• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.41 no.11
• /
• pp.1653-1660
• /
• 2016

The synthetic aperture rardar (SAR) is an active sensor using microwaves. It transmits a microwave signal, called a chirp pulse, and receives the reflected signal in a moving platform such as satellite and unmanned aerial vehicle. Since this sensor uses microwaves that can penetrate the atmosphere, SAR generates the images regardless of light and weather conditions. However SAR operates on the moving platform, the Doppler shift and the side-looking observation method should be considered. In addtion, a residual image or ghost image can be occurred according to selection of the pulse repetition frequency (PRF). In this paper, a range design of the PRF for the L-band spaceborne SAR system is studied for prevention of SAR image distortion. And the system is studied for prevention of SAR image distortion. And the system parameter and the PRF are calibrated iteratively according to the proposed system design procedure and design constraints. The MATLAB based on SAR system simulator has been developed to verify the validity of calculated PRF. The developed simulator assumes that SAR sensor is operated by the PRF calculated from the design. The results of the simulator show that the targets in image has a valid peak to side-lobe ratio (PSLR) so that the PRF can be used for the spaceborne SAR sensor.

• Journal of the Korean earth science society
• /
• v.39 no.1
• /
• pp.89-102
• /
• 2018

We analyzed the meteorological and radiation characteristics of Seoul metropolitan area using data from energy flux towers that were installed and operated by the Weather Information Service Engine (WISE). The meteorological and radiation variables included temperature, pressure, wind speed, wind direction, relative humidity, surface temperature, rainfall amount, upward and downward solar radiation, upward and downward longwave radiation, albedo and emissivity from 14 energy flux stations located in the Seoul metropolitan area from July 2016 to July 2017. According to the monthly data during the period, the albedo is low and emissivity is high at the Jungnang station in the urban and opposite at Bucheon station in the suburban area. For a station in natural state, the albedo was higher than urban stations because solar radiation reflects effectively. Relatively high temperatures were shown at stations located in urban area with low albedo and high emissivity, in general. However, temperature was high at Gajwa and Ttukseom stations, the albedo was relatively high due to the station environment surrounded by glass wall buildings and the Han river. In the station located in suburban area, both emissivity and temperature were low. Among these stations, Bucheon station had the highest emissivity values because the surface temperature was relatively lower than that of the suburban area. As a result, the albedo decreased and the emissivity increased at stations in urban areas. Additionally, Seoul metropolitan area had less than $100Wm^{-2}$ of net radiation, which implied that radiation energy could be absorbed in the atmosphere.

• Atmosphere
• /
• v.25 no.2
• /
• pp.261-270
• /
• 2015

Characteristics of snowfall and snow crystal habits have been investigated in the campaign of Experiment on Snow Storms At Yeongdong (ESSAY) using radiosonde soundings, Global Navigation Satellite System (GNSS), and a digital camera with a magnifier for taking a photograph of snowfall crystals. The analysis period is 6 to 14 February 2014, when the accumulated snowfall amount is 192.8 cm with the longest snowfall duration of 9 days. The synoptic situations are similar to those of the previous studies such as the Low pressure system passing by the far South of the Korean peninsula along with the Siberian High extending to northern Japan, which eventually results in the northeasterly or easterly flows and the long-lasting snowfall episodes in the Yeongdong region. In general, the ice clouds tended to exist below around 2~3 km with the consistent easterly flows, and the winds shifted to northerly~northwesterly above the clouds layer. The snow crystal habits observed in the ESSAY campaign were mainly dendrite, consisting of 70% of the entire habits. The rimed habits were frequently captured when two-layered clouds were observed, probably through the process of freezing of super-cooled droplets on the ice particles. The homogeneous habit such as dendrite was shown in case of shallow clouds with its thickness of below 500 m whereas various habits were captured such as dendrites, rimed dendrites, aggregates of dendrites, plates, rimed plates, etc in the thick cloud with its thickness greater than 1.5 km. The dendrites appeared to be dominant in the condition of cloud top temperature specifically ranging $-12{\sim}-16^{\circ}C$. However, the association of snow crystal habits with temperature and super-saturation in the cloud could not be examined in the current study. Better understandings of characteristics of snow crystal habits would contribute to preventing breakdown accidents such as a greenhouse destruction and collapse of a temporary building due to heavy snowfall, and traffic accidents due to snow-slippery road condition, providing a higher-level weather information of snow quality for skiers participating in the winter sports, and estimating more accurate snowfall amount, location, and duration with the fallspeed of solid precipitation.

