These images were rendered on a detailed software emulation of the Stargazer Image Generator which I helped to design in the late 1980's.
Each image took about an hour to draw on an SGI personal IRIS because it was a very detailed emulation of the prototype Stargazer hardware. These are scans of photographs of the image because no digital images from that project still exist.
The frigate on the seascape image is the "Bremen" and was modelled by Dan Jaquish, the helicopter in both shots is an AH1W and was modelled by Howard Hanna. Dan also did the ocean (which is a single polygon with bump mapping, per pixel lighting, shadow mapping, etc) and the snowscape. The land in the Bremen image and in the agricultural image was constructed from a height field of the Isle of Wight and textured with a mixture of photo texture and hand-painted maps the trees and hedgerows were automatically generated onto the dark areas in the texture map.
The snowscape image has individual trees going all the way out to the horizon - but through a clever collection of trickery, it manages to stay within the hard 8,000 polygon limit that Stargazer imposed.
Stargazer (if it had been completed) would have rendered images like this at 60Hz. Fairly remarkable for the late 1980's!