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There are three cameras in place for various monitoring at Anderson Mesa. Each of them is implemented with slightly different hardware and methods. However, all of the have one things in common: very inexpensive and relatively easy to implement.
(1) Day sky monitor.
This is the simplest of all the cameras. The camera is a D-Link DCS-1000 and is a self-contained video camera and web server. A good mail-order price for this camera is about $200. The stock lens is a 6mm C-mount video lens and provides a "normal" field of view of about 45 degree. In practice, this field is a little small for watching the sky. In March 2003 I expect to replace this lens with one having a shorter focal length (either 2.8mm or 4mm). Since this camera does not have any iris or focus controls, you can buy the cheapest lenses around. Extra lenses run about $20-40.
The camera is located inside the 42" telescope dome just inside a north-west facing window. The camera is not meant to be used outdoors and must be protected from the elements. The only thing it needs is power and a network connection. It can use DHCP but I have chosen to use a fixed IP address to simplify. The camera is capable of providing streaming video across the internet. However, I find that this operation interferes with the regular sampling of images that I use in other ways so this operation is not encouraged. Instead, I use a built in feature that will cause the camera to periodically upload an image to a computer on the network. These images are collected every 2 minutes and are managed, archived and served by the other computers on the network. Getting to the point of taking images and savingg them is a matter of minutes after getting it out of the box. The management of the data takes a bit more effort but isn't too bad. The images are filed on a day-by-day basis by a Perl script that runs once a day. Other Perl scripts allow looking at an animation loop one day at a time or just for the most recent two hours. The data rate from this camera is about 1.6Mb/day.
(2) Night sky monitor.
The goal of the night sky camera is to provide information about clouds at night, even when there is no moonlight. To accomplish this, I use a Watec 903K b/w video camera. (User "manual": page1, page2-3, page4.) It is a 1/3" CMOS CCD detector with a minimum lux rating of 0.0002 lux. In comparison, the day sky camera only works down to 2.5 lux. This camera is a stand-alone video camera that provides NTSC video and does not come with a lens. It costs about $360. It's quite small and lightweight and can be put into some pretty tight spaces if needed. To grab the video, I use a Hauppauge WinTV-GO card that I put into an old surplus Pentium 200Mhz computer. I installed RedHat 7.3 on the Pentium machine. This version has built in support for the WinTV card (bttv driver).
To collect the images, I started with a simple software package, mvc, which stands for motion video capture (I think). Originally, this software looks at the video image and saves an file when it sees a change. The program is quite small and simple lending itself quite nicely to modification. So, I took this program and ripped out the motion detection stuff and set it up to collect an image at some desired interval. For now, I use an interval of 60 seconds between images.
The default setup of the Watec camera is with automatic electronic shutter control, hi-AGC on, and AGC on (AGC = automatic gain control). The camera is mated to a Computar HG3808AFCS-HSP video-mode auto-iris lens, focal length 3.8mm, max aperture is f/0.8. The lens settings are set to full average brightness control. At night, the natural signal from the camera with the moon down does not yield a very useful image though it's not bad once you have illumination from the Moon.
To get enhanced night-time sensitivity the program coaddas 200 individual video frames and then subtracts a pre-determined dark/bias image. I estimated that this process increases the sensitivity by a factor of 10. After averaging, the gain can be turned up on the collected image giving rise to an image that can detect a cloud-free sky image with no moon light. If there is high cirrus that is darker than sky it can be seen in sillouette. The program also has some automatic gain logic built in that will keep the image in range even on brighter nights. This automatic gain algorithm combined with the auto-iris lens is so effective that it nearly eliminates the seam between night time mode (coadding, higher gain) and day time mode (single frame). Thus this camera can provide sky imaging information all day long.
(3) 31" Telescope monitor.
This camera is positioned on the wall of the dome looking at the telescope. It provides essential remote viewing of the telescope and dome which is essential during the robotic observing and especially when debugging failures. The camera is a stock CCTV camera and provides a remote feed to the control room. The signal has been split off and is also sent to a surplus Pentium computer running RedHat 7.2 and a WinTv card. This system runs the mvc program without modification (yet) and collects images when the scene changes. The cost of implementation of this system was basically just the $50 for the WinTV card. The camera was already present for other reasons and the computer was a throw-away.
Last updated 2003 Apr 2, 11:38pm MST
Marc W. Buie, Lowell Observatory