Räumlich integrierte Bodenfeuchtemessungen unter Verwendung von Radiofrequenzen im Langwellenbereich (RIBOLA) - Spatially Integrated Soil Humidity Measurements Using Radiofrequencies in the Long-wave Range

Wide-area integrated soil humidity measurements are required for many applications in meteorology, geology, hydrology, agriculture, and forestry. Use of electromagnetic waves in the frequency range from 30 kHz to 300 kHz allows for a continuous measurement of soil humidity at a spatial resolution of 10 – 20 km.
The measurement principle is based on determining the phase lag of an electromagnetic ground wave transmitted by a radio transmitter. The propagation behavior of a ground wave depends on the conductivity of the transmitting medium. The latter is largely dependent on the humidity of the medium.
As a signal source, the DCF77 time and normal frequency emitter in Mainflingen is used in the project. It operates at a frequency of 77.5 kHz and has a transmission power of 50 kW. To detect and analyze the transmitted signal, three measurement stations were installed along the route from Edingen to Karlsruhe at a distance of 20 km each (Figure 1).

 

Fig. 1: Schematic representation of the setup of receivers at the distance d from the transmitter (DCF77) and simplified representation of the behavior of the ground wave along the measurement path. ϕ – phase and A – amplitude of the wave. (Empfänger = Receiver, Bodenwelle = Ground wave)

The measurement setup consists of the following components: Notebook for data acquisition and control (Fig. 2), DCF77 receiver with antenna, GPS receiver with antenna, oscilloscope (Fig. 2), and heating system. The difference between the zero crossings of the received DCF77 signal and the GPS second signal is the most important parameter.

Nine SISOMOP stations located at equal distances along the measurement section between Edingen and KIT Campus North are used for calibration and validation of the new soil humidity measurement method. Soil humidity and soil temperature were measured at various depths (Fig. 3).

The measurements started in November 2012. They reveal a pronounced dependence of the phase values on conductivity change in the soil layer observed.

Poster & Presentations
Kiseleva, O., Hübner, C., Brandelik, A., Kalthoff, N., Kohler, M., Königer, F., Kottmeier, C.
Verfahren zur räumlich integrierten Bodefeuchtemessung unter Verwendung der Bodenwelle des Langwellensender DCF77.

Tagung der Deutschen Geophysikalischen Gesellschaft, Karlsruhe, 10.03.-13.03.2014 (Presentation at the Conference of the German Geophysical Society)
Kiseleva, O., Hübner, C., Brandelik, A., Kalthoff, N., Kohler, M., Königer, F., Kottmeier, C.

Messverfahren zur Bodenfeuchtebestimmung mit Hilfe von Radiowellen im Langwellenvereich.
Tag der Hydrologie 2014, Eichstätt, 20.03.-21.03.2014 (Poster presentation on the 2014 Day of Hydrology).