EEA/IDM/15/026/LOT2 Overview of Global DEM Doc. ID: EG-RPT-EEA-SC1-0023 Issue: 0.3 Date: 23/05/2017 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 Overview of Global DEM Assessment of the current global DEMs and requirements for an updated global DEM Document Code: EG-RPT-EEA-SC1-0023 Issue: 0.3 (draft) Date: 23/05/2017
Table 1- Reference 3D Product Specifications................................................................................................... 9 Table 2- SPOT DEM Precision Product Specifications ........................................................................................ 9 Table 3-SPOT DEM Product Specifications ...................................................................................................... 10 Table 4 - WorldDEM Product Specifications .................................................................................................... 11 Table 5-ALOS WORLD 3D Product Specifications ............................................................................................ 12 Table 6- NextMap World 30 Product Specifications ....................................................................................... 13 Table 7- NextMap World 10 Product Specifications ....................................................................................... 14 Table 8-Vricon DSM-10 Product Specifications ............................................................................................... 15 Table 9-Vricon DSM-0.5 Product Specifications .............................................................................................. 16 Table 10-Euro-Maps 3D Product Specifications .............................................................................................. 17 Table 11-PlanetDEM 30 Product Specifications .............................................................................................. 18 Table 12- SRTM 1arc sec Product Specifications ............................................................................................. 21 Table 13- ASTER GDEM V2 Product Specifications .......................................................................................... 22 Table 14-ALOSW3D 30 Product Specifications ................................................................................................ 23 Table 15-Comparison of different DEM options with regard to their specifications ...................................... 24
List of Figures
Figure 1- Elevation 30 Coverage ........................................................................................................................ 8 Figure 2-WorldDEM availability ....................................................................................................................... 11 Figure 3-ALOS WORLD 3D Standard availability .............................................................................................. 12 Figure 4-NextMap World 30 availability .......................................................................................................... 13 Figure 5-PlanetDEM Plus data availability ....................................................................................................... 18 Figure 6-SRTM coverage map .......................................................................................................................... 20 Figure 7-ASTER Global DEM coverage ............................................................................................................. 21 Figure 8-ALOS WORLD 3D 30 availability ........................................................................................................ 22 Legal Notice:
The contents of this report were compiled by e-GEOS and GAF AG under EEA contract 3436/R0-COPERNICUS/EEA.565659 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.
RD4 Product description of Reference 3D product: r469_9_reference3d_product_description_201105.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_14052014_20140826.pdf
RD8 Publication by JAXA (Japan Aerospace Exploration Agency): PRECISE GLOBAL DEM GENERATION BY ALOS PRISM: Validation_AW3D_isprsannals-II-4-71-2014.pdf
RD9 Publication by JAXA (Japan Aerospace Exploration Agency): VALIDATION OF ‘AW3D’ GLOBAL DSM GENERATED FROM ALOS PRISM: Validation_AW3D_isprs-annals-III-4-25-2016.pdf
RD10 End User License Agreement for IRS (Indian Remote Sensing Programme) based products of GAF AG: gf_enduser_license_EN_v4.2_20140528.pdf
RD11 Product description of Euro-Maps 3D product Product_info_EuroMaps3D_Engl_v3.0_20140611.pdf
RD12 Base License description for PlanetDEM 30 by PlanetObserver: Base_License_model_PlanetObserver_290914.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-B4-107-2016.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 2014 – 2020. 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
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.
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.
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.
2.1. 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
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 2002-2015 (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 2002-2015 (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.
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 2002-2015 (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 RD6.
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 2010-2014 / 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 website5 and on the DLR homepage6.
This product was generated by using data from the triple stereo ALOS Prism sensor, which was operational between 2006 and 2011. 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 website7 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 2006-2011 / 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
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 product9; On request, different licensing conditions may be possible.
Price ~ € 0.006 per sq.km (Single User License) Table 6- NextMap World 30 Product Specifications
Figure 4-NextMap World 30 availability10
More information is available on the NextMap 30 website11.
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 product12; 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 website13.
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 website14.
Horizontal resolution 10m
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
Coverage The aim is global (no coverage maps made available)
License conditions Enterprise license: unlimited users, perpetual, internal operations according to Vricon EULA terms 15; On request, different licensing conditions may be possible.