• Journal of Korea Water Resources Association
• /
• v.46 no.8
• /
• pp.857-871
• /
• 2013

The interest in rainfall observation and forecasting using remote sensing method like RADAR (Radio Detection and Ranging) and satellite image is increased according to increased damage by rapid weather change like regional torrential rain and flash flood. In this study, the basin runoff was calculated using adaptive neuro-fuzzy technique, one of the data driven model and MAPLE (McGill Algorithm for Precipitation Nowcasting by Lagrangian Extrapolation) forecasted precipitation data as one of the input variables. The flood estimation method using neuro-fuzzy technique and RADAR forecasted precipitation data was evaluated. Six rainfall events occurred at flood season in 2010 and 2011 in Chungju Reservoir basin were used for the input data. The flood estimation results according to the rainfall data used as training, checking and testing data in the model setup process were compared. The 15 models were composed of combination of the input variables and the results according to change of clustering methods were compared and analysed. From this study was that using the relatively larger clustering radius and the biggest flood ever happened for training data showed the better flood estimation. The model using MAPLE forecasted precipitation data showed relatively better result at inflow estimation Chungju Reservoir.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.12 no.4
• /
• pp.724-729
• /
• 2008

In the case of 'MAEMI', the Typhoon which formed in September, 2003, the largest-scale damage of tidal wave was caused by the co-occurrence of Typhoon surge and full tide. Until now Korea has been focusing on the calculating the amount of damage and its restoration to cope with these sea and harbor disasters. It is essential to establish some systematic counterplans to diminish such damages of large-scale tidal invasion on coastal lowlands considering the recent weather conditions of growing scale of typhoons. Therefore, the purpose of this research is to make the counterplans for prevention against disasters fulfilled effectively based on the data conducted by comparing and analyzing the accuracy between observation values and the results of estimating the greatest overflow area according to abnormal tidal levels centered on Masan area where there was the severest damage from tidal wave at that time. It's necessary utilize data like high-resolution satellite image and LiDAR(etc.) for correct analysis data considering geographical characteristics of dangerous area from the storm surge. And we must make a solution to minimize the damage by making data of dangerous section of flood into GIS Database using those data (as stated above) and drawing correcter damage function.

• Korean Journal of Remote Sensing
• /
• v.24 no.4
• /
• pp.309-324
• /
• 2008

In this study the retrieval algorithms have been developed to retrieve total precipitable water (TPW) from Terra/Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) infrared measurements using a physical iterative retrieval method and a split-window technique over East Asia. Retrieved results from these algorithms were validated against Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave/Imager (SSM/I) over ocean and radiosonde observation over land and were analyzed for investigating the key factors affecting the accuracy of results and physical processes of retrieval methods. Atmospheric profiles from Regional Data Assimilation and Prediction System (RDAPS), which produces analysis and prediction field of atmospheric variables over East Asia, were used as first-guess profiles for the physical retrieval algorithm. We used RTTOV-7 radiative transfer model to calculate the upwelling radiance at the top of the atmosphere. For the split-window technique, regression coefficients were obtained by relating the calculated brightness temperature to the paired radiosonde-estimated TPW. Physically retrieved TPWs were validated against SSM/I and radiosonde observations for 14 cases in August and December 2004 and results showed that the physical method improves the accuracy of TPW with smaller bias in comparison to TPWs of RDAPS data, MODIS products, and TPWs from split-window technique. Although physical iterative retrieval can reduce the bias of first-guess profiles and bring in more accurate TPWs, the retrieved results show the dependency upon initial guess fields. It is thought that the dependency is due to the fact that the water vapor absorption channels used in this study may not reflect moisture features in particular near surface.

• Korean Journal of Remote Sensing
• /
• v.34 no.6_3
• /
• pp.1329-1350
• /
• 2018

There have been many applications to observe Earth using synthetic aperture radar (SAR) since it could acquire Earth observation data without reference to weathers or local times. However researches about digital map generation using SAR have hardly been performed due to complex raw data processing. In this study, we suggested feasibility of producing digital map using SAR stereo images. We collected two sets, which include an ascending and a descending orbit acquisitions respectively, of KOMPSAT-5 stereo dataset. In order to suggest the feasibility of digital map generation from SAR stereo images, we performed 1) rational polynomial coefficient transformation from radar geometry, 2) digital resititution using KOMPSAT-5 stereo images, and 3) validation using digital-map-derived reference points and check points. As the results of two models, root mean squared errors of XY and Z direction were less than 1m for each model. We discussed that KOMPSAT-5 stereo image could generated 1:25,000 digital map which meets a standard of the digital map. The proposed results would contribute to generate and update digital maps for inaccessible areas and wherever weather conditions are unstable such as North Korea or Polar region.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.22 no.3
• /
• pp.118-134
• /
• 2017

The radiation observation data will be used importantly in research field such as climatology, weather, architecture, agro-livestock and marine science. The Ieodo Ocean Research Station (IORS) is regarded as an ideal observatory because its location can minimize the solar radiation reflection from the surrounding background and also the data produced here can serve as a reference data for radiation observation. This station has the potential to emerge as a significant observatory and join a global radiation observation group such as the Baseline Surface Radiation Network (BSRN), if the surrounding of observatory is improved and be equipped with the essential radiation measuring instruments (pyaranometer and pyrheliometer). IORS has observed the solar radiation using a pyranometer since November 2004 and the data from January 1, 2005 to December 31, 2015 were analyzed in this study. During the period of this study, the daily mean solar radiation observed from IORS decreased to $-3.80W/m^2/year$ due to the variation of the sensor response in addition to the natural environment. Since the yellow sand and fine dust from China are of great interest to scientists around the world, it is necessary to establish a basis of global joint response through the radiation data obtained at the Ieodo as well as at Sinan Gageocho and Ongjin Socheongcho Ocean Research Station. So it is an urgent need to improve the observatory surrounding and the accuracy of the observed data.

• Korean Journal of Remote Sensing
• /
• v.34 no.6_2
• /
• pp.1299-1310
• /
• 2018

In this study, we analyzed distribution and movement trends using in-situ observations and particle tracking methods to understand the movement of the drift ice in the Arctic Ocean. The in-situ movement data of the drift ice in the Arctic Ocean used ITP (Ice-Tethered Profiler) provided by NOAA (National Oceanic and Atmospheric Administration) from 2009 to 2018, which was analyzed with the location and speed for each year. Particle tracking simulates the movement of the drift ice using daily current and wind data provided by HYCOM (Hybrid Coordinate Ocean Model) and ECMWF (European Centre for Medium-Range Weather Forecasts, 2009-2017). In order to simulate the movement of the drift ice throughout the Arctic Ocean, ITP data, a field observation data, were used as input to calculate the relationship between the current and wind and follow up the Lagrangian particle tracking. Particle tracking simulations were conducted with two experiments taking into account the effects of current and the combined effects of current and wind, most of which were reproduced in the same way as in-situ observations, given the effects of currents and winds. The movement of the drift ice in the Arctic Ocean was reproduced using a wind-imposed equation, which analyzed the movement of the drift ice in a particular year. In 2010, the Arctic Ocean Index (AOI) was a negative year, with particles clearly moving along the Beaufort Gyre, resulting in relatively large movements in Beaufort Sea. On the other hand, in 2017 AOI was a positive year, with most particles not affected by Gyre, resulting in relatively low speed and distance. Around the pole, the speed of the drift ice is lower in 2017 than 2010. From seasonal characteristics in 2010 and 2017, the movement of the drift ice increase in winter 2010 (0.22 m/s) and decrease to spring 2010 (0.16 m/s). In the case of 2017, the movement is increased in summer (0.22 m/s) and decreased to spring time (0.13 m/s). As a result, the particle tracking method will be appropriate to understand long-term drift ice movement trends by linking them with satellite data in place of limited field observations.

• Journal of the Korean earth science society
• /
• v.37 no.1
• /
• pp.29-39
• /
• 2016

In this study, we estimated solar radiation by multiple regression analysis using sunshine duration and precipitation data, which are highly correlated to solar radiation. We found the regression equation using data obtained from GROM (Gangwon Regional Office of Metrology, station 105, 1980-2007) located in Gangneung, South Korea and validated the equation by applying data obtained from new GROM (newly relocated, station 104, 2009-2014) and data obtained from GWNU (Gangneung-Wonju National University, 2013-2014) located between stations 104 and 105. By using sunshine duration data alone, the estimation using data from station 104 resulted in a correlation coefficient of 0.96 and a standard error of $1.16MJm^{-2}$, which was similar to the previous results; the estimation using data from GWNU yielded better results with a correlation coefficient of 0.99 and a standard error of $0.57MJm^{-2}$. By using sunshine duration and precipitation data, the estimation (using data from station 104) yielded a correlation coefficient of 0.96 and a standard error of $0.99MJm^{-2}$, resulting in a lower standard error compared to what was obtained using sunshine duration data alone. The maximum solar radiation bias increased from -26.6% (March 2013) to -31.0% (February 2011) when both sunshine duration and precipitation data were incorporated into the estimation rather than when sunshine duration data alone was incorporated. This was attributed to the concentrated precipitation found during May and July-September, which resulted in negative coefficients of the estimating equation in other months. Therefore, the monthly average solar radiation should be estimated carefully when employing the monthly average precipitation for those places where precipitation is concentrated during summer, such as the Korean peninsula.