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PRISMA is a hyperspectral satellite mission launched by the Italian Space Agency (ASI) in April 2019. The mission is designed to collect data at global scale for a variety of applications, including those related to the cryosphere. This study presents an evaluation of PRISMA Level 1 (L1) and Level 2 (L2D) products for different snow conditions. To the aim, PRISMA data were collected at three sites: two in the Western European Alps (Torgnon and Plateau Rosa) and one in East Antarctica (Nansen Ice Shelf). PRISMA data were acquired contemporary to both field measurements and Sentinel-2 data. Simulated Top of the Atmosphere (TOA) radiance data were then compared to L1 PRISMA and Sentinel-2 TOA radiance. Bottom Of Atmosphere (BOA) reflectance from PRISMA L2D and Sentinel-2 L2A data were then evaluated by direct comparison with field data. Both TOA radiance and BOA reflectance PRISMA products were generally in good agreement with field data, showing a Mean Absolute Difference (MAD) lower than 5%. L1 PRISMA TOA radiance products resulted in higher MAD for the site of Torgnon, which features the highest topographic complexity within the investigated areas. In Plateau Rosa we obtained the best comparison between PRISMA L2D reflectance data and in situ measurements, with MAD values lower than 5% for the 400–900 nm range. The Nansen Ice Shelf instead resulted in MAD values <10% between PRISMA L2D and field data, while Sentinel-2 BOA reflectance showed higher values than other data sources.

I prodotti della pesca sono una delle eccellenze della grande cultura enogastronomica italiana. L’Italia con oltre 7900 km di coste offre una grande di varietà di prodotti ittici con una grande varietà di denominazioni dialettali. Per i loro principi nutritivi ricchi di proteine di alto valore biologico e lipidi contenenti importanti acidi grassi e vitamine particolarmente utili alla prevenzione di malattie legate all’apparato cardiocircolatorio sono una importante componente della “dieta mediterranea”. In contrapposizione a questi effetti benefici, per la loro particolare composizione biochimica e l’elevato contenuto di acqua si presentano facilmente deperibili, soggetti a contaminazioni batteriche, e chimiche legate principalmente all’attività antropica. Il presente lavoro prende in esame il mondo ittico in diversi aspetti, partendo dall’esame dell’economia legata ai prodotti ittici, il mercato ittico europeo e in particolare quello italiano. Le criticità intrinseche ed estrinseche dei prodotti della pesca, Il ruolo della tracciabilità quale strumento per garantirne la qualità, le proprietà nutritive e nutraceutiche, l’ecosostenibilità quale tema a cui il consumatore finale mostra sempre più attenzione, aspetti legati all’arrivo ne Mediterraneo di specie ittiche tossiche di origine lessepsiana, di nuove tossine ittiche emergenti grazie alla sempre maggiore richiesta di prodotti ittici e il conseguente aumento della globalizzazione della rete commerciale, di nuovi contaminati ambientali emergenti quali le microplastiche. Infine, vengono esaminati alcune tecniche strumentali di analisi in uso per garantirne la qualità, la sicurezza alimentare e l’esattezza delle informazioni che il consumatore finale deve conoscere. La parte sperimentale del lavoro si è occupata di verificare se esistesse una valida correlazione tra le tecniche di identificazione di specie di una eccellenza ittica italiana quale è il Gambero rosso di Mazara del Vallo è la sua localizzaz, Fish products are one of the excellences of the great Italian food and wine culture. Italy, with over 7900 km of coastline, offers a wide variety of fish products with a wide variety of dialect names. Due to their nutrients, rich in proteins of high biological value and lipids containing important fatty acids and vitamins, particularly useful for the prevention of diseases related to the cardiovascular system, they are an important component of the "Mediterranean diet". In contrast to these beneficial effects, due to their biochemical composition and high-water content, they are easily perishable, subject to bacterial and chemical contamination mainly linked to human activity. This paper examines the fish world in different aspects, starting from the examination of the economics linked to fish products, the European fish market and in particular the Italian one. The intrinsic and extrinsic criticalities of fishery products, the role of traceability as a tool to guarantee their quality, nutritional and nutraceutical properties, eco-sustainability as an issue to which the end consumer shows more and more attention, aspects related to the arrival in the Mediterranean of toxic fish species of Lessepsiana origin, of new emerging fish toxins thanks to the increasing demand for fish products and the consequent increase in globalization of the commercial network, of new emerging environmental contaminants such as microplastics. Finally, some instrumental analysis techniques in use are examined to ensure quality, food safety and the accuracy of the information that the final consumer must know. The experimental part of the work was concerned with verifying whether there was a valid correlation between the techniques for identifying species of an Italian fish excellence such as the Red Shrimp of Mazara del Vallo and its geographical location that increases its economic value. The guarantee of food safety must be ensured through appropriate legislation, the application of appr

Solar-induced chlorophyll fluorescence (SIF) is closely related to plant photosynthetic activity and has been used in different studies as a proxy for vegetation health status. However, in order to use SIF as a relevant indicator of plant physiological stress, it is necessary to accurately quantify the amount of light absorbed by the photosynthetic plant pigments, called the absorbed photosynthetically active radiation (APAR). The ratio between fluorescence emission and light absorption (i.e., SIF and APAR) is known as the fluorescence quantum efficiency (FQE). In this work, simultaneous measurements of SIF and reflected radiance were performed both at the leaf and canopy levels for Salvia farinacea and Datura stramonium plants. With the aim of disentangling the proportion of sunlit and shaded absorbed PAR, an ad hoc experimental setup was designed to provide a wide range of fraction vegetation cover (FVC) canopy settings. A linear spectral unmixing method was proposed to estimate the contribution of soil, sunlit, and shaded vegetation from the total reflectance spectrum measured at the canopy level. Later, the retrieved sunlit FVC (FVCsunlit) was used to estimate the (dominant) green APAR flux, and this was combined with the integral of the spectrally resolved fluorescence to calculate the FQE. The results of this study demonstrated that under no-stress conditions and independently of the FVC, similar FQE values were observed when SIF was properly normalised by the green APAR flux. The results obtained showed that the reflectance spectra retrieved using a linear unmixing method had a maximum RMSE of less than 0.03 along the spectrum. The FVCsunlit evaluation showed an RMSE of 14% with an R2 of 0.84. Moreover, the FQE values obtained at the top of the canopy (TOC) were found statistically comparable to the reference values at the leaf level. These results support further efforts to improve the interpretation of fluorescence based on field spectroscopy and the furthe

