Estimation of photolysis frequencies from TOMS satellite measurements and routine meteorological observations

A study on the estimation of J(O<sup>1</sup>D) and J(NO<sub>2</sub>) photolysis frequencies when limited ground based measurements (or even no measurements at all), are available is presented in this work. Photolysis frequencies can be directly measured by chemical actinometry and filter radiometry or can be calculated from actinic flux measurements. In several meteorological stations, none of the methods above are applicable due to the absence of sophisticated instruments such as actinometers, radiometers or spectroradiometers. In this case, it is possible to calculate photolysis frequencies with reasonable uncertainty using either a) standard meteorological observations, such as ozone, cloud coverage and horizontal visibility, available in various ground based stations, as input for a radiative transfer model or b) satellite observations of solar global irradiance available worldwide, in combination with an empirical method for the conversion of irradiance in photolysis frequencies. Both methods can provide photolysis frequencies with a standard deviation between 20% and 30%. The absolute level of agreement of the retrieved frequencies to those calculated from actual actinic flux measurements, for data from all meteorological conditions, is within ±5% for J(O<sup>1</sup>D) and less than 1% for J(NO<sub>2</sub>) for the first method, while for the second method it rises up to 25% for the case of J(O<sup>1</sup>D) and 12% for J(NO<sub>2</sub>), reflecting the overestimation of TOMS satellite irradiance when compared to ground based measurements of irradiance for the respective spectral regions. Due to the universality of the methods they can be practically applied to almost any station, thus overcoming problems concerning the availability of instruments measuring photolysis frequencies

A two-parameter wind speed algorithm for Ku-band altimeters

Globally distributed crossovers of altimeter and scatterometer observations clearly demonstrate that ocean altimeter backscatter correlates with both the near-surface wind speed and the sea state. Satellite data from TOPEX/Poseidon and NSCAT are used to develop an empirical altimeter wind speed model that attenuates the sea-state signature and improves upon the present operational altimeter wind model. The inversion is defined using a multilayer perceptron neural network with altimeter-derived backscatter and significant wave height as inputs. Comparisons between this new model and past single input routines indicates that the rms wind error is reduced by 10%–15% in tandem with the lowering of wind error residuals dependent on the sea state. Both model intercomparison and validation of the new routine are detailed, including the use of large independent data compilations that include the SeaWinds and ERS scatterometers, ECMWF wind fields, and buoy measurements. The model provides consistent improvement against these varied sources with a wind-independent bias below 0.3 m s?1. The continuous form of the defined function, along with the global data used in its derivation, suggest an algorithm suitable for operational application to Ku-band altimeters. Further model improvement through wave height inclusion is limited due to an inherent multivaluedness between any single realization of the altimeter measurement pair [?o, HS] and observed near-surface winds. This ambiguity indicates that HS is a limited proxy for variable gravity wave properties that impact upon altimeter backscatter

Comparative study of hard and fuzzy logic classifiers with qualitative and quantitative criteria for the discrimination of biophysical characteristics using satellite images

