In order to understand how a radar imaging system produces imagery, a comparison with optical imaging systems is useful. As a result, radar images can yield valuable information that is not available in VIR images. Therefore, sensors transmitting and/or receiving microwaves are able to 'see' through haze, cloud, light rain, snow, smoke, and pollution. Since microwaves are longer, they are not as affected by these types of small particle matter. VIR wavelengths can be dispersed or blocked before they reach the sensors. Water vapor, dust, smoke, airborne pollutants and other small particles close in magnitude to visible and infrared (VIR) wavelengths cause interference in the path between target and sensor. Radar band designations range from the Ka band occurring between 7.5 and 11.0 mm to the P band range between 30 and 100 cm.ġ2 Radar and the Electromagnetic SpectrumĪny system transmitting and/or receiving energy from the Earth's surface is affected by the atmosphere. Uses Microwave part of the spectrum Microwaves are much longer, ranging from 1 mm to 1 metre. The Japanese MOS (Marine Observation Satellite) and JERS satellite systems employ microwave scanning units.ġ1 Radar and the Electromagnetic Spectrum Microwave scanning radiometers only receive microwave energy. Passive radar systems sense low level microwave radiation given off by all objects in the natural environment.ġ0 Examples Radar imaging systems such as ERS (European Remote Sensing Satellite), JERS (Japan Earth Resources Satellite), and RADARSAT-1 are active systems. Active radar systems transmit short bursts or 'pulses' of electromagnetic energy in the direction of interest and record the origin and strength of the backscatter received from objects within the system's field of view. Imaging radar systems can be active or passive. These radars use a circular display screen to indicate objects surrounding the rotating antenna. Plan position indicators (PPI) produce a type of image. Radar systems may or may not be imaging systems An example of a non-imaging system is a doppler radar system that are used to measure vehicle speeds by measuring the frequency. Radar as a remote sensing tool became more commonly used as military systems were declassified and scientists developed new applications in mapping and resource monitoring. They were originally developed by the military. Radar systems were originally developed in order to detect the presence and position of objects using transmitted and received radio waves Due to the electromagnetic properties of radio waves radar systems are capable of collecting data in nearly all atmospheric conditions, by day and/or night.ħ Basics Imaging radar systems have been in use since the 1950s. ![]() An image may be represented and displayed in a digital format by subdividing the image into small equal-sized and shaped areas, called picture elements or pixels, and representing the brightness of each area with a numeric value or digital number.Ĥ Pixel Size most remote sensing images are composed of a matrix of picture elements, or pixels, which are the smallest units of an image If a sensor has a spatial resolution of 20 metres and an image from that sensor is displayed at full resolution, each pixel represents an area of 20m x 20m on the groundĦ Basics Radar is an acronym for RAdio Detection And Ranging. ![]() ![]() Thematic data is a type of raster data that is qualitative and categorical.Ģ Image Display An image refers to any pictorial representation, regardless of what wavelengths or remote sensing device has been used to detect and record the electromagnetic energy. 1 Types of Images There are two types of images: Continuous ThematicĬontinuous data is a type of raster data that is quantitative and has related, continuous values.
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