. From each specific area, key words in patent document were extracted by TF-IDF method and analyzed by social network. In the keyword network, core word of each specific technology were extracted according to their degree centrality. Then, the multi-word phrases were also built to represent the concept of core technologies. Finally, based on the analysis results, the development strategies for each specifics technical area of WPT in LRT filed will be provided.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.2A
• /
• pp.159-166
• /
• 2008

In this paper, we proposed an algorithm to solve the problem that can't maintain hop synchronization using only early-late gate tracking loop due to the drift of geo-stationary satellite in frequency hopping satellite communication system. When the signal is transferred to downlink through DRT(Dehop-Rebop Transponder), the problem with synchronization loss is occurred periodically when using only early-late gate tracking loop, because of energy loss in each side portion of hop due to orbital variation of the satellite. To solve this problem, we have developed Anti-Shrink synchronization tracking algorithm which uses the prediction value of transmission timing and the structure of inner-outer gate instead of early-late gate with the ranging information. Through simulations, we showed that the performance of the Anti-Shrink algorithm is better than that of simple inner-outer energy ratio algorithm and similar to that of conventional early-late tracking loop algorithm with ranging information. No synchronization failure in the proposed algorithm was occurred because of less energy loss and robustness without the ranging information.

• ETRI Journal
• /
• v.26 no.3
• /
• pp.218-228
• /
• 2004

Using stereo images with ephemeris data from the Korea Multi-Purpose Satellite-1 electro-optical camera (KOMPSAT-1 EOC), we performed geometric modeling for three-dimensional (3-D) positioning and evaluated its accuracy. In the geometric modeling procedures, we used ephemeris data included in the image header file to calculate the orbital parameters, sensor attitudes, and satellite position. An inconsistency between the time information of the ephemeris data and that of the center of the image frame was found, which caused a significant offset in satellite position. This time inconsistency was successfully adjusted. We modeled the actual satellite positions of the left and right images using only two ground control points and then achieved 3-D positioning using the KOMPSAT-1 EOC stereo images. The results show that the positioning accuracy was about 12-17 m root mean square error (RMSE) when 6.6 m resolution EOC stereo images were used along with the ephemeris data and only two ground control points (GCPs). If more accurate ephemeris data are provided in the near future, then a more accurate 3-D positioning will also be realized using only the EOC stereo images with ephemeris data and without the need for any GCPs.

• Journal of Astronomy and Space Sciences
• /
• v.37 no.2
• /
• pp.117-129
• /
• 2020

In a Satellite communication system, a link budget analysis is the detailed investigation of signal gains and losses moving through a channel from a sender to receiver. It inspects the fading of passed on data signal waves due to the process of spreading or propagation, including transmitter and receiver antenna gains, feeder cables, and related losses. The extent of the proposed tool is to make an effective, efficient, and user-friendly approach to calculate link budget analysis. It is also related to the satellite communication correlation framework by building up a graphical interface link analysis tool utilizing STK^® software with the interface of C# programming. It provides better kinds of graphical display techniques, exporting and importing data files, printing link information, access data, azimuth-elevation-range (AER), and simulation is also possible at once. The components of the link budget analysis tool include transmitter gain, effective isotropic radiated power (EIRP), free space loss, propagation loss, frequency Doppler shift, flux density, link margin, elevation plot, etc. This tool can be useful for amateur users (e.g., CubeSat developers in the universities) or nanosat developers who may not know about the RF communication system of the satellite and the orbital mechanics (e.g., orbit propagators) principle used in the satellite link analysis.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.216-216
• /
• 2003

The layered nickel oxides (LiNiO$_2$) have been studied for possible use as cathode materials i3l 4V lithium batteries. Although LiCoO$_2$ has been known as the best candidate material for Li-ion batteries, which produces the best performance LiNiO$_2$ is generally accepted as an attractive cathode material, because of its various advantages such as lower cost higher discharge capacity and better reversibility. In this investigation, we calculated the electric state of LiNiO$_2$ using DV-X$\alpha$ molecular orbital method in order to obtain the information of chemical bonding among the Li, Ni and O. In LiNiO$_2$, alternate layers of Li and Ni occupy the octahedral sites of a cubic close packing of oxide ions, making up a rhombohedral structure with an R-3m space group, Li in 3a, Ni in 3b, and O in 6c sites. On the basis of this, we made the cluster model and studied ionization of each atoms and interaction between atoms according to Mullilcen population analysis.

• Journal of Advanced Navigation Technology
• /
• v.4 no.2
• /
• pp.191-200
• /
• 2000

Recently, NORAD reported that only 6% of the total space objects cataloged in the table as above 10cm objects were being operated for the space missions and the others were just non-operated objects, such as rocket body, useless satellites which were finished their missions, and other fragments of space debris. A major contributor to the orbital debris background has been object breakup. Breakups generally are caused by explosions and collisions. Several international research groups and big countries' governments are trying to develop advanced technology for de-orbiting and to design new future satellites' modeling. The future need to be considered continuously that kind of technology and designing to preserve space and global environmental safety and to maintain welfare of mankind forever.

• Journal of Astronomy and Space Sciences
• /
• v.18 no.2
• /
• pp.129-136
• /
• 2001

The accuracy of GPS applications is heavily dependent on the satellite ephemeris and earth orientation parameter. Specially applications like as the real time monitoring of troposphere and ionosphere require real time or predicted ephemeris arid earth orientation parameter with very high quality. IGS is producing IGS ultra rapid product called IGU for real time applications which includes the information of ephemeris and earth orientation. IGU is being made available twice everyday at 3:00 and 15:00 UTC arid covers 48 hours. The first 24 hours of it are based on actual GPS observations and the second 24 hours extrapolated. We will construct the processing strategy for yielding ultra rapid product and demonstrate the propriety through producing it using 48 hours data of 32 stations.