Optical remote sensing-An overview

Remote sensors such as radiometers or spectero-radiometers on board of aircraft and satellites allow the observation of large areas of the earth surface at different wavelengths of electromagnetic radiation. This makes the remote sensing technology one of the most suited candidate for the analysis of the landscape and environment towards the understanding of natural phenomena, both in the prevention, management and mitigation of natural risks such as flooding and landslides, forest fires and volcanic eruptions, earthquakes, etc. Optical remote sensing (ORS) technologies came into existence in late 1980s. This technology is recognized to have a potential for the measurement of environmental flux but several factors such as cost contributed towards delay in its applications in wide areas. With the ability to provide the synoptic view rapidly, ORS has now become the most powerful tool. ORS deals with those parts of the electromagnetic spectrum characterized by the wavelength from visible (0.4 μm) to the near infrared (NIR) up to thermal infrared (TIR, 15 μm), collecting radiation reflected and emitted from the observed surfaces. In this range of frequencies data acquisition (measurements, signals and images) is released with sensors that utilize for the radiation collection optical instruments such as lens for refraction or mirrors for reflection mechanisms. The strong interaction of the EMR at these frequencies with the atmosphere and the presence of clouds constitute an important limiting factor on the potential observation of the earth surface. ORS imagery tools record an object transmission of electromagnetic energy from reflecting target to generate unique spectral information which is being successfully used in mapping land-use and cover agriculture, soil mapping, city planning, archaeological investigations, military observations, forestry, etc. This paper aims to provide a review of the recent progress in the field of ORS and then explains the various stages and the basic principles of remotely sensed data collection mechanism and its wide range applications.