HLS S30 - Multiple Sentinel-2 acquisitions the same tile on the same day?

[juliederey]

Hello,
I noticed that for some tiles and dates, there are multiple Sentinel-2 acquisitions available in the original ESA archive (from different orbits), but only one S30 granule is produced in HLS for that tile/date combination.
For example, on February 19, 2019, for tile T31TGK, the ESA archive contains two Sentinel-2 acquisitions (at 10:30:53 and 10:38:24) that are spatially complementary — one covers the northern part of the tile, the other covers the southern part. However, HLS only provides one S30 granule that covers only the northern portion, leaving nodata in the south.
My questions:
What are the selection criteria used by HLS when multiple Sentinel-2 acquisitions exist for the same tile on the same day?
Is there a minimum spatial coverage threshold required for an acquisition to be processed?
Why aren't complementary acquisitions mosaicked together to maximize spatial coverage?

Thank you for your help!

[LP DAAC - dgolon]

Hi @juliederey Apologies for the delay in response. We are looking into this. Thanks -- Danielle

[juliederey]

Hello Danielle,
I just wanted to gently follow up to see if there have been any updates on this issue.
Thank you!
Julie

[LP DAAC - dgolon]

Hi Julie! Thanks for following up. We are still looking into this but as soon as we have a solution, I'll let you know. I apologize for the delay. Thanks -- Danielle

[LP DAAC - dgolon]

Hi @juliederey Your question brought up a different issue we noticed that has been fixed in the forward stream, however it turned out to be unrelated to the questions you asked here. I apologize for the delay in response.

To answer your questions:

What are the selection criteria used by HLS when multiple Sentinel-2 acquisitions exist for the same tile on the same day?
In general:
HLS S30 images are processed if the following criteria is met:
− There’s a minimum solar zenith angle of 76 degrees (this mainly cuts out areas to the far north in winter).
− Cloud cover less than 95%.

Is there a minimum spatial coverage threshold required for an acquisition to be processed?
No

Why aren't complementary acquisitions mosaicked together to maximize spatial coverage?
These data are typically not mosaicked like that for other sensors as well, although there are some mosaics you can download. If you would like to receive the HLS complementary acquisition data mosaicked, then we recommend using AppEEARS: https://appeears.earthdatacloud.nasa.gov/ which will do the mosaicking for you. It also allows other features such as reprojecting and reformatting.

Please let us know if you have any additional questions. Thanks -- Danielle