Forel-Ule Algorithm For True Color Classification |

## User Interface

FU classification can be invoked from the menu by selecting Optical -> Thematic Water Processing-> FU classification.

#### Source Product Group

Source product: Here the user specifies the source product reflectance. The combo box presents a list of all products opened in the application. The user may select one of these or, by clicking on the button next to the combo box, choose a product from the file system.

#### Target Product Group

Name: to specify the name of the target product.
Save as: checkbox to specify whether the target product should be saved to the file system. The combo box presents a list of available file formats. The text field or the button next to it allow to specify a target directory.
Open in SNAP: Used to specify whether the target product should be opened in the application. When the target product is not saved, it is opened automatically.

#### Processing Parameters Panel

Copy all source bands:
Checking this option, will copy all the source bands to the target product.

Multiply input reflectance with PI:
Checking this option will multiply the reflectance with PI.

Valid pixel expression:
This expression is used to validate pixels. Only valid pixels will be considerd for processing. If no expression is specified the first applicable expression for the input product will be applied as in Valid expressions. If the expression is set to TRUE, then all pixels are considered to be valid. The ellipsis-button can be used to create a valid expression.

Default valid expressions

OLCI | WQSF_lsb.WATER and not WQSF_lsb.CLOUD
LQSF_WATER
S2A_MSI | TRUE
S2B_MSI | TRUE
MERIS | l2_flags.WATER
not l1p_flags.CC_LAND and not l1p_flags.CC_CLOUD
NOT l1_flags.LAND_OCEAN
MODIS, SEAWIFS, CZCS | not l2_flags.LAND and not l2_flags.CLDICE
MODIS500 | TRUE

Reflectance band name pattern:
The used reflectance band names must match the given pattern. Useful, if there is more then one spectrum in the product. Here a regular expression can be used. There is a nice tutorial on
.

Example expressions:

Rrs.* | Will match any name witch starts with 'Rrs'. E.g.: Rrs_04
reflec_\d\d_band | Will match any name witch starts with 'reflec_' and ends with '_band'. in the middle must be two digits. E.g.: reflec_12_band

Instrument:
Allows to select which instrument specific settings shall be used, if the auto detection fails.

Include dominant wavelength:
Whether or not to compute and include the dominant wavelength in the output. The default value is "false".
A laser emits light at just one wavelength. When this pure light is observed by the human eye we can calculate the chromaticity coordinates and the hue angle in the x-y diagram. The wavelength is called the "dominant wavelength" and is positioned on the locus, the outer boundary in the x-y diagram that can be observed.
The conversion from the hue angle to the dominant wavelength is done by a look-up-table.

Include intermediate results in output:
Whether or not the intermediate results shall be written to the target output. The default value is "true".
Intermediate results are results which are calculated during the computation of the hue angle. The following bands belong to the intermediate results:
X3, Y3, Z3, chrX, chrY, hue_band, poly_corr