10. March 2017
Void pixels due to clouds and snow pixels within 60 deg. of north and south latitudes in Version 1 were complemented by existing DEMs. Out of the areas are same with Version 1 product.As we already compared ALOS with SRTM-1(I saw the ALOS DEM as “the winner”) I am now interested in how this performs in a another setting. We are changing our focus from Mongolia to Germany and check how the new ALOS DEM works compared with SRTM 1.
ALOS and SRTM DataI downloaded the data from USGS EarthExplorer (SRTM 1) and the JAXA webpage. Both files are delivered as TIFFs. The ALOS dataset not only consists of one version but also has the median values of their algorithm results. The area of interest is located in Germany and shows urban structures (Berlin, city) as well as natural features (lakes, moraines and forests). You might get a first overview of the data with this gif:
QA resultsLet’s have a look at the North-Eastern part of this scene first. Prior moaning about the artefacts lets get even closer:
As we can see, the ALOS dataset provides much more detail. This is an optical sensor which operates at a 5x5m ground resolution. This results in a much better contrast even downsampled. We can see much sharper edges where anthropological features appear in the scene (like the highway and other patches). Furthermore the values of forested regions tend to be higher then in non-forested regions. As a SAR is even a bit ground penetrating in dry regions we can see some differences in height values: The SRTM values tend to be a bit higher even on “flat” surfaces like this highway: So how does it look like on a more or less plain surface? Let’s switch perspective: Here are the statistics for the Berlin Tempelhof airfield. This is most likely the the smoothest plane you will find across Germany. I’ve used a subset of the airfield to create the stats: