Ocean Colour Research Papers - Academia.edu (original) (raw)

2025

M. Rypdal and K. Rypdal, Late Quaternary temperature variability described as abrupt transitions on a 1/f noise background, Eart Syst. Dynam., 7, 281-293, 2016. doi: 10.5294/esd-7-281-2016.... more

2025, School of Remote Sensing Institute of Science Suranaree University of Technology

Deterioration of water quality and occurrences of red tide events were reported more often in recent years within UGoT zone. Hence, effective data observation system (for monitoring and warning purposes) with high accuracy and up-to-date information product is greatly essential. This need can be achieved through application of advanced geoinformatics technology which became main aim of this research from which three specific objectives were proposed; (1) to identify optimal model for the determination of concentration level for three important marine water constituents, i.e., chlorophylla, total suspended solids, and color dissolved organic matter, from the satellite-based MODIS data, (2) to observe variation in mapped concentration of the referred constituents and trophic state of water quality in the UGoT during years 2010 to 2012 and (3) to formulate credible red-tide susceptibility maps for the UGoT through the frequency ratio and simple additive weighting methods. First, the optimal models for concentration extraction of the Chl-a, TSS, and CDOM from MODIS-based reflectance data were identified as OC3M (R 2 = 0.60), TSM (R 2 = 0.72) and Chula (R 2 = 0.78), respectively. In addition, the primary ANN analysis (MLP type with optimal structure of 10:30:10:1) also demonstrated promising IV outcome for the prediction of those constituents. Derived concentration maps for each constituent (through their respective optimal models) from years 2010 to 2012 showed that concentration levels of these concerned constituents were relatively low in dry season and gradually rising towards their peak values in wet season. Top concentration areas for Chl-a (and also for the critical trophic states-eutrophic/hyper-eutrophic) and TSS were often located close to shore and to some major river mouths, but those of CDOM were appeared more widespread into deep-water zone. Effects of year 2011, mega flood over central Thailand were also apparent, especially, great drop of Chl-a (maximum/ mean) during wet season of 2011. Moreover, moderate correlation among studied constituents was found during dry season (R  0.4-0.6) while low correlation often evidenced in wet season. Finally, analysis of the red tide susceptibility maps formulated by SAW and FR methods indicated that, in general, highly prone areas to red tide occurred in shallow water zone. Thus dilplayed close to main river mouths, especially the Thachin and the Bang Pakong Rivers. For SAW case, Type 6 scenario (two factors: TSS and CDOM) gained best validation accuracy (AUC = 0.94), as well as that of the FR case (AUC = 0.75). However, apart from the AUC assessed outcome, the realistic outlook of the assessed map should be taken into consideration for its prediction ability also.

2025, Oceanological and Hydrobiological Studies

New satellite-based techniques open up new horizons to researchers and local communities. Concurrently, however, requirements and expectations with regard to satel-lite-based remote sensing products are increasingly higher. By relying on satellite-derived information, environmental observations can cover areas of a few to several metres resolution. Here we are dealing with freeof-charge and generally available sources of satellite-based information. The Piaśnica River mouth area was selected as an observation site representing a highly dynamic morphological transect. The paper compares products of cloud cover detection, supplied with data and available in the Copernicus database for a local area in the coastal zone of the Baltic Sea. The absolute difference did not exceed 5%, which confirms a high efficiency of the solutions offered. More than 96% of the clouded area determined for the Sentinel-2/MSI (Multispectral Instrument) was correctly identified when compared with supervised o...

2025, EARSeL …

Spring mean and maximum chlorophyll a (chl a) concentrations are main factors to determine the eutrophication status of the Belgian waters as agreed within OSPAR in 2002. Other important assessment parameters to measure the degree of nutrient enrichment -the amounts of inorganic phosphate and nitrogen in winter -appeared to be above thresholds for most measurements performed in the period 1974-2002. As the standard in situ monitoring programme does not give a clear picture of the temporal and spatial distribution of chl a, it is logical to complement these measurements with optical remote sensing. However, chlorophyll concentrations derived from sensors such as SeaWiFS are unreliable in the Case 2 waters of this region because of high particulate and dissolved yellow substance absorption. Another important limitation of ocean colour sensors is the amount of useful images due to cloud cover. The combination of data from different ocean colour sensors in order to enable a better temporal coverage might be hampered by the different chlorophyll retrieval algorithms used. This study compares different global chl a algorithms (MODIS, SeaWiFS, MERIS) as well as a turbid water algorithm for the Southern North Sea. This is done by running the different algorithms on in situ reflectance spectra collected at 107 stations in the period 2001-2002 over the Southern North Sea and comparing them with in situ chl a concentrations, as well as by running the algorithms on a MERIS image of the 29 th of July 2002. Based on this validation the accuracy of these products and their suitability for eutrophication monitoring in the Southern North Sea are assessed.

