Conor O'SullivanApr 23, 2023

I attempted to make a Timeseries gif using Landsat data. I used images of Howth and Bull Island in Dublin from 1980 to 2023. The first attempt was well 👇

Problem 1: I cropped the images but didn't realise positions would change depending on the image.

Problem 2: clouds!!!

Problem 3: what's with the black lines on some of the images?

Show threadJoseApr 23, 2023
@conorosully for Landsat, you probably want to use some high level surface reflectance product. These will have QA layers and a cloud mask to filter clouds out, as well as being corrected for atmospheric effects.
Show threadConor O'Sullivan

@jgomezdans I'm using Landsat level-2 which I believe has been corrected for atmospheric effects.

I wasn't aware of the QA layers. These are so useful! I think the _stac.json file will help with the first problem.

Apr 23, 2023 at 4:54pmWeb
Show threadHagollEOApr 23, 2023
@conorosully @jgomezdans Black lines come from Landsat 7, for which one of the mirrors is stuck. Landsat 7 is a scanner, with a small line of detectors that scans from left to right, and then right to left. Meanwhile, the satellite advances, which leaves a gap at the edges. There is a Scan Line Corrector (SLC) so that the scan lines get parallel, but it's not been working since 2003. They say Landsat 7 is in SLC off mode. There has been quite some literature to fill the gaps...
Show threadHagollEOApr 23, 2023

@conorosully @jgomezdans
And regarding problem 1, yes, the Landsat data are not resampled on a common grid, as for #Sentinel2. I think they do it only in the US for the standard products (but I have not checked for a while). There is also a Harmonized Landsat Sentinel2 data set that uses the Sentinel2 tile grid ( which was chosen by our team at @CNES )

https://www.earthdata.nasa.gov/esds/harmonized-landsat-sentinel-2

Harmonized Landsat and Sentinel-2 (HLS) | Earthdata

The Harmonized Landsat Sentinel (HLS) project combines data from Landsat-8 and Sentinel-2 into a harmonized, analysis-ready surface reflectance product.

Earthdata
Show threadConor O'SullivanApr 24, 2023

@ohagolle @jgomezdans

Thank you Oliver, that's really helpful!

The stuck mirror on Landsat 7 is also interesting. I guess there will be a 10 year period where data is questionable (ie. until lansat 8 was launched in 2013).

Show threadHagollEOApr 24, 2023
@conorosully @jgomezdans yes. But there was Landsat 5 until 2011.