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So I'm trying to filter sentinel-1 data in Google Earth Engine by time specifically rather than date. I'm trying to avoid morning acquisitions.

So I know that the acquisition start time is contained in the system:index as seen below

MMM_BB_TTTR_LFPP_YYYYMMDDTHHMMSS_YYYYMMDDTHHMMSS_OOOOOO_DDDDDD_CCCC.EEEE

S1A_IW_GRDH_1SDV_20230414T182236_20230414T182301_048096_05C825_9EB9

In my original approach, I tried to select any system:index instances that contained T18 using 'T18.*' as seen below.

 var sentinel1 = ee.ImageCollection('COPERNICUS/S1_GRD')
     .filter(ee.Filter.eq('instrumentMode', 'IW'))
     .filter(ee.Filter.eq('orbitProperties_pass', 'ASCENDING'))
     .filterDate('2023-03-01',  '2023-12-31')
     .filter(ee.Filter.eq('system:index', 'T18.*'))
     .filterBounds(ROI);

Obviously, this didn't work...it resulted in 0 images in my image collection.

Does any know how I should go about this?

1 Answer 1

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You want:

.filter(ee.Filter.stringContains('system:index', 'T18'))

However, I find it super unlikely this is doing what you think its doing. Those acquisition times are in UTC. It is, essentially, the time in London when the image was acquired. It has (essentially) nothing to do with time-of-day where the image was acquired.

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  • Hey Noel, that worked perfectly that a million for that!! Funnily enough, that should still work for me as I'm located in Ireland. Dumb luck wins out again I guess! Again, thanks for the help!
    – Mícheál
    Commented Apr 27 at 19:10

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