Timothy S. Farewell

Soil legacy data rescue via GlobalSoilMap and other international and national initiatives

Legacy soil data have been produced over 70 years in nearly all countries of the world. Unfortunately, data, information and knowledge are still currently fragmented and at risk of getting lost if they remain in a paper format. To process this legacy data into consistent, spatially explicit and continuous global soil information, data are being rescued and compiled into databases. Thousands of soil survey reports and maps have been scanned and made available online. The soil profile data reported by these data sources have been captured and compiled into databases. The total number of soil profiles rescued in the selected countries is about 800,000. Currently, data for 117, 000 profiles are compiled and harmonized according to GlobalSoilMap specifications in a world level database (WoSIS). The results presented at the country level are likely to be an underestimate. The majority of soil data is still not rescued and this effort should be pursued. The data have been used to produce soil property maps. We discuss the pro and cons of top-down and bottom-up approaches to produce such maps and we stress their complementarity. We give examples of success stories. The first global soil property maps using rescued data were produced by a top-down approach and were released at a limited resolution of 1km in 2014, followed by an update at a resolution of 250m in 2017. By the end of 2020, we aim to deliver the first worldwide product that fully meets the GlobalSoilMap specifications.

Soil geohazard mapping for improved asset management of UK local roads

Unclassified roads comprise 60 % of the road network in the United Kingdom (UK). The resilience of this locally important network is declining. It is considered by the Institution of Civil Engineers to be “at risk” and is ranked 26th in the world. Many factors contribute to the degradation and ultimate failure of particular road sections. However, several UK local authorities have identified that in drought conditions, road sections founded upon shrink–swell susceptible clay soils undergo significant deterioration compared with sections on non-susceptible soils. This arises from the local road network having little, if any, structural foundations. Consequently, droughts in East Anglia have resulted in millions of pounds of damage, leading authorities to seek emergency governmental funding. This paper assesses the use of soil-related geohazard assessments in providing soil-informed maintenance strategies for the asset management of the locally important road network of the UK. A case study draws upon the UK administrative county of Lincolnshire, where road assessment data have been analysed against mapped clay-subsidence risk. This reveals a statistically significant relationship between road condition and susceptible clay soils. Furthermore, incorporation of UKCP09 future climate projections within the geohazard models has highlighted roads likely to be at future risk of clay-related subsidence.

Monitoring the response of roads and railways to seasonal soil movement with persistent scatterers interferometry over six UK sites

Road and rail networks provide critical support for society, yet they can be degraded by seasonal soil movements. Currently, few transport network operators monitor small-scale soil movement, but understanding the conditions contributing to infrastructure failure can improve network resilience. Persistent Scatterers Interferometry (PSI) is a remote sensing technique offering the potential for near real-time ground movement monitoring over wide areas. This study tests the use of PSI for monitoring the response of major roads, minor roads, and railways to ground movement across six study sites in England, using Sentinel 1 data in VV polarisation in ascending orbit. Some soils are more stable than others—a national soil map was used to quantify the relationships between infrastructure movement and major soil groups. Vertical movement of transport infrastructure is a function of engineering design, soil properties, and traffic loading. Roads and railways built on soil groups prone to seasonal water-logging (Ground-water Gley soils, Surface-water Gley soils, Pelosols, and Brown soils) demonstrated seasonal subsidence and heave, associated with an increased risk of infrastructure degradation. Roads and railways over Podzolic soils demonstrated relative stability. Railways on Peat soils exhibited the most extreme continual subsidence of up to 7.5 mm year−1. Limitations of this study include the short observation period (~13 months, due to satellite data availability) and the regional scale of the soil map—mapping units contain multiple soil types with different ground movement potentials. Future use of a higher resolution soil map over a longer period will advance this research. Nevertheless, this study demonstrates the viability of PSI as a technique for measuring both seasonal soil-related ground movement and the associated impacts on road and rail infrastructure.

Knowledge-based soil attribute mapping in GIS: corrections and extensions to the expector method

The Expector Method provides an excellent basis for modelling soil and other environmental classes or properties using a combination of expert knowledge and empirical data. The ideas are based on probability theory, and hence can be given a rigorous mathematical underpinning. Nevertheless, concerns have arisen regarding the published algebra used in deriving the equations underlying the model. We present corrections to key equations, improved notation to encourage future use of this methodology, and a simplification of the map purity extension to the formula that allows different weights to be applied to the evidence layers. We illustrate the methodology with an example of mapping soil parent materials.

Assessing measures of map value for thematic maps with sparse data

The assessment of the accuracy of thematic maps or classified remotely sensed images has been much discussed, but no single approach has emerged as uniformly useful. Various success measures, such as kappa or the overall accuracy, can be derived for a map or classified image but, when addressing different aspects of the map such as the number and taxonomic detail of map classes, these measures may not be completely appropriate. In addition, strong arguments have been made that the use of kappa should be replaced with the use of allocation and quantity disagreement. Also, different measures of map accuracy may be combined into a single measure of ‘composite map value’, the form of which may be context specific. To illustrate this, we consider a composite map value metric (V*) that considers the overall predictive accuracy as well as the number, detail and accuracy of map classes. For recently suggested measures of map value, confidence intervals have not been considered. Our aim is to discuss generic methods to derive confidence intervals for assessment metrics with an emphasis on a simply implemented bootstrap procedure adapted for use with sparse confusion matrices with numerous zero entries.

Soil moisture content measurement using optical fiber long period gratings

The use of an optical fibre long period grating (LPG) as a soil moisture sensor is reported. Characterization of the device in both clay and sandy soils revealed a sensitivity to moisture levels in the range 10–50%, and the results were compared with the output from a Theta probe, the standard soil moisture sensor, which measures the impedance of the soil.