2025

were asked to rate 19 different statements, each related to an aspect of the model, using a 7-point Likert Scale. A total of 153 qualified responses were successfully collected and then analyzed using factors analysis. Upon performing the analysis, a total of five factors were extracted and then ranked according to the percentage of variances explained. The findings of this paper found that factors and aspects related to internal organizational factors had the most impact on the success of the Qatarization program. Next to that were factors related to the national educational structures, followed by national policies, economic regulations, and social and cultural factors respectively. v List of Figures .

2024, Proceedings of SPIE

SeaWiFS ocean-colour products for the Southwestern Atlantic Ocean are evaluated in comparison with in situ bio-optical data collected during the March 10-12, 2002 cruise from Ushuaia to Uruguay. Radiometric measurements and surface water sampling were carried out at 14 stations. The in situ dataset included HPLC chlorophyll-a concentration (chl-a), a ph ( ) spectral absorption coefficients of phytoplankton, suspended particles, and a cdom ( ) dissolved organic matter, R RS remote sensing reflectance, AOT and aerosol optical thickness. In general, the SeaWiFS-derived and SIMBAD measured AOT were low, but with a good agreement within SIMBAD uncertainty errors. The SeaWiFS-derived R RS was systematically underestimated, but still with good fits. The were high indicating the presence of small size cells with a low packaging effect. The HPLC pigment composition did not show strong variations amongst the sampled points, with communities most probably dominated by small cells. The phytoplankton community was more homogeneous in the southern stations, than in the northernmost stations influenced by the mixing of the Brazil and Malvinas Currents and the La Plata River discharge. The analyzes of the in situ a cdom (440) characterized the sampling stations as CDOM rich waters. All SeaWiFS chl-a algorithms showed reasonable performances. The empirical algorithms overestimated lower chl-a while underestimated higher concentrations. The GSM01 semi-analytical algorithm underestimated most chl-a values, while CARDER underestimated only the lower concentrations. It is expected that the accuracy of chlorophyll retrievals in coastal areas of the BMC can be improved by a proper tuning of the semi-analytical models with regional inherent optical properties measurements.

2024

Notre analyse des images confirme les résultats précédents et la possibilité de distinguer deux types d'échantillons de CZCS sur la plateforme adriatique. Le premier est allongé, bloqué le long de la cote italienne, et l'autre est large, étendu irrégulièrement sur le bassin intérieur. Pourtant-ainsi que nos explorations l'ont prouvé -les deux échantillons ne sont pas conditionnés par la saison, c'est-à-dire qu'ils peuvent apparaître aussi bien en été qu'en hiver. En été, quand la Mer Adriatique est stratifiée, les eaux sous l'influence du Pô se dispersent en surface vers le bassin intérieur. La décharge de l'estuaire du Pô peut retenir les eaux touchées par le fleuve dans l'étroite région côtière. En hiver, quand l'Adriatique septentrionale est bien mélangée le long de la verticale, les eaux touchées par le fleuve restent coincées dans la ligne côtière italienne, tout le long du bord de la plateforme et dans la direction de l'Adriatique méridionale. Pourtant, les bourrasques du vent «bura», très hétérogène dans l'espace, peuvent provoquer les intrusions dans le bassin intérieur.

2024

Recent efforts have allowed laying the foundations of an operational coastal oceanography system in the Basque Country region (southeastern Bay of Biscay). This strategy brings together climatological, oceanographic and meteorological institutions, in order to improve the way in which these services are working presently and merge the products to a unique operational system looking towards 2010. At the present time,

2024, Remote Sensing of the Ocean, Sea Ice, Coastal Waters, and Large Water Regions 2011

The study of spatio-temporal trends for key water quality parameters in the Maltese coastal waters is hindered by the lack of systematic observations spanning over the full domain and for sufficiently long time periods. Satellite data offers an alternative source of information, but requires ground truthing against in situ measurements. The aim of this study is to attempt the statistical comparison of MODIS ocean colour data, for a near-shore marine area off the north-east coastline of Malta, with in situ surface chlorophyll-a measurements, and to extract a twelve-month ocean colour data series for the same marine area. Peaks in surface chlorophyll-a concentration occurred in the January-February period, with lowest values being recorded during the early spring period. Log bias values indicate that the MODIS dataset under-estimates the surface chlorophyll-a values, whilst RMSD and r 2 values suggest that the match-up between satellite and in situ values is only partly consistent.

