• Journal of the Korea Institute of Military Science and Technology
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• v.27 no.1
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• pp.43-50
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• 2024

Large planar military antenna boasts a range of electrical components, including TRA(Transmit-Receive Assembly), signal processors, etc. which engage in computations and calculations. These processes generate a significant amount of heat, leading to unforeseen consequences for the equipment. To mitigate these adverse effects, it's imperative to implement a cooling system that can effectively reduce heat-related issues. Given the antenna's intricate nature and the multitude of components it houses, a two-step estimation process is necessary. The first step involves a comprehensive model calculation to determine the total flow characteristics, while the second step entails a thermal analysis of individual TRA set. In this study, we depicted an antenna set using simplified 3D models of its components, considering their material and thermal properties. The sequential analysis process facilitated the calculation of branched flow rates, providing insights into the individual TRA. This approach also allowed us to design a cooling system for the TRA set, assessing its thermal stability in high-temperature environments. To ensure the optimal performance of TRA, breaking down the analysis into stages based on the cooling system's structure can assist operators in predicting numerical results more effectively.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.06a
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• pp.3-17
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• 2004

Space-borne Earth observation technique is one of the most cost effective and rapidly advancing Earth science research tools today and the potential field and micro-wave radar applications have been leading the discipline. The traditional optical imaging systems including the well known Landsat, NOAA - AVHRR, SPOT, and IKONOS have steadily improved spatial imaging resolution but increasing cloud covers have the major deterrent. The new Earth observation satellites ENVISAT (launched on March 1 2002, specifically for Earth environment observation), ALOS (planned for launching in 2004 - 2005 period and ALOS stands for Advanced Land Observation Satellite), and RADARSAT-II (planned for launching in 2005) all have synthetic aperture radar (SAR) onboard, which all have partial or fully polarimetric imaging capabilities. These new types of polarimetric imaging radars with repeat orbit interferometric capabilities are opening up completely new possibilities in Earth system science research, in addition to the radar altimeter and scatterometer. The main advantage of a SAR system is the all weather imaging capability without Sun light and the newly developed interferometric capabilities, utilizing the phase information in SAR data further extends the observation capabilities of directional surface covers and neotectonic surface displacements. In addition, if one can utilize the newly available multiple frequency polarimetric information, the new generation of space-borne SAR systems is the future research tool for Earth observation and global environmental change monitoring. The potential field strength decreases as a function of the inverse square of the distance between the source and the observation point and geophysicists have traditionally been reluctant to make the potential field observation from any space-borne platforms. However, there have recently been a number of potential field missions such as ASTRID-2, Orsted, CHAMP, GRACE, GOCE. Of course these satellite sensors are most effective for low spatial resolution applications. For similar objects, AMPERE and NPOESS are being planned by the United States and France. The Earth science disciplines which utilize space-borne platforms most are the astronomy and atmospheric science. However in this talk we will focus our discussion on the solid Earth and physical oceanographic applications. The geodynamic applications actively being investigated from various space-borne platforms geological mapping, earthquake and volcano .elated tectonic deformation, generation of p.ecise digital elevation model (DEM), development of multi-temporal differential cross-track SAR interferometry, sea surface wind measurement, tidal flat geomorphology, sea surface wave dynamics, internal waves and high latitude cryogenics including sea ice problems.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.3
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• pp.311-319
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• 2019

This paper proposes an acceleration of the multi-level fast multipole algorithm(MLFMA) by using a double interpolation method. The MLFMA has been primarily used to conduct scattering analysis of electrically large targets, e.g. stealth aircraft. In the MLFMA, radiation functions of each basis functions are first precomputed, and then aggregated. After transfer calculations for the aggregations, each interaction is disaggregated, and then received in the testing function. The key idea of the proposed method is to decrease the sampling rates of the radiation and receiving functions. The computational complexity of the unit sphere integration in terms of the testing functions is thus highly alleviated. The remaining insufficient sampling rate is then complemented by using additional interpolation. We demonstrate the performance of the proposed method through radar cross-section(RCS) calculations for realistic aircraft.