Risalgono a più di mezzo secolo fa' i primi studi sul ruolo dell'orografia e delle variazioni longitudinali delle sorgenti di calore per la circolazione atmosferica delle medie latitudini. Nonostante sia stato raggiunto un buon livello di conoscenza del tema, nuove domande stanno nascendo per via del cambiamento climatico e dell'ingente utilizzo di modelli climatici, interessati da varie tipologie di errori. I tempi scala lunghi e l'impatto importante dei segnali termici oceanici hanno permesso uno studio approfondito delle interazioni tra la temperatura della superficie del mare e l'atmosfera. La superficie delle terre emerse ha ricevuto meno attenzione, sebbene possa diventare rilevante per la circolazione quando induce un riscaldamento o raffreddamento persistente nella bassa atmosfera. La persistenza del segnale termico terrestre non costituisce però una condizione sufficiente per determinare una risposta dinamica forte in atmosfera. Nella tesi ne sviluppiamo alcuni esempi. Con il riscaldamento climatico la superficie dei continenti dovrebbe scaldarsi più velocemente della superficie degli oceani; di conseguenza anche il contrasto termico tra i due dovrebbe cambiare. Decidiamo di concentrarci sulla stagione invernale dell'emisfero boreale. Un set di simulazioni a inverno perenne, girate con condizioni superficiali caratterizzate da un riscaldamento anomalo della superficie terrestre negli extratropici, mostra una riduzione degli elementi principali che contraddistinguono l'atmosfera delle medie latitudini, ovvero le correnti a getto e le onde stazionarie. È interessante notare che la risposta atmosferica è prevalentemente forzata dal riscaldamento del continente asiatico, con un ruolo secondario dell'America settentrionale. Partendo da questi risultati, esaminiamo la rappresentazione delle temperature asiatiche medie in un insieme di modelli climatici allo stato dell'arte, e troviamo ampie differenze tra i modelli soprattutto nell'altopiano tibetano e in Si, The first attempts to determine the role of orography and longitudinally varying heat sources for the mid-latitude atmospheric circulation date back to more than half a century ago. Whilst we have reached a good understanding of their interaction with the atmosphere, climate change and the wide use of climate models, characterised by common or individual biases, pose new interesting questions. Because of the long time scales and large impact of ocean-based signals, the interaction of the atmosphere with the sea surface temperature has been studied extensively. Less so for the land surface which, when inducing persistent low-level warming or cooling, may nonetheless become important for the atmospheric circulation. However, the persistence of the forcing by a land-based thermal source is not always sufficient to determine an important dynamical response in the atmosphere. Some examples are developed in the thesis. In a warmer climate the surface of the continents are expected to warm faster than the surface of the oceans, producing changes in the large-scale temperature contrast. During the winter season of the Northern Hemisphere, chosen as the setting for our analysis, the thermal contrast is projected to reduce. A set of perpetual-winter atmospheric simulations with prescribed surface conditions featuring an intense NH extratropical land warming reveals a strong reduction in the large-scale features of the mid-latitude atmosphere, i.e. stationary waves and jet streams. Interestingly, the response is induced mainly by the warming of the Asian continent, with North America playing only a secondary role. Prompted by this result, we examine the representation of Asian temperatures in a set of state-of-the-art climate models, and detect a large inter-model temperature spread over the Tibetan Plateau and Siberia. We show that anomalously low temperatures over the Tibetan Plateau - a region that is often affected by a cold model bias - reinforce the East Asia summer mons

Snow, as a fundamental reservoir of freshwater, is a crucial natural resource. Specifically, knowledge of snow density spatial and temporal variability could improve modelling of snow water equivalent, which is relevant for managing freshwater resources in context of ongoing climate change. The possibility of estimating snow density from remote sensing has great potential, considering the availability of satellite data and their ability to generate efficient monitoring systems from space. In this study, we present an innovative method that combines meteorological parameters, satellite data and field snow measurements to estimate thermal inertia of snow and snow density at a catchment scale. Thermal inertia represents the responsiveness of a material to variations in temperature and depends on the thermal conductivity, density and specific heat of the medium. By exploiting Landsat 8 data and meteorological modelling, we generated multitemporal thermal inertia maps in mountainous catchments in the Western European Alps (Aosta Valley, Italy), from incoming shortwave radiation, surface temperature and snow albedo. Thermal inertia was then used to develop an empirical regression model to infer snow density, demonstrating the possibility of mapping snow density from optical and thermal observations from space. The model allows for estimation of snow density with R2CV and RMSECV of 0.59 and 82 kg m−3, respectively. Thermal inertia and snow density maps are presented in terms of the evolution of snow cover throughout the hydrological season and in terms of their spatial variability in complex topography. This study could be considered a first attempt at using thermal inertia toward improved monitoring of the cryosphere. Limitations of and improvements to the proposed methods are also discussed. This study may also help in defining the scientific requirements for new satellite missions targeting the cryosphere. We believe that a new class of Earth Observation missions with t

Thermal structures at the sea surface are known to affect the overlying atmospheric dynamics over various spatio-temporal scales, from hourly and sub-kilometric to annual and O(1,000 km). The relevant mechanisms at play are generally identified by means of correlation coefficients (in space or time) or by linear regression analysis using appropriate couples of variables. For fine spatial scales, where sea surface temperature (SST) gradients get stronger, the advection might disrupt these correlations and, thus, mask the action of such mechanisms, just because of the chosen metrics. For example, at the oceanic sub-mesoscale, around 1–10 km and hourly time scales, the standard metrics used to identify the pressure adjustment mechanism (that involves the Laplacian of sea surface temperature, SST, and the wind divergence) may suffer from this issue, even for weak wind conditions. By exploiting high-resolution realistic numerical simulations with ad hoc SST forcing fields, we introduce some new metrics to evaluate the action of the pressure adjustment atmospheric response to the surface oceanic thermal structures. It is found that the most skillful metrics is based on the wind divergence and the SST second spatial derivative evaluated in the across direction of a locally defined background wind field.

