ARPA

ARPA — Automatic Radar Plotting Aid

ARPA (Automatic Radar Plotting Aid) is a sensor relative to ECDIS.

It performs the following tasks:

target detection;
calculation of target motion parameters;
target tracking;
calculation of passing conditions;
simulation of passing maneuvers;
target association;

A radar can be connected to ECDIS as ARPA.

Important

ECDIS does not contain a built-in ARPA system. ECDIS only receives and displays tracked target forms from an external ARPA via the NMEA protocol. All target detection, tracking, and motion prediction functions are performed by ARPA.

ARPA Setup

The sensor connection and setup are performed in accordance with the procedure.

Menu path
→ → Sensors → ARPA

Ensure that received message processing is correctly configured, header and message processing is enabled, and checksum verification is enabled.

ARPA transmits the following IEC 61162 sentence header:

RA — Radar;

Recommended ARPA Sentences

ARPA Sentences

$--RSD – Radar system data;
$--TLB – Target label;
$--TLL – Target latitude and longitude;
$--TTD – Tracked target data;
$--TTM – Tracked target message.

Important

If messages are not transmitted in the correct format or are transmitted with incorrect data, the display and processing of ARPA targets will not be possible.

Data transmission settings are configured in ARPA, not in ECDIS.

Tip

After connecting and configuring ARPA, enable the ARPA layer.

Target Association Setup

ARPA Sentences

No.	Parameter	Description
1	Supports targets association	Target association indicator in the ARPA sensor

Caution

Depending on the model, the radar may or may not support target association. Target association may be disabled in the radar by the user. Target association in the radar may not work for other reasons.

When configuring the ARPA sensor, specify whether the sensor supports target association:

Checkbox disabled — the sensor does not support target association. In this case, ECDIS independently performs association of targets received from ARPA (radar) and AIS.
Checkbox enabled — the sensor supports target association. In this case, ECDIS displays associated targets received from ARPA. ECDIS internal target association is disabled.

Caution

Incorrect ARPA sensor association settings may cause target duplication: the targets table and the screen will always display two targets instead of one associated target: an ARPA target and an AIS target.

ARPA Operational Features

Enabling ARPA Target Display

Tip

After connecting and configuring ARPA, enable the ARPA layer.

Menu path
→ Radar layer
or
→ → Targets → Show ARPA targets

Radar target settings

No.	Element	Description
1	Show ARPA targets	Enable Radar layer
2	ARPA and AIS target association	Enables/disables target association

After enabling the layer and configuring the visibility radius, ARPA targets will be displayed on the chart.

Warning

ARPA Target Limitations Compared to AIS

ARPA targets do not contain vessel identification information (name, MMSI, ship type, dimensions) or navigation status and destination information.

ARPA targets provide only:

Target position
Motion parameters (course, speed) — when transmitted by the connected ARPA system
Calculated approach parameters (CPA/TCPA)

For complete target identification and extended information, use AIS or ARPA and AIS target association.

Target Data Display

ARPA target settings are synchronized with the AIS target settings.

ARPA target data display

ARPA Target Data Features

Important

ARPA Dependency

ECDIS displays target data transmitted by ARPA. Positioning accuracy, motion parameters, and data update frequency depend entirely on ARPA settings and capabilities and radar configuration quality.

ECDIS does not accumulate target data for calculating target motion parameters (TMP) based on historical data. Motion vectors are displayed only when transmitted in real time from ARPA.

Data reception features:

Data update frequency is determined by the connected ARPA system settings
Motion parameters (speed vector, course) are displayed only when transmitted in TTD/TLB messages
Positioning accuracy depends on the radar characteristics and processing algorithms in the connected ARPA system

AIS Target Transmission Features

When sentences are connected — $--TLB and $--TTM — ARPA can relay AIS targets.

Guard Zone

Hint

The guard zone processes AIS, DSC, and ARPA targets equally.

The guard zone on the ENC is displayed only when the AIS layer is enabled. Target monitoring does not require visual display of the guard zone on the chart; alarms are generated for all dangerous targets.

CPA/TCPA

Hint

CPA/TCPA monitoring processes AIS targets and ARPA targets equally.

Lost Targets

In the settings, enable Lost target alert — targets for which no data is received from ARPA within the delay period will be marked as lost and removed from the chart with an appropriate warning generated.

Warnings are generated for all ARPA targets. After acknowledgement or after a specified time period, targets are removed from the chart.

Warning

Importance of Monitoring Lost Dangerous Targets

If data for a dangerous target (target with CPA/TCPA alarm or in the guard zone) stops being received, it remains on the chart until acknowledged or manually deleted. The navigator must manually track such targets, as the system does not delete them automatically, despite the cessation of data updates.

It is recommended to regularly check the currency of dangerous target data and manually delete lost targets after visual assessment of the situation.

ARPA and AIS Targets Association

Enable target association:

Menu path
→ → Targets → Settings → ARPA and AIS targets association

ARPA and AIS target association settings

Targets on the chart are displayed separately: AIS targets and ARPA targets. ECDIS performs verification of associated targets: whether an AIS target and an ARPA target are the same target, or whether they are different targets moving in the same direction.

Attention

ECDIS performs association only of AIS targets received from AIS and ARPA.

Association of AIS targets and radar targets is performed in ARPA and transmitted to ECDIS with an association indicator.

The criteria for target association are the motion parameters of the target transmitted by the radar in TTD/TLB messages and by AIS in VDM messages. Target association operates only on active AIS targets, i.e., the target must be within the auto-activation zone or be manually activated.

If Show associated radar targets as AIS targets (ARPA and AIS targets association) is enabled for AIS in the Filtration and Activation settings, the associated target will be displayed with the AIS target symbol, including vessel dimensions. When viewing target information in the multifunction window, the information will be shown as for an AIS target.

ARPA and AIS target association result

Table 1 ARPA Warnings
TEXT	CATEGORY	CONDITION
ARPA data reception stopped: <source name>	Alarm	When data from the connected ARPA system stops being received according to the configurable timeout.
ARPA data integrity violation: <source name>	Warning	If the sentence fails the CRC check.
Target data lost <target ID>	Warning	The waiting time for a message from the target has exceeded the set limit.
CPA/TCPA <target ID>	Alarm	The target does not meet safe passing criteria. The calculated CPA/TCPA of the ARPA target are simultaneously less than or equal to the set values. CPA and TCPA values are set in the CPA/TCPA settings section.
Dangerous target <target ID>	Alarm	The target has entered the guard zone. The guard zone radius is set in the Guard zones settings section.

Note

Alarm and Warning Processing

All alarms and warnings related to ARPA targets are displayed in the ECDIS notification area. The navigator should:

Acknowledge alarms promptly — especially when operating in areas with heavy traffic
Check alarm causes — review detailed target information in the multifunction window
Monitor lost dangerous targets — they remain on the chart and require manual control

Recommendations for Using ARPA Targets

Tip

Optimal Use of ARPA Targets

For effective use of ARPA targets, it is recommended:

Use in combination with AIS — enable ARPA and AIS target association for complete target information
Configure guard zone and CPA/TCPA — this ensures automatic monitoring of dangerous targets
Regularly check data currency — for dangerous targets, as lost dangerous targets remain on the chart
Use visual observation — for targets with limited information (no identification, vessel dimensions)