RADAR METEOROLOGY Yrd. Doç. Dr. Ali DENİZ

OUTLINE INTRODUCTION RADAR HARDWARE ELECTROMAGNETİC WAVES RADAR EQUATION FOR POINT TARGETS METEOROLOGICAL TARGETS DISCUSSIONS REFERENCES

RA dio D etection A nd R anging LI ght D etection A nd R anging wawelength RADIO RADAR Buderi – 1996 :THE INVENTION THAT CHANGED THE WORLD Young and Taylor – 1934 :PULSES OF ENERGY INTRODUCTION

Doppler Radars power speed RADAR DATAAUTOMATIC WARNINGS POLARIZATION KINDS SHAPES SIZES

RADAR HARDWARE reflector transmitter modulator Master Clock receiver display antenna waveguide duplexer

How Does Radar Work? single antenna target short pulses of energy send Return back The antenna rotates about a vertical axis, scanning the horizon in all directions To determine how high a storm is, met. radars can also aim their antennas above the horizon Whole cycle 10 to 20 elevation angles + 4 to 6 minutes DATA...DISPLAY

TYPES OF RADARS Monostatic and Bistatic radar CW and pulsed radar Doppler radar FM-CW radar Wind profilers and aircraft radars Airborn radar Shipboard radar Weather radar Dual-wavelength radar Polarization-diversity radar

RADARS USED IN AVIATION ARSR: ASR: TDWR: ARDE: L-band, =20 cm Detect aircraft Provide information on the position of aircrafts Detect microbursts, gustfronts, wind shifts, pecipitaion Follow aircraft on the ground at some airports

ELECTRO-MAGNETIC WAVES Radio & radar electro-magnetic radiation f : 1 Hz=1 cycle / second c: m/s : m

Elektromagnetic spectrum Skolnik, 1980.

Radar bands and corresponding frequency bands, (Rinehart, 2001). Radar BandsFrequencyWavelength HF3-30 MHz m VHF MHz10-1 m UHF MHz1-0.3 m L1-2 GHz30-15 cm S2-4 GHz15-8 cm C4-8 GHz8-4 cm X8-12 GHz4-2.5 cm Ku12-18 GHz cm K18-27 GHz cm Ka27-40 GHz cm mm or W GHz7.5-1 mm

REFRACTIVE INDEX c : the speed of light in a vacuum u: the speed of light in a medium n: refractive index c  u (always) n  1 (unitless parameter) Actually, it has two components ; k Absorption of coefficient of the medium For air; m=1.003

REFRACTIVITY[N] Atm. Press. (mb, hPa) Temp. (°K) Vap. Press. (mb, hPa) Num. of free electron / m 3 Freq. of the radar (Hz.) Under normal atmospheric contions; Ground N Z N

RADAR EQUATION FOR POINT TARGET radarstorms Rainrate and... radarPuls of energy into space by antenna Power A spherically expanding shell of energy r : the range from the radar Power density : S

The power intercepted bye the target target The amount of energy detected by radar will be: A e : The effective area of the receiving antenna

New! THE BACK-SCATTERING CROSS-SECTIONAL CROSS-SECTIONAL AREA OF THE TARGET Final Form SPHERICAL TARGETS A sphere is LARGE “Large” : A sphere is SMALL RAYLEIGH region “Small” :

In the Rayleigh region :: related to the complex index of refraction of the material Meteorological targets small RAYLEIGH REGION MET. RADAR USE SOME STANDART POINT TARGETS : Spheres, birds, aircraft, buildings, water towers and radio towers.... In conclusion; Point targets are imp. source of echo for many radars. By making careful measurements of the return from point targets, much canbe learned about the targets. Well-chosen point targets also make it possible to monitor the health and quantitative reliability of a particular radar system. (Battan, 1973)