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NowYouSea
Field validation - Lake Quily - June 2025

Our first tests in real conditions.

First deployment of a NowYouSea CTD in freshwater: sound speed profile measurement over 46 meters depth, with cross-validation against a professional probe.

Key figures

What the field confirmed.

< 0.35 %
Speed error
vs theoretical reference
63x
Higher resolution
vs standard CTD probe
~ 200 €
Component cost
vs 5,000+ EUR commercially
0.02 m vs 0.5 m
Vertical resolution
25x finer than commercial probe
Our approach

Measure precisely, cost little.

The speed of sound in water depends on temperature, salinity and pressure. Commercial probes take only a few measurements per descent. The NowYouSea CTD is a demonstrator: it proves that a low-cost measurement can approach the performance of very expensive professional instruments.

Performance vs commercial
~ 200 €
NowYouSea CTD
vs
5 000 €+
commercial probe
Sound speed error
< 0.35 %
measured field Quily 2025
Methodology

How we conducted the test.

1
Site: Lake Quily
June 24, 2025, freshwater, max depth 46 m. Site chosen for its accessibility and the stability of its water column.
2
Instrumented descent
Synchronized T/P sensors, slow and controlled descent. Continuous high-frequency sampling throughout the profile.
3
Sound speed calculation
Application of the Chen-Millero equation adapted for freshwater. Point-by-point calculation along the profile.
4
Cross-validation
Comparison with theoretical reference value and Valeport SVP professional probe at common depths.
5
Saltwater extension
The system was also tested at sea, at 100 m depth off Six-Fours (Mediterranean), confirming its mechanical integrity in saltwater.
Profil de célérité du son (0-46 m)
0 5 10 15 20 25 30 35 40 46 Depth (m) 1430 1440 1450 1460 1470 1480 1490 1500 Sound speed (m/s) thermocline +0.35 % +0.16 % -0.10 % NowYouSea CTD Reference probe Sound speed profile - Lake Quily, June 24, 2025
Thermocline: zone of rapid temperature transition between warm surface waters and cold deep waters. It significantly alters acoustic propagation.
Case study - Lake Quily - June 24, 2025
Site
Location
Lake Quily, Brittany
Date
June 24, 2025
Water type
Freshwater
Max depth
46 m
Measurements
Data points
~2 900
Resolution
63 pts/m avg.
Speed error
< 0.35 %
Surface T
~19 °C
Validation
Theoretical ref.
Chen-Millero
Pro probe
Valeport SVP
Result
Validated
Valeport cross-validation in progress. Raw data available on request.
Comparison table

NowYouSea vs alternatives.

Criterion Commercial CTD probe Scientific AUV NowYouSea CTD
Equipment cost 5 000 - 15 000 € 50 000 - 500 000 € ~ 200 €
Profile resolution ~1 pt/m 5-20 pts/m 63+ pts/m (validé)
Deployment Requires boat + trained operator Team + supervision One diver or a line
Open-source Non Non Yes - data and code
Freshwater Some models Depends on config Validated (Quily 2025)
Speed error < 0.5 % (declared) < 0.3 % (high-end) < 0.35 % (measured)
IoT integration No / CSV export Proprietary Natif MQTT / API
Valeport note: cross-validation with additional professional SVP probe. Data consolidation in progress.
Economic model

Accessible at scale.

NowYouSea CTD
~ 200 €
Sound speed error
< 0.35 % measured
Commercial probe
5 000 €+
Sound speed error
< 0.5 % declared

The cost breakthrough we bring is not accidental, it is structural. It unlocks use cases that were previously impossible to budget for.

A network of 10 NowYouSea stations costs less than a single high-end commercial CTD probe. This is not the same market: it is a new market.

Comparison
5 000 €+ commercial probe
~ 200 € NowYouSea CTD
That is 25x cheaper at equivalent performance on this test.
Price excludes labor and infrastructure. Target: native integration into the NowYouSea connected rock for zero additional sensor cost.
Integrable sensors

13 sensors. Modular architecture.

Each deployment combines those most relevant for the area and objective. See the full list on the homepage.

CTDConductivity, Temperature, Depth - D7
HydrophoneAnthropogenic noise, cetaceans - D11
Dissolved O2Deoxygenation, benthic stress - D5
Chlorophyll-aEutrophication, harmful algal blooms - D5
TurbiditySuspended matter, sensitive habitats - D7
Nitrates NO3Coastal river inputs - D5
Phosphates PO4Coastal eutrophication - D5
pHAcidification, sacrificial anodes - D8
Pressure/tide gaugeTides, storm surges - D7
ADCP currentCurrents, sea-lagoon transitions - D7
UV fluorometerPAH/CDOM, hydrocarbons - D8
NIS sensoreDNA, non-indigenous species - D2
AIS receiverVessel traffic, noise correlation - D11
Join the project

Interested in this data?

Whether you are a researcher, diver, consulting firm or simply curious: let's talk. Raw Quily data is available on request.

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