scholarly journals Ozone profile retrieval from nadir TROPOMI measurements in the UV range

2021 ◽  
Vol 14 (9) ◽  
pp. 6057-6082
Author(s):  
Nora Mettig ◽  
Mark Weber ◽  
Alexei Rozanov ◽  
Carlo Arosio ◽  
John P. Burrows ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Spectral Data ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Mean Deviation ◽  
Vertical Resolution ◽  
Ozone Profile ◽  
Ground Based Lidar ◽  
Using Data ◽  
Mean Differences

Abstract. The TOPAS (Tikhonov regularised Ozone Profile retrievAl with SCIATRAN) algorithm to retrieve vertical profiles of ozone from space-borne observations in nadir-viewing geometry has been developed at the Institute of Environmental Physics (IUP) of the University of Bremen and applied to the TROPOspheric Monitoring Instrument (TROPOMI) L1B spectral data version 2. Spectral data between 270 and 329 nm are used for the retrieval. A recalibration of the measured radiances is done using ozone profiles from MLS/Aura. Studies with synthetic spectra show that individual profiles in the stratosphere can be retrieved with an uncertainty of about 10 %. In the troposphere, the retrieval errors are larger depending on the a priori profile used. The vertical resolution above 18 km is about 6–10 km, and it degrades to 15–25 km below. The vertical resolution in the troposphere is strongly dependent on the solar zenith angle (SZA). The ozone profiles retrieved from TROPOMI with the TOPAS algorithm were validated using data from ozonesondes and stratospheric ozone lidars. Above 18 km, the comparison with sondes shows excellent agreement within less than ±5 % for all latitudes. The standard deviation of mean differences is about 10 %. Below 18 km, the relative mean deviation in the tropics and northern latitudes is still quite good, remaining within ±20 %. At southern latitudes, larger differences of up to +40 % occur between 10 and 15 km. The standard deviation is about 50 % between 7–18 km and about 25 % below 7 km. The validation of stratospheric ozone profiles with ground-based lidar measurements also shows very good agreement. The relative mean deviation is below ±5 % between 18–45 km, with a standard deviation of 10 %. TOPAS retrieval results for 1 d of TROPOMI observations were compared to ozone profiles from the Microwave Limb Sounder (MLS) on the Aura satellite and the Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP). The relative mean difference was found to be largely below ±5 % between 20–50 km, except at very high latitudes.

scholarly journals Ozone Profile Retrieval from nadir TROPOMI measurements in the UV range

2021 ◽  
Author(s):  
Nora Mettig ◽  
Mark Weber ◽  
Alexei Rozanov ◽  
Carlo Arosio ◽  
John P. Burrows ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Spectral Data ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Mean Deviation ◽  
Vertical Resolution ◽  
Northern Latitudes ◽  
Ground Based Lidar ◽  
Using Data ◽  
Mean Differences

Abstract. The TOPAS algorithm to retrieve vertical profiles of ozone from space-borne observations in nadir viewing geometry has been developed at the Institute of Environmental Physics (IUP) of the University of Bremen and applied to TROPOMI L1B spectral data version 2. The spectral data between 270 and 329 nm are used for the retrieval. A re-calibration of the measured radiances is done using ozone profiles from MLS/Aura. Studies with synthetic spectra show that individual profiles in the stratosphere can be retrieved with the accuracy of about 10 %. In the troposphere, the retrieval errors are larger depending on the a-priori profile used. The vertical resolution above 18 km is about 6–10 km and it degrades to 15–25 km below. The vertical resolution in the troposphere is strongly dependent on the solar zenith angle (SZA). The ozone profiles retrieved from TROPOMI with the TOPAS algorithm were validated using data from ozone sondes and stratospheric ozone lidars. Above 18 km, the comparison with sondes shows excellent agreement within less than ±5 % for all latitudes. The standard deviation of mean differences is about 10 %. Below 18 km, the relative mean deviation in the tropics and northern latitudes is still quite good remaining within ±20 %. At southern latitudes larger differences of up to +40 % occur between 10 and 15 km. The standard deviation is about 50 % between 7–18 km and about 25 % below 7 km. The validation of stratospheric ozone profiles with ground-based lidar measurements also shows very good agreement. The relative mean deviation is below ±5 % between 18–45 km with a standard deviation of 10 %. TOPAS retrieval results for one day of TROPOMI observations were compared to MLS and OMPS-LP data. The relative mean difference was found to be largely below ±5 % between 20–50 km with exception of very high latitudes.

