Weather radar system basics
This tutorial section on radar basics covers following sub topics:
Main Page Terminology Measurements Doppler Radar FMCW RADAR BANDs RADAR SCOPE Weather Radar Ground radar RANGE and RESOLUTION Range calculator
In general radar has been developed for detecting presence of aircrafts and ships during the world war. Later on advances in the radar technology lead to research in the sea, land and space. Weather radar has been developed for determining climatic conditions such as wind speed, cloud formations, sea water tides and so on.
Similar to the other radars, this type of radar also transmits radio frequency pulse and determines various parameters based on received scattered pulse wave. Targets here can be trees, clouds, raindrops, bumblebees and so on. It is this radar which helps pilot fly the aircraft in the thick dark cloud and poor visibility conditions. The weather radar usually transmit radio wave of about 3000MHz frequency (About 10cm wavelength). It transmits short pulses at this frequency at the rate of 1000 pulses per second.
The block diagram in the figure mentions basic components used in a typical weather radar system. It consists of transmitter, receiver, antenna system, feedhorn and radome.
• Transmitter consists of RF signal generation modules viz. modulator, RF upconverter and power amplifier.
• Receiver consists of RF signal analysis modules viz. LNA, RF downconverter, demodulator and display.
• Antenna is used to transmit the signal into the air and capture the RF signal from the air.
• Feedhorn focus the received signal into the receiver part and also directs the signal from the transmitter part to the antenna.
• Radome is used to protect antenna and other subsystems from high speed winds.
Refer VSAT system overview for complete details on these components.
Weather radar scanning techniques
For meteorology application radar uses scanning techniques such as PPI and RHI.
Plan Position Indicator (PPI): In this type, radar keeps elevation angle fixed and varies azimuth angle.
• If radar rotates about 360 degree, it is referred as surveillance scan.
• If it rotates less than 360 degree, it is referred as sector scan.
Range Height Indicator (RHI) : In this type, radar keeps its azimuth fixed and varies elevation. It is rotated towards the sky. Data for different elevation angles are collected for some time and later will be analyzed.