Price USD 1.99 per sq.km Table 8-Vricon DSM-10 Product Specifications
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 website17.
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 5 m
Horizontal accuracy <10m CE90
Vertical resolution 1m
Vertical accuracy <10m LE90 depending on the slope of the area (<20% ~ 5m; 20-40% ~ 7m; >40% ~10m).
Age of base data & update frequency 2005-2017 (ongoing) / Indian update missions planned
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 30m
Horizontal accuracy <10m CE90
Vertical resolution 1m
Vertical accuracy <10m LE90
Age of base data & update frequency Various input data / no updates
Type (DSM or DTM) DSM
Coverage global
License conditions Restricted Use Product; please see RD12 for base license conditions; On request, different licensing conditions may be possible.
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.
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 2015. 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 3.22 More information is available on the NASA website23. The data can be obtained through the USGS Earth Explorer24.
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 Center26
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 website27. The data can be obtained through the USGS Earth Explorer28, ECHO Reverb29 or LP DAAC Global Data Explorer30.
Age of base data & update frequency 2000-2009 (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 2006-2011. 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 availability32
The technical description of the DSM is available on the ALOS World 30 website33 The data are available after registration there34.
Age of base data & update frequency 2006-2011 / 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 Freely available Table 14-ALOSW3D 30 Product Specifications
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.
2.3. 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
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.
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
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.
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 ad-hoc 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:
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”
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.
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.
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 201236, 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 pre-processing 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 terrain-dependent 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 Zones38 initiative (2014-2015) 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 terrain-dependent 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: http://land.copernicus.eu/pan-european/high-resolution-layers/ 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: http://land.copernicus.eu/local/riparian-zones 39 Available via the Copernicus Land portal: http://land.copernicus.eu/local/riparian-zones/riparian-zones-delineation/view
of the Riparian Zones for the reference year 2012. 40 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 2018. 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 product41 provides a VHR LC/LU delineation for selected European biodiversity hotspots of the reference years 2006 and 2012. More than 160,000 km² of (buffered) Natura2000 areas were mapped as part of the Copernicus/GMES Initial Operations Phase until 2015. 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 mono-temporal 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: http://land.copernicus.eu/local/riparian-zones/land-cover-land-use-lclu-image/view 41 More information on the Natura2000 product at the Copernicus Land portal: http://land.copernicus.eu/local/natura/ 42 More details on the ECoLaSS project are available at: http://www.ecolass.eu 43 SENSAGRI project website: http://www.sensagri.eu/ 44 MULTIPLY project website: http://www.multiply-h2020.eu/
MULTIPLY develops a platform using physical radiative transfer models and advanced data assimilation concepts together with continuous satellite data acquisitions to produce a stream of fully characterised high spatial and temporal resolution estimates of land surface parameters such as albedo, LAI, fAPAR, chlorophyll content, etc.
All these developments of future CLMS services will necessitate an excellent operational pre-processing of satellite imagery in terms of geometric, topographic and illumination effects, across different Copernicus satellite data both from the Sentinel family (Sentinels 1, 2 and 3) and the Copernicus Contributing Missions (CCMs). This must be sustained by a consistent and freely available DEM with adequate quality. Only then, a precise multi-temporal co-registration and spectral calibration – irrespective of the different sensors’ observation geometries, terrain displacement and illumination effects and different spatial resolutions – will be possible. This will be mandatory to make the related novel multi-temporal, multi-sensor, sub-pixel and/or data assimilation approaches operationally feasible with a sufficient level of accuracy and reliability, at a high level of automation. At present, the EU-DEM fulfils these quality requirements only partially.
Furthermore, an improved EU-DEM could also serve the need for a uniform sole elevation data source as basis for ortho-rectification of pan-European satellite image coverages, such as of the ESA Data Warehouse or the Sentinel fleet of satellites. Such has been asked for at least since 2009 [RD17], however the current situation is still that different Copernicus Contributing Mission Entities (CCMEs) process their respective satellite data with different DEMs [RD18]. For example, SPOT-5 imagery as part of the ‘Optical HR Pan European coverage’ (HR_IMAGE_2015) have been processed with support of the SPOT ‘Reference 3D DEM’ complemented by SRTM, whereas Resourcesat-2 imagery within the same HR_IMAGE_2015 data collection have been using “SRTM, DEMs of national land surveying offices of Finland, Norway, Sweden, ASTER GDEM and where required other DEMs” [RD15]. Depending on actual image acquisition angles, this can cause deviations of up to several pixels between the different sensors’ image data and Copernicus services in steep terrain, especially when multi-sensor and/or time series approaches are employed.