TOPAS ozone profile retrieval from TROPOMI L1B version 2 dataset

2021 ◽  
Author(s):  
Nora Mettig ◽  
Mark Weber ◽  
Alexei Rozanov ◽  
Carlo Arosio ◽  
John P. Burrows ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Spectral Radiance ◽  
Absolute Calibration ◽  
Mean Deviation ◽  
Data Set ◽  
Ozone Profile ◽  
Ground Based Lidar ◽  
Mean Differences

<p>The TOPAS (Tikhonov regularized Ozone Profile retrievAl with SCIATRAN) algorithm to retrieve vertical profiles of ozone from space-borne observations in nadir viewing geometry has been developed at the Institute of Environmental Physics (IUP) of the University of Bremen and applied to TROPOMI L1B spectral data version 2. The data set covers the period from June 2018 to October 2019. But it is not available continuously, but for only single weeks of all 3 months. TROPOMI spectral radiance from channel UV1 and UV2 between 270 nm and 331 nm are used for the retrieval. Since the ozone profiles are very sensitive to absolute calibration at short wavelengths, a re-calibration of the measured radiances is required using comparisons with simulated radiances with ozone limb profiles from collocated MLS/Aura used as input. The time-independent re-calibration bases on simulations for cloud-free pixels of four orbits distributed over the time period. Studies with synthetic spectra show that individual profiles in the stratosphere can be retrieved with the accuracy of about 10%. In the troposphere, the retrieval errors are larger depending on the a-priori profile used. The vertical resolution is between 6 and 10 km above 18 km altitude and 15 – 25 km below. There are around 6 degree of freedom between 0 – 60 km. The TOPAS ozone profiles retrieved from TROPOMI were validated using data from ozone sondes and stratospheric ozone lidars. Above 18 km, the comparison with sondes shows excellent agreement within less than ± 5% for all latitudes. The standard deviation of mean differences is about 10%. Below 18 km, the relative mean deviation in the tropics and northern latitudes is still quite good remaining within ± 20%. At southern latitudes larger differences of up to +40% occur between 10 and 15 km. Here the standard deviation is about 50% between 7 and 18 km and about 25% below 7 km. The validation of stratospheric ozone profiles with ground-based lidar measurements also shows very good agreement. The relative mean deviation is below ± 5% in the 18 – 45 km range with a standard deviation of 10%. A pilot application for one day of TROPOMI data with a comparison to MLS and OMPS confirmed the lidar validation results. The relative mean difference between TROPOMI and MLS or OMPS is largely below ± 5% between 20 – 50 km except for the very high latitudes where differences are getting larger.</p>

scholarly journals Combined UV and IR ozone profile retrieval from TROPOMI and CrIS measurements

2021 ◽  
Author(s):  
Nora Mettig ◽  
Mark Weber ◽  
Alexei Rozanov ◽  
John P. Burrows ◽  
Pepijn Veefkind ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Stratospheric Ozone ◽  
Uv Spectra ◽  
Degree Of Freedom ◽  
Vertical Resolution ◽  
Ozone Profile ◽  
Infrared Spectral ◽  
Using Data ◽  
Uv Ozone ◽  
Vertical Ozone

Abstract. Vertical ozone profiles from combined spectral measurements in the ultraviolet and infrared spectral range were retrieved by using data from TROPOMI/S5P and CrIS/Suomi-NPP, which are flying in loose formation three minutes apart in the same orbit. A previous study of ozone profiles retrieved exclusively from TROPOMI UV spectra showed that the vertical resolution in the troposphere is clearly limited (Mettig et al, 2021). The vertical resolution and the vertical extent of the ozone profiles is improved by combining both wavelength ranges compared to retrievals limited to UV or IR spectral data only. The combined retrieval particularly improves the accuracy of the retrieved tropospheric ozone and to a lesser degree stratospheric ozone up to 30 km. An increase in the degree-of-freedom by one was found in the UV+IR retrieval compared to the UV-only retrieval. Compared to previous publications, which investigated combinations of UV and IR observations from the pairs OMI/TES and GOME-2/IASI, the degree of freedom is lower, which is attributed to the reduced spectral resolution of CrIS compared to TES or IASI. Tropospheric lidar and ozonesondes were used to validate the ozone profiles and tropospheric ozone column (TOC). From the comparison with tropospheric lidars both ozone profiles and TOCs show smaller biases for the retrieved data from the combined UV+IR observation than the UV observations alone. While the TOCs show good agreement, the profiles have a positive bias of more than 20 % between 10 and 15 km. The reason is probably a positive stratospheric bias from the IR retrieval. The comparison of the UV+IR and UV ozone profiles up to 30 km with MLS (Microwave Limb Sounder) demonstrates the improvement of the UV+IR profile in the stratosphere.

