scholarly journals Μελέτη επεισοδίων αερολυμάτων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου με τη χρήση σύγχρονων δορυφορικών δεδομένων

2012 ◽  
Author(s):  
Αντώνιος Γκίκας
Keyword(s):  
North Atlantic ◽  
Fine Fraction ◽  
Total Ozone Mapping Spectrometer ◽  
Ozone Monitoring Instrument ◽  
Santa Barbara ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Atmospheric Radiative Transfer ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Aerosol Index

Στην παρούσα Διδακτορική Διατριβή, μελετάται το καθεστώς των επεισοδίων αερολυμάτων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου, κατά την περίοδο 2000-2007. Πιο συγκεκριμένα, μελετώνται τα χωρικά και χρονικά χαρακτηριστικά της συχνότητας εμφάνισής τους, της έντασής τους και της διάρκειάς τους, ο ρόλος της ατμοσφαιρικής κυκλοφορίας που ευνοεί την εκδήλωσή τους, καθώς και η διαταραχή του ισοζυγίου της ηλιακής ακτινοβολίας που αυτά προκαλούν. Η ταυτοποίηση των επεισοδίων αερολυμάτων πραγματοποιείται με έναν αντικειμενικό και δυναμικό αλγόριθμο, ο οποίος αναπτύχθηκε στα πλαίσια της Διδακτορικής Διατριβής. Μέσω του αλγορίθμου, ορίζονται τα επίπεδα αποκοπής (threshold levels) και ταξινομούνται τα επεισόδια, με βάση την έντασή τους, σε ισχυρά και ακραία, καθώς και με βάση τον τύπο τους. Σε ό,τι αφορά στο δεύτερο διαχωρισμό, προέκυψαν οι εξής πέντε (5) τύποι επεισοδίων: (i) επεισόδια αερολυμάτων από αστικές/βιομηχανικές δραστηριότητες και καύση βιομάζας (Biomass Urban episodes, BU), (ii) επεισόδια αερολυμάτων ερημικής σκόνης (Desert Dust episodes, DD) (iii) επεισόδια αερολυμάτων θαλάσσιου τύπου (Sea-Salt-like episodes, SS-like), (iv) επεισόδια μίξης αερολυμάτων διαφορετικού τύπου (Mixed episodes, MX) και (v) επεισόδια τα οποία δεν κατατάσσονται σε κάποιον από τους προηγούμενους τύπους (Undetermined episodes, UN). Ως δεδομένα εισαγωγής στον αλγόριθμο χρησιμοποιούνται ημερήσιες δορυφορικές μετρήσεις, σε πλεγματική μορφή χωρικής ανάλυσης 1ox1o γεωγραφικού πλάτους και μήκους, για το οπτικό βάθος αερολυμάτων (Aerosol Optical Depth, AOD), τον εκθετικό παράγοντα Ångström (α) των αερολυμάτων, το δείκτη αερολυμάτων (Aerosol Index, ΑΙ), την αναλογία λεπτόκοκκων αερολυμάτων ως προς το σύνολό τους (Fine Fraction, FF) και τη μέση ενεργό ακτίνα (effective radius, reff). Τα δεδομένα αυτά ελήφθησαν από τους δορυφόρους MODIS (MODerate Resolution Imaging Spectroradiometer)-Terra, EP-TOMS (Earth Probe-Total Ozone Mapping Spectrometer) και ΟΜΙ (Ozone Monitoring Instrument)-Aura.