The predictability of the Northern Hemisphere stratosphere and its underlying dynamics are investigated in five state-of-the-art seasonal prediction systems from the Copernicus Climate Change Service (C3S) multi-model database. Special attention is devoted to the connection between the stratospheric polar vortex (SPV) and lower-stratosphere wave activity (LSWA). We find that in winter (December to February) dynamical forecasts initialised on the first of November are considerably more skilful than empirical forecasts based on October anomalies. Moreover, the coupling of the SPV with mid-latitude LSWA (i.e., meridional eddy heat flux) is generally well reproduced by the forecast systems, allowing for the identification of a robust link between the predictability of wave activity above the tropopause and the SPV skill. Our results highlight the importance of November-to-February LSWA, in particular in the Eurasian sector, for forecasts of the winter stratosphere. Finally, the role of potential sources of seasonal stratospheric predictability is considered: we find that the C3S multi-model overestimates the stratospheric response to El Niño–Southern Oscillation (ENSO) and underestimates the influence of the Quasi–Biennial Oscillation (QBO).

Low-level clouds over the tropical and sub-tropical oceans play a crucial role in the planetary radiative energy budget. However, they are challenging to model in climate simulations because they are affected by local processes that are still partially unknown. The control that mesoscale sea surface temperature (SST) structures have on the dynamics of the lower atmosphere on daily scales is emerging to be non-negligible and calls for more effort to be understood. During the EUREC4A field campaign, two of the research vessels (R/Vs) involved in the experiment sampled the edge of a cold mesoscale SST patch in the north-western tropical Atlantic, crossing a gradient of roughly 0.75°C/100 km. The comprehensive set of instruments carried by the R/Vs allows an unprecedented characterization of the atmospheric response to the cold water forcing. The cold ocean patch weakens the vertical atmospheric mixing, reducing the boundary layer depth of roughly 200 m and the horizontal wind intensity of approximately 3 m s−1. At the same time, the humidity content in the sub-cloud layer increases and these conditions decrease the latent heat flux (by roughly 80 W m−2) and reduce vertical velocity fluctuations, making it less likely that moisture exceeds the lifting condensation level. As a consequence, fewer and thinner low-level clouds form over cold water. Independent satellite measurements are found to agree with the in situ observations. The observed link between sea temperature and low-level clouds highlights its importance in the puzzle of modeling the sea-air-cloud interactions.

La seguente ricerca di dottorato ha come obiettivo lo sviluppo di nuove strategie in grado di migliorare la stima e l’interpretazione del segnale di fluorescenza indotto dalla luce solare (SIF) emesso dalla clorofilla. In particolare la SIF emessa a livello del suolo è stata utilizzata per migliorare la comprensione del funzionamento della vegetazione terrestre ed acque interne. Nuove metriche di fluorescenza sono state definite a partire dello spettro completo di SIF ottenuto tramite l’algoritmo SpecFit applicato a misure spettrali di campo Top-Of-Canopy. Tali metriche sono state concepite per caratterizzare lo spettro totale di SIF, in termini di valori massimi di emissione (SIFred, SIFfar-red), posizione dei picchi ed integrale di fluorescenza (SIFINT). Il loro comportamento su scale stagionale e giornaliera è stato dunque confrontato con la SIF valutata nelle bande di assorbimento dell’ossigeno atmosferico (SIF760, SIF687) ed indici di riflettanza (NDVIred-edge, CIred-edge, NIRv, PRI), questi ultimi usati come proxy di parametri biofisici di vegetazione. Il SIF valutato ai picchi mostra sempre una forte correlazione con i corrispondenti valori delle bande O2, mentre il SIFINT rappresenta un parametro più completo e mostra dinamiche peculiari. A scala diurna, l'uso combinato di indici di riflettanza e metriche SIF permette una migliore caratterizzazione delle dinamiche delle diverse colture investigate. Stagionalmente, gli indici di SIF e di riflettanza sono caratterizzati dalla medesima evoluzione temporale in quanto entrambi guidati da cambiamenti della luce incidente e nella biomassa della canopy, del suo contenuto di clorofilla. Tuttavia, a tale scala, il riassorbimento della fluorescenza che avviene a livello fogliare e di chioma affligge la forma spettrale e intensità della SIF. In accordo con l’analisi condotta su misure spettrali simulate, il riassorbimento impedisce la corretta stima del rendimento di fluorescenza (SIFyield): pertanto, correggere lo, The PhD research aimed to develop novel strategies able to better retrieve and interpret the chlorophyll Solar-Induced Fluorescence (SIF) signal emitted by terrestrial vegetation and inland waters at ground level, to advance the understanding of ecosystems structure and functioning. SIF metrics were defined taking advantage of the full SIF spectrum available from the recently developed “spectrum-fitting” algorithm (SpecFit). The metrics were designed to characterize the SIF spectrum, in terms of red and far-red peaks maximum values (SIFred, SIFfar-red), corresponding wavelengths and the spectrally integrated value (SIFINT). SIF typically evaluated in the O2-A (SIF760) and O2-B (SIF687) bands and reflectance indices (used as proxies for canopy biophysical parameters) have been compared to the SIF spectrum. The reflectance indices selected are the NDVIred-edge, CIred-edge, NIRv and PRI. The analysis has been carried out at seasonal/diurnal scales, exploiting top-of canopy (TOC) spectral measurements acquired over three crops. The SIF evaluated at the peaks always show a strong correlation with the corresponding O2 bands values, while the SIFINT represents a more complete parameter and shows peculiar dynamics. At diurnal scale, the combined use of reflectance indices and TOC SIF metrics allows to gain a better knowledge of the crops dynamics. Seasonally, the SIF and reflectance indices show more similar temporal evolution along the growth-phases because they are mainly driven by changes in the overall canopy biomass, chlorophyll content and incident light. The reabsorption of the SIF within the canopy-leaf system affects the overall SIF spectral shape and magnitude at this temporal scale. As demonstrated on the synthetic dataset, the reabsorption effect prevents an accurate evaluation of the fluorescence quantum yield (SIFyield). Correcting the TOC SIF spectrum for the reabsorption is pivotal. In this regard, two different approaches have been developed and tested. The

