In March, MCST began gradually implementing several calibration algorithm improvements into the Terra and Aqua MODIS Collection 6.1 Level 1B products for the reflective solar bands. The algorithm changes, which were previously developed and tested for the upcoming Collection 7 L1B reprocess, will improve the accuracy and stability of the MODIS reflectance and radiance products going forward. The changes began to be included in the Aqua v220.127.116.11 and Terra v18.104.22.168 LUTs and will be gradually phased in over about the next three months for Aqua and one year for Terra. The impact of these changes on the C6.1 L1B reflectance will be largest for the Terra VIS and SWIR bands. For details on the Collection 7 RSB algorithms, see https://mcst.gsfc.nasa.gov/content/collection-7.