## 3 Results
### Real Seismic Data Example  
To further study the effects of thawing and freezing on the seismic wavefield, we conducted three similar seismic experiments on permafrost in Adventtalen on Svalbard in the Norwegian Arctic in October 2013, January 2014, and August 2014. Permafrost in this area typically extends to a depth of around 100 m, and the upper approximately 1.2 m is the active layer that thaws seasonally [1]. There are several boreholes in the area that indicate that the upper approximately 2-3 m of sediments in Adventtalen are eolian with a lower salinity than the deeper sediments of marine origin that extend down to the bedrock at approximately 65 m depth. However, these boreholes were drilled with the objective of obtaining information about the deeper bedrock, and thus lack detailed information about the near-surface soil properties, such as saturation, salinity, and porosity [42]. [PERSON], et al. [43] studied  
Figure 4: Top: synthetic seismic gathers for **(a)** model T0 (initial model, \(-5\)\({}^{\circ}\)C through the column), **(b)** model T1 (top boundary temperature = +1 \({}^{\circ}\)C ), and **(c)** model T3 (top boundary temperature = +10 \({}^{\circ}\)C). Bottom: corresponding frequency-phase velocity spectra (FV-spectra) with theoretical modal curves computed from the input models overlaid for **(d)** model T0, **(e)** model T1, and **(f)** model T3. The traces are plotted with an Ormsby-filter (1–25–40–120 Hz) to enhance the low frequencies and reduce aliasing. The capital letters A–F indicate the various modes of surface waves: A, C, and E is the fundamental mode, and D and F is the first higher mode. several cores acquired throughout Adventdalen and showed that the near-surface geology is somewhat laterally homogenous in the area, but with some local variations. Temperature measurements from a borehole near the study site show that when the experiments were conducted in October, the surface temperature had been fluctuating around 0 \({}^{\circ}\)C for a couple of weeks. In January, surface temperature had been subzero since October (average surface temperature -9.81 \({}^{\circ}\)C), while in August, the surface temperature had been stable above zero since mid-May (average surface temperature 0.47 \({}^{\circ}\)C). From this, we presume that ice saturation in the ground was highest in January and lowest in August. We also assume that the ice saturation was more laterally heterogeneous in October than during the other two experiments because the temperatures were close to the freezing point in the weeks prior to this experiment. The soil may also have varied laterally, but this should not affect the time-lapse effect observed in the data, since all three experiments were conducted at the same location. The objective of the experiments was to acquire reflected, refracted, and surface waves, and we therefore used gimballed geophone strings as seismic receivers in all experiments. Each geophone string consisted of 8 geophones spread out over an interval of 2.5 m, which was also the group interval. Geophone strings reduce the effect of the ground roll (Rayleigh wave), and the actual group length is critical for acquiring surface waves. The array response dampens the ground roll at wavelengths equal to or shorter than the group length, but this effect rapidly decreases for longer wavelengths (lower frequencies). Figure 5 shows that for the seismic setup applied here, we get half of the full response already at around 80 Hz (4 m wavelength) for the air wave traveling at 330 m/s, and the quality improves rapidly with decreasing frequency (increasing wavelength). Therefore, we limit our study to frequencies \(<\)100 Hz, where the surface waves should be minorly filtered due to the geophone group length. The seismic source was firecrackers placed in a 0.2-0.3 m deep hole in the ground. These create an impulsive source signature. The receivers were placed along a 75 m long straight line, with the first receiver 9.5 m from the shot point.