Relay Federation Status

SensorThings on ATProto

Environmental sensor data from Irish monitoring networks, published as structured, cryptographically signed records on the AT Protocol.

What & Why

This application visualises environmental sensor data – water levels, ocean conditions, air quality – that has been published to an ATProto Personal Data Server (PDS) using the OGC SensorThings entity model encoded as ATProto Lexicons.

Each sensor reading is a signed record in a Merkle tree. The data is publicly addressable, verifiable, and replicable by anyone who subscribes to the PDS firehose, without an API key.

Why ATProto for sensor data?

Signed & content-addressed: Every commit is signed by the publisher’s key pair. Consumers can verify data integrity without trusting the transport.
Portable identity: Each data source has a DID (Decentralised Identifier) that survives server migration. If the PDS moves, all references remain valid.
Replication by default: Any firehose subscriber automatically receives and can mirror the full dataset. No backup infrastructure is required.
Schema as contract: The dev.sensorthings.* Lexicons define the data model. Any PDS publishing conformant records participates in the federation.

Entity Model

The data follows the OGC SensorThings API entity model. Six entity types describe what is being measured, by what, where, and when:

Thing

A physical station or platform hosting sensors. Carries a name, location (lat/lon), and open metadata. Example: OPW gauge 26021 on the River Suir at Clonmel.

Sensor

An instrument or procedure that produces observations. Links to a datasheet or SensorML description. Example: Vaisala WXT536 weather transmitter.

ObservedProperty

The phenomenon being measured. Linked to a controlled vocabulary URI (CF Standard Names, QUDT). Example: air_temperature, PM_2.5 concentration.

Datastream central join

The pivotal entity: links one Thing + one Sensor + one ObservedProperty. Carries the unit of measurement and a scale factor for decoding integer results. All observations belong to exactly one Datastream.

Observation

A single measurement: a timestamp, a result value, and a reference to its parent Datastream. This is the high-volume record type. Example: 7.34 °C at 10:15 UTC.

FeatureOfInterest

The real-world feature being observed. Often implicit (the Thing’s location). Explicit when the observation target differs from the sensor location. Example: a river reach downstream of the gauge.

Lexicons

Each entity type is an ATProto Lexicon – a schema that defines the record structure and how records reference each other via AT-URIs. The namespace is dev.sensorthings.*.

⋄

No floating-point numbers. ATProto’s data model only supports integers. All numeric measurements are stored as scaled integers: the Datastream declares a resultScaleFactor (e.g. 3), and the Observation stores an integer (e.g. 2134). The real value is 2134 × 10⁻³ = 2.134. This is the same pattern used by Protocol Buffers and financial systems.

Field	Type	Description
`name`	string	Human-readable station name
`description`	string	Optional longer description
`location`	geoPoint	WGS84 coordinates as `latE7`/`lonE7` (integer × 10⁷, ~1 cm precision)
`properties`	object	Open metadata (manufacturer, deployment date, etc.)

Record key: human-readable slug, e.g. sandy-mills

at://opw.sensorthings.dev/dev.sensorthings.thing/sandy-mills

Field	Type	Description
`name`	string	Instrument or procedure name
`encodingType`	string	IANA media type of the metadata field
`metadata`	string	URL to datasheet or SensorML document

Record key: slug, e.g. sandy-mills-level

at://opw.sensorthings.dev/dev.sensorthings.sensor/sandy-mills-level

Field	Type	Description
`name`	string	Property name (e.g. “Water Level”)
`definition`	URI	Controlled vocabulary reference – CF Standard Names, QUDT, NERC P07

Record key: slug, e.g. water-level

at://opw.sensorthings.dev/dev.sensorthings.observedProperty/water-level
  → definition: http://vocab.nerc.ac.uk/collection/P07/current/CFSN0052/

The Datastream ties everything together. It references a Thing, Sensor, and ObservedProperty, and carries the unit and scale factor needed to interpret observation values.

Field	Type	Description
`thing`	AT-URI	→ `dev.sensorthings.thing`
`sensor`	AT-URI	→ `dev.sensorthings.sensor`
`observedProperty`	AT-URI	→ `dev.sensorthings.observedProperty`
`unitOfMeasurement`	object	`name`, `symbol`, `definition` (QUDT/UCUM URI)
`resultScaleFactor`	integer	Divides integer results: real = value × 10⁻ⁿ
`verticalDatum`	string	For water level: datum URI or label (e.g. Malin Head OD)

