Assessment of the current global DEMs and requirements for an updated global DEM

Transcription

1 Framework Service Contract EEA/IDM/15/026/LOT 2 for Services supporting the European Environment Agency s (EEA) implementation of cross-cutting activities for coordination of the in situ component of the Copernicus Programme Services Call for tenders No EEA/IDM/15/026 Lot 2 Spatial data themes Assessment of the current global DEMs and requirements for an updated global DEM Document Code: EG-RPT-EEA-SC (draft)

2 Table of Contents 1. Introduction Overview of global DEMs Commercial DEMs Free and open DEMs Comparison commercial vs open data Copernicus Services Requirements for global DEM CLMS Global Land Component Hotspot Monitoring CEMS Mapping component CSS Support to External Action Service CLMS Pan-European and Local Component

3 List of Tables Table 1- Reference 3D Product Specifications... 9 Table 2- SPOT DEM Precision Product Specifications... 9 Table 3-SPOT DEM Product Specifications Table 4 - WorldDEM Product Specifications Table 5-ALOS WORLD 3D Product Specifications Table 6- NextMap World 30 Product Specifications Table 7- NextMap World 10 Product Specifications Table 8-Vricon DSM-10 Product Specifications Table 9-Vricon DSM-0.5 Product Specifications Table 10-Euro-Maps 3D Product Specifications Table 11-PlanetDEM 30 Product Specifications Table 12- SRTM 1arc sec Product Specifications Table 13- ASTER GDEM V2 Product Specifications Table 14-ALOSW3D 30 Product Specifications Table 15-Comparison of different DEM options with regard to their specifications List of Figures Figure 1- Elevation 30 Coverage... 8 Figure 2-WorldDEM availability Figure 3-ALOS WORLD 3D Standard availability Figure 4-NextMap World 30 availability Figure 5-PlanetDEM Plus data availability Figure 6-SRTM coverage map Figure 7-ASTER Global DEM coverage Figure 8-ALOS WORLD 3D 30 availability Legal Notice: The contents of this report were compiled by e-geos and GAF AG under EEA contract 3436/R0- COPERNICUS/EEA implementing Framework Service Contract EEA/IDM/15/026/Lot 2. Neither the European Environment Agency nor any person or company acting on its behalf is responsible for the use that may be made of the information that is contained in this report. 3

4 [DOCUMENT RELEASE] Name(s) Prepared by: Sergio Proietti, Francesca Lorenzon Andreas Uttenthaler, GAF Alexander Klaus, Markus Probeck Contributions: David Herrmann GAF Affiliation e-geos; Review: Henrik Steen Andersen European Environment Agency Endorsement: Sergio Proietti e-geos Approval: Henrik Steen Andersen European Environment Agency Prepared for: Represented by: (Project Manager) Contract No. European Environment Agency (EEA) Henrik Steen Andersen 3436/R0-Copernicus/EEA Implementing Framework Service Contract No EEA/IDM/15/026/Lot 2 [Change Record] Version Date Changes Draft /04/2017 First issue Draft /05/2017 According to comments provided by EEA Project Manager Draft /05/2017 According to comments provided by EEA Project Manager [Applicable Documents] ID Document AD1 Framework Service Contract EEA/IDM/15/026/Lot 2 AD2 Specific Contract No. 3436/R0-COPERNICUS/EEA [Reference Documents] ID RD1 RD2 RD3 Document End User License Agreement for Reference 3D product of Airbus Defence & Space: Reference3D_eula-r3d-vuk-august2011_ pdf End User License Agreement for SPOT DEM Precision product of Airbus Defence & Space: SPOT_DEM_Precision_eula-r3d-vuk-august2011.pdf End User License Agreement for SPOT DEM product of Airbus Defence & Space: SPOT_DEM_eula-spot1-7-vuk-january_2015_ pdf 4

5 RD4 Product description of Reference 3D product: r469_9_reference3d_product_description_ pdf RD5 Product description of SPOT DEM Precision product: r468_9_spot_dem_precision_product_description.pdf RD6 Product description of SPOT DEM product: r467_9_spot_dem_product_description.pdf RD7 End User License Agreement for WorldDEM product of Airbus Defence & Space: worlddem_eula_single_use_final_ _ pdf RD8 Publication by JAXA (Japan Aerospace Exploration Agency): PRECISE GLOBAL DEM GENERATION BY ALOS PRISM: Validation_AW3D_isprsannals-II pdf RD9 Publication by JAXA (Japan Aerospace Exploration Agency): VALIDATION OF AW3D GLOBAL DSM GENERATED FROM ALOS PRISM: Validation_AW3D_isprsannals-III pdf RD10 End User License Agreement for IRS (Indian Remote Sensing Programme) based products of GAF AG: gf_enduser_license_en_v4.2_ pdf RD11 Product description of Euro-Maps 3D product Product_info_EuroMaps3D_Engl_v3.0_ pdf RD12 Base License description for PlanetDEM 30 by PlanetObserver: Base_License_model_PlanetObserver_ pdf RD13 Product description of USGS for different global DSM datasets: Intro to DEMs and SRTM Versions.pdf RD14 Publication by JPL (Jet Propulsion Laboratory), ASTER Global DEM Version 3, and new ASTER Water Body Dataset isprs-archives-xli-b pdf RD15 Report on EU-DEM Statistical Validation, prepared by DHI-GRAS, August 2014, 27 pp. RD16 Report EU-DEM Upgrade Documentation EEA User Manual, Issue 1.2, prepared by INDRA, 14 October 2015, 12 pp. RD17 EC Call for Tenders No ENTR/2009/27: Implementation of an Initial GMES Service for Geospatial Reference Data Access (Lot 1: Implementation of an initial GMES service for geospatial reference data access covering Europe; Lot 2: Implementation of an initial GMES service for geospatial reference data access covering areas outside Europe). Tender Specifications Document Corrigendum, published June 2009 RD18 Copernicus Space Component Data Access Portfolio: Data Warehouse Issue 2.1 of 1 August 2016 prepared by B. Hoersch & V. Amans, ESA, 84 p. RD19 Review of EU-DEM and EU-HYDRO Upgrade - Requirements and Options Issue: 1.0 prepared by GAF, 28/03/2017 5

