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This thesis develops the technique of millimetre-wave radar at 94 GHz for close-range remote sensing of glaciers and terrestrial snow cover (the cryosphere). The capabilities of 94 GHz radar for cryosphere mapping are demonstrated using the 2ⁿᵈ generation All-weather Volcano Topography Imaging Sensor (AVTIS2), which maps 3D terrain from real-beam scanning. AVTIS2 acquires 3D point clouds of terrain and a comparison to co-located high density point clouds derived from Terrestrial Laser Scanner (TLS) data showed that AVTIS2 point cloud uncertainties were 1.5 m at 1.5 km and 3 m at 3 km. These values are smaller than other close-range radar systems used to map cryospheric terrain in 3D. Next, the distribution of Normalised Radar Cross Section (σ⁰) values over glacier ice at 94 GHz was found to be −17.0 < σ⁰ < −3.4; σ⁰ₘₑₐₙ = −9.9 dB and followed a log-normal distribution. These values are comparable to other terrain types at 94 GHz such as refrozen snow, wet snow and wet soil, hence glacier surfaces were found to be suitable targets for terrain mapping at 94 GHz. These fundamental results were used to apply the AVTIS2 94 GHz radar for monitoring snow cover and glacier calving. Field trials in Scotland showed that the transition of wet snow to a refrozen snowpack in response to reductions in air temperature could be detected from changes in 94 GHz σ⁰. Snow hazard features could also be identified, such as post-avalanche debris accumulations which manifest as localised increases in radar backscatter. Next, 3D AVTIS2 data was used to quantify glacier calving rates at the Hansbreen tidewater glacier in Svalbard. A time series of ice cliff morphology derived from the AVTIS2 3D data sets exposed the role of melt undercutting and demonstrated the critical role of the ocean on calving processes in Svalbard. The high accuracy 3D data acquired from AVTIS2 and the sensitivity of radar backscatter to surface changes has demonstrated the unique capabilities of 94 GHz radar for cryosphere mapping, paving the way forward for new applications and opportunities for close-range remote sensing of the cryosphere.

Glacial cirques throughout history give the alpine landscapes dimension. Over the past century, glaciologists have attempted to unravel the secrets behind the climate topography-glacier relationship which is evident. This thesis is a study written as journal articles in multiple parts which investigate the climatic relationship between cirques through their equilibrium line altitudes (ELAs) from extant to palaeo. Due to the time transgressive nature of cirques and their geomorphic formation through multiple glacial cycles, the question remains, what climatic relationship can be deduced from these geomorphic features? In this thesis, I compare equilibrium-line altitudes (ELAs) derived from satellite imagery using a GIS toolbox and apply the Area-Altitude Balance Ratio (AABR) and Accumulation-Area Ratio (AAR) compared to field measurements on the glacier. Using a worldwide dataset of 64 glaciers, the calculated ELAs and measured ELAs were correlated to find the smallest median difference between the measurements. It is recommended that the use of a globally representative AABR value of 1.56 is used for modern applications where a regional AABR value is unknown. This AABR value is also recommended when reconstructing palaeo glacier ELAs. This translates to ~0.42 of uncertainty for palaeotemperature estimation which is well below the uncertainty of other palaeo proxies. Since ELAs are commonly reconstructed to assess palaeoclimatic conditions, I wanted to test the validity of this relationship on modern glaciers. Due to the abundance of modern glaciers in Scandinavia, plus the regional climatic datasets, it was chosen as the study site for parts 2 and 3 of the thesis. I used open-source GLIMS polygons and a GIS toolbox to calculate ELAs for 513 modern glaciers to deduce any shortcomings or misinterpretations of what is known about cirque glaciers and their corresponding climate. For this study, I used the regional AABR value of 1.5. The results indicate that modern ELAs are strongly correlated to distance from the coast, which reflects the present-day precipitation pattern. It indicates that the transition from maritime to continental yields dominant characteristics in the present-day ELA patterns (Winkler et al., 2009). When split into macro-regions, additional strong correlations with latitude, longitude, aspect, summer temperature are evident. The final part of the thesis is a comparison of modern glacier cirques and 3984 geomorphic cirques without glaciers to compare and contrast the relationships with climate. Cirques, the bowl-shaped depressions with steep headwalls are frequently used to obtain palaeoclimatic information for alpine environments. Using cirque floor altitudes (CFAs) as a proxy for palaeo ELAs, the results indicate the topo-climatic factors of latitude, longitude, aspect, and distance from the coast maintain strong relationships with distance from the coast being the most prominent. The gradient inland most likely reflects a similar reduction in precipitation. To conclude, the evidence indicates that CFAs are a useful palaeoproxy for palaeo ELAs with the caveat that the glacial history of Scandinavia has regulated the areas for cirque formation and therefore CFAs.

