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

This study provides a satellite-based estimate of potential primary production in the Brazilian Southeast coast from in situ and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data. A non- spectral and vertically homogeneous semi-analytical algorithm and a spectral vertically non-homogeneous numerical algorithm were applied to the satellite ocean color data, which incorporate simultaneously measured in situ photosynthetic parameters. A vertically

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- Remote Sensing, Product Model, Ocean Color, Primary Production

Optical observations of the marine environment, giving information on ocean colour, have been increasingly used to provide a novel insight into a number of bio-geochemical and physical processes. The term ocean colour is used to indicate the visible light spectrum as observed at the sea surface that is related, by the processes of absorption and scattering, to the concentration of the water constituents. The feasibility and usefulness of satellite ocean colour remote sensing was first demonstrated by the Coastal Zone Colour Scanner (CZCS) on board Nimbus-7. More than a decade after the pioneer CZCS mission a new generation of ocean colour sensors has emerged. Indian Remote Sensing satellite P4, Ocean Colour Monitor (OCM) belongs to this new generation, and is equipped with channels and a resolution that can cater to the needs of the ocean colour community.

- by Shailesh Mohan
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- Remote Sensing, Indian Remote Sensing Satellites, Marine Environment, Ocean Colour

1] A method for the inversion of hyperspectral remote sensing was developed to determine the absorption coefficient for chromophoric dissolved organic matter (CDOM) in the Mississippi and Atchafalaya river plume regions and the northern Gulf of Mexico, where water types vary from Case 1 to turbid Case 2. Above-surface hyperspectral remote sensing data were measured by a ship-mounted spectroradiometer and then used to estimate CDOM. Simultaneously, water absorption and attenuation coefficients, CDOM and chlorophyll fluorescence, turbidities, and other related water properties were also measured at very high resolution (0.5-2 m) using in situ, underwater, and flow-through (shipboard, pumped) optical sensors. We separate a g , the absorption coefficient a of CDOM, from a dg (a of CDOM and nonalgal particles) based on two absorptionbackscattering relationships. The first is between a d (a of nonalgal particles) and b bp (total particulate backscattering coefficient), and the second is between a p (a of total particles) and b bp . These two relationships are referred as a d -based and a p -based methods, respectively. Consequently, based on Lee's quasi-analytical algorithm (QAA), we developed the so-called Extended Quasi-Analytical Algorithm (QAA-E) to decompose a dg , using both a d -based and a p -based methods. The absorption-backscattering relationships and the QAA-E were tested using synthetic and in situ data from the International Ocean-Colour Coordinating Group (IOCCG) as well as our own field data.

- by Qian Yu
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- Remote Sensing, Hyperspectral remote sensing, Multidisciplinary, Optical Sensor
- by Paul Dando and +2
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- Marine Biology, Oceanography, Time Series, Population Dynamics
- by Ranendu Ghosh
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- Remote Sensing, Satellite remote sensing, Level Of Detail (LOD), Forest fire

Data assembly and processing centers are essential elements of the operational oceanography infrastructure. They provide data and products nee ded by modeling and data assimilation systems; they also provide products directly useable for app lications. The paper will discuss the role and functions of the data centers for operational ocean ography and describe some of the main data assembly centers

- by Sylvie Pouliquen
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- Oceanography, Remote Sensing, Sea Ice, Sea surface temperature
- by Samantha Lavender
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- Oceanography, Remote Sensing, Satellite remote sensing, Carbon Cycle

Earth Observation satellites have traditionally been expensive to develop and launch and, as a consequence, have been targeted to cover the diverse needs of a large user community. Many niche applications in remote sensing are not exploited to their full potential or operating on a profitable basis and, as a result, spacebased Earth Observation has not yet made a similar impact into our everyday lives when compared with satellite communications.

