Validation of TROPOMI nadir ozone profile retrievals: Methodology and first results

2021 ◽  
Author(s):  
Arno Keppens ◽  
Jean-Christopher Lambert ◽  
Daan Hubert ◽  
Steven Compernolle ◽  
Tijl Verhoelst ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stratospheric Ozone ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Data Retrieval ◽  
Atmospheric Composition ◽  
Retrieval Algorithm ◽  
Validation Data ◽  
Ozone Profile ◽  
Early Afternoon

<p>Part of the space segment of EU’s Copernicus Earth Observation programme, the Sentinel-5 Precursor (S5P) mission is dedicated to global and European atmospheric composition measurements of air quality, climate and the stratospheric ozone layer. On board of the S5P early afternoon polar satellite, the imaging spectrometer TROPOMI (TROPOspheric Monitoring Instrument) performs nadir measurements of the Earth radiance within the UV-visible and near-infrared spectral ranges, from which atmospheric ozone profile data are retrieved. Developed at the Royal Netherlands Meteorological Institute (KNMI) and based on the optimal estimation method, TROPOMI’s operational ozone profile retrieval algorithm has recently been upgraded. With respect to early retrieval attempts, accuracy is expected to have improved significantly, also thanks to recent updates of the TROPOMI Level-1b data product. This work reports on the initial validation of the improved TROPOMI height-resolved ozone data in the troposphere and stratosphere, as collected both from the operational S5P Mission Performance Centre/Validation Data Analysis Facility (MPC/VDAF) and from the S5PVT scientific project CHEOPS-5p. Based on the same validation best practices as developed for and applied to heritage sensors like GOME-2, OMI and IASI (Keppens et al., 2015, 2018), the validation methodology relies on the analysis of data retrieval diagnostics – like the averaging kernels’ information content – and on comparisons of TROPOMI data with reference ozone profile measurements. The latter are acquired by ozonesonde, stratospheric lidar, and tropospheric lidar stations performing network operation in the context of WMO's Global Atmosphere Watch and its contributing networks NDACC and SHADOZ. The dependence of TROPOMI’s ozone profile uncertainty on several influence quantities like cloud fraction and measurement parameters like sun and scan angles is examined and discussed. This work concludes with a set of quality indicators, enabling users to verify the fitness-for-purpose of the S5P data.</p>

Validation of TROPOMI nadir ozone profile retrievals: Methodology and first results

2020 ◽  
Author(s):  
Arno Keppens ◽  
Daan Hubert ◽  
Jean-Christopher Lambert ◽  
Steven Compernolle ◽  
Tijl Verhoelst ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stratospheric Ozone ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Data Retrieval ◽  
Atmospheric Composition ◽  
Retrieval Algorithm ◽  
Validation Data ◽  
Ozone Profile ◽  
Early Afternoon

<p>Part of the space segment of EU’s Copernicus Earth Observation programme, the Sentinel-5 Precursor (S5P) mission is dedicated to global and European atmospheric composition measurements of air quality, climate and the stratospheric ozone layer. On board of the S5P early afternoon polar satellite, the imaging spectrometer TROPOMI (TROPOspheric Monitoring Instrument) performs nadir measurements of the Earth radiance within the UV-visible and near-infrared spectral ranges, from which atmospheric ozone profile data are retrieved. Developed at the Royal Netherlands Meteorological Institute (KNMI) and based on the optimal estimation method, TROPOMI’s operational ozone profile retrieval algorithm has recently been upgraded. With respect to early retrieval attempts, accuracy is expected to have improved significantly, also thanks to recent updates of the TROPOMI Level-1b data product. This work reports on the initial validation of the improved TROPOMI height-resolved ozone data in the troposphere and stratosphere, as collected both from the operational S5P Mission Performance Centre/Validation Data Analysis Facility (MPC/VDAF) and from the S5PVT scientific project CHEOPS-5p. Based on the same validation best practices as developed for and applied to heritage sensors like GOME-2, OMI and IASI (Keppens et al., 2015, 2018), the validation methodology relies on the analysis of data retrieval diagnostics – like the averaging kernels’ information content – and on comparisons of TROPOMI data with reference ozone profile measurements. The latter are acquired by ozonesonde, stratospheric lidar, and tropospheric lidar stations performing network operation in the context of WMO's Global Atmosphere Watch and its contributing networks NDACC and SHADOZ. The dependence of TROPOMI’s ozone profile uncertainty on several influence quantities like cloud fraction and measurement parameters like sun and scan angles is examined and discussed. This work concludes with a set of quality indicators enabling users to verify the fitness-for-purpose of the S5P data.</p>

scholarly journals Ground-Based Solar Absorption FTIR Spectroscopy: Characterization of Retrievals and First Results from a Novel Optical Design Instrument at a New NDACC Complementary Station

