This ATBD documentation attached to the catalogues describes how MODIS operates in space and provides the equations implemented by the L1B software to generate the MODIS MOD02 (Terra) and MYD02 (Aqua) data products. It is a summary document that presents the formulae and error budgets used to transform MODIS DN to radiance and reflectance. It describes the current (Collection 6), post -launch MODIS
calibration process and supersedes previous ATBDs [Barker et al. (Version 1), 1994] [MCST
(Version 2), May 1997] [MCST (Version 3), December 14, 2005] Analysis of instrumental on-orbit performance by MCST and investigation of L1B products by the Science Team have resulted in several L1B software updates and improvements. This ATBD corresponds to the Version 6.0 Terra and Aqua software releases. Prior to 2006, the MCST and the Science Data Support Team (SDST) provided software deliveries to the Goddard Distributed Archive and Analysis Center (GDAAC). Subsequently, the MODIS Adaptive Processing System (MODAPS) assumed the data production role formerly under
taken by the GDAAC. Product files are currently distributed using the Level 1 and Atmosphere and Archive Distribution System

The MODIS Adaptive Processing System (MODAPS) is currently generating an improved Collection 6.1 (061) for all MODIS Level-1 (L1) and higher-level Level-2 (L2) & Level-3 (L3) Atmosphere Team products. This decision to create a new improved Collection 6.1 (061) was driven by the need to address a number of issues in the current Collection 6 (006) Level-1B (L1B) data. These L1B issues had a negative impact in varying degrees in downstream MODIS Atmosphere Level-2 (L2) and Level-3 (L3) products, which are more fully described below.

The MODIS Atmosphere Team decided to use this reprocessing opportunity to implement some science improvements in their L2 and L3 products. The documents below describe Collection 6.1 (061) changes to L1B as well as all impacted (or improved) L2 and L3 MODIS Atmosphere data. Collection 6.1 reprocessing began in late summer 2017; began to be publically released beginning on 15 October 2017; and is expected to be completed by early summer 2018.