A massive quantity of historical intelligence satellite imagery from the KH-9 HEXAGON program is being declassified and will be made public in a series of releases that are scheduled over the coming year, intelligence community officials say.

Declassification of intelligence satellite imagery languished for years after President Clinton ordered the release of product from the Corona, Argon and Lanyard missions in the 1995 executive order 12951. Although the Clinton order also required the periodic review of imagery from other missions, that requirement was effectively ignored by intelligence agencies and neglected by congressional oversight.

But in a May 2010 memorandum Director of National Intelligence Dennis C. Blair ordered the “re-establishment” of the declassification review of intelligence imagery — though it had never been officially disestablished — with a particular focus on imagery from satellite systems that were deemed obsolete.

In January 2011, DNI James R. Clapper formally declared that the KH-9 HEXAGON program was obsolete, and that declassification review of all program imagery should therefore commence. KH-9 HEXAGON was operational from 1971 to 1984.

“The process to declassify imagery pursuant to EO 12951 began shortly after DNI Blair’s May 26, 2010 memorandum and has been ongoing, in earnest, with the goal of releasing as much imagery as possible to the public, consistent with national security,” said Michael G. Birmingham of the Office of the Director of National Intelligence. “Accordingly, The KH-9/HEXAGON system was declared obsolete in January 2011 and a phased declassification of its imagery has ensued.”

More than two years after the Blair memorandum, however, next to nothing has yet been made public.

“The notable challenges to this effort are the sheer volume of imagery and the logistics involved in cataloging the imagery and moving it to archive,” Mr. Birmingham told Secrecy News.

“For context, and to grasp the scope of the project, the KH-9/HEXAGON system provided coverage over hundreds of millions of square miles of territory during its 19 successful missions spanning 1971-1984. It is a daunting issue to address declassification of the program specifics associated with an obsolete system such as the KH-9, which involves the declassification of huge volumes of intelligence information gathered on thousands of targets worldwide during a 13 year time period.”

Daunting or not, the large bulk of the KH-9 imagery is expected to be released, with only perhaps 5% or so remaining classified.

“There is a schedule of multiple deliveries with final delivery of imagery scheduled for September 2013,” Mr. Birmingham said.