According Earth by the superimposition of images obtained from

According
to Department
of Environmental Protection State of Florida,
A wetland is a land area that
is saturated with water, either permanently or seasonally, such that it takes
on the characteristics of a distinct ecosystem 1. According to Khan et al, 2
wetland holds water for a significant duration sufficient to support organism
adapted to life in inundated or saturated soil condition and consists of wide
variety of types ranging from lakes, rivers and coastal forest to deep-water
paddy fields and ponds. According to American Society
of Civil Engineers (ASCE), a retention basin is used to manage storm water runoff to
prevent flooding and downstream erosion, and improve water quality in an adjacent
river, stream and lake or bay 3Any
city is surrounded by different types of wetlands. These wetlands are
subdivided into several categories. Two categories of wetland has been considered
in this study:  1)
Open water body comprises marshy and peaty inundated (during significant part
of the year) low-lying areas of the Balu floodplains.2)
Inland water body includes the lakes, ponds and connecting canals of different
water bodies in the city area.3.2. Data and Software Used:In
order to compare the wetland change of the Eastern Dhaka, data were collected by
digitizing the Google Earth and analyzing Landsat TM image. Google Earth is a virtual
globe, map and geographical information program that was
originally called EarthViewer 3D created by Keyhole, Inc. and now owned by
Google Inc. It maps the Earth by
the superimposition of images obtained from satellite
imagery, aerial photography and geographic information
system (GIS) onto a 3D globe. Most land areas are covered in
satellite imagery with a resolution of about 15 m per pixel in Google Earth.
Projected coordinate system of the Google Earth data is UTM (Universal Transverse
Mercator).For this study four years (2004, 2008, 2012 and 2016) Google Earth
Pro data was used. Data was acquired as KML file from Google Earth which was converted
into Bangladesh Transverse Mercator (BTM) projection system using ArcGIS
software. The Landsat program is
the longest-running enterprise for acquisition of satellite
imagery of Earth. Landsat
Thematic Mapper (TM) was sent on the space March 1, 1984 and was
active until June 5, 2013 4 .Images consist of seven spectral bands with a
spatial resolution of 30 meters. The Landsat TM image was collected from the
Landsat Look Viewer sponsored by United States Geological Survey (USGS) 5.In
this study one images of October 22, 1996 was downloaded in TIFF (Tagged Image
Format File) format. Projected coordinate systems of this image was WGS84
(World Geodetic System 84) which was converted into Bangladesh Transverse
Mercator (BTM) projection system using ArcGIS software.The
study has been carried out under the framework of Geographic Information System
(GIS). The Image Processing tasks have been carried out. GIS analysis has been
carried out using Arc Map 10.2.2 software (ESRI, Redlands, California, USA).Excel
was used to analysis vector data. Image processing software Picasa was used to
process the image and analysis the data. 
Table 1: Acquisition of data and source
list3.3. Data Processing and Analysis:Data
processing and analysis scheme used for the study is illustrated using a flow
chart as in the following figure: Figure: Flow chart for Analysis of Landsat Image.The
Landsat TM image was collected in .tiff (Tagged Image Format File) which
provides geo-referenced image in WGS84 Projected Coordinate System. Two images
from 22 October 1996 was used to cover study area. The geo-referenced two
photos were mosaic to obtain the image of the whole study area. Then thematic
data layers were generated from the geo-referenced images using on-screen
digitization technique .Wetlands were identified and redrawn using editor tools
in ArcMap. Polygon option was used as we needed area data for comparison. Data
layers were generated in ArcInfo vector format using the digitization tools of
Arc Map 10.2.2. In case of Google Earth Data Retrieval, wetlands were digitized
on Google earth as polygon and imported as .KML file. Which was converted into
layer using conversion tool of ArcMap. Then it was exported as Shape file (.shp).Resolution
of Google Earth images were very fine that no mosaic of images needed. Then
vector analysis was run as before. Area was measured in square meters which is
default in BTM Projected Coordinate System. 
Figure:
Flow chart of acquiring data from Google Earth. 
References: 1. Department of
Environmental Protection State of Florida www.dep.state.fl.us/evergladesforever/about/glossary.htm# 2.M. S. Khan, E. Huq, A. A.
Rahman, S. Huq, S. M. A.Rashid, and H. Ahmed, et
al., “Wetlands of Bangladesh,”Bangladesh Centre for
Advanced Studies (BCAS)in association with Nature
Conservation Movement (NACOM), Dhaka, Bangladesh, 1994. 3. American Society of Civil
Engineers ASCE Manual and Report on
Engineering Practice No. 87. 1998. ISBN 1-57278-039-8. Chapter 5. 4. N.M. “The LANDSAT
Tutorial Workbook: Basics of Satellite Remote Sensing”NASA Reference Publication
1078. NASA. Retrieved 20 September 2011. 5.
landsatlook.usgs.gov/viewer.html Study Area:The Eastern Dhaka is our study area which is located between longitude
90?24.78′ E   
& 90?29.37′ E   and latitude
between 23?54.98’N & 23?42.62’N. Eastern
Dhaka about 55,410,395 square meters of retention ponds were found which has
now at 2016 came down to about 3,819,937 square meters; which is about 7% of
the earlier. A total of 51,590,458 square meters of wetlands are lost in this
time . The physical geography of  Bangladesh is
varied and has an area characterized by two distinctive features: a broad deltaic plain subject to frequent flooding, and a small hilly region crossed by swiftly flowing rivers.Two major river Turag and
Buriganga are flowing  across the hole city . Balur river , Tongi khal ,
Joydevpur , Savar areas are beside the Eastern Dhaka.  This part of 
Dhaka is highly densed and this causes high ranged of infrastructure
development that is not well planned. That unplanned  structure decrease the wetland in drastical
rate which is so much dangerous for entire Dhaka not only for the eastern part
.  

It
is observed that some 60% of the eastern Dhaka regularly goes under water every
year between June and October due to lack of flood protection. Within our total
study region (1996-2016), Bangladesh faces floods in almost every year. But the
major flood s occurs in 1998 and 2004. In this continuation, 2008 also faced
flood which lasted for July- November. The flood water took a huge time to get
away from the low lands. But the other side’s condition is so much scaring. It
took

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