Mount St. Helens is a stratovolcano of the Cascade volcanic arc and is one of the most active in the United States. The present morphology is mainly due to the destructive eruption of 18 May 1980, triggered by a five-magnitude earthquake that caused the collapse of a vast sector of the northern part of the volcano. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independantly from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. The thesis reports new research aiming to find a link between seismic imaging of the volcano and its actual geomorphology and surficial geology by qualitative and quantitative approaches. As a first step for coda attenuation imaging, space weighting functions and kernels were used to model the spatial sensitivity of coda waves. While the diffusive approximation is valid for an active seismic dataset to model coda waveforms, it is not valid for the passive seismic dataset of Mount St Helens and, therefore, the multiple scattering was introduce. To measure the relative importance of scattering attenuation vs absorption at Mount St Helens, the Multiple Lapse Time Window Analysis (MLTWA) was applied. The quantities obtained with this technique are the Seismic Albedo B0 (ratio between scattering and total coda attenuation, between 0 and 1) and the Extinction Length (Le, reciprocal of the total attenuation). Results show the typical dominance of scattering attenuation in volcanoes at lower frequencies (3 - 6 Hz), while absorption is the primary attenuation mechanism at 12 Hz and 18 Hz. Still, the seismic albedo is anomalously high (0.95) at 3 Hz. The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2D frequency-dependant bulk sensitivity kernels for the S-wave coda in the multiple-scattering regime (using the Energy Transport Equations - ETE) and to validate the use of analytical diffusive kernels (AD, independant of MLTWA results). At 12 Hz, high coda-attenuation anomalies characterise the eastern side of the volcano using both kernels, in spatial correlation with low-velocity anomalies from literature, generally associated with the deep plumbing system of the volcano. The hypotheses underlying both MLTWA and sensitivity kernels are tested with radiative-transfer forward model of farand near-field envelopes in a half space using RADIATIVE3D. Here, a layered model was implemented with a shallower layer with increased scattering properties to model late coda envelopes. While the broadening of late coda phases improves, this model cannot explain the phases of the intermediate coda with higher amplitude than the direct waves. This behaviour is due to strong near-receiver scattering, which enhance anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only at frequencies higher than 3 Hz and in the far-field, diffusion onsets at late lapse times. At 3 Hz, the anomalous albedo, the forward modelling and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts. To better investigate the morphologies biasing the seismic wave path, a geomorphological map was necessary. Literature review pointed out the lack of this information for Mount St. Helens. So, a new geomorphology and surficial geology map has been created, based on a LiDAR acquired in 2003 with 3 m resolution. The effect of the 1980's blast on the entire area is evident, mostly on the northern sector of the volcano, which is covered by the debris avalanche and pyroclastic flow deposits. The volcano completely lost its typical conic shape, in favour of a horseshoe-shape crater rim, with an open side on the NS direction. The map is accompanied by a second one focusing on the geomorphological changes caused by the 2004 eruption, based on a LiDAR of 2009 (1 m resolution). Here, the main morphological variations affect the shape of the main glacier and the dome, both grown in the crater. A qualitative comparison between coda-attenuation imaging and the landforms of Mount St Helens has been done, using the first-ever geomorphological map of the volcano. The map highlighted extremely rough landforms (hummocky structures) in the complex debris avalanche deposit. The comparison with the tomography reveals several matches, not only with the debris avalanche itself but also with other areas of the south-western flank of Mount St Helens, like the Butte Camp dome, where a contrast in attenuation is possibly defining a fracture or a fault connected to this intrusive body. To better understand the influence of key morphologies, forward modelling of the seismic waveforms was fundamental. Starting from the velocity fluctuations obtained from the radiative transfer model, an forward model of the wave equation was introduced. The anisotropic model, following the qualitative observation, shows how the geomorphology is controlling the travel times of SH waves, in particular in two directions: WNW-ESE, following the trend of a buried fault along the South Fork Toutle Valley, and NS, consistent with the main morphological difference between south (mostly untouched by the 1980 eruption) and north (collapsed in 1980) of the volcano. A first analysis of the waveforms of a shallow event of 2005 recorded by three-components array shows a loss in high frequency content for the stations located on the debris avalanche of 1980, unlike other stations laying on older volcanic products. The isotropic model is well reproducing the arrival of the horizontal polarised S waves (SH) at higher frequencies (10 Hz), but not at lower ones (1 Hz and 6 Hz). The introduction of an anisotropic model at 1 Hz and 6 Hz is necessary to explain the arrivals for the stations in the north-northwestern side of the volcano.