In the GOES-13 Visible channel, there seems to be a morning/afternoon asymmetry in the data. I'm wondering what might cause this.

In this example data, the morning is the lower branch, and the afternoon is the upper branch. The y-axis is the pixel level (0..255), the x-axis is the Sun's local altitude above the horizon. The location is the Gulf of St. Lawrence, on the east coast of Canada.

Latitude +46.94N, longitude -63.21W (not far from the center of the images below.)

GOES Visible Channel

Morning, 10am local time: Morning, 10am local time

Afternoon, 4pm local time: enter image description here

  • $\begingroup$ It is hard to say based only on this figure. It could be sun reflection of the water surface or difference in cloud water in the atmosphere. Could you include two visible snapshots - one from the morning and one from the afternoon? $\endgroup$ Sep 26, 2014 at 15:47
  • $\begingroup$ Changes made... $\endgroup$
    – John
    Sep 26, 2014 at 16:35
  • 2
    $\begingroup$ The difference is very subtle, around 2% based on the scatter above. I would recommend looking for the persistence of the behavior over a longer period of time (say, last month or so). If the amplitude of the difference varies from day to day, the effect could be atmospheric (water vapor/droplets). $\endgroup$ Sep 26, 2014 at 16:50

1 Answer 1


The absolute accuracy for GOES-13 visible channel is 5%, so 2% is well within the noise. http://noaasis.noaa.gov/NOAASIS/ml/imager.html


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