Σε ετήσια βάση, τα ισχυρά επεισόδια εκδηλώνονται περισσότερο συχνά (έως 13.3 επεισόδια/έτος) στη Δ. Μεσόγειο και λιγότερο συχνά στην Α. Μεσόγειο (έως 2 επεισόδια/έτος). Αντίθετα, τα ακραία επεισόδια εκδηλώνονται με μεγαλύτερη συχνότητα στην Κ. Μεσόγειο (4 επεισόδια/έτος), ενώ οι μικρότερες συχνότητες παρατηρούνται στα βόρεια τμήματα της Βαλκανικής Χερσονήσου (0.3 επεισόδια/έτος). Η ένταση των ισχυρών επεισοδίων (εκπεφρασμένη σε τιμές AOD στα 550nm) κυμαίνεται μεταξύ 0.43 και 1.5, ενώ η ένταση των ακραίων επεισοδίων είναι μεγαλύτερη και κυμαίνεται μεταξύ 0.67 και 4.07. Κοινό χαρακτηριστικό, αποτελεί η μείωση της έντασης των επεισοδίων προς τα βορειότερα γεωγραφικά πλάτη, κυρίως εξαιτίας της εξασθένησης του μηχανισμού μεταφοράς ερημικής σκόνης. Το μεγαλύτερο ποσοστό (> 85%) των ισχυρών και ακραίων επεισοδίων διαρκεί μία (1) ημέρα. Κατά τη διάρκεια του έτους, τα επεισόδια εκδηλώνονται με μεγαλύτερη συχνότητα τους καλοκαιρινούς (Δ. Μεσόγειος) και εαρινούς μήνες (Κ. και Α. Μεσόγειος), ενώ το αντίστροφο ισχύει για το χειμώνα (επίδραση της βροχόπτωσης). Η συχνότητα εμφάνισης των επεισοδίων, κατά την περίοδο 2000-2007, εμφανίζει πτωτικές τάσεις (έως 100%), ενώ δεν παρατηρούνται σημαντικές τάσεις μεταβολής της έντασής τους.Το μεγαλύτερο ποσοστό των ισχυρών και κυρίως των ακραίων επεισοδίων στην περιοχή απαρτίζεται από επεισόδια ερημικής σκόνης (έως 71.5%), ενώ τα μικρότερα ποσοστά καταγράφονται για τα BU επεισόδια (έως 1.5%). Η περισσότερο συχνή εμφάνιση των επεισοδίων παρατηρείται: για τα BU επεισόδια (έως 1 επεισόδιο/έτος) στα βόρεια τμήματα της Βαλκανικής Χερσονήσου, για τα DD επεισόδια στη Δ. Μεσόγειο (έως 11.4 επεισόδια/έτος), για τα SS-like επεισόδια στην Ιβηρική Χερσόνησο και στη Χερσόνησο της Ανατολίας (3.9 επεισόδια/έτος) και για τα ΜΧ επεισόδια στα δυτικά τμήματα της θάλασσας της Μεσογείου (5 επεισόδια/έτος). Η μεγαλύτερη ένταση των ισχυρών BU επεισοδίων σημειώνεται στην Κοιλάδα του Πάδου (1.2) στην Ιταλία, ενώ για τα DD, SS-like και ΜΧ επεισόδια στον Κόλπο της Σίδρας και στη θαλάσσια περιοχή της Λιβύης (έως 1.6). Σε μεμονωμένες περιπτώσεις η ένταση των ακραίων SS-like και ΜΧ επεισοδίων μπορεί να ανέλθει έως 5 (τιμές AOD στα 550nm). Η μέγιστη συχνότητα, σε μηνιαία και περιοχική κλίμακα, των ισχυρών BU επεισοδίων σημειώθηκε τον Αύγουστο του 2003 (0.13 επεισόδια/κυψελίδα). Η ανάλυση μας αναδεικνύει χαρακτηριστικά εποχικού κύκλου για τα ισχυρά και ακραία DD επεισόδια, με τις μέγιστες συχνότητες να σημειώνονται τη ξηρή περίοδο του έτους και την άνοιξη, αντίστοιχα. Σύμφωνα με τα αποτελέσματά μας, προκύπτει συσχέτιση της συχνότητας εμφάνισης των DD επεισοδίων με την