scholarly journals Evaluation of ozone profile and tropospheric ozone retrievals from GEMS and OMI spectra

2013 ◽  
Vol 6 (2) ◽  
pp. 239-249 ◽  
Author(s):  
J. Bak ◽  
J. H. Kim ◽  
X. Liu ◽  
K. Chance ◽  
J. Kim
Keyword(s):  
Spectral Resolution ◽  
Tropospheric Ozone ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Ozone Monitoring Instrument ◽  
Satellite Platform ◽  
Ozone Profile ◽  
Retrieval Errors ◽  
Standard Deviations ◽  
Column Ozone

Abstract. South Korea is planning to launch the GEMS (Geostationary Environment Monitoring Spectrometer) instrument into the GeoKOMPSAT (Geostationary Korea Multi-Purpose SATellite) platform in 2018 to monitor tropospheric air pollutants on an hourly basis over East Asia. GEMS will measure backscattered UV radiances covering the 300–500 nm wavelength range with a spectral resolution of 0.6 nm. The main objective of this study is to evaluate ozone profiles and stratospheric column ozone amounts retrieved from simulated GEMS measurements. Ozone Monitoring Instrument (OMI) Level 1B radiances, which have the spectral range 270–500 nm at spectral resolution of 0.42–0.63 nm, are used to simulate the GEMS radiances. An optimal estimation-based ozone profile algorithm is used to retrieve ozone profiles from simulated GEMS radiances. Firstly, we compare the retrieval characteristics (including averaging kernels, degrees of freedom for signal, and retrieval error) derived from the 270–330 nm (OMI) and 300–330 nm (GEMS) wavelength ranges. This comparison shows that the effect of not using measurements below 300 nm on retrieval characteristics in the troposphere is insignificant. However, the stratospheric ozone information in terms of DFS decreases greatly from OMI to GEMS, by a factor of ∼2. The number of the independent pieces of information available from GEMS measurements is estimated to 3 on average in the stratosphere, with associated retrieval errors of ~1% in stratospheric column ozone. The difference between OMI and GEMS retrieval characteristics is apparent for retrieving ozone layers above ~20 km, with a reduction in the sensitivity and an increase in the retrieval errors for GEMS. We further investigate whether GEMS can resolve the stratospheric ozone variation observed from high vertical resolution Earth Observing System (EOS) Microwave Limb Sounder (MLS). The differences in stratospheric ozone profiles between GEMS and MLS are comparable to those between OMI and MLS below ~3 hPa (~40 km), except with slightly larger biases and larger standard deviations by up to 5%. At pressure altitudes above ~3 hPa, GEMS retrievals show strong influence of a priori and large differences with MLS, which, however, can be sufficiently improved by using better a priori information. The GEMS-MLS differences show negative biases of less than 4% for stratospheric column ozone, with standard deviations of 1–3%, while OMI retrievals show similar agreements with MLS except for 1% smaller biases at middle and high latitudes. Based on the comparisons, we conclude that GEMS will measure tropospheric ozone and stratospheric ozone columns with accuracy comparable to that of OMI and ozone profiles with slightly worse performance than that of OMI below ~3 hPa.

scholarly journals Optimal Estimation Method Retrievals of Stratospheric Ozone Profiles from a DIAL Lidar

2018 ◽  
Author(s):  
Ghazal Farhani ◽  
Robert J. Sica ◽  
Sophie Godin-Beekmann ◽  
Alexander Haefele
Keyword(s):  
Stratospheric Ozone ◽  
A Priori ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Uncertainty Budget ◽  
Small Contribution ◽  
Vertical Resolution ◽  
Density Profiles ◽  
Complete Uncertainty ◽  
The Difference

