Hongsik Yun

Optimal Methods of RTK-GPS/Accelerometer Integration to Monitor the Displacement of Structures

The accurate measurement of diverse displacements of structures is an important index for the evaluation of a structure’s safety. In this study, a comparative analysis was conducted to determine the integrated RTK-GPS/accelerometer method that can provide the most precise structure displacement measurements. For this purpose, three methods of calculating the dynamic displacements from the acceleration data were comparatively analyzed. In addition, two methods of determining dynamic, static, and quasi-static displacements by integrating the displacements measured from the RTK-GPS system and the accelerometer were also comparatively analyzed. To ensure precise comparison results, a cantilever beam was manufactured onto which diverse types of displacements were generated to evaluate the measurement accuracy by method. Linear variable differential transformer (LVDT) measurements were used as references for the evaluation to ensure accuracy. The study results showed that the most suitable method of measuring the dynamic displacement with the accelerometer was to calculate the displacement by filtering and double-integrating the acceleration data using the FIR band-pass filter. The integration method that uses frequency-based displacement extraction was most appropriate for the integrated RTK-GPS/accelerometer method of comprehensively measuring the dynamic, static, and quasi-static displacements.

Development of an RTK-GPS Positioning Application with an Improved Position Error Model for Smartphones

This study developed a smartphone application that provides wireless communication, NRTIP client, and RTK processing features, and which can simplify the Network RTK-GPS system while reducing the required cost. A determination method for an error model in Network RTK measurements was proposed, considering both random and autocorrelation errors, to accurately calculate the coordinates measured by the application using state estimation filters. The performance evaluation of the developed application showed that it could perform high-precision real-time positioning, within several centimeters of error range at a frequency of 20 Hz. A Kalman Filter was applied to the coordinates measured from the application, to evaluate the appropriateness of the determination method for an error model, as proposed in this study. The results were more accurate, compared with those of the existing error model, which only considered the random error.

Frequent Unscheduled Updates of the National Base Map Using the Land-Based Mobile Mapping System

This paper focuses on the use of the Land-based Mobile Mapping System (LMMS) for the unscheduled updates of a National Base Map, which has nationwide coverage and was made using aerial photogrammetry. The objectives of this research are to improve the weak points of LMMS surveying for its application to the updates of a National Base Map (NBM), which has rigorous accuracy and quality standards. For this, methods were suggested for the (1) improvement of the accuracy of the Global Positioning System/Inertial Navigation System (GPS/INS) in the long-term exposure of environments with poor GPS reception; (2) elimination of mutual deviations between LMMS data obtained in duplicate to meet resolution standards; (3) devising an effective way of mapping objects using LMMS data; and (4) analysis of updatable regions and map layers via LMMS. To verify the suggested methods, experiments and analyses were conducted using two LMMS devices in four target areas for unscheduled updates of the National Base Map.

A New Window-Based Program for Quality Control of GPS Sensing Data

The main purpose of this study is to develop a new Windows-based program that calculates a quality control parameter that shows the quality of GPS observations using Global Positing Sensing (GPS) data in a Receiver INdependent Exchange (RINEX) format. This new program, Global Positing Sensing Quality Control) (GPSQC), allows general GPS users to easily and intuitively check the quality of GPS observations before post-processing, which will lead to the improvement of GPS positioning precision in diverse areas of GPS applications. The GPSQC is designed to control the multi-path, cycle slip, and ionospheric errors of L1 and L2 signals in GPS observations. The GPSQC was developed using C#.NET language for the Window series with Microsoft Graphical User Interfaces (MS GUIs). This program gives brief information for GPS observations, time series plots, graphs of quality control parameters, and a summary report in MS word, Excel and PDF formats. It can simply perform quality checking of GPS observations that is difficult for surveyors conducting field work. We expect that GPSQC can be used to improve the accuracy of positioning and to solve time-consuming problems due to data loss and large errors in GPS observations.