κύμανση του Βορείου Ατλαντικού (North Atlantic Oscillation, ΝΑΟ) που είναι σε συμφωνία με ευρήματα προηγούμενων μελετών που ανέφεραν συσχέτιση του φορτίου των ερημικών αερολυμάτων στη Μεσόγειο με το ΝΑΟ. Με την εφαρμογή του μοντέλου HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory Model) μελετήθηκαν οι τροχιές των αερίων μαζών, για μια περίοδο 5 ημερών πριν την εκδήλωση ακραίων επεισοδίων διαφορετικών τύπων. Τέλος, τα αποτελέσματα του αλγορίθμου, για τις περιπτώσεις DD επεισοδίων, αξιολογήθηκαν επιτυχώς έναντι επίγειων μετρήσεων συγκέντρωσης του σωματιδιακού φορτίου (Dust PM10) και οπτικών ιδιοτήτων (AERONET).Επιχειρήθηκε, επίσης, η περιγραφή της ατμοσφαιρικής κυκλοφορίας, στην κατώτερη τροπόσφαιρα, και ο ρόλος της στην εκδήλωση επεισοδίων στην ευρύτερη περιοχή της λεκάνης της Μεσογείου. Για το σκοπό αυτό, τέθηκαν κριτήρια επιλογής των ημερών μελέτης, για τις οποίες η ατμοσφαιρική κυκλοφορία ταξινομήθηκε αντικειμενικά, με την εφαρμογή πολυμεταβλητών στατιστικών μεθόδων, όπως αυτών της Παραγοντικής Ανάλυσης (Factor Analysis S-mode) και της Ανάλυσης κατά Συστάδες (Cluster Analysis). Από την εφαρμοσθείσα μεθοδολογία, προέκυψαν 8 τύποι ατμοσφαιρικής κυκλοφορίας των οποίων τα χαρακτηριστικά περιγράφηκαν, ενώ προσδιορίστηκαν οι γεωγραφικές κατανομές της συχνότητας εμφάνισης των επεισοδίων, της έντασής τους και της επικράτησής τους (ισχυρά ή ακραία), για την κάθε Ομάδα (Cluster). Αντίστοιχη μελέτη πραγματοποιήθηκε και για την περιγραφή των τύπων ανάπτυξης της ατμοσφαιρικής κυκλοφορίας που οδηγούν στην πρόκληση επεισοδίων μεταφοράς ερημικής σκόνης, καταλήγοντας σε 6 Ομάδες. Τέλος, υπολογίστηκε η άμεση διαταραχή του ισοζυγίου της ακτινοβολίας (direct radiative effect, DRE) που προκαλείται από την εκδήλωση ακραίων επεισοδίων, διαφορετικού τύπου, υπό συνθήκες ανέφελου ουρανού. Οι υπολογισμοί πραγματοποιήθηκαν στην κορυφή της ατμόσφαιρας (TOA), στην ατμόσφαιρα (atmab) και στο έδαφος (surf, surfnet) με την εφαρμογή του μοντέλου διάδοσης ακτινοβολίας SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer). Σε τοπικό επίπεδο, κατά την εκδήλωση ακραίων DD επεισοδίων πάνω από θάλασσα, το σύστημα Γης-ατμόσφαιρας ψύχεται ανακλώντας περισσότερη ηλιακή ακτινοβολία κατά 85 W/m2, η ατμόσφαιρα θερμαίνεται απορροφώντας περισσότερη ηλιακή ακτινοβολία κατά 408 W/m2, ενώ το έδαφος ψύχεται δεχόμενο λιγότερη ακτινοβολία κατά 493 W/m2. Επίσης, ο υπολογιζόμενος ρυθμός θέρμανσης της ατμόσφαιρας, λόγω των επεισοδίων DD, ανέρχεται σε έως και 10 Κ/day, στα 2.5 Km, επιφέροντας σημαντικές τροποποιήσεις στη δυναμική της.

