This answer to Is there really microfilm on the Moon? includes a block quote which includes the following subquote:
The equipment was installed in the service module and consisted of a coherent synthetic aperature radar, the associated antennas, and an optical recorder. The radar system operated in the two RF bands of 5 megahertz (HF 1) and 15 megahertz (HF 2), or in the VHF band of 150 megahertz, and transmitted a series of swept frequency pulses. A small part of the pulse energy was reflected from the lunar surface and subsurface features and subsequently was detected by a receiver on the spacecraft. The radar video output from the receiver was recorded by the optical recorder on film, and the film cassette was retrieved during the transearth extravehicular activity.
Apollo Program Summary Report, section 3.3.4
SAR synthesizes a large aperture by capturing phase information from reflected radar signals from two different positions along a trajectory, then performing
interferometry target reconstruction1 computationally after the fact, which could be anything from milliseconds to years later.
- How can ICEYE-X1 capture 2D high resolution SAR images in "tens of seconds"?
- Detailed radar imaging of Tiangong-1; how do they do that?
- Parallel orbits around the Earth - effectively?
Another extreme example of a synthetic aperture (though not radar) is when radio telescopes record phase information from signals from a black hole onto hard drives, then fly boxes of hard drives to a single location for interferometry afterwards. (cf. Astronomy SE: 1, 2, 3, 4, 5, 6, 7)
However this is Apollo 17 and the recording medium is photographic emulsion!
Question: How (the heck) was coherent synthetic aperture radar (SAR) implemented using photographic emulsion for the Apollo 17 mission? How did they record and later recover phase information and reconstruct radar topographic data using interferometry from a piece of film?
1See @TheoH's excellent answer, which begins:
Synthetic Aperture Radar does not involve interferometry. As such, it is unrelated to aperture synthesis techniques in radio astronomy. (The question mentions interferometry and perhaps this should be corrected)