2024

The MESCLA approach: a MyOcean R&D proposal The MESCLA project, funded in the framework of the MyOcean 2009 R&D Call, is focused on the estimation and analysis of the vertical exchanges associated with mesoscale dynamics and of their interannual variability. MESCLA aims at: (1) Applying QG diagnostics to MyOcean products (model and observation based). (2) Comparing its results with corresponding primitive equation solutions. (3) Testing alternative techniques to combine satellite and in situ observations. through combined model, satellite and in situ data. Preliminary results of the MESCLA project Introduction: importance of vertical motion Method for estimating QG vertical velocities Omega equation. Vector Q formulation Adaptation of the Omega equation to MyOcean products Vertical motion associated with mesoscale and sub-mesoscale oceanic features is of fundamental importance for the exchanges of heat, fresh water and biogeochemical tracers between the surface and the ocean interior. Unfortunately, direct measurements of the vertical velocity are difficult to obtain for usual values (order 10's m/day). Various indirect methodologies have thus been proposed to estimate vertical velocity from observed density and geostrophic velocity fields. The most used technique is based on the solution of the quasi-geostrophic (QG) Omega equation.

2024, Journal of Coastal Research Special

Optical properties of oceanic waters have provided an important tool for observing large scale fluctuations in oceanic conditions by remote sensing. However, there are still problems with calibrating the algorithms that link remote sensing data with in situ measurements, particularly, in coastal areas where there are adjacency affects from land on the reflectance data observed by the satellite sensor. As part of a contract with the European Space Agency to validate the marine products of the MERIS (Medium Resolution Imaging Spectrometer) ...

2024

Ocean color satellite radiometers have widely proven their outstanding capabilities as diagnostic tools of the world ocean biogeochemical cycles. Recently, SeaWiFS, MODIS and MERIS images have been merged to provide a better coverage (see: http://www.globcolour.info). Notwithstanding this remarkable success, chlorophyll measurements in coastal zones are still affected by not negligible uncertainties. This study, by the comparison between lidar and satellite data in the Arctic Sea near the Svalbard Islands confirm this behavior: while the match-up of these sensors is good off shore, satellite values are substantially lower near the coasts.

2024

I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced... more

2024

The Carbonite-1 and -2 microsatellites launched in 2015 and 2018 are delivering high-resolution, high-definition colour video from space, providing a new dimension to Earth Observation and "big data" analytics. Single video imaging spacecraft have limited utility. In order to fully benefit from such spacecraft requires cost-effective observations with multiple opportunities per target per day, driving the need for large-scale constellations of ultralow cost spacecraft. The first constellation based on the two pilot missions is now in production, and will start commercial operation by 2020. Still-imagery has a number of limitations in applications related to surveillance, disaster monitoring and news gathering. Video can provide additional contextual information, and space borne video systems have been demonstrated several times over the past decades. Single video imaging spacecraft in LEO are limited in application, as they cannot cover specific target areas on the globe f...

2024

Mapping Total Suspended Matters from satellite data is hampered by optical complexity and often extreme turbidity. Extremely high concentrations of Suspended Particulate Matter (SPM), Chlorophyl (Chl) and Coloured Dissolved Organic Matter (CDOM), local differences, seasonal and tidal variations, and resuspension are important factors that lead to lack of efficiency in application of simple hydro-optical models in highly turbid waters. On the other hand atmospheric correction can be problematic if atmospheric haze is spatially variable. In this study, a coupled atmospheric radiative transfer model was used to investigate the seasonal and annual variation of water parameters concentration in the extremely turbid Wadden Sea for one decade. 150 MEdium Resolution Imaging Spectrometer (MERIS) images captured in 2000-2010 were used to provide top of atmosphere radiance, atmospheric and geometric parameters in the Wadden Sea. MODerate resolution atmospheric TRANsmission model (MODTRAN) was ...

2024, Remote Sensing of Environment

The 2013-2015 Hyperspectral Infrared Imager (HyspIRI) Preparatory Flight Campaign, using the Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS) and MODIS/ASTER Airborne Simulator (MASTER), seeks to demonstrate appropriate sensor signal, spatial and spectral resolution, and orbital pass geometry for a global mission to reveal ecological and climatic gradients expressed in the selected California, USA study area. One of the awarded projects focused on the flight transects covering the coastal ocean to demonstrate that the AVIRIS data can be used to infer phytoplankton functional types at the land-sea interface. Specifically, this project directly assesses whether HyspIRI can provide adequate signal in the complex aquatic environment of the coastal zone to address questions of algal bloom dynamics, water quality, transient responses to human disturbance, river runoff, and red tides. Phytoplankton functional type (PFT), or biodiversity, can be determined from ocean color using the Phytoplankton Detection with Optics (PHYDOTax) algorithm and this information can be used to detect and monitor for harmful algal blooms. PHYDOTax is sensitive to spectral shape and accurate retrievals of ocean color across the visible spectral range is needed. The specific goal of this paper is to address the challenges of sensor capabilities and atmospheric correction in coastal environments by assessing two atmospheric correction methods using AVIRIS data for the retrieval of ocean color for use in derived products of chlorophyll-a and phytoplankton functional type. The atmospheric correction algorithms Atmospheric Removal (ATREM) and Tafkaa were applied to AVIRIS imagery of Monterey Bay, CA collected on 10 April 2013 and 31 October 2013. Data products from the imagery were compared with shipboard measurements including chlorophyll-a from whole-water samples and phytoplankton community structure estimated from diagnostic pigment markers using CHEMical TAXonomy (CHEMTAX). Using ATREM and Tafkaa and a selected set of input parameters for the scenes, we were unable to produce accurate retrievals of ocean color for the determination of chlorophyll-a and phytoplankton diversity. A modified ATREM correction produced science-quality data in which chlorophyll-a was accurately estimated using the Ocean Color 3 (OC3) chlorophyll-a algorithm, but biodiversity using PHYDOTax was not accurately estimated. Improvements in sensor calibration, sensitivity, and atmospheric correction of the HyspIRI imagery data set is needed in order to adequately estimate biogeochemically meaningful data products for the ocean such as chlorophyll-a, inherent optical properties, or PFTs. The HyspIRI Science Team is seeking improvements so the HyspIRI Airborne Campaign data set can be used for algorithm development to understand biodiversity and ecosystem function of coastal habitats that are facing increasing threats of human impact and climate change.