scholarly journals Investigating the frequency and interannual variability in global above-cloud aerosol characteristics with CALIOP and OMI

2016 ◽  
Vol 16 (1) ◽  
pp. 47-69 ◽  
Author(s):  
R. Alfaro-Contreras ◽  
J. Zhang ◽  
J. R. Campbell ◽  
J. S. Reid
Keyword(s):  
Interannual Variability ◽  
Orthogonal Polarization ◽  
Cloud Detection ◽  
Ozone Monitoring Instrument ◽  
Data Set ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
First Time ◽  
Aerosol Index

Abstract. Seven and a half years (June 2006 to November 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud layer products are compared with collocated Ozone Monitoring Instrument (OMI) aerosol index (AI) data and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products in order to investigate variability in estimates of biannual and monthly above-cloud aerosol (ACA) events globally. The active- (CALIOP) and passive-based (OMI-MODIS) techniques have their advantages and caveats for ACA detection, and thus both are used to derive a thorough and robust comparison of daytime cloudy-sky ACA distribution and climatology. For the first time, baseline above-cloud aerosol optical depth (ACAOD) and AI thresholds are derived and examined (AI  =  1.0, ACAOD  =  0.015) for each sensor. Both OMI-MODIS and CALIOP-based daytime spatial distributions of ACA events show similar patterns during both study periods (December–May) and (June–November). Divergence exists in some regions, however, such as Southeast Asia during June through November, where daytime cloudy-sky ACA frequencies of up to 10 % are found from CALIOP yet are non-existent from the OMI-based method. Conversely, annual cloudy-sky ACA frequencies of 20–30 % are reported over northern Africa from the OMI-based method yet are largely undetected by the CALIOP-based method. Using a collocated OMI-MODIS-CALIOP data set, our study suggests that the cloudy-sky ACA frequency differences between the OMI-MODIS- and CALIOP-based methods are mostly due to differences in cloud detection capability between MODIS and CALIOP as well as QA flags used. An increasing interannual variability of  ∼  0.3–0.4 % per year (since 2009) in global monthly cloudy-sky ACA daytime frequency of occurrence is found using the OMI-MODIS-based method. Yet, CALIOP-based global daytime ACA frequencies exhibit a near-zero interannual variability. Further analysis suggests that the OMI-derived interannual variability in cloudy-sky ACA frequency may be affected by OMI row anomalies in later years. A few regions are found to have increasing slopes in interannual variability in cloudy-sky ACA frequency, including the Middle East and India. Regions with slightly negative slopes of the interannual variability in cloudy-sky ACA frequencies are found over South America and China, while remaining regions in the study show nearly zero change in ACA frequencies over time. The interannual variability in ACA frequency is not, however, statistically significant on both global and regional scales, given the relatively limited sample sizes. A longer data record of ACA events is needed in order to establish significant trends of ACA frequency regionally and globally.

scholarly journals Investigating the frequency and trends in global above-cloud aerosol characteristics with CALIOP and OMI

2015 ◽  
Vol 15 (4) ◽  
pp. 4173-4217 ◽  
Author(s):  
R. Alfaro-Contreras ◽  
J. Zhang ◽  
J. R. Campbell ◽  
J. S. Reid
Keyword(s):  
Orthogonal Polarization ◽  
Ozone Monitoring Instrument ◽  
Regional Trends ◽  
Data Record ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Increasing Trends ◽  
First Time ◽  
Aerosol Index

