Operational Use of Radar & ARPA

  • RADAR Overview

    • RADAR stands for RAdio Detection And Ranging.
    • Developed for military use during World War II.
    • Uses electromagnetic waves (radio waves) for detecting objects.

  • Radar Functionality

    • Measures range, direction, and speed of objects.
    • Pulses of radio waves are transmitted, reflected back from objects, returning energy processed to determine target location and speed.
    • Key Tasks Onboard Ships:
    • Collision avoidance.
    • Navigation assistance in poor visibility.

  • Radio Waves Characteristics

    • Radar waves travel straight like light, affected by atmospheric conditions.
    • Speed of radio waves is approximately 162,000 nautical miles/second.
    • Display of radar waves includes varying energy, frequency, amplitude, wavelength, and speed, with energy measured in watts.

  • Frequency Types

    • X Band: 3 cm wavelength (9,000 MHz) - sensitive for small vessels.
    • C Band: 5 cm wavelength (5,000 MHz) - suitable for navigation and performs well in adverse weather.
    • S Band: 10 cm wavelength (3,000 MHz) - covers larger areas, less affected by atmospheric conditions but requires larger antennas.

  • Radar Components

    • Five Major Components:
    1. Antenna
    2. Transmitter
    3. Receiver
    4. Display Unit
    5. Power Supply

  • Radar Scan Definitions

    • Radar Scan: 360° rotation of antenna.
    • Radar Sweep: Transmission of a single pulse.

  • Pulse Repetition Frequency (PRF)

    • Indicates number of pulses sent per second.
    • Longer pulses provide longer range but lower resolution; shorter pulses have better range resolution but less overall range.

  • Radar Range Factors

    • Effective detection depends on antenna height, target size, weather, and environmental influences.
    • Formula for Radar Horizon:
      R<em>MAX=2.2imes(ext√h</em>1+ext√h2)R<em>{MAX} = 2.2 imes ( ext{√}h</em>1 + ext{√}h_2)

    where h<em>1h<em>1: height of the radar, h</em>2h</em>2: height of the target.

  • Discrimination Capabilities

    • Range discrimination ability is affected by pulse length and spot size.
    • Bearing discrimination depends on horizontal beam width; improvements can be made with better focusing and brightness settings.

  • Environmental Effects

    • Conditions such as humidity, rain, fog, and sea clutter can hinder radar performance.
    • Techniques like Sensitivity Time Control (STC) help manage sea clutter visibility.
    • False Echoes can occur from reflections within the ship or interference from other radars.

  • Errors and Limitations

    • Antenna placement can create blind sectors where objects are not detected.
    • Accuracy can be influenced by heading marker error, radar shadow, and centering errors.

  • Measurement of Range

    • Range accuracy is high; typically involves fixed range rings for target distance assessment.
    • Variable range rings can enhance precision, adapted according to the situation.

These notes summarize the key concepts related to the operational use of radar and ARPA (Automatic Radar Plotting Aids), aiding in the understanding of radar technology and its applications in maritime contexts.