2024

The Medspiration Service, supported by ESA through its DUE Programme, has since June 2005 been providing sea surface temperature (SST) data products from a variety of different sensors in a uniform format following the protocol of the GODAE high resolution SST pilot project (GHRSST-PP). The provision of such data has made it much easier for major users of SST to work with data from several sources, and to blend them into single analysis products. One of Medspiration's tasks has been to convert AATSR SST data into the GHRSST format. The higher AATSR accuracy than other sources can lead to better weather forecasting, improved seasonal weather prediction, low-noise global SST maps used in a wide variety of ocean science applications, and stable climatologies for monitoring global change.

2024

2024, Global developments in …

Satellite data were used to assess phytoplankton dynamics in the Mediterranean Sea, in relation to blooming episodes of Alexandrium, the dinoflagellates genus which causes most (harmful) algal blooms in the basin. A comparison of in situ data, collected on the coast of Catalonia, Sardinia and Sicily in 2002-2003, with images recorded by the SeaWiFS-albeit hampered by space/time resolution too poor to discern small features in harbours, bays or beach areas, and by other limitations-suggests that the recurrence of Alexandrium is linked to local (near-coastal) factors, and only occasionally to larger mesoscale features typical of open waters. Examples are provided of the frequent decoupling between inshore and offshore blooming regimes, even in those cases when they seem to co-vary (e.g. considering inter-annual variability). Correspondences between imaged patterns and Alexandrium outbursts are seen to occur episodically, implying that the processes shaping the local (harmful) algal blooms and the regional blooms are different, or overlap only marginally. Thus, local measurements cannot be taken as representative of "larger scale" phenomena, while the satellite data might be useful to place local events into a regional contest, but not to explore the dynamics of "smaller scale" phenomena, which require direct in situ monitoring.

2024, Remote Sensing

The Eastern Lagoon of New Caledonia (ELNC) is a semi-enclosed system surrounded by an extensive coral reef barrier. The system has been suffering impacts from climate variability and anthropogenic activities, including mining exploitation. Satellite monitoring is thus an essential tool to detect such changes. The present study aimed to assess the bio-optical variability of the ELNC and examine the applicability of ocean colour algorithms, using in situ bio-optical and radiometric data, collected during the March 2014 CALIOPE 2 cruise. The chlorophyll a concentration (Chla) varied from 0.13-0.72 mg•m −3 , and the coastal stations were spectrally dominated by non-algal particles (NAP) and coloured dissolved organic matter (CDOM) (>80% of the total non-water absorption at 443 nm), due to the contribution of allochthonous sources. The phytoplankton specific absorption was generally lower (mean, 0.049 m 2 •mg Chla −1) than typical values observed for the corresponding Chla range, as well as the spectral slopes of the absorption of CDOM plus NAP (a dg) (mean, 0.016 nm −1) and of the particle backscattering coefficient (b bp) (mean, 0.07 nm −1). The remote sensing reflectance obtained using two in-water approaches and modelled from Inherent Optical Properties (IOPs) showed less than 20% relative percent differences (RPD). Chla estimates were highly biased for the empirical (OC4 and OC3) and semi-analytical (GSM, QAA, GIOP, LMI) algorithms, especially at the coastal stations. Excluding these stations, the GSM01 yielded the best retrievals with 35-40% RPD. a dg (443) was well retrieved by all algorithms with~18% RPD, and b bp (443) with~40% RPD. Turbidity algorithms also performed reasonably well (30% RPD), showing the capacity and usefulness of the derived products to monitor the water quality of the ELNC, provided accurate atmospheric correction of the satellite data. Regionally tuned algorithms may potentially improve the Chla retrievals, but better parameterization schemes that consider the spatiotemporal variability of the specific IOPs are still needed.

