The optical resolution is very good, and was first publicly revealed in Jane’s Defense Weekly of August 1984. Normally, oblique look angles through the atmosphere would be greatly degraded, but apparently they use adaptive optics to compensate. These images do not represent the true capability but hint at what’s possible:
http://oi53.tinypic.com/141lcvt.jpg
http://oi53.tinypic.com/205b8t0.jpg
Although fictional depictions often present similar resolution in the infrared spectrum, two items in basic physics place severe limits on this.
(1) Atmospheric water vapor strongly absorbs IR except in a few windows around 3-5 microns and 8-12 microns:
(2) Those wavelengths are much longer than 390nm to 700nm visible light. For a given diameter optic, angular resolution is inversely proportional to wavelength, based on Dawes’ Limit. We can calculate the theoretical linear resolution of a KH-11 recon satellite (2.4 meter mirror) in 500nm visible light, 5 micron IR and 12 micron IR at an orbital altitude of 150 statute miles.
We first determine the angular resolution then convert that to linear resolution:
Angular resolution is from Dawes’ Limit: Dawes' limit - Wikipedia
Angular resolution formula:
a = 250000 x W / d, where:
a = angular resolution in arc seconds
W = light wavelength in meters
d = telescope diameter in meters
Visible Light angular resolution:
a = 250000 x 500E-9 / 2.4 meters (KH-11 mirror size)
a = .05208 arc seconds
5 micron IR angular resolution:
a = 250000 x 5000E-9 / 2.4
a = 0.5208 arc seconds
12 micron IR angular resolution:
a = 250000 x 12000E-9 / 2.4
a = 1.25 arc seconds
Linear resolution formula:
s = tan (a) x d, where:
s = linear resolution in units determined by d
a = angular resolution in degrees
d = distance to object
Linear resolution at 150 mi altitude using 2.4m mirror and 500 nm visible light:
s = tan (1/(3600/.05)) x 150 miles x 5280 feet per mile
s = 0.192 ft resolution using 500 nm visible light
Linear resolution at 150 mi altitude using 2.4m mirror and 5 micron IR:
s = tan (1/(3600/.52)) x 150 miles x 5280 feet per mile
s = 2 ft resolution using 5 micron IR
Linear resolution at 150 mi altitude using 2.4m mirror and 12 micron IR:
s = tan (1/(3600/1.25)) x 150 miles x 5280 feet per mile
s = 2 ft resolution using 5 micron IR
s = 4.8 ft resolution using 12 micron IR
So with IR, the image will be very blurry – even if the detector sensitivity and other sources of thermal noise permitted full use of this theoretical capability.
In recent years, with the advent of mobile devices, cell phones, cordless phones, microwave data links, etc. electronic surveillance is as important as optical. According to the book Body of Secrets by James Bamford, the Magnum/Orion class of electronic intelligence satellites use gigantic parabolic antennas 160 feet in diameter to pick up signals:
http://www.globalsecurity.org/jhtml/jframe.html#http://www.globalsecurity.org/space/systems/images/sigintmagnumorion.jpg|||