Transformation of Vertical Datum Surface in the Coastal Area using Hybrid Geoid Models

ABSTRACT Lee, D.H., Yun, H.S., Jung, H.I., Cho, J.M.., Cho, J.H., Jung, W.C. and Hwang, J.S., 2013. Transformation of Vertical Datum Surface in the Coastal Area using Hybrid Geoid Models The national height system (NHS) of Korea is currently separated into land and sea, which makes it difficult to acquire homogenous and accurate height information throughout the nation. The NHS for land is defined by a bench-mark (BM) based on the mean sea level (MSL) of Incheon bay, which is managed by the National Geographic Information Institution (NGII), and that for seas is defined by the tidal bench-mark (TBM) based on the local MSL, which is managed by the Korea Hydrographic and Oceanographic Administration (KHOA). This is because these two institutions have different agendas in the use of height data. Therefore, once the differences between the vertical datum surfaces (VDS) on land and sea are considered, such differences could be converted into height information that is measured with different VDS. This study was conducted to homogenize height information for land and sea using the differences between hybrid geoid models fitted to the VDSs for land and sea and to develop a VDS transformation model that allows accurate transformation, with which to continuously and effectively unify the separated NHS throughout the whole area in Korea. For a precise hybrid geoid model, a precise gravimetric geoid model was first developed using the remove and restore (R-R) technique, based on all available gravity observations. Next, the differences between the height results based on each VDS of land and sea using 70 TBMs that had both results were compared and analyzed, and the geometric geoid height of TBM was calculated based on the VDS of land and sea through the precise GPS observations for 4 or more hours. Finally, the gravimetric geoid model was fitted to the acquired geometric geoid heights of TBMs to develop two hybrid geoid models, each of which is based on the VDS of land or sea, and to determine the differences between the two models as the VDS transformation model. The VDS transformation accuracy based on this model was approximately ±3 cm. It is expected that the results of this study can help minimize not only the confusion in the use of land and sea spatial information due to the disagreement between the two NHSs in Korea, but also the economic and time losses in the execution of coastal development and disaster prevention projects in the future.

Application study of red tide monitoring to desalination plants using chollian (COMS)

AbstractChollian (Communication, Ocean, and Meteorological Satellite (COMS)) is a geostationary satellite developed jointly by the Ministry of Land, Infrastructure, and Transport (MOLIT), the Ministry of Education (MOE), the Korea Communications Commission (KCC), and the Korea Meteorological Administration (KMA). Chollian serves not only as communications and weather satellites but also as a marine observation satellite capable of detecting ocean surface 8 times a day with Geostationary Ocean Color Imager (GOCI). Most of the recent desalination plants use Seawater Reverse Osmosis (SWRO) process, and chlorine cannot be used because the RO membrane in the main SWRO process is made of polyamide (PA). Therefore, it is very vulnerable to biofouling due to the influence of red algae and marine micro-organisms contained in seawater. This study aimed to evaluate the applicability of the “red tide monitoring system” capable of detecting and preventing the influx of red algae adversely affecting operation and maint...

Development of Soil Compaction Analysis Software (SCAN) Integrating a Low Cost GPS Receiver and Compactometer

A software for soil compaction analysis (SCAN) has been developed for evaluating the compaction states using the data from the GPS as well as a compactometer attached on the roller. The SCAN is distinguished from other previous software for intelligent compaction (IC) in that it can use the results from various types of GPS positioning methods, and it also has an optimal structure for remotely managing the large amounts of data gathered from numerous rollers. For this, several methods were developed: (1) improving the accuracy of low cost GPS receiver’s positioning results; (2) modeling the trajectory of a moving roller using a GPS receiver’s results and linking it with the data from the compactometer; and (3) extracting the information regarding the compaction states of the ground from the modeled trajectory, using spatial analysis methods. The SCAN was verified throughout various field compaction tests, and it has been confirmed that it can be a very effective tool in evaluating field compaction states.

