CMRT CMRT Navigation Integration & Display Systems 1 — Questions and Answers
Question 1: What is the primary purpose of ARPA (Automatic Radar Plotting Aid) in marine radar systems?
- To enhance display brightness
- To automatically track targets and predict collision risk (Correct answer)
- To calibrate antenna rotation speed
- To filter sea clutter
Correct answer: To automatically track targets and predict collision risk
ARPA automatically tracks radar targets, calculating their course, speed, and closest point of approach (CPA) to assess collision risk.
Question 2: In a radar overlay on an Electronic Chart Display (ECDIS), what must be synchronized between the two systems?
- Audio alert tones
- Position reference and heading data (Correct answer)
- Printer output format
- Screen refresh rate only
Correct answer: Position reference and heading data
Accurate radar overlay on ECDIS requires synchronized position (GPS) and heading data so radar returns align correctly with the chart.
Question 3: Which display mode shows radar targets relative to the vessel's bow and rotates as the ship turns?
- North-Up
- Course-Up
- Head-Up (Correct answer)
- True Motion
Correct answer: Head-Up
Head-Up mode displays targets relative to the ship's bow, with the top of the screen always representing the direction the vessel is heading.
Question 4: What does 'sea clutter' on a radar display represent?
- False echoes from nearby vessels
- Returns caused by rough sea surface waves near the antenna (Correct answer)
- Interference from other radar systems
- Electronic noise within the receiver
Correct answer: Returns caused by rough sea surface waves near the antenna
Sea clutter consists of radar returns from wave surfaces near the vessel, which can mask genuine targets at short range.
Question 5: Which NMEA sentence is most commonly used to feed GPS position data into a marine radar system?
- NMEA $GPVTG
- NMEA $GPGLL or $GPRMC (Correct answer)
- NMEA $GPGSV
- NMEA $GPGSA
Correct answer: NMEA $GPGLL or $GPRMC
$GPGLL (geographic position) and $GPRMC (recommended minimum data) both carry latitude/longitude and are standard feeds for radar position input.
Question 6: In True Motion display mode, what remains stationary on the radar screen?
- The own-ship symbol
- Stationary land and fixed targets (Correct answer)
- All tracked ARPA targets
- The heading line
Correct answer: Stationary land and fixed targets
In True Motion mode, stationary objects like land appear fixed on the screen while the own-ship symbol moves, reflecting actual vessel motion.
CMRT CMRT Navigation Integration & Display Systems 1
What is the primary purpose of ARPA (Automatic Radar Plotting Aid) in marine radar systems?