Ken Knapp wrote:
Raw satellite data are generally stored as integers (DN=digital
numbers) that are then
1. converted to radiances linearly (or sometimes non-linearly) that
can then be
2. converted to brightness temperatures.
With steps that are nonlinear, the scale factor offset doesn't work.
If a coefficient is tweaked/corrected, then the entire variable would
need to be rewritten.
Satellite data often use lookup tables to more easily and quickly
convert from DN to whatever (radiance/temperature). Updates would then
be made to calibration tables, rather than equations.
Can't equations, linear/non-linear, have coefficients, which can be updated?
So I would propose something like the following CDL where variable
/image/ has range from 0-255 and its attribute /lookup/ means that the
table to convert to meaningful units is /table_1
/
dimensions:
lat = 100
lon = 100
num_bins = 256
int image(lat,lon)
image:long_name = "GOES Water vapor channel"
image:units = "digital number"
image:lookup = "table_1"
image:valid_range = 0, 255
float table_1(num_bins)
table_1:long_name = "Brightness temperature"
table_1:units = "Kelvin"
Thoughts?
-Ken
This seems like a good idea, if "lookup" was some sort of recognized
standard
name.
Tom
--
Ken Knapp
Remote Sensing and Applications Division
National Climatic Data Center
151 Patton Ave
Asheville, NC 28801
828-271-4339 (voice) 828-271-4328 (fax)
IBTrACS: http://www.ncdc.noaa.gov/oa/ibtracs/
ISCCP B1: http://www.ncdc.noaa.gov/oa/rsad/isccpb1/
HURSAT: http://www.ncdc.noaa.gov/oa/rsad/hursat/
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