• 농업과학연구
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• 제41권4호
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• pp.473-480
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• 2014

Upon setting up a dedicated plastic greenhouse for tomato cultivation developed by the Rural Development Administration on the Gyehwa reclaimed land, this study was aimed at analyzing the problems can be occurred in the installation of plastic greenhouse on reclaimed lands as well as finding out solutions for improvement. A relatively cheaper wooden pile was used in the installation in order to supplement the soft ground conditions. Based on the results of ground investigation of the installation site, both the allowable bearing capacity and pulling resistance of the wooden pile with a diameter of 150 mm and a length of 10 m were computed and came out to be 30.645 kN. It was determined that the values were enough to withstand the maximum compressive force (17.206 kN) and the pullout force (20.435 kN) that are generally applied to the greenhouse footing. There are three problems aroused in the process of greenhouse installation, and the corresponding countermeasures are as follow. First, due to the slightly bent shape of the wooden pile, there were phenomenon such as deviation, torsion, and fracture when driving the pile. This could be prevented by the use of the backhoe (0.2) rotating tongs, which are holding the pile, to drive the pile while pushing to the direction of the driving and fixing it until 5 m below ground and applying a soft vibrating pressure until the first 2 m. Second, there exists a concrete independent footing between the column of the greenhouse and the wooden pile driven to the underground water level. Since it is difficult to accurately drive the pile on this independent footing, the problem of footing baseplate used to fix the column being off the independent footing was occurred. In order to handle with this matter, the diameter of the independent footing was changed from 200 mm to 300 mm. Last, after films were covered in the condition that the reinforcing frame and bracing are not installed, there was a phenomenon of columns being pushed away by the strong wind to the maximum of $11m{\cdot}s^{-1}$. It is encouraged to avoid constructions in winter, and the film covering jobs always to be done after the frame construction is completely over. The height of the independent footing was measured for 9 months after the completion of the greenhouse installation, and it was found to be within the margin of error meaning that there was no subsidence. The extent to the framework distortion and the value of inclinometers as well showed not much alteration. In other words, the wooden pile was designed to have a sufficient bearing capacity.

• 한국지진공학회논문집
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• 제23권6호
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• pp.321-327
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• 2019

We performed seismic noise level analysis to access the proper functioning of 11 newly established seismic stations in the southeastern region of Korea. One-hour long segments of seismograms were selected from the continuous data of the 3 elements for 61 days from March 1, 2019. For each segment of data, the power spectral density (PSD) was estimated from the continuous back ground noise data of the 3 elements for periods ranging from 0.02~100 s. The median noise levels (NLs) of the stations were compared with the new noise model (NNM) of USGS and NLs of station TJN installed in a tunnel on a granite basement. We observed that the NLs of the newly installed seismometers were between the upper and lower limit of the NNM. In a comparison with the noise level of station TJN, the new seismometers had their own noteworthy features. The NLs from accelerometers (Epi-sensors) were ~ 40 dB higher than the NLs from velocimeters (STS-sensors) for periods > 10 s, which is because the small and light Epi-sensors are sensitive to environmental changes. Daily and weekly variations in spectral noise level were observed clearly in short periods < 1 s, and these are considered to be related to human activities. The seismometers in boreholes showed ~20 dB weaker NLs in the cultural noise band. The NLs of accelerometers at a depth of 30 m were also much lower by 30 dB for long periods > 10 sec. Overall the functioning of the new velocimeter and accelerometer stations was reliable for periods ranging from 0.02~100 s and 0.02~10 s, respectively.