2024

The chlorophyll-a concentration (Chla) of surface waters can be retrieved from space using an empirical polynomial function of the maximum band ratio (MBR), i.e., the maximum ratio of remote sensing reflectance between blue and green bands. Recent studies have revealed significant deviations in the relation between MBR and Chla across the oceans. The present work aimed to access the main sources of MBR variability across the Sub-tropical South Atlantic and Southeast Pacific, using in situ data. The data was collected at 19 bio-optical CTD stations and 40 flow-through stations during a cruise onboard the R/V Melville, from South Africa to Chile (February-March, 2011). The MBR was derived from modeled remote sensing reflectance using absorption and backscattering measurements. Multivariate analyses were used to explain the variations with bio-optical properties and phytoplankton pigments. Chla overestimations were associated to high specific phytoplankton absorption, specific particle...

2024, Zenodo (CERN European Organization for Nuclear Research)

Assessing the user needs and valuation for a future SBG mission involves considering the entire value chain for EO data (see graphic below). The target audience of this user-centered study-the end-user decision-makers-are several steps removed from sources like NASA. Thus, understanding the value chain of participants is important, and for this reason, RTI's research targeted end users but also intermediary product developers, service providers, and boundary organizations that have both specific technical insights and knowledge of their respective application domains. This study also sought to assess the maturity of EO data use and specifically hyperspectral imaging spectroscopy (HIS) and combined TIR imaging, used by end users and intermediaries. Early-stage innovators and lead users in established "communities of practice" were identified for potential collaboration. Pathways to further engage and support early adopters that are less mature, but promising "communities of potential" have also been noted for each select "primary" application area. By engaging and soliciting insights from across the value chain and for communities of varied EO and HIS adoption maturity, a comprehensive and broadly inclusive SBG assessment was possible.

2024, SPIE Proceedings

The ANTARES network seeks to understand the variability of the coastal environment on a continental scale and the local, regional, and global factors and processes that modulate this variability. The target are coastal zones of South America and the Caribbean Sea. The initial approach includes developing time series of in situ and satellite-based environmental observations in coastal and oceanic regions. The network is constituted by experts that seek to exchange ideas, develop an infrastructure for mutual logistical and knowledge support, and link in situ time series of observations located around the Americas with real-time and historical satellite-derived time series of relevant products. A major objective is to generate information that will be distributed publicly and openly in the service of coastal ocean research, resource management, science-based policy making and education in the Americas. As a first stage, the network has linked oceanographic time series located in Argentina, Brazil, Chile and Venezuela. The group has also developed an online tool to examine satellite data collected with sensors such as NASA's MODIS. Specifically, continental-scale high-resolution (1 km) maps of chlorophyll and sea surface temperature are generated and served daily over the web according to specifications of users within the ANTARES network. Other satellite-derived variables will be added as support for the network is solidified. ANTARES makes data available and offers simple analysis tools that anyone can use with the ultimate goal of improving coastal assessments, management and policies.

2024, Journal of the Indian Society of Remote Sensing

Potential fishing zones (PFZ's) are those regions where the fishes aggregate due to an abundance of food and they are demarcated by tracing those regions in the ocean, where a sharp sea surface temperature (SST) gradient along with optimal chlorophyll (Chl) concentration co-exists at a given time. In this regard, Indian National Centre for Ocean Information Services (INCOIS) disseminates the daily PFZ forecasts in Bay of Bengal and Arabian Sea to aid the fishermen community. The present study is an endeavor to develop a local spatial model derived Potential Fishing Zone (PFZ) in the northern Bay of Bengal (nBoB) lying adjacent to the West Bengal coast. Satellite derived SST and chlorophyll data obtained for two consecutive winter seasons of 2010-11 and 2011-12 were used to generate line density (LD) raster. Shapefiles of INCOIS predicted PFZs were overlaid on these LD raster to extract the corresponding pixel values. Histogram ranges of the extracted pixels were fixed and same values lying in the LD raster of both SST and chlorophyll other than INCOIS PFZs were detected by a spatial model in ERDAS. The PFZs thus derived were validated against the ground fish catch data and it was observed that good fish catch was seen in the model derived additional PFZs also. The catch per unit effort (CPUE) values was found to be very close to that of the CPUE value of PFZ advisories of INCOIS. However, the CPUE in the non PFZ areas were significantly lower than the former two categories.

2024, Perspectives in Water Pollution

2024, Journal of Marine Systems

Coupled biological/physical models of marine systems serve many purposes including the synthesis of information, hypothesis generation, and as a tool for numerical experimentation. However, marine system models are increasingly used for prediction to support high-stakes decision-making. In such applications it is imperative that a rigorous model skill assessment is conducted so that the model's capabilities are tested and understood. Herein, we review several metrics and approaches useful to evaluate model skill. The definition of skill and the determination of the skill level necessary for a given application is context specific and no single metric is likely to reveal all aspects of model skill. Thus, we recommend the use of several metrics, in concert, to provide a more thorough appraisal. The routine application and presentation of rigorous skill assessment metrics will also serve the broader interests of the modeling community, ultimately resulting in improved forecasting abilities as well as helping us recognize our limitations.

