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I have downloaded a Sentinel-2 scene and there are some interesting rainbow like stripes trailing an airplane. This is an rgb image but the stripes are also visible on the other bands. You can tell it is an airplane stripe because there is a very clear airplane symbol in front of the stripes. What interests me is that there are more than two bands visible, although the airplane should only have two trailing stripes. So the airplane is in different positions on different bands.

Sentinel 2 screenshot

Sentinel 2 panchromatic image of band 4

Any idea how it is possible these airplane stripes could have been formed?

  • You may want to ask this on the Photography stackexchange site as well. – Dan C Dec 4 '17 at 18:17
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A few months ago I wrote a technical blog post (Planespotting) on intra-detector parallax effects in Sentinel-2 imagery, which can cause aircraft contrails to appear as rainbow stripes. The post also discusses inter-detector parallax effect and motion effects, which also can cause color shifts.

Here is a summary of intra-detector spectral band parallax:

  1. the Sentinel-2 detectors use a stripe filter to separate incoming light into distinct spectral channels,
  2. the angular separation of the channels requires the satellite to move in order to see the same point on the Earth's surface in multiple spectral channels, and
  3. the Sentinel-2 ground processing system uses the elevation of the ground to form the image, causing objects located above the ground surface (such as aircraft) to appear displaced when comparing different spectral channels.

Here is an illustration of the effect, courtesy of Don McCurdy:

Illustration of spectral band parallax

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  • Thank you for your answer. I was under the impression satellites used a set if prisms to distinguish the different channels and therefor only one image is taken per scene. I understand from your answer multiple images are needed to create one scene? – PythonStudent Dec 6 '17 at 12:17
  • See here the actual temporal offset between bands (Table 2): earth.esa.int/web/sentinel/technical-guides/sentinel-2-msi/… – iled Aug 20 '19 at 23:16
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What you're seeing here is simple light dispersion, as seen in a normal rainbow. White light (containing all wavelengths) refracts off of a curved surface such as a glass prism or a raindrop in a cloud, and the different wavelengths(B, G, R, IR, etc.) are bent and become visible at what appears to be different positions.

Trails from planes, called "Aerodynamic Contrails", display the same phenomenon. The pressure of the air passing over the fuselage apparently causes the temperature to drop, and in such a small area surrounded by warmth this causes moisture to condense in these cloud trails. The light disersion is in essence the same, then, as a rainbow seen in a rain shower.

This is an amazing picture though, as capturing these even with normal visible light photography on aircraft seems to be quite rare!

Update: You pointed out that the trails are different (the actual plane appears in different locations in the RGB image, in line with the corresponding color/band presumably). I believe that the effect really is the contrails and light dispersion, but that the different band sensors on the Sentinel instrument are capturing from slightly different positions/times. A fast-moving object such as an aircraft will then be moving along its path on different bands, and the trails/aircrafts in the individual band images will be moving laterally in the inverse direction from the Sentinel's satellite motion.

From the Sentinel-2 MSI sensor technical documentation, sourced here:

"Two distinct arrays of 12 detectors mounted on each focal plane covering VNIR and SWIR channels respectively. The 12 detectors on each focal plane are in a staggered configuration to cover the entire field of view."

The follow-up diagrams show what I believe to be the case, that for normal Earth observation at non-elevated features there would be no effect caused by this separation, but a unique feature such as aircraft would show up in this way.

Here are sources on dispersion and photographing contrails: http://www.atmo.arizona.edu/students/courselinks/spring13/atmo170a1s1/1S1P_stuff/atmos_optical_phenomena/optical_phenomena.html

http://www.telegraph.co.uk/news/2016/05/17/amazing-photo-captures-rare-rainbow-contrails-plane-effect/

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    I'm not sure that's what's going on. Enlarge the picture and you'll notice that the plane itself appears three times as res, blue, and green, as well. – Zipper1365 Dec 4 '17 at 17:56
  • You're right, I hadn't noticed that. See the updated answer above. – AlecZ Dec 4 '17 at 18:08

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