introduction to radar

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Information about introduction to radar
Science

Published on May 9, 2014

Author: avinashsimhadri9

Source: slideshare.net

RADAR DATA ACQUISITION SYSTEM KUNAL GUPTA 13BCH0005 S. AVINASH 13BEC0671 GUNJAN SINGH 13BEE0214

RADAR INTRODUCTION •WHAT IS RADAR HISTORY •HOW IT DEVELOPED •FRIST USERS APPLICATIONS •FIELDS WHERE IT IS USED PRINCIPLES •REFLECTION •POLARISATION •DOPPLER EFFECT •RADAR EQUATION SIGNAL PROCESSING •DISTANCE MEASUREMENT •SPEED MEASUREMENT •PULSE DOPPLER SIGNAL PROCESSING •PLOT AND TRACK EXTRACTION

OBJECT DETECTION SYSTEM THAT USES RADIO WAVES DETERMINES RANGE, ALTITUDE, DIRECTION OR SPEED OF OBJECTS CAN DETACT SHIPS, SPACECRAFTS, MISSILES, WEATHER REPORTS, ETC DISH TRANSMITS PULSES OF RADIOWAVES THAT BOUNES OBJECTS IN THEIR PATH OBJECT RETURNS TINY WAVPART OF E’S ENERGY BACK TO THE DISH ANOTHER TYPE IS LIDAR THAT USES VISIBLE LIGHT RATHER THAN RW

HISTORY OF RADAR 1886 •GERMAN PHYSICIST HEINRICH HERTZ SHOWED THAT RADIO WAVES COULD BE REFLECTED FROM SOLID OBJECTS. 1895 •ALEXANDER POPOR, A RUSSIAN PHYSICS INSTRUCTOR DEVELOPED AN APPARATUS USING COHERER TUBE FOR DETECTING DISTANT LIGHTNING STRIKES. 1904 •CHRISTIAN HÜLSMEYER, A GERMAN INVENTOR, WAS THE FIRST TO USE RADIO WAVES TO DETECT "THE PRESENCE OF DISTANT METALLIC OBJECTS“. 1922 •U.S. NAVY RESEARCHES, A. HOYT TAYLOR AND LEO C. YOUNG , HAD A TRANSMITTER AND A RECEIVER ON OPPOSITE SIDES OF THE POTOMAC RIVER AND DISCOVERED THAT A SHIP PASSING THROUGH THE BEAM PATH CAUSED THE RECEIVED SIGNAL TO FADE IN AND OUT. 1934 • FRENCH RESEARCH BRANCH OF THE COMPAGNIE GÉNÉRALE DE TÉLÉGRAPHIE SANS FIL (CSF), HEADED BY MAURICE PONTE, WITH HENRI GUTTON, SYLVAIN BERLINE, AND M. HUGON BEGAN DEVELOPING AN OBSTACLE- LOCATING RADIO APPARATUS. 1935 •SOVIET MILITARY ENGINEER P. K. OSHCHEPKOV, IN COLLABORATION WITH LENINGRAD ELECTROPHYSICAL INSTITUTE, PRODUCED AN EXPERIMENTAL APPARATUS, RAPID, CAPABLE OF DETECTING AN AIRCRAFT WITHIN 3 KM OF A RECEIVER. 1936 •FULL RADAR, EVOLVED AS A PULSE SYSTEM DEMONSTRATED BY ROBERT M. PAGE, AN AMERICAN NAVAL RESEARCHER.