2024, OCEANS 2009

The oceans and coastal areas are dynamic environments in which variability occurs at a wide range of temporal scales, from seconds to years to decades and longer. Some very good time series now exist at specific locations, that permit characterization of this variability as well as of longer-term trends, but for much of the world ocean the in situ data is sparse and such characterization is not possible, or possible only by extrapolation. For these less well-studied areas, satellite imagery and gridded products created from a combination of satellite and in situ data are the only available sources of continuous historical information. Satellite imagery provides regular, spatially synoptic, global information, at spatial resolutions on the order of 1km and temporal resolutions typically measured in days. Some sensors offer higher spatial resolutions but at lower temporal resolution. With accumulated time series of up to 30 years or longer for some satellites and other gridded dataset...

2024, Zenodo (CERN European Organization for Nuclear Research)

2024

An advanced operational semi-empirical algorithm for processing satellite remote sensing data in the visible region is described. Based on the Levenberg-Marquardt multivariate optimization procedure, the algorithm is developed for retrieving major water colour producing agents: chlorophyll-a, suspended minerals and dissolved organics. Two assurance units incorporated by the algorithm are intended to flag pixels with inaccurate atmospheric correction and specific hydro-optical properties not covered by the applied hydro-optical model. The hydro-optical model is a set of spectral cross-sections of absorption and backscattering of the colour producing agents. The combination of the optimization procedure and a replaceable hydro-optical model makes the developed algorithm not specific to a particular satellite sensor or a water body. The algorithm performance efficiency is amply illustrated for SeaWiFS, MODIS and MERIS images over a variety of water bodies.

2024

The dual view of the Advanced Along Track Scanning Radiometer (AATSR) allows for the accurate retrieval of aerosol properties over land using an algorithm in which these two views are used to eliminate the influence of the land reflectance on the top of the atmosphere radiation. The algorithm uses the AATSR IR and visible wavebands for cloud detection and the visible wavebands for aerosol retrieval. The retrieval is based on minimizing the error function between modeled and measured TOA reflectances, using all available wavelengths. The TOA reflectances are modeled for a variety of aerosol mixtures. Hence, both the aerosol optical depth at various wavelengths (and thus the Ångström coefficient) and the mixing ratio of the dominant aerosol types can be determined. The results are evaluated by comparison with independent data: sun photometers and, when available, aerosol composition. In this contribution, the AATSR results are evaluated, based on comparisons between AATSR and MODIS AOD, and AERONET data. Results are used for assimilation in a regional scale chemistry transport model. The goal is to use satellite data for the determination of PM2.5. Other applications at TNO are in the synergisitic use with other satellites such as MSG SEVIRI and OMI.

2024, Deep Sea Research Part II: Topical Studies in Oceanography

The "rst Southern Ocean Iron RElease Experiment (SOIREE) was performed during February 1999 in Antarctic waters south of Australia (613S, 1403E), in order to verify whether iron supply controls the magnitude of phytoplankton production in this high nutrient low chlorophyll (HNLC) region. This paper describes iron distributions in the upper ocean during our 13-day site occupation, and presents a pelagic iron budget to account for the observed losses of dissolved and total iron from waters of the fertilised patch. Iron concentrations were measured underway during daily transects through the patch and in vertical pro"les of the 65-m mixed layer. High internal consistency was noted between data obtained using contrasting sampling and analytical techniques. A pre-infusion survey con"rmed the extremely low ambient dissolved (0.1 nM) and total (0.4 nM) iron concentrations. The initial enrichment elevated the dissolved iron concentration to 2.7 nM. Thereafter, dissolved iron was rapidly depleted inside the patch to 0.2}0.3 nM, necessitating three re-infusions. A distinct biological response was observed in iron-fertilised waters, relative to outside the patch, unequivocally con"rming that iron limits phytoplankton growth rates and biomass at this site in summer.

2024, OCEANS 2008

Challenges facing ocean remote sensing are as unlimited as the variety of sea surface dynamics and meteorological conditions across the globe and their range of spatial and time scales. Ultimate goals are to be able to make accurate estimates of selected key sets of geophysical variables, with the intention of either making predictions across time and spatial boundaries, or advancing fundamental knowledge through development of empirical relationships and/or theoretical models. Improvements are constantly being sought in both our understanding of the geophysical processes themselves, the sensor physics and the electromagnetic and microwave properties of the surface and its associated air-sea interface, as well as the sampling capabilities to ensure proper monitoring using the vast number of specialized technologies that can be selected to concentrate on one or a few of the physical processes for accurate measurements. The increasing quality, quantity and duration of these ocean observations are then critically important for practical applications as well as to assess local or global climate changes, both from natural and man-made influences.

