Browsing by Author "Tonooka, H."

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Assessing the potential of satellite and ground spectral data for Chlorophyll-a monitoring in Lake Kasumigaura, Japan
(IEEE, 2014) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
The suitability of a handheld spectrometer and ASTER satellite data for monitoring Chlorophyll-a (Chl-a) in Lake Kasumigaura, Japan was tested in July 2010 to December 2013. ASTER based Chl-a retrieval algorithms were developed support with in-situ Chl-a, MODIS OC3 Chl-a and Kakemaoki and Koshin automated water quality monitoring stations Chl-a. ASTER VNIR band ratio were regressively analyzed with the corrected MODIS Chl-a and automated station values obtained for each ASTER date on a day by day basis. The regression equation of the ASTER band ratio (B1/B2), with highest correlation was used to generate high-resolution Chl-a distribution maps. Significant correlation between the ratio of the reflectance peak at 705 nm and the Chl-a absorption at 678 nm and the in-situ Chl-a content was observed and these reflectance ratios were used to establish spectrometric Chl-a estimation algorithms. Proposed algorithms can be successfully adopted to determine localized environmental effects in the Lake.
Change detection in the channel segment of Negombo Estuary, Sri Lanka using time series satellite data and its possible impacts on estuarine productivity
(The Asian Fisheries Society, 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
CHLOROPHYLL-A MONITORING IN SRI LANKAN ESTUARIES USING ALOS/ANVIR-2 DATA
(International Geo Science and Remote Sensing symposium, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Coastal water body database to monitor the water quality and land use changes from remote sensing data
(Remote Sensing Society of Japan (RSSJ), 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Comparison of three chlorophyll-a estimation approaches using ASTER data acquired over Sri Lankan coastal water bodies
(Malaysian Journal of Remote Sensing & GIS (MJRS&GIS), 2015) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
In the present study, we compare the following Chlorophyll–a (Chl-a) estimation algorithms using ASTER data acquired over Sri Lankan coastal water bodies: (1) the simple band-ratio algorithm with simple atmospheric correction using dark object subtraction (DOS); (2) the single band-ratio algorithm with radiative transfer-based atmospheric correction using ENVI’s FLAASH software including MODTRAN; and (3) our previously proposed algorithm based on combinations of ASTER and corrected MODIS Ocean Color-3 (OC3) data. First, several ASTER band ratios were regressively analyzed with in-situ Chl-a data acquired from the Negombo estuary and Puttalam lagoon in the west coast of Sri Lanka, and the band ratio with the highest correlation was selected. Then, time-series Chl-a distribution maps with the spatial resolution of ASTER/VNIR (15 m) were generated using the above three methods, and compared with the in-situ Chl-a data. Based on the result obtained, the FLAASH and ASTER/OC3 based methods showed high correlation with the in-situ Chl-a values (R2 = 0.96 and 0.92 respectively), while the DOS based method showed low correlation (R2 = 0.61), which indicates that the ASTER/OC3 based method will give equivalent performance to the FLAASH based method even though it does not need user-based atmospheric correction like the DOS and the FLAASH based methods.
Development of coastal water body database on KISSEL server
(IEEE, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Monitoring of coastal water bodies in all the relevant aspects was highly important for the sustainable use of those. To achieve this all the research findings should be easy access and presenting those in a user friendly manner will be more advantage. In Sri Lanka, there was not fully or never developed database on research findings especially on coastal water bodies. Thus we developed a Sri Lankan coastal water body database (CWBDS) on KISSEL server system which can be benefitted all the interest communities including general public. Presently it include water quality data over two decades of lagoons and estuaries and in near future it will update with support from universities and research organizations including research on biodiversity, fisheries, land use, socio economics, topography, water circulation, pollution etc.
Eutrophication Trends in Bolgoda North Lake, Sri Lanka
(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Perera, B.D.C.; Wijeyaratne, M.J.S.; Dahanayaka, D.D.G.L.; Tonooka, H.; Minato, A.; Ozawa, S.