APPLICATIONS OF RADAR METEOROLOGIST S USE RADAR TO MONITOR PRECIP ITATION AND WIND. IT HAS BECOME THE PRIMARY TOOL FOR SHORT- TERM WEATHER FORECASTING A ND WATCHING FOR SEVERE WEATHER SUCH AS THUNDERSTOR MS, WINTER STORMS, PRECIPITATION TYPES, ETC. IN AVIATION, AIRCRAFT ARE EQUIPPED WITH RADAR DEVICES THAT WARN OF AIRCRAFT OR OTHER OBSTACLES IN OR APPROACHING THEIR PATH, DISPLAY WEATHER INFORMATION, AND GIVE ACCURATE ALTITUDE READINGS. MARINE RADARS ARE USED TO MEASURE THE BEARING AND DISTANCE OF SHIPS TO PREVENT COLLISION WITH OTHER SHIPS, TO NAVIGATE, AND TO FIX THEIR POSITION AT SEA. IN PORT, VESSEL TRAFFIC SERVICE RADAR SYSTEMS ARE USED. FOR MILITARY PURPOSES: TO LOCATE AIR, GROUND AND SEA TARGETS. THIS EVOLVED IN THE CIVILIAN FIELD INTO APPLICATIONS FOR AIRCRAFT, SHIPS, AND ROADS. GEOLOGISTS USE SPECIALISED GROUND- PENETRATING RADARS TO MAP THE COMPOSITION OF EARTH'S CRUST. POLICE FORCES USE RADAR GUNS TO MONITOR VEHICLE SPEEDS ON THE ROADS

PRINCIPLES OF RADAR

REFLECTION IF ELECTROMAGNETIC WAVES TRAVELING THROUGH ONE MATERIAL MEET ANOTHER, HAVING A VERY DIFFERENT DIELECTRIC CONSTANT FROM THE FIRST, THE WAVES WILL REFLECT OR SCATTER FROM THE BOUNDARY BETWEEN THE MATERIALS. THIS MEANS THAT A SOLID OBJECT IN AIR OR IN A VACUUM WILL USUALLY SCATTER RADAR (RADIO) WAVES FROM ITS SURFACE. THE EXTENT TO WHICH AN OBJECT REFLECTS OR SCATTERS RADIO WAVES IS CALLED ITS RADAR CROSS SECTION.

FREQUENCY SHIFT IS CAUSED BY MOTION THAT CHANGES THE NUMBER OF WAVELENGTHS BETWEEN THE REFLECTOR AND THE RADAR. SEA-BASED RADAR SYSTEMS, SEMI-ACTIVE RADAR HOMING, WEATHER RADAR, MILITARY AIRCRAFT, AND RADAR ASTRONOMY RELY ON THE DOPPLER EFFECT TO ENHANCE PERFORMANCE. DOPPLER SHIFT DEPENDS UPON WHETHER THE RADAR CONFIGURATION IS ACTIVE OR PASSIVE. ACTIVE RADAR TRANSMITS A SIGNAL THAT IS REFLECTED BACK TO THE RECEIVER. PASSIVE RADAR DEPENDS UPON THE OBJECT SENDING A SIGNAL TO THE RECEIVER. DOPPLER MEASUREMENT IS RELIABLE ONLY IF THE SAMPLING RATE EXCEEDS THE NYQUIST FREQUENCY FOR THE FREQUENCY SHIFT PRODUCED BY RADIAL MOTION.

POLARIZATION IN ALL ELECTROMAGNETIC RADIATION, THE ELECTRIC FIELD IS PERPENDICULAR TO THE DIRECTION OF PROPAGATION, AND THIS DIRECTION OF THE ELECTRIC FIELD IS THE POLARIZATION OF THE WAVE. IN THE TRANSMITTED RADAR SIGNAL THE POLARIZATION CAN BE CONTROLLED FOR DIFFERENT EFFECTS. RADARS USE HORIZONTAL, VERTICAL, LINEAR AND CIRCULAR POLARIZATION TO DETECT DIFFERENT TYPES OF REFLECTIONS. EXAMPLES CIRCULAR POLARIZATION-MINIMIZE INTERFERENCE CAUSED BY RAIN. LINEAR POLARIZATION- INDICATE METAL SURFACE RANDOM POLARIZATION-INDICATE FRACTAL SURFACE

RADAR EQUATION THE POWER PR RETURNING TO THE RECEIVING ANTENNA IS GIVEN BY THE EQUATION: PT = TRANSMITTER POWER GT = GAIN OF THE TRANSMITTING ANTENNA AR = EFFECTIVE APERTURE (AREA) OF THE RECEIVING ANTENNA σ = RADAR CROSS SECTION, OR SCATTERING COEFFICIENT, OF THE TARGET F = PATTERN PROPAGATION FACTOR RT = DISTANCE FROM THE TRANSMITTER TO THE TARGET RR = DISTANCE FROM THE TARGET TO THE RECEIVER.