The emission of solar-induced chlorophyll fluorescence (F) is a pivotal process to infer vegetation health and functioning that can be monitored by remote sensing. However, most of the current remote sensing methods retrieve only F at top-of-canopy level, therefore making the link with physiological processes occurring at photosystem level not trivial. In this study, we develop a novel machine learning Fourier (phasor)-based algorithm to retrieve F both at canopy level and after considering the reabsorption (i.e. photosystem level), consistently with relevant biophysical variables, exploiting the canopy apparent reflectance spectra (Rapp). In particular, Rapp is divided in consecutive spectral windows, where the Discrete Fourier Transform (DFT) is computed. Then, the DFT results in each window are exploited to estimate the fluorescence spectra and biophysical parameters, together with their uncertainties, by means of a supervised machine learning algorithm coupled to a statistical-based retrieval pipeline. The algorithm has been trained through synthetic Rapp spectra, obtained from simulations based on a Radiative Transfer (RT) model. As a proof of concept, the theoretical approach is then applied to experimental data, acquired both from crops and forests, at close and high soil-sensor distance respectively, to evaluate the retrieval accuracy of biophysical and F parameters. In particular, for the first time Rapp is used to extract the temporal evolution of F at canopy and photosystem levels and its quantum efficiency together with different biophysical variables, during the growing season of two agricultural crops. Furthermore, tower-based solar-induced fluorescence measurements in a deciduous forest are exploited to evaluate the performance of our algorithm when the atmospheric reabsorption and scattering are not negligible. The reliability of the proposed method is evaluated through a comparison with F spectra extracted from the state of the art SpecFit retrieval

The upcoming Fluorescence Explorer (FLEX) mission will provide sun-induced fluorescence (SIF) products at unprecedented spatial resolution. Thus, accurate calibration and validation (cal/val) of these products are key to guarantee robust SIF estimates for the assessment and quantification of photosynthetic processes. In this study, we address one specific component of the uncertainty budget related to SIF retrieval: the spatial representativeness of in situ SIF observations compared to medium-resolution SIF products (e.g., 300 m pixel size). Here, we propose an approach to evaluate an optimal sampling strategy to characterise the spatial representativeness of in situ SIF observations based on high-spatial-resolution SIF data. This approach was applied for demonstration purposes to two agricultural areas that have been extensively characterized with a HyPlant airborne imaging spectrometer in recent years. First, we determined the spatial representativeness of an increasing number of sampling points with respect to a reference area (either monocultural crop fields or hypothetical FLEX pixels characterised by different land cover types). Then, we compared different sampling approaches to determine which strategy provided the most representative reference data for a given area. Results show that between 3 and 13.5 sampling points are needed to characterise the average SIF value of both monocultural fields and hypothetical FLEX pixels of the agricultural areas considered in this study. The number of sampling points tends to increase with the standard deviation of SIF of the reference area, as well as with the number of land cover classes in a FLEX pixel, even if the increase is not always statistically significant. This study contributes to guiding cal/val activities for the upcoming FLEX mission, providing useful insights for the selection of the validation site network and particularly for the definition of the best sampling scheme for each site.

Aerosols play a crucial role in climate through different feedback mechanisms, affecting radiation, clouds, and air column stability. This study focuses on the altitude dependence of the cloud-mediated indirect effects of aerosols in the Great Alpine Region (GAR), an area characterized by high pollution levels from anthropic activities in the Po Valley and a complex orography with some of the highest mountains in Europe. Using a regional atmospheric model, 5-year-long convective-permitting sensitivity experiments have been run with different surface aerosol fluxes. The results show that seasonal mean cloud cover, temperature, and precipitations are affected by the aerosol concentrations in the air column and that the response to pollution is both elevation- and season-dependent. The overall cloud cover increase with aerosol levels leads to either surface cooling or warming depending on the surface albedo (snow covered or not). Furthermore, different types of clouds have a different response: while the lifetime of low-pressure-system clouds and orographic clouds is generally increased at high levels of aerosols, convective clouds (typical of the summer season) can decrease at high levels of pollution due to the reduction in strong updrafts associated with an increased air column stability.

The upcoming Fluorescence Explorer (FLEX) satellite mission aims to provide high quality radiometric measurements for subsequent retrieval of sun-induced chlorophyll fluorescence (SIF). The combination of SIF with other observations stemming from the FLEX/Sentinel-3 tandem mission holds the potential to assess complex ecosystem processes. The calibration and validation (cal/val) of these radiometric measurements and derived products are central but challenging components of the mission. This contribution outlines strategies for the assessment of in situ radiometric measurements and retrieved SIF. We demonstrate how in situ spectrometer measurements can be analysed in terms of radiometric, spectral and spatial uncertainties. The analysis of more than 200 k spectra yields an average bias between two radiometric measurements by two individual spectrometers of 8%, with a larger variability in measurements of downwelling radiance (25%) compared to upwelling radiance (6%). Spectral shifts in the spectrometer relevant for SIF retrievals are consistently below 1 spectral pixel (up to 0.75). Found spectral shifts appear to be mostly dependent on temperature (as measured by a temperature probe in the instrument). Retrieved SIF shows a low variability of 1.8% compared with a noise reduced SIF estimate based on APAR. A combination of airborne imaging and in situ non-imaging fluorescence spectroscopy highlights the importance of a homogenous sampling surface and holds the potential to further uncover SIF retrieval issues as here shown for early evening acquisitions. Our experiments clearly indicate the need for careful site selection, measurement protocols, as well as the need for harmonized processing. This work thus contributes to guiding cal/val activities for the upcoming FLEX mission.

