‘The application of millimetre-wave radar to the study of the cryosphere.’
Supervisors: Dr Duncan Robertson, Dr David Macfarlane, Prof. Doug Benn (University of St Andrews), Prof. Brice Rea, Dr Matteo Spagnolo (University of Aberdeen) and Prof. Luca De Siena (Johannes Gutenberg University, Mainz).
Earth Observation satellites have transformed our understanding of the cryosphere, but they still lack the temporal resolution required to monitor glaciers on the scale of hours to days. This ‘blind-spot’ in the satellite time series can be filled by ground-based measurements. My PhD will develop the use of millimetre wave radar as a new tool for mapping and monitoring glaciers. Millimetre wave radar offers a trade-off between imaging resolution and operation during adverse weather conditions, and can acquire an almost continuous time-series of glacier change even in conditions of reduced visibility. I will be developing the AVTIS (the All-weather Volcano Topography Imaging Sensor) radar developing by the millimetre-wave group at the University of St Andrews for this purpose. The instrument can measure surface reflectivity and generate DEMs of glaciers surfaces, thus deriving data products of major interest to the glaciology community.
My research objectives are:
- Quantify the scattering properties of glacier ice at millimetre wavelengths.
- Develop new tools in terrain classification and surface elevation extraction to analyse millimetre wave data.
- Investigate the process of iceberg calving from tidewater glaciers using high-resolution DEMs and measurements of surface reflectivity.
Scattering properties of glacier ice at millimetre wavelengths
Above shows an image of the AVTIS instrument deployed at Rhône Glacier, Switzerland, in summer 2019. In this field campaign we measured the first ever backscatter measurements of glacier ice at 94 GHz (~3 mm). AVTIS transmits along multiple Lines of Sight in azimuth and elevation, from which point clouds are generated and subsquently DEMs of the surface. Our aim was to quantify the Normalised Radar Cross Section (usually denoted by σ0), which is a complex function of the surface dielectric properties, roughness and viewing geometry. This information will be used to understand how the signal interacts with the icy surface of a glacier and improve data processing techniques.
New millimetre wave radar analysis tools
Currently, AVTIS generates point clouds by calculating the range to the maximum received power along each Line of Sight, from which DEMs are created. My PhD will seek to improve upon this method by utilising techniques developed in the Lidar community and apply them here. The techniques I will seek to develop include: (1) Gaussian decomposition of radar waveforms, (2) geospatial waveform stacking and (3) deconvolution. These methods will seek to increase the density of points in the point cloud and improve the accuracy of the resultant DEM. Further, I will also develop techniques to classify terrain in millimetre wave radar data using values of σ0 and point cloud geometries.
Investigating glacier calving processes
The process of iceberg calving from glaciers and ice sheets remains one of the largest unknown quantities in future predictions of sea level rise. I will use the AVTIS millimetre wave radar to generate high spatial and temporal resolution measurements of glacier calving fronts to investigate this process in more detail. Specifically, we will generate DEMs of glacier ice cliffs and use this to quantify the rate of calving. Further, maps of surface reflectivity will help elucidate changes in the surface structure of the ice. Overall, these observations will help us understand the complex process of iceberg calving in greater detail than previously possible.