What do the various levels of AMSR-E data represent?

The following table describes the different levels of AMSR-E data.

Level-0 Reconstructed, unprocessed instrument/payload data at full resolution; any and all communications artifacts, for example, synchronization frames, communications headers, and duplicate data removed.
Level-1A Reconstructed, unprocessed instrument data at full resolution, time-referenced, and annotated with ancillary information, including radiometric and geometric calibration coefficients and georeferencing parameters. For example, platform ephemeris computed and appended but not applied to the Level-0 data.
Level-1B Level-1A data that have been processed to sensor units. Not all instruments will have a Level-1B equivalent.
Level-2 Derived geophysical variables at the same resolution and location as the Level-1 source data.
Level-3 Derived geophysical variables mapped on uniform space-time grid scales, usually with some completeness and consistency.
Level-4 Model output or results from analyses of lower level data. For example, variables derived from multiple measurements.