Satellite based Coastal Monitoring System (SCMS) under Oceanography

Oceanography is a branch of science which deals with the study of ocean.  It is the Physical, Chemical, Biological and Geological aspects of the oceans. The ocean extends from the shallow estuarine areas to the deeper locations of the ocean. Generally, the division is responsible in applications of space and satellite based remote sensing technology in coastal, offshore and open sea for exploration and exploitation of available resources therein.

Our Bay, the marine area of Bangladesh, is characterized by a semi-enclosed tropical basin. The coastline of the country comprises about 710 km extending from the tip of Teknaf in the south-east to the south-west coast of Satkhira. An area about 166000 km2 along more than hundreds of off-shore Islands (OSI) of Bay of Bengal (BoB), Bangladesh have been exists. Natural resources in this area have been used for multiple purposes and have strongly influenced socio-economic development.

Conventional methods for collecting information about coastal as well as off-shore Island are relatively costly and time consuming. Remote Sensing (RS) observation with its unique capability to provide cost-effective support in compiling the latest information about the environment of the OSI, while Global Navigation Satellite System (GNSS) use to collect field information for increase the accuracy of RS data and GIS facilitates uses for multidisciplinary analysis and decision support. Integrated analysis comes under the economic jurisdiction of Bangladesh for exploration, exploitation, conservation and management of its marine resources.

Under Satellite based Coastal Monitoring System (SCMS) the following recent past and current research activities are running.

Monitoring and Mapping of Coastal Morphological Changes using RS, GIS and GNSS Technology
(Central Region)

Central region of our coast begins from the Tebegins from the Tentulia river to the big Feni river estuary including the mouth of the Meghna river upto the confluence of the Padma (Ganges-Brahmaputra) and the Meghna river near Chadpur. Heavy sediment load and one of the most complex tropical esturian ecosystems of the world characterize this region. The coastline is most irregular, and consists of a series of islands, where the rivers are continuously changing their courses; the funnel shaped apex of the Bay of Bengal is relatively shallow, surrounded by numerous islands and estuarine channels- Tetulia-Rabanabad channel, Hatiya channel, and Sandwip channel. The area is dominated by semi-diurnal tidal currents, the maximum tidal range of 5 meters occurs in the Meghna estuary which gradually decreases southeastwards along the Chittagong coast. Since the last two hundred years the Meghna estuary went through intensive morphological changes with migration and the growth of islands in the southern direction. This region is also subject to the impact of cyclone and storm surges causing an innumerable loss of life and property. Figure 1a shows the exposed and interior coast including study area. Figure 1b shows the study area of satellite image.

In this study, satellite data of Landsat MSS (80 m) 1973, Landsat TM (30 m) 1989 and 2010 also tidal data of 1989 and 2010 were used to generate digital data base of different time period, analysis of plain/tidal land, erosion/accretion and waterways/channel behavior and finally produce digital map of coastal area. The study reveals that 87254.6 (hector) areas have been reclaimed in central coast during 1973-2010. To over come the above study the following activities have been developed.

      For land water separation, Near-Infrared band (0.76 to 0.90 μm) has been used because band 4 of Landat-TM is suitable for land and water separation.  In this case digital number (DN) values of water have been collected carefully from the histogram of the selected images and applied the collected vales in the developed algorithm.

      For erosion and accretion of off-shore Island (OSI), raster base GIS as well as ArcGIS based analysis have been applied for generation of erosion and accretion map of coastal area as well as OSI of Bangladesh.

      For waterways/channel behavior and tidal flat mapping, multi-temporal data have been analyzed based on raster base GIS and ArcGIS.

      Inventory of the off-shore islands under different time period and construction of temporal GIS database. 

Specifically, the generated digital data base of this study will be helpful for better planning, policy formulation, and decision-making in national development. To over come the above study the following activities have been developed.

In order to study the coastal morphological changes using RS, GIS and GNSS Technology the following objectives have been pursued

      To generate coastal morphological data sets 1973, 1989 and 2010.

