Test in Japan (2007)
Taking Images and Enhancement of Dynamic Range
- An image taken by the camera consists of 8-bit data.
- The sensitive brightness range of the camera can be changed by setting the parameter ``BR''.
- Since the state of the whole sky/clouds does not significantly change in timescale of < 30 seconds, the effective dynamic range can be enhanced (to ~9.5-bit) by taking images successively with several different settings of the camera and then combining them (see below).
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Test Run at the Ibaraki Univ.
A student (W. Kimura) is setting up the camera on the rooftop of our university building
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From another angle
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Example of the images
- (1)-(7) in the below figure are the images with different settings of the paramete "BR". (see the figure caption below for the more detail). Each of them consists of 8-bit data. Note that bright area in the bottom-middle in each panel corresponds to the emission from the temperature standard.
- After applying some appropriate offset to each image, all of them combined into a single "averaged" image (the panel "Ave"). After masking the non-sky area, the value is converted into an emissivity map by using the value of the temperature standard, which is assumed to be blackbody (the panel "in \epsilon").
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Detailed explanation of the above figures
Raw data for every single time consist of 7 images with a different brightness parameter of the infrared camera ("BR" = -10,0,4,8,12,16,20). The parameter "BR" gets larger, the camera gets more sensitive to the difference in less bright regions. We used the image of "BR"=-10 (1) to determine the brightness level of the temperature standard, which is usually much brighter than the sky and clouds. Other six images (BR= 0 -- 20; (2)-(7)) are for the sky.
- Zipped Fits file of the above data is available.
- GIF animation; you can find clouds as well as the Sun...
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Calibration Curve
- We determine the calibration curve by taking images of stuffs with various temperatures (-10 to 60 deg Celsius); we used a high-temperature cavity blackbody for a higher temperature and a cold metallic cup with salty ice for a lower temperature.
- We found that the output after applying some appropriate offset to unify number count with different camera setting is quite propotional to the Planck function integrated over 8-12 micron, as shown below.
- We exploit the formula below when we derive the emissivity of the sky.
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