# mGEODAR--A Mobile Radar System for Detection and Monitoring of Gravitational Mass-Movements
## 3 Measurements and Results
### Moving Point Target  
A freespace range radar measurement was performed along a straight road with a moving car as target. Both radar antennas were set up approximately 1.5 m above ground with a spacing of 4 m. The external 5 W power amplifier was used for these measurements in between the transmitter board and the transmit antenna. The frequency \(f_{lo}\) was set to 8 GHz instead of the found optimum from Section 3.1, and thus the signal-to-noise ratio is expected to be lower than the optimum.  
Figure 6 shows the range-time diagrams of a car driving away from the radar location at range 0 m. The slope of the streak signature in the range-time diagram gives the velocity of the car. The car accelerates for the first 100 m, and reaches a constant velocity of approximately 15 m/s. Note, both panels result from two different measurements as the research mode (A) and the detection mode (B) cannot be measured simultaneously.  
Figure 5: **(A) Peak intensity of cable length (\(P\)) and averaged background (\(B\)) in a 90 m loop test setting for different \(f_{lo}\) frequencies and both measuring modes. Error bars are two standard deviations wide. (B) Signal-to-noise ratio between cable peak \(P\) and background intensity \(B\) for the research mode with 400 MHz ramp (blue) and the detection mode with 30 MHz ramp (red).**  
The colour intensity is a moving target identification (MTI) based on the digital filter described in Section 2.5. The values are displayed in decibel referenced to a measurement of the same scene without any movement, thus, non-moving regions in the MTI are ideally zero. However, speckle-like noise appears especially for the research mode (Figure 6A) that could be dealt with by averaging across single chirp pulses. For the detection mode (Figure 6B), such averaging is already done along the 25 short pulses during one burst (see Section 2.3). The SNR in the MTI image of the car compared to the background is approximately 10 dB for the research mode and 5 dB for the detection mode. The moving car gives a clear discrete target in the MTI data that exceeds the speckle-like background noise at least for ranges below 200 m.  
The temporal and spatial resolution of both measuring modes is shown in the insets of Panel A and B that both span approximately over 20 m and 1.5 s. The car in the research mode measurement in panel A spans several range bins with each a spatial resolution of \(\Delta r=0.375\) m. However, the detection mode in panel B has a resolution of \(\Delta r=5\) m and the car appears in a single range bin at each time.  
The effect of the active baseband filter (Section 2.4) is clearly visible at ranges below 20 m. To prevent any cross-talk and direct coupling between the transmit and receive antennas, the baseband filter strongly suppresses all low frequencies in the deramp signal. Furthermore, the signal intensity of the car drops slightly between a range of 100 m and 200 m. The geometric attenuation is only partly compensated by the filter. For ranges larger than 200 m the signal intensity diminishes further due to additional attenuation of a disturbed Fresnel zone. The Fresnel ellipsoid touches the ground as the antenna were only slightly raised above ground. This is usually not a problem with measurements in the mountains as the antennas are mounted high on the opposite slope of the flow path rather than measuring complete parallel to the ground.