14 Encounters

Vessels meet at sea for a variety of reasons, including transshipment (transferring catch, crew, fuel, etc.), and these encounters between vessels are of interest for monitoring illegal behavior.

14.1 Key Tables

pipe_ais_v3_published.product_events_encounter - Same as the encounters table but with a schema intended for use in products and consumed by the APIs. This means that there is one row for each of the two vessels in an encounter and the two rows must be joined together to have the information associated with both vessels on the same row (see query examples). This is a view of product_events_encounter_vYYYYMMDD that always provides data from the latest version (vYYYYMMDD) of the table but using the underlying table is deprecated and will be removed in a future pipeline release. Instead, the product_events_encounter view should be used.
pipe_ais_v3_published.product_events_encounter_vYYYYMMDD (deprecated) - This is the underlying table that pipe_ais_v3_published.product_events_encounter is based on. The YYYYMMDD suffix indicates the date of the version of the table. Usage of this table is deprecated and will be removed in a future pipeline release. Instead, the product_events_encounter view should be used.
pipe_ais_v3_published.encounters - Source table for the product_events_encounter_vYYYYMMDD table. This is not filtered by speed and has one row per encounter.

14.1.1 Source Tables

14.2 Data Description

When two vessels are observed in close proximity for an extended period of time it is considered an encounter. product_events_encounters applies the additional constraint that both vessels must be moving very slowly. Encounters occur when:

2 vessels within 500 meters of each other Minimum duration of 2 hours 10 kilometers from a coastal anchorage traveling <2 knots [product_events_encounters only]

For more information, see data training slides on encounter and loitering events HERE.

14.2.0.1 Definitions used in RFMO Transshipment Reports

GFW, in partnership with The Pew Charitable Trusts, has produced annual reports covering the years of 2017-2019 on transshipment activity in the the five major tuna RFMOs. These reports compare reported activity to potential transshipment, fishing, and port activity detected on AIS. The definitions of encounter and loitering events used for these reports are as follows.

Encounters: when two vessels are within 500 meters of each other for at least 2 hours and traveling at < 2 knots, while at least 10 kilometers from a coastal anchorage (Miller et al. 2018).

14.3 Caveats & Known Issues

GFW has never created encounters for short events on either side of the UTC day boundary - specifically those that start between 10pm and 12am or end between 12am and 2am. This is a known issue that will be fixed in the future, for more information see PIPELINE-2137 and this Slack thread
Point nature of events; if ais transmission is poor, the average location can be inconsistent with full location of tracks during time period. In addition, due to the way events are combined across days, average event parameters are approximate.
Due to the definition of encounter and loitering events, loitering events can overlap with encounter events.
Maintaining up to date identity changes of carrier and fishing vessels of interest in encounters between carrier and fishing vessels. Always use the most up-to-date identity tables, and verify results when possible.
Vessels may encounter more than one vessel at a time, an issue that comes up frequently in the presence of gear, but also occasionally with multiple vessels meeting.

14.4 Example queries

Needs updating. Removed links until queries are updated/removed.

encounters_1_ssvid.sql - this query pulls information on both vessels in the encounter, including vessel attributes that are nested within the event_vessels field
encounters_2_carriers_fishing.sql - this query identifies encounters between carrier and fishing vessels, pulling from the shiptype attribute used in Products (eg mirroring the encounters you would expect to see in Products as of June 2023 when this query was drafted).
encounters_3_iccat.sql - new example query that pulls out encounters that occurred inside ICCAT. Pulls using the ICCAT shapefile in the pipe_regions_layers bin. Technically you could also use the method in the below example query to identify encounters in ICCAT - both pulling region information from within the published events table, and using the regions shapefiles in the pipe_regions_layers should yield the same results.
encounters_3_no_take_mpa.sql - new example query that pulls out encounters that occurred inside a no take MPA based on the region information in the Map.
encounters_4_original_table.sql - this query pull encounters with an average speed of greater than 2 knots from the original encounter table that is the base for the published event encounter table. Note, for the most part, the only encounters in the original table that are not in the published_event_encounter table, are those encounters with an average speed above 2 knots.
published_events_unnest_auth_info.sql - how to pull event authorization from published event table schema
loitering_overlap_encounters.sql
analysis-pew-ts-reports/rfmo/rfmo-yyyy: see queries folder for BQ data pull and analysis folder for data cleaning and analysis