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how per pixel lat/lon may influence the ICOL processing results?
Dear all,

What is the effect on ICOL processing if I attach pixel geocoding prior to ICOL process a MER FR L1b image? Would it be different if was not attached and then ICOL will use the nominal latitude and longitude coordinates interpolated from tie points?

The following question is just to confirm that ICOL cannot modify the nominal Tie-Points values of lat/lon.

Can ICOL modify the nominal Tie-Points values of lat/lon ?

These questions are related to another closely related question posted in ODESA forum.

Thank you,

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RE: how per pixel lat/lon may influence the ICOL processing results?
Answer Answer (Unmark)
5/8/12 10:31 PM as a reply to Jose M. Beltran.
Dear Jose,

ICOL is not modifying the geo-coding of the input product. ICOL is solely applying a radiometric correction and does not perform any correction to the geolocation. Hence, there is no reason for ICOL to modify either the tie-point grid, or the lat-lon bands of AMORGOSS'ed products.

ICOL needs to know the coastline property of a pixel in order to calculate the distance to land, and the land-water property of a pixel in order to restrict processing if wished by the user.

The current version ICOL 2.7.4 is getting this information from the L1b flags. Hence ICOL 2.7.4 does not use latitude or longitude information. The results are not different if you work with tie-point geocoding or AMORGOS lat-lon bands.

This will change with the next release of ICOL, which will come shortly after the BEAM 4.10 release (or together with it). This new version comes with its own land-water database, based on SRTM data. This is more precise than the MERIS L1b land-water and coastline flags. ICOL uses the geocoding of the product to point into this database.

If a product is not preprocessed with AMORGOS, ICOL uses the tie-point grid lat-lon coordinates as geocoding. If a product has been pre-processed with AMORGOS, and if the user has made the setting in beam.config file (*), ICOL uses the new lat-lon bands created by AMORGOS as geocoding (**).


Here is the relevant section of <beam-home>/config/beam.config:
1# Controls whether a PixelGeoCoding is attached to MERIS FRG/FSG products (e.g. created with AMORGOS),
2# if an Envisat (N1) data file is opened.
3# The default value is 'false', meaning that a Tie-point geo-coding is used instead.
4beam.envisat.usePixelGeoCoding = true

If you don't like editing a config file, and if don't need a N1 output from ICOL, you can open your N1 file in VISAT, apply attach pixel geocoding, and save as dimap. N1 does not offer the possibility to specify a geocoding, but dimap does. Running ICOL on this dimap file has the same effect as changing the config and running on N1.
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