Spatio-Temporal Variability of Suspended Particulate Matter in a High-Arctic Estuary (Adventfjorden, Svalbard) Using Sentinel-2 Time-Series

Arctic coasts, which feature land-ocean transport of freshwater, sediments, and other terrestrial material, are impacted by climate change, including increased temperatures, melting glaciers, changes in precipitation and runoff. These trends are assumed to affect productivity in fjordic estuaries. However, the spatial extent and temporal variation of the freshwater-driven darkening of fjords remain unresolved. The present study illustrates the spatio-temporal variability of suspended particulate matter (SPM) in the Adventfjorden estuary, Svalbard, using in-situ field campaigns and ocean colour remote sensing (OCRS) via high-resolution Sentinel-2 imagery. To compute SPM concentration (CSPMsat), a semi-analytical algorithm was regionally calibrated using local in-situ data, which improved the accuracy of satellite-derived SPM concentration by ~20% (MRD). Analysis of SPM concentration for two consecutive years (2019, 2020) revealed strong seasonality of SPM in Adventfjorden. Highest estimated SPM concentrations and river plume extent (% of fjord with CSPMsat > 30 mg L−1) occurred during June, July, and August. Concurrently, we observed a strong relationship between river plume extent and average air temperature over the 24 h prior to the observation (R2 = 0.69). Considering predicted changes to environmental conditions in the Arctic region, this study highlights the importance of the rapidly changing environmental parameters and the significance of remote sensing in analysing fluxes in light attenuating particles, especially in the coastal Arctic Ocean.publishedVersio

Glider and satellite monitoring of the variability of the suspended particle distribution and size in the Rhône ROFI

An experiment was carried out in the Gulf of Lions (NW Mediterranean) in February 2014 to assess the temporal and spatial variability of the distribution and size of suspended particulate matter (SPM) in the Rhône Region of Freshwater Influence (ROFI). A set of observations from an autonomous underwater glider, satellite ocean color data, and meteorological and hydrological time-series data highlighted the high variability of the Rhône River surface turbid plume and presence of a bottom nepheloid layer (BNL) that depended on wind and river discharge conditions. While continental winds pushed the surface plume offshore, marine winds pressed the plume at the coast and favored the sedimentation of as well as nourishment of the BNL. Moderate storm events favored breakage of the plume stratification and along-shelf transport of Rhône River particles. The spectral slopes of glider and satellite-derived light backscattering coefficients, γ, were used as a proxies of the SPM size distribution. The results clearly showed that the change of the SPM size in the nepheloid layers was induced by the flocculation of fine sediments, which became finer seaward throughout the ROFI, as well as the effect of rough weather in the breakup of flocs

Glider and satellite monitoring of the variability of the suspended particle distribution and size in the Rhône ROFI

An experiment was carried out in the Gulf of Lions (NW Mediterranean) in February 2014 to assess the temporal and spatial variability of the distribution and size of suspended particulate matter (SPM) in the Rhône Region of Freshwater Influence (ROFI). A set of observations from an autonomous underwater glider, satellite ocean color data, and meteorological and hydrological time-series data highlighted the high variability of the Rhône River surface turbid plume and presence of a bottom nepheloid layer (BNL) that depended on wind and river discharge conditions. While continental winds pushed the surface plume offshore, marine winds pressed the plume at the coast and favored the sedimentation of as well as nourishment of the BNL. Moderate storm events favored breakage of the plume stratification and along-shelf transport of Rhône River particles. The spectral slopes of glider and satellite-derived light backscattering coefficients, γ, were used as a proxies of the SPM size distribution. The results clearly showed that the change of the SPM size in the nepheloid layers was induced by the flocculation of fine sediments, which became finer seaward throughout the ROFI, as well as the effect of rough weather in the breakup of flocs

Spatio-temporal distribution of temperature, salinity and suspended sediment on the deltaic front of the Magdalena River: Influence on nutrient concentration and primary productivity

