Remote sensing is broadly defined as the science and art of collecting information about objects. The area or phenomena from distance without being in physical likewise contact with them.
Human eye is therefore most familiar example of a remote sensing system. In fact, sight, smell and hearing are all rudimentary forms of remote sensing. However, the term remote sensing is restrict to methods that employ electromagnetic energy ( such as light, heat, microwave ) as means of detecting and measuring target characteristics.
Air craft and satellites are the common platforms use for remote sensing. Collection of data is usually carry out by highly sophisticated sensors ( i.e. camera, multi spectral scanner, radar etc. ). The information carrier, or communication link is the electromagnetic energy.
Classification of Remote sensing
- Passive R.S.
- Active R.S.
Passive remote sensing
It uses sun as a source of EM energy. It’s records the energy that is naturally radiate and/ or reflect from the objects.
Active remote sensing
It uses its own source of EM energy. It’s is direct towards the object and return energy is measure.
Idealize Remote sensing system
- Energy source
- Propagation of energy through atmosphere.
- Energy interaction with earth’s surface features.
- Airborne/ space borne sensors receiving the reflect and emit energy.
- Transmission of data to earth station and generation of data produce.
- Multiple data users
Principles of Remote sensing
It employ electromagnetic energy. Moreover, to a great extent relies on the interaction of electromagnetic energy with the matter. It refers to the sensing of EM radiation, which is reflect, scatter or emit from the object.
It is a form of energy that moves with the velocity of light ( 3 x 10^8 m/sec ) in a similarly harmonic pattern. Electro magnetic Energy consisting of sinusoidal waves, equally and repetitively space in time. It has therefore two fields : ( i ) electrical field and ( ii ) magnetic field. Both are however orthogonal to each other. In which the electric components are vertical as well as magnetic components are horizontal.
Electromagnetic energy consists of photons having particle like properties such as energy and momentum. The EM energy is characterized in terms of velocity c ( = 3 x 10^8 m/s ), wave length and frequency f. These parameters are relate by the equation :
wavelength = c/f
The amplitude is the maximum value of the electric field. It is a measure of the amount of energy that is transport by the wave.
Wave theory concept explains how EM energy propagates in the form of a wave. However, this energy can only be detect when it interacts with the matter. This interaction suggests that the energy consists of many discrete units refer as photons whose energy (Q) is given by :
Q = h.f = h.c/ wavelength
h = Plank’s constant = 6.6252 x 10^-34 J-s
Although visible light is the most obvious manifestation of EM radiation, other forms also exist. EM radiation can be produce however at a range of wave lengths. It can be categorize according to its position into discrete regions which is generally refer to electromagnetic spectrum. Thus the electromagnetic spectrum is the continuum of energy that ranges from meters to nano meters in wave length travels at the speed of light. It propagates through a vacuum likewise the outer space.
All matter radiates a range of electromagnetic energy, with the peak intensity however shifting toward progressively shorter wave length at an increasing temperature of the matter. In general, the wave lengths and frequencies vary from shorter wavelength high frequency cosmic waves to long wave length low frequency radio waves .
Remote sensing observation platforms
- Air borne platforms
- Space based platforms
Air borne platforms
Remote sensing of the surface of the earth has a long history, however dating from the use of cameras carried by balloons and pigeons in the eighteenth and nineteenth centuries. Later, air craft mount systems were developed for military purposes during the early part of 20th century.
Air borne remote sensing was used in 1960’s and as well as 1970’s. Air craft were however mostly used as RS platforms for obtaining photographs. Aircraft carrying the RS equipment should therefore have maximum stability, free from vibrations and fly with uniform speed.
Space based platforms
Space borne remote sensing platforms, such as a satellite, offer several advantages over airborne platforms. It provides synoptic view ( i.e. observations of large area in a single image ), systematic and repetitive coverage.
Types of Space borne platform
- Low altitude near polar orbiting satellites.
- High altitude Geo-stationary satellites.
Applications of Remote sensing
- Land use and soils
- Urban Land use
- Water resources
- Coastal Environment
- Ocean Resources
- Street network based applications
- Land parcel based application
- Natural resources based applications
- Facilities management
- Digital elevation models