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When I browse images from https://earthexplorer.usgs.gov/, I can see that all of the images from Landsat are all tilted/rotated at a certain angle.

Why are they rotated? And what's that for?

Below is an image I got from https://earthexplorer.usgs.gov/.

LandsatLook Image from Landsat 8

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    Because images are processed to north-up orientation but the paths of the satellites do not go straight from south to north. You will find a map about the paths easily from the web.
    – user30184
    Sep 9, 2018 at 20:11
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    See for example landsat.usgs.gov/sites/default/files/images/wrs2nb.gif and landsat.usgs.gov/sites/default/files/images/wrs2.gif.
    – user30184
    Sep 9, 2018 at 21:07
  • Thank you so much. The satellite follows the red path, so we need to rotate the images so that it will be parallel to the green line.
    – Huyen
    Sep 9, 2018 at 21:26
  • @Huyen You wont need to rotate the images. They should be in the right spatial location. North is still towards the top of the screen, it is just that the satellite captures information in a path that doesnt travel along the N-S path. If you load your spatial information onto the map (assuming the coordinate systems are the same) then they should match up correctly. You may need to download more than 1 image set and mosaic them together to make a "regular" shaped image of your area of interest.
    – Keagan Allan
    Sep 10, 2018 at 1:37
  • Addition to useful comments, here is a short clip from NASA showing the Landsat 8 satellite orbit. youtube.com/watch?v=P-lbujsVa2M
    – Shiko
    Sep 10, 2018 at 3:24

2 Answers 2

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I had an extensive talk with my professor about this.

The reason for this tilting/rotation is the USGS satellite imagery is already geocoded (Geocoding is the process of transforming a description of a location—such as a pair of coordinates, an address, or a name of a place—to a location on the earth's surface) or you may say the geometric distortions have already been rectified.

Sources of geometric distortion:

  1. sensor characteristics -optical disorrtions

    • aspect ratio
    • non-linear mirror velocity
    • detector geometry & scanning sequence

  2. viewing geometry

    • panoramic effect
    • earth curvature

  3. motions of the aircraft/satellite or target

    • attitude changes (pitch, roll, yaw)
    • position variations (altitude, slew)
    • earth rotation

Distortions appear as: - changes of scale over the image

  • irregularities in the angular relationships among the image elements

  • displacement of objects in an image

  • occlusion of one image element by another

For an illustration: The image 1 is the raw imagery whereas the image 2 is the geocoded one.

raw image

geocoded image

Image sources:https://docplayer.net/50693884-Geocoding-rudiger-gens.html

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  • And what about the satellite path? Have you seen the comments under the question? It seems you did not directly address the question. Perhaps the satellite path is explained by the geocoding? It is not clear how the satellite path fits in the context of your answer. Can you clarify?
    – Andre Silva
    Sep 10, 2018 at 13:22
  • I didn't answer the comments and regarding the USGS the reason is geometric corrections and USGS geocodes the image themselves that is why. Regarding the question, I answered why tilted/rotated.
    – Maxima
    Sep 10, 2018 at 13:25
  • I did not mean you should have answered the comments; I meant it was cited in comments the tilted/rotation feature of the images was due to the satellite orbit path, which apparently is not addressed in your answer. So, I wonder if the satellite path has or has not anything to do with the question’s subject (because based on own research I thought it had).
    – Andre Silva
    Sep 10, 2018 at 13:31
  • I think the images follow the satellite path, so they were taken along with that path. To rotate it is to direct the image along the N-S line.
    – Huyen
    Sep 10, 2018 at 20:47
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Each near-polar Landsat orbit takes about 90 minutes to complete. The Earth rotates beneath the satellite at a rate of 15 degrees per hour (time zones are split into 15 degree segments). The satellite crosses the equator along its descending path at approximately 09:00 local time in each orbit. Thus each time a satellite starts its descending orbit, the Earth has rotated a bit. The orbital inclination of 98.2 degrees is designed to ensure successive passes overlap the previous pass. That is why Landsat scenes are rotated 8.2 degrees east of TN.

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