1. Comparison among Reference Solar Spectra using TROPOMI Solar Measurements
Mina Kang1, Myoung-Hwan Ahn1, Quintus Kleipool2 and Pepijn Veefkind2
Department of Atmospheric Science and Engineering, Ewha Womans University
2 Royal Netherlands Meteorological Institute (KNMI)

2. Outline of the Presentation
TROPOMI Instrument
TROPOMI Solar Irradiance
Reference Solar Spectra
TROPOMI In-Orbit ISRF
Comparison among Reference Solar Spectra
Some Concluding Remarks

3. UV-Vis-NIR-SWIR nadir viewing pushbroom grating spectrometer
TROPOMI Instrument
Successful launch of TROPOMI (TROPospheric Ozone Monitoring Instrument) on board the sentinel 5 precursor
TROPOMI
UV-Vis-NIR-SWIR nadir viewing pushbroom grating spectrometer
Spectral Range
nm, nm, nm
Spectral Resolution nm
Spatial Resolution (Nadir)
7 x 7 km2
Courtesy: ESA, Copernicus

4. TROPOMI Instrument Total Column O3, NO2, CO, SO2, CH4, CH2O, H2O, BrO
Tropospheric column
O3, NO2
O3 Profile
Aerosol
AI, AOD, Aerosol Type
Courtesy: ESA, Copernicus

5. TROPOMI Instrument Vicarious Calibration for UV-Vis Satellite
Courtesy: ESA
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
GEMS
TEMPO
Sentinel-4
Sentinel-5p
Sentinel-5

6. TROPOMI Instrument Vicarious Calibration using GEO and LEO Satellite
After the GEMS is launched, we can utilize the AMI which is korea’s advanced metrological imager.
We are evaluating the possibility of calibration of VIS channel of GEMS using detected DCC from IR sensor.
As a preliminary test, we compared AHI radiance with convolved tropomi radiances.
AHI Radiance (Ch.1; 4.7 μm)
Convolved TROPOMI Radiance with AHI SRF

7. TROPOMI Solar Irradiance
TROPOMI Measured Solar Irradiance
Solar Irradiance obtained from In-orbit test ( ; only single day)
TROPOMI Solar Measurement
Ratio of Band 2 & Band 3
Inconsistency between band 2 and band 3

8. TROPOMI Solar Irradiance
TROPOMI Measured Solar Irradiance
In-orbit test data ( )
TROPOMI Solar Measurements (SWIR)
TROPOMI Solar Measurements (NIR)
Spike seen in SWIR
Need further quality check

9. Reference Solar Spectra
Currently Available Reference Solar Spectra
Spectrum
Wavelength range [nm]
Spectral resolution [nm]
Spectral sampling [nm]
Uncertainty [%]
References
NRLSSI2
1.00
2-4
Coddington et al. (2015)
ATLAS
2-4 for nm
Thuillier et al. (2004)
WHI
0.01
2-4 for nm
Woods et al. (2008)
KNMI
0.025
<4 for nm
Dobber et al. (2006)
SAO2010
0.04
< 5 for nm
Chance and Kurucz (2010)
JPL
Toon et al. (2014)

10. Reference Solar Spectra
Reference Solar Spectra of TROPOMI
High Resolution Reference Solar Spectra
TROPOMI Solar Irradiance
KNMI (Dobber et al)
SAO2010 (Chane and Kurucz)
JPL (Toon et al)
Band1: [ nm]
Band2: [ nm]
Band3: [ nm]
Band4: [ nm]
Band5: [ nm]
Band6: [ nm]
Band7: [ nm]
Band8: [ nm]
KNMI
SAO2010
SAO2010
JPL

