GONG ClassicMerge: Pipeline and Product
  A recent processing effort has been undertaken in order to extend the range-of-coverage of the GONG merged dopplergrams. The GONG-Classic-era observations have now been merged to provide, albeit at lower resolution, mrvzi data as far back as May of 1995. The contents of this document provide an overview of what these data look like, the processing steps used to generate them from the original site observations, and the outcomes of a few initial quality-assurance tests designed to validate the final merged images. Based on these tests, the GONG project is releasing this data product to the user community (http://nisp.nso.edu/data). 
Anna L. H. Hughes, Kiran Jain, Shukur Kholikov, and the NISP Solar   Interior Group (National Solar Observatory)
astro-ph.IM astro-ph.SR