Record key: descriptive slug, e.g. sandy-mills-level-od

at://opw.sensorthings.dev/dev.sensorthings.datastream/sandy-mills-level-od
  → thing: at://…/thing/sandy-mills
  → sensor: at://…/sensor/sandy-mills-level
  → observedProperty: at://…/observedProperty/water-level
  → unitOfMeasurement: { name: "metre", symbol: "m" }
  → resultScaleFactor: 3
  → verticalDatum: "http://…/EPSG/0/5731"

Field	Type	Description
`datastream`	AT-URI	→ parent Datastream (carries unit & scale)
`phenomenonTime`	datetime	When the phenomenon was observed (ISO 8601)
`result`	union	Discriminated by `$type` – see below
`resultQuality`	token	`good`, `suspect`, or `missing`

Result types

numericResult categoryResult booleanResult arrayResult geoPointResult

Most observations use numericResult: a single scaled integer. Decode it using the parent Datastream’s resultScaleFactor.

// Water level observation: 30756 ÷ 10³ = 30.756 m (Malin Head OD)
{
  "datastream": "at://…/datastream/sandy-mills-level-od",
  "phenomenonTime": "2026-02-08T16:00:00Z",
  "result": { "$type": "…#numericResult", "value": 30756 }
}

Packs up to 1,440 observations for a single Datastream into one record, covering a time window (typically one day). Reduces commit overhead for high-frequency or historical data.

Field	Type	Description
`datastream`	AT-URI	→ parent Datastream
`windowStart`	datetime	Start of the batch window
`windowEnd`	datetime	End of the batch window
`observations`	array	Array of `{ t, result, q }` entries

Record key: {datastream-slug}:{compact-date}, e.g. sandy-mills-level-od:20260210T000000Z

Bundles multiple co-produced results from a single act of sensing. Used when measurements have no independent existence – e.g. wave statistics (H_s, H_max, T_p, mean period, mean direction) computed from the same accelerometer burst.

Field	Type	Description
`thing`	AT-URI	→ `thing` (not a Datastream – each entry carries its own property)
`sensor`	AT-URI	→ `sensor` that co-produced the results
`phenomenonTime`	datetime	Observation timestamp
`entries`	array	Up to 32 entries, each with its own `observedProperty`, `unit`, `scaleFactor`, and `result`

Used by the Marine Institute buoy network for wave statistics.

How records reference each other

Records point to each other using AT-URIs – stable, globally unique identifiers of the form:

at://{DID or handle}/{collection NSID}/{record key}

For example, an Observation references its Datastream by AT-URI. The Datastream in turn references its Thing, Sensor, and ObservedProperty by AT-URI. You can walk the entire reference graph from any record – try it in the Records browser.

Networks

Four Irish environmental monitoring networks are currently publishing:

OPW Water Level

Hydrology

Source: waterlevel.ie
Stations: ~50 active (of ~380 total network)
Cadence: Every 15 minutes
Parameters: Water level (local gauge zero & Ordnance Datum Malin Head)
Handle: opw.sensorthings.dev

Marine Buoys

Oceanography

Source: ERDDAP (Marine Institute)
Stations: 5 buoys (M2–M6)
Cadence: Hourly
Parameters: Atmospheric pressure, air & sea temp, humidity, wind, waves (H_s, H_max, T_p, period, direction)
Handle: marine.sensorthings.dev

EPA Air Quality

Air Quality

Source: airquality.ie
Stations: ~114 monitors
Cadence: Hourly
Parameters: PM₁₀, PM_2.5, NO₂, O₃, SO₂, CO
Handle: epa.sensorthings.dev

Met Eireann

Weather

Source: met.ie Open Data (CC BY 4.0)
Stations: ~25 synoptic stations
Cadence: Hourly
Parameters: Temperature, humidity, pressure, wind speed/direction, rainfall, present weather
Handle: met.sensorthings.dev

Consuming the Data

You don’t need this visualisation app to access the data. It is all publicly available on the PDS.

Browse records (REST)

List all records of a given type using the standard ATProto listRecords endpoint:

GET https://pds.sensorthings.dev/xrpc/
  com.atproto.repo.listRecords
  ?repo=opw.sensorthings.dev
  &collection=dev.sensorthings.thing

Fetch a single record with getRecord:

GET …/com.atproto.repo.getRecord
  ?repo=opw.sensorthings.dev
  &collection=dev.sensorthings.thing
  &rkey=sandy-mills

Subscribe to the firehose (WebSocket)

Receive all new commits in real time – the same mechanism this app uses:

wss://pds.sensorthings.dev/xrpc/
  com.atproto.sync.subscribeRepos

Events arrive as CBOR-encoded commit frames. Filter for dev.sensorthings.* collections to process only sensor data. No authentication required.

Links

PDS ATProto Spec Lexicon Spec OGC SensorThings

Station Freshness