SIGNAL PROCESSING DISTANCE MEASUREMENT TRANSIT TIME FREQUENCY MODULATION SPEED MEASUREMENT PULSE DOPPLER SIGNAL PROCESSING PLOT AND TRACK EXTRACTION

DISTANCE MEASUREMENT •TRANSMIT A SHORT PULSE OF RADIO SIGNAL AND MEASURE THE TIME IT TAKES FOR THE REFLECTION TO RETURN •THE DISTANCE IS ONE-HALF THE PRODUCT OF THE ROUND TRIP TIME FR(BECAUSE THE SIGNAL HAS TO TRAVEL TO THE TARGET AND THEN BACK TO THE RECEIVER) AND THE SPEED OF THE SIGNAL TIME-OF-FLIGHT •THIS TECHNIQUE CAN BE USED IN CONTINUOUS WAVE RADAR AND IS OFTEN FOUND IN AIRCRAFT RADAR ALTIMETERS. •IN THESE SYSTEMS A "CARRIER" RADAR SIGNAL IS FREQUENCY MODULATED IN A PREDICTABLE WAY, TYPICALLY VARYING UP AND DOWN WITH A SINE WAVE AT AUDIO FREQUENCIES. THE SIGNAL IS THEN SENT OUT FROM ONE ANTENNA AND RECEIVED ON ANOTHER, TYPICALLY LOCATED ON THE BOTTOM OF THE AIRCRAFT FREQUENCY MODULATION

SPEED MEASUREMENT SPEED IS THE CHANGE IN DISTANCE TO AN OBJECT WITH RESPECT TO TIME. MOST MODERN RADAR SYSTEMS USE THIS PRINCIPLE INTO DOPPLER RADAR AND PULSE- DOPPLER RADAR SYSTEMS (WEATHER RADAR, MILITARY RADAR, ETC...) CONTINUOUS WAVE RADAR IS IDEAL FOR DETERMINING THE RADIAL COMPONENT OF A TARGET'S VELOCITY. WHEN USING A PULSED RADAR, THE VARIATION BETWEEN THE PHASE OF SUCCESSIVE RETURNS GIVES THE DISTANCE THE TARGET HAS MOVED BETWEEN PULSES, AND THUS ITS SPEED CAN BE CALCULATED.

PULSE-DOPPLER SIGNAL PROCESSING PULSE-DOPPLER SIGNAL PROCESSING INCLUDES FREQUENCY FILTERING IN THE DETECTION PROCESS. THE SPACE BETWEEN EACH TRANSMIT PULSE IS DIVIDED INTO RANGE CELLS OR RANGE GATES. THE PRIMARY PURPOSE IS TO MEASURE BOTH THE AMPLITUDE AND FREQUENCY OF THE AGGREGATE REFLECTED SIGNAL FROM MULTIPLE DISTANCES. PULSE-DOPPLER SIGNAL PROCESSING ALSO PRODUCES AUDIBLE SIGNALS THAT CAN BE USED FOR THREAT IDENTIFICATION.

PLOT AND TRACK EXTRACTION A TRACK ALGORITHM IS A RADAR PERFORMANCE ENHANCEMENT STRATEGY. TRACKING ALGORITHMS PROVIDE THE ABILITY TO PREDICT FUTURE POSITION OF MULTIPLE MOVING OBJECTS BASED ON THE HISTORY OF THE INDIVIDUAL POSITIONS BEING REPORTED BY SENSOR SYSTEMS. •NEAREST NEIGHBOR •PROBABILISTIC DATA ASSOCIATION •MULTIPLE HYPOTHESIS TRACKING •INTERACTIVE MULTIPLE MODEL (IMM) TRACK ALGORITHMS

COMPONENTS OF A RADAR ALEXANDER POPOR MARINE RADAR GROUND PENETRATING RADAR RADAR GUN RADAR FUNCTIONING

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