The standard version of the UMP-1 sensor is designed for the application with a cable connection to a data logger. The data logger provides the power supply of the UMP-1 and stores the collected data. The data can either be read out by using a laptop with an interface cable connection to the logger or by remote data transmission. This design of the UMP-1 is especially suitable for measurement sites with multiple sensors (in connection with a data logger) and for long term observations (e.g. hydrological measurement sites or lysimeters).

The UMP-1 is water proof and can be installed in any depth (vertically or horizontally). The sensor consists of a plastic sensor body and two stainless steel antennas. The output signal can either be analog or digital (RS485), which makes it possible to integrate the sensor in other bus systems.

The UMP-1 determines the soil moisture by measuring the relative permittivity (ɛr) of the soil. The measurement principle neither corresponds to the TDR nor to the FDR method. The sensor sends a continuous signal at a constant frequency (60 MHz). Unlike the FDR method, the phase shift (offset in time) between the original and reflected signal is measured. To each measured offset in time a relative permittivity is assigned. This relationship is determined for each sensor during the sensor calibration. This information is stored and listed in a tabular form. Based on the measured ɛr the water content in percent of volume is estimated via the regression function by Topp and Davis. In case other methods to estimate the water content based on ɛare desired, it is also possible to read out the measured relative permittivity values.

The sensor additionally measures the soil temperature (°C) and electrical conductivity (mS/cm) of the soil. The measurement of the electrical conductivity is done independently from the measurement of ɛr. Since ɛris also salt-dependent, high electrical conductivities can lead to an overestimation of ɛr. In these cases the measured electrical conductivity can be used to correct the estimated water content values.


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  • high accuracy
  • additional measurement of temperature
  • Independent conductivity measurements
  • inexpensive
  • data loggers at hand can be used
  • data are stored in one data set with all other data from the same plot



Measurement frequency for water content: 60 MHz
Antenna length: 100 mm
Antenna diameter: 3 mm
Water content measurement range: 0 … 100 % Vol. water content
Water content accuracy: ±2%
Dielectric coefficient ε measurement range: 0 … 80
Electrical conductivity measurement range: 0.001 … 5mS/cm
Optional data extension to 40mS/cm possible
Electrical conductivity accuracy: ±1%
Soil temperature measurement range: -20 … +60°C
Soil temperature accuracy: ±0.2°C (across the entire temperature range)
Measurement volume: 1000 ml
Working temperature range: -20 … +60°C



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