David G. Macfarlane

University of St Andrews

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Field testing of the AVTIS radarometer at Soufriere Hills and Arenal volcanoes.

G. Wadge David G. Macfarlane Duncan A. Robertson A. J. Hale H. Pinkerton

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Chapter 13 AVTIS observations of lava dome growth at Soufrière Hills Volcano, Montserrat: 2004 to 2011

Geological Society London Memoirs (2014)

G. Wadge David G. Macfarlane Henry Odbert A. Stinton Duncan A. Robertson

Abstract To solve the problem of lava dome growth at Soufrière Hills Volcano (SHV) being invisible and unmeasured owing to cloud, we have designed, built and deployed a ground-based millimetre-wave radar/radiometer: the All-weather Volcano Topography Imaging Sensor (AVTIS). In this chapter, after an outline technical sketch of the instruments, we describe the campaigns between 2004 and 2011 used to test their capabilities. We then present results from the campaigns to illustrate how signals of volcanological interest can be retrieved. The primary measurements of AVTIS are range (to within, at best, about 1 m), and, from that, topography, topographical change and effusion rates, and surface temperature (to within a few degrees Celsius). Changes in radar reflectivity can indicate surface processes (e.g. mass wasting). Surface motion within the instantaneous field of view produces a Doppler signal that allows detection of rockfall. Attenuation of the signal by rain along the path can, when stacked temporally, give an image of rain cloud structure and, by calibration, a rate of rainfall. We regard a strategy of two radars – one permanantly mounted (at Windy Hill) autonomous instrument, and the other used as a rover – as being best for capturing dome growth.

Lava dome

Dome (geology)

10.1144/m39.13

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Millimetre wave FMCW radar as a tool for 3D Terrain mapping of volcanic topography

AGU Fall Meeting Abstracts (2012)

David G. Macfarlane G. Wadge Henry Odbert A. Stinton D. Roberston

Early-warning radar

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94 GHz Radar Backscatter Characteristics of Alpine Glacier Ice

Geophysical Research Letters (2023)

William D. Harcourt Duncan A. Robertson David G. Macfarlane Brice R. Rea Matteo Spagnolo

Abstract Measuring the radar backscatter characteristics of glacier ice at different frequencies and incidence angles is fundamental to predicting the glacier mapping performance of a sensor. However, such measurements at 94 GHz do not exist. To address this knowledge gap, we collected 94 GHz radar backscatter data from the surface of Rhônegletscher in Switzerland using the All‐Weather Volcano Topography Imaging Sensor (AVTIS2) real‐aperture Frequency Modulated Continuous Wave radar. We determine the mean normalized radar cross section to be −9.9 dB. The distribution closely follows a log‐normal distribution with a high goodness of fit ( R 2 = 0.99) which suggests that radar backscatter is diffuse and driven by surface roughness. Further, we quantified the uncertainty of AVTIS2 3D point clouds to be 1.30–3.72 m, which is smaller than other ground‐based glacier surface mapping radars. These results demonstrate that glacier surfaces are an efficient scattering target at 94 GHz, hence demonstrating the suitability of millimeter‐wave radar for glacier monitoring.

Backscatter (email)

10.1029/2023gl104721

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Lava dome growth and mass wasting measured by a time series of ground‐based radar and seismicity observations

Journal of Geophysical Research Atmospheres (2008)

G. Wadge David G. Macfarlane Henry Odbert M. R. James J. K. Hole

Exogenous growth of Peléean lava domes involves the addition of lava from a central summit vent and mass wasting on the flanks as rockfalls and pyroclastic flows. These processes were investigated at the Soufrière Hills Volcano, Montserrat, between 30 March and 10 April 2006, using a ground‐based imaging millimeter‐wave radar, AVTIS, to measure the shape of the dome and talus surface and rockfall seismicity combined with camera observations to infer pyroclastic flow deposit volumes. The topographic evolution of the lava dome was recorded in a time series of radar range and intensity measurements from a distance of 6 km, recording a southeastward shift in the locus of talus deposition with time, and an average height increase for the talus surface of about 2 m a day. The AVTIS measurements show an acceleration in lava extrusion rate on 5 April, with a 2‐day lag in the equivalent change in the rockfall seismicity record. The dense rock equivalent volumetric budget of lava added and dispersed, including the respective proportions of the total for each component, was calculated using: (1) AVTIS range and intensity measurements of the change in summit lava (∼1.5 × 10 6 m 3 , 22%), (2) AVTIS range measurements to measure the talus growth (∼3.9 × 10 6 m 3 , 57%), and (3) rockfall seismicity to measure the pyroclastic flow deposit volumes (∼1.4 × 10 6 m 3 , 21%), which gives an overall dense rock equivalent extrusion rate of about 7 m 3 ·s −1 . These figures demonstrate how efficient nonexplosive lava dome growth can be in generating large volumes of primary clastic deposits, a process that, by reducing the proportion of erupted lava stored in the summit region, will reduce the likelihood of large hazardous pyroclastic flows.

