Microwave Radar Systems for Cryosphere Monitoring

The cryosphere is the part of the Earth covered by frozen water and experiencing temperatures below 0°C for at least part of the year. In latest years, the warming temperatures, and the change of the climate act to reduce the mass of permanent ice and to limit the creation of new snow and ice. This causes several problems, such as scarce freshwater availability, natural disasters, and modification of several landscapes, especially in the mid-latitude areas. The accurate and continuous monitoring of these regions has become crucial to understand the dynamics of ongoing changes and to assess the associated environmental and socio-economic impacts. Several technological methods have been developed, despite one of the most used technique is still manual analysis. For non-invasive observations, photogrammetry, Global Navigation Satellite Systems (GNSS) or Remotely Piloted Aircraft Systems (RPAS) are used for small areas, while satellite images are employed for bigger areas. Moreover, Ground Penetrating Radar (GPR) and seismic methods are powerful instruments, able to detect different layers. In particular, radar allows to acquire high spatial and temporal resolution data, and it can be tailored to supply accurate information about different cryospheric bodies. By using different frequencies, it can penetrate and interact with the medium in different ways. The principal parameters which can be investigated by means of radar systems are the depth of the medium D, either snow or ice, and its density, the Liquid Water Content (LWC) and the Snow Water Equivalent (SWE). A standard GPR can obtain such information, but it needs the support of assumptions, external measurements, or very complicated techniques barely applicable in the field. In order to overcome such limitations and improve the accuracy of the measurement, a novel ground-based radar system called Snowave has been developed. Snowave is a dual receiver radar architecture able to compute the depth and the dielectric constant of a medium without any external aids or assumptions, and thus solving ambiguities in determining wave velocity within the medium. This principle was already shown in previous works. In this work, a more accurate investigation on the applicability is presented, moving through several snow conditions (various depths and densities), including also wet snow. Especially for this last condition, different frequencies have been studied and tested. One big enhancement of the system is related to the possibility to monitor not only snow coverage, but also glaciers. Indeed, few works have been done in this direction: in order to fully investigate such dense medium, with a relatively high dielectric constant and very high thickness, different kinds of radiators are needed. Some custom-made antennas were simulated, produced and then tested in glacial environment, returning a complete result about the condition of the glacier, with more information with respect to a standard GPR. In addition to the work relative to the field campaign, a preparatory study on the problems occurring using an above-the-ground configuration has been done, from an attempt with a lighter and smaller radar used on a fixed platform, to the development of a combined analytical and full-wave model to predict the effect of the surface roughness on the backscattering when using an off-nadir configuration. In this case, the model was cross-checked with satellite backscattering data. However, this methodology can also be extended to systems operating in close proximity to the ground, e.g. with Snowave on a fixed or a mobile platform. In conclusion, this thesis presents the validation of a radar system for cryospheric monitoring, able to provide insights into the dynamics of the cryosphere and to enhance the ability to predict and mitigate climate change impacts and/or natural hazards.