Large amounts of methane (CH4) are known to be emitted from permafrost environments during the autumn freeze‐in, but the specific soil conditions leading up to these bursts are unclear. Therefore, we used an ultrawide band ground‐penetrating radar in Northeast Greenland in autumn 2009 to estimate the volumetric composition inside the soil through dielectric characterization from 200 to 3200 MHz. Our results suggest a compression of the gas reservoir during the phase transition of soil water, which is accompanied by a peak in surface CH4 emissions. About 1 week thereafter, there seems to be a decompression event, consistent with ground cracking which allows the gas reservoir to expand again. This coincides with the largest CH4 emission, exceeding the summer maximum by a factor of 4. We argue that these complementary measurement techniques are needed to come to an understanding of tundra CH4 bursts connected to soil freezing.

Abstract-This paper presents results from an outdoor measurement campaign for ultra-wideband channels at gas stations. The results are particularly relevant for "infostations" where large amounts of data are downloaded to a user within a short period of time.We describe the measurement setup and present a novel high-resolution algorithm that allows the identification of the scatterers that give rise to multipath components. As input, the algorithm uses measurements of the transfer function between a single-antenna transmitter and a long uniform linear virtual array as receiver. The size of the array ensures that the incoming waves are spherical, which improves the estimation accuracy of scatterer locations. Insight is given on how these components can be tracked in the impulse response of a spatially varying terminal.We then group the detected scatterers into clusters, and investigate the angular power variations of waves arriving at the receiver from the clusters. This defines the cluster's "radiation pattern."Using sample measurements we show how obstacles obstruct the line-of-sight component -a phenomenon commonly referred to as "shadowing." We compare the measurement data in the shadowing regions (locations of the receiver experiencing shadowing) with the theoretical results predicted by diffraction theory and find a good match between the two.

Abstract-In this paper we establish a geometry-based stochastic ultra-wideband channel model for gas stations. We statistically describe the two-dimensional spatial location and power of clustered scatterers, and the shape of their visibility and shadowing regions. We also separately model the diffuse part of the impulse response (i.e., the part that cannot be explained by the scatterers' multipath components), and show that its amplitude fading statistics can be best described by a Weibull distribution with a delay dependent beta-parameter. A step-bystep implementation recipe demonstrates how the model can be built. Finally, we validate our model by comparing simulated and measured channel parameters such as the rms delay spread.Index Terms-Geometry-based stochastic channel model (GSCM), outdoor, ultra-wideband (UWB), wireless propagation.