“Remote Sensing can be defined as the science and art of obtaining information about an object, area or phenomenon through the analysis of data acquired by a device which is not in contact with the object, area or phenomenon under investigation by making use of electromagnetic radiation.”
The above is the technical definition for remote sensing. In simpler words, remote sensing can be defined as getting information about an object with out being in contact with it.
Elements or Stages of Remote Sensing Process:
Following are various elements of remote sensing process. These elements are required to conduct a successful remote sensing process.
1. Source of Energy:
A source of supply for energy is required for remote sensing process. Electromagnetic radiation generated from the source is used for capturing properties of objects/surface in the remote sensing process. Depending on what is source of energy, remote sensing is classified into 2 types. 1) Passive remote sensing and 2) Active Remote sensing. In passive remote sensing sun is the main source of energy. In case of active remote sensing, an external source of energy is used for remote sensing.
2. Interacting Atmosphere:
The electromagnetic radiation released from the source radiates in all directions. In this process, some of it travels through atmosphere towards objects on the earth surface. While traveling in the atmosphere, different types of interactions take place between energy and atmosphere (scattering, absorption). This causes a change in direction and properties of the energy in transport.
3. Interaction of energy with earth surface objects:
After traveling through the atmosphere, the energy reaches the earth surface, where it interacts with various types of objects. Depending on magnitude and type of energy, object surface and properties, various types of interactions take place between energy and earth surface objects. Some of these interactions include reflection, absorption and transmission etc.
4. Re-transmission of Energy into the Atmosphere:
During the interaction of energy with earth surface objects, some part of it is transmitted back into the atmosphere. This energy is regarded as the response of the object for incident radiation. This energy travels towards sensors present in the atmosphere onboard the satellites or cameras.
5. Capture of Energy by Satellites and Sensors:
This is the next stage of remote sensing. Here, the re-transmitted energy is captured by the sensors present in the atmosphere. The record the magnitude of various wavelengths of energy flowing from the surface objects. This recorded details constitute the raw data in remote sensing. Primarily, this raw data is recorded in analog format which is converted into digital format for remote sensing process.
6. Transmission of data to earth:
The recorded data transmitted onto the earth surface using antennas located at various ground stations. The data collected at ground stations is stored in hard disks, magnetic tapes etc., and is used in further processing.
7.Processing of Data:
This raw data received from the satellite sensors are not directly usable, as it contains lot of unwanted details often. Other than this, some times clouds present in the atmosphere obstructs the data capture. This causes problems with data interpretation. Also, some times there may be problem with sensor or platform.
Hence, the collected data goes through pre-processing stage, where certain types of corrections are performed for data. Then, in the data processing stage the raw data is analyzed and interpreted by the experts using various software and tools such as GIS for deriving useful information for the public and scientific community. This processed data is used in so many applications of remote sensing in general.
The processed and raw data are supplied to the users (which include scientific community and general public) in the form of maps and images etc., at various levels.
This data becomes information and several types of other products at the end.