Chlorophyll-a (Chl-a) concentration in the Bolgoda North Lake (06.400 – 06. 480 N; 079. 550 -079. 580 E), which is a shallow brackish water body situated in the western coastal region of Sri Lanka, was determined through correlating Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) optical sensor data with in-situ data measured from April 2013 to October 2013 in 05 sampling sites. ASTER band ratio of B1/B2 which gave the highest correlation with in-situ Chl-a data was used to generate 15 m resolution Chl-a distribution maps. Chl-a distribution maps generated using ASTER data indicated that most areas of Bolgoda North Lake were eutrophic. Some regions of the Weras Ganga which flows into the Lake showed very high Chl-a concentrations during April indicating hypereutrophic conditions while in June, September and October these areas indicated eutrophic conditions. Observations on land use pattern revealed that industrial zones border these areas. High Chl-a concentrations were also observed in the areas bordered by the lands with low income houses from which household waste as well as sewage are discharged directly to the lake. Chl-a distribution maps developed for 2005, 2008, 2010 and 2011 revealed that eutrophication of the Bolgoda North Lake has gradually increased in the recent past. This may possibly be due to the increase in the industrial effluents as a result of industrial development in the area and also due to increased population of low income groups that live in some areas bordering the lake.
Evaluation of Chlorophyll retrieval algorithm using an intermittently closed tidal estuary: The Chilaw lagoon in the west coast of Sri Lanka
(Remote Sensing Society of Japan (RSSJ), 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Feasibility Study for the Estimation of the Chlrophyll-a Using ASTER Data in an Eutrophic Lake, Sri Lanka
(Japan Geoscience Union, Japan., 2014) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
The objective of this study is to evaluate the performance of the previously proposed band ratio approach in estimating Chl-a in Bolgoda Lake, Sri Lanka as a representative example of Case II waters. Lake is located at western province in an area with lot of industries and also with some agricultural activities. Considerable amount of industrial effluents are discharged into it. Illegal filling and also encroachment has occurred in the recent past. This study focused on to determine the trends in eutrophication via Chl-a changes during the recent past, make predictions and recommend mitigatory measures and suggest precautionary measures to restore the environment. From March to December 2013, water samples at 5 points of Lake were collected once per month parallel to ASTER overpass and Chl-a of each sample was measured using a laboratory spectrophotometer. Cloud-free ASTER scenes acquired over Lake under clear sky conditions were selected during 2000 to 2013 for Chl-a estimation and trend analysis. All the ASTER images were atmospherically corrected using FLAASH and in-situ Chl-a data on Lake were regressively analyzed with atmospherically corrected three ASTER VNIR band ratios such as B1/B2 of the same date. Finally, the regression equation of the band ratio with highest correlation (B1/B2; R2 = 0.78) was used to develop algorithm for generation of 15-m resolution Chl-a distribution maps using atmospherically corrected time series satellite imageries in day by day basis. This method applied for ASTER band 1/2 ratio due to Chl-a is positively correlated with the green band reflectance and negatively correlated with the red band reflectance. Therefore, the reflectance ratio of green and red bands becomes a robust parameter to estimate the Chl-a content. According to the ASTER based Chl-a distribution maps it is clearly evident that eutrophication of the Bolgoda Lake has been gradually increased from 2005-2011. Further, results showed that there were significant eutrophic conditions throughout the year 2013 in several parts of the Lake and considerable spatial heterogeneity with higher concentrations being recorded water stagnant areas and in water adjacent to freshwater outlets. It is clear that Bolgoda Lake is apparently a disposal site of various discharges of factories in addition to poor drainage and sewage systems present in this area. Highly unplanned urbanization and absolutely lack of adequate waste disposal management facilities in industries close to Lake have resulted in pollution of water. If the present trend of waste disposal and unplanned urbanization continue, they would create enormous environmental problems in future. Results of the present study showed that information from satellite remote sensing can play a useful role in determining the changes in Chl-a related to eutrophication in Bolgoda Lake and in the development of time series Chl-a distribution maps. Such information is important for the future predictions, development and management of this area as well as in the conservation of biodiversity. Therefore we recommend incorporation with this technique for routine monitoring of water quality using multi satellite data such as ASTER in inland water bodies like Bolgoda Lake in the future.
