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.
Its a great source of DEM data, Thanks for sharing. However, Coastal data in Subarctic zones showing some mysterious results like the value of water is -48, that’s ok. Still, the coastal zone is also showing the negative value for a long stretch landward. I have checked with Google earth, SRTM data, where the actual value is say +2. This data is showing -32. So is there any Datum correction or some scale factor etc. for the coastal zones?
Please note that this dataset is geoid corrected so that the values that you see are the geoidal height.
I have the same problem. now what should I do to see the correct elevation? Thanks (I use ArcGIS)
I haven’t used personally but you may try this: https://desktop.arcgis.com/en/arcmap/10.3/manage-data/raster-and-images/wkflw-converting-from-orthometric-to-ellipsoidal-heights.htm
It is important to be aware 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. And, as mentioned above, there is a geoid correction applied, which is why the values may differ from the original SRTM or NED values.
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.
Heidi, you are correct. We decided not to use those DEMs anymore as it is – at least in our Region of Southern Chili – worse than the real Alos Palsar DEM (30m). For example, the orthometric height of the 12.5m product was 20 m above the CP height and the 30m product was much more congruent as well. The term high resolution DEM is misleading here.
pleas help how to download 12.5 dem
Hello Heidi –
I am using Sentinel 1 C-band SAR to create DEMs for my own region of interest. The resulting DSMs have values ranging from (approx) 9000-13500m. The protocol followed is that recommended by the ESA and the ASF from where I downloaded the original SAR data.
However that DSM elevation range is obviously wrong, since I know from the SRTM data set and actual field geodetic points that the range of elevation within my small 2000 ha catchment is ~330 to ~2700m. I planned on using the S1 SAR to see larger surface changes due to road building, hill leveling and landslide in the region.
Are you familiar with the S1 SAR product / protocol to recommend a way forward and explain what is happening?
Thanks for you help in advance.