Definition of Remote Sensing:
Remote sensing means acquiring information about a phenomenon object or surface while at a distance from it. This name is attributed to recent technology in which satellites and spacecraft are used for collecting information about the earth's surface. This was an outcome of developments in various technological fields from 1960 onward.
Remote Sensing is the art, science and technology of observing an object scene, or phenomenon by instrument-based techniques.
Concept of Remote Sensing:
Remote: because observation is done at a distance without physical contact with the object of interest.
Sensing: Detection of energy, such as light or another form of electromagnetic energy.
Remote Sensing is the science of acquiring, processing and interpreting images that record the interaction between electromagnetic energy and matter. (Sabins, 1996)
The term Remote Sensing means the sensing of the Earth's surface from space by making use of the properties of electromagnetic waves emitted, reflected by the sensed objects, for the purpose of improving natural resources management, land use and the protection of the environment. (UN, 1999)
Components of Remote Sensing:
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| Figure 1: Remote Sensing process |
Remote Sensing Process:
The process in remote sensing involves an interaction between incident radiation and the targets of interest. The following seven elements are involved in this process:
Energy Source or Illumination (A) - the first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest.
Radiation and the Atmosphere (B) - as the energy travels from its source to the target, it will come in contact with and interact with the atmosphere it passes through. This interaction may take place a second time as the energy travels from the target to the sensor.
Interaction with the Target (C) - once the energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.
Recording of Energy by the Sensor (D) - after the energy has been scattered by, or emitted from the target, we require a sensor (remote - not in contact with the target) to collect and record the electromagnetic radiation.
Transmission, Reception, and Processing (E) - the energy recorded by the sensor has to be transmitted, often in electronic form, to a receiving and processing station where the data are processed into an image (hardcopy and/or digital).
Interpretation and Analysis (F) - the processed image is interpreted, visually and/or digitally, to extract information about the target which was illuminated.
Application (G) - the final element of the remote sensing process is achieved when we apply the information we have been able to extract from the imagery about the target in order to better understand it, reveal some new information, or assist in solving a particular problem.
- Geospatial data acquisition (GDA): Collection, processing and analysis of data for various purposes:
- Water management
- Land management
- Resource management, etc.
- Data : representations that can be manipulated by a computer
- Information : interpreted data
Principles of Remote Sensing:
Detection and discrimination of objects or surface features means detecting and recording of radiant energy reflected or emitted by objects or surface material. Different objects return different amount and kind of energy in different bands of the electromagnetic spectrum, incident upon it. This unique property depends on the property of material (structural, chemical, and physical), surface roughness, angle of incidence, intensity, and wavelength of radiant energy.
The Remote Sensing is basically a multi-disciplinary science which includes a combination of various disciplines such as optics, spectroscopy, photography, computer, electronics and telecommunication, satellite launching etc. All these technologies are integrated to act as one complete system in itself, known as Remote Sensing System. There are a number of stages in a Remote System, working as links in a complete, and each of them is important for successful operation.
Stages in Remote Sensing:
1. Emission of electromagnetic radiation, or EMR (sun/self- emission)
2. Transmission of energy from the source to the surface of the earth, as well as absorption and scattering
3. Interaction of EMR with the earth's surface: reflection and emission
4. Transmission of energy from the surface to the remote sensor
5. Sensor data output
6. Data transmission, processing and analysis
What We See:
At temperature above absolute zero, all objects radiate electromagnetic energy by virtue of their atomic and molecular oscillations. The total amount of emitted radiation increases with the body's absolute temperature and peaks at progressively shorter wavelengths. The sun, being a major source of energy, radiation and illumination, having a sharp power peak around 0.5 micrometer, allows capturing reflected light with conventional (and some not-so-conventional) cameras and films.
The basic strategy for sensing electromagnetic radiation is clear. Everything in nature has its own unique distribution of reflected, emitted and absorbed radiation. These spectral characteristics, if ingeniously exploited, can be used to distinguish one thing from another or to obtain information about shape, size and other physical and chemical properties. In so far as we know the spectral characteristics, we can pick an appropriate detector to make the desired measurement, remembering that for a given collector's diameter we get our greatest spatial resolution where wavelengths are shortest and energies greatest, and that these energies decrease at longer wavelengths and distances.
Modern Remote Sensing Technology versus Conventional Aerial Photography:
The use of different and extended portions of the electromagnetic spectrum, development in sensor technology, different platforms for remote sensing (spacecraft, in addition to aircraft), emphasis on the use of spectral information as compared to spatial information, advancement in image processing and enhancement techniques, and automated image analysis in addition to manual interpretation are points for comparison of conventional aerial photography with modern remote sensing system.
During early half of twentieth century, aerial photos were used in military surveys and topographical mapping. Main advantage of aerial photos has been the high spatial resolution with fine details and therefore they are still used for mapping at large scale such as in route surveys, town planning, construction project surveying, cadastral mapping etc. Modern remote sensing system provide satellite images suitable for medium scale mapping used in natural resources surveys and monitoring such as forestry, geology, watershed management etc. However the future generation satellites are going to provide much high-resolution images for more versatile applications.
Remote Sensing in India:
Indian remote sensing programme was started in late seventies with Indian built Bhaskara-I and Bhaskara-II satellites launched from Soviet Union in June 1978 and November 1981 respectively. Indigenous launch capability has also been developed to launch 1000 Kg. Remote Sensing Satellite into polar orbit. The Department of Space (DOS)/ Indian Space Research Organisation (ISRO) has been actively engaged in development of state of art remote sensing capabilities along with other related activities. ISRO Satellite Centre (ISAC), Bangalore is responsible for design, development and management of remote sensing satellites. Space Application Centre (SAC), Ahmedabad is engaged in development of sensors (cameras & scanners) & data processing software, analysis of remote sensing data, and related research. National Remote Sensing Agency (NRSA), Hyderabad is responsible for acquisition, processing and dissemination of remote sensing data, analysis of data for different applications and training of users. The National Natural Resources Management System (NNRMS) is responsible for execution of application projects through the establishment of a no. of Regional Remote Sensing Service Centre (RRSSC) throughout the country. Many user agencies, Govt. Departments, State Governments, and academic institutes have also established remote sensing infrastructure for various applications.
Advantages and Disadvantages of Remote Sensing:
Remote sensing has come a long way in recent years and is an impressive surveying technique with many different advantages and disadvantages.
Advantages of Remote Sensing:
- Remote Sensing Technology Can Survey Large and Inaccessible Areas or AOI.
- Remote Sensing Data Can Have a Wide Range of Uses for Users.
- Point Cloud Software Calculate and Analyzes Data Quickly.
- Remote Sensing Doesn’t Disturb People or the Environment, Because it's Work Silently.
Disadvantages of Remote Sensing:
- Remote Sensing Instruments Need to Be Calibrated For Process.
- Expensive to build and operate the data.
- Measurement uncertainty can be large.
- resolution is often coarse.
- Data interpretation can be difficult.
- High-Resolution Data from Remote Sensing Can Be Hard to Store.
History of remote sensing:
Application of Remote Sensing:
Remote sensing meaning in hindi - सुदूर संवेदन
Remote sensing meaning in bengali - দূর অনুধাবন
RS full form - Remote Sensing
what is remote sensing
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