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I've been examining satellite imagery (Sentinel-2) and noticed that water can look significantly different in images from different relative orbits (seems to happen consistently for the examples below). Does anyone know why this is (this is during summer and not frozen/ice)? I looked at the angles and it appeared there's reasonable overlap in angles (Zenith?), although the brighter one is a larger angle. Both Sentinel-2A, and around the same time of day, and L2A product.

Obviously water is highly reflective -- is it related to that? Trying to make sure there isn't something about the data quality I need to know about.

bright

enter image description here

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    Sun glint probably
    – user2856
    Commented Mar 27, 2021 at 2:56
  • Interesting - had never heard this term before. I guess it's not uncommon? Commented Mar 27, 2021 at 4:50
  • Its not just the water areas that are different- see for example fields in NE corner which are mottled in on image and deep green in the other. Could it be surface temperature? Commented Mar 27, 2021 at 5:16
  • The fields are due to timing (crop growth occurred). But definitely the water continues to look like this in each situation where i compare the same spot with different relative orbits no matter the timing. Commented Mar 27, 2021 at 5:18
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    Sun glint is very common, can be corrected if you're interested in properties of the water column but don't care about the land.
    – user2856
    Commented Mar 27, 2021 at 7:12

2 Answers 2

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In addition to sun glint, the "roughness" of the water's surface, as affected by prevailing winds, can alter the reflected light. Imagine the difference in a body of water between a glassy-smooth surface on a calm day versus a choppy surface with tall, white-capped waves on a windy day.

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It is likely to be sun glint. As much as I hate to cite Wikipedia, this description is quite good:

Sunglint is a phenomenon that occurs when sunlight reflects off the surface of the ocean at the same angle that a satellite or other sensor is viewing the surface. In the affected area of the image, smooth ocean water becomes a silvery mirror, while rougher surface waters appear dark.

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