An Effective Use of Synthetic Aperture Radar Imaging Technique Over Optical Remote Sensing and Real Aperture Radar for Mapping of Earth Surface Features

Abstract

Remote sensing is rightly described as an activity of recording/ observing/ perceiving (sensing) objects or events that are located at far away (remote) places. In remote sensing, the sensors are not in direct physical contact with the objects or events that are being observed. The information to be sensed needs a physical carrier (say, microwave) to travel from objects/events to the sensing device through an intervening medium (clouds, water vapour, air). Normally, the electromagnetic wave is used as an information carrier. The output of a remote sensing system is usually an image (bi-spectral (grayscale)/trispectral (RGB)/ hyperspectral (many bands)) representing the scene which is being observed. Further steps of image analysis and interpretation(visual/machine) is required in order to extract useful information from the recorded image. In general sense, the human visual system is a classic example of a remote sensing system. Data in the form of 2-D images which are mapped from optical remote sensing, after going through a series of processing steps, is ready for human interpretation and can be used for several applications like mapping of land cover, classification of various crops, in weather forecasting and monitoring, etc. However, the problems of constant cloud coverage and other atmospheric disturbances dominantly persist in optical images that often lead to erroneous data interpretation. So, in order to correctly interpret the mapped mages from satellite or aeroplane platforms, we have to rely on the data received from synthetic aperture radar (SAR) that has this unique capability to operate nearly under all weather conditions. Also, SAR imaging used by space-crafts is advantageous over any other method of earth feature mapping (i.e. optical, thermal) as it uses energy harnessed from its on-board solar panels to recharge its batteries and in turn generate the microwave bursts of energy, which it then transmits towards the surface of the earth. The primary aim of this paper is to illustrate the crucial point of differences between optical and radar remote sensing and how a real aperture radar (RAR) imaging technique differs from its counterpart i.e. synthetic aperture radar (SAR) in terms of range, azimuth resolution. We have also discussed as to how we can conceptualize a SAR antenna using the properties of RAR.