The Role of Remote Sensing in Geo-environmental Managment

Mitigating the impact of mining activity is a significant challenge for environmental management. New approaches are required based on environmental information from in-situ, airborne and satellite observations. Airborne hyperspectral remote sensing and geophysical techniques are two such approaches being pursued at the BGS to characterise mine waste and its host rocks and then to monitor its dispersal in the environment. This paper will report on two projects that have followed on from the successful completion of the MINEO project. MINEO applied hyperspectral remote sensing to a range of active and abandoned mining environments across Europe. Parys Mountain, on Anglesey, was the first site under investigation using HyMap data following MINEO. Here, the main task has been mapping the different tailings and characterising them mineralogically. Secondary investigations have involved the study of vegetation stress around the mine. Low-level airborne geophysical data already exist for the Bolsover area from the HiRES-1 survey in 1998. HyMap data acquired during the NERC SAR and Hyperspectral Campaign (SHAC) over the Shirebrook mine within the HiRES-1 area have been used to evaluate the use of airborne geophysical and hyperspectral data together to map open cast mines in the region. Mine site classifications were developed based on both field and image spectral interpretations. In all these projects, various techniques have been applied in order to classify mine sites in terms of mineralogy and contamination. The approach adopted is to use MNF and PPI approaches to extract end-member spectra and then classify the data using the SAM algorithm. INTRODUCTION Mining in Europe has left a legacy of mine waste in various forms. Following the World Summit on Sustainable development (Johannesburg, 2002), European directives on soils and water, and related British legislation demand improvements in mitigating the effects of mining activities. Remote sensing, and specifically hyperspectral remote sensing, techniques are being developed to provide non-invasive methods of characterising mine waste. When combined with geochemical data, terrain models and hydrogeological data, remote sensing becomes a very powerful tool for determining the hazard rating for a site, with particular emphasis on transport of waste away from a site. Since 2001 many advances have been made in the operational use of hyperspectral remote sensing, especially within the European community. This is in part due to the success of the MINEO project, an EC 5 Framework research and development project which focussed on the development of hyperspectral data processing techniques for the characterisation of mine waste in the temperate European environment. Until then many hyperspectral studies had involved exploration for economic minerals in an arid environment with little or no vegetation cover. Techniques were developed within the MINEO project to map various different types of mine waste and also develop site-specific spectral libraries for mine waste characterisation and the analysis of vegetation stress. The UK MINEO study site is an area of abandoned tin mining in Cornwall. Mineralisation in the region occurred in several phases with the emplacement of granite [1]. Mining began in the Bronze age, peaked in the late 19 century, and then declined post War, before ceasing in the 1990's. This has left a landscape scattered with abandoned mining adits, disturbed ground and mine shafts [2]. There are several environmental issues associated with mining pollution in the region. © EARSeL and Warsaw University, Warsaw 2005. Proceedings of 4th EARSeL Workshop on Imaging Spectroscopy. New quality in environmental studies. Zagajewski B., Sobczak M., Wrzesień M., (eds) Since the MINEO project officially closed in 2003 several related studies have followed, using the hyperspectral data processing techniques developed during the MINEO project at other mine sites within the UK. To further develop metaliferous mine classification techniques BGS initially focussed on the abandoned copper mine at Parys Mountain. The mine is located near the north east coast of Anglesey, North Wales. Mining activity at Parys Mountain has left a legacy of mine waste and scattered spoil covering an area of around 3km. So unique is the variety of lithologies and minerals and resulting flora and fauna at Parys Mountain that several Sites of Special Scientific Interest (SSSI) have been established on the mountain. Weathering of the tailings results in the formation of colourful red and yellow hydrous iron oxides and a diverse range of sulphate minerals [3]. Weathering at the site is harsh, with sulphuric acid being generated by the oxidation of pyrite and other sulphide minerals. It is this diversity of minerals and weathering products that make this site so challenging to characterize and map. One of the deliverables of the HiRES (High-resolution Resource and Environmental Surveys) project was to demonstrate the potential synergy of airborne geophysics and airborne (thermal and hyperspectral) remote sensing. Low-level, high-resolution airborne geophysics already exists for the North Nottinghamshire coalfields. The next stage in the project has been to evaluate the possibility of using airborne geophysical and hyperspectral data together to map open cast mines in the region. HyMap data was also available over this region and so was chosen to characterise and map non-metaliferous mine waste. Due to the low reflectance of the mine waste material this was a more challenging mining environment to characterise the mine waste spectrally. The dark colour of the coal waste leads to lower signal to noise. Techniques were developed for characterising organic material and associated waste materials, such as brick waste from demolished mine buildings. The main objectives of all this work are to develop repeatable techniques for characterising and mapping mine waste using advanced earth observation techniques and, in conjunction, develop site specific spectral libraries for distinct waste types for use in other studies at other mine sites. At all test sites described above vegetation stress has also been evident. Techniques such as NDVI have been used to identify areas of less vigorous vegetation associated with mine waste. Vegetation stress is a useful indicator of what lies beneath, especially at sites such as Shirebrook where extensive remediation has occurred. METHODS Techniques used to map mine waste at the Parys Mountain and Shirebrook sites were first employed during the MINEO project that ran from 2000 to 2003 [4]. The methods developed were used on the UK MINEO HyMap dataset to map mine waste in the Camborne – Redruth region of Cornwall, Southwest England. Mineralisation in Cornwall is more diffuse than both the Parys Mountain and Shirebrook sites, but the same techniques are still relevant as the mining in all cases produced waste products that are spectrally distinct. HyMap Data The HyMap data used for the Parys Mountain and HiRES studies were flown as part of the SAR and Hyperspectral Campaign (SHAC) in 2000. HyMap data has 126 bands and covers the wavelength range from 0.45 2.5 μm. HyMap provides contiguous spectral coverage, except across the atmospheric water vapour bands, and has bandwidths between 15 and 20 nm. Pixel size is typically between 3 and 10m, depending on flying height. The Parys Mountain dataset comprises four flight lines covering an area of around 60km2, covering Parys Mountain itself and also the land to the northwest and to the sea. The Shirebrook data set comprises 8 strips of HyMap data and covers an area of around 90km.