Measuring Systems

Classical Heatflow

The Heatflow Probe is an instrument for the measurement of the thermal gradient and the thermal conductivity. With both parameters the heat flux density can be determined. The instrument is capable to measure in-situ values with 22 sensors down to a depth of 6 m below the seafloor. Besides the temperature sensor string, an extra heating wire is attached to the probe. That wire provides a heat pulse for the measurement of thermal conductivity. In summary the temperature gradient is measured along 22 points with a resolution of 0.001 K and in addition 22 in-situ values of thermal conductivity, and hence, the heat flux density is determined in one go. Download Flyer HeatFlowProbe (engl.) (pdf-file)

The FIELAX HeatFlowProbe (6000 m or 10000 m) is also available for purchase.

Please find our product description for more information or contact Download Product description FIELAX HeatFlowProbe (engl.) (pdf-file).


For in-situ temperature and thermal conductivity measurements in shear resistant marine sediments, typical for shallow seas, coastal and continental shelf regions, FIELAX GmbH combined the functional components of the FIELAX HeatFlowProbe with a VKG6 type Vibrocorer. We name this new measuring device “VibroHeat”. With the ability to penetrate even through harsh layers such as gas hydrates, permafrost soils or “sands”, the technical application is not restricted to soft sediment conditions anymore. Download Flyer VibroHeat (engl.) (pdf-Datei)


In cooperation with Marine Sampling Holland, FIELAX has further developed its heatflow measurement system to work with a CPT unit used for in-situ geotechnical measurements, in order to overcome possible liquefaction, which may occur in very sandy sediments due to the vibrocoring. Therefore the sensorstring was adapted to fit into a standard coiled CPT-tube of 6 m length i.e. the number of temperature sensors was reduced to 13 temperature sensors at a spacing of 42 cm.

Principle of Measurement

The FIELAX heatflow measuring system records temperature as a function of time. The temperatures are recorded with 22 thermistors that are placed within a sensor string. The sensor string also contains a heating wire with which a distinct amount of energy is released into the sediments.

  • A: lowering to seabed
  • B: penetrating into seabed
  • C: measuring thermal decay of frictional heat
  • D: heat pulse
  • E: measuring thermal decay of heat pulse
  • F: pullout and retrieve to surface

What is Heatflow?

The term ‘geothermal heatflow’ refers to the thermal energy that dissipates constantly from its sources within the earth to the surface, either by convection or conduction. Geothermal heat is the driving force for a variety of multi-scale geologic processes taking place in the earth’s crust e.g. plate tectonics. It is also driving chemical reactions like the thermal degradation of organic matter, which leads to hydrocarbon (oil and gas) formation. The internal temperature of the earth increases with depth. Near the surface, the average geothermal gradient is relatively constant with on average 30 K for every kilometer of depth. However, there are also places where it can be higher e.g. along mid-ocean ridges or mantle plumes.

How is heatflow determined?

Even though called heatflow measurements, heatflow itself is not measured directly. But based on the assumption, that heat conduction is the dominant transport process through the earth´s crust, and conductive heatflow occurs in the direction of decreasing temperature, heatflow can be calculated as the product of the vertical thermal gradient and thermal conductivity (Fouriers law). If however other mechanisms like heat advection are involved (for example fluid flow processes), heat transport may be characterized by non-linear thermal gradients and also occur horizontally.

What is the use of heatflow measurements?

In the field of petroleum geology heatflow measurements are essential in the exploration of new oil and gas reservoirs, as they provide critical constraints for sedimentary basin modeling and aid in thermal maturity calculations. Heatflow measurements also enable stability analysis of gas hydrate deposits.

The booming offshore wind energy market has opened a new field of activity for heatflow measurements, as in particular thermal conductivity values provide useful information for estimating the dissipation mechanisms of thermal energy and also the environmental impact of power cables.

Read our brochures for detailed information:

“Heatflow” brochure “Prediction of Sediment Temperatures” brochure

TRT measurements Off-/Near-/Inshore Holland – cooperation with MSH

This autumn, FIELAX has gathered data for two cable route projects with Marine Sampling Holland ( We have measured a total of more than 100 profiles of temperature and TRT (thermal resistivity) data offshore Holland as well as in the Ijsselmeer. As the requirement was high resulotion profiling to a sub-bottom-depth of >6m, special coiled sensor tubes with a total length of 8m were manufactured. Read more