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					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


         cu (always)               n1 (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  4r   2            r   : the range from the radar

                                  Pt
Power density : S             S
                                 4r 2
  P                The power intercepted bye the target


P 
     Pt gA                                    target
     4r 2

  The amount of energy detected by radar will be:


      P . Ae                           Pt . g . A . Ae
 Pr                            Pr 
      4r 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.

				
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