• 대한원격탐사학회지
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• 제21권1호
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• pp.31-49
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• 2005

We first review some history of the Global Geodynamics Project (GGP), particularly in the progress of ground-satellite gravity comparisons. The GGP Satellite Project has involved the measurement of ground-based superconducting gravimeters (SGs) in Europe for several years and we make quantitative comparisons with the latest satellite GRACE data and hydrological models. The primary goal is to recover information about seasonal hydrology cycles, and we find a good correlation at the microgal level between the data and modeling. One interesting feature of the data is low soil moisture resulting from the European heat wave in 2003. An issue with the ground-based stations is the possibility of mass variations in the soil above a station, and particularly for underground stations these have to be modeled precisely. Based on this work with a regional array, we estimate the effectiveness of future SG arrays to measure co-seismic deformation and silent-slip events. Finally we consider gravity surveys in volcanic areas, and predict the accuracy in modeling subsurface density variations over time periods from months to years.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.267-270
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• 2006

COMS has two imaging payloads, MI (Meteorological Imager) and GOCI (Geostationary Ocean Colour Imager). In GOCI case, data are packaged per each slot - one part of 16 two-dimensional arrays for imaging sensors - so its generation algorithm is simple. But MI case, data are made up with sequences of 480 bit blocks and are transmitted to its ground station sequentially. Moreover there is no time information in each 480 bit MI block, so a system in its ground system should be attaching time information at received MI blocks. DM (Decomposition Module) is one module of IMPS that receives Raw Data from DATS and generates Level 0 Products that include time tagging. This paper explains DM design for MI of COMS payloads.

• Journal of Positioning, Navigation, and Timing
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• 제6권3호
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• pp.125-133
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• 2017

Time comparison is necessary for the verification and synchronization of the clock. Two-way satellite time and frequency (TWSTFT) is a method for time comparison over long distances. This method includes errors such as atmospheric effects, satellite motion, and environmental conditions. Ionospheric delay is one of the significant time comparison error in case of the carrier-phase TWSTFT (TWCP). Global Ionosphere Map (GIM) from Center for Orbit Determination in Europe (CODE) is used to compare with Bernese. Thin shell model of the ionosphere is used for the calculation of the Ionosphere Pierce Point (IPP) between stations and a GEO satellite. Korea Research Institute of Standards and Science (KRISS) and Koganei (KGNI) stations are used, and the analysis is conducted at 29 January 2017. Vertical Total Electron Content (VTEC) which is generated by Bernese at the latitude and longitude of the receiver by processing a Receiver Independent Exchange (RINEX) observation file that is generated from the receiver has demonstrated adequacy by showing similar variation trends with the CODE GIM. Bernese also has showed the capability to produce high resolution IONosphere map EXchange (IONEX) data compared to the CODE GIM. At each station IPP, VTEC difference in two stations showed absolute maximum 3.3 and 2.3 Total Electron Content Unit (TECU) in Bernese and GIM, respectively. The ionospheric delay of the TWCP has showed maximum 5.69 and 2.54 ps from Bernese and CODE GIM, respectively. Bernese could correct up to 6.29 ps in ionospheric delay rather than using CODE GIM. The peak-to-peak value of the ionospheric delay for TWCP in Bernese is about 10 ps, and this has to be eliminated to get high precision TWCP results. The $10^{-16}$ level uncertainty of atomic clock corresponds to 10 ps for 1 day averaging time, so time synchronization performance needs less than 10 ps. Current time synchronization of a satellite and ground station is about 2 ns level, but the smaller required performance, like less than 1 ns, the better. In this perspective, since the ionospheric delay could exceed over 100 ps in a long baseline different from this short baseline case, the elimination of the ionospheric delay is thought to be important for more high precision time synchronization of a satellite and ground station. This paper showed detailed method how to eliminate ionospheric delay for TWCP, and a specific case is applied by using this technique. Anyone could apply this method to establish high precision TWCP capability, and it is possible to use other software such as GIPSYOASIS and GPSTk. This TWCP could be applied in the high precision atomic clocks and used in the ground stations of the future domestic satellite navigation system.

