Philippa J. Mason

Landslide hazard assessment in the Three Gorges area of the Yangtze River using ASTER imagery

The Three Gorges Dam Project (TGP) has raised international attention because of its great potential for hydro-electrical power generation and flood control, as well as for its potential hazardous effects on the environment and ecology, and for the migration and resettlement of local inhabitants. Slope instability is one common problem in the Three Gorges area and this paper reports a regional assessment of landslide hazard based on ASTER imagery and Digital Elevation Model (DEM), in combination with limited field investigation. A simple model based on the geometric mean and Boolean decision rules has been applied to a multi-criterion dataset to generate a map of landslide hazard.

Hyperspectral remote sensing for mineral exploration in Pulang, Yunnan Province, China

The launch of the first spaceborne hyperspectral instrument, Hyperion, in 2000 has provoked further research into its capabilities with regard to mineral exploration. Our study in the remote, mountainous region of Pulang, China employed a two-step progressive approach, first to locate target areas characterized by hydrothermal mineral alteration, using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and secondly, to attempt detailed mineral mapping using Hyperion. The preliminary target detection involved principal components and broad-band spectral analysis and led to the detection of two target areas characterized by argillic alteration, iron-oxide- and sulphate-bearing minerals. A focused hyperspectral study followed using Spectral Angle Mapper (SAM) and Mixture Tuned Matched Filtering (MTMF) techniques, which allowed mineral species to be discriminated and mapped in more detail. This combined broad-band and hyperspectral approach is feasible and advantageous for mineral exploration in remote areas where primary information is limited or unavailable.

Linking the morphology of fluvial fan systems to aquifer stratigraphy in the Sutlej‐Yamuna plain of northwest India

The Indo-Gangetic foreland basin has some of the highest rates of groundwater extraction in the world, focused in the states of Punjab and Haryana in northwest India. Any assessment of the effects of extraction on groundwater variation requires understanding of the geometry and sedimentary architecture of the alluvial aquifers, which in turn are set by their geomorphic and depositional setting. To assess the overall architecture of the aquifer system, we used satellite imagery and digital elevation models to map the geomorphology of the Sutlej and Yamuna fan systems, while aquifer geometry was assessed using 243 wells that extend to ∼200 m depth. Aquifers formed by sandy channel bodies in the subsurface of the Sutlej and Yamuna fans have a median thickness of 7 and 6 m, respectively, and follow heavy-tailed thickness distributions. These distributions, along with evidence of persistence in aquifer fractions as determined from compensation analysis, indicate persistent reoccupation of channel positions and suggest that the major aquifers consist of stacked, multistoried channel bodies. The percentage of aquifer material in individual boreholes decreases down fan, although the exponent on the aquifer body thickness distribution remains similar, indicating that the total number of aquifer bodies decreases down fan but that individual bodies do not thin appreciably, particularly on the Yamuna fan. The interfan area and the fan marginal zone have thinner aquifers and a lower proportion of aquifer material, even in proximal locations. We conclude that geomorphic setting provides a first-order control on the thickness, geometry, and stacking pattern of aquifer bodies across this critical region.

Measurement of the left‐lateral displacement of Ms 8.1 Kunlun earthquake on 14 November 2001 using Landsat‐7 ETM+ imagery

An imageodesy study has been carried out, using pre‐ and post‐event Landsat‐7 Enhanced Thematic Mapper Plus (ETM+) images, to reveal regional co‐seismic displacement caused by the Ms 8.1 Kunlun earthquake in November 2001. The two Landsat scenes, Kusai Lake and Buka Daban, cover an area of some 57 600 km2 (320 km W–E and about 180 km N–S), which includes most of the fault rupture zone. The co‐seismic displacement measured in the Kusai Lake scene shows that the average left‐lateral shift along the Kunlun fault is 4.8 m (ranging from 1.5 to 8.1 m) and the maximum shift appears west of the Kusai Lake. The splayed nature of the fault to the west of Buka Daban, where the fault splits into three branches, causes the displacement pattern to become complicated. Here the average left‐lateral shift, between the south side of the southern branch and the north side of the northern branch, is 4.6 m (ranging from 1.0 to 8.2 m). Our results also illustrate that the south side of the fault is the ‘active’ block, moving significantly in an east–south‐easterly direction, relative to the largely ‘stable’ northern block.

Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

Urbanism in the Bronze-age Indus Civilisation (~4.6–3.9 thousand years before the present, ka) has been linked to water resources provided by large Himalayan river systems, although the largest concentrations of urban-scale Indus settlements are located far from extant Himalayan rivers. Here we analyse the sedimentary architecture, chronology and provenance of a major palaeochannel associated with many of these settlements. We show that the palaeochannel is a former course of the Sutlej River, the third largest of the present-day Himalayan rivers. Using optically stimulated luminescence dating of sand grains, we demonstrate that flow of the Sutlej in this course terminated considerably earlier than Indus occupation, with diversion to its present course complete shortly after ~8 ka. Indus urban settlements thus developed along an abandoned river valley rather than an active Himalayan river. Confinement of the Sutlej to its present incised course after ~8 ka likely reduced its propensity to re-route frequently thus enabling long-term stability for Indus settlements sited along the relict palaeochannel.The Bronze-age Indus civilisation (4.6–3.9 ka) was thought to have been linked to the development of water resources in the Himalayas. Here, the authors show that along the former course of the Sutlej River the Indus settlements developed along the abandoned river valley rather than an active Himalayan river.

Drift-filled hollows in Battersea: investigation of the structure and geology along the route of the Northern Line Extension, London

Drift-filled hollows (DFHs) are a major subsurface hazard for engineering in London. They are characterized by a steeply inclined cone-shaped hollow into (sometimes through) the London Clay Formation, filled with unconsolidated fine- to coarse-grained drift and often covered by terrace gravels, making them difficult to identify at the surface. Their origin remains uncertain but most probably formed towards the end of glacial epochs by meltwater scouring, perhaps of collapsed pingos. Usually associated with tributaries to the Thames, DFHs are particularly prevalent in the Battersea area, through which the Northern Line Extension (NLE) is to be built. This study uses 283 public borehole records and site reports to build a 3D geological ground model of two known DFHs in the Battersea area to develop a more complete understanding of their origin. We show that DFHs are probably older than previously assumed, dating from the end-Anglian (Marine Isotope Stage (MIS) 12), c. 300 kyr ago, before the deposition of the River Terrace Deposits. The two DFHs modelled fall into distinct types: a small shallow DFH that is probably a purely scour feature in origin, and a larger, deeper DFH that probably formed by the scouring of a perhaps fault-controlled pingo. It is unclear whether the faults controlled pingo formation passively by acting as a conduit for water, or in a more active sense by driving ground movements. Both DFHs represent a significant hazard for the NLE and require more detailed investigations to properly constrain their extent.

Adaptive local kriging to retrieve slant-range surface motion maps of the Wenchuan earthquake

Kriging is a widely used technique for raster data interpolation from point samples, such as in the generation of digital elevation models and geochemical maps. The quality of the result depends on both spatial distribution of the sampled values and nature of the semivariogram model, which fits an empirical global function to the sample data set to predict values at the unknown locations. However, such a semivariogram model may not be suitable for data sets with complex local trends in spatial distribution, such as those observed in differential interferometric synthetic aperture radar (DInSAR) data of the Wenchuan earthquake. Here we propose a modified kriging method, adaptive local kriging (ALK), for the retrieval of data lost through decoherence in Advanced Land Observing Satellite (ALOS) phased array L-band synthetic aperture radar (PALSAR) DInSAR data, within the intensely deformed fault zone of the 2008 Wenchuan earthquake. In ALK, a series of dynamic linear local semivariogram models is used rather than a global semivariogram for the whole data set. The localized adaptive approach ensures accurate interpolation in the areas of good DInSAR data with small decoherence gaps and avoids drastic errors in the extensive decoherence gaps; the overall value prediction is thus significantly improved, as confirmed by comparison with the original DInSAR data and fidelity verification experiments.

