Measures the interference between direct and reflected signals during all the satellite passages.
THE SMIGOL REFLECTOMETER The Soil Moisture Interference-pattern GNSS Observations at L-band (SMIGOL) Reflectometer is the instrument implementing the IPT. Figure 1. The SMIGOL Reflectometer architecture. elevation angle of GPS satellite changes (Fig. 2).
Samples @ 1 s
received interferometric power depends on the elevation angle (Fig. 3)
Figure 2. The received power is function of the GPS satellite position
From theory the notches evolution dependence on the elevation angles is found, fig. 6.
SNOW MONITORING USING GNSS-R TECHNIQUES
For the first DoY of measurement, select the notches in the received powers sequences and compute the snow thickness based on fig. 6.
In order to solve the uncertainly, assume that 5 cm is the snow thickness (known from ground-truth), and choose the nearest solution.
The solution for each satellite is stored for being used as the calibration measurement.
From that measurement the evolution of notches is tracked. The criterion to solve the uncertainty, when processing the following measurement days, has been stated to be that snow falling affects all the surface in the same way and then the most probable solution obtained from fig. 6 is selected.
Figure 6. Theoretical evolution of notches. The notches position and the number of them (each black line defines the evolution of one notch) describe the snow thickness. The snow layer has been simulated considering a snow wetness volume of 2% and a snow density of 8 %.