Abstract. This paper provides a detailed description of the first principle Optimal Estimation Method (OEM) which is applied to ozone retrieval analysis using Differential Absorption Lidar (DIAL) measurements. The air density, detector dead times, background coefficients, and lidar constants are simultaneously retrieved along with ozone density profiles. Using an averaging kernel, the OEM provides the vertical resolution of the retrieval as a function of altitude. A maximum acceptable height at which the a priori has a small contribution to the retrieval is calculated for each profile as well. Moreover, a complete uncertainty budget including both systematic and statistical uncertainties is given for each individual retrieved profile. Long term stratospheric DIAL ozone measurements have been carried out at the Observatoire de Haute-Provence (OHP) since 1985. The OEM is applied to 3 nights of measurements at OHP during an intensive ozone campaign in July 2017 where coincident lidar-ozonesonde measurements are available. The retrieved ozone density profiles are in good agreement with both traditional analysis and the ozonesonde measurements. For the three nights of measurements, below 15 km the difference between the OEM and the sonde profiles is less than 25 %, at altitudes between 15 km to 25 km the difference is less than 10 %, and the OEM can successfully catch many variations of ozone which are detected in the sonde profiles due to its ability to adjust its vertical resolution as the signal varies. Above 25 km the difference between the OEM and the sonde profiles does not exceed 20 %.

scholarly journals Optimal estimation method retrievals of stratospheric ozone profiles from a DIAL

2019 ◽  
Vol 12 (4) ◽  
pp. 2097-2111 ◽  
Author(s):  
Ghazal Farhani ◽  
Robert J. Sica ◽  
Sophie Godin-Beekmann ◽  
Alexander Haefele
Keyword(s):  
Stratospheric Ozone ◽  
A Priori ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Uncertainty Budget ◽  
Small Contribution ◽  
Vertical Resolution ◽  
Density Profiles ◽  
Complete Uncertainty ◽  
The Difference

Abstract. This paper provides a detailed description of a first-principle optimal estimation method (OEM) applied to ozone retrieval analysis using differential absorption lidar (DIAL) measurements. The air density, detector dead times, background coefficients, and lidar constants are simultaneously retrieved along with ozone density profiles. Using an averaging kernel, the OEM provides the vertical resolution of the retrieval as a function of altitude. A maximum acceptable height at which the a priori has a small contribution to the retrieval is calculated for each profile as well. Moreover, a complete uncertainty budget including both systematic and statistical uncertainties is given for each individual retrieved profile. Long-term stratospheric DIAL ozone measurements have been carried out at the Observatoire de Haute-Provence (OHP) since 1985. The OEM is applied to three nights of measurements at OHP during an intensive ozone campaign in July 2017 for which coincident lidar–ozonesonde measurements are available. The retrieved ozone density profiles are in good agreement with both traditional analysis and the ozonesonde measurements. For the three nights of measurements, below 15 km the difference between the OEM and the sonde profiles is less than 25 %, and at altitudes between 15 and 25 km the difference is less than 10 %; the OEM can successfully catch many variations in ozone, which are detected in the sonde profiles due to its ability to adjust its vertical resolution as the signal varies. Above 25 km the difference between the OEM and the sonde profiles does not exceed 20 %.

scholarly journals Evaluation of ozone profile and tropospheric ozone retrievals from GEMS and OMI spectra

2012 ◽  
Vol 5 (5) ◽  
pp. 6733-6762 ◽  
Author(s):  
J. Bak ◽  
J. H. Kim ◽  
X. Liu ◽  
K. Chance ◽  
J. Kim
Keyword(s):  
Spectral Resolution ◽  
Tropospheric Ozone ◽  
Degrees Of Freedom ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Ozone Monitoring Instrument ◽  
Ozone Profile ◽  
Retrieval Errors ◽  
Standard Deviations ◽  
Column Ozone

