• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2000.11a
• /
• pp.361-362
• /
• 2000

대기오염을 해결하기 위한 서울시의 노력에 의해 아황산가스(SO$_2$), 총먼지(TSP)등의 1차 오염물질들은 어느 정도 개선되어 왔으나, 일반 시민들의 체감대기오염도는 과거에 비해 더욱 악화되었으며, 이는 교통량의 급격한 증가로 인한 고농도 오존사례와 같은 광화학스모그와 시정악화가 가장 대표적인 것으로 우리시의 현안문제로 대두하고 있는 실정이다. 이에 본 연구에서는 시정의 시간적인 변동성과 시정 악화를 야기하는 인자들을 파악하여 이에 대한 대처방안을 모색하고자 한다. (중략)

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2002.04a
• /
• pp.167-168
• /
• 2002

서울 지역의 스모그 현상은 1차 오염물질에 의해 생기는 런던형 스모그 및 광화학 반응에 의한 LA형 스모그와는 다른 양상을 나타내고 있는데, 그 특성이 명확히 밝혀지지 않고 있다. 서울 지역의 스모그 특성을 체계적으로 밝혀내기 위해서는 스모그 현상에 대한 현장조사 연구뿐만 아니라 챔버 실험을 통한 스모그 생성과정에 대한 체계적인 연구도 필요하다. 시정장애(visibility reduction) 현상을 거치는 대기의 기상 특성을 보면 대부분 상대습도가 높은 조건이 낮에도 지속되는 경우가 대부분이다. (중략)

• Journal of Korean Society for Atmospheric Environment
• /
• v.29 no.3
• /
• pp.264-274
• /
• 2013

This study investigates long-term trends and characteristics of aerosol light scattering coefficient at Seoul and Baengnyeongdo in order to understand aerosol optical and radiative properties around Korea. The analysis period is limited to one year of 2011. First, the aerosol scattering coefficients (${\sigma}_{sp}$) of both sites show strong linear dependence on the $PM_{2.5}$ mass concentrations with significant correlations between both. Further, correlations and sensitivity between ${\sigma}_{sp}$ and $PM_{2.5}$ increase with relative humidity, implying both relationships are strongly dependent upon moisture amounts in the atmosphere. This study applied 3-step careful quality control procedures to the analysis of ${\sigma}_{sp}$ for the insurance of data confidence. For the relationship analysis of extinction coefficients (${\sigma}_{ext}$) to visibility and aerosol optical depth, ${\sigma}_{sp}$ observed at 3 p.m. have been used with help of aerosol absorption coefficients (${\sigma}_{ap}$) in order to remove its dependence upon relative humidity, and also those of rainy period have been excluded. As expected, ${\sigma}_{ext}$ estimated are inversely proportional to visibility observation by eye. Finally, aerosol extinction coefficients have been vertically integrated with an assumption of nearly well-mixed within an e-folding height to determine aerosol optical depth, and compared with those retrieved from sunphotometer. The results show a reasonable agreement in spite of an inherent difference of each definition. We expect these findings would help to eventually understand aerosol radiative forcing and its effect on the regional climate change around Korea.

• Atmosphere
• /
• v.29 no.5
• /
• pp.639-658
• /
• 2019

The classification of fog type and the characteristics of fog based on fog events over South Korea were investigated using a 3-year (2015~2017) visibility meter data. One-minute visibility meter data were used to identify fog with present weather codes and surface observation data. The concept of fog events was adopted for the better definition of fog properties and more objective classification through the detailed investigation of life cycle of fog. Decision tree method was used to classify the fog types and the final fog types were radiation fog, advection fog, precipitation fog, cloud base lowering fog and morning evaporation fog. We enhanced objectivity in classifying the types of fog by adding the satellite and the buoy observations to the conventional usage of AWS and ceilometer data. Radiation fog, the most common type in South Korea, frequently occurs in inland during autumn. A considerable number of advection fogs occur in island area in summer, especially in July. Precipitation fog accounts for more than a quarter of the total fog events and frequently occurs in islands and coastal areas. Cloud base lowering fog, classified using ceilometer, occurs occasionally for all areas but the occurrence rate is relatively high in east and west coastal area. Morning evaporation fog type is rarely observed in inland. The occurrence rate of thick fog with visibility less than 100 meters is amount to 21% of total fog events. Although advection fog develops into thick fog frequently, radiation fog shows the minimum visibility, in some cases.

• Korean Journal of Remote Sensing
• /
• v.33 no.4
• /
• pp.359-375
• /
• 2017

We developed fog detection algorithm (KNU_FDA) based on the optical and textural properties of fog using satellite (COMS) and ground observation data. The optical properties are dual channel difference (DCD: BT3.7 - BT11) and albedo, and the textural properties are normalized local standard deviation of IR1 and visible channels. Temperature difference between air temperature and BT11 is applied to discriminate the fog from other clouds. Fog detection is performed according to the solar zenith angle of pixel because of the different availability of satellite data: day, night and dawn/dusk. Post-processing is also performed to increase the probability of detection (POD), in particular, at the edge of main fog area. The fog probability is calculated by the weighted sum of threshold tests. The initial threshold and weighting values are optimized using sensitivity tests for the varying threshold values using receiver operating characteristic analysis. The validation results with ground visibility data for the validation cases showed that the performance of KNU_FDA show relatively consistent detection skills but it clearly depends on the fog types and time of day. The average POD and FAR (False Alarm Ratio) for the training and validation cases are ranged from 0.76 to 0.90 and from 0.41 to 0.63, respectively. In general, the performance is relatively good for the fog without high cloud and strong fog but that is significantly decreased for the weak fog. In order to improve the detection skills and stability, optimization of threshold and weighting values are needed through the various training cases.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.49 no.1
• /
• pp.67-72
• /
• 2012

In this paper, we present an image enhancement method for atmospherically degraded images using atmospheric light and transmission based on color analysis. We first generate a normalized image using maximum value of each RGB color channel. Then, each atmospheric light is estimated from RGB color channel respectively by calculating reflectance of an image. We also, generate a transmission using gamma coefficients from the Y channel of the image. We can significantly enhance the visibility of an image by using the estimated atmospheric light and the transmission. The proposed algorithm can remove atmospheric degradation components better than existing techniques because the color prevents color distortion which is common problem of existing techniques. Experimental results demonstrate that the proposed algorithm can improve visibility be removing fog, smoke, and dust.

• Proceedings of the KSRS Conference
• /
• 1998.09a
• /
• pp.103-109
• /
• 1998

A technique on atmospheric correction algorithm for a single band (0.76-0.90 $\mu$m) reflective of Landsat TM imagery has been developed using a radiation transfer model simulation. It proceeds in two steps: First, calculation of the surface reflectance of each pixel based on precomputed planetary albedo functions for actual atmospheres(e. g. radiosonde) and two kinds of atmospheric visibility states. Second, approximate correction of the adjacency pixel effect by taking into account the average reflectance in an 7 $\times$ 7 pixel neighbourhood and using appropriate land cover classification in reflectance. The correction functions are provided by MODTRAN model.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2008.04a
• /
• pp.434-435
• /
• 2008

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2006.04a
• /
• pp.401-403
• /
• 2006

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2008.10a
• /
• pp.262-263
• /
• 2008