Abstract. Seven and a half years (June 2006–November 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud layer products are compared with collocated Ozone Monitoring Instrument (OMI) Aerosol Index (AI) data and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, to investigate variability in estimates of bi-annual and monthly above-cloud aerosol (ACA) events globally. The active- (CALIOP) and passive-based (OMI-MODIS) techniques have their advantages and caveats for ACA detection, and thus both are used to get a thorough and robust comparison of daytime cloudy-sky ACA distribution and climatology. For the first time, baseline above-cloud aerosol optical depth (ACAOD) and AI thresholds are derived and examined (AI = 1.0, ACAOD = 0.015) for each sensor. Both OMI-MODIS and CALIOP-based daytime spatial distributions of ACA events show similar patterns during both study periods (December–May) and (June–November). Divergence exists in some regions, however, such as Southeast Asia during June through November, where daytime cloudy-sky ACA frequencies of up to 10% are found from CALIOP yet are non-existent from the OMI-based method. Conversely, annual cloudy-sky ACA frequencies of 20–30% are reported over Northern Africa from the OMI-based method, yet are largely undetected by the CALIOP-based method. This is possibly due to a misclassification of thick dust plumes as clouds by the OMI-MODIS based method. An increasing trend of ~0.5% per year (since 2009) in global monthly cloudy-sky ACA daytime frequency of occurrence is found using the OMI-MODIS based method. Yet, CALIOP-based global daytime ACA frequencies exhibit a near-zero trend. Further analysis suggests that the OMI derived cloudy-sky ACA frequency trend may be affected by OMI row anomalies in later years. A few regions are found to have increasing trends of cloudy-sky ACA frequency, including the Middle-East and India. Regions with slightly negative cloudy-sky ACA frequency trends are found over South America and the Southern Oceans, while remaining regions in the study show a near-zero trend. Global and regional trends are not statistically significant, though, given relatively lacking sample sizes. A longer data record of ACA events is needed in order to establish a more significant trend of ACA frequency regionally and globally.

scholarly journals A Climatological Assessment of Intense Desert Dust Episodes over the Broader Mediterranean Basin Based on Satellite Data

2021 ◽  
Vol 13 (15) ◽  
pp. 2895
Author(s):  
Maria Gavrouzou ◽  
Nikolaos Hatzianastassiou ◽  
Antonis Gkikas ◽  
Christos J. Lolis ◽  
Nikolaos Mihalopoulos
Keyword(s):  
Mediterranean Basin ◽  
Eastern Mediterranean ◽  
Mean Value ◽  
Early Spring ◽  
Dust Aerosol ◽  
Ozone Monitoring Instrument ◽  
Central Mediterranean ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer

A satellite algorithm able to identify Dust Aerosols (DA) is applied for a climatological investigation of Dust Aerosol Episodes (DAEs) over the greater Mediterranean Basin (MB), one of the most climatologically sensitive regions of the globe. The algorithm first distinguishes DA among other aerosol types (such as Sea Salt and Biomass Burning) by applying threshold values on key aerosol optical properties describing their loading, size and absorptivity, namely Aerosol Optical Depth (AOD), Aerosol Index (AI) and Ångström Exponent (α). The algorithm operates on a daily and 1° × 1° geographical cell basis over the 15-year period 2005–2019. Daily gridded spectral AOD data are taken from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua Collection 6.1, and are used to calculate the α data, which are then introduced into the algorithm, while AI data are obtained by the Ozone Monitoring Instrument (OMI) -Aura- Near-UV aerosol product OMAERUV dataset. The algorithm determines the occurrence of Dust Aerosol Episode Days (DAEDs), whenever high loads of DA (higher than their climatological mean value plus two/four standard deviations for strong/extreme DAEDs) exist over extended areas (more than 30 pixels or 300,000 km2). The identified DAEDs are finally grouped into Dust Aerosol Episode Cases (DAECs), consisting of at least one DAED. According to the algorithm results, 166 (116 strong and 50 extreme) DAEDs occurred over the MB during the study period. DAEDs are observed mostly in spring (47%) and summer (38%), with strong DAEDs occurring primarily in spring and summer and extreme ones in spring. Decreasing, but not statistically significant, trends of the frequency, spatial extent and intensity of DAECs are revealed. Moreover, a total number of 98 DAECs was found, primarily in spring (46 DAECs) and secondarily in summer (36 DAECs). The seasonal distribution of the frequency of DAECs varies geographically, being highest in early spring over the eastern Mediterranean, in late spring over the central Mediterranean and in summer over the western MB.

scholarly journals A high spatial resolution retrieval of NO<sub>2</sub> column densities from OMI: method and evaluation