6 1. INTRODUCTION Elevation data are crucial for a broad range of applications with different technical requirements and use cases in the various fields of earth observation. Within the EC, in the framework of the Copernicus Programme, there is a full awareness of the necessity to have reliable Elevation information for the most of the Copernicus Services. For this reason, GMES and then the Copernicus Programme, since 2009, put a lot of effort in assessing, defining requirements and finally creating a reliable and complete European Digital Elevation Model (EU-DEM) that has been recently released. Further to this, the EC raised awareness on the need of a Global DEM as most of the Copernicus Services provide products and services on global scale. The mandate and objective of this report is to offer a comprehensive, independent and objective analysis of the current availability of Global DEM both commercial and free and open and to provide a first list of requirements for those Copernicus Services that make an extensive use of Global DEMs. In detail, Chapter 2 provides an overview of the currently available DEMs with global coverage, both commercial and free and open. A synthetic comparison table of different DEM options with regard to their specifications is also proposed. Chapter 3 provides an overview of those Copernicus Services that for their provision of maps and products on global scale, rely on the availability of global DEM products. For each service, a list of DEMs related technical requirements is then presented. The information was collected directly from the Service Providers by means of consultations with the coordinators and the technical managers. Where possible and applicable, this report provides the link to the respective Reference Documents [RD1-RD19] as listed above, or provides a URL for obtaining further information. 6

7 2. OVERVIEW OF GLOBAL DEMS This chapter provides a detailed overview of the current availability and technical/other specifications of globally available Digital Elevation Models (DEMs) with a spatial resolution of 30m or better. It does neither aim to make an evaluation or ranking, nor suggest a selection. 1 There are two main categories, as addressed by this report: commercial DEMs (section 2.1) and freely available DEMs (section 2.2). The commercial DEMs also comprise DEMs which can or will be produced for larger areas worldwide, like VRICON or Euro-Maps 3D product. In these cases, the data situation is very good and DSMs can be derived for large regions / groups of countries. These DEMs are currently available only for some areas / regions worldwide. The third section of this chapter focuses on a comparison of the relative advantages and disadvantages of commercial vs. free and open DEMs according to a number of relevant criteria. In general, such assessment of global DEM options requires some assumptions on the requirements of the different end-users. The product specifications in the commercial and free & open DEMs chapter are grouped into the following categories: Horizontal resolution is always defined in metres, even though some of the DSMs / DTMs are delivered in geographic projection. The horizontal accuracy is the absolute horizontal accuracy and is normally stated as RMSE or CE90 by the data providers. The vertical resolution is directly linked to the graduation of the height values and respectively to the data type. If the DSMs are delivered as 16 bit signed integer data, the vertical resolution is 1m. If the data type is 32 bit float, the graduation of the height values is finer (dm or cm). The vertical accuracy is defined as the absolute vertical accuracy and is mostly stated as RMSE or LE90 by the data providers. The age of base data shows the time span of the data that was used for the DEM generation. For some products, this is easily identifiable on a global scale, because satellite missions are already finished (e.g. ALOS World 3D and WorldDEM). But for most products, it is difficult to give final numbers, because either satellite missions are still operational (e.g. Cartosat-1 which is used for Euro-Maps 3D generation or the DigitalGlobe VHR satellites that are used for the Vricon DSM generation) or the input data is a mix of different elevation models that consist themselves of different input data (e.g. PlanetDEM 30, NextMap DSMs). For some products, the acquisition dates of base data are part of the metadata files, and with this information the data age can be determined on a finer level (e.g. tiles). 1 Such would be beyond the scope of this report and would require to do a prioritisation of some user requirements over others, a definition of the product target specifications, knowledge of the envisaged budget and timeframe, as well as probably some practical tests of the selected product(s) s target requirements against high quality reference (in-situ) data. 7

8 The field update frequency shows if there are identically constructed satellite missions planned for an update DSM / DTM generation or if ongoing satellite missions could provide an update DSM / DTM over the same areas. Type of Digital Elevation Model (DEM) means either Digital Surface Model (DSM), which shows the first reflectance of the surface (incl. vegetation and buildings) or a Digital Terrain Model (DTM), which represents the surface of the bare earth. Coverage means how many sq.km of the earth are already covered by the DEM (either fully edited or raw). The license conditions of the DEMs are mostly described in EULAs (End User License Agreements) of the data providers the corresponding license documents are referenced in the tables. Prices are normally given as or USD per sq.km. or sometimes also as overall prices for continents or for the whole globe Commercial DEMs This section provides an overview of the relevant commercial DEMs currently being offered, together with standardised tables of their key technical specifications. Elevation30 is a Digital Surface Model product suite derived from SPOT 5 optical satellite data, developed in partnership by Airbus Defence and Space and the French Survey and Mapping Agency IGN. The DSM coverage can be seen in Figure 1 Figure 1- Elevation 30 Coverage (red: already available; pink: Suitable SPOT 5 HRS data available) 8