Lava dome

Mass wasting

Rockfall

Dome (geology)

10.1029/2007jb005466

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Use of a portable topographic mapping millimetre wave radar at an active lava flow

Geophysical Research Letters (2006)

David G. Macfarlane G. Wadge Duncan A. Robertson M. R. James H. Pinkerton

A ground‐based millimetre wave radar, AVTIS (All‐weather Volcano Topography Imaging Sensor), has been developed for topographic monitoring. The instrument is portable and capable of measurements over ranges up to ∼7 km through cloud and at night. In April and May 2005, AVTIS was deployed at Arenal Volcano, Costa Rica, in order to determine topographic changes associated with the advance of a lava flow. This is the first reported application of mm‐wave radar technology to the measurement of lava flux rates. Three topographic data sets of the flow were acquired from observation distances of ∼3 km over an eight day period, during which the flow front was detected to have advanced ∼200 m. Topographic differences between the data sets indicated a flow thickness of ∼10 m, and a dense rock equivalent lava flux of ∼0.20 ± 0.08 m 3 s −1 .

10.1029/2005gl025005

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Citations (24)

3D Terrain Mapping and Filtering From Coarse-Resolution Data Cubes Extracted From Real-Aperture 94-GHz Radar

IEEE Transactions on Geoscience and Remote Sensing (2024)

William D. Harcourt David G. Macfarlane Duncan A. Robertson

Accurate, high-resolution 3D mapping of environmental terrain is critical in a range of disciplines. In this study, we develop a new technique, called the PCFilt-94 algorithm, to extract 3D point clouds from coarse resolution millimetre-wave radar data cubes and quantify their associated uncertainties. A technique to non-coherently average neighbouring waveforms surrounding each AVTIS2 range profile was developed in order to reduce speckle and was found to reduce point cloud uncertainty by 13% at long range and 20% at short range. Further, a Voronoi-based point cloud outlier removal algorithm was implemented which iteratively removes outliers in a point cloud until the process converges to the removal of 0 points. Taken together, the new processing methodology produces a stable point cloud, which means that: 1) it is repeatable even when using different point cloud extraction and filtering parameter values during pre-processing, and 2) is less sensitive to over-filtering through the point cloud processing workflow. Using an optimal number of Ground Control Points (GCPs) for georeferencing, which was determined to be 3 at close range (<1.5 km) and 5 at long range (>3 km), point cloud uncertainty was estimated to be approximately 1.5 m at 1.5 km to 3 m at 3 km and followed a Lorentzian distribution. These uncertainties are smaller than those reported for other close-range radar systems used for terrain mapping. The results of this study should be used as a benchmark for future application of millimetre-wave radar systems for 3D terrain mapping.

10.1109/tgrs.2024.3353676

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Spatial and temporal variations in 94 GHz radar backscatter from a springtime snowpack

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2024)

William D. Harcourt Duncan A. Robertson David G. Macfarlane Brice R. Rea M. R. James

Snowpack

Backscatter (email)

10.1109/jstars.2024.3522583

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94 GHz radar mapping of terrestrial snow cover

William D. Harcourt Duncan A. Robertson David G. Macfarlane Brice R. Rea M. R. James