There are several known sources of geometric distortion between the various Copernicus EO data (both Sentinels and HR/VHR CCM data), such as the procedure of image co-registration to previous time steps’ image coverages instead of absolute geo-location to a consistent common reference; missing inter-alia scene co-registration within the same image coverage (example VHR2015), and also the use of different DEMs by the CCMEs and ESA. From a CLMS services’ perspective, at least the latter error contribution could be resolved by having available and jointly using one uniform and consistent, high-quality DEM for Europe.
Beyond the core CLMS products and their envisaged evolution, a consistent European DEM of further improved quality would be also beneficial for various kinds of downstream Land applications on more regional scale, such as water storage and volume assessment, assessment of precipitation run-off and flood risk, risk assessment of landslides and soil erosion as well as various applications in urban and mountainous areas.
Furthermore, the current EU-DEM is also available for use by research and academia, public authorities, private companies and the general public. The dataset is fully, freely and openly available for download via the Copernicus Land portal, which allows the EEA to track the amount and origin of the downloads. In this way, download statistics have been regularly captured since 1st July 2015 by the EEA. An evaluation of these download statistics from the Copernicus Land portal shows that the EU-DEM v1.1 has experienced a huge increase in public download since first availability on the portal in the first half of 2016. Already in the second half of 2016, the dataset
has been downloaded 783 times, making it the third most downloaded product of all 28 ranked products. This also ranked among the biggest download increases captured so far. Only the long-established CORINE Land Cover (2012) and the Urban Atlas (2012) products showed higher overall download numbers in the second half of 2016. The top-5 countries from which users downloaded the EU-DEM were France, Germany, the Netherlands, Bulgaria and the United Kingdom. This clearly underpins the need for a consistent and freely available DEM that can be used as an accepted common standard for Copernicus and general Earth Observation applications in Europe.
Summing up, for geometric processing of current HR satellite imagery, the original horizontal resolution of a reference DEM should at least be 30m, whereas for a VHR imagery correction it should preferentially be significantly better. The horizontal and vertical resolution and accuracies of the used DEM should be well documented, and range around 10m or better - which complies to the current state of the art for medium quality/resolution DEMs (see Table 15). To enable a proper data processing without introducing DEM effects, void areas should preferentially have been filled and DEM artefacts corrected. For any kind of hydrological applications, consistency of the DEM with water body surfaces and the river network should be ensured. At least European-wide homogeneity of the DEM dataset and a good quality also in higher geographic latitudes are a prerequisite. Global coverage would be an additional asset for the continental component of the CLMS, considering future outreach potential beyond Europe. The minimum license requirement should be for use by ESA and the CCMEs in HR imagery processing as well as by the thematic Copernicus services for product generation. It would be very beneficial though to have – beyond that – a DEM product fully available to the general public, with the potential to become the European elevation reference dataset for the next years to come.
REQUIREMENTS:
Horizontal resolution: 30m or better for HR imagery/products; 5-10m preferred for VHR imagery/products
Horizontal accuracy: 10m or better, clearly documented
Vertical resolution: 1m
Vertical accuracy: 5-7m
Homogeneity: mandatory (specifically also in higher latitudes). Voids filled, artefacts corrected, water surfaces edited, river flows ensured.
Maintenance: NA
Type (DTM/DSM): for majority of requirements DSM; for hydrological applications DTM
Coverage: at least EEA-39 countries. Global would be an asset.
Data policy: Minimum = use by ESA, CCMEs (of HR data), CLMS services. Preferred: fully open to general public.
![gecnet.kku.ac.th · of Agriculture and Cooperation DEM [MOAC DEM]) SRTM DEM 5 SRTM DEM 5 Suriya Polpoon ... Earth's land surface is freely available for download from internet. Taking](https://static.documents.pub/doc/80x56/5f088e027e708231d4229689/of-agriculture-and-cooperation-dem-moac-dem-srtm-dem-5-srtm-dem-5-suriya-polpoon.jpg)