• Korean Journal of Remote Sensing
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• v.18 no.4
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• pp.209-220
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• 2002

We carried out studies on SAR image intensity and interferometric phase over oyster sea farms. Strong backscattering was observed in amplitude images, and that was considered as a radar signal double bouncing from horizontal bars. These sea farming structures are not visible in satellite optical images except IKONOS image, so that it demonstrates the value of radar remote sensing as an effective tool in support of sea farm detection. The intensity of the image is sensitive to system parameters including wavelength, polarization, and look direction, but does not correlate to tide height. We found that the strongest backscattering can be obtained by L-band HH-polarization with a look direction perpendicular to the horizontal bar. We also succeeded in generating 21 coherent JERS-1 SAR interferometric pairs over the oyster farms. The general trend of the fringe rate of the interferometric phases appeared to be governed by altitude of ambiguity. The general trend was modeled by an inverse function and removed to have a residual phase. The residual phase showed a linear relation with the tide height. The results demonstrate for the first time that SAR can possibly be used to estimate sea level. However, the r.m.s. error of a regression line is 11.7 cm, and that is so far too large to make reliable assessments of sea level in practical applications. Further studies is required to improve the accuracy specifically using multi-polarization SAR data.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.55-62
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• 2011

The precise orbit determination (POD) of low earth orbiter (LEO) has complied with its required positioning accuracy by the double-differencing of observations between International GNSS Service (IGS) and LEO to eliminate the common clock error of the global positioning system (GPS) satellites and receiver. Using this method, we also have achieved the 1 m positioning accuracy of Korea Multi-Purpose Satellite (KOMPSAT)-2. However double-differencing POD has huge load of processing the global network of lots of ground stations because LEO turns around the Earth with rapid velocity. And both the centimeter accuracy and the near real time (NRT) processing have been needed in the LEO POD applications--atmospheric sounding or urgent image processing--as well as the surveying. An alternative to differential GPS for high accuracy NRT POD is precise point positioning (PPP) to use measurements from one satellite receiver only, to replace the broadcast navigation message with precise post processed values from IGS, and to have phase measurements of dual frequency GPS receiver. PPP can obtain positioning accuracy comparable to that of differential positioning. KOMPSAT-5 has a precise dual frequency GPS flight receiver (integrated GPS and occultation receiver, IGOR) to satisfy the accuracy requirements of 20 cm positioning accuracy for highly precise synthetic aperture radar image processing and to collect GPS radio occultation measurements for atmospheric sounding. In this paper we obtained about 3-5 cm positioning accuracies using the real GPS data of the Gravity Recover and Climate Experiment (GRACE) satellites loaded the Blackjack receiver, a predecessor of IGOR. And it is important to reduce the latency of orbit determination processing in the NRT POD. This latency is determined as the volume of GPS measurements. Thus changing the sampling intervals, we show their latency to able to reduce without the precision degradation as the assessment of their precision.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.9
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• pp.1088-1095
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• 2019

The information and communication technology that is being developed recently has been greatly influencing the automobile market. In recent years, devices equipped with IT technology have been installed for the safety and convenience of the driver. However, it has the advantage of increased convenience as well as the disadvantage of increasing traffic accidents due to driver's distraction. In order to prevent such accidents, it is necessary to develop safety systems of various types and ways. In this paper implements a platform that can recognize LDWS and FCWS and PDWS by using a single camera without using radar sensor and camera fusion and stereo camera method using two or more sensors, and proposes to study multi-function driving safety platform using a single camera by analyzing recognition rate evaluation and validity on a vehicle.

• Korean Journal of Remote Sensing
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• v.38 no.5_1
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• pp.497-510
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• 2022

Agricultural reservoirs are essential structures for water supplies during dry period in the Korean peninsula, where water resources are temporally unequally distributed. For efficient water management, systematic and effective monitoring of medium-small reservoirs is required. Synthetic Aperture Radar (SAR) provides a way for continuous monitoring of those, with its capability of all-weather observation. This study aims to evaluate the applicability of SAR in monitoring medium-small reservoirs using Sentinel-1 (10 m resolution) and Capella X-SAR (1 m resolution), at Chari (CR), Galjeon (GJ), Dwitgol (DG) reservoirs located in Ulsan, Korea. Water detected results applying Z fuzzy function-based threshold (Z-thresh) and Chan-vese (CV), an object detection-based segmentation algorithm, are quantitatively evaluated using UAV-detected water boundary (UWB). Accuracy metrics from Z-thresh were 0.87, 0.89, 0.77 (at CR, GJ, DG, respectively) using Sentinel-1 and 0.78, 0.72, 0.81 using Capella, and improvements were observed when CV was applied (Sentinel-1: 0.94, 0.89, 0.84, Capella: 0.92, 0.89, 0.93). Boundaries of the waterbody detected from Capella agreed relatively well with UWB; however, false- and un-detections occurred from speckle noises, due to its high resolution. When masked with optical sensor-based supplementary images, improvements up to 13% were observed. More effective water resource management is expected to be possible with continuous monitoring of available water quantity, when more accurate and precise SAR-based water detection technique is developed.