Dong-Seob Song

Remote sensing of atmospheric water vapor variation from GPS measurements during a severe weather event

The Global Positioning System (GPS) provides a relatively inexpensive method to remotely sense atmospheric water vapor in all weather conditions. In this study, we applied the GPS meteorology technique to monitor the precipitable water vapor (PWV) variation during a severe weather event (typhoon EWINIAR). The Korean weighted mean temperature equation (KWMTE), customized for the Korean Peninsula, was used to improve the accuracy of the GPS PWV estimation. The time series and the comparison with the images of MTSAT/CMAX and the GPS PWV contour maps indicated that the temporal change of GPS PWV was closely related to the progress of the typhoon. The correlation between the maximum GPS PWV and the maximum rainfall caused by the typhoon was also higher than that for the quiet weather period. Furthermore, the peak in the time series of GPS PWV was generally in good agreement with the time when the maximum rainfall was recorded. Our results therefore confirm that GPS meteorology is an efficient PWV sensing technique, capable of capturing the complex characteristics of water vapor distribution and its temporal variation during a period of severe weather events.

HORIZONTAL DATUM TRANSFORMATION BY DISTORTION MODELLING IN KOREA

Abstract This paper describes the development of a transformation grid for transforming horizontal spatial data from the local geodetic datum to a geocentric datum in Korea. We used least squares collocation as the method for modelling the distortion that remains after the application of a standard seven-parameter similarity transformation. In the experimental tests, the RMSEs in latitude and longitude coordinates are ±0.016m and ±0.007m, respectively, after the distortion modelling, whereas it was indicated that transformation accuracy is improved about 98% by distortion correction. This is a reasonable result, which should give users confidence in transforming data from the local geodetic datum to the geocentric and vice versa for medium scale maps.

Time series analysis of shoreline changes in Gonghyunjin and Songjiho Beaches, South Korea using aerial photographs and remotely sensed imagery

ABSTRACT Kim, I.H., Lee, H.S. and Song, D.S., 2013. Time series analysis of shoreline changes in Gonghyunjin and Songjiho Beaches, South Korea using aerial photographs and remotely sensed imagery Given the speed and pervasiveness of anthropogenic landcover changes, especially in coastal areas, monitoring shoreline alterations and their impacts is critical for intelligent coastal development and beach use management. In this study, we describe a monitoring and analysis framework that uses aerial photography, remotely sensed imagery, and field surveys to detect changes in beach width and area along Gonghyunjin and Songjiho Beaches in South Korea. We used IKONOS imagery acquired in 2004; aerial photographs captured in 1991, 2005, 2009 and 2010; and field surveys conducted in 2010 and 2011. Based on comparisons of these data sources, we detected widespread erosion on both beaches starting in 2004, resulting in 12% reduction in the plane area of these beaches between 2004 and 2010. Most dramatically, we noted that beach width eroded by 28.5 m at the point 700 m south of Gonghyunjin Harbor, and similar declines occurred at several other locations. Erosion occurred at these locations because extended breakwaters in the Gonghyunjin Harbor either blocked or interrupted drift sand transport processes, causing sand to be carried away from some locations without accretion to replenish it. In addition, according to field surveys, we determined that erosion and accretion processes continued to vary seasonally in 2010 and 2011, resulting in smaller overall changes than those in the study years prior to 2010. However, we suggest that severe erosion may occur in the future at some locations if sand continues to be transported north onto Songjiho Beach without replenishment. Thus, we demonstrated that the construction of artificial structures around the harbor caused changes along the shoreline. Our monitoring framework has important applications for future observation of anthropogenically driven changes to this coastal area and serves as an applicable tool in other coastal regions worldwide.

Verification of accuracy of precipitable water vapour from GPS during typhoon Rusa

Abstract This paper presents GPS meteorology using GPS observations obtained from the Korean permanent GPS network during a severe weather condition. Our first experimental studies in Korea were based on data collected from seventeen GPS stations and four radiosonde stations during the period of Typhoon Rusa from 31 August to 1 September 2002. The root mean square difference (RMSD) between the GPS Precipitable Water Vapour (PWV) and the radiosonde-PWV was at the 7.2 mm level. In this new study, a least square analysis was used to reduce the large RMSD and without bias, the RMSD was reduced to 5.7 mm. The mean of the RMSD without consideration of Typhoon Rusa effect was 6.9 mm, whereas the RMSD of GPS-PWV with consideration of the Rusa effect was worse with 9.4 mm. The large RMSD during Typhoon Rusa was due to the change of the observation direction of the balloon based radiosonde by high wind speeds.