2011 ◽  
Vol 11 (4) ◽  
pp. 12411-12440 ◽  
Author(s):  
A. R. Russell ◽  
A. E. Perring ◽  
L. C. Valin ◽  
E. Bucsela ◽  
E. C. Browne ◽  
...  
Keyword(s):  
Boundary Layer ◽  
The Arctic ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Aircraft Observations ◽  
Vertical Column Density ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Better Than

Abstract. We present a new retrieval of tropospheric NO2 vertical column density from the Ozone Monitoring Instrument (OMI) based on high spatial and temporal resolution terrain and profile inputs. We find non-negligible impacts on the retrieved NO2 column for terrain pressure (±20%), albedo (±40%), and NO2 vertical profile (−75%–+10%). We compare our NO2 product, the Berkeley High-Resolution (BEHR) product, with operational retrievals and find that the operational retrievals are biased high (30%) over remote areas and biased low (8%) over urban regions. We validate the operational and BEHR products using boundary layer aircraft observations from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS-CA) field campaign which occurred in June 2008 in California. Results indicate that columns derived using our boundary layer extrapolation method show good agreement with satellite observations (R2 = 0.65–0.83; N = 68) and provide a more robust validation of satellite-observed NO2 column than those determined using full vertical spirals (R2 = 0.26; N = 5) as in previous work. Agreement between aircraft observations and the BEHR product (R2 = 0.83) is better than agreement with the operational products (R2 = 0.65–0.72). We also show that agreement between satellite and aircraft observations for all products can be further improved (e.g. BEHR: R2 = 0.91) using cloud information from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument instead of the OMI cloud product. These results indicate that much of the variance in the operational products can be attributed to coarse resolution terrain and profile parameters.

scholarly journals Estimates of aerosol absorption over India using multi-satellite retrieval

2013 ◽  
Vol 31 (10) ◽  
pp. 1773-1778 ◽  
Author(s):  
D. Narasimhan ◽  
S. K. Satheesh
Keyword(s):  
Regional Distribution ◽  
Single Scattering ◽  
Ozone Monitoring Instrument ◽  
Satellite Retrieval ◽  
Aerosol Absorption ◽  
Moderate Resolution ◽  
Indian Landmass ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
First Time

Abstract. Aerosol absorption is poorly quantified because of the lack of adequate measurements. It has been shown that the Ozone Monitoring Instrument (OMI) aboard EOS-Aura and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard EOS-Aqua, which fly in formation as part of the A-train, provide an excellent opportunity to improve the accuracy of aerosol retrievals. Here, we follow a multi-satellite approach to estimate the regional distribution of aerosol absorption over continental India for the first time. Annually and regionally averaged aerosol single-scattering albedo over the Indian landmass is estimated as 0.94 ± 0.03. Our study demonstrates the potential of multi-satellite data analysis to improve the accuracy of retrieval of aerosol absorption over land.

scholarly journals A high spatial resolution retrieval of NO<sub> 2</sub> column densities from OMI: method and evaluation

2011 ◽  
Vol 11 (16) ◽  
pp. 8543-8554 ◽  
Author(s):  
A. R. Russell ◽  
A. E. Perring ◽  
L. C. Valin ◽  
E. J. Bucsela ◽  
E. C. Browne ◽  
...  
Keyword(s):  
Boundary Layer ◽  
The Arctic ◽  
Ozone Monitoring Instrument ◽  
Vertical Column ◽  
Aircraft Observations ◽  
Vertical Column Density ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Better Than

