Radar Navigation

-- Pulse Repetition Frequency (PRF)

# of pulses/second. Greater PRF reduces time available to listen. Longer ranges require lower PRFs.

-- Beamwidth error

A radar beam widens as it gets further away from the Ship causing distortion of objects detected. Increases as the vessel moves further away from the object detected.

-- Attenuation error

Absorption and subsequent scattering of the beam energy as it is transferred through the atmosphere. Usually leads to a significant reduction in the strength of the echo. More pronounced in instances where there is a high frequency and short wavelengths.

-- Receiver

Amplifies the returning echoes and demodulates them for display (increasing Doppler shift analysis).

Limitations

Blind Arcs & Blank Sectors. Sea and Rain affect RADAR performance. EM Transmission Hazards. Bearing resolution can be poor.

Using EBL

Contact Management by RADAR - Which contact concerns you? Use the EBL to determine CBDR and risk of collision on a contact: - Place an EBL on the contact. - If the contact tracks down the EBL, CBDR and a risk of collision exists.

Tools: Variable Range Marker (VRM)

Controllable range ring. Used to: - Mark turns. - Set range(s) for contact reporting. - Set range(s) to monitor distance to land or a RADAR aid. - Maintain position in channel by monitoring cross track error.

Process of finding RADAR error prior to getting underway

Determine GPS (pier-side true position). Measure true distance to RADAR aid forward/aft. Determine RADAR distance to same RADAR aids. The difference is the RADAR error.

Advantages

Determine range of objects. Day, night and low visibility use. Fixes may be determined at greater distances from land than by visual means. Calculation of the position may be obtained from just a single object (using range and bearing, running fix). Can be used to detect the presence of heavy precipitation.

-- Index error

Difference between the ranges of two points on a map and the range detected by the radar. Measured by obtaining a pierside fix by all available means. Measure the ranges: - Charted range to a NAVAID. - Radar range to same NAVAID. - Compare; difference is the error. Best detected by selecting two objects (one forward, one aft) to determine the error.

-- Display

Display info and provide access to functions.

Contact tracking

Embedded software allows automatic or manual contact tracking. CPA / TCPA / Course / Speed / Range / Bearing. Be aware - there is a time delay for radar to build an accurate solution! AIS and other sensor information can also be displayed.

Max/min ranges

Every RADAR has max/min range. Min is determined by pulse length. - Radar cannot receive a returning echo until the trailing edge of the pulse has cleared the antenna and the transmit/receive switch has been switched to receive. Maximum determined by frequency, peak power, pulse length and pulse repetition frequency (PRF): - Usually limited by the curvature of the earth to line of sight or slightly greater. - Attenuation/reduction of signal strength.

Radar settings

Filters are used to block unwanted returns (auto or manually): - Rain: returns from atmospheric conditions. - Sea: sea clutter. Gain (amplification of return) can also be adjusted. - RADAR video image is determined by these settings.

-- Transmission frequency

Higher = short range/better resolution. Lower = longer range/poorer resolution. High frequency: fire control radar, imaging radar. Low frequency: ground-penetrating radar, counter-stealth radar.

Tools: Electronic Bearing Line (EBL)

Incorporates Electronic Bearing Line (EBL). Line from own ship (or offset point). Can be set to any bearing. Used to: - Determine the bearing drift/movement of a contact (monitor for CBDR--constant bearing decreasing range). - Assist identifying land marks. - Mark turns.

-- Duplexer

Isolates the receiver from the transmitter while permitting them to share a common antenna.

Tactical Applications: Task Group Sector Screen

LOOK AT SLIDES.

ECDIS - RADAR Image Overlay

Most common Navigation Radars are interoperable and integrated with ECDIS software, including ECDIS-N (VMS). Radar Image Overlay (RIO) allows immediate assessment as to whether real time, computed position is correct. If the Radar Image is not aligned to the land there is either an issue with the radar or the position ECDIS thinks it is in. Other systems feed into Radar such as the Gyro. If you have a gyro fault, this will impact Radar capability. For example, a gyro error of 2 degrees will impact how the RIO is aligned to the chart. The longer the distance from the object, the greater the error. This means you have lost a quick, easy, visual means of proving the ECDIS to be correct!

-- Multiple echoes

Multiple echoes occur as a result of several reverberations of the echoes from a different ship and from own ship multiple times. The display screen may show more than two or three objects being detected.

Maritime applications

Navigation - Fixing / Pilotage. Spatial Awareness / Anti-Collision. Weapons / Targeting. Aircraft Control. Weather Detection.

Uses

Navigation: - RADAR LOP / PI / Anchor. Anti-Collision: - Detect and track. - Positioning (e.g. DIVTACs). - Rules of the Road: all available means, use of radar plotting, safe speed considerations. Targeting / Fire Control. Aircraft Control. Weather Detection / Avoidance.

Using RADAR during pilotage

Parallel Indexes (PIs): Allows continuous monitoring of ship's position relative to planned track: - Draw line parallel to track touching conspicuous radar point. - Measure distance from this line to track using EBL. Can also be used for: - Restricted Water Transits. - Underway Replenishment. - Reduced or poor visibility situations. - Reduced number of Visual NAVAIDs. - To Assess set & drift.

-- Transmitter

Produces electromagnetic waves of energy.

RADAR stands for History

Radio Detection and Ranging. Developed during early 1900s. Military applications since 1935. Beyond visual visual range detection of objects. Provided Britain's Royal Air Force with air superiority over the Luftwaffe.

RADAR image and height of tide

Shoreline with large tidal ranges can change its RADAR image between low and high tides.

Disadvantages

Subject to mechanical and electrical failure. Max and Min Ranges. Interpretation of display not always easy: - Assumptions based on "scanty radar information". Small objects may not be detected (esp. in high sea states). Requires transmission from the ship: - May not be tactically desirable (EMCON, or emission control, Policy). - Can be counter detected and tracked.

-- Double echoes

These happen when radar signals bounce off differing parts of the ship and back to the receiver.

How RADAR works

Transmission and Reception of Radio (EM) Waves. - EM Waves Travel at Speed of Light - Dist (Range) = Time / Spd (3 x 108 ms-1). - Applications in all environments include contact detection, targeting and NAVIGATION. - Frequency / Pulse Length selected for desired range and image resolution. - Navigation RADARs usually have a high frequency and low pulse length which causes them to have higher resolution, but shorter range. Reflection (Echo) is received, amplified and processed by the RADAR into an image.

-- Antenna

Transmit outgoing pulses/receive returning echoes.

-- Pulse length

Transmit period. Ensure radar transmits sufficient power to generate detectable echo.

Anchoring by RADAR

Use: - PI (parallel index): monitor position relative to track. - EBL: monitor Head Bearing and Drop Bearing. - VRM: count down for Drop Range. NAVAID ahead of Ship is best to be used. - RADAR Operator relays ranges for the head range to mark the distance from anchorage. It is perfectly possible to anchor the Ship without ever looking out of the window! Think ResVis!

-- Indirect wave error

When a radar beam is emitted from the vessel, it is supposed to travel in a straight line direct to the contact. However, there are instances where the beam falls into the sea and it is deflected further which makes it travel a longer distance than if it would have traveled in a straight line.