APPLICATIONS OF REMOTE SENSING (RS), GEOGRAPHICAL
INFORMATION SYSTEM (GIS) & GLOBAL POSITIONING SYSTEM (GPS) IN FISHERIES
- Amod Ashok Salgaonkar, Trivesh Suresh Mayekar,
Avinash Rambhau Rasal, Kiran Rasal, Balkrishna Hotekar, Rakesh Jadhav, Amar
Gaikwad
Corresponding author e-mail ID : amodcife@gmail.com
REMOTE
SENSING :
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.
GEOGRAPHICAL
INFORMATION SYSTEM (GIS) :
¤
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.
POSITIONING SYSTEM (GPS) :
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.
