All --
I'm starting to think there may be a problem with the GOES-16 channel 7 GRB
NetCDF data. I wrote a short test code
(included below) that calculates brightness temperature and produces a png file
with an abbreviated color table for comparison
with the NESDIS https://www.star.nesdis.noaa.gov/GOES/GOES16_CONUS.php imagery.
When using the channel 7 data,
the calculated imagery appears noticeably warmer, but when using channel 14
data (for example), the images appear
very close in value.
Would someone else mind taking a look at this and confirm whether this might be
the case, or whether I'm just losing my mind?
Thanks!
Art
_________________________________________________________________________________________________________
from netCDF4 import Dataset
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import LinearSegmentedColormap
filename =
"amazon/OR_ABI-L1b-RadC-M3C07_G16_s20180151547235_e20180151550019_c20180151550058.nc"
#filename =
"amazon/OR_ABI-L1b-RadC-M3C14_G16_s20180151547235_e20180151550008_c20180151550050.nc"
dataset = Dataset(filename,'r')
# Get coefficients for calculation of brightness temperature
planck_fk1 = dataset.variables['planck_fk1'][:]
planck_fk2 = dataset.variables['planck_fk2'][:]
planck_bc1 = dataset.variables['planck_bc1'][:]
planck_bc2 = dataset.variables['planck_bc2'][:]
print("planck_fk1: ",planck_fk1)
print("planck_fk2: ",planck_fk2)
print("planck_bc1: ",planck_bc1)
print("planck_bc2: ",planck_bc2)
# Read the radiance data
rad = dataset.variables['Rad'][:]
dataset.close()
# Calculate brightness temperature
bt = ( (planck_fk2 / (np.log( (planck_fk1/rad)+1 ))) - planck_bc1 ) /
planck_bc2
bt = bt - 273.15
# Create a color table to compare against
https://www.star.nesdis.noaa.gov/GOES/GOES16_CONUS.php imagery
red = []
green = []
blue = []
valmin=-110.
valmax=55.
red.append( [0.0, 0.0, 0.0] )
green.append( [0.0, 0.0, 0.0] )
blue.append( [0.0, 0.0, 0.0] )
red.append( [ (-50.0-valmin)/(valmax-valmin), 0.0, 0.0 ] )
green.append( [ (-50.0-valmin)/(valmax-valmin), 1.0, 1.0 ] )
blue.append( [ (-50.0-valmin)/(valmax-valmin), 0.0, 0.0 ] )
red.append( [ (-40.0-valmin)/(valmax-valmin), 0.0, 0.0 ] )
green.append( [ (-40.0-valmin)/(valmax-valmin), 0.0, 0.0 ] )
blue.append( [ (-40.0-valmin)/(valmax-valmin), 0.4, 0.4 ] )
red.append( [ (-30.0-valmin)/(valmax-valmin), 0.0, 0.8 ] )
green.append( [ (-30.0-valmin)/(valmax-valmin), 1.0, 0.8 ] )
blue.append( [ (-30.0-valmin)/(valmax-valmin), 1.0, 0.8 ] )
red.append( [ 1.0, 0.0, 0.0 ] )
green.append( [ 1.0, 0.0, 0.0 ] )
blue.append( [ 1.0, 0.0, 0.0 ] )
cdict = {'red': red, 'green': green, 'blue': blue}
ctbl = LinearSegmentedColormap('custom', cdict)
# Set the figure size
fig = plt.figure(1, figsize=(23, 15))
# Display the image
im = plt.imshow(bt, cmap=ctbl, vmin=valmin, vmax=valmax )
# Display a color bar
cb = plt.colorbar( orientation='vertical', shrink=0.7, pad=0.01, aspect=30 )
cb.set_label("Brightness Temperature (C)")
# Save the image to a png file
plt.savefig('plot.png', dpi=100)
> From: "Pete Pokrandt" <poker@xxxxxxxxxxxx>
> To: "ARTHUR AUGUST PERSON" <aap1@xxxxxxx>
> Cc: "ldm-users" <ldm-users@xxxxxxxxxxxxxxxx>
> Sent: Saturday, January 13, 2018 9:03:11 PM
> Subject: Re: [ldm-users] Problem calculating GOES-16 brightness temperature
> from
> radiance
> Forgot to cc to the list.
> Here's a commented version of the script that I'm currently using to plot ABI
> channel 13 (clear channel IR window) but the calculation for BT should work
> for
> any of the channels 7-16.
