In This Space
Elevation map (Source: WesternGeco)
Elevation data is an essential component of many analyses derived from EO. Elevation mapping is predominantly represented by a Digital Elevation Model (DEM). The terms DEM, Digital Surface Model (DSM) and Digital Terrain Model (DTM) are often used interchangeably, the DSM will take into account the surface features (such as buildings or trees) and DTM will focus on bare earth. Most data providers use the term DEM as the generic term to describe DSM and DTM, as such DEM will be used for this product sheet.
Elevation maps are useful at a variety of scales from regional to basin to project area, depending on the requirements the user can select the best suited resolution to address the challenge. While DEM with a resolution ≥ 30 m are freely available, resolutions better than 30 m these are normally commercial datasets. See input data sources for more details.
From EO sources there are two main ways of creating a DEM.
A DEM is raster file containing information of elevation for each pixel. Lower resolution DEM data ≥ 30 m is freely available off the shelf, while ≥ 12 m is available of the shelf, but needs to be acquired commercially. For resolutions < 12 m DEM data is not available off the shelf and has to be produced on client’s request.
Known restrictions / limitations
Lifecycle stage and demand
All lifecycle stages: Can be used at all stages with the cycle. Elevation mapping is useful for the oil and gas industry some examples below.
Surface Geology modelling
Logistics planning and operations
Geographic coverage and demand
Global coverage (with a few restrictions see below).
OTM:058 Identifying ground conditions susceptible to poor coupling
HC:1101 Identify areas with soft sediments to avoid strong attenuation
Input data sources
Optical: VHR1, VHR2, HR1, HR2
Radar: VHR1, VHR2, HR1, HR2, MR1, MR2
Spatial resolution and coverage
Spatial resolution: 1 m – 1 km pixel size
Minimum Mapping Unit (MMU)
n/a (the product is directly based on the input data; the smallest unit is one pixel)
Accuracy / constraints
Spatial accuracy: For horizontal accuracy the goal would be one pixel, but depends on reference data
Accuracies for a few off-the-shelf elevation products:
Accuracy assessment approach & quality control measures
Field survey spread over 16 locations of a 25 km2 area DEM, using DGPS or RTK surveying and processing the results.
Frequency / timeliness
Frequency: The frequency is constrained by satellite revisit and acquisition, but also processing requirements. Depending on the requirements of the customer the best suitable satellite sensor has to be chosen regarding spatial / spectral resolution as well as revisit frequency and timeliness. For coarser resolution DEMs, static products exist for most parts of the globe.
Timeliness of deliverable: Stereo acquisitions for precision DEMs (VHR1 data for example) often need to be tasked. There are certain criteria which need to be fulfilled for this tasking i.e. the time between acquisitions, the cloud cover, the angle of the image required. To get the required accuracy ground control points are needed. The timeframe for archived data is about 3 week, for tasking it can go up to months. Off-the-shelf products can be delivered within a few days.
1 km (GTOPO30), 90 m (SRTM version 3) and 30 m (Aster GDEM2) DEM are freely available. For higher resolution this data needs to be commercially acquired. These data sets for example are Elevation 30 (SPOT DEM 30 m), WorldDEM (TanDEM-X 12 m).
For higher resolutions (e.g. Elevation 8 (SPOT DEM 8 m), Elevation 4 & 1 (Pleiades DEM 4 m & 1 m), WorldView Elevation Suite (4 m & 1 m)) processing will have to take place, whether there are suitable images in archive or if they need to be tasked. Working to time frames that fit in with GCP collect is important as well.
Delivery / output format
|Peer Reviewer:||Hatfield Consultants|
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Internal – Project consortium and science partners
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