2007 ◽  
Vol 24 (3) ◽  
pp. 432-448 ◽  
Author(s):  
A. Wiacek ◽  
J. R. Taylor ◽  
K. Strong ◽  
R. Saari ◽  
T. E. Kerzenmacher ◽  
...  
Keyword(s):  
High Resolution ◽  
Stratospheric Ozone ◽  
Phase Error ◽  
Optical Design ◽  
Estimation Method ◽  
Optical Path Difference ◽  
Atmospheric Composition ◽  
Retrieval Algorithm ◽  
Atmospheric Measurements ◽  
Solar Absorption

Abstract The authors describe the optical design of a high-resolution Fourier Transform Spectrometer (FTS), which serves as the primary instrument at the University of Toronto Atmospheric Observatory (TAO). The FTS is dedicated to ground-based infrared solar absorption atmospheric measurements from Toronto, Ontario, Canada. Instrument performance is discussed in terms of instrumental line shape (ILS) and phase error and modulation efficiency as a function of optical path difference. Typical measurement parameters are presented together with retrieval parameters used to derive total and partial column concentrations of ozone. Retrievals at TAO employ the optimal estimation method (OEM), and some impacts of the necessary a priori constraints are examined. In March 2004, after participating in a retrieval algorithm user intercomparison exercise, the TAO FTS was granted the status of a Complementary Observation Station within the international community of high-resolution FTS users in the Network for the Detection of Atmospheric Composition and Change (NDACC). During this exercise, average differences between total columns retrieved from the same spectra by different users were below 2.1% for O3, HCl, and N2O in the blind phase, and below 1% in the open phase, when all retrieval constraints were identical. Finally, a 2.5-yr time series of monthly mean stratospheric ozone columns agrees within 3% with those retrieved from Optical Spectrograph and Infrared Imager System (OSIRIS) measurements on board the Odin satellite, which is within the errors of both measurement platforms.

scholarly journals Retrieval algorithm for CO<sub>2</sub> and CH<sub>4</sub> column abundances from short-wavelength infrared spectral observations by the Greenhouse Gases Observing Satellite

2010 ◽  
Vol 3 (6) ◽  
pp. 4791-4833 ◽  
Author(s):  
Y. Yoshida ◽  
Y. Ota ◽  
N. Eguchi ◽  
N. Kikuchi ◽  
K. Nobuta ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Greenhouse Gases ◽  
Short Wavelength ◽  
Near Infrared ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Detection Methods ◽  
Retrieval Algorithm ◽  
Random Errors ◽  
Cloud Detection

Abstract. The Greenhouse gases Observing SATellite (GOSAT) was launched on 23 January 2009 to monitor the global distributions of carbon dioxide and methane from space. It has operated continuously since then. Here we describe a retrieval algorithm for column abundances of these gases from the short-wavelength infrared spectra obtained by the Thermal And Near infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS). The algorithm consists of three steps. First, cloud-free observational scenes are selected by several cloud-detection methods. Then, column abundances of carbon dioxide and methane are retrieved based on the optimal estimation method. Finally, the retrieval quality is examined to exclude low-quality and/or aerosol-contaminated results. Most of the retrieval random errors come from the instrumental noise. The interferences by auxiliary parameters retrieved simultaneously with gas abundances are small. The evaluated precisions of the retrieved column abundances for single observations are less than 1% in most cases. The interhemispherical differences and the temporal variation patterns of the retrieved column abundances agree well with the current state of knowledge.

scholarly journals Information operator approach applied to the retrieval of the vertical distribution of atmospheric constituents from ground-based high-resolution FTIR measurements

2012 ◽  
Vol 5 (1) ◽  
pp. 161-180 ◽  
Author(s):  
C. Senten ◽  
M. De Mazière ◽  
G. Vanhaelewyn ◽  
C. Vigouroux
Keyword(s):  
Vertical Distribution ◽  
Tikhonov Regularization ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Atmospheric Composition ◽  
High Spectral Resolution ◽  
Retrieval Algorithm ◽  
Operator Approach ◽  
Information Operator ◽  
The Vertical Distribution

Abstract. The analysis of high spectral resolution Fourier Transform infrared (FTIR) solar absorption spectra is an important issue in remote sensing. If this is done carefully, one can obtain information, not only about the total column abundances, but also about the vertical distribution of various constituents in the atmosphere. This work introduces the application of the information operator approach for extracting vertical profile information from ground-based FTIR measurements. The algorithm is implemented and tested within the well-known retrieval code SFIT2, adapting the optimal estimation method such as to take into account only the significant contributions to the solution. In particular, we demonstrate the feasibility of the method in an application to ground-based FTIR spectra taken in the framework of the Network for the Detection of Atmospheric Composition Change (NDACC) at Ile de La Réunion (21° S, 55° E). A thorough comparison is made between the original optimal estimation method, Tikhonov regularization and this alternative retrieval algorithm, regarding information content, retrieval robustness and corresponding full error budget evaluation for the target species ozone (O3), nitrous oxide (N2O), methane (CH4), and carbon monoxide (CO). It is shown that the information operator approach performs well and in most cases yields both a better accuracy and stability than the optimal estimation method. Additionally, the information operator approach has the advantage of being less sensitive to the choice of a priori information than the optimal estimation method and Tikhonov regularization. On the other hand, in general the Tikhonov regularization results seem to be slightly better than the optimal estimation method and information operator approach results when it comes to error budgets and column stability.

scholarly journals Evaluation of tropospheric and stratospheric ozone trends over Western Europe from ground-based FTIR network observations

2008 ◽  
Vol 8 (23) ◽  
pp. 6865-6886 ◽  
Author(s):  
C. Vigouroux ◽  
M. De Mazière ◽  
P. Demoulin ◽  
C. Servais ◽  
F. Hase ◽  
...  
Keyword(s):  
Time Series ◽  
Western Europe ◽  
Stratospheric Ozone ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Atmospheric Composition ◽  
Total Column Ozone ◽  
Ozone Trends ◽  
Column Ozone ◽  
Total Column

Abstract. Within the European project UFTIR (Time series of Upper Free Troposphere observations from an European ground-based FTIR network), six ground-based stations in Western Europe, from 79° N to 28° N, all equipped with Fourier Transform infrared (FTIR) instruments and part of the Network for the Detection of Atmospheric Composition Change (NDACC), have joined their efforts to evaluate the trends of several direct and indirect greenhouse gases over the period 1995–2004. The retrievals of CO, CH4, C2H6, N2O, CHClF2, and O3 have been optimized. Using the optimal estimation method, some vertical information can be obtained in addition to total column amounts. A bootstrap resampling method has been implemented to determine annual partial and total column trends for the target gases. The present work focuses on the ozone results. The retrieved time series of partial and total ozone columns are validated with ground-based correlative data (Brewer, Dobson, UV-Vis, ozonesondes, and Lidar). The observed total column ozone trends are in agreement with previous studies: 1) no total column ozone trend is seen at the lowest latitude station Izaña (28° N); 2) slightly positive total column trends are seen at the two mid-latitude stations Zugspitze and Jungfraujoch (47° N), only one of them being significant; 3) the highest latitude stations Harestua (60° N), Kiruna (68° N) and Ny-Ålesund (79° N) show significant positive total column trends. Following the vertical information contained in the ozone FTIR retrievals, we provide partial columns trends for the layers: ground-10 km, 10–18 km, 18–27 km, and 27–42 km, which helps to distinguish the contributions from dynamical and chemical changes on the total column ozone trends. We obtain no statistically significant trends in the ground-10 km layer for five out of the six ground-based stations. We find significant positive trends for the lowermost stratosphere at the two mid-latitude stations, and at Ny-Ålesund. We find smaller, but significant trends for the 18–27 km layer at Kiruna, Harestua, Jungfraujoch, and Izaña. The results for the upper layer are quite contrasted: we find significant positive trends at Kiruna, Harestua, and Jungfraujoch, and significant negative trends at Zugspitze and Izaña. These ozone partial columns trends are discussed and compared with previous studies.

scholarly journals Evaluation of tropospheric and stratospheric ozone trends over Western Europe from ground-based FTIR network observations

2008 ◽  
Vol 8 (2) ◽  
pp. 5007-5060 ◽  
Author(s):  
C. Vigouroux ◽  
M. De Mazière ◽  
P. Demoulin ◽  
C. Servais ◽  
F. Hase ◽  
...  
Keyword(s):  
Time Series ◽  
Western Europe ◽  
Stratospheric Ozone ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Atmospheric Composition ◽  
Total Column Ozone ◽  
Ozone Trends ◽  
Column Ozone ◽  
Total Column

Abstract. Within the European project UFTIR (Time series of Upper Free Troposphere observations from an European ground-based FTIR network), six ground-based stations in Western Europe, from 79° N to 28° N, all equipped with Fourier Transform infrared (FTIR) instruments and part of the Network for the Detection of Atmospheric Composition Change (NDACC), have joined their efforts to evaluate the trend of several direct and indirect greenhouse gases over the period 1995–2004. The retrievals of CO, CH4, C2H6, N2O, CHClF2, and O3 have been optimized. Using the optimal estimation method, some vertical information can be obtained in addition to total column amounts. A bootstrap resampling method has been implemented to determine annual partial and total column trends for the target gases. The present work focuses on the ozone results. The retrieved time series of partial and total ozone columns are validated with ground-based correlative data (Brewer, Dobson, UV-Vis, ozonesondes, and Lidar). The observed total column ozone trends are in agreement with previous studies: 1) no total column ozone trend is seen at the lowest latitude station Izaña (28° N); 2) slightly positive total column trends are seen at the two mid-latitude stations Zugspitze and Jungfraujoch (47° N), only one of them being significant; 3) the highest latitude stations Harestua (60° N), Kiruna (68° N) and Ny-Ålesund (79° N) show significant positive total column trends. Following the vertical information contained in the ozone FTIR retrievals, we provide partial columns trends for the layers: ground-10 km, 10–18 km, 18–27 km, and 27–42 km, which helps to distinguish the contributions from dynamical and chemical changes on the total column ozone trends. We obtain no statistically significant trends in the ground–10 km layer for five out of the six ground-based stations. We find significant positive trends for the lowermost stratosphere at the two mid-latitude stations, and at Ny-Ålesund. We find smaller, but significant trends for the 18–27 km layer at Kiruna, Harestua, Jungfraujoch, and Izaña. The results for the upper layer are quite contrasted: we find significant positive trends at Kiruna, Harestua, and Jungfraujoch, and significant negative trends at Zugspitze and Izaña. These ozone partial columns trends are discussed and confronted to previous studies.

scholarly journals Evaluation of SCIAMACHY Level-1 data versions using nadir ozone profile retrievals in the period 2003–2011

2018 ◽  
Vol 11 (4) ◽  
pp. 2345-2360 ◽  
Author(s):  
Sweta Shah ◽  
Olaf N. E. Tuinder ◽  
Jacob C. A. van Peet ◽  
Adrianus T. J. de Laat ◽  
Piet Stammes
Keyword(s):  
Pressure Range ◽  
Stratospheric Ozone ◽  
Spectral Shift ◽  
Retrieval Algorithm ◽  
Visible Range ◽  
L1 Data ◽  
Ozone Profile ◽  
Level 1 ◽  
Scanning Imaging ◽  
Radiance Data

Abstract. Ozone profile retrieval from nadir-viewing satellite instruments operating in the ultraviolet–visible range requires accurate calibration of Level-1 (L1) radiance data. Here we study the effects of calibration on the derived Level-2 (L2) ozone profiles for three versions of SCanning Imaging Absorption spectroMeter for Atmospheric ChartograpHY (SCIAMACHY) L1 data: version 7 (v7), version 7 with m-factors (v7mfac) and version 8 (v8). We retrieve nadir ozone profiles from the SCIAMACHY instrument that flew on board Envisat using the Ozone ProfilE Retrieval Algorithm (OPERA) developed at KNMI with a focus on stratospheric ozone. We study and assess the quality of these profiles and compare retrieved L2 products from L1 SCIAMACHY data versions from the years 2003 to 2011 without further radiometric correction. From validation of the profiles against ozone sonde measurements, we find that the v8 performs better than v7 and v7mfac due to correction for the scan-angle dependency of the instrument's optical degradation. Validation for the years 2003 and 2009 with ozone sondes shows deviations of SCIAMACHY ozone profiles of 0.8–15 % in the stratosphere (corresponding to pressure range ∼ 100–10 hPa) and 2.5–100 % in the troposphere (corresponding to pressure range ∼ 1000–100 hPa), depending on the latitude and the L1 version used. Using L1 v8 for the years 2003–2011 leads to deviations of ∼ 1–11 % in stratospheric ozone and ∼ 1–45 % in tropospheric ozone. The SCIAMACHY L1 v8 data can still be improved upon in the 265–330 nm range used for ozone profile retrieval. The slit function can be improved with a spectral shift and squeeze, which leads to a few percent residue reduction compared to reference solar irradiance spectra. Furthermore, studies of the ratio of measured to simulated reflectance spectra show that a bias correction in the reflectance for wavelengths below 300 nm appears to be necessary.

