NASA’s Earth Observing System Data and Information System (EOSDIS) is the data distribution system facilitated with NASA’s Distributed Active Archive Centers (DAACs). Alaska Satellite Facility (ASF) is one of the DAAC providing various data sources to the public for free. We will use the ASF website (as of 28th October 2019) to download the 12.5 m historical datasets (2006-2011) on high-resolution DEM from ALOS PALSAR.
PALSAR is the L-band Synthetic Aperture Radar (SAR), i.e. it is able to capture the image all-weather and has day and night observation. Below is the different acquisition beam mode for the PALSAR. Read more on the mission on the JAXA website.
The Radiometric Terrain Correction (RTC) product has been created and released by ASF. Below is the coverage of the RTC dataset. It’s available worldwide except for some very high northern hemisphere.
They are usually available as two product levels: high-resolution and low-resolution. Both high-and-low resolutions have DEM provided in 12.5 m as Int16 GeoTIFF format.
Now, let’s go ahead and download the datasets.
- We need NASA Earth Data login credentials. So, go ahead, and create an account on the NASA Earth Data Login.
- Go ahead and open up the ASF Data Search Platform. Click the User icon as shown in the red box below, and log in with the Earth Data credentials that you created in 1.
- Click on the Dataset and select ALOS PALSAR. Draw your area of interest by dragging the mouse to create a rectangle bounding box. Select the Start Date and End Date.
You can filter to include only the Lo-Res Terrain Correction and High-Res Terrain Correction product.
- If you want to download all these images programmatically, click on Add all results to queue.
Then move to the Downloads icon on the top-right side. Click on the Data Download. And then you can download the python script to download all the data at once.
- If you unzip the product, you will see multiple files. The DEM file is the one with .dem.tif extension. Load in QGIS or any GIS software to make sure they are what you expected, and use them in your project.
Note: Please note that the DEMs included with the ALOS PALSAR RTC products from ASF are NOT generated from ALOS PALSAR data. They are the DEMs that were used for RTC processing, which were simply mosaicked and clipped from publicly-available DEMs, such as SRTM and NED. They have been resampled to match the pixel spacing of the RTC product (12.5m for the high-res product), but that is NOT an indication of the original DEM resolution.
Please refer to https://asf.alaska.edu/data-sets/derived-data-sets/alos-palsar-rtc/alos-palsar-radiometric-terrain-correction/#dem_information for more information on the DEMs included with the ALOS PALSAR RTC products.