• 항공우주기술
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• 제6권2호
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• pp.211-218
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• 2007

이중 편파는 직교성을 갖는 두개의 편파를 의미하며 통신상에서 두 개의 독립적인 채널로 간주되어 저궤도 위성에서 관측한 대용량의 데이터를 효과적으로 전송하는데 사용되어 진다. 하지만, 현실적으로 두 개의 편파는 서로가 완벽하게 독립적이지 않기 때문에 각 채널에는 간섭신호가 발생되어 결국 통과대역내의 잡음을 상승 시키는 문제를 야기한다. XPD(Cross-Polarization Discrimination)는 수신안테나와 동일한 편파로 송신된 신호와 상반된 편파로 송신된 신호가 수신 안테나의 출력에서 발생될 때 두 신호간의 비를 나타낸 것이다. 본 논문에서는 KOMPSAT-2에서 마치 이중 편파가 적용된 것처럼 가정한 뒤에 위성과 지상국간의 XPD의 영향을 분석하였다. 본 논문에서의 분석을 통해 99%의 환경적인 가용성과 0.5dB의 위성안테나 축비를 가정하였을 때, 2.5dB의 worst한 축비를 갖는 지상국 안테나를 고려함에도 불구하고 3dB 이상의 링크 마진을 확인할 수 있었다.

• 한국농림기상학회지
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• 제4권4호
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• pp.197-202
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• 2002

A new method is used to estimate the amount of water evaporation from Class A Pan with higher precision and accuracy. The principle of method is to detect the weight change of a buoyant sinker resulting from a change in water level of Class A Pan. A strain-gauge load cell is used to measure the weight change. Field observation of evaporation was done at Pohang Meteorological Station from June 24 to August 4, 2002. By using this new method, it is possible to measure hourly evaporation accurately even under a strong solar radiation and wind disturbance, enabling a direct comparison of evaporation with other meteorological elements. At night, under low humidity and high wind speed conditions, more evaporation was recorded than during daytime. Maximum evaporation rates observed during this period exceed 1.0 mm/hour under the sunny and windy conditions with low humidity. To understand relationships between meteorological elements and latent heat flux at ground level, we suggest intensive held experiments using high accuracy evaporation recording instruments with hourly time interval.

• Earthquakes and Structures
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• 제3권5호
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• pp.675-694
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• 2012

The 2008 Iwate-Miyagi Nairiku earthquake ($M_w$ 6.9, $M_{jma}$ 7.2) occurred on 14 June 2008 in Japan. The amplification and asymmetric waveform of the vertical acceleration at the ground surface recorded by accelerometers at station IWTH25, situated 3 km from the source, were remarkable in two ways. First, the vertical acceleration was extremely large (PGA = 38.66 $m/s^2$ for the vertical component, PGA = 42.78 $m/s^2$ for the sum of the three components). Second, an unusual asymmetric waveform, which is too far above the zero acceleration axis, as well as large upward spikes were observed. Using a multidegree-of-freedom (MDF) system consisting of a one-dimensional continuum subjected to vertical acceleration recorded at a depth of 260 m below ground level, the present paper clarifies numerically that these singular phenomena in the surface vertical acceleration records occurred as a result of the jumping and collision of a layer in vertical motion. We herein propose a new mechanism for such jumping and collision of ground layers. The unexpected extensive landslides that occurred in the area around the epicenter are believed to have been produced by such jumping under the influence of vertical acceleration.

• 한국측량학회:학술대회논문집
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• 한국측량학회 2007년도 춘계학술발표회 논문집
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• pp.27-30
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• 2007

The objective of this study is to improve an accuracy of PWV estimates using GPS in Korea. We determined a weighted mean temperature equation by a linear regression method based on 6 radiosonde meteorological observations, for a total 17,129 profiles, from 2003 to 2005. Weighted mean temperature, Tm, is a key parameter in the retrieval of atmospheric PWV from ground-based GPS measurements of zenith path delay. The accuracy of the GPS-derived PWV is proportional to the accuracy of Tm. And we applied the reduction of air Pressure to GPS station altitude. The reduction value of air pressure from mean sea level to GPS stations altitude is adopted a reverse sea level correction.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.423-428
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• 2008

The monitoring efficiency of the aircraft noise monitoring stations is decided to the reference noise level and the infringement of each monitoring stations. We are calculate the monitoring efficiency of three noise monitoring stations among twelve in the vicinity of Gimpo Int'l Airport. As a result, the monitoring efficiency shows that the noise monitoring stations #3,#5 and #6 are 14.3%, 18.5% and 29.3% respectively, #6 which is underneath the flight track is higher efficiency than another two stations.