SeaWiFS

SeaWiFS

From the same OceanColor website as the MODIS data (gsfc.nasa.gov) you can download SeaWiFS data, a particularly good source for chlorophyll-a at sea and NDVI on land.

• the SeaWiFS Standard Mapped Products are already geocoded in WGS84 so should be easy to load into a lat/lon location with r.in.gdal (at least this is true for PAR maps).

• Processing is very similar to the MODIS and AVHRR examples.

In some data I worked with, NULL was represented by -32767. This can be cleaned up using the r.null module:

MAP=S2010235.L3m_DAY_CHL_chlor_a_9km
r.null $map setnull=-32767

Inspecting the HDF file with "gdalinfo" tell us that this data has a slope of 1 and intercept of 0, so does not need to be processed with r.mapcalc.

You can download some preprocessed color rules for Chlorophyll-a from the GRASS addons SVN (based on NASA's GSFC OceanColor website's rules) and apply them with the r.colors module.

r.colors $map rules=~/grass_addons/palette_chl_etc.gcolors

or use a simple equalized histogram to spread the colors to where the data is:

r.colors $map color=bcyr -e

See also

• MODIS
• AVHRR