Once defined the General Configuration of a LUT, the second step consists on introducing the Key Input Variables for the selected atmospheric RTM. A window will pop-up so that the user selects the file containing the LUT nodes distribution. Currently, two options are compatible with ALG: (1) a previously generated LUT in a .h5 file, or (2) an ascii .txt file containing the variables values in a tabulated matrix:
Once selected the file, ALG will open an alternative version of the Key Input Variables window:
When opening this step, ALG will automatically read the selected file and the key input variables associated to the selected RTM from the
RTMconf.xml file. In case of selecting a .h5 file, ALG will automatically associate the
variable names with the loaded LUT. However, this will be only possible when the selected RTM is the same as the LUT being loaded. Otherwise, the user must select the appropriate
variable names from the corresponding pop-up menu. Notice that all variables should be associated to a variable name/ID and cannot have an "unknown" name.
Note: Read the "Key Input Variables" sub-section of the selected Third-party Software (RTMs) for more
information about the key input variables.
Users have the options to remove one or more variables by selecting them and clicking the Remove button. Altenatively, users can add a new variable by pressing the Add variable button. In this last case, a new row will be added to the table with empty cells as values and an "unknown" variable ID. When the user will select a valid variable ID, the cells will automatically be filled with a random value between the minimum/maximum values defined in the RTMconf.xml file. Users can further edit the cell values clicking on a cell and introducing the desired values.
Users can further edit the existing LUT nodes by selecting a subset of the loaded nodes. From the pop-up menu in the Select subset panel, users can choose one of the two following options: (1) a selection of LUT nodes based on filtering the values by minimum/maximum boundaries or (2) select a random subset. For the first option, users will have to press the Apply button. A window will pop-up, where users can edit the minimum/maximum ranges of the various variables. After pressing the Save button the table will be updated removing those LUT nodes that are not within the specified boundaries.
For the second option, the user has to specify the percentage of the LUT size. In the figure below, 75% of the current LUT nodes will be randomly selected for the final LUT, removing the remaining 25%. Press the Apply button to apply the subset selection.
Once introduced all the input key variables names and edit the desired values, the user should click on the Next button at the bottom-left corner to proceed defining the spectral configuration of the LUT output atmospheric transfer functions. This will update the LUT configuration .xml file (e.g., C:\ALG\LUTs_folder\LUTfile.xml), storing these key input variables for their later use in the execution of the atmospheric RTMs and generation of input data.