Provenance
NPIC Photographic Interpretation Report PIR-024/77; declassified via the CIA FOIA Reading Room (CIA-RDP78T05162A000500010025-9). A work of the US government - public domain.
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By 1977 Soviet mobile troposcatter had spread far enough through the western military districts and the Groups of Forces that NPIC compiled a dedicated survey of it: Soviet Troposcatter Equipment Locations in Europe (TSR). This is the parent document that later imagery reporting kept updating; the October 1980 report on the network in Poland cites it by number.
It marks the shift in Western attention from the fixed Arctic trunk line of the 1960s to the mobile R-410 generation that NATO would meet in every exercise, crisis, and export customer of the 1980s: the equipment the interpreters called TWIN PLATE.
Source: CIA FOIA Reading Room (archived). Public domain as a US government work.