Integration of multisource data for chlorophyll-a monitoring in Negombo estuary, Sri Lanka
(IEEE, 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
In order to estimate chlorophyll-a concentration (Chl-a) for tropical coastal estuarine environments using satellite optical sensor, observations were conducted from 1987 to 2009 in Negombo estuary, Sri Lanka, with support with available in-situ measurements. Landsat band ratios were regressively analyzed with available in-situ Chl-a data. This relationship was used for correcting MODIS OC3 Chl-a values, and then ASTER band ratios were regressively analyzed with the corrected MODIS values. The regression equations obtained for ASTER and Landsat were used to develop algorithms for generation of 15m and 30m resolution Chl-a distribution maps, respectively, in Negombo estuary using atmospherically-corrected time-series imageries. The results indicate that some parts of the estuary have increased eutrophication conditions during 1987-2009.
Monitoring eutrophication trends in Bolgoda North Lake, Sri Lanka by Satellite Remote Sensing
(Central Fisheries Research Institute (CFRI) Trabzon, Turkey in cooperation with Japan International Cooperation Agency (JICA), Japan, 2016) Dahanayaka, D.D.G.L.; Perera, B.D.C.; Wijeyaratne, M.J.S.; Tonooka, H.
This study was aimed to determine the present level and past trends of eutrophication of the Bolgoda North lake, Sri Lanka using in situ Chlorophyll-a (Chl-a) measurements and remote sensing data obtained from Advanced Space-borne Thermal Emission and Reflectance Radiometer (ASTER) satellite data. From March to October 2013, Chl-a, nitrate and phosphate contents of the lake were measured once a month on the days of ASTER overpass and using standard laboratory methods. Cloud-free ASTER images of the lake for the 2000-2013 period were atmospherically corrected using Fast Line-ofsight Atmospheric Analysis of Hypercubes (FLAASH) and in-situ Chl-a data were regressed with atmospherically corrected three ASTER Visible and Near Infrared band ratios of the same date. The green/red band ratio, which had the highest coefficient of determination, was used to develop algorithm for generation of 15-m resolution Chl-a distribution maps. Results indicated that eutrophication of this lake has increased from 2008 to 2011. Heavy eutrophic conditions were noted in several regions of the lake in 2013, especially in water stagnant areas and adjacent to freshwater inlets. Unplanned urbanization and inadequate facilities for waste management have resulted in heavy eutrophication of the water body. If the present trends of waste disposal and unplanned urbanization continue, enormous environmental problems would be resulted in future.
Monitoring land use changes and their impacts on the productivity of Negambo Estuary, Sri Lanka using time series satellite data
(Asian Fisheries Society, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
On natural disasters in the Asia Pacific region
(Faculty of Social Sciences, University of Kelaniya, 2009) Ozawa, S.; Dassanayake, G.; Patu, V.; Tonooka, H.; Noguchi, H.; Itaba, M.; Minato, A.; Karunathilake, K.
Preliminary estimation of chlorophyll concentration in a tropical coastal lagoon in Sri Lanka
(Remote Sensing Society of Japan (RSSJ), 2010) Dahanayaka, D.D.G.L.; Tonooka, H.; Minato, A.; Dassanayaka, G.; Wijeyaratne, M.J.S.; Ozawa, S.
