How to centralize access to Analysis Ready Data?

Overview

VirtualAir provides a unified way to centralize and access Analysis Ready Data (ARD) from distributed air quality observatories. The platform supports OGC SensorThings API (STA) compatible observatories

It uses a two-tier architecture that separates observatory registration from data access, enabling integration of STA-based sensor networks while ensuring full interoperability through standardized APIs.

Platform Components

1. VirtualAirApi

Central registry service for SensorThings observatory metadata.

2. VirtualAirDataApi

Standardized data access layer implementing OGC SensorThings API v1.1.

3. Web Interface

User-friendly portal for registering and managing STA-compatible observatories.

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What This Architecture Enables

• Register observatories once in a central catalog

• Expose data through a unified, interoperable STA endpoint

• Provide Analysis Ready Data with automatic aggregation and processing

• Enable cross-network data discovery across multiple SensorThings observatories

Why is this relevant?

1. Interoperability Across Sensor Networks

VirtualAir reduces fragmentation by:

• Implementing the OGC SensorThings API standard

• Providing a neutral, harmonized data model

• Supporting OData-style queries ($filter, $expand, $top, $skip)

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2. Analysis Ready Data Built-In

VirtualAir delivers ARD features out of the box:

• Automated hourly aggregations (min, max, avg, stddev)

• Quality metrics for each aggregation window

• Temporal aggregation via MultiDatastreams

• Standardized units (e.g., μg/m³)

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3. Simplified Data Discovery

Users can:

• Query a single endpoint for all observatories

• Explore sensors, parameters, and locations

• Access real-time and historical observations

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4. Minimal Integration Effort

• Observatory operators register once

• Data consumers integrate once

• No need to maintain multiple observatory connections

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5. Standards Compliance

VirtualAir supports:

• STAPLUS

• ISO 8601 time formats

• GeoJSON

• OGC O&M (Observation & Measurements)

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System Architecture

• Observatory owners register their SensorThings API endpoint using the VirtualAir Web Interface or by calling the VirtualAirApi directly.

• The VirtualAirApi validates the endpoint and stores its metadata (base URL, version, extensions, unique code) in the PostgreSQL registry database.

• Data consumers query the VirtualAirDataApi, a unified STA-compatible gateway.

• The Data API:

  • Retrieves metadata from the registry

  • Connects to the registered SensorThings observatories

  • Fetches observations

  • Performs automatic aggregation (hourly, daily, etc.)

  • Produces Analysis Ready Data (ARD)

• The ARD is returned to the consumer as a standardized SensorThings API v1.1 JSON response.

How to Use VirtualAir

For Observatory Operators

Option 1: Web Interface (recommended)

Visit: https://web-virtualair.nilu.no/

Register your STAPLUS-compatible SensorThings observatory.

Provide:

• Base URL (SensorThings API)

• API version

• Optional extensions

After registration you will:

• Receive a unique 4-character observatory code

• Your observatory becomes accessible via VirtualAir

Option 2: API Registration

Endpoint: POST /observatory → https://api-virtualairco.nilu.no/

Authentication: JWT

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Request Body

{
  "baseurl": "https://your-observatory.example.com/v1.1",
  "version": "1.1",
  "extension": null,
  "formatnavlinks": null
}

Response

{
  "id": 1,
  "code": "ABCD",
  "baseurl": "https://your-observatory.example.com/v1.1"
}

For Data Consumers

Base URL: https://api-virtualair.nilu.no/v1.1

Implements the full SensorThings API v1.1.

Example Queries

1. Discover all observatories

GET /Things

1. **Observations from a Datastream

GET /Things(1)/Datastreams(123)/Observations

1. **Filter by time

GET /Datastreams(123)/Observations?$filter=phenomenonTime ge 2024-01-01T00:00:00Z and phenomenonTime le 2024-01-31T23:59:59Z

1. **Hourly aggregated ARD

GET /MultiDatastreams?$filter=properties/aggregateUnit eq 'Hours' and properties/aggregateFor eq '/Datastreams(123)'&$expand=Observations

Response includes:

• Averages

• Min / Max values

• Standard deviation

• Observation counts

• Expand related entities

1. **Expand related entities

GET /Things?$expand=Locations,Datastreams

Technical Implementation

Technologies

• .NET 8

• PostgreSQL

• Dapper

• Docker

• Swagger / OpenAPI

• JWT Authentication

Features

• Caching

• Pagination

• OData query support

• Standardized error responses

• CORS support

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Useful Resources

Standards

• OGC SensorThings API

• ISO 8601

• EEA Units of Measurement

VirtualAir

• Web Interface: https://web-virtualair.nilu.no/

• Data API: https://api-virtualair.nilu.no/v1.1

• Registration API: https://api-virtualairco.nilu.no/

Developer Resources

• GitHub Repositories:

  • VirtualAir Web

  • VirtualAir API

  • VirtualAir Deployment

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Getting Started

1. Explore the API

2. Register your observatory

3. Query data

4. Integrate VirtualAir into your applications

Support

• Consult API documentation

• Review the SensorThings API standard

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• How to offer observations with a neutral data model and in an interoperable API?