Identification of Ground Engineering Hazards in London Through the Use of Predictive 4D Geomodelling Tools

Unexpected ground conditions are responsible for a number of engineering problems and hazards across London. A major reason for the unexpected nature of these events is the historical proprietary approach to site investigation, which has restricted knowledge transfer and inhibited the development of a London-wide geological context. Recent changes mean that much of these data are now accessible in the public domain for site investigation and useful in predicting the engineering hazards resulting from complex and variable geology. We advocate applying predictive 4D modelling to better constrain geological structures, facies, fissures and groundwater flow, and adopting an iterative approach that both informs local site models and updates the regional context. Reverse normal faulting, indicative of basin inversion, pull-apart structures and periglacial scour/pingo features are identified in a pilot study regional model. Applying this model to a small site investigation predicted otherwise unexpected faulting, generating horizontal fissuring that causes water to flow along the length of the fault system. Widely adopting this approach in London and other urban areas may substantially reduce the risk of unexpected ground hazards.

Three-dimensional surface displacement map of the 2008 Wenchuan earthquake derived from Phase Correlation (PC) sub-pixel offset method and Adaptive Local Kriging (alk) DInSAR data

Differential Interferometric Synthetic Aperture Radar (DInSAR) is an effective technique to measures the surface displacement caused by strong earthquakes, such as the 2008 Wenchuan earthquake in China. However, in the area subject to the most significant deformation along the Longmenshan fault zone, the coherence between pre- and after- earthquake SAR images is completely lost because of the earthquake induced violent and chaotic destruction on the land surface and consequently, no surface displacement data can be measured. The missing data were recovered using Adaptive Local Kriging (ALK) method to produce a complete Line Of Sight (LOS) displacement map. As a further step to characterize the 3D (three-dimensional) co-seismic deformation, horizontal displacement maps were generated using the Phase Correlation based Image Analysis System (PCIAS), and in combination with the ALK DInSAR data, the vertical displacement map can then be decomposed. Thus, a 3D displacement dataset is accomplished. This dataset shows the thrust and right-lateral strike slip motions along the Longmenshan fault system with two major uplift in Yingxiu and Beichuan areas respectively.

The Earth as a planet

The Remote Sensing and Photogrammetry Society’s Annual Conference provides an excellent opportunity for members to meet and present their work on any aspect of remote sensing or photogrammetry. Each year, however, a special theme is chosen as a focus for the conference and, for RSPSoc2017, the topic chosen was ‘The Earth as a Planet’. RSPSoc2017 was held in the Royal School of Mines, Department of Earth Science & Engineering, at Imperial College London from 5 to 8 September 2017. The conference was well attended, with delegates travelling from 18 countries outside the UK. The Satellite Applications Catapult & UK Space Agency ran their annual Space Placements in Industry (SPIN) Showcase on Wednesday 6th Sept, in parallel with the main conference, and it was attended by students and corporate internship hosts. A series of poster presentations and talks ran throughout the day, and the event finished with a visit to the 3D visualisation suite at Imperial College London where ‘SPINterns’ were treated to a virtual field trip on the surface of Mars, led by Prof Sanjeev Gupta. The talks in the main conference sessions were of a very high standard, and there were two excellent keynote talks from Mike James (Lancaster University) on the state-of-the art in structure-from-motion, and by Kathie Bowden, on the future direction of EO in the UK. In addition to sessions on land cover, risk & hazards, operation and validation (commercial issues), new sensors, geomorphology, heritage & archaeology, spatial and spectral sciences, there were double sessions each on InSAR and on planetary science. Of the ten papers in the planetary science sessions, eight were dedicated to Mars and the remaining two covered developments in Venus geoscience. The planetary papers included discussions of: