TROPOMI/S5P Total Column Water Vapor validation against AERONET ground-based measurements

Water vapor plays an important role in the greenhouse effect, rendering it an atmospheric constituent that requires continuous and global monitoring by different types of remote sensing instruments. The TROPOspheric Monitoring Instrument Sentinel-5 Precursor (TROPOMI/S5P) Total Column Water Vapor (TCWV) is a new product retrieved from the visible blue spectral range (435–455 nm), using an algorithm that was originally developed for the GOME-2/MetOp sensors. For the purposes of this work, 2.5 years of continuous satellite observations at high spatial resolution are validated against co-located (in space and in time) precipitable water Level 2.0 (quality-assured) ground-based measurements from the NASA AERONET (AErosol RObotic NETwork). The network uses Cimel Sun photometers located at approximately 1300 stations globally to monitor precipitable water among other products. Based on data availability, 369 of the stations were used in this study. The two datasets, satellite- and ground-based, were co-located, and the relative differences of the comparisons were calculated and statistically analyzed. The Pearson correlation coefficient of the two products is found to be 0.91, and the mean bias of the overall relative percentage differences is of the order of −2.7 %. For the Northern Hemisphere midlatitudes (30–60∘ N), where the density of the ground-based stations is high, the mean relative bias was found to be −1.8 %, while in the tropics (±15∘) the TROPOMI TCWV product has a relative dry bias of up to −10 %. The effect of various algorithm and geophysical parameters, such as air mass factor, solar zenith angle, clouds and albedo, is also presented and discussed. It was found that the cloud properties affect the validation results, leading the TCWV to a dry bias of −20 % for low cloud heights (cloud top pressure (CTP) >800 hPa). Moreover, cloud albedo introduces a wet bias of 15 % when it is below 0.3 and a dry bias up to −25 % when the clouds are more reflective. Overall, the TROPOMI/S5P TCWV product, on a global scale and for moderate albedo and cloudiness, agrees well at  % with the AERONET observations but probably within about −8 % to −13 % with respect to the “truth”

Almost one year of TROPOMI/S5P total ozone column data: global ground-based validation

Póster presentado en: ATMOS 2018, celebrado en Salzburgo (Austria) del 26 al 29 de noviembre de 2018.In this work we present the validation results of almost one year of TROPOMI Near Real Time (NRTI) and OFFLine (OFFL) data against ground-based quality-assured Brewer and Dobson total ozone column (TOC) measurements deposited in the World Ozone and Ultraviolet Radiation Data Center (WOUDC). Additionally, comparisons to Brewer measurements from the European Brewer Network (EUBREWNET) and the Canadian Network are performed, as well as to twilight zenith-sky measurements obtained with ZSL-DOAS (Zenith Scattered Light Differential Optical Absorption Spectroscopy) instruments, that form part of the SAOZ network (Système d'Analyse par Observation Zénitale) of the Network for the Detection of Atmospheric Composition Change (NDACC). Through the comparison of the TROPOMI measurements to the total ozone ground-based measurements from stations that are distributed globally, as the background truth, the dependence of the new instrument on latitude, cloud properties, solar zenith and viewing angles, among others, is examined. Validation results show that the mean bias and the standard deviation of the percentage difference between TROPOMI and QA ground TOC meet the product requirements

TROPOMI/S5P total ozone column data: global ground-based validation and consistency with other satellite missions

In this work, the TROPOMI near real time (NRTI) and offline (OFFL) total ozone column (TOC) products are presented and compared to daily ground-based quality-assured Brewer and Dobson TOC measurements deposited in the World Ozone and Ultraviolet Radiation Data Centre (WOUDC). Additional comparisons to individual Brewer measurements from the Canadian Brewer Network and the European Brewer Network (Eubrewnet) are performed. Furthermore, twilight zenith-sky measurements obtained with ZSL-DOAS (Zenith Scattered Light Differential Optical Absorption Spectroscopy) instruments, which form part of the SAOZ network (Système d'Analyse par Observation Zénitale), are used for the validation. The quality of the TROPOMI TOC data is evaluated in terms of the influence of location, solar zenith angle, viewing angle, season, effective temperature, surface albedo and clouds. For this purpose, globally distributed ground-based measurements have been utilized as the background truth. The overall statistical analysis of the global comparison shows that the mean bias and the mean standard deviation of the percentage difference between TROPOMI and ground-based TOC is within 0 –1.5 % and 2.5 %–4.5 %, respectively. The mean bias that results from the comparisons is well within the S5P product requirements, while the mean standard deviation is very close to those limits, especially considering that the statistics shown here originate both from the satellite and the ground-based measurements.This research has been supported by the European Space Agency “Preparation and Operations of the Mission Performance Centre (MPC) for the Copernicus Sentinel-5 Precursor Satellite” (contract no. 4000117151/16/1-LG)

Contribution to the study of the variability of the ultaviolet radiation spectrum in various time scales

The object of this thesis is the study of the spectral ultraviolet irradiance variability, in various time scales. For the purposes of the thesis the spectral measurements of the two Brewer spectroradiometers operating at the Laboratory of Atmospheric Physics, Thessaloniki, Greece, since 1989 and 1993, respectively, were used. In the first chapter a short reference is made to solar ultraviolet radiation ant its properties as well as the methods of its attenuation during its transmission through the Earth’s atmosphere. Furthermore, the principles of operation of the Brewer spectroradiometer and the methodology of its absolute calibration are described. In the second chapter the methodology followed during the re-evaluation of the spectral measurements data set, is described. Following, all the corrections that were applied to the measurements of the two instruments during their quality control are analyzed and an estimation of the total uncertainty of their measurements is performed. In the third chapter the results of the comparison of the synchronous spectral measurements of the two Brewer spectroradiometers are presented and the achievement of a very satisfying agreement between them is concluded. In the following chapter the long term variability of the ultraviolet irradiance is examined using both erythemal dose values, as well as spectral measurements of the two instruments during the time period of 1993 – 2005, for many different time scales. Finally, in the fifth chapter of this thesis the dependence of the ultraviolet irradiance and its long term variability to the respective long term variability of three different atmospheric parameters, such as cloudiness, total ozone and aerosol optical depth, is examined. eΤο αντικείμενο αυτής της διατριβής είναι η μελέτη των μεταβολών του φάσματος της υπεριώδους ακτινοβολίας σε διάφορες κλίμακες χρόνου. Στα πλαίσια της διατριβής επεξεργάστηκαν και αναλύθηκαν οι φασματικές μετρήσεις των δύο φασματοφωτομέτρων Brewer που λειτουργούν στο Εργαστήριο Φυσικής της Ατμόσφαιρας από το 1989 και το 1993, αντίστοιχα. Στο πρώτο κεφάλαιο γίνεται μια σύντομη αναφορά στην ηλιακή υπεριώδη ακτινοβολία και τις ιδιότητές της, όπως είναι οι φασματικές περιοχές που την αποτελούν, αλλά και στους τρόπους εξασθένησής της κατά τη διέλευσή της από την ατμόσφαιρα της Γης. Επίσης, περιγράφεται το φασματοφωτόμετρο Brewer ως όργανο φασματικής μέτρησης της UV ακτινοβολίας και η μέθοδος απόλυτης βαθμονόμησής του. Στο δεύτερο κεφάλαιο αναπτύσσεται η μεθοδολογία που ακολουθήθηκε για την επανεκτίμηση του αρχείου των μετρήσεων της υπεριώδους ακτινοβολίας, που έγιναν με τα δύο φασματοφωτόμετρα Brewer. Στη συνέχεια αναλύονται οι διορθώσεις που εφαρμόστηκαν στις παραπάνω μετρήσεις κατά τη διάρκεια του ποιοτικού τους ελέγχου και γίνεται μία εκτίμηση της συνολικής αβεβαιότητας του τελικού αρχείου των μετρήσεων των δύο οργάνων. Στο τρίτο κεφάλαιο πραγματοποιείται η σύγκριση των σύγχρονων μετρήσεων των δύο φασματοφωτομέτρων Brewer, όπου διαπιστώνεται η επίτευξη πολύ καλών επιπέδων συμφωνίας μεταξύ τους. Επίσης, εξετάζεται η εξάρτηση του λόγου των σύγχρονων μετρήσεών τους από παράγοντες όπως είναι η ηλιακή ζενίθια γωνία, η θερμοκρασία και το μήκος κύματος. Στο τέταρτο κεφάλαιο που ακολουθεί, υπολογίζονται οι μακροχρόνιες τάσεις της υπεριώδους ακτινοβολίας για το χρονικό διάστημα 1993 – 2005, χρησιμοποιώντας τιμές της ερυθηματογόνου δόσης ή απλά τις φασματικές μετρήσεις των οργάνων, για διάφορες κλίμακες χρόνου. Τέλος, στο πέμπτο κεφάλαιο εξετάζεται η εξάρτηση της υπεριώδους ακτινοβολίας και των μακροχρόνιων τάσεών της από τις αντίστοιχες μακροχρόνιες τάσεις διαφόρων ατμοσφαιρικών παραμέτρων που την επηρεάζουν όπως είναι η νεφοκάλυψη, η συγκέντρωση του ολικού όζοντος και το οπτικό βάθος των αιωρούμενων σωματιδίων

