0

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

1 Answer 1

0

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

2
  • 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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.