2024, Frontiers in remote sensing

It is common in estuarine waters to place fixed monitoring stations, with the advantages of easy maintenance and continuous measurements. These two features make fixed monitoring stations indispensable for understanding the optical complexity of estuarine waters and enable an improved quantification of uncertainties in satellite-derived water quality variables. However, comparing the point-scale measurements of stationary monitoring systems to time-snapshots of satellite pixels suffers from additional uncertainties related to temporal/spatial discrepancies. This research presents a method for validating satellite-derived water quality variables with the continuous measurements of a fixed monitoring station in the Ems Dollard estuary on the Dutch-German borders. The method has two steps; first, similar in-situ measurements are grouped. Second, satellite observations are upscaled to match these point measurements in time and spatial scales. The upscaling approach was based on harmonizing the probability distribution functions of satellite observations and in-situ measurements using the first and second moments. The fixed station provided a continuous record of data on suspended particulate matter (SPM) and chlorophyll-a (Chl-a) concentrations at 1 min intervals for 1 year (2016-2017). Satellite observations were provided by Sentinel-2 (MultiSpectral Instrument, S2-MSI) and Sentinel-3 (Ocean and Land Color Instrument, S3-OLCI) sensors for the same location and time of in-situ measurements. Compared to traditional validation procedures, the proposed method has improved the overall fit and produced valuable information on the ranges of goodness-of-fit measures (slope, intercept, correlation coefficient, and normalized root-mean-square deviation). The correlation coefficient between measured and derived SPM concentrations has improved from 0.16 to 0.52 for S2-MSI and 0.14 to 0.84 for S3-OLCI. For the Chl-a matchup, the improvement was from 0.26 to 0.82 and from 0.14 to 0.63 for S2-MSI and S3-OLCI, respectively. The uncertainty in the derived SPM and Chl-a concentrations was reduced by 30 and 23% for S2-SMI and by 28 and 16% for S3-OLCI. The high correlation and reduced uncertainty signify that the matchup pairs are observing the same fluctuations in the measured variable. These new goodness-of-fit measures correspond to the results of the performed sensitivity analysis, previous literature, and reflect the inherent accuracy of the applied derivation model.

2024, Remote Sensing

Since the article “Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades” by Kulk et al [...]

2024, Remote Sensing of Environment

Lake Tanganyika, the second largest freshwater ecosystem in Africa, is characterised by a significant heterogeneity in phytoplankton concentration linked to its particular hydrodynamics. To gather a proper understanding of primary production, it is necessary to consider spatial and temporal dynamics throughout the lake. In the present work, daily MODIS-AQUA satellite measurements were used to estimate chlorophyll-a concentrations and the diffuse attenuation coefficient (K490) for surface waters. The spatial regionalisation of Lake Tanganyika, based on Empirical Orthogonal Functions of the chlorophyll-a dataset (July 2002-November 2005), allowed for the separation of the lake in 11 spatially coherent and co-varying regions, with 2 delocalised coastal regions. Temporal patterns of chlorophyll-a showed significant differences between regions. Estimation of the daily primary production in each region indicates that the dry season is more productive than the wet season in all regions with few exceptions. Whole-lake daily primary productivity calculated on an annual basis (2003) was 646 ± 142 mg C m − 2 day − 1. Comparing our estimation to previous studies, photosynthetic production in Lake Tanganyika appears to be presently lower (about 15%), which is consistent with other studies which used phytoplankton biovolume and changes of δ 13 C in the lake sediments. The decrease in lake productivity in recent decades may be associated to changes in climate conditions.

2024, Biogeosciences

Extensive observations were made during the late Southwest Monsoon of 2004 over the Indian and Omani shelves, and along a transect that extended from the southern coast of Oman to the central west coast of India, tracking the southern leg of the US JGOFS expedition (1994-1995) in the west. The data are used, in conjunction with satellite-derived data, to investigate long-term trends in chlorophyll and sea surface temperature, indicators of upwelling intensity, and to understand factors that control primary production (PP) in the Arabian Sea, focussing on the role of iron. Our results do not support an intensification of upwelling in the western Arabian Sea, reported to have been caused by the decline in the winter/spring Eurasian snow cover since 1997. We also noticed, for the first time, an unexpected development of high-nutrient, low-chlorophyll condition off the southern Omani coast. This feature, coupled with other characteristics of the system, such as a narrow shelf and relatively low iron concentrations in surface waters, suggest a close similarity between the Omani upwelling system and the Peruvian and California upwelling systems, where PP is limited by iron. Iron limitation of PP may complicate simple relationship between upwelling and PP assumed by previous workers, and contribute to the anomalous offshore occurrence of the most severe oxygen (O 2) depletion in the region. Over the much wider Indian shelf, which experiences large-scale bottom water O 2-depletion in summer, adequate iron supply from re

