The Level 1B data set contains calibrated and geolocated at-aperture radiances generated from Level 1A sensor counts and GEO files. Details of the algorithm and file specification are available here. There are differences between the Level 1B produced and distributed by OBPG and the Standard Level 1B files produced by MODIS Calibration Support Team (MCST). This is because OBPG uses the Ocean subsetted Level 1A files as input to the Level 1B processing which necessitates code modifications.
OBPG Level 1B code:
Allows processing to proceed when the high-resolution 250-meter and 500-meter SDS fields are missing from the input Level-1A
Handles the extended counts in bands 10, 12, 13lo, and 16
The standard Level-1B format for 1-km data includes a pair of SDS fields for 250-meter and 500-meter that have been aggregated to 1-km. Since the Ocean Level-1A input does not include the high-resolution bands, these aggregated fields would normally be unfilled. The OBPG uses this free space to store the extended ocean band information from bands 10, 12, 13lo, and 16, as these high reflectance values will not fit into the standard scaled integer fields provided for the Level-1B reflectances (EV_1km_RefSB).
