Is this process meant to capture all modes in the waveform or is this simply a method of identifying the ground return?
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Sorry for the delay, we needed to get direction from the GEDI Science team on this, fowwlowing is their response:
The two data layers that you have indicated, “num_detectedmodes” and “selected_mode”, are only part of the bigger picture here. The “num_detectedmodes” layer is simply a count of how many modes were detected in the rxwaveform by a specific algorithm. The “selected_mode” layer contains the index location of the lowest non-noise mode within the rx_modelocs/rx_modeamps/rx_modewidths arrays which are located within each of the “rx_processing_a<n>” subgroups. Each granule contains multiple “rx_processing_a<n>” subgroups in each beam where “<n>” represents the algorithm settings used to interpret the rxwaveform. To determine which “rx_processing_a<n>” subgroup the “selected_mode” and “num_detectedmodes” refer to, use the “selected_algorithm” data layer which will indicate which algorithm detected the lowest non-noise mode. For more information on “selected_mode” layer see section 4.3.6 in the GEDI L2A Algorithm Theoretical Basis Document.
Generally, the mode indicated in “selected_mode” is going to be the lowest (rightmost) mode within the rxwaveform but can be different after further processing. If the selected mode is not the lowest mode, a flag for the reason for why that mode was selected can be found in the “selected_mode_flag” layer. The explanation of the flags contained within “selected_mode_flag” can be found in Table 6 in the GEDI L2A Algorithm Theoretical Basis Document.
While all modes within the waveform as determined by each algorithm are captured in these data, the “selected_mode” and “selected_algorithm” can be used to indicate what the lowest non-noise mode is within the rxwaveform. A thorough read of the GEDI L2A Algorithm Theoretical Basis Document is recommended for more details on how these data layers, in combination with other data layers, are used to determine the ground return.