ARC SST Processor - Creating new coefficient files |

The ARC SST Tool uses coefficient files during the SST and ASDI processing.
These files are located in:

> `<SNAP-USERHOME>/snap/opttbx/opttbx-arc/src/main/resources/auxdata/arc`

`<SNAP-USERHOME>` is the `.snap` folder located in the in the user home directory.

A coefficient file is a standard java properties file consisting of key/value pairs and comments. When the SST processor starts up, it scans the SST auxiliary data directory for coefficient files and shows these in the GUI as entries in the coefficient file list for both nadir and dual views. It is possible to add any number of customized coefficient files to these folders when following the simple syntax:

A comment line begins with a "#" and is ignored during the parsing operation.

Each coefficient file should contain a band name and short description, denoted as:

        name = short_name
        description = my coefficient description

The description string is shown in the user interface coefficient selection box.

The coefficient file defines a multi-dimensional lookup table of linear retrieval coefficients to use at specified viewing geometry (nadir and forward view path length) and TCWV values. It is necessary to specify the full set of coefficients at at-least two points along each axis. For cases where the coefficients do not vary with a particular parameter such as the ASDI coefficients the coefficients should simply be repeated to indicate that the coefficients do not vary along that axis.

The three axis for the lookup table are: nadir path length, forward path length, TCWV.

Example:

        secnad = 1, 1.0743021
        secfwd = 0, 1
        wvband = 0, 1

indicates that coefficients will be specified at nadir path lengths of 1 and 1.07 (the centre and edge of the ATSR nadir-view), forward-view path lengths of 0 and 1 (these are unphysical values used for a coefficient set which does not vary with forward-view path length), and TCWV values of 0 and 1 (again this set of coefficients does not depend on TCWV)

For every combination of lookup parameters there must be a corresponding set of coefficients. The example above specifies the smallest possibly lookup table: 2x2x2 with a total of 8 coefficients required. The coefficients are specified in standard array order, with secnad the fastest varying axis, then secfwd, and wvband the slowest varying axis.

For each combination of lookup parameters there must be a set of 7 coefficients (corresponding to the 3.7n, 11n, 12n, 3.7f, 11f, 12f, and constant terms). Coefficient values consist of a number of comma separated floating point values. It is recommended that 7 values are printed on each line

Example:

        coeffs = 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179

which are the coefficients for the AATSR ASDI. This set only uses three channels: 11 micron nadir, 11 micron forward, and 12 micron forward. The coefficients only depend on the nadir-view path length, with the first two lines specifiying the coefficients at the centre swath (secnad=1) and edge of swath (secnad=1.07). The same coefficients are then repeated a further three times for the unused dimensions (secfwd and wvband).

Here is a complete coefficent file as example:

        # Source file: ASDI_AATSR.coef
        name = ASDI
        description = AATSR Saharan Dust Index
        secnad = 1, 1.0743021
        secfwd = 0, 1
        wvband = 0, 1
        coeffs = 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179, \
                 0.0, 0.39602999, 0.0, 0.0,-0.75792998, 0.3619000,-0.01226863, \
                 0.0, 0.34224000, 0.0, 0.0,-0.58267001, 0.2404300,-0.01465179