How to produce high-resolution DEMs from new Sentinel-1 data?

Question

This is a general question relating to the new Sentinel-1 data. I'm interested in the potential for using this data to create high resolution DEMs in GIS (I use QGIS), to investigate archaeological sites and landscapes and model their change.

The European Space Agency Copernicus program satellite Sentinel-1a has recently been commissioned, with data just beginning to become available on the ESA Data hub website (https://scihub.esa.int/). This data can be viewed and processed using specially prepared software called Sentinel-1 Toolbox (https://earth.esa.int/web/sentinel-tbx/sentinel-1-toolbox). The radar data will allow land surface observations and changes in land surfaces to be modelled using 'synthetic aperture radar interferometry', with most examples given so far detailing the impact of earthquakes or other large-scale natural landscape changes (https://earth.esa.int/web/sentinel/thematic-content/-/article/radar-vision-maps-napa-valley-earthquake). After searching the internet I have found that, other than the ESA's own website, there appears to be little information on the practical use of this new data.

Is there any literature on how to produce high-resolution DEMs from this new Sentinel-1 data?

Answer 1

I'm guessing you never worked with SAR data before, so I'll break your question down into parts I can answer:

1) Create high resolution DEMs in GIS

The process of creating a DEM just from SAR data is quite complex and requires a lot of processing power and memory. I don't know of a GIS software that implements DEM creation due to these constraints.

2) Investigate sites/landscapes and model their change

If you want to model/observe elevation change Differential Interferometry is the key word you should be looking for. This approach enables you to observe even small changes in elevation without the complex process of creating two DEMs.

3) How to produce high-resolution DEMs

This is a complex process requiring a lot of steps. I highly suggest you read up on SAR Interferometry in general, since Sentinel-1 data has basically the same (dis)-advantages as any other SAR data.

ESA provides a free book containing all relevant information regarding SAR interferometry, be it from a mathemathical as well as a processing viewpoint:

ESA: InSAR principles

Steps required to create a DEM

• co-register scenes
• calculate baselines
• create interferogram and extract phase information
• correct for sensor movement, flat earth removal, athmosphere, etc.
• convert differential phase to absolute phase differences
• phase unwrapping
• phase to height conversion
• correct for absolute elevation, phase jumps, etc.

This is obviously just an outline. The detailed processes for each step are explained in the book I refered to and, in theory, can all be executed with the S1-Toolbox (soon to be SNAP) or the Next ESA SAR Toolbox (NEST).

Answer 2

Here I found an article "Preliminary results of using Sentinel-1 SAR data for DSM generation", 2015. As I understood, the vertical accuracy will not be better than 20m (an average height of a single tree). That is comparable to the SRTMGL1, GDEM2 accuracy.

I didn't find it useful to improve the SRTM DEM, by filling the forest masked areas in the SRTM1GL (to get rid of the tree cover vertical offset). I am not a SAR, DEM-specialist, though.

Answer 3

Response From an INSAR professor

Dear Eric

I heard from XXXXX that you are interested in an (InSAR) DEM, I presume over an area in Kenya? Please note that there are already such products available, e.g. the SRTM DEM and products from the TanDEM-X mission. Both InSAR missions were tuned to obtain the best quality DEM's, as they worked in the single-pass bi-static mode, which prevents atmospheric error signal from entering in the DEM. With Sentinel-1a and Sentinel-1b it is not possible to make a single-pass product, as they are not flying in (bi-static) Tandem. It is possible to make mono-static repeat-pass DEM's from either Sentinel-1a or Sentinel-1b, but the repeat pass configuration will introduce atmospheric-induced DEM errors with hundreds of meters of error, i.e., much worse than the DEM products of e.g. SRTM, which you can easily download for free. Moreover, also the spatial resolution will be much worse.

For this reason, I assume that your request may not be necessary. Please inform me if you have any further questions