When calculating the bright temperature, I used ERA5 data. ERA5 data has 37 pressure levels,the 37 pressure levels: 1, 2, 3, 5, 7, 10, 20, 30, 50, 70, 100, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 775, 800, 825, 850, 875, 900, 925, 950, 975, 1000. But I don’t know what pressureLevels and pressureLayers are respectively.What should the pressureLevels and pressureLayers of ERA5 be?
Hello Meng,
so, I am assuming that you want to run the CRTM with ERA5 data?
The ERA5 pressure levels are not directly related to CRTM pressure layers and levels.
In the CRTM radiative transfer solver, the 1D radiation path is discretized into N layers.
The levels are the N+1 boundaries of the layers.
The CRTM level pressure is the pressure at the layer boundaries, and the CRTM layer pressure is the average pressure of a given layer.
Let me know if you have any further questions.
Thank you. Your reply helps me a lot. I want to run the CRTM with ERA5 data. ERA5 data has 37 pressure levels, so it has 36 pressure layers, and each layer pressure is the average pressure of a given layer.Is that right?
Roughly correct, using the hypsometric equation, you can derive the layer pressure, it’s not a linear average though.
Thanks a lot. But I don’t quite understand how to use the hypsometric equation, could you please tell me more about it?
Hi, Su
May I ask how you solved it in the end? I also want to use the data of era5, if it is convenient, I hope I can refer to how you deal with it.
Thanks a lot!
The CRTM provides a function to evaluate the hypsometric equation:
USE CRTM_Hypsometric, ONLY: HypsometricEq
which computes the layer virtual temperature from the level pressure and an array of level geometric height.
So you do need to specify the level geometric height as an additional degree of freedom.
At the moment I do not know if ERA5 also provides level geometric height data.
The layer temperature is the only additional information you need to run the CRTM.
The layer pressure can be obtained from the layer density and the ideal gas equation, if desired.
Hi, @StegmannJCSDA
Sorry to bother you.
I also want to use the data of ERA5 to run CRTM mode. The ERA5 data provides geometric height, temperature, absorbed gas and other data on 37 pressure levels within the range of 1-1000hPa. In addition, it also provides the pressure, temperature and other data of the surface.
I would like to compare the results of the different modes.
When using LBLRTM, I use the surface data as the first layer and then add the other 37 pressure level data, so I set the number of atmospheric profile boundaries to 38. LBLRTM instruction says that these are data on the layer boundary. The TAPE5 files I used are as follows:
$ 111t5ref 06/12/96 CAMEX NASA Flt #93-169 09/29/93 Wallops Island *ARM Ret O3*
HI=1 F4=1 CN=1 AE=0 EM=1 SC=3 FI=0 PL=0 TS=0 AM=1 MG=0 LA=0 OD=0 XS=0 00 00
781.646 1400.894 -0.001 REJ=0
302.1 -1.000 -1.000
0 2 38 1 1 3 1 0 0 0.000 0.000
824.0000 0.0000 180.0000
0.000 0.075 0.299 0.528 0.761 1.000 1.244 1.495
1.752 2.016 2.286 2.565 3.146 3.764 4.422 5.127
5.886 6.708 7.607 8.599 9.711 10.977 11.683 12.452
13.298 14.245 15.329 16.618 18.664 20.664 23.770 26.311
30.692 33.139 35.522 39.290 42.286 47.734
38 INPUT FOR CAMEX
0.000 1008.399 302.066 AA L CAC
1.86121041e+01 3.68500000e+02 5.25739203e-05
0.075 1000.000 299.913 AA L CAC
1.86121041e+01 3.63000000e+02 5.25739203e-05
0.299 975.000 298.074 AA L CAC
1.81627210e+01 3.63000000e+02 5.53343429e-05
0.528 950.000 296.539 AA L CAC
1.78844956e+01 3.63000000e+02 5.56103851e-05
0.761 925.000 295.498 AA L CAC
1.72258779e+01 3.63000000e+02 5.39541316e-05
1.000 900.000 294.194 AA L CAC
1.67139130e+01 3.63000000e+02 5.28499626e-05
1.244 875.000 293.211 AA L CAC
1.58441758e+01 3.63000000e+02 5.20218358e-05
1.495 850.000 291.958 AA L CAC
1.51991301e+01 3.63000000e+02 5.14697513e-05
1.752 825.000 290.735 AA L CAC
1.46487113e+01 3.63000000e+02 5.03655823e-05
2.016 800.000 289.580 AA L CAC
1.41914112e+01 3.64200000e+02 4.98134978e-05
2.286 775.000 288.345 AA L CAC
1.34834067e+01 3.66300000e+02 5.03655823e-05
2.565 750.000 287.251 AA L CAC
1.25439246e+01 3.68000000e+02 5.14697513e-05
3.146 700.000 284.817 AA L CAC
9.35828120e+00 3.68500000e+02 5.69905964e-05
3.764 650.000 281.730 AA L CAC
6.40072230e+00 3.68500000e+02 7.49333430e-05
4.422 600.000 278.178 AA L CAC
4.87085946e+00 3.68500000e+02 6.14072725e-05
5.127 550.000 274.215 AA L CAC
2.31103475e+00 3.68500000e+02 4.56728640e-05
5.886 500.000 269.062 AA L CAC
1.83375374e+00 3.68500000e+02 4.65009907e-05
6.708 450.000 263.183 AA L CAC
1.78021985e+00 3.68500000e+02 4.89853710e-05
7.607 400.000 257.630 AA L CAC
7.03133073e-01 3.68500000e+02 5.67145541e-05
8.599 350.000 250.398 AA L CAC
3.95501708e-01 3.68500000e+02 5.97510189e-05
9.711 300.000 242.169 AA L CAC