The characteristics of estuaries depend mainly on the magnitude and variability of river discharge and tidal forcing (Kjerfve, 1994). Estuaries present strong temporal and spatial gradients with respect to their physical, chemical and biological properties, as a result of changes in fluvial contributions (Nogueira et al., 1997). Therefore, biogeochemical processes are extremely complex (Fourqurean et al., 1993; Fernández-Nóvoa et al., 2015). Temperature and salinity are the most relevant features of coastal marine ecosystem dynamics (Urquhart et al., 2013), as variations in these parameters can influence the movement of water masses, water column stratification caused by density differences, transport of sediments, and mixing conditions (Bianchi, 2007; Geyer, 2010; Obeso-Nieblas et al., 2012; Osadchiev et al., 2017). Also, temperature and salinity may play roles in nutrient distributions and concentrations (Windom et al., 2006), and biogeochemical processes and ecological productivity, through alterations in biochemical reactions that regulate the enzymatic processes of respiration and photosynthesis (Xia and Jiang, 2015; Quamrul et al., 2016). The physical dynamics of estuaries/deltas of the micro-tidal domain, which are highly stratified and turbid, have been little studied. Therefore, we lack detailed knowledge regarding relationships among spatio-temporal variations in salinity and temperature, the extent and structure of convergence fronts and the mixed layer, nutrient distribution and primary productivity in this type of estuary

Remote sensing data as a tool to monitor and mitigate natural catastrophes resulting from anthropogenic activities