      To generate morphological changes between 1973-1989-2010.

      To study the behavior of the process (Erosion and Accretion) of some selected OSI and River/Channel of the study area for the above period and generate maps.

      Inventory of the off-shore islands under different time period and construction of temporal GIS database.

 

Results and Analysis of Central Coast

(A) Analysis the coastal morphological changes

Figure 2 shows the GIS analysis of Morphological Changes of Central Coast between 1973-1989-2010

Text Box: Figure 2: GIS analysis of Morphological Changes of Central Coast between 1973 -1989 -2010

 

Figure 3 shows the Bar diagram of Morphological Changes of Central Coast between 1973-1989-2010

 

 

 

 

 

 

 

 

 

 

Text Box: Figure 3 shows the Bar diagram of Morphological Changes of Central Coast between 1973-1989-2010

 

 

It is clear seen from the figure 4 that total land has been reclaimed 87254 hectare in 2010 with respect to 1973. During 37 years period total accretion and erosion was 161333 hec and 74079 hec respectively. Figure 4 shows the Pie-chart of central coast during (1973-2010).

 

(B) Analysis the behavior of the process (Erosion and Accretion) of some selected OSI and River/Channel of the study area for the above period and generate maps (to be continued).

(C) Inventory of the off-shore islands under different time period and construction of temporal GIS database (to be continued).

 

 

 

Bathymetry mapping using Landsat-TM data

 

Coastal bathymetry is important for monitoring the emergence of new land, navigational channel maintenance as well as for fish resources tracking purposes. But coastal bathymetry undergoes frequent changes due to coastal processes such as erosion and deposition of soil.  As a result, hydrographic charts in these areas have to be updated frequently. But Hydrographic surveying by conventional ship borne sounding technique is slow and expensive. Remote sensing techniques can be used with limited ground observation to study and monitoring these changes. The unique character of the shorter weave length visible channel, such as blue (0.45-0.52m) has the ability to penetrate water to a significant depth and generates radiance that reflects submarine albedo. In this study, an attempt has been made to prepare a digital map showing the distribution of bathymetry using Landsat-TM data over coastal area (figure 1) of Bangladesh. Three simple algorithm of (i) land water delineation based on blue band, (ii) pixel intensities (Xi) and (iii) water depth (Z) were used for bathymetry mapping. The result  depicted that the average water depth recorded in this image was in between 1 to 12.5 meter depth. The depth of sea-bed varies with locations. The mouth of Haringhata river is shallower than the Shahbazpur channel because of the contribution of soil. In addition, the natural shape of the selected area supported the opportunity of deposition process and erosion. Thus, the lower water depth measurement was estimated from the satellite image. Figure 2 shows the bathymetry mapping over study area. The result was compared with theoretically idea of water depth of the location since the absent of ground measurement data.

 

Sea Surface Temperature (SST) mapping using Landsat-TM data

 

Sea Surface Temperature (SST) is important for climate modeling, study of the earth's heat balance, atmospheric and oceanic circulation patterns and anomalies (such as El Nio/La Nia) in global scale. It is also important for tropical cyclogenesis. In local scale it is used as an indicator of the environment required for the living of some marine biota. Conventional techniques of obtaining SST is time consuming and expensive. The satellite remote sensing techniques found very useful. A number of studies have been performed on bathymetry and SST mapping using TM, AVHRR and MODIS data but most of the studies have been conducted outside of Bangladesh. In this study, an attempt has been made to prepare a digital map showing the distribution of SST using Landsat-TM data over coastal area (same of bathymetry study area) of Bangladesh. The radiance and effective temperature based on Markham et. al. (1986) was used to estimate the actual temperature (T). The distribution of SST varies of location. Higher the surface temperature at the location near the shoreline compared to location farther. Distribution of higher temperature contributed by suspended sediment and residential area. Figure 3 shows the SST distribution over study area. The result was compared with theoretically idea of the typical SST and water depth of the since the absent of ground measurement data.