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Scaling of Cloud Top Temperature product of MODIS Aqua level 2

Posted: Tue Oct 03, 2023 12:30 am America/New_York
by aakashmodis
Hello,
I am facing problem while scaling the Cloud_Top_Temperature product of MODIS Aqua level 2. This product is having following thing to get the meaningful values:
Cloud_Top_Temperature(Cell_Along_Swath_5km:mod06, Cell_Across_Swath_5km:mod06) ;
Cloud_Top_Temperature:valid_range = 0s, 20000s ;
Cloud_Top_Temperature:_FillValue = -32768s ;
Cloud_Top_Temperature:long_name = "Temperature from Ancillary Data at Retrieved Cloud Top Pressure Level" ;
Cloud_Top_Temperature:units = "K" ;
Cloud_Top_Temperature:scale_factor = 0.009999999776482582 ;
Cloud_Top_Temperature:add_offset = -15000. ;
Cloud_Top_Temperature:Parameter_Type = "Output" ;
Cloud_Top_Temperature:Cell_Along_Swath_Sampling = 3, 2038, 5 ;
Cloud_Top_Temperature:Cell_Across_Swath_Sampling = 3, 1348, 5 ;
Cloud_Top_Temperature:Geolocation_Pointer = "Internal geolocation arrays" .

My concern is the 'add_offset' (-15000 or with scale_factor= -150) because applying that factor I am getting negative values of cloud top temperature in units of Kelvin, which is impossible.

Please provide your solution.

Re: Scaling of Cloud Top Temperature product of MODIS Aqua level 2

Posted: Tue Oct 03, 2023 7:36 am America/New_York
by LAADS_UserServices_M
The values you listed are correct. The "add_offset" value is a negative value:
units = K
scale_factor = 0.009999999776482582
add_offset = -15000.0
The following equation should be used to get to the real value:

value = scale_factor * ( stored_value - add_offset )
so for a stored integer value of 6942, the real value in deg. K would be
= 0.009999999776482582 * (6942 - (-15000.0))

Re: Scaling of Cloud Top Temperature product of MODIS Aqua level 2

Posted: Wed Oct 04, 2023 12:29 pm America/New_York
by aakashmodis
Thank you for your response, this is very helpful for me.