Sen2cor DEM usage

Optical Toolbox sen2cor
1

Hi all,

I am using sen2cor from the command line under Ubuntu 14. It works just fine but somehow it doesn’t use a DEM (“DEM is not present, flat surface assumed”).
I know that I can use a local DEM by modifying the L2A_GIPP.xml. But to my understanding if no local DEM is set, it should download a DEM automatically.

Is there some hidden setting to activate the automatic DEM download?

UPDATE
Some further question:
If I use a local DEM

  • What is the required format? Geotiff?
  • Can it be in tiles or must it be one global file?
  • What is the required CRS? WGS84? UTM Zones?

Jan

2

Hi Jan,

you will find the answers in the L2A_GIPP.xml, which is located in the cfg folder of your sen2cor user installation:

	<DEM_Directory>NONE</DEM_Directory>
	<!-- should be either a directory under SEN2CORHOME or 'NONE'. If NONE, no DEM will be used -->
	<DEM_Reference>http://data_public:GDdci@data.cgiar-csi.org/srtm/tiles/GeoTIFF/</DEM_Reference>
	<!-- will be ignored if DEM is false. Either a DEM will be downloaded from this reference, if no local DEM is available -->

use e.g. “dem/srtm” as directory, which should be located in $SEN2COR_HOME

Yes it’s Geotiff, see header below. The processor will read the required Geoinfo from the L1C metadata, so you don’t have to care for that.

Currently we only support the dems provided by cgiar, (see reference above). The processor is automatically downloading the needed DEMs and assembles them, if multiple tiles are needed. More info on the process can be found in the user manual.

Geotiff_Information:
Version: 1
Key_Revision: 1.0
Tagged_Information:
ModelTiepointTag (2,3):
0 0 0
10 50 0
ModelPixelScaleTag (1,3):
0.000833333333 0.000833333333 0
End_Of_Tags.
Keyed_Information:
GTModelTypeGeoKey (Short,1): ModelTypeGeographic
GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
GeographicTypeGeoKey (Short,1): GCS_WGS_84
GeogCitationGeoKey (Ascii,7): “WGS 84”
GeogAngularUnitsGeoKey (Short,1): Angular_Degree
End_Of_Keys.
End_Of_Geotiff.

GCS: 4326/WGS 84
Datum: 6326/World Geodetic System 1984
Ellipsoid: 7030/WGS 84 (6378137.00,6356752.31)
Prime Meridian: 8901/Greenwich (0.000000/ 0d 0’ 0.00"E)

PROJ.4 Definition: +proj=latlong +ellps=WGS84 +to_meter=1.0000000000

Corner Coordinates:
Upper Left (10.0000000,50.0000000)
Lower Left (10.0000000,45.0000000)
Upper Right (15.0000000,50.0000000)
Lower Right (15.0000000,45.0000000)
Center (12.5000000,47.5000000)

1 Like
3

Could i use my own dem or only the default one (SRTM 90m);;;

I have installed the last version of sen2cor (2.2.1).

4

I changed the “none” to “dem/srtm” to motivate Sen2Cor to use DEM during atmospheric correction.
I had 30 m resolution SRTM data (1 arc) for the area of interest and placed it in the following folder:

C:\Users\Saeid\Documents\sen2cor\srtm

During the correction, Sen2Cor realized to use a DEM, but it tried to download it from the website rather than using provided files. The download process was really slow, accordingly after more than an hour I aborted the process.
I wonder if the specified path for the 30 m data is correct and if the data should be named in a specific way. The data current name of the tiles in geotiff format are:

e050_n34.dt1
e051_n34.dt1

Furthermore, wonder if an image should be fully covered by the selected DEM or partial coverage for the area of interest is enough?

5

Is it possible to use other DEM’s, such as LiDAR derived models?

Cheers

1 Like
6

I use the above mentioned method and I am not able to apply the dem for 10m resolution, is there a way or it is not possible?