[GRASS-user] Create and analyse scatter plots against two rasters

[Nikos Alexandris]

* Huub Munstege <hmunstege at yahoo.com> [2015-06-11 08:12:51 +0000]:

> Dear Grass community, our objective is to monitor the soil moisture
> index (SMI) of small catchments in Mali and the impact of irrigation
> structures.  We have taken note of the many articles on this subject
> and as it  looks now we can utilize the huge Landsat archive available
> on the web.  With the Landsat bands and the GRASS modules we're able
> to produce rasters for the surface temperature

For LST from Landsat 8, you might find this interesting:
<https://github.com/NikosAlexandris/i.landsat8.swlst>.  Plan is to
move it in the addons repository after more testing (anyone willing to
test is welcome, feedback is essential)

> and for the NDVI
> values. To determine th SMI value it's necessary to do a regression
> analyses (the so called 'wet edge' and 'dry edge' in a scatter plot
> between the two mentioned rasters. How can we achieve this?

Have a look at 

- d.correlate
- r.series
- r.regression.line (and maybe r.regression.multi)
- r.regression.series

though I am pretty sure you'll love the t.* modules for time seris
analyes:

- http://grass.osgeo.org/grass70/manuals/temporalintro.html /
  http://www.geostat-course.org/system/files/Presentation_0.pdf

- http://ncsu-osgeorel.github.io/grass-temporal-workshop/

- http://grasswiki.osgeo.org/wiki/Temporal_data_processing


Of course, you can also use R to do the work for it and get results/maps
back in GRASS for further processing.

Kind regards, Nikos