scholarly journals Round-robin evaluation of nadir ozone profile retrievals: methodology and application to MetOp-A GOME-2

2014 ◽  
Vol 7 (11) ◽  
pp. 11481-11546 ◽  
Author(s):  
A. Keppens ◽  
J.-C. Lambert ◽  
J. Granville ◽  
G. Miles ◽  
R. Siddans ◽  
...  
Keyword(s):  
Information Content ◽  
Optimal Estimation ◽  
Round Robin ◽  
Atmospheric Composition ◽  
User Requirements ◽  
Satellite Measurements ◽  
Estimation Algorithms ◽  
Ozone Profile ◽  
Reference Measurements ◽  
Resolution Estimation

Abstract. A methodology for the round-robin evaluation and geophysical validation of ozone profile data retrieved from nadir UV backscatter satellite measurements is detailed and discussed, consisting of dataset content studies, information content studies, co-location studies, and comparisons with reference measurements. Within ESA's Climate Change Initiative on ozone (Ozone_cci project), the proposed round-robin procedure is applied to two nadir ozone profile datasets retrieved at KNMI and RAL, using their respective OPERA v1.26 and RAL v2.1 optimal estimation algorithms, from MetOp-A GOME-2 measurements taken in 2008. The ground-based comparisons use ozonesonde and lidar profiles as reference data, acquired by the Network for the Detection of Atmospheric Composition Change (NDACC), Southern Hemisphere Additional Ozonesonde programme (SHADOZ), and other stations of WMO's Global Atmosphere Watch. This direct illustration highlights practical issues that inevitably emerge from discrepancies in e.g. profile representation and vertical smoothing, for which different recipes are investigated and discussed. Several approaches for information content quantification, vertical resolution estimation, and reference profile resampling are compared and applied as well. The paper concludes with compliance estimates of the two GOME-2 ozone profile datasets with user requirements from GCOS and from climate modellers.

scholarly journals Retrieval of temperature from a multiple channel pure rotational Raman backscatter lidar using an optimal estimation method

2019 ◽  
Vol 12 (11) ◽  
pp. 5801-5816 ◽  
Author(s):  
Shayamila Mahagammulla Gamage ◽  
Robert J. Sica ◽  
Giovanni Martucci ◽  
Alexander Haefele
Keyword(s):  
Estimation Method ◽  
Optimal Estimation ◽  
Uncertainty Budget ◽  
Temperature Measurements ◽  
New Method ◽  
Retrieval Algorithm ◽  
Coupling Constant ◽  
Raman Lidar ◽  
Multiple Channel ◽  
Lidar Measurements

Abstract. We present a new method for retrieving temperature from pure rotational Raman (PRR) lidar measurements. Our optimal estimation method (OEM) used in this study uses the full physics of PRR scattering and does not require any assumption of the form for a calibration function nor does it require fitting of calibration factors over a large range of temperatures. The only calibration required is the estimation of the ratio of the lidar constants of the two PRR channels (coupling constant) that can be evaluated at a single or multiple height bins using a simple analytic expression. The uncertainty budget of our OEM retrieval includes both statistical and systematic uncertainties, including the uncertainty in the determination of the coupling constant on the temperature. We show that the error due to calibration can be reduced significantly using our method, in particular in the upper troposphere when calibration is only possible over a limited temperature range. Some other advantages of our OEM over the traditional Raman lidar temperature retrieval algorithm include not requiring correction or gluing to the raw lidar measurements, providing a cutoff height for the temperature retrievals that specifies the height to which the retrieved profile is independent of the a priori temperature profile, and the retrieval's vertical resolution as a function of height. The new method is tested on PRR temperature measurements from the MeteoSwiss RAman Lidar for Meteorological Observations system in clear and cloudy sky conditions, compared to temperature calculated using the traditional PRR calibration formulas, and validated with coincident radiosonde temperature measurements in clear and cloudy conditions during both daytime and nighttime.

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 %.

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