Error in Product "MODIS/Terra Vegetation Indices Monthly L3 Global 1 km SIN Grid" for March and August 2024

[akscharf]

I have recently downloaded all monthly tiles over all available years (2000-present) of the product "MODIS/Terra Vegetation Indices Monthly L3 Global 1 km SIN Grid". All rasters are complete, besides March and August 2024 (see plots attached). In these two many tiles are missing. I checked the 16day product, and there it seems that all tiles are available. To exclude that this was caused by problems while downloading (using R library appeears) I also checked on the earthdata search webinterface, and found the same pattern. My guess is that something when wrong during the calculation of the monthly dataset.
Thank you!
Anne Scharf

[akscharf]

I guess fixing this will take some time. How exactly are the monthly data averaged?. In the documentation it says "In generating this monthly product, the algorithm ingests all the MOD13A2 products that overlap the month and employs a weighted temporal average." Is this algorithm available? Than I could calculate the monthly layers myself for the time being, that would be very helpful. Thanks!

[LP DAAC - lien]

Hi Anne,
Sorry for the missing data issue, and thank you for the heads-up. We are checking into this and will let you know when the data is available.
Thanks,
Brett

[akscharf]

Hi Brett,
can you estimate how long it will take (days, weeks, month,...) for the corrected data to be available?
Thank you!
Anne

[LP DAAC - lien]

Hi Anne,
Now that the data providers are aware of the missing data, I think it should just be a matter of days.
For how the MOD13A2 product values are weighted to derive the monthly values let's use the month of June for example. June has three 16-day composite periods that contribute to the value of the June MOD13A3. The composite beginning on May25 contributes the first 9 days, the composite from June 10 contributes 16 days and the one from June 26 contributes 4 days. Each day consists of 3.33% of the monthly value so the first 9 days are 30% the next 16 are 53.28% and the last 4 are 13+ of the pixel values.
Please let me know if you have any questions.
Thanks,
Brett

[akscharf]

Hi Brett,
thank you so much for the explanation of how the monthly layer is calculated. That is very helpful. I will wait some days, and if the data takes longer to be available that I just calculated myself.
Thanks!
Anne

[LP DAAC - lien]

Hi Anne,

I think all the missing months are in. Please let me know if you notice anymore, and thanks for your patience.
Brett

[akscharf]

Hi Brett,
thank you so much for this quick fix! I plotted all monthly layers from 2000-2025 and these 2 were the only ones with errors.
Thank you so much again.
Best,
Anne