I am having a hard time to figure out what this information refers to. It is stated at the product description of Terra MODIS MOD11A1 product (Wan et al.,2015). (from https://lpdaac.usgs.gov/products/mod11a1v006/)

(It is also mentioned at the dataset page of Earth Engine Data Catalog at https://developers.google.com/earth-engine/datasets/catalog/MODIS_006_MOD11A1)

"Above 30 degrees latitude, some pixels may have multiple observations where the criteria for clear-sky are met. When this occurs, the pixel value is a result of the average of all qualifying observations."

From Version 5, temporal averaging was removed from the MOD11A1 products, and they have now LST data by instantaneous observations. I am saying this based on;

For daily MOD11A1 product, in the MODIS LST Products User's Guide of Version 4 products (by Wan Z. (2006) ) there was this information " As latitude increases beyond 30 degrees, the LST value at some grids in the MOD11A1 product may be the average value of LSTs retrieved from multiple MODIS observations in clear-sky conditions in day or night. If LST values from single clear-sky MODIS observations are required for all grids, the MOD11_L2 LST product and MODIS geolation product (MOD03) should be used instead."

Which was changed into "As latitude increases beyond 30 degrees, there may be multiple MODIS observations in clear-sky conditions. In V5 MOD11A1 product, LST values at all grids are from single clear-sky MODIS observations by selecting LSTs in MOD11_L2 files at smaller viewing zenith angles or the LSTs at larger zenith angles but their values being larger by at least 2K" in the Collection-5 MODIS Land Surface Temperature Products Users' Guide (Wan Z., (September 2006).

In this context, I would like to ask if anybody could help with the above information? What type of averaging is being referred to?


Based on the satellite orbit and sensor viewing characteristics, there are can be overlapping observations at high-latitudes within a day. This video is a nice animation of the Aqua satellite swath: https://youtu.be/d4QLDlAumOc?t=24. Notice how some areas get imaged twice in the north.

That is what "the pixel value is a result of the average of all qualifying observations." is referencing. So, if a location is observed multiple times which meets the quality assurance criteria (no clouds, no sensor saturation, etc.) then the level 3 data (MOD11A1V006) is the average of those observations.

Hopefully this sheds some light into how the dataset is generated.

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