Towards an Algorithm for Near Real Time Profiling of Aerosol Species, Trace Gases, and Clouds Based on the Synergy of Remote Sensing Instruments

In this manuscript we present the concept of a novel algorithmic chain that aims to a dataset of unprecedented detail in the vertical distribution of multiple atmospheric components in near real time conditions. The analysis will be based on the following remote sensing instruments: a depolarization Raman lidar, a visible and a thermal all-sky camera, a Brewer spectrophotometer, and up to three mini DOAS/MAX-DOAS systems. Based on both individual and synergistic processing of the data collected, novel products will be made available in near real time conditions to the end users. Columnar aerosol information from the spectrophotometers will be combined with lidar data to retrieve vertical profiles of individual aerosol species. Cloud layers will be detected and classified based mainly on the synergy of the lidar and the sky cameras and a realistic 3D representation of cloud conditions around the measurement site will be produced. Lidar profiles will be implemented as a priori information for radiative transfer purposes, that are necessary in order to obtain high quality trace gases profiles from the DOAS/MAX-DOAS spectrophotometer. Fast synergistic data processing will ensure that the algorithm can be applied for near real time public data dissemination in the future

Towards an Algorithm for Near Real Time Profiling of Aerosol Species, Trace Gases, and Clouds Based on the Synergy of Remote Sensing Instruments

In this manuscript we present the concept of a novel algorithmic chain that aims to a dataset of unprecedented detail in the vertical distribution of multiple atmospheric components in near real time conditions. The analysis will be based on the following remote sensing instruments: a depolarization Raman lidar, a visible and a thermal all-sky camera, a Brewer spectrophotometer, and up to three mini DOAS/MAX-DOAS systems. Based on both individual and synergistic processing of the data collected, novel products will be made available in near real time conditions to the end users. Columnar aerosol information from the spectrophotometers will be combined with lidar data to retrieve vertical profiles of individual aerosol species. Cloud layers will be detected and classified based mainly on the synergy of the lidar and the sky cameras and a realistic 3D representation of cloud conditions around the measurement site will be produced. Lidar profiles will be implemented as a priori information for radiative transfer purposes, that are necessary in order to obtain high quality trace gases profiles from the DOAS/MAX-DOAS spectrophotometer. Fast synergistic data processing will ensure that the algorithm can be applied for near real time public data dissemination in the future

Portable Device for Characterizing the Angular Response of UV Spectroradiometers

see attachedJRC.I.5-Physical and chemical exposure