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Art, Did you ever get this figured out? I plotted up an ABI full disk image from the GRB Radiance data coming in from both the Unidata DIFAX feed and from the tiled NOAAPORT CMI data. They seem pretty much the same to me, considering resolution differences - 2km for GRB vs 6km for the NOAAPORT data. GRB image - http://whirlwind.aos.wisc.edu/~wxp/goes16/test/201801210430_fulldisk_grb.jpg NOAAPORT image - http://whirlwind.aos.wisc.edu/~wxp/goes16/test/201801210430_fulldisk.jpg 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: ldm-users-bounces@xxxxxxxxxxxxxxxx <ldm-users-bounces@xxxxxxxxxxxxxxxx> on behalf of Arthur A Person <aap1@xxxxxxx> Sent: Monday, January 15, 2018 4:45 PM To: ldm-users Subject: Re: [ldm-users] Problem calculating GOES-16 brightness temperature from radiance 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 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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