Applications

Snow and glaciers play an important role in the climate system as they have a strong influence on the radiation balance. Additionally both act as an important source of fresh water. Radar remote sensing allows large coverage observation of regions that are difficult to access and can provide data about mass balance of glaciers, very accurate ice velocities, information about snow fall and the water stored in the snow pack. Even avalanche activity and the risk of serac-falls can be monitored using radar instruments during all weather conditions at day and night.

We use space-borne, air-borne and ground-based radar sensors to observe processes in the cryosphere. The ground based radar system called KAPRI, operating in Ku-band (17.2 GHz), is a fully polarimetric and interferometric radar system and allows for measurements with a high temporal resolution which is not achievable with satellite data. This resolution is necessary to monitor fast processes such as avalanches and variations in snow properties through the course of a day.

In summer 2015, the Radar was installed at the Domhütte, in the canton of Wallis, to observe the Bisgletscher, a fast moving Glacier that represents a geohazard.

Images of the glacier were acquired every 2 minutes between July and September. The measurement data was used for near real time monitoring of the potentially dangerous glacier; the large dataset also represents a very good opportunity to develop and test novel processing techniques for time series of interferometric and polarimetric data.

We study how plant growth and changes in soil moisture affect space-borne radar measurements of deformations of the Earth's surface

Using a technique called Differential Interferometric SAR (DInSAR), scientists can measure deformations of the Earth’s surface from space. The centimetre accuracies that can be achieved have made this technique useful for characterizing many processes and movements, such as those related to volcanic activities, the movement of glaciers, or subsidence caused by permafrost-thaw. This measurement works by combining two radar acquisitions from different times. During this time gap, the moisture content of the soil can change and such changes can impact the DInSAR signals and thus the deformation estimates.

We want to characterize the properties and magnitudes of these effects. To this end, we analyse satellite and airborne measurements, and we also conduct dedicated experiments using the group's ground-based radar systems. Our goals are:

• to model the effect of soil moisture changes in mineral and organic soils on DInSAR measurements
• to elucidate the impact of vegetation dynamics on these measurements
• to estimate soil moisture changes and vegetation parameters from radar data
• to improve deformation estimates by correcting for these effects and quantifying the associated uncertainties

Current research activities are focused on the development and validation of methodologies for estimation of crop condition (e.g. crop height, extinction coefficients and growth stage) by means of Polarimetric SAR (Pol-SAR) and Polarimetric SAR Interferometry (Pol-InSAR).

These studies may help to characterize the morphology and the dielectric properties of different crop types, as well as the interaction of the vegetation with polarized waves at different frequencies. The current studies focus on:

• Estimation of the morphology and the growth stage of rice fields using a probabilistic inversion of a morphology based polarimetric electromagnetic scattering model
• Multi-parameter (i.e. multi-frequency, -baseline, -temporal) Pol-InSAR inversion for biophysical parameters (e.g. height, extinction coefficients) retrieval from airborne data
  
• These studies may help in devising new acquisition strategies for crop parameter estimation (such as airborne campaigns or future satellite missions like Tandem-L).

An accurate assessment of surface or structural deformation — subsidence or uplift — has been the objective of various studies in the field of environmental sciences and engineering geology over the last few decades. It can be caused by various geophysical processes (natural as well as anthropogenic), such as tectonic and volcanic activities, mass movements on unstable slopes, and mining and groundwater pumping, construction-related activities, etc. In each case, a general monitoring and measurement of the deformation is important owing to various environmental, economic and safety considerations. Traditionally, repeated leveling-based methods, and afterwards GPS-based approaches or a combination of both, were used to monitor and measure land deformation in concerned regions. However, leveling and GPS measurements can only be performed locally (for discrete locations), and therefore, they are not suitable for a wide range assessment of land deformation.  

In the context of large-scale and long-term monitoring of deformation in urban areas, PSI with space-borne SAR data stacks has proven to be an invaluable tool. However, an inherent limitation associated with PSI is that, by definition, a PS is a single dominant scatterer within a range–azimuth resolution cell. Therefore, pixels containing backscatter of comparable energy from multiple scatterers, which may individually exhibit point-like behavior, are rejected. This situation arises often in layovers. Urban areas typically have buildings of different heights, and layovers such as those between the ground and the facade of a nearby building, or the rooftop of one building and the facade of a higher building in proximity, occur ubiquitously. A local PSI analysis of such buildings may suffer from poor deformation sampling due to the rejection of such layovers. To overcome this limitation, we investigate the combined use of PSI and tomography.