9 Three DSMs are part of the Elevation30 product suite. These are described in more detail below. The data are delivered in the DIMAP format or in DTED format as well as in geographic projection with WGS84 horizontal datum and EGM96 geoid. Reference3D The Reference 3D dataset contains the 30m resolution DSM, an ortho-image and different quality layers. Horizontal resolution 30m (20m also possible) Horizontal accuracy 10m CE90 Vertical resolution 1m Vertical accuracy 10m LE90 for flat or rolling terrain (slope <=20%) 2 Age of base data & update frequency (SPOT-5 general lifetime) / No update planned Type (DSM or DTM) DSM Coverage 80 Mio sq.km (status by end of 2014) License conditions Restricted use product; see details in RD1; On request, different licensing conditions may be possible. Price 7 per sq.km (Single User License) +35% for Multi User License (up to 30 users) Table 1- Reference 3D Product Specifications SPOT DEM Precision The SPOT DEM Precision product contains the 30m DSM and different quality layers (no ortho image included). Horizontal resolution 30m (20m also possible) Horizontal accuracy 15m CE90 Vertical resolution 1m Vertical accuracy 10m LE90 for flat or rolling terrain (slope <=20%) 2 Age of base data & update frequency (SPOT-5 general lifetime) / No update planned Type (DSM or DTM) DSM Coverage 80 Mio sq.km (Status End of 2014) License conditions Restricted use product; see RD2; On request, different licensing conditions may be possible Price 4.50 per sq.km (Single User License) +35% for Multi User License (up to 30 users) Table 2- SPOT DEM Precision Product Specifications 2 Vertical accuracies of DEMs are in general dependent on slope. In steeper terrain, the data provider cannot guarantee the same level of vertical accuracy as for flat or moderately undulated ( rolling ) terrain. 9

10 SPOT DEM This product only contains the 30m resolution DSM, and no ortho-image or quality layers. Horizontal resolution 30m (20m also possible) Horizontal accuracy 10 m CE90 Vertical resolution 1m Vertical accuracy 10m LE90 for flat or rolling terrain (slope <=20%) 2 Age of base data & update frequency (SPOT-5 general lifetime) / No update planned Type (DSM or DTM) DSM Coverage 80 Mio sq.km (Status End of 2014) License conditions Restricted use product; see RD3; On request, different licensing conditions may be possible. Price 2.30 per sq.km (Single User License) +35% for Multi User License (up to 30 users) Table 3-SPOT DEM Product Specifications In non-reference3d areas, the vertical accuracy is <20m LE90 and the horizontal accuracy is < 30m CE90. Further technical information about the Elevation30 product suite is available on the Airbus Defence & Space website 3 as well as in RD4, RD5 and RD

11 WorldDEM WorldDEM is a DSM realised as a public-private partnership between Airbus Defense & Space and the German Aerospace Center (DLR). The product is based on data from the TanDEM-X Mission (TerraSAR-X add-on for Digital Elevation Measurements). WorldDEM is already available as unedited DEM for the whole world and edited for major parts of Africa and Southeast Asia (seefigure 2). The data are delivered in geographic projection with WGS84 horizontal datum and EGM2008 geoid. The bit depth is 32 bit floating and the file format is GeoTIFF. Horizontal resolution 12m Horizontal accuracy < 10m CE90 Vertical resolution 1 dm Vertical accuracy < 4m LE90 (10m LE90 for DTM) Age of base data & update frequency / update mission planned >2020 Type (DSM or DTM) DSM (DTM possible) Coverage Global (see also Figure 2) License conditions Property of Airbus; Subject to the German Satellite Data Security Act; free use and distribution of derivative works: see RD7. On request, different licensing conditions may be possible. Price 10 per sq.km (Single User License) DSM 16 per sq.km (Single User License) DTM Prices for Multi User License have to be requested according to Airbus DS Table 4 - WorldDEM Product Specifications Figure 2-WorldDEM availability (Status: 31st March 2017; dark green available off-the-shelf; light green: to be edited) 4 Further product information is available on the Airbus DS website 5 and on the DLR homepage

12 ALOS WORLD 3D Standard This product was generated by using data from the triple stereo ALOS Prism sensor, which was operational between 2006 and The 5m commercial DSM dataset is the basis for the freely available 30m dataset (as described in section 2.2). Even though the DSM is available globally, some void areas remain because of clouds and difficult surface structure (e.g. deserts) over various regions. In these areas, the DSM is filled with SRTM or other available DEM sources. A coverage overview is given in Figure 3 below. Further information on the dataset can be found on the ALOS World 3D website 7 and in RD8 and RD9. Horizontal resolution 5m Horizontal accuracy 5m RMSE Vertical resolution 1m Vertical accuracy 5m RMSE Age of base data & update frequency / maybe ALOS-3 satellite can be used for update (>2019) Type (DSM or DTM) DSM (DTM possible) Coverage Global (see alsofigure 3) License conditions No license information was provided. Price 4 per sq.km (Single User License) DSM ~12.8 per sq.km (Single User License) DTM Table 5-ALOS WORLD 3D Product Specifications Figure 3-ALOS WORLD 3D Standard availability

