[GRASS-user] Sentinel2- flooding

GRASS GRASS user
1

Hi,

I’ve obtained an image from sentinel2 where it shows flooding. Just wondering are there tools in Grass to classify an image in order to pull out these “flooded” pixels?

Thanks

···

Le gach dea ghui,

Shane Carey
GIS and Data Solutions Consultant

2

I Think there isn’t any tool pre-configured. You need to find an index to calculate “flooded” cells and then you can simply use r.mapcalc

R

Il giorno ven 7 dic 2018 alle ore 14:45 Shane Carey <careyshan@gmail.com> ha scritto:

Hi,

I’ve obtained an image from sentinel2 where it shows flooding. Just wondering are there tools in Grass to classify an image in order to pull out these “flooded” pixels?

Thanks

Le gach dea ghui,

Shane Carey
GIS and Data Solutions Consultant

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

3

Ok, thanks.

···

Le gach dea ghui,

Shane Carey
GIS and Data Solutions Consultant

4

Hi Shane,

Following up on robertos answer:

You could try the Normalized Difference Water Index (NDWI) which is computed for S-2 as:

ndwi = (B08-B11)/(B08+B11)

or alternatively

ndwi = (B03 - B08) / (B03 + B08)

See e.g.: https://github.com/sentinel-hub/custom-scripts/blob/master/sentinel-2/ndwi/script.js

You could also take a look at Sentinel-1 for flooding / water bodies. However, Sentinel-1 would have to be pre-processed in SNAP/gpt.

Cheers

Stefan

···

Ok, thanks.

Le gach dea ghui,

Shane Carey

GIS and Data Solutions Consultant

On Fri, Dec 7, 2018 at 2:45 PM Roberto Marzocchi <roberto.marzocchi@gmail.com> wrote:

I Think there isn’t any tool pre-configured. You need to find an index to calculate “flooded” cells and then you can simply use r.mapcalc

R

Il giorno ven 7 dic 2018 alle ore 14:45 Shane Carey <careyshan@gmail.com> ha scritto:

Hi,

I’ve obtained an image from sentinel2 where it shows flooding. Just wondering are there tools in Grass to classify an image in order to pull out these “flooded” pixels?

Thanks

–

Le gach dea ghui,

Shane Carey

GIS and Data Solutions Consultant

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

5

Great thanks

···

Le gach dea ghui,

Shane Carey
GIS and Data Solutions Consultant

6

On Fri, Dec 7, 2018 at 8:14 PM Stefan Blumentrath
<Stefan.Blumentrath@nina.no> wrote:

Hi Shane,

Following up on robertos answer:

You could try the Normalized Difference Water Index (NDWI) which is computed for S-2 as:

ndwi = (B08-B11)/(B08+B11)

or alternatively

ndwi = (B03 - B08) / (B03 + B08)

See e.g.: https://github.com/sentinel-hub/custom-scripts/blob/master/sentinel-2/ndwi/script.js

... or just adapt the bands here:

https://grass.osgeo.org/grass74/manuals/i.vi.html#calculation-of-ndvi

You could also take a look at Sentinel-1 for flooding / water bodies. However, Sentinel-1 would have to be pre-processed in SNAP/gpt.

Yes, Sentinel-1 is probably more relevant when it comes to
identification of flooded areas.

Markus

7

Great - thanks all. I’ll let you know how I get on.
Thanks

···

Le gach dea ghui,

Shane Carey
GIS and Data Solutions Consultant