The role of electromagnetic wave propagation is determining the target range. RADAR range is fundamentally a timing problem: the system measures how long a pulse takes to travel to a target and return. The radio waves travel at the speed of light, enabling predictable timing relationships, with the concept of converting travel time (microseconds) into distance (nautical miles). The key constants used in marine RADAR calculations:
- RADAR range constant: 150 meters per microsecond
- One RADAR mile: 12.34 microseconds
Distance–Time Relationships is an important concept in marine RADAR. The following examples illustrate the concept:
- Three nautical miles: A radio wave travels this distance in 18.51 microseconds.
- Five-mile target: The echo returns in 61.7 microseconds.
- Ten nautical miles: A pulse travels out and back in 123.4 microseconds.
- 308.4 microseconds echo: Corresponds to a target at 25 nautical miles.
RADAR systems use these values internally: synchronizer and timing circuits convert microsecond measurements into range displays, and the operator sees these calculations on the PPI (Plan Position Indicator). Understanding these numbers improves the interpretation of RADAR returns, which has operational importance for navigators. It highlights implications for collision avoidance, navigation in restricted visibility, and target tracking. Mastering the fundamentals of RADAR timing reinforces that accurate range interpretation depends on understanding the relationship between microseconds and nautical miles.