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- Amod Ashok Salgaonkar, Trivesh Suresh Mayekar, Avinash Rambhau Rasal, Kiran Rasal, Balkrishna Hotekar, Rakesh Jadhav, Amar Gaikwad

Corresponding author e-mail ID :



         Remote Sensing (RS) refers to the branch of science which derives information about objects from measurements made from a distance i.e. without actually coming into contact with them. Conventionally remote sensing deals with the use of light i.e. electromagnetic radiation as the medium of interaction. RS refers to the identification of earth features by detecting the characteristics electromagnetic radiation that is reflected by the earth surface. Every object reflects a portion of electromagnetic radiation incident on it depending upon its physical properties. In addition, objects also emit electromagnetic radiation depending upon their temperature & emmisivity. Reflectance pattern at different wave lengths for each object is different. Such a set of characteristics is known as spectral signature of the object. This unables identification & discrimination of objects. Visual perception of objects is the best example of remote sensing.

Stages in remote sensing :

1)    Requirement of an energy source (Sun is the main source of energy during day time.)

2)    Energy  interaction with the atmosphere

3)    Interaction with the target

4)    Recording of energy by sensor

5)    Data transmission & processing

6)    Image processing & analysis

7)    Application

Advantages of the remote sensing:

The major advantages of remote sensing over ground based methods are   

a)    Synoptic view: It facilitates the study of various features of earth surface in their spatial relation to each other & helps to delineate the required features & phenomenon.

b)    Accessibility: It makes it possible to gather information about inaccessible areas where it is not possible to gather information through ground surveys.

c)    Time: These techniques save time & efforts as information about large area can be gathered quickly.

d)    Multidisciplinary applications: Remote sensing data are useful to different disciplines such as geology, fisheries, forestry, land use etc.

Applications of Remote Sensing in fisheries :

1)    Remote sensing data help in regular management of water resources.

2)    Remote sensing techniques are useful in finding different types of bioresources.

3)    Remote sensing plays potential role in both rapid & comprehensive EIA.

4)    For detection and monitoring of the water pollution, remote sensing prove useful.

5)    Remote sensing is applicable in acquiring information regarding offshore engineering activities, fisheries surveillance, ocean features, coastal regions and storm forecast operations.

6)    Remotely sensed data provides the necessary spatial data on suspended sediments, dissolved organic matter, phytoplankton, algal blooms & oil slicks etc which will useful in management of fish stocks, monitor the water quality & natural water pollution such as oil or algal blooms, which are harmful to aquatic life.

7)    Remote sensing techniques are giving necessary data needed for monitoring changes on coastal erosion, shoreline monitoring & management, loss of natural habitat, sea level rise, wetland mapping urbanization, sewage disposal and aquatic population etc.

8)    Remote sensing is very useful in identifying Potential Fishing Zones (PFZ). This data is very useful for fishermen because they came to know likely occurrence of fish shoals which helps them for getting more catch.

9)    Continuous monitoring of land use or land cover with remote sensing imageries have been of immense use in providing information on temporal & spatial changes in area under aquaculture, mangrove areas, coral reef mapping & other land use patterns.


       GIS may be defined as the integration of computer hard & software with spatially referred digital data so that storage, retrieval, manipulation, analysis and display all forms of geographically referenced information.

       GIS is a computer assisted system that can input, store, retrieve, analyse & display geographically referenced information useful for decision making.

            The definition of GIS is not that important but it must encompass

            i.         Data & concepts concepts concerned with spatial distribution (Geographical).

              ii.         Notion of conveying data, ideas or analysis (Information).

               iii.         Sequence of inputs, processes & outputs (System).  


Geographic reference concepts:

                   Available maps of different thematic layers are used to create GIS. The maps are in two dimension where as the earth's surface is a 3-dimensional ellipsoid. Every map has a projection & scale. Georeferencing concepts need to be understood to know how maps are created by projecting the 3-dimension earth's surface into a 2-dimensional plane of analogue map. Georeferencing involves two stages-

1.Specifying the 3-dimensional co-ordinate system that is used for locating points on the earth's surface that is Geographic Co-ordinate system

2.Projected co-ordinate system used for projecting into two dimensional analogue maps.


Components of GIS:

                GIS runs on the whole spectrum of computer hardware ranging from portable personal computers to a multi-user supercomputer & is programmed in a wide variety of software languages. There are number of elements that are essential for effective GIS operation.

1)    The presence of a processor with sufficient power to run the software.

2)    Sufficient memory for storage of large volume of data.

3)    A good quality high resolution colour screen.

4)    Data input & output devices.

5)    Liveware.

Functions of GIS:

A.   Data pre-processing, manipulation & retrieval

B.    Data analysis

C.    Data display

D.   Database management


Advantages of GIS:

o      It helps the planners in efficient & cost effective decision making based on multiple scenarios available.

o      GIS allows integration of all types of data together based on geographical & locational components of data.

o      GIS is application oriented.

o      Frequent revision of digitized GIS data is possible.

o      Changes over time can easily & rapidly monitored through GIS.

o      GIS technology enables high quality output.

o      Spatial patterns & processes can be effectively described & explained by GIS.


Applications of GIS in Fisheries :

    Identification of suitable sites for freshwater & brackishwater aquaculture.