13 NextMap World 30 This DSM is based on Aster GDEM, SRTM, GTOPO30 and other elevation data, and most artefacts have been removed, according to the data provider Intermap. There is a global availability of this dataset as presented in Figure 4 below, which also shows the main input data distribution. The DSM is delivered in geographic projection with WGS84 horizontal datum and EGM96 geoid. The data format is 32 bit floating point elevations and the data is delivered as 1 x1 tiles. Ocean values are set to 0 and water bodies are flattened. Horizontal resolution 30m Horizontal accuracy Not specified Vertical resolution 1 dm Vertical accuracy 10m LE95 Age of base data & update frequency Aster GDEM, SRTM, GTOPO30 and various other input data / no updates Type (DSM or DTM) DSM Coverage Global (see alsofigure 4) License conditions Restricted use product 9 ; On request, different licensing conditions may be possible. Price ~ per sq.km (Single User License) Table 6- NextMap World 30 Product Specifications Figure 4-NextMap World 30 availability 10 More information is available on the NextMap 30 website

14 NextMap World 10 This 10m dataset was sub-sampled by Intermap from the 30m product by using a patent-pending Terrain Filter and Frequency Fusion technology. Product coverage is the same as for NextMap World 30 (see Figure 4 above). The spatial resolution is 10m and the absolute vertical accuracy of the DSM is 10m LE95. The DSM is delivered in geographic projection with WGS84 horizontal datum and EGM96 geoid. The data format is 32 bit floating point elevations and the data is delivered as 1 x1 tiles. Ocean values are set to 0 and water bodies are flattened. Horizontal resolution 10m Horizontal accuracy Not specified Vertical resolution 1 dm Vertical accuracy 10m LE95 Age of base data & update frequency Various input data / no updates Type (DSM or DTM) DSM (DTM possible) Coverage Global (see alsofigure 4) License conditions Restricted use product 12 ; On request, different licensing conditions may be possible. Price No standard price for areas larger than 25,000 sq.km - Prices have to be individually requested. Table 7- NextMap World 10 Product Specifications More information is available on the NextMap 10 website

15 The Vricon product suite comprises DSMs with 10m and 0.5m horizontal resolution: Vricon DSM-10 This 10m resolution Digital Surface Model (DSM) has been produced from commercial optical satellite imagery of DigitalGlobe s archive of high-resolution satellite imagery. Because of the very good satellite archive image situation, this product can be generated worldwide according to the data provider. The file format is GeoTiff and it is a 32 bit floating dataset. The aim of this dataset is a global coverage, however no coverage maps seem to be made openly available. Some further product information is available on the VRICON website 14. Horizontal resolution Horizontal accuracy Vertical resolution Vertical accuracy Age of base data & update frequency Type (DSM or DTM) Coverage License conditions Price Table 8-Vricon DSM-10 Product Specifications 10m 3m CE90 1 dm 3m LE90 Multi archive data (no a-priori statement possible) / updates are possible when suitable VHR stereo data are available DSM The aim is global (no coverage maps made available) Enterprise license: unlimited users, perpetual, internal operations according to Vricon EULA terms 15 ; On request, different licensing conditions may be possible. USD 1.99 per sq.km

16 Vricon DSM-0.5 The Vricon DSM 0.5 product is a 0.5m resolution Digital Surface Model (DSM) derived from commercial optical satellite imagery of DigitalGlobe s archive of high-resolution satellite imagery. Horizontal resolution 0.5m Horizontal accuracy 3m CE90 Vertical resolution 1 dm Vertical accuracy 3m LE90 Age of base data & update frequency Multi archive data (no a-priori statement possible) / updates are possible when suitable VHR stereo data are available Type (DSM or DTM) DSM and DTM Coverage The aim is global (no coverage maps made available) License conditions Enterprise license: unlimited users, perpetual, internal operations according to Vricon EULA terms 16 ; On request, different licensing conditions may be possible. Price USD 25 per sq.km (up to 200,000 sq.km) DSM USD 35 per sq.km (up to 200,000 sq.km) DTM for larger areas pricing on request Table 9-Vricon DSM-0.5 Product Specifications Further product information is available on the VRICON website

17 Euro-Maps 3D This 5m resolution Digital Surface Model (DSM) is generated from Indian optical Cartosat-1 stereo satellite data. The file format is GeoTIFF and the bit depth of the DSM is 16 bit signed integer. The DSM can be delivered either in UTM or in geographic projection with WGS84 horizontal datum and EGM96 geoid. A corresponding ortho-image layer of IRS P5 can be provided together with the DSM. There are currently more than two Mio sq.km fully edited available worldwide. This full editing level comprises removal of various kinds of DEM artefacts, water body masking as well as ensuring the consistent stream flow of rivers. Approximately 2.5 Mio sq.km are additionally processed as a standard (unedited) DSM. For Europe and some other regions worldwide, the Euro-Maps 3D DSM can be generated area-wide, on request. A global product is up to now not possible due of insufficient data situation in some regions, mainly caused by clouds. Horizontal resolution Horizontal accuracy Vertical resolution Vertical accuracy Age of base data & update frequency Type (DSM or DTM) Coverage License conditions Price Table 10-Euro-Maps 3D Product Specifications 5 m <10m CE90 1m <10m LE90 depending on the slope of the area (<20% ~ 5m; 20-40% ~ 7m; >40% ~10m) (ongoing) / Indian update missions planned DSM (DTM possible on request) > 2 Mio sq.km fully edited; additional 2.5 Mio. sq.km standard DSM Restricted Use Product, please see RD10; On request, different licensing conditions are possible. 4 per sq.km only DSM or 4.50 per sq.km DSM + ortho layer (IRS P5) More information is available on the GAF website and in RD

