Radar and Satellites

Wing Commander Rajagopal

Radar and Satellite Reports

Types of Weather Radar

  • Ground weather radars are classified according to their function.
  • Quantitative Radars (10 cm): Measure the intensity and rate of precipitation.
  • Ultra-Sensitive Radars: Detect cloud convection and study Clear Air Turbulence (CAT), gravity waves and lee waves.
  • Plan Position Indicator (PPI): Displays weather echoes in plan view using range and bearing.
  • Range Height Indicator (RHI): Displays the altitude or vertical profile of weather echoes such as Cumulonimbus (CB) cells.
  • Doppler Weather Radar (DWR): Uses the Doppler principle to detect and forecast thunderstorms, tornadoes, heavy rainfall, dust storms and sandstorms.
  • Doppler radars estimate wind velocity and help predict wind shear, turbulence and Clear Air Turbulence (CAT).
  • They can also detect gust fronts, micro-bursts, downbursts and tornadoes.

Indian Weather Radars

  • The Indian Integrated Upper Air Sounding System (IIUASS) is an indigenous X-band weather and wind-finding multi-meteorological radar system.
  • The Radiosonde network consists of:
    • 14 S-band (10 cm) radars.
    • 25 Digital X-band (3 cm) radars.
    • 5 Doppler Weather Radars (DWR).
  • The system has a usable range of approximately 200 km and a maximum range of 400 km.
  • Operational weather monitoring is generally carried out between 25 NM and 75 NM.

Weather Radar Echoes

  • Cloud Echoes:
    • Stratiform clouds produce diffuse echoes with a bright band caused by melting ice crystals or snowflakes.
    • Convective clouds produce sharp-edged echoes. Blurred edges indicate weakening clouds.
    • A line of echoes generally indicates a squall line.
    • Strong echoes with high tops indicate Cumulonimbus (CB) clouds.
    • Severe storms produce intense, sharply defined echoes due to large supercooled water droplets.
    • Hook-shaped or appendage echoes indicate violent storms.
    • A figure-six pattern, dry holes, rapid development, broad horizontal echoes and converging echoes are associated with tornadoes.
    • Weak storms may appear as a bright band.

Airborne Weather Radar (AWR)

  • Airborne Weather Radars are generally X-band (3 cm) radars designed to detect large water droplets in clouds.
  • The radar scans using a conical beam covering approximately 70° on either side of the aircraft.
  • Modern radars are multimode, digital, lightweight and support:
    • Weather detection.
    • Ground mapping.
    • Transponder operations.

Colour Codes in Airborne Weather Radar

  • Red: Heavy precipitation, thunderstorms, hail, strong winds, tornadoes, severe turbulence and rainfall greater than 12 mm/hr.
  • Yellow: Moderate precipitation, reduced visibility, moderate turbulence and rainfall between 4–12 mm/hr.
  • Green: Light precipitation, slight turbulence, reduced visibility and rainfall between 1–4 mm/hr.

Example of Radar Report (RAREP)

IDENTIFIER              RAREP
STATION INDEX NUMBER    12345
DATE & TIME (UTC)       15030
AZIMUTH/RANGE (KM)      270/050 300/060 350/025
ECHO CHARACTER          SQL LN
INTENSITY TREND         INCG
ALTITUDE                ALTD
DIRECTION/RANGE/ALT     270/09/050
BRIGHT BAND             280/30
ANOMALOUS PROPAGATION   AP 300/330/150

Types of Meteorological Satellites

  • Polar-Orbiting Satellites:
    • Orbit between 650 km and 1000 km.
    • Cover the Earth twice every 24 hours.
    • Pass over the same location approximately every 12 hours.
    • Example: NOAA (K, L, M Series).
  • Geostationary Satellites:
    • Orbit at approximately 36,000 km above the Equator.
    • Remain over the same geographical position because their orbital period matches Earth’s rotation.
    • Examples:
      • GOES (USA)
      • EUMETSAT (Europe)
      • Japanese Geostationary Satellite (130°E)
      • INSAT (India)
    • Five geostationary satellites are sufficient to provide nearly global coverage.
    • Satellite imagery is generally updated every 3 hours.
  • Indian Meteorological Satellites: KALPANA, INSAT-3D and METSAT.
  • The India Meteorological Department (IMD) also receives meteorological data from NOAA, MODIS (USA) and OCEANSAT.

Satellite Imagery

  • Satellite imagery is analysed using:
    • Brightness.
    • Texture.
    • Pattern.
    • Shape.
    • Structure.
    • Size.
  • Radiometers onboard satellites measure:
    • Radiation.
    • Cloud-top temperature.
    • Earth’s surface temperature.
  • These measurements are processed to generate information on:
    • Vertical temperature profile.
    • Humidity.
    • Cloud-top height.
    • Sea surface temperature.
    • Upper winds.
    • Convective clouds.
    • Mesoscale weather systems.

Example of Satellite Bulletin


IDENTIFIER              SAT BLTN
SATELLITE INFORMATION   BASED ON METSAT PIC
DATE & TIME             271200 UTC
CONVECTIVE CLOUDS       CURVED BAND OF VORTEX OVER EC BAY HAS REDUCED,
                        NOW CENTRED OVER 16N/91E RPT 16N/91E
LOW/MEDIUM CLOUDS       SCT TO BKN LOW/MED CLOUDS,
                        EMBDD MOD TO INT CONVECTION OVER
                        BAY OF BENGAL, ARABIAN SEA,
                        INDIAN OCEAN =