[libertyhouse]

The U-2 is the only U.S. surveillance aircraft still flying a "wet film" camera called the Optical Bar Camera, or OBC. Ironically, this relatively old technology keeps the U-2 mission from being completely transitioned to other aircraft like Global Hawk, due to the film imagery being easily releasable and able to be declassified.

Around 2007, a PC-104 embedded computer running Linux was integrated into the OBC camera to allow correlation of flight data with the imagery, as well as supply an OBC camera status page on the cockpit multi-function display.

[sorenjan]

Why is film easier to declassify and release than digital imagery?

[kilo_bravo_3]

Film's properties are known and understood and there aren't any "super films" that are better or more capable than another country's. Lenses are also understood.

With electro-optical (EO) sensors, great care must be taken to reduce the quality of the final product when it is publicly released so that adversaries do not gain a complete understanding of the what the sensors are capable of.

Film creates "better" images, but modern EO sensors are more capable in certain circumstances.

There is all kinds of computational and electronic trickery one can do to obtain images that may be impossible to capture on film that you want to keep secret, like fusing short wavelength IR with visible light or using it to discipline visible light to correct or reduce atmospheric distortion. Other EO technologies can determine what an object is made of from great distances.

Technologies like that you want to keep secret.

In a hypothetical Cuban Missile Crisis set in 2019, US analysts would have visible, near- and short wavelength-infrared, thermal, and pan-chromatic imagery to look at, but the 2019 version of Adlai Stevenson would still only show the visible images at the UN.

[dsfyu404ed]

Less opportunity for sigint types to deduce information about the image source from the images and less opportunity for reversing whatever algorithm/processes were used to reduce quality (in order to make a "releasable" copy) in order to re-create that information.

[libertyhouse]

I probably shouldn't have said it's "easier" to declassify. It's more of simply being a matter of deciding that the NIIRS (basically resolution) rating of the imagery from the OBC is low enough relative to other sensors and collection platforms that it won't provide much of an advantage to an adversary.

The embedded Linux system that was added to the OBC also provided a continuously variable Velocity over Height (V/H) control that allowed the OBC to collect imagery at lower altitudes than what it was originally designed for. This improves the quality of the imagery but at a lower area coverage rate as a tradeoff.

Film from the OBC is digitzed, ortho-rectified, and exploited as soft-copy. Back in the day it was done on mechanical light tables.

A good video that shows some of the film and other details is located here: https://www.youtube.com/watch?v=uemrNDEWgzA