Friday, October 29, 2010
It's been a few months since we took the first infrared images with SOFIA and FORCAST. I promised some more detail on how we produced the "first light" images so here it is. Since people can't see infrared light we need a way to display the images from the camera using colors we can see. FORCAST records raw images through filters that pass infrared light of different wavelengths. These filters work just like red, green, or blue filters do in visibile light. When a computer displays a digital image it can be with any color map. A color map is a list of the colors the computer uses when it displays pixels of different brightness in an image. One of the simplest looking color maps is "gray scale"; shades of gray indicate brightness usually with white being brightest and black indicating faintest. But a color map can display brightness variations in an image in any color you like. Here's and image of Jupiter in visible light (color image at right) and in infrared light displayed with a blue color map:
For the first light image of Jupiter we used a red color map to represent infrared light recorded through a 37 micron filter, green to represent infrared light recorded through a 24 micron filter, and blue to represent 5.4 micron light. Here's the result:
Now we add the three images together to get a "false color" image of what Jupiter might look like if humans could see infrared (see www.ithaca.edu/frequent_flyer/first_light/ for more details on interpreting false color images). Note that false color images can represent any measurable quantity. Perhaps the most common false color image you have likely seen is a radar weather map of precipitation, which uses visible colors to represent reflectivity of radar waves (also a form of light that humans can't see) off of rain droplets. Our false color image displays infrared brightness at three different wavelengths. Here's the final result that USRA/FORCAST team member Jim De Buizer created:
The smaller dots in this image are three of Jupiter's moons. Note that we usually measure wavelength in microns (thousandths of a millimeter). We use the symbol 'µm' for microns so 5.4 µm is 0.0054 millimeters. For comparison, the average human hair diameter is about 50 µm.
We're back in Palmdale preparing for more SOFIA flights. We'll do two flights of telescope tests followed by three flights doing new astronomical observations! More updates coming soon.