18 PlanetDEM 30 PlanetObserver is offering worldwide edited DSMs with 90m and 30m horizontal resolution based on a combination of SRTM 1 or 3 Arc-Second, ASTER GDEM v2, NSIDC (US National Snow and Ice Data Center), AGDC (Alaska Gasline Development Corp.), CDED (Canadian Digital Elevation Data) and cartographic sources. For the current assessment, the PlanetDEM 30 plus DSM product (see Figure 5) is relevant. It is mainly based on SRTM 1 Arc-Second data. This version is entirely corrected for artefacts and completed with many other high quality source data, according to the data provider. Horizontal resolution Horizontal accuracy Vertical resolution Vertical accuracy Age of base data & update frequency Type (DSM or DTM) Coverage License conditions Price Table 11-PlanetDEM 30 Product Specifications 30m <10m CE90 1m <10m LE90 Various input data / no updates DSM global Restricted Use Product; please see RD12 for base license conditions; On request, different licensing conditions may be possible. 25,000 (base license) 50,000 (enterprise license) Figure 5-PlanetDEM Plus data availability 20 Further information on the PlanetDEM product is available on the PlanetObserver website

19 Summary All the above listed commercial products have in common that they have been automatically and / or manually refined after processing, in order to remove different kinds of artefacts (e.g. spikes, wells, mole runs). In most cases, also water bodies are edited in terms of consistent height values for ocean (0) and lakes and in terms of guaranteeing the consistent flow of rivers. Some data providers offer ortho image layers together with their DEMs. Some data sources are available globally as off-the-shelf products, whereas others are currently available only for parts of the globe and are being produced as customized products on request. Some data providers like Airbus Defence & Space for WorldDEM or NTT DATA and RESTEC for ALOS WORLD 3D 5m are also offering Digital Terrain Models as standard products. These DTMs could be more suitable for e.g. ortho-rectification of VHR datasets. However, the related prices are significantly higher. 19

20 2.2. Free and open DEMs This section provides an overview of the relevant freely available DEMs, together with standardised tables of their key technical specifications. SRTM 1arc sec (30m) This DSM is based on NASA s Shuttle Radar Topography Mission from the year 2000, flown on the Space Shuttle. The 1 arc second product version with horizontal 30 m resolution was made freely available by the United States in late The dataset is available for all land areas between 60 N and 56 S (see Figure 6). The vertical accuracy is on average better than 10 m LE90 and the horizontal accuracy is better than 20m CE90. The most recent version released by NASA is a void-filled version known as "SRTM Plus" or SRTM NASA Version More information is available on the NASA website 23. The data can be obtained through the USGS Earth Explorer 24. Figure 6-SRTM coverage map 25 Horizontal resolution Horizontal accuracy Vertical resolution Vertical accuracy 30m 7-12m CE90 1m 6-9m LE

21 Age of base data & update frequency 2000 / no update Type (DSM or DTM) DSM Coverage Between 60 N and 56 S License conditions No restrictions on the use of data received from USGS EROS Center 26 Price Freely available Table 12- SRTM 1arc sec Product Specifications Aster GDEM v2 This global product was provided by NASA and METI/Japan Space Systems on October 17, 2011 (see Figure 7) and was generated by stereo correlation of optical ASTER images collected by the ASTER instrument on-board the Terra satellite from different periods. The currently available version 2 shows significant improvements in terms of minimisation of voids and artefacts and flattening of water bodies. Nevertheless, many artefacts and anomalies are still present in the dataset. Compared to SRTM, the Aster GDEM includes also tiles with small islands. An updated version 3 with additional DEMs for each tile and additional water body mask is planned (see RD13 and RD14). More information can be found on the NASA website 27. The data can be obtained through the USGS Earth Explorer 28, ECHO Reverb 29 or LP DAAC Global Data Explorer 30. Figure 7-ASTER Global DEM coverage

22 Horizontal resolution 30m Horizontal accuracy 15-20m CE90 Vertical resolution 1m Vertical accuracy 15-20m LE90 Age of base data & update frequency (updated version 3 is planned) Type (DSM or DTM) DSM Coverage Between 83 N and 83 S License conditions When presenting/publishing ASTER GDEM v2 data, users shall include a citation "ASTER GDEM is a product of NASA and METI." Price Freely available Table 13- ASTER GDEM V2 Product Specifications ALOS WORLD 3D 30 The ALOS World 3D 30 m DSM was released by the Japan Aerospace Exploration Agency (JAXA) and was generated by using ALOS Prism Triple-Stereo satellite data from the years The commercial 5m product described in chapter 2.1 has been resampled to 30m in order to provide a 30m free product. The accuracy of this dataset is 5m vertical RMSE. In March 2017, a completely void-filled version between 60 N and 56 S (see Figure 8) has been made available. No particular statement regarding the DEM data sources used for void filling is given in the related documentation. Each dataset is delivered as average and median resampled mesh version from the original 5m dataset and with additional information layers such as a mask layer with information about e.g. clouds, snow, ice and sea. Figure 8-ALOS WORLD 3D 30 availability 32 The technical description of the DSM is available on the ALOS World 30 website 33 The data are available after registration there

23 Horizontal resolution 30m Horizontal accuracy 7m CE90 Vertical resolution 1m Vertical accuracy 7m LE90 Age of base data & update frequency / maybe ALOS-3 satellite can be used for update (>2019) Type (DSM or DTM) DSM Coverage Between 82N and 82 S License conditions When the user provides or publishes the products and services to a third party using this dataset, it is necessary to display that the Price Table 14-ALOSW3D 30 Product Specifications original data is provided by JAXA: JAXA 35 Freely available Summary Basically, three global free DEM data sources are currently available each with different strengths and drawbacks, as described above. All above specifications of these freely available DEMs have been collected from the data providers product documentations and websites Comparison commercial vs open data The obvious relative advantages of commercial DEMs (as compared to free and open DEMs) are that they are fully quality controlled, typical artefacts have been edited and largely removed, and they typically have a higher spatial resolution and better accuracies. On the other hand, the major relative disadvantages of commercial DEMs are the licensing costs and license conditions that do not always meet the requirements of the end-users (e.g. multiple use, derived products, etc.). Standard license conditions typically do not reflect a wide use case / user group, but sometimes indicate that individual customised license conditions could be offered upon request. The following Relative scale: from ++ (very advantageous) to (very unfavourable) * = As a standard, data providers offer specific license models for a defined limited number of users. Individual license models seem however mostly possible and would have to be individually requested from the data providers. Uplift payments for multiple users are to be expected. Table 15 provides an assessment of the relative advantages and disadvantages of all previously presented commercial and free & open DEMs. It aims to relatively assess the most relevant

24 technical and quality specifications, with a relative qualitative scale from ++ (very advantageous) to - - (very unfavourable). Additionally to the categories presented in the sections above, the Relative scale: from ++ (very advantageous) to (very unfavourable) * = As a standard, data providers offer specific license models for a defined limited number of users. Individual license models seem however mostly possible and would have to be individually requested from the data providers. Uplift payments for multiple users are to be expected. Table 15 adds Surface representation as an additional criterion, meaning the level of correctly captured surface detail of the data. Sometimes up- or down sampling steps lead to a seemingly better or worse spatial resolution than what the dataset is able to realistically offer. It should be highlighted that this assessment does neither aim to make a ranking, nor suggest a selection of one or more DEMs, which would have to be specific to a certain use case/scenario. It rather aims to provide a factual basis for further such decisions. DEMs commercial Spatial Resolution (m) Vertical Accuracy (m) Horizontal Accuracy (m) Price License Condition Global Coverage Base Data age Artefact Editing * Surface representation Reference 3D SPOT DEM * Precision SPOT DEM * WorldDEM * ALOS 5 5 (RMSE) 5 - * World 3D (RMSE) 5m NextMap * (LE95) NextMap ? * (LE95) VRICON * VRICON 0.5 0, * Euro-Maps * D PlanetDEM * DEMs freely available SRTM 1arcsec (30m) Aster GDEM ALOS WORLD 3D Spatial Resolution (m) Vertical Accuracy (m) Horizontal Accuracy (m) Price License Condition Global Coverage Base Data age Artefact Editing Surface representation

25 30m Relative scale: from ++ (very advantageous) to (very unfavourable) * = As a standard, data providers offer specific license models for a defined limited number of users. Individual license models seem however mostly possible and would have to be individually requested from the data providers. Uplift payments for multiple users are to be expected. Table 15-Comparison of different DEM options with regard to their specifications 25

26 3. COPERNICUS SERVICES REQUIREMENTS FOR GLOBAL DEM The main goal of this section is to depict an overview on those Copernicus Services that make an extensive use of Global DEMs and to provide a first high level list of Global DEM related technical requirements. The Copernicus Services taken into consideration in the following sections are: 1. Copernicus Land Monitoring Service (CLMS) - Global Land, in particular the Hot Spot Mapping Service 2. Copernicus Emergency Management Service (CEMS), specifically the Mapping component 3. Copernicus Security Service (CSS), especially the Support to External Action Service 4. Copernicus Land Monitoring Service (CLMS) - Local and Pan-European Service Each of the first three sections section contain a short description of the Service, a list of tasks (performed by the Service) that need a DEM to be carried out and finally a list of Global DEM related technical requirements. For the time being, within the three above mentioned Copernicus Services, the Global DEMs normally used are the 1 arcsec resolution SRTM and the ASTER DEM. Both of them show serious problems that are clearly known and well documented also in the previous section 2.3. In brief, the 1 arcsec resolution SRTM suffer from the lack of information above 50 north and below 50 south latitude while the ASTER DEM, recently released, contains anomalies and artifacts that will impede effectiveness for use in certain applications as stated by NASA itself. The use and the related fitness for purpose of the ALOS WORLD 3D 30 is ongoing as the dataset has been only recently released (March 2017). The fourth section, related to the CLMS Local and Pan-European Service reporting the requirements for an updated EU-DEM has been extracted from the section 5 of the Review of EU-DEM and EU-HYDRO Upgrade Requirements and Options report [RD-19] and has been here reported for the sake of completeness. 26

27 3.1. CLMS Global Land Component Hotspot Monitoring The Hot Spot Mapping Service (HSM) is one of the activity performed within the Global Land component of the Copernicus Programme. The main objective of this activity is to provide detailed land information on specific areas of interest for the European Union (EU) outside of EU territory. The service will answer to adhoc requests and focus mainly within the domain of the sustainable management of natural resources. The DEM is necessary for the ortho-rectification and geo-referencing process of images used to perform the land classification. DEMs are used within HSM mainly for the following tasks: 1. orthorectification of optical images 2. geocoding of SAR images. Orthorectification of optical images and geocoding of SAR images are both necessary to get geometrically corrected images removing optical distortions derived from the sensor system itself. The service is mainly based on the classification of HR images and to perform the above mentioned tasks uses SRTM and ASTER DEMs that, in terms of resolution and accuracy, are compliant with the Service requirements. The gap is more related to the coverage as a DEM with an actual global coverage is still missing. REQUIREMENTS: Horizontal resolution: 30m at least Horizontal accuracy: 10m Vertical resolution: 1m Vertical accuracy: 7m Homogeneity: mandatory Maintenance: NA Type (DTM/DSM): DSM Coverage: global Data policy: open 27

