GEODETIC DETACHMENT(Geodesy)

Geodesy is one of the oldest science that determines the size & shape of the Earth & the inter relation of selected points on its surface. It also deals to provide an accurate geometrical framework for the control of Topographical & other Surveys, to locate tile origins of Survey (Geodetic origin & Grid origin), to define coordinate systems for three dimensional positioning and to determine the variation of phenomena near to or on the surface of the earth such as Gravitv, Tides, Earth Rotation, Crustal Movement & Deflection of Plumb Line etc.

Geodetic Detachment is an important unit of SOB under Defense Survey Directorate to carryout Geodetic activities in Bangladesh.

Geodetic Detachment

TOTAL MANPOWER : 17

•	Asstt. Director (Survey)	:01	(Class I = 01)
•	Sub Asstt.Supdt.	:02
•	Technical Assistant	:05
•	Surveyor	:02	(Class III = 14)
•	Computer	:04
•	Driver	:01
•	MLSS	:02	(Class IV = 02)

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                 Total                                 :17

>GEODETIC CONTROL POINTS OF BANGLADESH

[AS ON ..............,2012]

 

RESPONSIBILITIES OF GEODETIC DETACHMENT

• To maintain the National Horizontal and Vertical datum at GULSHAN, DHAKA, the Tidal Observatory at RANGADIA, CHITTAGONG and six Permanent GNSS Station at Dhaka, Chittagong, Rajshahi, Khulna, Maulavibazar & Rangpur.
• To establish Geodetic control point [Horizontal (by Traverse, Triangulation and Global Navigation Satellite System) & vertical (by precise leveling)] throughout the country and maintain them.
• To carryout tidal observation, determination and maintainingof Mean Sea Level (MSL).
• Preservation of Geodetic control point data & tidal data and provide them to various users as per requirement.
• To carryout departmental and extra- departmental ground control survey work as per requirement.
• To update the Geodetic control points by re-survey if there is any major change.
• Preparation of Geoidal Model & Geoid Map of Bangladesh.

Techniques of Geodetic survey

• Triangulation by Transit
• Trilateration by EDM         [ Electronic Distance Measuring Instrument]
• Travesing by Totalstation                  [ Transit & EDM ]
• Levelling by Level
• Baseline measurement by GPS

MAJOR EQUIPMENTS USED IN GEODETIC DETACHMENT

Determination of horizontal Datum of Bangladesh.

Although a geodetic control point in Gulshan had been used as a temporary horizontal datum of Bangladesh before 1990, the accuracy of its coordinates had not examined and the coordinates referred to Everest 1830. Because GPS refers to WGS 84, it is better to give not only Everest 1830 coordinates but also WGS 84 coordinates to the control points in Bangladesh. Consequently, the geodetic horizontal datum of Bangladesh was established in Glushan by repairing of the old control point monument and the coordinates on WGS 84 were determined by global GPS observations refers to four IGS observation stations; Wettzell (Germany), Hartebeesthoek (South Africa), Yaragadee (Australia) and Tsukuba (Japan) shown in Figure.

These four stations are operating not only continuous GPS observation stations for International GPS Society (IGS) but also Very Long Baseline Interferometry (VLBI) site or Satellite Laser Ranging (SLR) site. VLBI and SLR arc the most precise global geodetic observation technique which can determine the coordinates in few milimetres accuracy and arc operating to maintain the global geodetic reference system. This means that the coordinates of these stations are maintained most precisely. The GPS observation which connects the datum of Bangladesh to the stations was carried out for seven days, from 17 September to 23 September in 1994. The data was processed by Geodetic Department, GSI, Japan, using GAMIT baseline analysis software developed by Massachusetts Institute of Technology and University of California, and GLOBK network adjustment software developed by Massachusetts Institute of Technology, University of California and Harvard University.

FOUNDATION STONE	National Geodetic Horizontal Datum Of Bangladesh

On the other hand, the most reliable coordinates on Everest 1830 was examined using GPS data for first order control point surveying. The GPS network included 24 old existing monuments which had coordinates on Everest 1830. The network was adjusted by free network adjustment technique using 19 stations out ofthe 24 old stations to examine the reliability of the old coordinates. As a result, the coordinates of this adjustment was adopted as the "Old" Everest 1830 coordinates.

Finally, both of the coordinates on WGS 84 and on "Old" Everest 1830 were given to the Datum of Bangladesh in Gulshan, then the transformation parameters between the two coordinate systems at the datum was computed.

GNSS(Global Navigation satellite System )/GPS (Global Positioning System)

 Geodetic Detachment of SOBcarriedoutGNSS/GPS observation since 1994. To established Geodetic network (Horizontal) throughout the country by GNSS/GPS survey and get co-ordinates in WGS-84.

Horizontal Control Network	GPS Observation

•  Horizontal Control Points Connected by GPS  ......883

Any Govt./NGO and other private organization should get the information/data by applying through SOB web site form. Then payment consulate price for that.