The aim of this thesis was the employment of hard and soft classifiers for land cover/use classification on an area with ecological importance protected by Ramsar Convention (Lake Koronia in Northern Greece), and the use of output thematic maps in the development of new spatially environmental indicators according to DPSIR model proposed by European Environmental Agency. More specifically, four different classification algorithms were used and each one belonged to a different category of classifiers (hard or soft classifiers, parametric or non- parametric classifiers, like neural networks). The use of selected field test sites and confusion matrices resulted in the production of a site specific accuracy assessment for these classifiers. Moreover, using a modified equation of the landscape metric Shannon Eveness’ Index (MSHEI), the homogeneity of classification inside the agriparcels in the agricultural zone of the study area was estimated. The fuzzy neural network SONeFMUC (Self-Organized Neuro Fuzzy Multistage Classifier) performed better than the other algorithms and the output thematic map contributed to the calculation of pressure and state indicators in the area. Three pressure indicators were estimated: the Irrigation Pressure Index, the Fertilization Pressure Index and the Urbanization Pressure Index. An innovative technique for the estimation of these indicators was the use of Edge Contast Index (ECON). ECON was utilized for the calculation of the pressure that is forced on an agriparcel from its adjacent agriparcel. Additionally, an appropriate methodology was applied in the wetland of Koronia in order to evaluate its functions through its basic attributes. These attributes were estimated using image classification and collateral geographic data. The proposed methodology for the calculation of pressure and state indicators could be useful for the selection of appropriate alternative scenarios by the local authorities in order to deal with the environmental problems of the area.Ο σκοπός της παρούσας διατριβής ήταν η μελέτη ανελαστικών και ελαστικών μεθόδων για την ταξινόμηση βιοφυσικών στοιχείων μίας οικολογικά ευαίσθητης περιοχής με δορυφορικά δεδομένα όπου το αποτέλεσμα της ταξινόμησης χρησιμοποιήθηκε για την ανάπτυξη νέων περιβαλλοντικών χωρικών δεικτών σύμφωνα με το μοντέλο DPSIR που προτείνει η Ευρωπαϊκή Υπηρεσία Περιβάλλοντος. Ειδικότερα, χρησιμοποιήθηκαν τέσσερις αλγόριθμοι ταξινόμησης που ανήκουν σε διαφορετική κατηγορία ταξινομητών ως προς την απόφαση που παίρνουν για την ταξινόμηση των εικονοστοιχείων (ανελαστικοί - ασαφούς λογικής) και ως προς τον τρόπο εκπαίδευσή τους (παραμετρικοί - μη παραμετρικοί), και εξετάσθηκε η ποσοτική και η ποιοτική τους ακρίβεια. Συγκεκριμένα, μετρήθηκε η ποσοτική ακρίβεια με τη χρήση του πίνακα λαθών (Confusion Matrix), από δεδομένα αναφοράς που συλλέχθηκαν με εργασία πεδίου. Επίσης, για την ποιοτική τους ακρίβεια προτάθηκε η χρησιμοποίηση ενός τροποποιημένου δείκτη τοπίου, του Shannon Evenness’ Index, ο οποίος συνέβαλλε στην εκτίμηση της ομοιομορφίας της ταξινόμησης μέσα στα αγροτεμάχια της αγροτικής ζώνης της περιοχής μελέτης. Η έρευνα έδειξε ότι τα συγκριτικά καλύτερα αποτελέσματα έδωσε το ασαφές νευρωνικό δίκτυο SONeFMUC (Self-Organized Neuro Fuzzy Multistage Classifier), όπου ο παραγόμενος θεματικός χάρτης χρησιμοποιήθηκε για τον υπολογισμό δεικτών πίεσης και κατάστασης. Συγκεκριμένα αναπτύχθηκαν τρεις δείκτες πίεσης: Ο δείκτης άρδευσης Ι.P.I, λίπανσης F.P.I. και οικιστικής ανάπτυξης U.P.I. Ένα καινοτόμο στοιχείο αυτών των δεικτών ήταν ο υπολογισμός του επιμέρους δείκτη τοπίου Edge Contrast Ιndex, ο οποίος υπολογίζει την πίεση που ασκεί κάθε αγροτεμάχιο από τα γειτονικά του, στον υγρότοπο της Κορώνειας, Επίσης, αναπτύχθηκε κατάλληλη μεθοδολογία όπου αξιολογήθηκαν οι λειτουργίες του υγρότοπου μέσω των ιδιοτήτων του, που με τη σειρά τους εκτιμήθηκαν μέσω δεικτών από την ταξινομημένη εικόνα και επιπλέον γεωγραφικά δεδομένα. Η μεθοδολογία η οποία χρησιμοποιήθηκε τόσο για τους δείκτες πίεσης όσο και για τους δείκτες κατάστασης μπορεί να αποτελέσει ένα χρήσιμο εργαλείο στην επιλογή των κατάλληλων εναλλακτικών σεναρίων, ώστε να ληφθούν διαχειριστικά μέτρα αντιμετώπισης των περιβαλλοντικών προβλημάτων που παρουσιάζει ο υγρότοπος της Κορώνειας

NO₂ and HCHO photolysis frequencies from irradiance measurements in Thessaloniki, Greece

International audienceAn empirical approach for the retrieval of nitrogen dioxide (NO2) and formaldehyde (HCHO) photolysis frequencies from measurements of global irradiance is presented in this work. Four months of synchronous measurements of actinic flux and global irradiance performed in Thessaloniki, Greece by a Bentham spectroradiometer were used to extract polynomials for the conversion of global irradiance to photolysis frequencies [(NO2) and J(HCHO)]. The comparison of these photolysis frequency values to the corresponding values calculated by spectral actinic flux measurements, showed a ratio very close to unity for all J's with a standard deviation of 6% for J(NO2) and 3% for J(HCHO). Additional sets of polynomials were also extracted to allow determination of J(NO2) by spectroradiometers with lower upper wavelength limits such as single and double Brewer spectroradiometers within acceptable uncertainty (corresponding ratio was 1 and standard deviation was 6% for double and 10% for single Brewers). The validity of the method under different atmospheric conditions was also examined by applying the polynomials to another set of actinic flux and global irradiance measurements performed in May 2004, in Buchhofen, Germany. In this case, comparing J values extracted from the polynomials to those calculated from actinic flux, showed equivalent results, demonstrating that the method can also be applied to other measurement sites

Actinic flux and O¹D photolysis frequencies retrieved from spectral measurements of irradiance at Thessaloniki, Greece

International audienceThe results of two methods retrieving actinic flux and ozone photolysis frequencies (JO1D), from measurements of irradiance with a Brewer MKIII spectroradiometer are investigated in this paper. The first method uses actinic flux retrieved from irradiance measurements by the use of known formulas while the second is an empirical method converting irradiance to JO1D through polynomials extracted from a study of synchronous actinic flux and irradiance measurements. When examining the actinic fluxes derived from the first method to those measured by an actinic flux spectrometer data agree within ±10% for solar zenith angles lower than 75° for the UV-B and the UV-A wavelength band. Also, the actinic to global irradiance ratio derived, deviates within ±6% for solar zenith angles lower than 70° compared with cloudless sky calculations of the TUV model. For both cases the deviations are in the order of the magnitude of the measurement or model uncertainties. Values of JO1D calculated by the second method show a mean ratio of 0.99±0.10 (1?) and 0.98±0.06 for all data and for cloudless skies respectively when compared with values of JO1D derived by a Bentham actinic flux spectroradiometer. Finally, the agreement of the two methods is within ±5% comparing two years' data of JO1D retrieved from irradiance measurements at Thessaloniki, Greece. The use of such methods on extensive data sets of global irradiance can provide JO1D values with acceptable uncertainty, a parameter of particular importance for chemical process studies