28 3.2. CEMS Mapping component The Mapping component of the Copernicus Emergency Management Service (CEMS) can be split in two different activities: Rapid Mapping and Risk & Recovery. Rapid Mapping provides all actors involved in the management of natural disasters, man-made emergency situations and humanitarian crises, with timely and accurate geospatial information derived from satellite remote sensing and completed by available in situ or open data sources. The information generated by the service can be used as supplied (e.g. as digital or printed map outputs) and it may support geospatial analysis and decision making processes of emergency managers. The DEM is used as the primary source of map physiography and elevation information and for the ortho-rectification and geo-referencing process of image data sets acquired, processed and classified in the frame of emergency activations. Additionally, the relevant elevation information can be used for deriving contour lines or spot heights. This information is provided to the authorised users of the emergency service activations as vector data or integrated into digital raster maps. Summing up, the main tasks requiring a DEM are: 1. Orthorectification of optical images 2. Geocoding of SAR images 3. Contour lines and spot heights extraction 4. Terrain slope mask for the flood extraction refinement The CEMS provides maps mainly based on VHR images so for orthorectification of optical images and geocoding of SAR images, it would be of utmost importance to have a more accurate Global DEM. Currently the DEMs used, SRTM and ASTER DEM, have an insufficient accuracy and a non-global spacial coverage as already mentioned. Contour lines, joining points of equal elevation, and spot heights are derived by the DEM. It s clear that the accuracy of the contour lines is directly linked to the vertical and horizontal accuracy of the DEM. The slope mask layer shows the steepness or the degree of incline of a surface and is quite useful in performing a flooding map as it allows to get an highly reliable flood extension avoiding false positive REQUIREMENTS: Horizontal resolution: 10m at least Horizontal accuracy: 5m Vertical resolution: 1m Vertical accuracy: 5m Homogeneity: mandatory Maintenance: NA Type (DTM/DSM): DSM Coverage: global Data policy: open 28

29 Risk & Recovery produces geo-information to support decision for prevention, preparedness, disaster risk reduction or recovery phases of a crisis, including reconstruction planning and progress monitoring. Further to the tasks carried out within the Rapid Mapping (performed also within the Risk and Recovery framework), there are other activities that required a more accurate DEM. In detail: 1. Flood /landslide hazard assessment 2. Flood /landslide modelling Flood /landslide hazard assessment and modelling products aim to identify those areas which could be affected by a damaging flood/landslide and assessing the probability of the flood/landslide occurring. To perform these tasks, among other such as past landslide/flood history and bedrock, a numbers of layers, derived from a DEM are required. The main ones are: topography, river network, slope steepness and slope orientation. To be able to provide a reliable and accurate product, a DEM with high horizontal and vertical accuracy is required. REQUIREMENTS: Horizontal resolution: 1m Horizontal accuracy: 3m Vertical resolution: 0,1m Vertical accuracy: 1m Homogeneity: mandatory Maintenance: NA Type (DTM/DSM): DTM Coverage: global Data policy: open 29

30 3.3. CSS Support to External Action Service The Support to European Union External Action SEA is the last Service, in chronological order, being implemented by the European Commission within the Copernicus Programme. SEA Service supplies information and intelligence data to support the operations of the European External Action Service (EEAS), including mapping and geo-information products ready for use in crisis situations. Among the Copernicus services mentioned in this report, the SEA Service is the one that make the widest use of the DEM to extract various information, indeed DEMs are used by the SEA Service for a number of tasks: 1. Orthorectification of optical images 2. Geocoding of SAR images 3. Contour lines extraction 4. River network 5. Slope analysis 6. Aspect analysis 7. Visibility analysis 8. Optimal off-road route 9. Support to identification of Potential Landing Helicopter Area The SEA Service provides maps built on VHR images so, for orthorectification of optical images and geocoding of SAR images an actual global DEM with a world-wide coverage and an improved general accuracy would be greatly beneficial. As for the remaining tasks (above listed from 3 to 9), an improved global DEM would be of utmost importance as it would allow to generate more reliable, accurate and complete information layers that are, for their nature, highly dependent by the DEM accuracy. Indeed, the Slope analysis shows the steepness or the degree of incline of a surface and for a particular location is computed as the maximum rate of change of elevation between that location and its surroundings. Aspect analysis points out the orientation of slope, measured clockwise in degrees from 0 to 360, where 0 is north-facing, 90 is east-facing, 180 is south-facing, and 270 is west-facing. Visibility analysis is of help in determining the visibility on a surface from point to point along a given line of sight or across the entire surface in a viewshed. REQUIREMENTS: Horizontal resolution: 1m Horizontal accuracy: 3m Vertical resolution: 0,1m Vertical accuracy: 1m Homogeneity: mandatory Maintenance: NA Type (DTM/DSM): DSM Coverage: global Data policy: open 30

