ACRIST Tools

• How do I start the MEGS prototype?
• Is there a description of the MERIS products?
• What is the pixel-to-pixel mode?
• What are the different options of the Level 2 MEGS prototype?
• What is a modifier?
• What is the meaning of the switch to force l2 classification used in the modifiers?
• Which environment variables may modify MEGS behaviour?
• What is the procedure to perform a only-atmospheric simulation?
• What is the procedure to perform a only-ocean processing simulation?
• When I perform a MEGS simulation using the pixel-to-pixel mode, what are the breakpoints available in the forward model?
• I would like to create a MEGS Level 2 simulation w/ a given geometry (a given sun zenith angle for example), what do I need to do?
• Is there a way to visualize a MEGS product without going through a simulation of the MEGS interface ?
• How do I use the batch mode from MEGS or MERSS to have my simulations executed at a specific time ?

- check if a display is available for MEGS windows

echo $DISPLAY (answer should be something like host:0, host being your computer's name)
if not, you must set it (ex: export DISPLAY=pim37.0 under bash or ksh)

cd /megs/megs.major.minor (ex: /megs/megs.4.1)

there is no need to append '&' to the command.

The full description of all auxiliary products, and L1/L2 products may be found in the IODD (Input/Output Data Definition) document.

The compilation switch -D_PIXEL_TEST determines how the program operates :

  - if NOT set, the processor runs from a L1B product, block by block.

    The three steps of the L2 processing are in turn applied to each block, depending on the command line option -s<value>
    This mode is the nominal mode of the prototype when run from the GUI.

    The sequence is selected by the user with the command line option -s<value>
    The parameters of each pixel are read from stdin before processing by the routine getUserParam and written to stdout after processing

There are two options to the level 2 MEGS prototype :

-h displays the usage message on the standart output ;

-s followed immediatly by a number (for example -s0 or -s10) given between 0 and 11
specifies the mode in which the prototype is to be operated :

0: all steps are processed
1-3: step 1-3 only is processed
4-10: pixel by pixel test modes with the following processing
4  : confidence only
5  : ocean proc only
6  : water + land atmospheric corr
7  : water + land atmospheric corr + ocean proc
8  : confidence+water+land atmospheric corr
9  : cloud processing only
10  : water-vapour processing only
11  : TOAVI processing only
12 : simulation de bout en bout a partir de la reflectance TOA
le format d'entree est le meme que pour le mode -s0 (simulation de bout en
bout), en remplacant les 16 radiances par 16 reflectances.
13 : classification et corrections atmosphériques, a partir de la
radiance TOA
le format d'entree est le meme que pour le mode -s0.
14 : classification et corrections atmosphériques, a partir de la
réflectance TOA
le format d'entree est le meme que pour le mode -s0, en remplacant les 16
radiances par 16 reflectances.
input file templates for the MEGS prototype used in pixel-to-pixel modes are stored under /megs_test/validation/templates.

• -1 : the switch is ignored and each modulus is disactivated/activated depending on pixel values ;
•  0 : the concerned modulus is systematically disactivated (i.e. if the land classification switch is set to 0, the prototype will never go through the land modulus) ;
•  1 : the concerned modulus is systematically activated.

• MEGS_HOME : if set AND exported, give the MEGS home location used to read products description.

Ex: export MEGS_HOME=/megs/megs.4.0 (bash or ksh) will enable further MEGS executions to use 4.0 version databases definitions, while accessing currently launched MEGS folders/simulations.
To get rid of this variable, one may type unset MEGS_HOME
This feature is present in all MEGS versions binaries.
• DATABASE_BINHDR : if set to any value and exported, instructs MEGS that the databases files have (old) binary headers. MEGS 4.1 is the first version using ascii headers, this variable should be set if MEGS_HOME points to an older version of MEGS.

Ex: export DATABASE_BINHDR=y (bash or ksh). CAUTION: export DATABASE_BINHDR=n will have exactly the same meaning, as only the presence of this environment variable is significant.
This feature is only present in the binaries of MEGS versions >= 4.1 . Older versions cannot handle ascii headers.
• DATABASE_DIR : this variable should generally stay unset. It gives the location of the directory containing the products formats definition files, like database.db or index*.txa. By default (if unset), this location is computed as $MEGS_HOME/resources/databases. One may use this variable in rare cases, when the same interface version must use both original and new test databases formats.

Ex: export DATABASE_DIR=/megs_aux/testing/databases (bash or ksh).
This feature is only present in the binaries of MEGS versions >= 4.1 .
 
• NO_LOCK : this variable should stay UNSET unless you know exactly what you are doing. If you set this variable,  it disable the locking

mechanism in data_base

• Start MERSS and go under the geometrie folder.
• Copy any simulation to create your own geometry simulation.
• Change the values of the following modifiers to tailor your MERIS image to cover your zone of interest :

          to check the location of your simulation, validate it and a pop-up window will show with infos on your simulation.

• Validate your simulation.
• Execute your simulation (you can abort it after the geometry module where the geomap.iom file is created).
• Export the geometry into an ASCII file using the following command :

• Using the MomToMerss tool, create a MERSS ltmub radiance file with the ASCII geometry file you have just created and a previously created MOM file (that you may have generated with the TOAModel tool)..
• Import the ltmub file in MERSS.
• Execute the MERSS simulation using the ltmub file you have just created after having adjusted the im, id, ih, imn, is modifiers (month, day, hour, minute and seconds of the simulation) to have a simulation compatible with the geometry.
• Export the packets that you have just created with the MERSS simulator.
• Import those MERSS packets in the MEGS simulator.
• Execute a Level 1 MEGS simulation using those packets.
• Execute a level 2 MEGS simulation using the Level 1 product you have just created.

            /simul/users/pg/bin/megs4.1 filename will give you the analysis display that you have under the interface without starting MEGS.

The acri user is the only user authorized to execute simulations in a batch mode ; therefore, start the MEGS (or MERSS) interface after having logged in as the acri user. Then, from the window where you validate your simulation, pull down the execute menu and you will see a batch mode button. Click on this button to specify at which time you want to have your simulation be executed.