Dear All,
I am trying to produce some Chlorophyll-a netCDF files which follow the COARDS-CF
conventions.
In doing this I have stumbled upon the following problem:
My 'raw' data is stored as bytes, and in order to transform it to 'real'
Chlorophyll I need to perform the following operation:
real_data = 10 ^ (scale_factor * raw_data + add_offset)
Unfortunately I have noticed that the netCDF functions which access the file
(i.e. ncview & ferret) perform the transformation in the following way:
real_data = (scale_factor * raw_data + add_offset)
Therefore the problem is that the logarithmic scaling is not being recognized
and the transformation is being done erroneously.
Is there any way I can force the netCDF file to interpret my attributes with
the correct scaling equation ? Is logarithmic scaling supported by netCDF
files ?
I am grateful for any information and/or suggestions you can give me.
Best Regards,
Pepe
P.S. I have attached below a copy of an ncdump -h output:
netcdf S20032132003243_L3m_CHL {
dimensions:
longitude = 4096 ;
latitude = 2048 ;
variables:
float longitude(longitude) ;
longitude:standard_name = "longitude" ;
longitude:long_name = "Longitude" ;
longitude:units = "degrees_east" ;
longitude:step = "0.0878906" ;
longitude:valid_min = "-179.9561" ;
longitude:valid_max = "179.9561" ;
longitude:axis = "X" ;
float latitude(latitude) ;
latitude:standard_name = "latitude" ;
latitude:long_name = "Latitude" ;
latitude:units = "degrees_north" ;
latitude:step = "0.0878906" ;
latitude:valid_min = "-89.9561" ;
latitude:valid_max = "89.9561" ;
latitude:axis = "Y" ;
byte l3m_data(latitude, longitude) ;
l3m_data:standard_name = "chlorophyll_concentration_in_sea_water"
;
l3m_data:long_name = "Chlorophyll-a concentration" ;
l3m_data:units = "mg/m3" ;
l3m_data:base = "10.0" ;
l3m_data:scale_factor = "0.0150000" ;
l3m_data:add_offset = "-2.00000" ;
l3m_data:valid_min = "0" ;
l3m_data:valid_max = "254" ;
l3m_data:_FillValue = '\377' ;
l3m_data:missing_value = "255" ;
// global attributes:
:Product = "Chlorophyll-a Monthly Mean" ;
:Measure = "Mean" ;
:Year = "2003" ;
:Month = "August" ;
:Start_Day = "213" ;
:End_Day = "243" ;
:Map_Projection = "Equidistant Cylindrical" ;
:Scaling = "Logarithmic" ;
:Scaling_Equation = "Chl = base**((scale_factor*l3m_data)
+ add_offset)" ;
:Conventions = "COARDS-CF" ;
}
*************************************************
Pepe S. D. Juevara
- No debe cambiarse de caballo al cruzar el r?o -
*************************************************
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Received on Mon Mar 21 2005 - 03:21:16 GMT
