What is remote sensing:
Remote sensing is the acquisition of information about an object or a phenomena without being directly in touch with that object or phenomena.
According to FF Sabins “Remote sensing is the science of acquiring, processing and interpreting images that record the interaction between electromagnetic energy and matter.”
Electromagnetic energy is a form of energy that can be reflected or emitted from objects through electrical or magnetic waves traveling through space. Electromagnetic radiation is a type of electromagnetic energy. The range of all types of electromagnetic radiation is termed as electromagnetic spectrum.
Different objects on the earth surface have different frequencies of radiation. What is emitted by water will not be similar to what is emitted by trees or rocks or sand. Hence electromagnetic spectrum helps us in identifying different types of objects.
The types of electromagnetic radiation are broadly classified into the following classes:
- Gamma radiation
- X-ray radiation
- Ultraviolet radiation
- Visible radiation
- Infrared radiation
- Terahertz radiation
- Microwave radiation
- Radio waves
Identification of oasis in a desert area by applying remote sensing:
Oasis: Oasis is an isolated plot of land within a desert consisting of water body, few vegetation and may also have some kind of habitats. Oasis are generally formed from underground water bodies.
How to identify oasis: Vegetation has a unique spectral signature as it reflects more optical/near infrared while absorbs most of blue and red regions of the spectrum. In the near infrared region the reflectance are higher. So it has a reddish appearance.
Water body have 3 main types of reflectance- Surface reflectance, Bottom reflectance and Volume reflectance. Clear water irradiates very little solar irradiance but turbid water reflects more blue lights. So its appearance in a satellite image will be blue it may range up to green if it has some vegetation within it. And finally coming to sand he most important feature of a desert, we can identify it easily as it will be a long track of bare soil without vegetation and it appears on the satellite imagery depending upon the type of mineral content of the sand. It can be red or pink if it has lots of iron oxide or it may be brown black or grey as well if it has volcanic contents.
Hence a sudden appearance of water body and vegetation within a long track of bare land containing sand can be considered as Oasis.
Why to Identify Oasis: Explorers exploring in large desert areas often prefer to stay nearby water bodies so a map showing exact location of oasis will help them and make their work easier.