1.75711162e-01 3.68500000e+02 7.49333430e-05
10.977 250.000 232.039 AA L CAC
9.05093384e-02 3.68500000e+02 1.13027174e-04
11.683 225.000 226.103 AA L CAC
6.14803984e-02 3.68500000e+02 1.25725118e-04
12.452 200.000 219.918 AA L CAC
3.99914428e-02 3.68500000e+02 1.38423062e-04
13.298 175.000 213.436 AA L CAC
2.67964700e-02 3.68500000e+02 1.43667864e-04
14.245 150.000 206.550 AA L CAC
1.62404918e-02 3.68500000e+02 1.42839738e-04
15.329 125.000 199.800 AA L CAC
6.43851206e-03 3.68500000e+02 2.09918005e-04
16.618 100.000 196.381 AA L CAC
3.79951751e-03 3.68500000e+02 3.69194386e-04
18.664 70.000 197.588 AA L CAC
3.42251829e-03 3.68500000e+02 8.54476670e-04
20.664 50.000 207.076 AA L CAC
2.66851985e-03 3.68500000e+02 2.42267272e-03
23.770 30.000 212.494 AA L CAC
2.66851985e-03 3.68500000e+02 6.78524451e-03
26.311 20.000 214.161 AA L CAC
2.66851985e-03 3.68500000e+02 1.12154467e-02
30.692 10.000 227.280 AA L CAC
3.04551907e-03 3.68500000e+02 1.62543220e-02
33.139 7.000 238.804 AA L CAC
3.04551907e-03 3.68500000e+02 1.59131337e-02
35.522 5.000 245.872 AA L CAC
3.04551907e-03 3.68500000e+02 1.36349570e-02
39.290 3.000 252.812 AA L CAC
3.42251829e-03 3.68500000e+02 1.04450127e-02
42.286 2.000 258.746 AA L CAC
3.42251829e-03 3.68500000e+02 8.09644522e-03
47.734 1.000 269.767 AA L CAC
3.79951751e-03 3.68500000e+02 4.61803677e-03
0.500 781.646 1400.894 1 1 0.010 12 1 1 11
-1.
$ Transfer to ASCII plotting data
HI=0 F4=0 CN=0 AE=0 EM=0 SC=0 FI=0 PL=1 TS=0 AM=0 MG=1 LA=0 MS=0 XS=0 0 0
# Plot title not used
781.646 1400.894 10.2000 100.0000 5 0 10 0 1.000 0 0 0
0.0000 1.2000 7.0200 0.2000 4 0 1 0 1 0 0 3 27
781.646 1400.894 10.2000 100.0000 5 0 12 0 1.000 0 0 0
0.0000 1.2000 7.0200 0.2000 4 0 1 1 1 0 0 3 28
-1.
%%%%%
Now I’m wondering, if I wrote the LBLRTM TAPE5 file this way (assuming this is correct), what my level and layer should be set accordingly in CRTM.
- Was level set to 39 and layer set to 38, and the layer pressure, temperature and absorbed gas use the corresponding values of the 38 boundaries in TAPE5, and then the level pressure value was obtained by interpolation or some other equation?
- Or level was set to 38 and laye to 37, the level pressure use the pressure values of the 38 boundary in TAPE5, and the layer pressure, temperature and absorbed gas values were calculated using the hypsometric equation and other equations you mentioned above?
Any reply would be appreciated.
Thank you!
Hello @kkllww.
No problem, this is actually a good question. First, I encourage you to review the CRTM user guide to get a full overview of how to enter atmospheric data into the CRTM.
That aside, a CRTM atmospheric profile consists of layers that are essentially the center of finite volume cells. The levels are the boundaries between the cells.
That means that TOA is your lowest pressure level (array index 0) and the surface is your highest pressure level (array index n_layers) and that you’ll always have one level more than the number of layers.
There is some ambiguity in computing the level and layer values.
-
First, you can simply interpolate between levels and layers.
-
Second, the CRTM provides a module
Level_Layer_Conversionwith conversion functions from Layer values to Level values. -
Third, you can use
MODULE CRTM_Hypsometricto compute the layer temperature from the level geometric height and pressure.
It is important to keep track which approach you used.
@kkllww your TAPE5 file looks good at first glance but I haven’t tested it.
It is important to keep in mind that LBLRTM will give you monochromatic results, whereas the CRTM only provides results at instrument channel resolution, so it is never an apples to apples comparison.
@kkllww if you are working on an ERA5 converter for the CRTM, feel free to add it to the CRTM repository, as it might be very useful for other people as well.
Hi, @StegmannJCSDA
Thank you so much for your reply and suggestions.
I convolved the monochromatic result obtained by LBLRTM with the SRF of the instrument to get the channel brightness temperature and then compared it with CRTM BT results.
Thank you for your advice. I have understood the meaning of level and layer. I will try these methods you mentioned first, and add it to github if I could work it out.
Thanks again for your help!
Best Regards
1 Like
Hi,
It might not be polite to ask you this question here. please forgive me.
Can the channel average transmittance be compared? I tried to compare the channel transmittance output by RTTOV, and then convolved the monochromatic optical transmittance calculated by LBLRTM with the spectral response function. Comparing the two, I found that there is a big difference, whether it is column or Layer, I haven’t tested CRTM yet. I googled this issue and saw the discussion here and wanted to ask for advice.