Retrieval of Chlorophyll- a using satellite and ground spectral data in Japanese and Sri Lankan water bodies
(SPIE, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
The suitability of a handheld spectrometer and ASTER satellite data for monitoring water quality in coastal waters of Sri Lanka and inland waters of Japan was tested in November 2010 to March 2012. In-situ Chlorophyll-a (Chl-a), turbidity, total suspended solid, secchi depth and reflectance data were measured at ASTER overpass times in Negombo estuary, Trincomalee bay, Puttalam and Chilaw lagoons, Sri Lanka, and in Lake Senba and Lake Kasumigaura, Japan. ASTER based Chl-a retrieval algorithms were developed support with in-situ Chl-a and MODIS OC3 Chl-a. The original MODIS Chl-a and the in-situ Chl-a were regressively analyzed for determination of a MODIS Chl-a correction equation because it may overestimate in tropical coastal waters. Then, three ASTER VNIR band ratios were compared for correlation with the corrected MODIS Chl-a and in-situ Chl-a. Finally, the regression equation of the ASTER band ratio, B1/B2, with highest correlation was used for generation of high-resolution Chl-a distribution maps. Significant correlation between the ratio of the reflectance peak at 705 nm and the Chl-a absorption at 678 nm and the in-situ Chl-a content was observed and these reflectance ratios were used to establish spectrometric Chl-a estimation algorithms. The proposed algorithms successfully determined localized environmental effects in the study areas. ASTER-based high resolution Chl-a distribution maps will be derived more precisely by further correction of these algorithms, which will be useful in mitigate impacts of the environment change in those coastal and inland water environments. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Two decadal trends of surface chlorophyll-aconcentrations in tropical lagoon environments in Sri Lanka using satellite and in-situ data
(Asian Association on Remote Sensing, 2013) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Two decadal trends of chlorophyll-a concentration (Chl-a) in Negombo estuary, Sri Lanka, were analyzed with satellite optical sensor data observed from 1987 to 2011 and in-situ measurements. Landsat band ratios were first regressively analyzed with insitu Chl-a data, and the regression equation obtained was used for generation of 30 m-resolution Chl-a distribution maps using time-series Landsat images which had been atmospherically corrected. This Landsat-based regression equation was also used to correct MODIS Ocean Color 3 (OC3) Chl-a products with an overestimation error for a tropical region, and the corrected MODIS OC3 values were then regressively analyzed with ASTER band ratios on a day-by-day basis for each ASTER observation date due to unavailability of in-situ measurements at ASTER observation dates. These regression equations based on ASTER/ MODIS-OC3 were then used for generation of 15 m-resolution Chl-a distribution maps using time series ASTER and MODISOC3 images. The above equations obtained from the Negombo estuary were also applied to Chilaw lagoon near Negombo estuary for evaluation of this approach. The results indicated that channel segments and some other parts of the Negombo estuary increased eutrophication during 1987-2011, particularly during 2000-2011, with consistency between Landsat-based and ASTER-based estimates. As a conclusion, it is mentioned that our methodology can be effectively used for prediction and mitigation of localized environmental problems including sudden fish kills frequently occurred in Negombo estuary, as a costeffective tool complementing regular monitoring programs.
Use of Kissel Server as a Platform for the Expansion of Research on the Water Quality of Asian Water Bodies
(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Monitoring of all relevant aspects of water bodies is highly important for their sustainable use. To achieve this all research findings should be easy accessible and presenting those in a user friendly manner will be highly advantageous. Therefore, development of a database on the coastal water bodies of Sri Lanka on KISSEL server system was initiated, for the benefit of all interest groups including the general public. Presently it contains water quality data of lagoons and estuaries for over two decades. This was extended from a local scale to a regional scale. In this extension, algorithm improvement or tuning based on in-situ data sets was carried out for optimization. The aim was to expand the databases on water bodies using satellite analysis within selected Asian countries. It was initiated through KISSEL server system to benefit pollution monitoring and sustainable use of water bodies. Water bodies of Japan, Sri Lanka, Vietnam, Thailand, Indonesia and Philippines were selected considering their economic and ecological importance. In-situ research parallel to satellite overpass were conducted on the following water bodies. Local Universities and/or Research Institutes collaborated with the collection of field data and will involve in future continuous monitoring programs and KISSEL related activities.