Regional/National products and applications

The detection of leaks in underground pipelines is a fundamental and expensive task for operators of water and sewage networks in urban areas. Subsidence is an indicator of a problem. In fact, subsidence of a few centimetres around buried pipelines can cause leaks in the pipes. These leaks can then accelerate the erosion around the problem area, disrupting service and possibly causing larger problems. Traditional field inspections for the regular monitoring of wide areas require great financial resources and time. Operators of water and sewage networks spend many resources maintaining their assets and fighting against water leakages and structural problems. Identifying subsidence before it becomes critical is a challenge and satellite remote sensing can help. In detail, satellite radar monitoring identifies trends in the displacement of the ground, which can predict problems underground. These data, when exploited through Interferometric Synthetic Aperture Radar (InSAR) analysis, can provide changes in the ground level with millimetre accuracy.

Planetek Italia succeeded in creating a vertical application called Rheticus® Network Alert that addresses users’ needs in the utilities industry, by integrating contents generated by its Rheticus® platform and based on radar data. Rheticus® platform works as a big hub that processes satellite imagery and geospatial data automatically and delivers geo-information services ready-to-use by end users. Rheticus® Network Alert is a vertical solution for companies managing pipeline networks in urban areas, which indicates locations of concern and lets operators to act upon the information, simplify maintenance activities and prioritise inspection. Rheticus® Network Alert is based on Rheticus® Displacement, the service for continual monitoring of ground displacements through the exploitation of Sentinel-1 radar data that ensure a global coverage. Rheticus® Displacement provides monthly monitoring of millimetre displacements of ground surface or infrastructures in areas with active landslide or subsidence phenomena. The mapping activity is made through the monitoring of points on the ground characterised by high stability, called Persistent Scatterers (PS). PS are produced through a fully automatic Multi-Temporal SAR Interferometry (MT-InSAR) processing chain based on the SPINUA^© algorithm (“Stable Point Interferometry even in Un-urbanized Areas”) developed by GAP. With Rheticus® Displacement it is possible to measure the distance between the satellite and PS on the ground over time, recording the time elapsed between the electromagnetic wave emission and the reception of the backscattered signal. Thanks to six-day revisiting time of the Sentinel-1 constellation, the service provides repeated measurements of the sensor-target distance along the satellite’s line-of-sight. The comparison of distances measured over time allows the computation of ground or infrastructure displacements with millimetre precision.

HERA, one of the main Italian operator in the utilities industry, activated Rheticus® Displacement and Rheticus® Network Alert over an urban area of interest in order to monitor the stability of its assets. Thanks to the service, HERA successfully detected and is now monitoring the instability of a settling tank within a wastewater treatment plant. Even more operators worldwide are adopting Rheticus® Displacement and Rheticus® Network Alert to effectively maintain and inspect their assets, identify up-to-date risks and act upon the information.

The High Resolution Layer (HRL) Imperviousness is part of the pan-European component of the Copernicus Land Monitoring Service (CLMS) that provides consistent information on land characteristics across Europe for 5 specific topics: Imperviousness, Forest, Grassland, Water/Wetness, and Small Woody Features. The objective of the HRL Imperviousness is to consistently monitor changes in sealed surfaces and built-up areas on pan-European scale. The HRL Imperviousness supports the analysis of pressures on ecosystems or the vulnerability of people and infrastructure to natural hazards. As such, it provides key information for policy evaluation, thematic assessments (e.g. as part of EEA, SOER 2015), and the general public. The product is a basis for more evidence-based policy decisions.

The idea of the HRL Imperviousness was born in GMES research projects, comprising the EC FP6 Geoland and the ESA GMES Service Elements SAGE and Land, in order to provide insight into urban sprawl as one of the pressing environmental challenges in Europe. This initial service development led to the first-ever operational tender in the frame of GMES Land Monitoring by the EEA. Since then the HRL Imperviousness provides a comprehensive mapping of the urban development over the last decade in a three year cycle from 2006 onwards. In spring 2018, the third update of the HRL Imperviousness 2015 based on advanced time-series approaches and the re-processing of all historical products was completed and is available for view services and download on the CLMS portal.