2024, International Journal of Remote Sensing

MERIS on Envisat delivers imaging spectroscopy data at 300m spatial resolution. MERIS has demonstrated its great potential for regional and global land cover mapping. This paper illustrates that the combination of the spatial, spectral, and temporal dimensions of MERIS has, in addition, the potential to retrieve sub-pixel land cover composition. Three MERIS FR Level 1b scenes acquired over The Netherlands in April, July and August 2003 were used in this study to derive fractional composition of 9 main land cover types. Linear spectral unmixing (with an optimized number of endmembers per pixel) was applied in both a mono-and multi-temporal fashion. A morphological eccentricity index (MEI) was used to explore the MERIS spatial dimension and, subsequently, to support the selection of the endmembers. The Dutch land use database (LGN5) was used as a reference in this study. Classification accuracy was assessed both at sub-pixel and per-pixel level. The best classification results were obtained for the combined image of April and July with a classification accuracy above 58%. In general, sub-pixel and per-pixel classification accuracies were similar. Spectral confusion was detected for several classes and dates indicating that the phenological status plays an important role in choosing the optimal acquisition date combination.

2024, Multimedia Research

Fishing, if sustainably managed, plays a crucial role in providing jobs and feeding the world. However, the exploitation of potential fishery resources is still underutilized in the fishing industry. Fish catch in the Potential Fishing Zones (PFZs) is 3 to 4 times higher when compared to non-PFZ areas. Remote Sensing (RS) provides reliable data on oceanographic conditions and supports marine environmental monitoring and assessment. This research aims to highlight the efficiency of remotely sensed data and advanced satellite image processing techniques to determine PFZs using Geographic Information Systems (GIS). The study focuses on the distribution of chlorophyll-A (Chl-A), sea-surface temperature (SST), and Particulate Organic Carbon (POC) concentrations, using MODIS (Moderate Resolution Imaging Spectro radiometer) satellite imagery with are solution of 4km. The methodology was implemented in Moroccan waters as a case study from January to December 2021. The results indicate that the suspected PFZs are between September and December 2021, mostly found in the region of Dakhla Oued Eddahab in the south of Morocco. The results were compared to the fishing catches given by the Ministry of Agriculture, Maritime Fisheries, Rural Development, and Waters and Forests of Morocco (published on 12/09/2022).

2024, Thalassas: An International Journal of Marine Sciences

Harmful Algae Blooms (HABs) in the Rias Baixas area (Galicia) cause a strong ecological and economic impact, since they can even force the closure of the rafts production areas for mollusc culture. In this work, we introduce a method for detection and monitoring of HABs in Galicia based on the analysis of map products derived from optical satellite images, including chlorophyll a concentration or species indicators. The approach is developed in the framework of CoastObs project, which started in 2017 and explores the potential of new Sentinel satellites for coastal water monitoring, suggesting different applications such as seagrass, phytoplankton size class or HABs detection. Preliminary results obtained using a set of images acquired on July 2018 suggest the great potential of this approach, which could complement the existing monitoring program based on direct observations.

2024, Biogeosciences

The replenishment of consumed oxygen in the open ocean oxygen minimum zone (OMZ) off northwest Africa is accomplished by oxygen transport across and along density surfaces, i.e. diapycnal and isopycnal oxygen supply. Here the diapycnal oxygen supply is investigated using a large observational set of oxygen profiles and diapycnal mixing data from years 2008 to 2010. Diapycnal mixing is inferred from different sources: (i) a large-scale tracer release experiment, (ii) microstructure profiles, and (iii) shipboard acoustic current measurements plus density profiles. From these measurements, the average diapycnal diffusivity in the studied depth interval from 150 to 500 m is estimated to be 1×10 −5 m 2 s −1 , with lower and upper 95 % confidence limits of 0.8 × 10 −5 m 2 s −1 and 1.4 × 10 −5 m 2 s −1. Diapycnal diffusivity in this depth range is predominantly caused by turbulence, and shows no significant vertical gradient. Diapycnal mixing is found to contribute substantially to the oxygen supply of the OMZ. Within the OMZ core, 1.5 µmol kg −1 yr −1 of oxygen is supplied via diapycnal mixing, contributing about one-third of the total demand. This oxygen which is supplied via diapycnal mixing originates from oxygen that has been laterally supplied within the upper Central Water layer above the OMZ, and within the Antarctic Intermediate Water layer below the OMZ. Due to the existence of a separate shallow oxygen minimum at about 100 m depth throughout most of the study area, there is no net vertical oxygen flux from the surface layer into the Central Water layer. Thus all oxygen supply of the OMZ is associated with remote pathways.