This thesis demonstrates how remotely sensed satellite acquisitions can be used to addresses some of the natural catastrophes resulting from anthropogenic activities. Examples from both land and water systems are used to illustrate the breath of this toolbox. The effects of global climate change on biological systems and the wellbeing of everyday people are becoming less easy to ignore. In addition, our oceans are facing multiple large-scale stressors, including microplastics as a recently recognized threat, which place at risk the resources which a large percentage of the world’s population depends on for their livelihood. The cause of many of these changes stem from anthropogenic activities, but lacking understanding of complex ecosystems limits our ability to make definite conclusions as to cause and effect. The difficulty to collect on-the-ground data sufficient enough to capture processes working over scales of hundred of kilometers up to the entire globe is often a limitation to research. Remote sensing systems help ameliorate this issue through providing tools to better monitor environmental changes over large areas. The examples provided in this thesis focus on (Section I) tropical peatland fire characteristics and burning in Southeast Asia as a significant contributor to greenhouse gas emissions and (Section II) spread of river-based plastic pollution in coastal ocean systems. Section I specifically focuses on fires within Indonesia, which holds more than half of all known peatlands in the tropical zone and are estimated to represent a carbon pool of 82–92 gigatons. A brief description of recent development activities within Indonesia is presented in Section I of the Introduction, followed by meteorological processes responsible for extended drought periods in the region, and the situation of current fire control within the country. Chapter 1 presents an example of the large improvement in fire detection, as well as measurement of fire front characteristics, provided by a state-of-the-art thermal remote sensing. Chapter 2 goes into detail describing how an active satellite sensor system is able to provide much quicker and more accurate estimates of burned area for the tropics than other existing methods dependent on passive satellite sensor systems. Both these methods provide powerful tools for development of an improved system to monitor fire over Indonesia. The goal of such a monitoring system would be to reduce fire emissions from this large country, which according to global climate models play an important role in global climate change. Section II focuses on aquatic plastic pollution flowing from a freshwater system into the coastal oceans. A background of the issue of plastic pollution along with the current status of plastic debris in both oceans and inland river systems is presented in Section II of the Introduction. Chapter 3 describes development and comparison of two different modelling efforts to display how plastic particles being emitted from a major river are accumulating along the nearby coastline. The goal of this work is to present how remote sensing data could be used to in conjunction with ocean current modelling to create a comprehensive particle tracking monitoring system.Diese Arbeit zeigt, wie aus der Ferne wahrgenommene Satellitenaufnahmen dazu verwendet werden können, sich einigen Naturkatastrophen, die aus anthropogenen Aktivitäten resultieren, zu widmen. Anhand von Beispielen aus Land- und Wassersystemen wird der Umfang dieses technischen Werkzeugkastens dargestellt. Die Auswirkungen des globalen Klimawandels auf biologische Systeme und das Wohlbefinden des Menschen lassen sich nicht mehr ignorieren. Darüber hinaus sind unsere Ozeane mehreren großen Stressfaktoren ausgesetzt, einschließlich Mikroplastik als eine seit kurzem anerkennte Bedrohung, welche die Ressourcen gefährden, von denen der Lebensunterhalt eines großen Teils der Weltbevölkerung abhängt. Die Ursache vieler dieser Veränderungen liegt in anthropogenen Aktivitäten, aber mangelndes Verständnis für komplexe Ökosysteme begrenzt unsere Fähigkeit, eindeutige Rückschlüsse auf Ursache und Wirkung zu treffen. Die Schwierigkeit, Daten vor Ort zu sammeln, die ausreichen, um Prozesse zu erfassen, die über Hunderte von Kilometern bis hin zum gesamten Globus arbeiten, ist oft eine Einschränkung der Forschung. Fernerkundungssysteme tragen dazu bei, dieses Problem zu beheben, indem sie Werkzeuge zur besseren Überwachung von Umweltveränderungen in großen Gebieten bereitstellen. Die Beispiele in dieser Arbeit konzentrieren sich auf („Section I“) Feuermerkmale und Brandflächen der tropischen Torfgebiete in Südostasien als signifikanter Beitrag zu Treibhausgasemissionen und („Section II“) Ausbreitung von Fluss-basiertem Plastikmüll in küstennahen Meeressystemen. Section I konzentriert sich speziell auf die Brände in Indonesien, welches mehr als die Hälfte aller bekannten Torfgebiete in der tropischen Zone besitzt und auf einen Kohlenstoffpool von 82-92 Gigatonnen geschätzt wird. Eine kurze Beschreibung der jüngsten Entwicklungstätigkeiten in Indonesien wird in Section I der Einleitung vorgestellt, gefolgt von meteorologischen Prozessen, die für ausgedehnte Dürreperioden in der Region verantwortlich sind, und der Situation der aktuellen Feuerkontrolle innerhalb des Landes. Chapter 1 zeigt ein Beispiel für die große Verbesserung der Branddetektion sowie die Messung der Brandfronteigenschaften, die durch eine moderne thermische Fernerkundung erreicht werden können. In Chapter 2 wird ausführlich beschrieben, wie ein aktives Satellitensensorsystem in der Lage ist, schnellere und genauere Schätzungen der verbrannten Fläche für die Tropen zu liefern als andere existierende Methoden, die von passiven Satellitensensorsystemen abhängen. Beide Methoden bieten leistungsstarke Werkzeuge für die Entwicklung eines verbesserten Systems zur Brandüberwachung von Indonesien. Ziel eines solchen Überwachungssystems wäre es, Brandemissionen aus diesem großen Land zu reduzieren, das nach globalen Klimamodellen eine wichtige Rolle im globalen Klimawandel spielt. Section II konzentriert sich auf die Verschmutzung von Wasserplastik, die von einem Süßwassersystem in die Küstenmeere fließt. Ein Hintergrund des Problems der Plastikverschmutzung zusammen mit dem gegenwärtigen Status von Plastiktrümmern sowohl in Ozeanen als auch Binnenflusssystemen wird in Section II der Einleitung dargestellt. Chapter 3 beschreibt die Entwicklung und den Vergleich von zwei verschiedenen Modellierungsbemühungen, um zu zeigen, wie sich Kunststoffpartikel, die von einem großen Fluss emittiert werden, entlang der nahen Küstenlinie ansammeln. Das Ziel dieser Arbeit ist zu zeigen, wie Fernerkundungsdaten in Verbindung mit Meeresströmungsmodellierung verwendet werden können, um ein umfassendes Teilchenverfolgungsüberwachungssystem zu schaffen

Glider-based active acoustic monitoring of currents and turbidity in the coastal zone

The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increases the probability of capturing sporadic meteorological events, such as storms and floods, which are key elements of sediment dynamics. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload, and an RDI 600 kHz phased array ADCP. Two deployments were carried out during two contrasting periods of the year in the Rhone River region of freshwater influence (ROFI). Coastal absolute currents were reconstructed using the shear method and bottom tracking measurements, and generally appear to be in geostrophic balance. The responses of the acoustic backscatter index and optical turbidity signals appear to be linked to changes of the particle size distribution in the water column. Significantly, this study shows the interest of using a glider-ADCP for coastal zone monitoring. However, the comparison between suspended particulate matter dynamics from satellites and gliders also suggests that a synoptic view of the processes involved requires a multiplatform approach, especially in systems with high spatial and temporal variability, such as the Rhone ROFI area