Vegetation responds at varying temporal scales to changing soil water availability. These process dynamics complicate assessments of plant-water relations but also offer various access points to advance understanding of vegetation responses to environmental change. Remote sensing (RS) provides large capacity to quantify sensitive and robust information of vegetation responses and underlying abiotic change driver across observational scales. Retrieved RS based vegetation parameters are often sensitive to various environmental and plant specific factors in addition to the targeted plant response. Further, individual plant responses to water limitation act at different temporal and spatial scales, while RS sampling schemes are often not optimized to assess these dynamics. The combination of these aspects complicates the interpretation of RS parameter when assessing plant-water relations. We consequently aim to advance insight on the sensitivity of physiological, biochemical and structural RS parameter for plant adaptation in response to emerging soil water limitation. We made a field experiment in maize in Tuscany (Central Italy), while irrigation was stopped in some areas of the drip-irrigated field. Within a period of two weeks, we measured the hydraulic and physiological state of maize plants in situ and complemented these detailed measurements with extensive airborne observations (e.g. sun-induced chlorophyll fluorescence (SIF), vegetation indices sensitive for photosynthesis, pigment and water content, land surface temperature). We observe a double response of far-red SIF with a short-term increase after manifestation of soil water limitation and a decrease afterwards. We identify different response times of RS parameter representing different plant adaptation mechanisms ranging from short term responses (e.g. stomatal conductance, photosynthesis) to medium term changes (e.g. pigment decomposition, changing leaf water content). Our study demonstrates complementari

In this study, we are testing a proxy for red and far-red Sun-induced fluorescence (SIF) using an integrated fuzzy logic modelling approach, termed as SIFfuzzy and SIFfuzzy-APAR. The SIF emitted from the core of the photosynthesis and observed at the top-of-canopy is regulated by three major controlling factors: (1) light interception and absorption by canopy plant cover; (2) escape fraction of SIF photons (fesc); (3) light use efficiency and non-photochemical quenching (NPQ) processes. In our study, we proposed and validated a fuzzy logic modelling approach that uses different combinations of spectral vegetation indices (SVIs) reflecting such controlling factors to approximate the potential SIF signals at 760 nm and 687 nm. The HyPlant derived and field validated SVIs (i.e., SR, NDVI, EVI, NDVIre, PRI) have been processed through the membership transformation in the first stage, and in the next stage the membership transformed maps have been processed through the Fuzzy Gamma simulation to calculate the SIFfuzzy. To test whether the inclusion of absorbed photosynthetic active radiation (APAR) increases the accuracy of the model, the SIFfuzzy was multiplied by APAR (SIFfuzzy-APAR). The agreement between the modelled SIFfuzzy and actual SIF airborne retrievals expressed by R2 ranged from 0.38 to 0.69 for SIF760 and from 0.85 to 0.92 for SIF687. The inclusion of APAR improved the R2 value between SIFfuzzy-APAR and actual SIF. This study showed, for the first time, that a diverse set of SVIs considered as proxies of different vegetation traits, such as biochemical, structural, and functional, can be successfully combined to work as a first-order proxy of SIF. The previous studies mainly included the far-red SIF whereas, in this study, we have also focused on red SIF along with far-red SIF. The analysis carried out at 1 m spatial resolution permits to better infer SIF behaviour at an ecosystem-relevant scale.

We experimentally quantified the impact of cloud fraction and cloud type on the heating rate (HR) of black and brown carbon (HRBC and HRBrC). In particular, we examined in more detail the cloud effect on the HR detected in a previous study (Ferrero et al., 2018). High-time-resolution measurements of the aerosol absorption coefficient at multiple wavelengths were coupled with spectral measurements of the direct, diffuse and surface reflected irradiance and with lidar-ceilometer data during a field campaign in Milan, Po Valley (Italy). The experimental set-up allowed for a direct determination of the total HR (and its speciation: HRBC and HRBrC) in all-sky conditions (from clear-sky conditions to cloudy). The highest total HR values were found in the middle of winter (1.43±0.05Kd-1), and the lowest were in spring (0.54±0.02Kd-1). Overall, the HRBrC accounted for 13.7±0.2% of the total HR, with the BrC being characterized by an absorption Ångström exponent (AAE) of 3.49±0.01. To investigate the role of clouds, sky conditions were classified in terms of cloudiness (fraction of the sky covered by clouds: oktas) and cloud type (stratus, St; cumulus, Cu; stratocumulus, Sc; altostratus, As; altocumulus, Ac; cirrus, Ci; and cirrocumulus-cirrostratus, Cc-Cs). During the campaign, clear-sky conditions were present 23% of the time, with the remaining time (77 %) being characterized by cloudy conditions. The average cloudiness was 3.58±0.04 oktas (highest in February at 4.56±0.07 oktas and lowest in November at 2.91±0.06 oktas). St clouds were mostly responsible for overcast conditions (7-8 oktas, frequency of 87% and 96 %); Sc clouds dominated the intermediate cloudiness conditions (5-6 oktas, frequency of 47% and 66 %); and the transition from Cc-Cs to Sc determined moderate cloudiness (3-4 oktas); finally, low cloudiness (1-2 oktas) was mostly dominated by Ci and Cu (frequency of 59% and 40 %, respectively). HR measurements showed a constant decrease with increasing cloudines

