Automatic Geophysical Observatory (AGO) Imager:

The instrument developed for use in the AGOs is illustrated to the left. The camera is hermetically sealed under a dome (1) and a conventional all sky lens (2) is used to form a 3 inch intermediate image in the vicinity of a special interference filter (4). The filter has two narrow (~ 4 nm wide) passbands centered at 427.8 nm and 630 nm. The filter consists of a narrow-band interference element without blocking. The filter is located on the telecentric path of the lens (3) to ensure that the rays are as parallel with the optic axis as possible (given that the beam is at F/4). The intermediate image is re-imaged by lens groups (8) and (11) to form an image on the photo-cathode of the image intensifier (13). In collimated space between the two lenses (8) and (11), where the beams are less parallel, a set of blocking filters (9) are included which are constructed from two separate half filters. Each half filter selects and isolates one of the passbands of the narrowband filter. A prism (10) is included to bend each half image off the center of the image intensifier axis. Thus two images of the same sky are produced side by side on the image intensifier photocathode, which are separately filtered by the narrow band filters. The image intensifier (13) amplifies both images and the phosphor is re-imaged on the CCD (15) by the lens (14). The CCD electronics boards (16) provide the necessary signals to integrate the CCD for 8 seconds. This CCD signal is connected to the camera-controller electronics through connector (17) and the whole system is sealed in a hermetic container (18). The electronics consist of a single frame digital memory and a low power computer capable of compressing the images by a factor of 20 and transmitting them to the AGO data system. The domes are kept clear by wind scouring and perhaps benefit from waste heat which passes from the AGO through the camera port to the dome. Since the AGO station power is limited the camera has an average power consumption of less than 5 Watts. These cameras have worked reliably for several years in unattended, unmanned environments.

Further data from the Antarctic AGO's and other stations like South Pole, McMurdo, and Halley can be found at: