Hi all, We've had several comments lately about the difficulty of interpreting cloud camera images. The truth is, even those of us who work with it every night are having some difficulty. The instrument belongs to Sloan and therefore we (the ARC community) can't make changes to the hardware or the fundamental software, but Bill Ketzeback is working on a new image display that should be better for interpreting some sky conditions. That should be available very soon (perhaps within the week). In the meantime, Bill has added some more explanation to the main IRSC web page, and I thought a short message to the community might also help. I think the main source of confusion arises from the fact that the image display is actually a difference of the latest image minus a combination of several previous images. This helps to get rid of a number of stable, warm structures which otherwise would swamp out everything else: the trees, the domes, and the supports for the camera itself. This differencing also makes the camera much more sensitive to very thin clouds, so that it's easy to tell the difference between photometric and non-photometric skies. But when thicker clouds are present, the image gets confusing. The camera is configured so that white is warm and black is cold, but the differencing adds a layer of complexity: white on a difference image indicates a position where a cloud or other warm object is NOW, while black on a difference image indicates a position where a warm object used to be and is no longer. Grey on the difference image indicates no change: either an unchanging clear sky, or very thick, featureless overcast. Experience over the last few months has led us to believe that images with a standard deviation of less than 10 usually indicate photometric skies; but under some circumstances, extremely thick clouds can also produce a low standard deviation. When just a few clouds are around, their trails are easily visible on the cloud camera, and the direction and speed of their motion is apparent on a single image. Multiple clouds tend to make a messy image, and it's hard to judge the thickness of the clouds from the cloudcam. The next generation image, which will be available soon, is a raw IR image with the stable structures carefully masked off. The masking isn't perfect, so this approach is less sensitive to thin clouds; however, it should be much easier to judge the thickness and behavior of heaver clouds using the second image. The plan is to display both images side by side, for use in different circumstances. I hope this explanation is helpful to some of the folks who've been confused. Be on the lookout over the next few weeks or months for lots of useful stuff to be added to the web page, thanks to Bill. Russet. APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 658 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO