Water quality sensors for research and citizen science

Water measurement starts with the property

“Water quality” covers many different properties. Colour, clarity, spectral reflectance, temperature, nutrients, microbial contamination and specific pollutants do not come from one universal phone sensor. A credible project first identifies the property and reference method, then designs the instrument, protocol, participant guidance, calibration, quality control and data infrastructure around it.

Pocket Science has two prominent but different water-observation lineages. iSPEX2 is currently a professional research instrument, not a citizen-science app or project. It supports low-cost above-water radiometry on a smartphone. Mini Secchi supports participatory observations of water colour and clarity. Both connect a physical method to software and a research workflow, but their audiences, measurements and readiness differ.

Two water quality sensor lineages

Mini Secchi: water colour and clarity

Mini Secchi modernises two established visual observations. Participants lower a compact disk to record Secchi depth and compare natural water colour with the Forel–Ule scale. The app guides the procedure and stores observation context for the research programme.

The research record spans the original printable device, Lake Vembanad citizen monitoring, estuarine research, satellite-product evaluation, Horizon 2020 MONOCLE and an instrumented open-source profiling prototype. In 2026 Pocket Science signed a new contract with the University of Exeter and the US SOCON collaboration to rebuild and improve Mini Secchi.

Read the Mini Secchi publications and project evidence

iSPEX2: above-water spectral reflectance

iSPEX2 places a calibrated optical add-on in front of a smartphone camera. A defined sequence of water, sky and grey-card observations supports the derivation of above-water Rrs. PML successfully derived Rrs with iSPEX2 during professional campaigns, supported extensively by Pocket Science. The result is a low-cost research route that can be compared directly with much more expensive ocean-colour radiometry in the tested workflow.

The preserved evidence includes WISP-3 reference data from Venice, selected So-Rad matchups from the PML campaign and a reference protocol built around systems such as So-Rad with TriOS-RAMSES radiometers. This supports comparison of above-water Rrs measurements; it is not a claim that the instruments have identical automation, calibration traceability or operating ranges.

The evidence chain includes the 2014 iSPEX1 atmospheric campaign paper, the 2019 SPECTACLE camera-calibration framework, the 2020 iSPEX2 instrument paper, 2022 research on calibrated smartphone radiometry above water, and the 2024 preregistered aquatic validation. The public project documents continuing international campaigns in 2025 and 2026. Pocket Science now maintains a complete local preservation mirror of its 11 wiki pages, 359 public files and source integrity metadata.

iSPEX2 is not yet a consumer-ready general water-quality sensor. The research batch is fully distributed, no units can currently be ordered and air-quality use has not been implemented or validated for iSPEX2.

Read the iSPEX2 publications and open validation evidence

Which method fits which question?

Need	Relevant route	Important boundary
Participatory water colour and clarity	Mini Secchi	A visual field method, not a universal pollution or safety test.
Above-water spectral Rrs research	iSPEX2	Research instrument requiring protocol, calibration and processing; currently unavailable to order.
Temperature, conductivity, oxygen or another existing sensor	A sensor-connected app	Validity follows the selected instrument, calibration and deployment method.
A new camera-derived or optical property	Research and validation phase	The method needs an appropriate reference before field claims are made.
Participation, dashboards and long-term data access	A complete observatory	Governance, support and operating lifetime need explicit ownership.

What Pocket Science can build

• Guided field apps
  Mobile and web procedures, offline work, multilingual interfaces, context and method-specific checks.
• Sensor and camera integration
  Connected instruments, optical attachments, phone cameras and processing where the research requires them.
• Calibration and validation workflows
  Reference comparisons, provenance, quality indicators and versioned processing with scientific partners.
• Researcher tools
  Dashboards, review routes, documented exports, APIs and FAIR-data connections.
• Self-hosted infrastructure
  Managed security, privacy, backups and monitoring without dependence on an external public-cloud platform.
• Participation and continuity
  Recruitment, onboarding, feedback, end-user support and an operating plan beyond launch.

Evidence, not a black box

For Mini Secchi, start with the 2025 open-access synthesis and its cited project literature. For iSPEX2, inspect the preserved open programme archive and preregistered aquatic validation. Pocket Science keeps the distinction between a published method, a successful research result and a consumer-ready product explicit.

Plan a citizen science water project

Bring the water property, reference method, intended participants, field environment, platforms, data needs and operating lifetime. Pocket Science can help turn that into a scoped sensor-connected app or a complete participatory observatory. Start with the research question.