RADAR METEOROLOGY Yrd. Doç. Dr. Ali DENİZ OUTLINE INTRODUCTION RADAR HARDWARE ELECTROMAGNETİC WAVES RADAR EQUATION FOR POINT TARGETS METEOROLOGICAL TARGETS DISCUSSIONS REFERENCES INTRODUCTION RAdio Detection And Ranging wawelength LIght Detection And Ranging RADIO RADAR Buderi – 1996 : THE INVENTION THAT CHANGED THE WORLD Young and Taylor – 1934 : PULSES OF ENERGY power Doppler Radars speed RADAR DATA AUTOMATIC WARNINGS KINDS SHAPES POLARIZATION SIZES RADAR HARDWARE reflector antenna waveguide duplexer transmitter receiver modulator display Master Clock How Does Radar Work? single antenna Return target back send short pulses of energy 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 10 to 20 elevation angles + Whole cycle DATA ...DISPLAY 4 to 6 minutes 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 L-band, =20 cm ARSR : Detect aircraft Provide information on the ASR : position of aircrafts TDWR : Detect microbursts, gustfronts, wind shifts, pecipitaion ARDE : Follow aircraft on the ground at some airports ELECTRO-MAGNETIC WAVES Radio & radar electro-magnetic radiation c f : 1 Hz=1 cycle / second f c: m/s : m Elektromagnetic spectrum Skolnik, 1980. Radar bands and corresponding frequency bands, (Rinehart, 2001). Radar Bands Frequency Wavelength HF 3-30 MHz 100-10 m VHF 30-300 MHz 10-1 m UHF 300-1000 MHz 1-0.3 m L 1-2 GHz 30-15 cm S 2-4 GHz 15-8 cm C 4-8 GHz 8-4 cm X 8-12 GHz 4-2.5 cm Ku 12-18 GHz 2.5-1.7 cm K 18-27 GHz 1.7-1.2 cm Ka 27-40 GHz 1.2-0.75 cm mm or W 40-300 GHz 7.5-1 mm REFRACTIVE INDEX c c : the speed of light in a vacuum n u: the speed of light in a medium u n: refractive index cu (always) n1 (unitless parameter) Actually, it has two components ; m n ik i 1 k Absorption of coefficient of the medium For air; m=1.003 REFRACTIVITY [N] Atm. Press. (mb, hPa) Temp. (°K) 77.6 e 7 Ne Vap. Press. (mb, hPa) N P 4810 4.03.10 2 T T f Num. of free electron / m3 Freq. of the radar (Hz.) Under normal atmospheric contions; Ground N Z N RADAR EQUATION FOR POINT TARGET radar storms Rainrate and ... radar Puls of energy into space by antenna Power A spherically expanding shell of energy Area 4r 2 r : the range from the radar Pt Power density : S S 4r 2 P The power intercepted bye the target P Pt gA target 4r 2 The amount of energy detected by radar will be: P . Ae Pt . g . A . Ae Pr Pr 4r 2 4 2 r 4 Ae : The effective area of the receiving antenna gλ 2 Pt . g 2 .2 A Ae Pr 4π 64 r 3 4 THE BACK-SCATTERING New! CROSS-SECTIONAL AREA OF THE TARGET A Pt . g 2 .2 Final Form Pr 64 3 r 4 SPHERICAL TARGETS A sphere is LARGE r 2 “Large” : D / 10 RAYLEIGH A sphere is SMALL region “Small” : D / 0.1 2 : 5 K D 6 (Battan, 1973) In the Rayleigh region 4 2 K : related to the complex index of refraction of the material Meteorological targets small RAYLEIGH MET. RADAR USE REGION 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.