| FUB/Wew Water Processor Op |
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The FUB/WeW Water Processor Op makes use of MERIS Level-1b TOA radiances in the bands 1-7, 9-10 and 12-14 to retrieve the following case II water properties and atmospheric properties above case II waters :
The retrieval is based on four separate artificial neural networks which were trained on the basis of the results of extensive radiative transfer simulations with the MOMO code by taking varying atmospheric and oceanic conditions into account. All networks were validated against in-situ measurements.
During the Plugin processing the MERIS Level-1b data are masked prior to the retrival by applying the following combination mask :
The masked pixel's values are set to 5.
Non-masked pixels are then normalized for an atmosphere's ozone contents of 344 Dobson units by calculating transmission correction factors.
Notice that the AOT wavelengths 440, 670 and 870 nm correspond to the AERONET data wavelengths for a convenient direct comparison with in situ data.
Each pixel is checked against the input and output values margin of the trained networks. Additional flags are set in case of a neural network failure for input and output separately.
The radiative transfer simulation code and the retrieval algorithm are described in detail in the papers cited in the references section below. We would like to stress the fact that the operator is applicable over case II only, thus it is likely to fail over the open ocean by producing negative remote sensing (RS) water-leaving reflectances.
The FUB/WeW water processor op can be invoked from the VISAT tool menu by selecting
the FUB/WeW WATER Processor Op (MERIS) command. On the command line the FUB/WeW water processor op is
available by means of the Graph Processing Tool gpt which is located in the BEAM bin
directory. Typing gpt FUB.Water -h displays further information.
Selecting the FUB/WeW WATER Processor Op (MERIS) command from the VISAT tool menu pops up the following dialog:
Source product: Here the user specifies the 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.
Name: Used to specify the name of the target product.
Save as: Used 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 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.
Run Creates the target product. The FUB/WeW water processing is actually deferred until its band data are accessed, either by writing the product to a file or by viewing its band data. When the Save as option is checked, the processing is triggered automatically.
Close Closes the dialog.
File The entries found in this menu allow to save the current processing parameters to disk and to open a saved parameter set from disk.
Help Displays this help page.
Fischer J., and Grassl H., "Radiative transfer in an atmosphere-ocean system: an azimuthally dependent matrixoperator approach", Applied Optics, 23, 1032-1039, 1984.
Fell F., and Fischer J., "Numerical simulation of the light field in the atmosphere-ocean system using the matrixoperator method", Journal of Quantitative Spectroscopy & Radiative Transfer, 69, 351-388, 2001.
Schroeder Th., Schaale M., Fell F. and Fischer J., "Atmospheric correction algorithm for MERIS data: A neural network approach", In: Proceedings of the Ocean Optics XVI Conference, Santa Fe, New Mexico, USA, published on CD ROM, 2002.
Schroeder Th., Fischer J., Schaale M. and Fell F., "Artificial neural network based atmospheric correction algorithm: Application to MERIS data", In: P roceedings of the International Society for Optical Engineering (SPIE), Vol. 4892, Hangzhou, China, 2002.
Schroeder Th., and Fischer J., "Atmospheric correction of MERIS imagery above case-2 waters", In: Proceedings of the 2003 MERIS User Workshop, ESA ESRIN, Frascati, Italy, 2003.
Schroeder, Th., "Fernerkundung von Wasserinhaltsstoffen in Kuestengeweassern mit MERIS unter Anwendung expliziter und impliziter Atmosphaerenkorrektur- verfahren", Ph.D. Dissertation, Freie Universitatet Berlin, Berlin (Germany), 2005, http:/www.diss.fu-berlin.de/2005/78