Algae Inflow Monitoring using Satellite Images for the Process Control of the Gijang Desalination Plant in Busan, South Korea

ABSTRACT Song, M.-S.; Yun, H.-S.; Kim, T.-W., and Cho, J.-M., 2017. Algae inflow monitoring using satellite images for the process control of the Gijang desalination plant in Busan, South Korea. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 159–163. Coconut Creek (Florida), ISSN 0749-0208. Climate change has recently been taking place due to the sudden rise of water temperature resulting from global warming and the red tides adversely affected the seawater desalination plant directly or indirectly every year. Harmful Algal Blooms (HABs) occur if the perishable organic pollutants, minerals, and growth stimulating substances are abundantly dissolved in the water and if solar radiation, water temperature, salinity, and other environmental conditions are met. Once the algae are agglomerated by the wind and tide, high-density red tide occurs. This may also cause damages to the desalination plants. RO membrane in the main process cannot be cleaned by the chlorination for membrane cleaning because the material of RO membrane is polyamide. Therefore, the algae and microorganisms contained in seawater have a negative impact on membrane fouling. Accordingly, pre-treatment method for blocking the inflow of algae by monitoring the occurrence of HABs is more effective than post-processing method that is used for cleaning after the membrane is already contaminated. In this study, algae inflow monitoring was carried out through satellite image analysis looking for an appropriate analysis algorithm of chlorophyll-a concentration by using the Geostationary Ocean Color Imager (GOCI) Data Processing System (GDPS) for the process control of Gijang desalination plant. Accordingly, the chlorophyll-a concentration analyzed by OC2 algorithm for algae inflow monitoring is the most suitable algorithm.

Convergence Technique Study on Red Tide Prediction in the Littoral Sea

ABSTRACT Kim, T.-W.; Kim, J.-H.; Song, M.-S., and Yun, H.-S., 2017. Convergence technique study on red tide prediction in the littoral sea. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 254–258. Coconut Creek (Florida), ISSN 0749-0208. Active research has been conducted on tracking red tides by combining remotely sensed satellite images and numerically predicted ocean currents. Recent ocean observing satellite images have low spatial resolution and temporal limitations. Such convergence technologies are developed to overcome these shortcomings. Chollian, which is the worlds first oceanographic satellite capable of observing ocean surface in a “geostationary orbit”, can detect the current expansion and intensity of Harmful Algal Blooms (HABs). This Geostationary Ocean Color Imager (GOCI) can combine HABs patch with tidal current to predict where the bloom will travel on the Korean peninsula coast because it takes photographs at 500 m spatial resolution 8 times a day. HABs initially occurred at 9 a.m. on August 17, 2015, and were most likely to flow into the seawater desalination plant at 1 p.m.. Intake managers who operate and maintain (O&M) seawater desalination plants can track the inflow possibility hourly using this convergence technology. The inflow possibility was predicted by Linear Directional Mean (LDM) spatial analysis in GIS environment. This product can provide seawater intake managers with timely information as a useful decision-making tool.

A Study of Shoreline Changes in Antarctica (Terra Nova Bay) Based on SAR Data

ABSTRACT Cho, J.H., Cho, J.M., Yun, H.S., Kim, T.W., Kim, C.W., 2013. A Study of Shoreline Changes in Antarctica (Terra Nova Bay) Based on SAR Data Unlike optical imaging, Synthetic Aperture Radar imaging can produce images regardless of the weather and the time of day, which makes it a useful tool for collecting topographical data in tropical rainforests and in the North and South Poles, where traditional optical imaging is ineffective due to the rapidly changing weather. For this study, this researcher acquired SAR imagery of Terra Nova Bay, located near the South Pole, from October 8, 2011 to March 11, 2012 to observe the changes in its shoreline in summer. SAR imagery was captured once every 11th day to determine the exact time in summer when the glaciers and ice along the shore melt. The acquired stereo SAR imagery data were then processed by applying the radargrammetric method along the shoreline to reduce the speckles specific to the SAR data, and to ensure the accuracy of the coordinates and the size of the satellite imagery, before converting them to DEM at 10m intervals, which again generated orthorectified imagery. The generated orthorectified images were then converted to a digital map with the UTM coordinate system via vectorizing, which visually represented on the map the changes that took place in the shoreline in summer.The study showed that the region was covered with ice from March to early November, which affected the activity in the base, including the access of the ice breaker. Due to the warming climate, there was no sea ice in the Terra Nova Bay for about a month in February. The ice in that area started to melt on November 21 and froze again on February 28. Accordingly, it was concluded that the best time to access the South Pole to build the Antarctic base is mid-December, and the construction crew must evacuate the area no later than March to ensure the safety of the mission.