Establishment of Vertical Control Network in Bangladesh with new MSL
 

Before 1990 we did not have our own MSL, so we used the height with respect to old MSL located in India. And we could not do the network adjustment. But with tile effective financial and technical assistance of the Government of Japan through Japan International Cooperation Agency (JICA) we stepped to a new area of First Order Leveling Network during 1991- 1995 under a grant aided project.

 

Foundation Stone	National Vertical Datum, Gulshan, Dhaka	National GeodeticVertical Datum Of Bangladesh

During that period we established a Tidal Observatory at Rangadia, Chittagong, a National Vertical Datum ‘atGulshan, Dhaka, 465 benchmarks on about 2386 km first order leveling route covering 70% area of the country excluding coastal and hill tract districts.

To extend the vertical control network in the districts of coastal and hill tract area of the country, Survey of Bangladesh has taken a geodetic leveling work in 2001 and was completed in 2004 under Annual Development Project (ADP) of the Govt. of Bangladesh.

In 1992, Tidal Station established between the jetty of Chittagong Fertilizer Ltd (CUFL) & Karnafuly Fertilizer Company (KAFCO) in the bank of Karnafuly river at Rangadia in Chittagong; to measurement MSL of Bangladesh. Tidal data (Long term data) is being collected for observing natural climate, rise & fall problem, i.e. `high and low water’ problem. Tidal data is being collected by two methods –Digital System & Analogue system. We collect data in PCMC card & then download to a computer & print it. We collect 6 seconds raw data. Analogue data is being collected by counting graph paper. We compare it with digital data. After collecting data, we convert it in excel (text data i.e. hourly data)format & storedin Compact Disk.

Yearly MSL: Yearly MSL is being calculated by averaging monthly data of a year, monthly MSL is being calculated by averaging daily data of a month & daily MSL is being calculated by averaging hourly tide level & 24 hours of a day.

 

Tidal Station, Rangadia, Chittagong	Tidal Station, Rangadia, Chittagong	Digital Fuess Type Tide Gauge

It becomes Indian Ocean Tsunami Warning System under International oceanographic Commission of UNESCO by Global Sea Level Observing System from June, 2007.So Tidal station is very important  internationally when it related with Global Sea Level Observing System.

Any Govt/NGO and other private organization should get the information/data by applying through SOB web site form. Then payment consulate price for that.

Leveling
Geodetic Detachmentmainly done High Precession(HP)leveling. To established Geodetic vertical control point covering the country by leveling survey.

 

Digital Levelling Observation	Digital Levelling Observation
River Crossing	Analogue Levelling Observation

Vertical control Network

• Vertical Control Points Connected by Leveling : ....1711

At present total 1st Orderleveling route approximately : 3800 km

And total 2nd Orderleveling route approximately : 5800 km

Any Govt/NGO and other private organization should get the information/data by applying through SOB web site form. Then payment consulate price for that.

PERMANENT GNSS STATION Network in Bangladesh

The main focus to establish GNSS CORS (Continuously Operating Reference Station) Network, which are mainly collection and installation of digital equipment of GNSS Stations and Data Centre (Server). The GNSS Network will be the Infrastructure of precise positioning and navigation in Bangladesh.

SOB established six Permanent GNSS Station at Dhaka, Chittagong, Rajshahi, Khulna, Maulavibazar & Rangpur, which were continuously operating since 19 December,2011. It has

Permanent GNSS Station	GNSS Network	GNSS CORS Station

also Data Center (server) for GNSS CORS. Inside Server VRS(Virtual Reference Station) Software is running. We compute six CORS station with respect to IGS Station surrounding Bangladesh in Bernese & input the co-ordinate to the VRS NET as a reference. This is aWeb based service to deliver GPS/GNSS data to all users.

SOB VRS WEB IP: 202.53.170.98:8011

The objectives of GNSS Station are:

• To render GNSS (GPS) service to the RTK (Real Time Kinematics) & Post Processing GNSS (GPS) users (first and foremost the Survey of Bangladesh) by providing reference GNSS (GPS) data and correction messages through internet.
• To monitor the tectonics plate movement in Bangladesh.
• To predict earthquake vulnerability of different areas in Bangladesh.
• To update all Geodetic control network of Bangladesh with better accuracy.
• To detect the displacement and subsidence precisely after major disasters in order to estimate damage assessment.

Bangladesh Metrological Department can use the GNSS data for more precise and real time weather forecast. Directorate of Land Records and Surveys (DLRS) will be able to make Digital Mouza Map very easily, quickly and precisely by using this GNSS Network.BIWTA can carry out very precise Hydrographic survey and navigation with the help of proposed GNSS Network.

Layout design, alignment Survey of complex projects like Padma Bridge, Ruppur Atomic Power Plant, Subway, expressway, Sky rail, etc. becomes faster, precise and cost economic.Citizens can benefit from modern technology like car tracking, car navigation, fleet management, children tracking, etc.Disaster preparedness and response becomes easier due to precise positioning and elevation data.