11. TROPOMI In-Orbit ISRFs
Derive TROPOMI In-Orbit Instrument Spectral Response Function
Asymmetric Super-Gaussian analytic function (Beirle et al 2016) is used.
𝑇𝑅𝑂𝑃𝑂𝑀𝐼 𝑆𝑜𝑙𝑎𝑟 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡= 𝑅𝑒𝑓𝑠𝑜𝑙 𝜆 𝝓 𝑨𝑺𝑮,𝝀 𝑑𝜆 𝝓 𝑨𝑺𝑮,𝝀 𝑑𝜆 × 𝑨 𝟎 + 𝑨 𝟏 𝜆− 𝜆 𝑎𝑣𝑔 + 𝑨 𝟐 𝜆− 𝜆 𝑎𝑣𝑔 𝑨 𝟑 𝜆− 𝜆 𝑎𝑣𝑔 3
𝐴𝑆𝐺 𝜆 (𝑥)= 𝒌 2𝝕Γ 1/𝑘 × 𝑒 − 𝑥 𝜛− 𝑎 𝜛 𝑘− 𝒂 𝒌 𝑒 − 𝑥 𝜛+ 𝑎 𝜛 𝑘+ 𝒂 𝒌
TROPOMI Solar Irradiance
High Resolution Reference Solar Spectra
Derived TROPOMI ISRF
Spectral Fitting based on Optimal Estimation Algorithm

12. TROPOMI In-Orbit ISRFs
TROPOMI Instrument Spectral Response Function UV
Flat-topped, trapezium-like
FWHM: 0.45 to 0.5 nm
UVIS
Triangular + Gaussian, asymmetric
FWHM: 0.45 to 0.65 nm
NIR
Gaussian with rounded top
FWHM: 0.34 to 0.35 nm

13. TROPOMI In-Orbit ISRFs
TROPOMI Instrument Spectral Response Function
Stable derivation regardless of reference solar spectrum; KNMI or SAO2010
KNMI
SAO2010

14. Comparison among Reference Solar Spectra
TROPOMI Measured Solar Irradiance
Compare the band 2 and band 3 irradiances with reference solar spectrum (Dobber et al. 2006)
Absolute deviations with reference spectrum
Relatively high disagreement in band 3
Ratio of TROPOMI Measurements and KNMI ㅊ

15. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 1 Irradiance vs. KNMI/SAO2010
Use averaged B1 irradiance
( to nm)

16. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 2 Irradiance vs. KNMI/SAO2010
Use averaged B2 irradiance
( to nm)

17. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 3 Irradiance vs. KNMI/SAO2010
Use averaged B3 irradiance
( to nm)

18. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 4 Irradiance vs. KNMI/SAO2010
Use averaged B4 irradiance
( to )

19. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 5 Irradiance vs. SAO2010/JPL
Use averaged B5 irradiance
( to )

20. Comparison among Reference Solar Spectra
Comparison Reference Solar Spectra and TROPOMI Irradiance
Band 6 Irradiance vs. SAO2010/JPL
Use averaged B6 irradiance
( to )

21. KNMI vs. TROPOMI (B1) SAO2010 vs. TROPOMI (B1) KNMI vs. TROPOMI (B2)
Band 1
Y = 1.011x+0.008
R = 0.999
Band 2
Y = 1.171x-0.003
R = 0.996
KNMI vs. TROPOMI (B1)
SAO2010 vs. TROPOMI (B1)
Band 2
Y = 0.982x+0.016
R = 0.997
Y = 1.042x-0.027
R = 0.996
KNMI vs. TROPOMI (B2)
SAO2010 vs. TROPOMI (B2)
( to )

22. SAO2010 vs. TROPOMI (B3) KNMI vs. TROPOMI (B3) KNMI vs. TROPOMI (B4)
Band 3
Y = 0.960x+0.112
R = 0.992
Y = 0.972x+0.122
R = 0.994
SAO2010 vs. TROPOMI (B3)
KNMI vs. TROPOMI (B3)
Band 4
Y = 1.018x+0.014
R = 0.998
Y = 1.023x-0.071
R = 0.999
KNMI vs. TROPOMI (B4)
SAO2010 vs. TROPOMI (B4)
( to )

23. SAO2010 vs. TROPOMI (B5) JPL vs. TROPOMI (B5) SAO2010 vs. TROPOMI (B6)
Band 5
Y = 0.907x+0.575
R = 0.961
Band 5
Y = 0.990x+0.133
R = 0.994
SAO2010 vs. TROPOMI (B6)
JPL vs. TROPOMI (B6)
Band 6
Y = 1.022x-0.017
R = 0.988
Band 6
Y = 1.001x+0.061
R = 0.997