31 3.4. CLMS Pan-European and Local Component Additional to the requirements of the Global component of the Copernicus Land Monitoring Service (CLMS) as described above, also the pan-european and the Local components have dedicated requirements towards a Digital Elevation Model with adequate accuracy. As per the scope of these components, the requirements point predominantly towards a European DEM. So far, the services are using the EU-DEM as made available by the European Environment Agency (EEA), but clear improvement potentials and needs have been identified by previous analyses (e.g. RD15) and voiced by the services themselves. In that sense, a global-level Copernicus DEM with improved specifications and a timely availability could serve this need for an improved DEM. To underpin the respective requirements, this section provides an extensive inventory of the actual current use and expected future use of a European DEM. In the CLMS s continental component, first use of a pan-european DEM (specifically the EU-DEM) was made in the GMES Initial Operations (GIO) phase by the various industrial consortia producing the five High-Resolution Layers (HRLs) of land cover/land use (LC/LU) characteristics (Imperviousness, Forest, Grassland, Wetlands and Water) for the reference year , under contract of the EEA. The use of the EU-DEM has significantly increased for the currently ongoing production of four of the five updated and extended High-Resolution Layers for the reference year 2015 (Imperviousness, Forest, Grassland and Water/Wetness) 37. This current HRL update is being implemented since 2016 by an industrial consortium of earth observation service providers, addressing all five HRLs in a more consistent and synergistic manner. Specifically, a common preprocessing chain of HR optical satellite imagery (from the ESA Data Warehouse; Sentinel-2; Landsat) is applied, in order to enable geometrically and radiometrically consistent time series analyses. The approach makes use of the EU-DEM for image geometry validation and geometric correction where needed, as well as for consistent topographic normalisation of terraindependent illumination effects in the imagery. For this task, a mixed approach has been implemented, much like suggested e.g. by [RD16]. Imagery of the Scandinavian countries plus Iceland, as well as of the Azores and the Canary Islands are pre-processed with (aggregated) freely available national DEMs of higher initial quality. The pan-european EU-DEM s quality in these regions is recognised to not meet the respective operational services requirements, specifically in terms of surface representation, horizontal and vertical accuracy. Additionally, the HR Water/Wetness Layer 2015 uses the EU-DEM operationally for calculation of intermediate wetness indices. In the CLMS s local component, it has primarily been the GIO-phase Riparian Zones 38 initiative ( ) making extensive use of both, the EU-DEM and the associated EU-HYDRO products. Specifically the delineation of Riparian Zones by means of a GIS-based modelling approach made use of the EU-HYDRO dataset s delineation and characterisation of European river courses and surface water bodies for identifying and localising the relevant riparian zone areas and associated lakes of all large and medium-sized European river systems and their floodplains. Complementary, the EU-DEM was used for calculating topography-dependent wetness indices and for terraindependent modelling of the spatial extent of the potential, observable and actual Riparian Zone. 39 The EU-DEM has further been used as ancillary dataset supporting the discrimination of specific LC/LU classes by means of topographic criteria in the mapping of 556,658 km² of Riparian land cover/land use (LC/LU) from very-high resolution (VHR) satellite imagery, within the spatial extent 36 More information at the Copernicus Land portal: 37 The fifth HR Layer 2015 on Small Woody Features uses VHR imagery as basis for classification and is therefore out of scope 38 More information at the Copernicus Land portal: 39 Available via the Copernicus Land portal: 31

32 of the Riparian Zones for the reference year Since the Riparian Zones LC/LU product discriminates 79 different LC/LU classes, the use of such ancillary data and information is indispensable. Since early 2017, the Riparian-Zones LC/LU product is spatially being extended also to riparian zones of small-sized European rivers for the reference year 2012, and will be consistently updated in the near future for the reference year A high-quality DEM will remain an important input to this monitoring activity. Similar to the Riparian Zones LC/LU product, also the local component s GIO Natura2000 product 41 provides a VHR LC/LU delineation for selected European biodiversity hotspots of the reference years 2006 and More than 160,000 km² of (buffered) Natura2000 areas were mapped as part of the Copernicus/GMES Initial Operations Phase until Established under the 1992 Habitats Directive, the Natura2000 sites constitute an EU-wide network of nature protection areas, aiming to ensure the long-term survival of Europe's most valuable and threatened species and habitats. Also for this service, topographic criteria were applied to the EU- DEM for discriminating the occurrence of specific, ecologically important LC/LU classes (such as alpine grassland). Since early 2017, the investigation of the status and development of these important protected areas is significantly spatially extended, aiming to reach more than 630,000 km² of overall mapped area by 2018/19. Beyond the regular service maintenance and evolution efforts undertaken by the EEA as Entrusted European Entity (EEE) in charge of the continental and local component of the LMCS, there are also several accompanying research and development activities ongoing, aiming to investigate, develop, prototypically test and suggest candidate products and services for the next generation of the Copernicus Land Monitoring Service, such as the EU-funded Horizon2020 research projects ECoLaSS (Evolution of COpernicus LAnd Services based on Sentinel data) 42, SENSAGRI (SENtinels Synergy for AGRIculture) 43 or MULTIPLY (MULTIscale Sentinel land surface information retrieval PLatform). 44 For example, ECoLaSS is amongst others investigating the main users and stakeholders requirements in terms of new and improved future Copernicus Land services, specifically of the continental and the global component. First assessments indicate that future land monitoring approaches from pan-european to global scale will increasingly move away from largely monotemporal classification approaches to time series and multi-sensor analyses, integrating optical and SAR data where possible. In this context, the project focuses on developing improvements of existing products towards higher update frequencies, such as incremental updates of HRLs. Additionally, there are potential new thematic products on snow/ice cover, arable land and phenology currently discussed among stakeholders for possible implementation as part of the Copernicus Land Monitoring Service portfolio in the coming years. All these products have in common that they will require dedicated long time series analyses. Furthermore, new services are expected to use a more stringent and improved calibration of density and density change products (such as Imperviousness Density, Tree Cover Density), moving from classification to further characterisation. SENSAGRI aims to exploit the synergy of optical and radar measurements of Sentinel-1 and Sentinel-2 to develop an innovative portfolio of prototype agricultural monitoring services, such as more robust, accurate, frequently updated and comprehensive crop maps. 40 Available via the Copernicus Land portal: 41 More information on the Natura2000 product at the Copernicus Land portal: 42 More details on the ECoLaSS project are available at: 43 SENSAGRI project website: 44 MULTIPLY project website: 32