• 대한원격탐사학회지
• /
• 제25권6호
• /
• pp.475-486
• /
• 2009

Harmful algal blooms (HAB) caused by the dominant species Cochlodinium polykrikoides (C. polykrikoides) appear in the South Sea of Korea and are particularly present in summer and fall seasons. Environmental factors such as water temperature, weather conditions (air temperature, cloud cover, sunshine, precipitation and wind) influence on the initiation and subsequent development of HAB. The purpose of this research was to study spatial and temporal variations of HAB in the Yeosu area using environmental (oceanic and meteorological) and satellite data. Chlorophyll-a concentrations were calculated using Sea-viewing Wide Field-of-view Sensor (SeaWiFS) images by an Ocean Chlorophyll 4 (OC4) algorithm, and HAB were estimated using the Red tide index Chlorophyll Algorithm (RCA). We also used the surface velocity of sequential satellite images applying the Maximum Cross Correlation method to detect chlorophyll-a movement. The results showed that the water temperature during HAB occurrences in August 2002-2008 was $19.4-30.2^{\circ}C$. In terms of the frequency of the mean of cell density of C. polykrikoides, the cell density of the HAB found at low (<300 cells/ml), medium (300-1000 cells/ml), and high (>1000 cells/ml) levels were 27.01%, 37.44%, and 35.55%, respectively. Meteorological data for 2002-2008 showed that the mean air temperature, precipitation, wind speed and direction, and sunshine duration were $22.39^{\circ}C$, 6.54 mm/day, 3.98 m/s (southwesterly), and 1-11.7 h, respectively. Our results suggest that HAB events in the Yeosu area can be triggered and extended by heavy precipitation and massive movement of HAB from the East China Sea. Satellite images data from July to October 2002-2006 showed that the OC4 algorithm generally estimated high chlorophyll-a concentration ($2-20\;mg/m^3$) throughout the coastal area, whereas the RCA estimated concentrations at $2-10\;mg/m^3$. The surface velocity of chlorophyll-a movement from sequential satellite images revealed the same patterns in the direction of the Tsushima Warm Current.

• 대한원격탐사학회지
• /
• 제26권2호
• /
• pp.189-207
• /
• 2010

GOCI(정지궤도 해색센서) 해수환경분석 알고리즘들은 해양 광 특성 현장관측 자료들을 이용하여 개발되었다. 사용된 자료는 1998년부터 2009년까지 한반도 주변 해역에서 총 1348개 정점에서 얻어진 엽록소 농도(Chl-a), 부유물 농도(SS), 용존유기물의 흡광계수($a_{dom}$), 원격반사도($R_{rs}$) 현장자료들이다. GOCI 엽록소 농도 산출 알고리즘(GOCI Chl-a)은 부유물과 용존유기물의 영향을 모두 고려하고 네 개의 원격반사도 밴드비를 이용하여 개발하였다. GOCI Chl-a 알고리즘은 다른 알고리즘들보다 현장관측자료에 근사한 엽록소 농도 값을 산출하였다. SeaWiFS 영상자료에서 GOCI Chl-a 알고리즘은 SeaWiFS 표준 엽록소 산출 알고리즘들보다 평균 46 % 정도 보정된 엽록소 농도 값을 산출하였다. GOCI 부유물 농도 산출 알고리즘(GOCI SS)은 보편적인 두 개의 원격반사도 밴드비를 사용하지 않고, Ahn et al.(2001)의 원격반사도 단일밴드 방법을 사용하여 개발하였다. GOCI 용존유기물 산출 알고리즘(GOCI $a_{dom}$)은 원격반사도 밴드비 $R_{rs}(412)/R_{rs}(555)$와 $a_{dom}(\lambda)$)의 상관관계를 이용하여 개발하였다. GOCI 엽록소 형광 알고리즘과 GOCI 적조분석 알고리즘은 Ahn and Shanmugam(2007)와 Ahn and Shanmugam(2006)의 연구들에 의해 각각 개발되었다. 2010년 6월경에 GOCI의 성공적인 발사가 이루어지면 추후 GOCI 자료의 검보정 연구를 통해 개발된 알고리즘들의 문제점을 분석하고, 한반도 주변 해역의 해양 광 특성 현장자료의 지속적인 업데이트를 통한 알고리즘들의 개선작업이 이루어질 것이다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2002년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.208-208
• /
• 2002