24. Comparison among Reference Solar Spectra
TK: TROPOMI vs. KNMI
TS: TROPOMI vs. SAO2010
SK: SAO2010 vs. KNMI
TJ : TROPOMI vs. JPL
JS : JPL vs. SAO2010
Comparison Reference Solar Spectra and TROPOMI Irradiance
Averaged ratio and differences indicates that TROPOMI measurements show good quality.
still preliminary and issues have been identified that will be corrected at the end of the commissioning phase.
Band1 [ nm]
Band2: [ nm]
Band3: [ nm]
Band4: [ nm]
Band5: [ nm]
Band6: [ nm]
Ratio
Difference [%]
Spectrum TK TS SK TJ JS
Band 1
0.967
0.849
1.140
-3.311
-15.05
13.99
Band 4
0.987
0.979
1.001
-1.252
-2.118
1.009
Band 2
0.997
0.978
1.020
-0.304
-2.168
2.012
Band 5
0.984
0.995
-2.107
-1.596
-0.519
Band 3
0.972
0.956
1.018
-2.772
-4.448
1.772
Band 6
0.982
1.002
-1.799
-2.024
0.230
( to )

25. Concluding Remarks
TROPOMI successfully launched onboard the Sentinel 5 precursor
S5p and S5 are expected to be a good reference for GEMS/TEMPO/S4
Current available reference solar spectra have been compared using TROPOMI preliminary solar measurement
Although already of good quality, a few issues regrading the TROPOMI irradiance data to be identified and corrected with the Level 1b algorithm update

26. Acknowledgement
The presented work has been performed in the frame of the Sentinel 5P Calibration & Validation (S5P CalVal) Project. Results are based on the use of S-5P in-flight data still subject to in-depth validation activities prior to final release.

27. Thank you :D

28. Reference Solar Spectra
Reference Solar Spectra of TROPOMI
Spectral Range [nm]
Description
Accuracy
UV-VIS-NIR nm
Dobber et al (2006)
[Spectral Resolution nm]
[Spectral Sampling 0.01 nm]
4-5 % nm
Chance and Kurucz (2010)
[Spectral Resolution 0.04 nm]
5 %
SWIR nm
Thuiller et al (2004)
2 % nm 2%

30. Spectral Resolution [nm] Spectral Sampling [nm]
Spectrometer UV
UVIS
NIR
SWIR
Band ID 1 2 3 4 5 6 7 8
Spectral Range [nm]
Spectral Resolution [nm]
0.5
0.55
0.25
0.23
Spectral Sampling [nm]
0.06
0.2
0.1
<0.1
Spatial Sampling [km2]
21x28
7x7
7x1.8
SNR
100
1500
500

31. Current References SAO2010 vs. KNMI reference spectrum
There are noticeable differences between the two at TEMPO/GEMS resolution (FWHM = 0.6 nm)
% differences with 0.6 nm FWHM Gaussian SRF
When we compare these spectra at tempo and gems resolution, there are non negligible differences the two.
the differences between spectra can show larger variations locally. Especially, in short wavelength range the differences btw two is up to 8 %.
SAO 2010
KNMI --
---
Convolved KNMI
Convolved SAO
Comparison between SAO2010 and KNMI at initial resolution and lower resolution (FWHM= 0.6 nm)
Differences between SAO2010 and KNMI (FWHM= 0.6 nm)

32. Current References SAO2010 vs. KNMI reference spectrum
Composite spectrum from different data sources
SAO2010 is not absolutely calibrated!
Differences between sao2010 and KNMI spectrum are mainly caused by using of the different data sources.
SAO2010 is composite spectrum based on hall and Anderson and kurucz 2005.
Kurucz 2005 is updated version of kurucz 1984, it is additionally applied atmospheric correction.
It means that while sao2010 is updated version of sao96, but it is only updated kittpeak data not absolutely calibrated.
On the other hand, KNMI is based on SAO96, but is applied additional radiometric calibration with low resolution spectra (SUSIM and Balloon measurement)
Wavelength range/sampling ratio/resolution (FWHM)