Fibre-optic temperature sensing for streams, lakes and groundwater exchange
Where does groundwater enter the stream, and how much?
Where does groundwater enter the stream, and how much?
Groundwater keeps its temperature while the stream follows the day and the night. A cable on the bed turns that difference into a map of the whole reach, every fifteen minutes, for the whole season, without a single point sensor to maintain.
- Inflow zones marked along the reach, ranked by strength, from the damping and phase lag of the daily cycle.
- Night-time cold anomalies versus a smoothed baseline, which pick up inflows the daily cycle misses.
- Losing reaches, where the daily amplitude grows instead of shrinks.
- Water level, air temperature and your own sensors in the same file, on the same clock.
The event, and the signal
- Day and night, the stream warms and cools.
- Groundwater entering at one point keeps its own temperature all day.
- On the cable, the daily swing is everywhere except there: that is the inflow.
Setup
| Fibre | An armoured sensing cable laid on the bed, weighted every few metres. Comes with the rental in the length you need, single-mode or multimode. |
| Length | A few hundred metres to several kilometres of reach per instrument. |
| Power | A battery and a panel on the bank. At one profile every fifteen minutes the box runs for weeks between visits; at one an hour, for months. |
| Sensors | Water level, conductivity, weather and PT100 probes plug into the box's field inputs. |
| Term | A season, month by month. Two weeks is enough for a first inflow map. |
The measurement
Each half-metre of cable records the stream temperature. Over a few days the daily cycle is fitted bin by bin. Where groundwater enters, the cycle is damped and delayed; where the stream loses water to the bed, it is amplified. The analysis is the published amplitude-and-phase method applied along the cable, and the result is a map with the inflow zones coloured.
Deliverables
- Map or distance axis of the reach with inflow zones by strength
- Heatmap of temperature against distance and time for the season
- Table of zones with chainage, night anomaly, damping ratio and persistence
- netCDF that loads straight into the open-source hydrology toolchain
On the dashboard, through the API, and as files. All three, always.
Asked before
- How long does the cable have to be in the water before a result?
- Three full days gives a first map. A week is better, and a season shows how the inflows change with stage.
- Does burial or shading spoil the measurement?
- They change the amplitude locally, which is why every flagged zone is checked by an analyst against the raw heatmap before it goes into the report.
- Can I keep the cable in over winter?
- Yes. The armoured cable is made for it, and the box runs on a battery and a panel at a reduced schedule.
Other things the same box does
- Glaciers and permafrost
What is the borehole doing through the winter, when nobody can get there?
You get An hourly or four-hourly profile of the whole borehole, every day of the season.
Read more - Geothermal
What is the ground made of, layer by layer, and is the field slowly cooling?
You get Thermal conductivity and borehole resistance per depth interval, with uncertainty, from one test.
Read more - Dark-fibre seismology
Can the telecom fibre under the road become a seismic array?
You get Quantitative strain rate on every channel, not event flags.
Read more
Put your fibre to work.
Tell us about your fibre and your question. You get a call, a plan for your site and a monthly price.