È noto che le precipitazioni invernali europee sono ben stimate nei dati di rianalisi e nelle simulazioni dai modelli dato che sono altamente correlate con modi con variabilità su larga scala e a bassa frequenza come l'oscillazione del Nord Atlantico (NAO) e l'oscillazione artica (AO). Dal momento che NAO e AO sono principalmente modi di variabilità invernale, la capacità di stimare le precipitazioni è più limitata nelle altre stagioni, soprattutto in estate, in cui (quando) le precipitazioni sono principalmente dovute alla convezione a mesoscala. La prima parte dello studio utilizza dati osservativi, dati di rianalisi e l'output del modello WRF (Weather Research and Forecast) per studiare i cambiamenti recenti negli eventi estremi di precipitazione giornaliera in Europa. Si è stato riscontrato che nelle stagioni estive e di transizione, sono più le regioni che hanno registrato un aumento di eventi di precipitazioni estreme rispetto a quelle che hanno registrato una tendenza al ribasso. Questo è coerente con le tendenze del riscaldamento globale con per via della relazione di Clausius-Clapeyron. è stato studiato anche il valore aggiunto dell'utilizzo di un modello ad alta risoluzione che consenta la convezione per stimare gli estremi delle precipitazioni. I risultati mostrano che WRF riesca a correggere il fallimento della rianalisi ERA-Interim per I risultati mostrano che WRF riesce, al contrario di ERA-Interim, a catturare le tendenze positive delle precipitazioni estreme europee sia in estate che nelle stagioni di transizione indicate dai dati osservativi (EOBS) e dalla letteratura precedente. D'altra parte, sono di più le aree in Europa che hanno registrato tendenze negative nelle precipitazioni estreme rispetto alle aree con tendenze positive. Questo si tratta di una conseguenza del recente trend positivo)della NAO negli ultimi decenni, che ha causato eventi NAO positivi più frequenti, riducendo le precipitazioni estreme in più regioni in Europa. D, European wintertime precipitation is known to be skilfully estimated in reanalysis data and model simulations since it is highly correlated with large scale, low frequency modes of variability, namely the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). Since the NAO and AO are mainly a wintertime mode of variability, the skill of estimating precipitation becomes more limited in the other seasons, most importantly in the summer, in which precipitation is mainly a result of mesoscale convection. The first part of the study uses observational data, reanalysis data, and the output of Weather Research and Forecast (WRF) model to study the recent changes of extreme daily precipitation events over Europe. It is found that in summer and transition seasons, more regions recorded an increase of extreme precipitation events than regions that recorded a decreasing trend. This is consistent with the global warming trends with Clausius-Clapeyron relation. The added value of using a high resolution, convection-permitting model to estimate precipitation extremes is deduced. The results show that WRF succeeds to correct the failure of ERA-Interim reanalysis to capture the positive trends of European extreme precipitation in summer and transition seasons that are indicated by the observational data (EOBS) and previous literature. On the other hand, more regions in Europe recorded negative extreme precipitation trends than regions with positive trends. This is found to be a consequence of the recent positive trend of the NAO over the past decades, causing more frequent positive NAO events, reducing extreme precipitation outbreaks to more regions in Europe. As the NAO and the highly correlated AO are changing, further investigations to the nature of the two oscillations are carried out. Reanalysis data and climate model simulations of historical and warm climates are used to show that the relation between the two oscillations changes with climate warming. The two modes ar

La frequenza degli episodi di coral bleaching è aumentata interrottamente nelle ultime decadi a causa dell’incremento di temperatura registrato nei diversi oceani del pianeta. Nell’Arcipelago Maldiviano, tali eventi sono stati osservati principalmente nei mesi seguenti il picco di episodi El-Niño molto intensi. Il bleaching tuttavia non è stato uniforme e alcuni reef sono stati colpiti solo marginalmente. Ho utilizzato i dati da satellite e un modello oceanico regionale (CROCO) per investigare la variabilità, sia spaziale sia temporale, della temperatura superficiale dell’oceano (SST) e quantificare l’entità relativa di episodi legati ad ENSO, confrontandoli con l’effetto dell’incremento della temperatura negli ultimi decenni. In linea con altri studi effettuati, è stato confermato che il trend di temperatura aumenta significativamente la frequenza di episodi di stress termico per i coralli. È stato anche scoperto che, durante la stagione più calda, l’interazione tra le correnti e la ripida batimetria è responsabile di una diminuzione locale della temperatura elimina virgole avanati e dietro nell’Arcipelago di circa 0.2°C rispetto all'oceano circostante. Questo raffreddamento riduce notevolmente la frequenza di condizioni di mortalità per i coralli. La riduzione della SST attorno alle Maldive è probabilmente collegata all’Island Mass Effect: l’incremento di produttività intorno a isole di dimensione ridotte scoperto negli anni sessanta e documentato in tutto il mondo. Nonostante il suo effetto sulla produttività marina, l’esatto quadro dei processi che stanno dietro al raffreddamento locale e l’input di nutrienti che accresce la produttività è ancora incerto. Dall'analisi delle variazioni di SST e della produttività primaria netta (NPP) intorno a numerose isole ed arcipelaghi di piccole dimensioni sono stati identificati due tipi di pattern. Intorno ad isole con un'altitudine considerevole e dimensioni maggiori, infatti, sono visibili anomalie calde, The frequency of coral bleaching events has been increasing in recent decades due to the temperature rise registered in most regions near the ocean. Their occurrence in the Maldivian Archipelago has been observed in the months following the peak of strong El Niño events. Bleaching has not been uniform, and some reefs have been only marginally impacted. I have used satellite observations and a regional ocean model (CROCO) to explore the spatial and temporal variability of sea surface temperatures (SSTs), and quantify the relative magnitude of ENSO-related episodes with respect to the recent warming. In line with other studies, it is confirmed that the long-term trend in SST significantly increases the frequency of stress conditions for the Maldivian corals. It is also found that the interaction between currents and the steep bathymetry is responsible for a local cooling of about 0.2°C in the Archipelago during the warmest season, with respect to the surrounding waters. This cooling largely reduces the frequency of mortality conditions. The reduced SST surrounding the Maldives is probably linked to the Island Mass Effect: the enhanced productivity around small islands discovered in the sixties and documented worldwide. Despite its effects on marine productivity, the exact description of the physical processes behind the local cooling and nutrient input that enhances productivity is still unclear. From the analysis of SST variations and net primary productivity (NPP) around small islands and archipelagos, two kinds of signals can be identified, depending on the altitude and dimension of the islands. Around islands with considerable elevation and greatest diameters, cold/warm anomalies, most likely corresponding to upwelling/downwelling zones, emerge. Warmer areas don’t appear around smaller islands that usually display only a local cooling. Several oceanic and atmospheric processes might be involved. The case of the Maldives has been analyzed in detail using CROCO wit

Leaf nitrogen content (LNC), an indicator for the amount of photosynthetic proteins, plays an important role to understand plant function and status. In previous studies, vegetation indices (VIs) have been demonstrated to monitor LNC non-destructively, but which is influenced by backgrounds, and lacks specificity for nitrogen stress. In this study, sun-induced chlorophyll fluorescence (SIF), a novel technique related to plant physiology state, was proposed to estimate area-based and mass-based LNC at both leaf and canopy scales. In addition, SIF indices were evaluated to retrieve photosynthesis nitrogen use efficiency (PNUE), an important trait of leaf economics and physiology, based on the relationships between SIF, photosynthesis, and LNC. This study was conducted on two field experiments of winter wheat with different nitrogen regimes in Rugao, Jiangsu Province, China during 2016-2017 and 2017-2018 growing seasons. We took measurements of SIF, reflectance, biochemical and growth structural parameters at the leaf and canopy scales. The SIF signal was collected using ASD (Analytical Spectral Devices, Boulder, CO, USA) and QEpro (Ocean Optics, Dunedin, FL, USA) spectrometers at the two observational scales, with a full width at half maximum (FWHM) of 1.4 nm and 0.13 nm, respectively. SIF indices were calculated based on the SIF signal extracted at two oxygen absorption bands. Our results demonstrated that area-based LNC was better related to SIF indices and VIs than mass-based LNC. SIF ratio index (SIFR) and normalized SIF index (SIFN), defined as SIF761/SIF687 and (SIF761-SIF687)/(SIF761+SIF687) separately, performed better in monitoring area-based LNC at the two observation scales than CIred edge, which performed best in VIs group. Compared with CIred edge, the best estimation accuracy of SIF indices for area-based LNC increased by 0.08 and 0.02 at the leaf and canopy scales, separately. And when using SIFR and SIFN to monitor area-based LNC, there is no saturatio

We propose a signal deconvolution procedure for imaging spectrometer data, where a measured point spread function (PSF) is deconvolved itself before being used for deconvolution of the signal. We evaluate the effectiveness of our procedure for improvement of the spatio-spectral signal, as well as our target application, i.e. estimation of sun-induced fluorescence (SIF). Imaging spectrometers are well established instruments for remote sensing. When used for scientific purposes these instruments are usually calibrated on a regular basis. In our case the point spread function of the optics is measured in an elaborate procedure with a tunable monochromator point light source. PSFs are measured at different pixel positions of the imaging sensor, i.e. at different spatio-spectral locations, and averaged in order to get an as accurate PSF as possible. We investigate error sources in this calibration process by simulating the procedure in silico. Averaging as well as the spectral and spatial width of the point source introduce some smoothness in the measured PSF. We propose corrective measures, i.e. deconvolution of the PSF itself and median instead of mean averaging, leading to a set of sharper PSFs. We test the performance of these PSFs in deconvolving simulated as well as real hyperspectral images. For deconvolution we test a set of well-known, off the shelf deconvolution algorithms. Quantitatively in terms of PSNR (Peak Signal to Noise Ratio) a combination of Wiener filtering and sharpened PSFs yields strongest improvements, while using Wiener filtering with non-sharpened PSFs even deteriorates the signal. Comparing deconvolution results of the simulated data with results of real data reveals, that visually very similar effects can be observed. This well supports the assumption, that our findings are also valid for real spatio-spectral data. Surprisingly, the choice of PSF, sharpened or not, is of little effect for SIF estimation with the iFLD algorithm in the O2A band

The aim of this study is to test a series of methods relying on hyperspectral measurements to characterize phytoplankton in clear lake waters. The phytoplankton temporal evolutions were analyzed exploiting remote sensed indices and metrics linked to the amount of light reaching the target (EPAR), the chlorophyll-a concentration ([Chl-a]OC4) and the fluorescence emission proxy. The latter one evaluated by an adapted version of the Fluorescence Line Height algorithm (FFLH). A peculiar trend was observed around the solar noon during the clear sky days. It is characterized by a drop of the FFLH metric and the [Chl-a]OC4 index. In addition to remote sensed parameters, water samples were also collected and analyzed to characterize the water body and to evaluate the in-situ fluorescence (FF) and absorbed light (FA). The relations between the remote sensed quantities and the in-situ values were employed to develop and test several phytoplankton primary production (PP) models. Promising results were achieved replacing the FA by the EPAR or FFLH in the equation evaluating a PP proxy (R2 > 0.65). This study represents a preliminary outcome supporting the PP monitoring in inland waters by means of remote sensing-based indices and fluorescence metrics.

The detection and repairment of methane leaks from fossil fuel production activities have been identified as a key climate change mitigation strategy. Several types of optical satellite sensors have recently shown potential to support this task. Spaceborne imaging spectrometers measuring in the 400–2500 nm spectral range belong to this group. These instruments measure the solar radiation reflected by the Earth in hundreds of spectral channels with a typical spectral resolution of 10 nm and a spatial resolution of 30 m. The PRISMA mission from the Italian Space Agency is the first system of this type providing data openly to the international scientific community. In this work, we evaluate the potential of PRISMA to map methane point emissions, which are typical for fossil fuel production activities. Our retrieval of methane concentration enhancements is based on a matched-filter based algorithm applied to PRISMA spectra in the 2300 nm shortwave infrared spectral region. We perform a simulation-based sensitivity analysis to assess the retrieval performance for different sites. We find that surface brightness and homogeneity are major drivers for the detection and quantification of methane plumes with PRISMA, with retrieval precision errors ranging from 61 to 197 parts-per-billion in the evaluated images. The potential of PRISMA for methane mapping is further illustrated by real plume detections at different methane hotspot regions, including oil and gas extraction fields in Algeria, Turkmenistan, and the USA (Permian Basin), and coal mines in the Shanxi region in China. Our study reports several important findings regarding the potential and limitations of PRISMA for methane mapping, most of which can be extrapolated to upcoming satellite imaging spectroscopy missions.

Hyperspectral airborne imagery can provide rich information on plant physiological and structural properties at a scale intermediate to that of proximal and satellite remote sensing and has broad applications in assessing ecosystem function and biodiversity. A key processing step of airborne hyperspectral data is the atmospheric correction that compensates for path radiance, aerosol effects and gas absorption to derive an accurate surface reflectance that can be compared across time and space. In practice, routine correction procedures are often customized for various platforms without fully reporting or checking the errors systematically in the atmospheric correction. Such errors can have significant effects on downstream analyses such as vegetation indices or trait retrievals, and not all subsequent analyses are equally affected by the accuracy of reflectance retrievals. In this study, we examined the errors in three types of atmospheric correction methods including a radiative transfer model (RTM), empirical line correction (ELC) and a hybrid method that combines elements of the two via Bayesian inference. Our results revealed that the individual correction methods had different effects on the reflectance retrievals that impacted downstream measurements. Including spectral measurements from ground vegetation targets in addition to painted calibration targets improved the performance of the ELC method. The hybrid method yielded reflectance spectra that most closely matched the spectra of the ground validation data. The errors in vegetation indices differed with the methods, and certain indices (such as PRI) were more affected than indices that rely on stable, broader spectral features (e.g., NDVI). Plant pigment retrievals via partial least squares regression were less sensitive to errors in atmospheric correction. These findings demonstrate that obtaining high-quality, field spectral measurements over well-characterized calibration targets and representative land

Using 25 years of ERA5 reanalysis data, this study shows that wind divergence is partially driven by small-scale sea surface temperature (SST) patterns via their effect on the boundary layer stability. Moreover, strong warm-to-cold fronts (the upper quartile) are associated with a mean increase of cloud cover of 10% ± 5% and a mean increase in the probability of a rain event of 15% ± 6%, with respect to the average values. The cloud and rainfall dependence on SST fronts is more pronounced in Fall, probably due to the stronger SST gradients present at the end of the summer season.

