HRCAM: the high resolution all-sky camera
HRCAM (High
Resolution CAMera) is a digital SLR
camera (Canon EOS 50D; 15 megapixels) equipped with a fish-eye lens
(Sigma 4.5-mm f/2.8) for all-sky coverage on a 1.6 crop sensor. It was
first installed in PLATO at Dome A during January 2010. It takes
images of the sky above Dome A every few minutes for the purpose of
determining the cloud cover, sky brightness, sky transparency, and
aurora distribution. It is complimentary in many ways to Gattini, although it doesn't employ the
accurately known astronomical filters that Gattini uses, nor can it
see as deeply. On the positive side it is capable of imaging clouds
when the sun is up.
An HRCAM image taken on 27 January 2010, just as the Chinese expedition
was leaving Dome A. You can see a tractor and five or so sleds at bottom left.
The "clouds" at bottom left and top right are tractor exhausts. Snodar is visible at the top, various aerials and towers are visible on the left. The image reaches the horizon in all directions.
An enlargement of one section of the above image, demonstrating the resolution of the camera and lens, even at the extreme edge of the field.
The HRCAM instrument. The fish-eye lens is flush with the top, and
does not have a window. The reflective metal cover is designed to
shed snow, and have low emissivity so that it can be heated
efficiently. The holes on the bottom left are for a dehumidifying
system. The single Milspec connector provides 24VDC power and a
100Mbps LAN connection. The enclosure includes an ARM-based computer
running Linux. The camera is controlled via a USB connection using
gphoto2. The instrument is designed to operate down to -80C. The raw
images are stored on an array of four 500GB spinning hard-disks inside
PLATO. Exposure times vary from 1/2000th of a second to 120 seconds
depending on the sky brightness, and are automatically set by the
software. Thumbnail images (20kB in size) are sent back via PLATO's
Iridium satellite link. Our aim is to use the raw images to extract
quantitative information on sky brightness in the three camera
filters.
Contacts
Primary designer and constructor: Daniel Luong-Van
Principal Investigators: Daniel Luong-Van and Michael Ashley
Participating institutions in alphabetical order
|
University of New South Wales, Australia |