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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
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