    Management of marine fisheries & coastal regulation zone.

    Study of land-use pattern including mangroves & forest cover of a particular area.

    Planning for water body resource zonation & mapping of aquatic species.

    Fish disease modeling & management.

    Study of temporal/spatial changes in fish production & consumption.

    Environmental Impact Assessment.

    Distribution of different fish species in relation to physical habitat characteristics.

    Study of spatial variations in demand / supply balance.



The Global Positioning System (GPS) is a location system based on a constellation of

 about 24 satellites orbiting the earth at altitudes of approximately 11000 miles.GPS is widely used by civilians as well as defense personnel. GPS was developed by the United States Department of Defense (DOD), for application as a military locating utility. GPS satellites are orbited high enough to avoid the problems associated with land based systems, yet can provide accurate positioning 24 hours a day, anywhere in the world. DGPS has found its greatest utility in the field of Geographic Information System ( GIS ). With some consideration for error, GPS can provide any point on earth with a unique address (its precise location). GPS tells us "where", whereas GIS tells us "what".



Components  of  GPS :

             GPS is not a single unit. It is a system & has a following three major components.

1.     Satellites

2.     Ground Control Stations

3.     GPS receivers or units


1. Satellites: There are 24 satellites & 3 spare satellites. The exact location of each of the satellites at any given moment is known. Very accurate clocks are installed onboard these satellites. The satellites send radio signals continuously towards earth. These signals contain several pieces of information such as satellite ID number, time stamp, exact position of satellite etc.

2. Ground Control Stations: These are five control stations to monitor the satellites. These stations unable the information on earth to be transmitted to the satellites. Control stations track satellites & update the position of each satellites continuously. These stations ensure accuracy of the system.

3. GPS receivers: GPS units are referred to as receivers. These units receive radio signals from satellites, which contain important information such as time stamp, satellite ID number, satellite position etc. The receiver knows exactly when the signal leaves the satellite (time stamp) and when the signal arrives at the receiver. Hence, it is possible to calculate the distance from satellites as distance → time × velocity of light. The receiver also knows the exact position of satellite via the signal. The receiver is therefore able to determine its exact distance from satellite.

Working of GPS: 

The Global Positioning System (GPS) is a satellite navigation system providing worldwide coverage. A group of 24 satellites, circling twice-daily 20,000 km above the earth's surface, transmit coded signals that are picked up by GPS receivers. The constellation of navigation satellites around the earth enables position to be determined anywhere at any time, and in any weather condition - for free!

By recognising the codes for each satellite, the receiver can determine the time taken for the signal to be transmitted. The GPS uses this information to then calculate the distance to each satellite. Once four or more satellites are located, the GPS "triangulates" the distances to provide a location on the earth's surface, i.e. longitude, latitude, and elevation.

However, the signal is still prone to a number of errors that can reduce the positional accuracy. These include atmospheric errors, multi-path errors, satellite and receiver errors, and intentional errors.

Atmospheric errors are introduced as the signal passes through the atmospheric layers. Charged particles and moisture droplets delay the signal, leading to timing inaccuracies. Atmospheric errors may range from 3 to 50 m, depending on the time of day and the arrangement of satellites in the sky. A "dual-frequency" GPS minimises these errors through computer modelling or by comparing the relative speeds of two different signals - but these receivers are costly.

Multi-path errors occur when the signal bounces off obstructions, such as buildings or sheds, before reaching the receiver. Such errors may exceed 100 m in certain situations. Complex signal rejection procedures - or simply using the GPS in wide-open spaces - should minimise these errors.

Satellite (or "ephemeris") errors result when the broadcast orbit differs from the actual orbit. The US Department of Defence uses radar to determine these errors, and any updated positional information can be added to the satellite code to reduce this error. Receiver errors result largely from noise or the use of inaccurate clocks inside the GPS unit - but can be minimised with more expensive clocks.

To prevent hostile parties using GPS, an intentional error was added to the satellite signal. This code degradation, known as "selective availability" (SA), introduced a random clock error into each satellite. When SA is operative, range measurements may be biased by as much as 30-50 m. Applying a "differential correction" minimized this intentional error however, SA was removed in May 2000, vastly improving the accuracy of all GPS units.


Functions of GPS:

       For connecting & storing points.

       For collecting & storing routes, a path between two or more points.

       'GOTO' function is useful in guiding to a predetermined point.

       GPS can be programmed to 'beep' when you are within a certain distance of the defined way point.

       Marine GPS with built-in tide tables provide information & ranges for any date & any place.

       GPS can calculate ground speed as you walk, run, drive or fly.

       In addition to providing with your latitude & longitude, GPS provides you with altitude information. 


Applications of GPS in Fisheries GIS:

    It is providing to be a useful tool in providing cost effective data for creation & updation of  GIS.

    Provide ground control points (GCP's) for remote sensing applications.

    The latest GPS equipment includes software which can allow for the capture of any attribute or feature data along with its GPS given position, so as to form a field mapping system. The data obtained can then be directly exported to GIS package.

    In marine fisheries, it would allow for a survey vessel to continuously monitor water quality along any transect while recording the exact location. The real time mapping of data could then be done.

    It is also possible to record trawlers location & also trawler catch data at a specified interval of time & at the end of a fishing trip, the vessel would have a complete record on disk of catch against location.

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