Pre-Processing and Pixel Classification

Pre-Processing and Pixel Classification

I/O Parameters

Selecting the CoastColour Processors (MERIS)... entry from the VISAT 'Processing --> Thematic Water Processing' sub-menu opens another sub-menu with the three entries 'Pre-Processing and Pixel Classification...', 'Atmospheric Correction...', and 'In-Water Processing...'. Selecting 'Pre-Processing and Pixel Classification...' from this sub-menu pops up the 'Pre-Processing and Pixel Classification' dialog:

Coastcolour L1P Processing Dialog

Source Products

MERIS L1B product: Here the user specifies the MERIS L1b source product. The combo box presents a list of all products open in VISAT. 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: Used to specify the name of the target product.

Save to: Used to specify whether the target product should be saved to the file system. The combo box presents a list of file formats, currently BEAM-DIMAP, GeoTIFF, and HDF5.

Open in VISAT: Used to specify whether the target product should be opened in VISAT. When the the target product is not saved, it is opened in VISAT automatically.

Processing Parameters

Selecting the Processing Parameters tab in the 'Pre-Processing and Pixel Classification' dialog switches to the following view:

Coastcolour L1P Processing Parameters

Parameters

Perform ICOL correction: This checkbox indicates if the ICOL adjacency effect correction shall in addition be applied on the input radiances. NOTE: This additional step becomes very time- and memory-consuming with increasing product size! We would recommend not to run the ICOL step within CoastColour processing for products larger than about 1000x1000 pixel. In that case, the ICOL standalone processor should instead be used with an L1P product as input. For this puropse, please install ICOL through the BEAM Module Manager (see [L1P-1]). However, this still might be slow. In any case, we would recommend, if possible, to generate product subsets with the BEAM product sub-setting tool (see [L1P-2]) before running ICOL.

Perform re-calibration: This checkbox indicates if the correction from MERIS 2nd to 3rd reprocessing quality shall be applied.

Perform Smile-effect correction: This checkbox indicates if the MERIS Smile-effect correction shall be applied.

Perform equalization: This checkbox indicates if the detector-to-detector systematic radiometric differences in MERIS L1b data products shall be removed.

Check for sea/lake ice also outside sea ice climatology area: This checkbox indicates if the algorithm checks for sea/lake ice also outside the sea ice climatology area.

Width of cloud buffer (# of pixels): This value is the width of a cloud 'safety buffer' around a pixel which was classified as cloudy.

Write Cloud Probability Feature Value to the CC L1P target product: This checkbox indicates if the Cloud Probability Feature Value shall be written to the target product. This value is a floating point number in the interval [1.0, 2.0] describing the increasing probability of a pixel being cloudy (1.0 = certainly clear, 2.0 = certainly cloudy).

Width of cloud buffer (# of pixels): This value is the width of a cloud 'safety buffer' around a pixel which was classified as cloudy.

Cloud screening 'ambiguous' threshold: This value is the threshold of Cloud Probability Feature Value above which a cloud is regarded as still ambiguous.

Cloud screening 'sure' threshold: This value is the threshold of Cloud Probability Feature Value above which a cloud is regarded as sure.


Flag Codings

MERIS L1B source product

The 'l1_flags' band in the MERIS L1B source product has the standard coding as shown below:

File Menu

CC L1P target product

The CC L1P target product provides an additional flag band 'l1p_flags' with a coding as shown below:

File Menu

Menu Bar

'File' Menu

Selecting the File entry in the Menu Bar opens the following view:

File Menu

Open Parameters...: When this entry is selected, an 'Open File' dialog will appear. Here, a BEAM GPF parameters XML file can be selected, containing 'Pre-Processing and Pixel Classification' parameters which were saved earlier. These parameters will be loaded and applied for an upcoming processing.

Save Parameters...: When this entry is selected, a 'Save File' dialog will appear. Here, the current set of 'Pre-Processing and Pixel Classification' parameters can be saved into a BEAM GPF parameters XML file for later re-usage.

Display Parameters...: When this entry is selected, the current set of 'Pre-Processing and Pixel Classification' parameters will be displayed in XML format (see below).

L1P File Menu Display Parms

'Help' Menu

Selecting the Help entry in the Menu Bar opens the following view:

Help Menu

Help: When this entry is selected, this online help is opened in a separate window.

About...: When this entry is selected, an 'About' dialog for the current processor is opened (see below).

L1P Help Menu About

Button Group

Button Group

Run: When this button is clicked, the processing will be started with the selected parameters.

Close: When this button is clicked, the processor tool window will be closed.



Processing from Command Line

Since the CoastColour processors make use of the BEAM graph processing framework, they can be used also with the 'gpt' command line tool outside BEAM-VISAT. The graph processing is invoked by the command
To obtain general help on the graph processing, use the command
Specific help on the 'Pre-Processing and Pixel Classification' can be obtained with
Information on the usage and a list of all available parameters are given.

CC L1P parameters




The processing from the command line can also be invoked using graph XML files. For example, a CoastColour pre-processing and pixel classification could be started with
with a MERIS L1b input file 'MER_cc_l1b_test.dim' (given in BEAM Dimap format) in the current directory, and a graph XML file 'test_cc_l1p.xml' in the XML format as shown in the figure above.

References

[L1P-1] BEAM Module Manager Help Documentation: www.brockmann-consult.de/beam/doc/help/visat/ModuleManager.html

[L1P-2] BEAM Product Subsetting Help Documentation: www.brockmann-consult.de/beam/doc/help/visat/ProductSubsetDialog.html