The production of the Imperviousness products for the years 2006, 2009, and 2012 was based mostly on a mono- or bi-temporal coverage with IRS-P6, SPOT-5 and RapidEye image data. Within the Copernicus project for 2015, highly automated pixel-based methods were developed, allowing a seamless production in 20m and 100m spatial resolution. The applied approach is based on seasonal composites from multi-sensor and multi-temporal data including Sentinel-2, SPOT-5, IRS-P6, and Landsat 8. Based on the relationship between the Normalized Difference Vegetation Index (NDVI) and vegetation presence, or absence, respectively, the built-up densities were determined. For this purpose, an absolute calibration of NDVI metrics to the actual imperviousness degrees, extracted from an explicitly and independent produced reference database based on IMAGE 2015 VHR EO data, was done. A relative image-to-image calibration approach, based on a histogram matching, was performed between the latest imperviousness degrees and those of the historical production. To determine the changes between two status layers the differences in imperviousness degree were calculated under consideration of spectral and spatial thresholds.

With Sentinel-2, a new era started, which provides dense data coverage at global levels. This improvement offers new potential for implementing fully automated approaches to derive a harmonized HRL Imperviousness time-series. For future production, the full use of the sensors from the Copernicus satellite missions will allow further improvements in terms of data quality and consistency. Complementary Sentinel-1 data has been investigated at GeoVille to exploit the additional power of combining SAR and optical data for a better delineation of built-up areas, especially in areas with a high amount of permanent open soil.

The Copernicus Urban Atlas is manged by the European Environment Agency (EEA) and provides pan-European, comparable and detailed 27-class land use and land cover map data for the main Functional Urban Areas (FUAs). The 2006 edition covered all EU urban areas with more than 100.000 inhabitants and all EU27 member state capital cities as defined by the Urban Audit, whilst the 2012 update and recent extension covers in addition to the cities mapped in 2006, all urban areas with a population above 50.000 inhabitants over the 39 member and cooperating countries of the EEA corresponding to a total of over 800 FUAs from Iceland to Turkey covering an area of nearly 1.3 million km² that is about 22% of Europe. In addition, a digital height model (DHM) was generated for 31 capitals of EU and EFTA countries (~ 18,000 km²) based on homogenous, high-resolution IRS-P5 Cartosat-1 stereo satellite data. The main purpose of the DHM is to improve the correlation between UA residential areas and population census data to better disaggregate such data for urban planning and studies.

The 2018 update of the Urban Atlas will provide an update of the 2012 coverage. For the first time, the 2018 update will be relying on the upcoming VHR2018 dataset for detailed mapping over artificial areas and Sentinel-2 data for change detection and characterisation over rural areas. This raises a number of challenges particularly linked to the complex changes of the 2012 FUA delineation and the extension to a large number of smaller urban areas. The methodology adopted is based on the optimisation of the production process based on an optimised combination of automated Object Based Image Analysis (OBIA) techniques and Computer Assisted Photo-Interpretation (CAPI) to ensure the most efficient methodology is applied whilst exceeding the minimum quality requirements. Whenever possible, processing steps were combined to avoid unnecessary duplication of tasks.

To ensure the highest level of homogeneity and compliance with the product specifications, a thorough internal independent validation procedure was developed at FUA level as part of the 2006 exercise and adapted for the 2012 and 2018 update and extension. A comparison between the internal validation procedure and independent validation exercises is made for selected representative FUAs. Results show that the internal validation procedure tend to provide lower accuracy than that of the independent validation exercise. Analysis suggest that a potential explanation could be related to the different sampling procedure.

Land use/cover evolution statistics for the 2006-2012 period are presented and compared with the same results from CLC suggesting that CLC tend to underestimate artificial areas by up to 7% in relative terms over the area covered by the Urban Atlas. Conclusions are drawn by presenting the status of the production to date and future prospects for the development of the product.

Urban planners have acknowledged the need for geo-spatial data for urban planning, however many developing countries are still lagging behind in the operational utility of Earth Observation (EO) for extraction of spatial data for their urban programmes. In this context the International Finance Institutes (IFIs) who support/fund urban planning have an important role in promoting the utilisation of these technologies for improved urban planning in developing countries. Since 2008, the European Space Agency (ESA) has collaborated with the IFIs to better understand and develop the role of EO in the development programmes. In 2016 a Consortium of European EO Service Providers initiated the ESA Earth Observation for Sustainable Development (EO4SD) Urban project to support IFIs Urban Development programmes with a suite of geo-spatial data. The project has an overall objective to introduce the advancements of EO technologies to the Banks in order to mainstream EO data into the work practices of Municipalities/City Planners in developing countries.