Preliminary 3D Assessment of Coastal Erosion by Data Integration between Airborne LiDAR and DGPS Field Observations

ABSTRACT Song, D.S., Kim, I.H. and Lee, H.S., 2013. Preliminary study of 3D Assessment of Coastal Erosion by Data Integration between Airborne LiDAR and DGPS Field Observations The airborne Light Detection And Ranging (LiDAR) system has been allowed in monitoring various natural hazards, so highly accurate and airborne LiDAR data have been used in the field of oceanic sciences, including a digital terrain modeling and bathymetric mapping. In this study, we adopted airborne LiDAR measurements to assess coastal erosion for the first time. The airborne LiDAR data were acquired along the east coastal zone of Korea (shoreline is about 205km). The 3D topographical data and digital orthophotos, which were obtained from aerial LiDAR with a digital camera, were integrated with the beach profiles conducted by the VRS-based DGPS surveying. The integrated dataset were relocated into a developed flight simulator module, which is a Dynamic geographical information system solution with Digital AirScape (D-DAS), for the 3D visual analysis of erosion status. The 3D visual result of seasonal and yearly variability with respect to beach width is validated to understand the evolution trends of the coastal environment on the test areas. Preliminary result from this study shows the potential availability of LiDAR data and the additional opportunities within the 3 dimensional monitoring of coastal evolution, for a detailed evaluation of erosion supported by the Coastal Erosion Monitoring Program (CEMP). Additionally, we expect that the early introduction of the airborne LiDAR Bathymetry (ALB) system in Korea, such as Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS), will be used for more effective and deliberative monitoring of coastal erosion in the coastal zone management program.

Shoreline changes due to groin construction in Namae and Sodol Beaches, South Korea

ABSTRACT Kim, I.H., Lee, H.S., Cho, W.C. and Song, D.S., 2013. Shoreline changes due to groin construction in Namae and Sodol Beaches, South Korea The present study beach has a long stretch of 5.27km bounded by Namae Harbor in north and Sodol Harbor in south which are located in the eastern coast of Korea. In 2007, a groin was constructed at the southern part of Namae Harbor. In order to analyze the pattern of shoreline change due to the groin construction, a beach survey has been accomplished since 2008 right after the groin construction. The temporal and spatial changes in beach topography are also investigated based on the echo sounding data. The survey data along the coastline showed that a continuous accretion occurred around the groin in the south of Namae Harbor due to the north-directed currents mainly due to diffracted waves formed after the groin construction. Thus the southern beach of study area has been eroded steadily. Also, beach widths and plane area of the beach in the south of the groin were decreased in summer and was increased in winter season. In winter, the ground-based surveying was even impossible due to the severe sand loss in the southern part of study area. Moreover, the survey results revealed that the beach volume was increased and foreshore slope became steeper in 2011 than 2010 survey. Therefore, the continuous beach monitoring along the shoreline is necessary, especially in the seriously eroding beach such as Sodol Beach. More fundamental measures for reliable prediction of potential beach change prior to complementary construction of coastal structures are also needed to maintain the value of the beach.

A Correlation Analysis between a Swim Zone Width and Beach Survey Data in Sokcho Beach

ABSTRACT Lee, H.S., Kim, I.H., Song, D.S. and Lee, J.L., 2013. A Correlation Analysis between a Swim Zone Width and Beach Survey Data in Sokcho Beach Sokcho Beach is the 3 km-long sand beach located on the east coast of South Korea. Beach profile surveying and grain size sampling in four control sections were carried out in order to investigate the relationships of swim zone width between the median size, beach face slope, and scale factor. It is found that temporal variation in the southern part of beach is the most severe due to the presence of Oeongchi headland. As the result of the correlation analysis, the correlation factor of the swim zone width to the scale factor was estimated rather high (0.596). The present study shows the grains size is not an adequate indicator in estimating the swim zone width. Regular monitoring of the region is required to determine the seasonal changes, the sediment transport, and the changes in the sedimentation environment, and to acquire an accurate understanding of the beach environment and of the changes that it is undergoing.