Abstract. Korea is planning to launch the GEMS (Geostationary Environment Monitoring Spectrometer) instrument into a Geostationary (GEO) platform in 2018 to monitor tropospheric air pollutants on an hourly basis over East Asia. GEMS will measure backscattered UV radiances covering the 300–500 nm wavelength range with a spectral resolution of 0.6 nm. The main objective of this study is to evaluate ozone profiles and stratospheric column ozone amounts retrieved from simulated GEMS measurements. Ozone Monitoring Instrument (OMI) Level 1B radiances, which have the spectral range 270–500 nm at spectral resolution of 0.42–0.63 nm, are used to simulate the GEMS radiances. An optimal estimation-based ozone profile algorithm is used to retrieve ozone profiles from simulated GEMS radiances. Firstly, we compare the retrieval characteristics (including averaging kernels, degrees of freedom for signal, and retrieval error) derived from the 270–330 nm (OMI) and 300–330 nm (GEMS) wavelength ranges. This comparison shows that the effect of not using measurements below 300 nm on tropospheric ozone retrievals is insignificant. However, the stratospheric ozone information decreases greatly from OMI to GEMS, by a factor of ∼2. The number of the independent pieces of information available from GEMS measurements is estimated to 3 on average in the stratosphere, with associated retrieval errors of ∼1% in stratospheric column ozone. The difference between OMI and GEMS retrieval characteristics is apparent for retrieving ozone layers above ∼20 km, with a reduction in the sensitivity and an increase in the retrieval errors for GEMS. We further investigate whether GEMS can resolve the stratospheric ozone variation observed from high vertical resolution EOS Microwave Limb Sounder (MLS). The differences in stratospheric ozone profiles between GEMS and MLS are comparable to those between OMI and MLS above ∼3 hPa (∼40 km) except with slightly larger biases and larger standard deviations by up to 5%. At pressure altitudes above ∼3 hPa, GEMS retrievals show strong influence of a priori and large differences with MLS, which, however, can be sufficiently improved by using better a priori information. The GEMS-MLS differences show negative biases of less than 4% for stratospheric column ozone, with standard deviations of 1–3%, while OMI retrievals show similar agreements with MLS except for 1% smaller biases at mid and high latitudes. Based on the comparisons, we conclude that GEMS will measure tropospheric ozone and stratospheric ozone columns with accuracy comparable to that of OMI and ozone profiles with slightly worse performance than that of OMI below ∼3 hPa.

scholarly journals A global ozone climatology from ozone soundings via trajectory mapping: a stratospheric perspective

2013 ◽  
Vol 13 (22) ◽  
pp. 11441-11464 ◽  
Author(s):  
J. Liu ◽  
D. W. Tarasick ◽  
V. E. Fioletov ◽  
C. McLinden ◽  
T. Zhao ◽  
...  
Keyword(s):  
Satellite Data ◽  
Lower Stratosphere ◽  
Stratospheric Ozone ◽  
A Priori ◽  
Forecast Model ◽  
Reanalysis Data ◽  
Trajectory Mapping ◽  
Decadal Variations ◽  
Mean Differences ◽  
The 1960S

Abstract. This study explores a domain-filling trajectory approach to generate a global ozone climatology from relatively sparse ozonesonde data. Global ozone soundings comprising 51 898 profiles at 116 stations over 44 yr (1965–2008) are used, from which forward and backward trajectories are calculated from meteorological reanalysis data to map ozone measurements to other locations and so fill in the spatial domain. The resulting global ozone climatology is archived monthly for five decades from the 1960s to the 2000s on a grid of 5° × 5° × 1 km (latitude, longitude, and altitude), from the surface to 26 km altitude. It is also archived yearly for the same period. The climatology is validated at 20 selected ozonesonde stations by comparing the actual ozone sounding profile with that derived through trajectory mapping of ozone sounding data from all stations except the one being compared. The two sets of profiles are in good agreement, both overall with correlation coefficient r = 0.991 and root mean square (RMS) of 224 ppbv and individually with r from 0.975 to 0.998 and RMS from 87 to 482 ppbv. The ozone climatology is also compared with two sets of satellite data from the Satellite Aerosol and Gas Experiment (SAGE) and the Optical Spectrography and InfraRed Imager System (OSIRIS). The ozone climatology compares well with SAGE and OSIRIS data in both seasonal and zonal means. The mean differences are generally quite small, with maximum differences of 20% above 15 km. The agreement is better in the Northern Hemisphere, where there are more ozonesonde stations, than in the Southern Hemisphere; it is also better in the middle and high latitudes than in the tropics where reanalysis winds are less accurate. This ozone climatology captures known features in the stratosphere as well as seasonal and decadal variations of these features. The climatology clearly shows the depletion of ozone from the 1970s to the mid 1990s and ozone increases in the 2000s in the lower stratosphere. When this climatology is used as the upper boundary condition in an Environment Canada operational chemical forecast model, the forecast is improved in the vicinity of the upper troposphere-lower stratosphere (UTLS) region. This ozone climatology is latitudinally, longitudinally, and vertically resolved and it offers more complete high latitude coverage as well as a much longer record than current satellite data. As the climatology depends on neither a priori data nor photochemical modeling, it provides independent information and insight that can supplement satellite data and model simulations of stratospheric ozone.