In Phase 1 of the project, 16 global Cities serving 3 MDBs were mapped and for each City, Baseline Land Use/Land Cover (LU/LC) data for two points in time (between 2015/2016 and 2005/2006) as well as some derived products such as Green Areas, Transport Networks, Informal Settlements, Population Density were provided to the Banks and their City counterparts. Some Special products, such as Building Heights, Terrain Motion and Flood Hazard/Risk were also provided. In total, approximately 204 products and 132 maps were delivered. The stakeholder engagement included the demarcation of Core and Peri-urban Areas of Interest (AoIs), the description of the EO-based products and their potential utility for urban analytical work, and a consultative process on relevant Land Use class nomenclature. The Core Urban areas were mapped using Very high Resolution (VHR) EO data whereas the Peri-urban areas were based on the use High Resolution data such as historic Landsat and current Sentinel data. Harmonized approaches for production were also implemented; for example the use of a harmonized LU nomenclature ensured a consistency on the class hierarchy and provided the potential for comparative studies between the Cities nationally or regionally. The overall accuracies achieved for the various products ranged from 85-95%. All methods and results were described in City Operations Report delivered to each City; the Reports included the accuracy assessment and the related Quality Control (QC) documentation.

The majority of Users were interested in the downstream applications of the geo-spatial products and examples of analytic work provided included assessment of urban growth over time, LU/LC change over time, and assessment of flood prone/flood risk areas. User feedback on the overall utility of the products has been very positive with the request for additional collaboration. Thus in Phase 2 there is a strong focus on stakeholder engagement via further enhancement of spatial analytic work as well as capacity building in order to further enhance user awareness and utility of the products.

With the launch by European Space Agency of the Sentinel-1 mission, which offers free access to satellite data, initiatives are emerging in order to propose ground motion measurement based on InSAR (SAR Interferometry) advanced technique known as the Persistent Scatterer Interferometry (or PSI) into the Copernicus service portfolio. It is in this framework that the development of a European ground motion service is proposed as a part of the Copernicus Land Service.

As a precursor of such a service, the French Space Agency CNES - Centre National d’Etudes Spatiales - launched a pilot project over the whole metropolitan French Territory. The company TRE ALTAMIRA was appointed to process 3-year ascending and descending Sentinel-1 data; the results show the motion of hundreds of millions of stable scatterers distributed over the considered area of 551 500 km². Overall, about 7600 Sentinel-1 images acquired from October 2014 to October 2017 were processed in order to generate information on ground motion over the whole French Territory. Only reflectors known as Persistent Scatterer (or PS) were considered in the pilot project, allowing a high density of measurement points to be achieved in urban areas.

In addition to those activities, TRE ALTAMIRA provides operational surveillance services for infrastructure operators and engineering companies using High Resolution imagery which is more adapted to analyses at infrastructure and building scale. Two case study will be presented, in Paris and Dax.

TRE ALTAMIRA was commissioned by the Société du Grand Paris to monitor the impact of the 200-km underground metro construction. As a first step, a retrospective study of the ground motion was carried out based on not only ERS and Envisat data archive but also high-resolution images available since 2011. As the first groundworks started in 2016, systematic satellite monitoring was initiated. The coverage of Paris metropolitan area is provided by the TerraSAR-X high-resolution satellite with an unrivalled measurement point density in an urban context (> 10,000 points/km²). Monthly InSAR measurement updates based on 11-day image acquisitions complement in-situ real time auscultation by remotely monitoring a larger area.

The city of Dax is emblematic case of a municipality concerned by risk management related to an active geological underground (salt diapir), abandoned mines and Adour River flood events. A pilot project was conducted in 2009 with CNES support using ENVISAT archive; promising results have resulted in the implementation of a 4-year high resolution surveillance.

On those two areas, a comparative analysis of medium and high resolution InSAR measurements will be performed; measurement points densities will be compared but also the perimeter of areas of motion that are detected as well as the intensity of the detected displacement.