Relationship between chlorophyll a in the East China Sea and spectral bands (412, 443,490, (510), 555, (676,765) in) of OSMI (Ocean Scanning Multi-Spectral Imager) including the profile multi-spectral radiometer (PRR-800) was studied. The values of remote sensing reflectance (Rrs) at the bands corresponding to the field chlorophyll a in α in the East China Sea were much higher than those in clear waters off California, USA. In case of the particle absorptions related to the chlorophyll a concentration at the spectral bands (440, 670 nm) were much higher in the East China Sea than the ones in the clean waters off California. The normalized water leaving radiances (nLw) at 412, 443, 490, 555 m of OSMI and field chlorophyll a in the East China Sea were correlated each other. According to the results, the relationship between field chlorophyll a and nLw 410 m in OSMI bands was the lowest, whereas that between the field chlorophyll a and nLw 555 nm in the bands was the highest. Reciprocal action between the field chlorophyll a and the band ratio of the OSMI bands (nLw410/nLw555, nLw443/nLw555, nLw490/nLw555) was also studied. Correlation between the chlorophyll a and the band ratio (nLw490/nLw555) was highest in the OSMI bands. Relationship between the chlorophyll a and the ratio (nLw443/nLw555) was higher than one in the nLw410/nLw555. The difference in the estimated chlorophyll α (mg/m3) between OSMI and SeaWiFS (Sea Viewing Wide Field-of-View Sensor) at the special observing stations in the northern eastern sea of Jeju Island in february 25, 2002 was about less than 0.3 mg/m3 within 3 hours. It is suggested that OC2 (ocean color chlorophyll 2 algorithm) be used to get much better estimation of chlorophyll α from OSMI than the ones from the updated algorithms as OC4.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
• /
• pp.479-482
• /
• 2006

The absorption coefficient and backscattering properties of phytoplankton were calculated from the Mie theory. Given a simple case that phytoplankton and mineral particles are the only constitutions in seawater, the reflectance $b_b({\lambda})/[a({\lambda})+b_b({\lambda})]$was analyzed. Then the chlorophyll concentrations were estimated from remote sensing OC2 algorithm. The results show that reflectance in short wavelength region is more sensitive to the Chl variation; High mineral concentrations in seawater have significant influence on the reflectance spectrum; the existence of high mineral concentration may result in the mistake in chlorophyll estimation from OC2 algorithm.

• 대한원격탐사학회지
• /
• 제24권4호
• /
• pp.325-331
• /
• 2008

본 연구는 MODIS에서 제공하는 클로로필 정보를 기반으로 하여 2단계 필터링을 통해 우리나라 동해, 남해 연안에 대규모로 발생했던 Cochlodinium polykrikoides 적조를 탐지하는 알고리즘을 제시한다. 일반적으로 적조 탐지 연구들은 클로로필과 적조 발생의 상관성을 이용하여 클로로필의 농도가 높은 해역을 적조 발생 해역으로 탐지한다. 하지만 이 방법의 문제점은 적조가 발생하지 않은 해역을 적조 발생 해역으로 탐지함으로써 포함오차(Commission error)를 발생시킨다는 것이다. 따라서 본 연구에서는 이러한 문제점을 극복하기 위해 MODIS에서 제공하는 클로로필 정보를 바탕으로 적조 발생 해역을 추출하고, 2단계 필터 링 과정을 적용함으로써 진해, 여수, 남해도 부근 해역에서 발생한 포함오차를 제거하였으며, 그 결과를 국립수산과학원의 적조속보자료와 함께 시각적 정량적으로 평가하여 본 연구에서 제안한 알고리즘의 효용성을 검증하였다.

• 한국환경과학회지
• /
• 제10권6호
• /
• pp.431-436
• /
• 2001

Variations in phytoplankton concentrations result from changes of the ocean color caused by phytoplankton pigments. Thus, ocean spectral reflectance for low chlorophyll waters are blue and high chlorophyll waters tend to have green reflectance. In the Korea region, clear waters and the open sea in the Kuroshio regions of the East China Sea have low chlorophyll. As one moves even closer In the northwestern part of the East China Sea, the situation becomes much more optically complicated, with contributions not only from higher concentration of phytoplankton, but also from sediments and dissolved materials from terrestrial and sea bottom sources. The color often approaches yellow-brown in the turbidity waters (Case Ⅱ waters). To verify satellite ocean color retrievals, or to develop new algorithms for complex case Ⅱ regions requires ship-based studies. In this study, we compared the chlorophyll retrievals from NASA's SeaWiFS sensor with chlorophyll values determined with standard fluorometric methods during two cruises on Korean NFRDI ships. For the SeaWiFS data, we used the standard NASA SeaWiFS algorithm to estimate the chlorophyll_a distribution around the Korean waters using Orbview/ SeaWiFS satellite data acquired by our HPRT station at NFRDl. We studied In find out the relationship between the measured chlorophyll_a from the ship and the estimated chlorophyll_a from the SeaWiFs satellite data around the northern part of the East China Sea, in February, and May, 2000. The relationship between the measured chlorophyll_a and the SeaWiFS chlorophyll_a shows following the equations (1) In the northern part of the East China Sea. Chlorophyll_a =0.121Ln(X) + 0.504, R²= 0.73 (1) We also determined total suspended sediment mass (55) and compared it with SeaWiFS spectral band ratio. A suspended solid algorithm was composed of in-.situ data and the ratio (L/sub WN/(490 ㎚)L/sub WN/(555 ㎚) of the SeaWiFS wavelength bands. The relationship between the measured suspended solid and the SeaWiFS band ratio shows following the equation (2) in the northern part of the East China Sea. SS = -0.703 Ln(X) + 2.237, R²= 0.62 (2) In the near future, NFRDI will develop algorithms for quantifying the ocean color properties around the Korean waters, with the data from regular ocean observations using its own research vessels and from three satellites, KOMPSAT/OSMl, Terra/MODIS and Orbview/SeaWiFS.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
• /
• pp.487-490
• /
• 2006