Abstract. We present a new retrieval of tropospheric NO2 vertical column density from the Ozone Monitoring Instrument (OMI) based on high spatial and temporal resolution terrain and profile inputs. We compare our NO2 product, the Berkeley High-Resolution (BEHR) product, with operational retrievals and find that the operational retrievals are biased high (30 %) over remote areas and biased low (8 %) over urban regions. Additionally, we find non-negligible impacts on the retrieved NO2 column for terrain pressure (±20 %), albedo (±40 %), and NO2 vertical profile (−75 %–+10 %). We validate the operational and BEHR products using boundary layer aircraft observations from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS-CA) field campaign which occurred in June 2008 in California. Results indicate that columns derived using our boundary layer extrapolation method show good agreement with satellite observations (R2 = 0.65–0.83; N = 68) and provide a more robust validation of satellite-observed NO2 column than those determined using full vertical spirals (R2 = 0.26; N = 5) as in previous work. Agreement between aircraft observations and the BEHR product (R2 = 0.83) is better than agreement with the operational products (R2 = 0.65–0.72). We also show that agreement between satellite and aircraft observations can be further improved (e.g. BEHR: R2 = 0.91) using cloud information from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument instead of the OMI cloud product. These results indicate that much of the variance in the operational products can be attributed to coarse resolution terrain pressure, albedo, and profile parameters implemented in the retrievals.

scholarly journals Characterization of wildfire NO<sub>x</sub> emissions using MODIS fire radiative power and OMI tropospheric NO<sub>2</sub> columns

2011 ◽  
Vol 11 (2) ◽  
pp. 5351-5378 ◽  
Author(s):  
A. K. Mebust ◽  
A. R. Russell ◽  
R. C. Hudman ◽  
L. C. Valin ◽  
R. C. Cohen
Keyword(s):  
Ozone Monitoring Instrument ◽  
Tropospheric No2 ◽  
Radiative Power ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
In Fire ◽  
Land Types ◽  
Fire Radiative Power

Abstract. We use observations of fire radiative power (FRP) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and tropospheric NO2 column measurements from the Ozone Monitoring Instrument (OMI) to derive NO2 wildfire emission coefficients (g MJ−1) for three land types over California and Nevada. Retrieved emission coefficients were 0.279 ± 0.077, 0.342 ± 0.053, and 0.696 ± 0.088 g MJ−1 NO2 for forest, grass and shrub fuels, respectively. These emission coefficients reproduce ratios of emissions with fuel type reported previously using independent methods. However, the magnitude of these coefficients is lower than prior estimates, which suggests either a negative bias in the OMI NO2 retrieval over regions of active emissions, or that the average fire observed in our study has a smaller ratio of flaming to smoldering combustion than measurements used in prior estimates of emissions. Our results indicate that satellite data can provide an extensive characterization of the variability in fire NOx emissions; 67% of the variability in emissions in this region can be accounted for using an FRP-based parameterization.

scholarly journals Aerosol direct radiative effect over clouds from a synergy of Ozone Monitoring Instrument (OMI) and Moderate Resolution Imaging Spectroradiometer (MODIS) reflectances