Optimal GPS positioning solutions interval for a crustal deformation estimation

GPS is an essential tool in positioning which requires high precision such as velocity field estimation of tectonic plates. However it takes long time for this kind GPS solutions because of defective automatic GPS data processing system. Therefore, it is importa nt that the determination of GPS data processing interval to obtain requisite accuracy in a study of crustal deformation parameter estimation. So, the Gipsy-Oasis II software was used to estimate daily deformation of GPS stations with orbital and atmospheric parameters and least square linear fitting technique was used to estimate the velocity of the GPS stations. In this relative solution of daily positioning, the standard deviation which is scale of precision turned out better than 4mm. In this study, to determinet he optimal time-interval for a crustal deformation estimation, three kinds of time-interval was adopted, which is 2-day, 5-day and 10-day time-interval and were compared to daily solutions by the standard deviation of velocity from the calculation results. Researchresults shows that the Std of the horizontal crustal motion parameter was 1.44 times (Std=±0.66mm/yr), 2.24 times (Std=±1.03mm/yr) and 3.20 times (Std=±1.47mm/yr) worse than the Std used to obtain of the daily positioning result (Std=±0.46mm/yr). The crustal motion magnitude varied irregularly for the 2-day interval. So, we made conclusion that the 2-day interval can be applied to process GPS data for rapid velocity field estimation.

Evaluating of Coastal Erosion Status from CEMP results in Eastern Coast, South Korea

ABSTRACT Song, D.S; Kim, I.H.; Choi, J.S., and Lee, H.S., 2016. Evaluating of Coastal Erosion Status from CEMP results in Eastern Coast, South Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1407 - 1411. Coconut Creek (Florida), ISSN 0749-0208. The Gangwon province, which is located in the mid-eastern part of the Korean Peninsula, started the Coastal Erosion Monitoring Program (CEMP) on 2006 and has been currently progressing. The CEMP in the eastern coast of Gangwon province is carried out in all the 41 littoral drift cells. In this study, we compared and evaluated a level of beach erosion based on the four years CEMP results. The indicators for coastal erosion evaluation in South Korea are consists of the beach width change (40 points), the beach area change (30 pts), the hinterland risk vulnerability (20 pts), the population (5 pts) and the nature conservation value (5 pts). The coastal erosion levels from the absolute evaluation point by the indicators were separated four phases through the A phase (stable, and well preserved beach with over 90 evaluation indicator points), the B phase (occurred an accretion or erosion, but relatively stable beach with 70~89 pts), the C phase (damage on beach or hinterland caused from erosion will be appeared, and with 50~69 pts), and the D phase (occurring heavy damage on beach or hinterland by continuous erosion with below 50 pts) on the 41 littoral drift sectors, which are including 79 beaches. The evaluation result shows that a serious erosion phenomenon in the eastern coast area of Korea has been increasing. Especially, the eroded beach sectors with the C and D phase were extremely increased in 2014 (A=0, B=18, C=47, D=14), compared with the monitoring result in 2010 (A=5, B=26, C=31, D=17).

Quantitative Behaviour Characteristics Analysis of GPS Buoy in Rip Current Generation

ABSTRACT Song, D.S; Kim, G.Y., and Lee, J.L., 2016. Quantitative behaviour characteristics analysis of GPS buoy in rip current generation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1242 - 1246. Coconut Creek (Florida), ISSN 0749-0208. GPS buoys have been used to acquire sea level change data, current measurements and other oceanic variables in sea for the purposes of vertical datum determination, tide correction, radar altimeter calibration, ocean environment and marine pollution monitoring. The occurrence of rip currents in the Haeundae beach, which is one of the most famous beaches in South Korea, has been threatening beach-goer security in summer season annually. Therefore, we adopted a GPS buoy system for an experiment which is to investigate rip current velocity; it is sporadic and may quickly upsurge within minutes due to larger arriving wave groups or nearshore flow uncertainties. In this study, for high accurate positioning of buoy equipment, a Satellite Based Argumentation System DGPS data logger was deployed to investigate within floating object, and it can be acquired three-dimensional coordinate or geodetic position of buoy with continuous NMEA-0183 protocol during 24 hours. The wave height and current profile measured by in-situ Acoustic Doppler Current Profilers in a cross-shore array were compared with the GPS-derived current velocity, it is being clearly increased before and after generation of rip current, and wave period also was lengthened when a rip current generated. The results presented in this study indicate that by using the GPS buoy system is a reasonable alternative for the measuring of rip current behaviour.