Earthdata Forum

Hello,

I have noticed an inconsistency between the MODIS Aqua monthly mean and daily mean products. I am looking at the variables "Cloud_Effective_Radius_37_Liquid_Mean" and "Cloud_Effective_Radius_37_Liquid_Mean_Mean", with the understanding that the MYD08_M3 should be the mean of the daily mean dataset.

I have downloaded all the datasets from LAADS DAAC at ladsweb.modaps.eosdis.nasa.gov/ using wget.

I am looking at the month of November in 2006, my monthly dataset is MYD08_M3.A2006305.061.2018028002918.hdf, and the daily dataset is the MYD08_D3.A2006 ranging from DOY 305 to 334 inclusive.

I have attached a plot of the differences between the mean of the daily means and the monthly mean data for the Cloud_Effective_Radius_37_Liquid variable.

Could you help me figure out what is going wrong here?

Thank you

Our SME looked into the MYD08_M3.A2006305.061 and daily dataset MYD08_D3.A2006 from DOY 305 to 334 and sent the following:

“Cloud_Effective_Radius_37_Liquid_Mean_Mean” is computed by averaging non-fill daily means from MYD08_D3 files within the month. The averaging computation uses the Pixel_Weighted scheme (it is specified in the local attributes, see yellow highlight part below). It is weighted by the daily pixel count.
short Cloud_Effective_Radius_37_Liquid_Mean_Mean(YDim=180, XDim=360);
:valid_range = 400S, 3000S; // short
:_FillValue = -9999S; // short
:long_name = "Liquid Water Cloud Effective Particle Radius from band 20: Mean of Daily Mean";
:add_offset = 0.0; // double
:Level_2_Pixel_Values_Read_As = "Real";
:Included_Level_2_Nighttime_Data = "False";
:Quality_Assurance_Data_Set = "Quality_Assurance_1km";
:Statistic_Type = "Simple";
:QA_Byte = 7S; // short
:QA_Useful_Flag_Bit = 3S; // short
:QA_Value_Start_Bit = 0S; // short
:QA_Value_Num_Bits = 2S; // short
:Aggregation_Data_Set = "Quality_Assurance_1km";
:Aggregation_Byte = 2S; // short
:Aggregation_Value_Start_Bit = 0S; // short
:Aggregation_Value_Num_Bits = 3S; // short
:Aggregation_Category_Values = 2S; // short
:Aggregation_Valid_Category_Values = 1S, 2S, 3S, 4S; // short
:Derived_From_Level_3_Daily_Data_Set = "Cloud_Effective_Radius_37_Liquid_Mean";
:Weighting = "Pixel_Weighted";
:Weighted_Parameter_Data_Set = "Cloud_Retrieval_Fraction_37_Liquid_Pixel_Counts";
:units = "microns";
:scale_factor = 0.009999999776482582; // double


More detailed information can be found from Section 4.1 (Page 28-32) of the ATBD for L3 MxD08 daily and monthly products.The ATBD link is:

https://atmosphere-imager.gsfc.nasa.gov/sites/default/files/ModAtmo/L3_ATBD_C6_C61_2019_02_20.pdf