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I've been using the Google Earth Engine API in an attempt to access Landsat 8 imagery for land use change detection in the South China Sea. Initial investigations suggest that Google may have removed imagery of this area from their collection, as when I run the code in the link below all images are clipped to the surrounding mainland coastline of each country.

https://code.earthengine.google.com/b2d2927d5f8abb7c77444cc03dc8ece8

Having checked the following, https://earthexplorer.usgs.gov/ I can confirm that suitable Landsat 8 imagery does exist for this ROI, so my question is:

Is there any documentation where Google specifies why this has been excluded from their Landsat 8 collection? Or have a made a mistake in the code above that somehow excludes the imagery I am looking for?

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You're using the Landsat 8 T1_SR collection, which is based on the Tier 1 data. For data to be included in Tier 1 (by the USGS), it has to have a geometric calibration accuracy of ~15m. None of the images that occur in the sea meet that criteria, so they are only included the in the Tier-2 collection (and therefore aren't very well registered).

You can tell which collection an image is in by the last 2 letters of its ID: LC08_L1GT_121049_20181222_20181227_01_T2

That's a Tier 2 image over the sea.

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