question about ISCCP-H monthly data

[Genevieve Rose Hizon Lorenzo]

Good day,

I downloaded some of the monthly data from

https://www.ncei.noaa.gov/thredds/catalog/cdr/isccp_hgm_agg/files/catalog.html

I just have some questions about the data... I'm interested in the ff data, and I want to verify if

1) after I open the data I just multiply it by 0.1 and then add 50?  Then also

2) it says the fill value is 32767, but when I look at at data in matlab there are these values -7.45058059692383e-07, I'm not sure I understand.

cldamt_irtypes    
           Size:       360x180x3x1
           Dimensions: lon,lat,cloud_irtype,time
           Datatype:   int16
           Attributes:
                       long_name     = 'Mean cloud amount for IR-cloud types'
                       units         = 'percent'
                       valid_min     = -500
                       valid_max     = 500
                       scale_factor  = 0.1
                       _FillValue    = 32767
                       description   = 'Cloud detected by IR threshold regardless of VIS threshold, IR type determined by cloud top pressure for blackbody'
                       standard_name = 'isccp_cloud_area_fraction'
                       add_offset    = 50

Thank you,

Genie Lorenzo

PhD student

University of Arizona

[Ken Knapp - NOAA Federal]

Hi

Thanks for your question. 

For clarity, I went to the link you provided and selected one specific file:

https://www.ncei.noaa.gov/thredds/catalog/cdr/isccp_hgm_agg/files/catalog.html?dataset=cdr/isccp_hgm_agg/files/isccp-basic/hgm/ISCCP-Basic.HGM.v01r00.GLOBAL.1983.07.99.9999.GPC.10KM.CS00.EA1.00.nc

I downloaded the netCDF file (the HTTPS server link).

The netCDF header shows what you sent. 

When I investigate the file, I find 611 missing data grid cells with a value of 32767. I suspect that matlab performs the scaling operation when it reads in the data? Because the netCDF dump shows the values as described.

Hope this helps-

-Ken

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Ken Knapp,
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NOAA National Centers for Environmental Information

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[Genevieve Rose Hizon Lorenzo]

Thank you Ken,

Okay I guess too that matlab already does the scaling, thank you... however maybe there are some rounding errors (for those values that are -7.45058059692383e-07 should be zero?).

I plotted July 2015 for ISCCP (attached), and also the MODIS (MCD06COSP_M3_MODIS) product cloud mask , and am wondering about the discrepancy and wonder if I'm looking at the same parameters.

Thank you,

Genie