<p>Terrestrial snow cover is a perennial feature throughout the global cryosphere, taking the form of individual snow patches during summer and becoming more spatially continuous in winter. The characteristics and conditions of these snowpacks can be altered by rapid changes in temperature and precipitation, significantly impacting local ecosystems, upland hydrology and snow avalanche risks. In Scotland, for example, monitoring the hazards associated with snowpack alterations is a central focus of the Scottish Avalanche Information Service (SAIS) and is essential to ensuring the safety of local communities, hill walkers and mountaineers. In this context, the development of new remote sensing techniques for snow monitoring will help the SAIS develop avalanche forecasts and potentially without the need to undertake arduous and dangerous fieldwork. Here, we aim to develop the utility of millimetre-wave radar at 94 GHz as a new remote sensing tool for monitoring snowpacks. We use a ground-based 94 GHz, real-aperture system called AVTIS2 which mechanically scans across a scene of interest to generate radar backscatter images and 3D Digital Elevation Models (DEMs). AVTIS2 uses a narrow beamwidth of 0.35&#176; (i.e. a spot size of 6 m per km) and has a maximum range of ~6 km, enabling kilometre-scale mapping at high angular resolution. This radar system has previously been successful in monitoring the topographic changes of volcanic lava domes, measuring the dynamics of active lava flows and quantifying 94 GHz radar backscatter from glacier ice. We aim to deploy the AVTIS2 millimetre-wave radar in the Cairngorms National Park, Scotland, in January/February 2021 and validate our measurements with a co-located Terrestrial Laser Scanner (TLS). Additionally, we will acquire in situ observations of snow properties to gain a better understanding of how 94 GHz radar signals interact with the snowpack. Overall, we will report on the following: (1) the radar backscatter characteristics from a variety of snow surface conditions at millimetre wavelengths; (2) point cloud and DEM differences between AVTIS2 and TLS measurements over snow-covered terrain; and (3) the effect of snowpack properties on radar backscatter and how this can be used to understand snow-associated hazards.</p>

Snowpack

Elevation (ballistics)

10.5194/egusphere-egu21-2747

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Millimetre-wave radar observations of glacier calving at Hansbreen (Svalbard) correlated with TLS, time-lapse camera images and seismic records

William D. Harcourt Duncan A. Robertson David G. Macfarlane Brice R. Rea Matteo Spagnolo

<p>The release of icebergs into the ocean through glacier calving is a major source of mass loss from tidewater glaciers across the Arctic. However, there are very few direct measurements of calving activity in Svalbard at daily to sub-daily resolution which impedes our understanding of how these processes influence ice discharge and therefore regional patterns of mass balance. Quantifying ice loss from Svalbard is important because the archipelago contains ~10% of the total Arctic glacier area and holds a sea-level equivalent of ~1.5 cm. In this contribution, we generate an 8-day time series from August 2021 of calving activity at sub-daily resolution for the Hansbreen tidewater glacier in Svalbard using a suite of state-of-the-art remote sensing instruments. Millimetre-wave radar at 94 GHz (called AVTIS2) was used to map the 3D structure of the Hansbreen frontal ice cliff, so that terminus change could be tracked and the volume of ice released through calving quantified. Millimetre-wave radar can map glacier surfaces at high angular resolution and through most weather conditions, hence is not impeded by poor weather conditions unlike instruments such as Terrestrial Laser Scanners (TLS). AVTIS2 mechanically scans across the scene of interest, measures radar backscatter along each Line of Sight (LoS) and generates 3D point clouds by calculating the range to maximum received power along each LoS. In this study, an angular area of 83&#176; (azimuth) x 5&#176; (elevation) was scanned which ensured the entire marine-terminating portions of the ice front were measured throughout the study period. The 3D AVTIS2 point clouds were validated using a coincident survey from a TLS (Riegl LPM-321) and a time-lapse camera deployed at the same location to provide additional validation and knowledge of environmental conditions throughout the study period. Calving events from both datasets were correlated to seismic activity recorded by two networks of geophones deployed in the vicinity of the glacier terminus. We will report on the following: (1) the calving rate of Hansbreen in August 2021, (2) the volume of ice released into the ocean through calving during the 8-day study period, (3) the capabilities of millimetre-wave radar for monitoring glacier calving fronts versus optical approaches (TLS and time-lapse camera images), and (4) calving processes at Hansbreen. This study pushes forward our understanding of frontal ablation processes in Svalbard and demonstrates new possibilities for ground-based remote sensing of ice-ocean interactions.</p>

Tidewater

Tidewater glacier cycle

Glacier mass balance

10.5194/egusphere-egu22-143

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Citations (2)