2019 ◽  
Vol 12 (9) ◽  
pp. 5119-5135 ◽  
Author(s):  
Martin de Graaf ◽  
L. Gijsbert Tilstra ◽  
Piet Stammes
Keyword(s):  
Spatial Resolution ◽  
Spectral Resolution ◽  
Data Retrieval ◽  
Radiative Effect ◽  
Ozone Monitoring Instrument ◽  
Monitoring Instrument ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Ozone Monitoring ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. The retrieval of geophysical parameters is increasingly dependent on synergistic use of satellite instruments. More sophisticated parameters can be retrieved and the accuracy of retrievals can be increased when more information is combined. In this paper, a synergistic application of Ozone Monitoring Instrument (OMI), on the Aura platform, and Moderate Resolution Imaging Spectroradiometer (MODIS), on the Aqua platform, Level 1B reflectances is described, enabling the retrieval of the aerosol direct radiative effect (DRE) over clouds using the differential aerosol absorption (DAA) technique. This technique was first developed for reflectances from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) on the Environmental Satellite (Envisat), which had the unique capability of measuring contiguous radiances from the ultraviolet (UV) at 240 to 1750 nm in the shortwave-infrared (SWIR), at a moderate spectral resolution of 0.2 to 1.5 nm. However, the spatial resolution and global coverage of SCIAMACHY was limited, and Envisat stopped delivering data in 2012. In order to continue the DRE data retrieval, reflectances from OMI and MODIS, flying in formation, were combined from the UV to the SWIR. This resulted in reflectances at a limited but sufficient spectral resolution, available at the OMI pixel grid, which have a much higher spatial resolution and coverage than SCIAMACHY. The combined reflectance spectra allow the retrieval of cloud microphysical parameters in the SWIR, and the subsequent retrieval of aerosol DRE over cloud scenes using the DAA technique. For liquid cloud scenes in the south-east Atlantic region with cloud fraction (CF) >0.3, the area-averaged instantaneous aerosol DRE over clouds in June to August 2006 was 25 Wm−2 with a standard deviation of 30 Wm−2. The maximum area-averaged instantaneous DRE from OMI–MODIS in August 2006 was 75.6±13 Wm−2. The new aerosol DRE over-cloud dataset from OMI–MODIS is compared to the SCIAMACHY dataset for the period 2006 to 2009, showing a very high correlation. The OMI–MODIS DRE dataset over the Atlantic Ocean is highly correlated to above-cloud AOT measurements from OMI and MODIS. It is related to AOT measurements over Ascension Island in 2016, showing the transport of smoke all the way from its source region in Africa over the Atlantic to Ascension and beyond.

scholarly journals How big is an OMI pixel?

2016 ◽  
Vol 9 (8) ◽  
pp. 3607-3618 ◽  
Author(s):  
Martin de Graaf ◽  
Holger Sihler ◽  
Lieuwe G. Tilstra ◽  
Piet Stammes
Keyword(s):  
Gaussian Function ◽  
Experimental Tests ◽  
Integration Time ◽  
Ozone Monitoring Instrument ◽  
Imaging Spectrometer ◽  
Charge Coupled Device ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Reflectance Measurements

Abstract. The Ozone Monitoring Instrument (OMI) is a push-broom imaging spectrometer, observing solar radiation backscattered by the Earth's atmosphere and surface. The incoming radiation is detected using a static imaging CCD (charge-coupled device) detector array with no moving parts, as opposed to most of the previous satellite spectrometers, which used a moving mirror to scan the Earth in the across-track direction. The field of view (FoV) of detector pixels is the solid angle from which radiation is observed, averaged over the integration time of a measurement. The OMI FoV is not quadrangular, which is common for scanning instruments, but rather super-Gaussian shaped and overlapping with the FoV of neighbouring pixels. This has consequences for pixel-area-dependent applications, like cloud fraction products, and visualisation.The shapes and sizes of OMI FoVs were determined pre-flight by theoretical and experimental tests but never verified after launch. In this paper the OMI FoV is characterised using collocated MODerate resolution Imaging Spectroradiometer (MODIS) reflectance measurements. MODIS measurements have a much higher spatial resolution than OMI measurements and spectrally overlap at 469 nm. The OMI FoV was verified by finding the highest correlation between MODIS and OMI reflectances in cloud-free scenes, assuming a 2-D super-Gaussian function with varying size and shape to represent the OMI FoV. Our results show that the OMPIXCOR product 75FoV corner coordinates are accurate as the full width at half maximum (FWHM) of a super-Gaussian FoV model when this function is assumed. The softness of the function edges, modelled by the super-Gaussian exponents, is different in both directions and is view angle dependent.The optimal overlap function between OMI and MODIS reflectances is scene dependent and highly dependent on time differences between overpasses, especially with clouds in the scene. For partially clouded scenes, the optimal overlap function was represented by super-Gaussian exponents around 1 or smaller, which indicates that this function is unsuitable to represent the overlap sensitivity function in these cases. This was especially true for scenes before 2008, when the time differences between Aqua and Aura overpasses was about 15 min, instead of 8 min after 2008. During the time between overpasses, clouds change the scene reflectance, reducing the correlation and influencing the shape of the optimal overlap function.

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