NO2 videos from a measurement at the Großkraftwerk Mannheim

<p>These three videos show image sequences recorded with an NO₂ camera based on gas correlation spectroscopy. The frame rate is 0.2 Hz and the resolution is 0.92 x 0.92 square meters (i.e. one pixel width and height corresponds to 0.92 meters).</p> <p>The measurement principle goes as follows:</p> <p>Two cameras are placed behind glas cells, one is empty and one is filled with a high column density of&nbsp;NO₂. If light is scattered into the two cameras and traverses&nbsp;<strong>no</strong>&nbsp;atmospheric NO₂ on its way, there will be a significant difference in measured intensity due to the attenuation in the cell filled with NO₂. Whereas, if light reaching the instrument traverses a bit of NO₂ in the atmosphere, it will arrive pre-attenuated and the cell will make a smaller difference. Thus, the (logarithmic) intensity ratio can be used as a measure for the atmospheric column density.</p> <p>The images show such ratios&nbsp;<span class="math-tex">\(\ln(I_2/I_1)\)</span>, where&nbsp;<span class="math-tex">\(I_2\)</span>&nbsp;and&nbsp;<span class="math-tex">\(I_1\)</span>&nbsp;are the intensities measured by the pixels of two imaging sensors. A reference image against the zenith sky and dark images and a signal offset are subtracted.</p> <p>The three videos show differently postprocessed versions of the image sequence:</p> <p>1. raw-video: Just the logarithmic intensity ratio as explained above.</p> <p>2. 4-video: The same, but with postprocessing applied in order to reduce the background signal. The top right shows the sequence with a broadband surface fit subtracted from each individual image. The bottom left shows the sequence with the time-minimum&nbsp;of each pixel subtracted. The bottom right shows the combination of both methods.</p> <p>3. corr-video: Just the bottom right sequence of 4-video.</p>