Investigation of Colored Dissolved Organic Matter and Dissolved Organic Carbon Using Combination of Ocean Color Data and Numerical Model in the Northern Gulf of Mexico

The first part of this thesis includes evaluating and developing empirical band ratio algorithms for the estimation of colored dissolved organic matter (CDOM) and dissolved organic carbon (DOC) for SeaWiFS, MODIS and MERIS ocean color sensors for the northern Gulf of Mexico. For CDOM, matchup comparison between SeaWiFS-derived CDOM absorption coefficients and in situ absorption measurements at 412 nm (aCDOM(412)) were examined using the D’Sa et al. (2006) and the Mannino et al. (2008) algorithms. These reflectance band ratio algorithms were also assessed to retrieve aCDOM(412) from MODIS and MERIS data using the Rrs(488)/Rrs(555) and Rrs(510)/Rrs(560) band ratios, respectively. Since DOC cannot be measured directly by remote sensors, CDOM as the colored component of DOC is utilized as a proxy to estimate DOC remotely. A seasonal relationship between CDOM and DOC was established for the summer and spring-winter with high correlation for both periods. Seasonal band ratio empirical algorithms to estimate DOC were thus developed. In the second part of this study, a numerical model to study CDOM dynamics in the northern Gulf of Mexico was examined. To derive surface CDOM concentration maps from simulated salinity output from the Navy Coastal Ocean Model (NCOM), a highly correlated linear inverse relationship between CDOM and salinity is required which was examined for both inner-shelf and outer-shelf areas for the spring-winter and the summer periods. Applying these relationships on NCOM simulated salinity resulted in hourly maps of CDOM exhibiting high consistency with CDOM patterns derived from SeaWiFS sensor. Overlaying the NCOM-derived CDOM maps on the simulated currents showed the profound effect of currents on CDOM advection. Cold fronts strongly impact CDOM advection in both the inner and outer shelves by flushing CDOM-laden waters out of the coastal bays

Numerical Experiment of Sediment Dynamics over a Dredged Pit on the Louisiana Shelf

Sediment transport over Sandy Point dredge pit in the northern Gulf of Mexico was examined using field measurements and a finely resolved numerical model. Delft3D model with well-vetted computational grid and input parameters was used. Numerical experiments were performed to examine the effect of wind-generated waves, wind-driven currents and their interaction on sediment dynamics in our study area during a cold front in November 2014 and fair-weather conditions between July and August of 2015. Sediment dispersal from the lower Mississippi River, sediment resuspension, transport and deposition with high spatial and temporal resolution were simulated. A reliable satellite-derived near-surface suspended particulate matter (SPM) map was employed to provide an initial condition in a numerical model and support the model calibration/verification. To prepare SPM maps, short-wave infrared (SWIR) and near-infrared atmospheric correction algorithms on remote sensing reflectance (Rrs) products from Landsat-8 OLI and Management Unit of the North Sea Mathematical Models (MUMM) and SWIR.NIR atmospheric correction algorithms on Rrs products from MODIS-Aqua were evaluated. Results indicated that SWIR atmospheric correction algorithm was the suitable algorithm for Landsat-8 OLI and SWIR.NIR atmospheric correction algorithm outperformed MUMM algorithm for MODIS. Delft3D Flow, wave and sediment transport were validated using LSU WAVCIS (Wave-Current-Surge Information System) and NDBC (National Data Buoy Center) data for both events. Results suggested that the primary source of sediment for the Sandy Point dredge pit during a cold front was re-suspension due to the fortified bottom shear stress (BSS) by wind-induced waves and currents. Strong southward wind-driven currents during the cold front passage dispersed sediments from the Mississippi River passes and inhibited riverine sediment supply from the Sandy Point dredge pit. Results also showed that total cold front passages in a year (30-40 passages per year) contribute to the sedimentation thickness over Sandy Point dredge pit from 16% to 24% of the total sedimentation thickness annually. Results indicated that during the fair-weather event, Mississippi River plays a pivotal role in providing sediment for Sandy Point dredge pit and about 60% of deposited sediments are from the Mississippi River plume