I want to know the difference about TOA T1 and T2. Are they two repeating collections? I want to use the imagecollection (merge from Landsat TOA T1 and T2). How can i achieve it?
As stated in the Landsat website:
'The Collection definition consists of three categories: Tier 1, Tier 2, and Real-Time. Data in Tier 1 meet formal geometric and radiometric quality criteria. Tier 2 do not meet the Tier 1 criteria. The Real-Time Tier contains data immediately after acquisitions that use estimated parameters. Real-Time data are reprocessed and assessed for inclusion into Tier 1 or Tier 2 as soon as final parameters are available.'
you can try to use google earth engine to access and analyze any Landsat collection that you wish.