> I am using just the radiance values read in from the netcdf files, without
> applying any scale/offset to them. Perhaps the netcdf4 read does that for us?
> I
> am reading the scale and offset info in for reference, and printing them out,
> but I am not using them in my calculations at all.
> If for some reason, the attachment doesn't come through, you can get the file
> at
> [ http://sysadm.aos.wisc.edu/~poker/goes16_GRB_fulldisk_IR13_ircm.py |
> http://sysadm.aos.wisc.edu/~poker/goes16_GRB_fulldisk_IR13_ircm.py ]
> Hope this helps,
> Pete
> [
> http://www.weather.com/tv/shows/wx-geeks/video/the-incredible-shrinking-cold-pool
> ] --
> Pete Pokrandt - Systems Programmer
> UW-Madison Dept of Atmospheric and Oceanic Sciences
> 608-262-3086 - poker@xxxxxxxxxxxx
> From: Arthur A Person <aap1@xxxxxxx>
> Sent: Saturday, January 13, 2018 9:04 AM
> To: Pete Pokrandt
> Cc: ldm-users
> Subject: Re: [ldm-users] Problem calculating GOES-16 brightness temperature
> from
> radiance
> Pete,
> Thanks for the help. Actually, I already tried adding parens to the equation,
> including the variation you
> suggested, but the results are the same. Do you have a few lines of code that
> worked for you that you'd
> be willing to share? Or, do you recall whether there's any issue with netCDF
> auto-scaling the input data,
> or any units conversion that has to be included that's not in the
> documentation?
> Thanks... Art
>> From: "Pete Pokrandt" <poker@xxxxxxxxxxxx>
>> To: "ARTHUR AUGUST PERSON" <aap1@xxxxxxx>, "ldm-users"
>> <ldm-users@xxxxxxxxxxxxxxxx>
>> Sent: Friday, January 12, 2018 11:47:08 AM
>> Subject: Re: [ldm-users] Problem calculating GOES-16 brightness temperature
>> from
>> radiance
>> Art,
>> I think it may be a parenthesis/order of operations issue. I seem to recall
>> having this same issue when I first started working with the GRB data.
>> Try this:
>> bt = ( planck_fk2 / ( np.log((planck_fk1 / rad) + 1 )) - planck_bc1) /
>> planck_bc2
>> Pete
>> From: ldm-users-bounces@xxxxxxxxxxxxxxxx
>> <ldm-users-bounces@xxxxxxxxxxxxxxxx> on
>> behalf of Arthur A Person <aap1@xxxxxxx>
>> Sent: Friday, January 12, 2018 7:43 AM
>> To: ldm-users@xxxxxxxxxxxxxxxx
>> Subject: [ldm-users] Problem calculating GOES-16 brightness temperature from
>> radiance
>> Hi...
>> I'm trying to calculate brightness temperature from radiance for GOES-16 IR
>> channel 7 using rebroadcast data
>> but my values compared to McIDAS imagery are coming out 15 to 20 degrees C
>> too
>> warm. I'm using the following
>> values and code:
>> Test imagery:
>> OR_ABI-L1b-RadC-M3C07_G16_s20180112232223_e20180112235008_c20180112235045.nc
>> rad (radiance) is read in from and auto-scaled by netCDF,
>> planck_fk1: 202263.0
>> planck_fk2: 3698.18994140625
>> planck_bc1: 0.4336099922657013
>> planck_bc2: 0.9993900060653687
>> bt = ( planck_fk2 / np.log( (planck_fk1/rad)+1 ) - planck_bc1 ) / planck_bc2
>> bt = bt - 273.15
>> Can anyone tell me if I'm missing a step or spot a dumb mistake?
>> Thanks... Art
>> --
>> Arthur A. Person
>> Assistant Research Professor, System Administrator
>> Penn State Department of Meteorology and Atmospheric Science
>> email: aap1@xxxxxxx, phone: 814-863-1563
> --
> Arthur A. Person
> Assistant Research Professor, System Administrator
> Penn State Department of Meteorology and Atmospheric Science
> email: aap1@xxxxxxx, phone: 814-863-1563
--
Arthur A. Person
Assistant Research Professor, System Administrator
Penn State Department of Meteorology and Atmospheric Science
email: aap1@xxxxxxx, phone: 814-863-1563
