Global AW3D30

ALOS Data in WindPRO - Site near Kassel.

ALOS: Advanced Land Observing Satellite "DAICHI". Image credit: JAXA.

Introduction

The “ALOS World 3D 30 m mesh (AW3D30)" dataset is recent digital surface model (DSM) with global coverage. The version 2.1 of the dataset was released in early 2018 – and it holds a global coverage in a 30m (1-arc-second) resolution. The dataset was created with the aim for a target vertical accuracy of 5m RMSE – and a horizontal accuracy of 5m. AW3D30 was generated from data obtained from the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) - an instrument that was carried onboard the Japanese Advanced Land Observing Satellite (ALOS). The ALOS satellite was launched on January 24th 2006; it had an expected target life of 5 years. After a successful mission it ended its operations during May 2011 due to a power anomaly. This dataset was produced by JAXA - Japan's Aerospace Exploration Agency.

Dataset Overview

• Spatial Coverage : Global - coverage is most of land bodies on earth
• Reolution : 1 arc-second (30m)
• Data-type: Digital Surface Model (DSM)
• Coordinate system in source data: Geographic WGS (EPSG:4326)

Recommendations

The AW3D30 dataset is very interesting for wind-resource application due to its acurracy and resolution. However, since the dataset was obtained using optical sensors, then many of the satellite images used in the DEM-creation could be covered with clouds or have low contrast – such as ice and snow. Such areas are problematic for an optical-stereorography approach. If such problematic errors exists in the imagery, then these cloud or snow/iceareas have been void filled with data from alternative sources – using a data from SRTM3, DEM10 data in Japan or PRISM DSM. As such, the EMD recommendation is currently to use the AW3D30 dataset as a supplement to other sources such as SRTM1 or other global/regional datasets - and to validate if any void-fills have been caried out in your model domain.

The AW3D30 quality mask is available from within the windPRO area object, and we recommend that you inspect it (look for void-filled areas) in the following way:

1. Open your windPRO project and create a new area-object
2. Set purpose to '3d Animation and Photomontage'
3. Go to the - 'Import/Export' tab - and press the 'online-data' button
4. Choose the 'AW3D30 Elevation Model - Quality Mask' - and press 'OK' to load the data
5. Go-to the 'presentation' tab - and set checkmark in 'Transparent' for the 'Boundary Line' - then press 'OK'
6. Right-click the area-object icon - remove the 'edit-mode' and choose to 'show legend'

Accuracy of AW3D30

Digital elevation models are evaluated using ground control points (GCP’s). For the AW3D30, several evaluations exists: A preliminary study by (Tadono et al., 2016) showed that the AW3D30 dataset has a vertical accuracy of 4.40m (RMSE) and a bias of -0.44m – considering 5121 independent ground control points (GCP’s) with global distribution. The same study reported that SRTM v. 3 had a RMSE of 7.50m and a -1.00m bias at the same locations.

Availability from within windPRO

The DSM-data and the associated quality mask are available directly from within windPRO. The DSM elevation data is delivered as gridded data with a spatial resolution of 1 arc second. As a part of the processing of the DSM elevation data from our EMD server, the user has an option of choosing whether the data downloaded should be received as either raw gridded data or converted to height contour lines. In order to use the data for energy yield calculations, the data must be converted to contours. These data be accessed from the online-services in the following three objects:

• DSM-Data in the line object (with purpose to height contour lines)
• DSM-Data in the elevation grid object
• Quality mask from AW3D30 is accessed from the area-object

Acknowledgement and Credits

The AlosWorld 3D 30m data is provided by JAXA which also holds copyright of the data. JAXA is acknowledged for the development and release of this free dataset - and thus for aiding the development of renewable energy and wind energy in particular.

External Links

• More information on ALOS DSM project is available at http://www.eorc.jaxa.jp/ALOS/en/about/about_index.htm
• AW3D30 - Product description from JAXA (pdf-format) - here