scholarly journals Characterization of ozone profiles derived from Aura TES and OMI radiances

2013 ◽  
Vol 13 (6) ◽  
pp. 3445-3462 ◽  
Author(s):  
D. Fu ◽  
J. R. Worden ◽  
X. Liu ◽  
S. S. Kulawik ◽  
K. W. Bowman ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Surface Ozone ◽  
A Priori ◽  
Lower Troposphere ◽  
Vertical Resolution ◽  
Ozone Monitoring Instrument ◽  
Near Surface ◽  
Production Code ◽  
Ozone Profile

Abstract. We present satellite based ozone profile estimates derived by combining radiances measured at thermal infrared (TIR) wavelengths from the Aura Tropospheric Emission Spectrometer (TES) and ultraviolet (UV) wavelengths measured by the Aura Ozone Monitoring Instrument (OMI). The advantage of using these combined wavelengths and instruments for sounding ozone over either instrument alone is improved sensitivity near the surface as well as the capability to consistently resolve the lower troposphere, upper troposphere, and lower stratosphere for scenes with varying geophysical states. For example, the vertical resolution of ozone estimates from either TES or OMI varies strongly by surface albedo and temperature. Typically, TES provides 1.6 degrees of freedom for signal (DOFS) and OMI provides less than 1 DOFS in the troposphere. The combination provides 2 DOFS in the troposphere with approximately 0.4 DOFS for near surface ozone (surface to 700 hPa). We evaluated these new ozone profile estimates with ozonesonde measurements and found that calculated errors for the joint TES and OMI ozone profile estimates are in reasonable agreement with actual errors as derived by the root-mean-square (RMS) difference between the ozonesondes and the joint TES/OMI ozone estimates. We also used a common a priori profile in the retrievals in order to evaluate the capability of different retrieval approaches on capturing near-surface ozone variability. We found that the vertical resolution of the joint TES/OMI ozone profile estimates shows significant improvements on quantifying variations in near-surface ozone with RMS differences of 49.9% and correlation coefficient of R = 0.58 for the TES/OMI near-surface estimates as compared to 67.2% RMS difference and R = 0.33 for TES and 115.8% RMS difference and R = 0.09 for OMI. This comparison removes the impacts of using the climatological a priori in the retrievals. However, it results in artificially large sonde/retrieval differences. The TES/OMI ozone profiles from the production code of joint retrievals will use climatological a priori and therefore will have more realistic ozone estimates than those from using a common a priori volume mixing ratio profile.

scholarly journals Using self organising maps to explore ozone profile validation results – SCIAMACHY limb compared to ground-based lidar observations

2014 ◽  
Vol 7 (4) ◽  
pp. 4373-4406
Author(s):  
J. A. E. van Gijsel ◽  
R. Zurita-Milla ◽  
P. Stammes ◽  
S. Godin-Beekmann ◽  
T. Leblanc ◽  
...  
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
A Priori ◽  
Relative Difference ◽  
Full Time ◽  
Self Organizing Map ◽  
Ozone Profile ◽  
The Difference ◽  
Ground Based Lidar ◽  
Lidar Observations

Abstract. Traditional validation of atmospheric profiles is based on the intercomparison of two or more datasets in predefined ranges or classes of a given observational characteristic such as latitude or solar zenith angle. In this study we train a self organizing map (SOM) with a full time series of relative difference profiles of SCIAMACHY limb v5.02 and lidar ozone profiles from seven observation sites. Each individual observation characteristic is then mapped to the obtained SOM to investigate to which degree variation in this characteristic is explanatory for the variation seen in the SOM map. For the studied datasets, altitude-dependent relations for the global dataset were found between the difference profiles and studied variables. From the lowest altitude studied (18 km) ascending, the most influencing factors were found to be longitude, followed by solar zenith angle and latitude, sensor age and again solar zenith angle together with the day of the year at the highest altitudes studied here (up to 45 km). Clustering into three classes showed that there are also some local dependencies, with for instance one cluster having a much stronger correlation with the sensor age (days since launch) between 36 and 42 km. It was shown that the proposed approach provides a powerful tool for the exploring of differences between datasets without being limited to a-priori defined data subsets.

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