Ocean Color Monitor (OCM) onboard the Indian Remote Sensing Satellite IRS-P4 has been used to retrieve chlorophyll concentration in the Bay of Bengal and the Arabian Sea using a bio-optical algorithm. Cloud masking and atmospheric corrections have been performed before applying mapping function to derive chlorophyll concentration from IRS-P4 OCM data. We have retrieved chlorophyll concentration from OCM, and MODIS during the summer and winter season along the eastern and western coast of India at every 1 degree latitude at increasing distance (25, 50, 100, 150 and 200km) away from the coast as well as near river mouths for the period 2000-2003. We have also studied spatial and temporal dynamics of monthly MODIS Aqua (for period July 2002-April 2004). The seasonal dynamics of chlorophyll concentration over the Bay of Bengal and the Arabian Sea have been discussed using OCM and MODIS for both the coastal region and the open sea.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 1998년도 Proceedings of International Symposium on Remote Sensing
• /
• pp.307-312
• /
• 1998

The paper first describes the atmospheric correction algorithm for the Ocean Color and Temperature Scanner (OCTS) visible band data used at Earth Observation Center (EOC) of National Space Development Agency of Japan (NASDA). It uses 10 candidate aerosol models including "Asian dust model" introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670 and 865 nm bands where the reflectance of the water body can be discarded, the algorithm selects a pair of aerosol models that accounts best for the observed spectral reflectances to synthesize the aerosol reflectance in other bands. The paper also evaluates the performance of the algorithm by comparing the satellite estimates of water-leaving radiance and chlorophyll-a concentration with selected buoy-and ship-measured data. In comparison with the old CZCS-type atmospheric correction algorithm where the aerosol reflectance is as-sumed to be spectrally independent, the OCTS algorithm records factor 2-3 less error in estimating the normalized water-leaving radiances. In terms of chlorophyll-a concentration estimation, however, the accuracy stays vey similar compared to that of the CZCS-type algorithm. This is considered to be due to the nature of in-water algorithm which relies on spectral ratio of water-leaving radiances.

• 대한원격탐사학회지
• /
• 제14권3호
• /
• pp.262-276
• /
• 1998

The paper first describes the atmospheric correction algorithm for the Ocean Color and Temperature Scanner (OCTS) visible band data used at Earth Observation Center (EOC) of National Space Development Agenrr of japan (NASDA). It uses 10 candidate aerosol models including "Asian dust model" introduced in consideration of the unique feature of aerosols over the east Asian waters. Based on the observations at 670 and 865 nm bands where the reflectance of the water body can be discarded, the algorithm selects a pair of aerosol models that accounts best for the observed spectral reflectances to synthesize the aerosol reflectance in other bands. The paper also evaluates the performance of the algorithm by comparing the satellite estimates of water-leaving radiance and chlorophyll-a concentration with selected buoy- and ship-measured data. In comparison with the old CZCS-type atmospheric correction algorithm where the aerosol reflectance is assumed to be spectrally independent, the OCTS algorithm records factor 2-3 less error in estimating the normalized water-leaving radiances. In terms of chlorophyll-a concentration estimation, however, the accuracy stays very similar compared to that of the CZCS-type algorithm. This is considered to be due to the nature of in-water algorithm which relies on spectral ratio of water-leaving radiances.

• 대한원격탐사학회지
• /
• 제16권4호
• /
• pp.315-325
• /
• 2000

Observations were made to validate ocean color algorithms in the Ulleung Basin, East Sea in May 2000. Small scale and meso-scale surveys were conducted for the validation of ocean color products (nLw: normalized water-leaving radiance and chlorophyll concentration). There were discrepancies between SeaWiFS and in situ nLw showing the current aerosol models of standard SeaWiFS processing software are less than adequate (Gordon and Wang, 1994). Applying the standard SeaWiFS in-water algorithm resulted in an overestimation of chlorophyll concentration. This is because that CDOM absorption was higher than the estimated chlorophyll absorption. TSS concentration was also high. Therefore, the study region deviated from Case 1 waters. The source of these materials seems to be the entrainment of coastal water by the Tsushima Warm Current. Study of the bio-optical properties in other season is desirable.