The PRISMA satellite mission launched on March 22nd, 2019 is one of the latest spaceborne imaging spectroscopy mission for Earth Observation. The PRISMA satellite comprises a high-spectral resolution VNIR-SWIR imaging spectrometer and a panchromatic camera. In summer 2019, first operations during the commissioning phase were mainly devoted to acquisitions in specific areas for evaluating instrument functioning, in-flight performance, and mission data product accuracy. A field and airborne campaign was carried out over an agriculture area in Italy to collect in-situ multi-source spectroscopy measurements at different scales simultaneously with PRISMA. The spectral, radiometric and spatial performance of PRISMA Level 1 Top-Of-Atmosphere radiance (LTOA) product were analyzed. The in-situ surface reflectance measurements over different landcovers were propagated to LTOA using MODTRAN5 radiative transfer simulations and compared with satellite observations. Overall, this work offers a first quantitative evaluation about the PRISMA mission performance and imaging spectroscopy LTOA data product consistency. Our results show that the spectral smile is less than 5 nm, the average spectral resolution is 13 nm and 11 nm (VNIR and SWIR respectively) and it varies ±2 nm across track. The radiometric comparison between PRISMA and field/airborne spectroscopy shows a difference lower than 5% for NIR and SWIR, whereas it is included in the 2–7% range in the VIS. The estimated instrument signal to noise ratio (SNR) is ≈400–500 in the NIR and part of the SWIR (<1300 nm), lower SNR values were found at shorter (<700 nm) and longer wavelengths (>1600 nm). The VNIR-to-SWIR spatial co-registration error is below 8 m and the spatial resolution is 37.11 m and 38.38 m for VNIR and SWIR respectively. The results are in-line with the expectations and mission requirements and indicate that acquired images are suitable for further scientific applications. However, this first assessment

Using a combination of multi-directional SAR and TIR measurements, the Harmony Earth Explorer 10 mission candidate will provide high resolution simultaneous measurements of surface stress, surface currents SST and wave spectra over oceans, 3-D deformation vectors over solid Earth, and time-series of surface elevation changes over volcanic areas and land ice masses. This will serve a series of science objectives aimed at better understating multi-scale processed and feedbacks in the Earth System.

PRISMA, in orbit since March the 22nd 2019, opened the user access in spring 2020. After one year, many hundreds of users have gained the capability to program new acquisitions or download image products from the online archive containing more than 67k datasets, under a quasi-open & free data policy and licensing scheme. During this time frame and despite the COVID-19 related difficulties, PRISMA performed normal operations delivering not only nominal verified quality data to users but establishing collaborations with other space agencies, in order to enable and support synergies with other hyperspectral missions. This paper describes the mission and the results achieved in this first period of full operational usage.

This study presents a first assessment of the Top-Of-Atmosphere (TOA) radiances measured in the visible and near-infrared (VNIR) wavelengths from PRISMA (PRecursore IperSpettrale della Missione Applicativa), the new hyperspectral satellite sensor of the Italian Space Agency in orbit since March 2019. In particular, the radiometrically calibrated PRISMA Level 1 TOA radiances were compared to the TOA radiances simulated with a radiative transfer code, starting from in situ measurements of water reflectance. In situ data were obtained from a set of fixed position autonomous radiometers covering a wide range of water types, encompassing coastal and inland waters. A total of nine match-ups between PRISMA and in situ measurements distributed from July 2019 to June 2020 were analysed. Recognising the role of Sentinel-2 for inland and coastal waters applications, the TOA radiances measured from concurrent Sentinel-2 observations were added to the comparison. The results overall demonstrated that PRISMA VNIR sensor is providing TOA radiances with the same magnitude and shape of those in situ simulated (spectral angle difference, SA, between 0.80 and 3.39; root mean square difference, RMSD, between 0.98 and 4.76 [mW m−2 sr−1 nm−1]), with slightly larger differences at shorter wavelengths. The PRISMA TOA radiances were also found very similar to Sentinel-2 data (RMSD < 3.78 [mW m−2 sr−1 nm−1]), and encourage a synergic use of both sensors for aquatic applications. Further analyses with a higher number of match-ups between PRISMA, in situ and Sentinel-2 data are however recommended to fully characterize the on-orbit calibration of PRISMA for its exploitation in aquatic ecosystem mapping.

Passive measurement of sun-induced chlorophyll fluorescence (F) represents the most promising tool to quantify changes in photosynthetic functioning on a large scale. However, the complex relationship between this signal and other photosynthesis-related processes restricts its interpretation under stress conditions. To address this issue, we conducted a field campaign by combining daily airborne and ground-based measurements of F (normalized to photosynthetically active radiation), reflectance and surface temperature and related the observed changes to stress-induced variations in photosynthesis. A lawn carpet was sprayed with different doses of the herbicide Dicuran. Canopy-level measurements of gross primary productivity indicated dosage-dependent inhibition of photosynthesis by the herbicide. Dosage-dependent changes in normalized F were also detected. After spraying, we first observed a rapid increase in normalized F and in the Photochemical Reflectance Index, possibly due to the blockage of electron transport by Dicuran and the resultant impairment of xanthophyll-mediated non-photochemical quenching. This initial increase was followed by a gradual decrease in both signals, which coincided with a decline in pigment-related reflectance indices. In parallel, we also detected a canopy temperature increase after the treatment. These results demonstrate the potential of using F coupled with relevant reflectance indices to estimate stress-induced changes in canopy photosynthesis.