I am using GEE to run the Mann-Kendall trend test on NDVI over my study area from 2001 to 2023. I want to show the NDVI trend for each individual month for the 22 years, which means January 2001,2002...2023; Feburary 2001,2002...2023....Now I am just using January to test if the Mann-Kendall test is working or not. I follow the tutorial here: https://developers.google.com/earth-engine/tutorials/community/nonparametric-trends

However, the result shows nothing on the map (0 bands). Does anyone know why and how to solve it? Here is my code: https://code.earthengine.google.com/8dbfec725689e50a5927cd14d4219d94

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You're NDVI images have no system:time_start, so the join on that field produces an empty collection.

  • Thank you @Noel. I have added the system:time_start , but it turned out the result shows a complete white map. Does it mean there is missing data?code.earthengine.google.com/7d6a0dbdfc50f17fc1816798f6503a00 Apr 3 at 13:10
  • I think it means your math isn't right; you're multiplying a NDVI value (a small number between 0 and 1) times the difference of two NDVI numbers, also likely to be a small number between -1 and 1, and then casting that to an int() (ie: truncating). The results will likely always be 0. Remove the int() and you get "something"... is it right? Dunno. Apr 4 at 14:07

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