Remote sensing of ocean colour yields information on the constituents of sea water, such as the concentration of phytoplankton pigments, suspended sediments and yellow substances. It is well understood that the study of ocean colour is significantly related with the primary production and zonation of potential fishing sites in coastal and oceanic waters. The maior pigment constituent is predominated by chlorophyll-a (ocean colour pigment of phytoplankton). The chlorophyll mapping on regular basis plays a major role in assessing water quality and classifying different water types. IRS P-3 MOS-B satellite data for three consecutive passes of path 94, during the period of January-February 1997 have been used to derive chlorophyll-a concentration. The present study emphasizes on the chlorophyll mapping using IRS-P3 MOS-B data for the coastal and offshore water of Maharashtra coast, India.

- by Shailesh Nayak
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- Remote Sensing, Water quality, Geomatic Engineering, Suspended Sediment

New production in the Irminger basin over the annual cycle 20012002 is estimated by considering changes in inorganic nutrient standing stocks between April and August 2002, with additional terms for nutrient fluxes across the thermocline... more

- by Richard Sanders
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- Geology, Oceanography, Seasonality, Atmospheric deposition

The distribution of chlorophyll-a in the Barents Sea was observed from the optical satellite instrument Sea-viewing Wide Field-of-view Sensor (SeaWiFS) during May 1999. In the same period water samples were collected in situ and analysed. Contrary to previous studies of phytoplankton distribution in the Barents Sea, we rigourously analysed the chlorophyll-a distribution characteristics with respect to sea ice and oceanographic conditions, spatially and temporally. The spatial distribution of surface chlorophyll-a was analysed and related, statistically, to the ice edge and sea ice concentrations from the Special Sensor Microwave Imager (SSM/I) satellite instrument. The highest chlorophyll-a concentrations were observed near the ice edge, and then decreased further into the ice. The spatial variability of the chlorophyll-a concentrations in this region was high, even in open water along the ice edge. The chlorophyll-a observations indicated a strong primary bloom about 2 weeks after the ice edge had retreated from a given measurement point. There were also indications of several minor blooms about 2 weeks after the initial bloom. The vertical distributions of chlorophyll-a are presented for nine different stations in the Marginal Ice Zone (MIZ) of the northern Barents Sea and discussed in terms of simultaneously measured temperature -salinity CTD profiles. Water mass properties and sea ice history have a significant impact on the vertical distribution of phytoplankton. The surface chlorophyll-a concentration was about 60% higher ( F 70% S.D.) than the total column average. The correlation coefficient was 0.87, indicating that surface values are good predictors for relative levels of total phytoplankton biomass during spring conditions. We propose a method to identify the stage of the phytoplankton bloom based on satellite observations of chlorophyll-a, temperature, salinity and sea ice history. Based on an extensive set of field measurements at different times from many locations in the Barents Sea, we have produced empirical formulae to estimate the integrated chlorophyll-a content for the water column from surface (satellite) measurements during early spring (homogeneous water masses) and bloom conditions. D 0924-7963/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 -7 9 6 3 ( 0 2 ) 0 0 0 7 7 -5

- by Else Hegseth
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- Oceanography, Sea Ice, Concentration, Microwave Imaging

Coastal area is an area of transition from terrestrial to marine ecosystems. This area is generally suffered by human, including gold mining activities. The existence of gold in Bombana discovered 2008, making the region as the center of public attention. The appearance of a gold mine in this region other than a blessing, but also brought new problems, especially in coastal areas. Therefore, a routine monitoring is needed to maintain environmental sustainability. Total Suspended Solid (TSS) is one of parameters that are often used for waters quality monitoring. In this research multi-temporal Landsat 8 (2013 to 2015) and in-situ measurement (November 20, 2015) were used to estimate the distribution of TSS. From the analysis, the concentration of TSS in 2014 decreased by 2.88% (36.97 g/m3) and increased by 6.76% (81.64 g/m3) in 2015. The results showed that all estimated-TSS overestimated the permissible water quality threshold (TSS ≤ 80 g/m3), it could be concluded that the gold mining activities in this area has decreased coastal ecological quality.

Bio-optical spectral properties were determined on fresh suspensions of Trichodesmium spp. collected in a tropical lagoon and put in seawater tanks (total chlorophyll concentrations range between 0.1 and 3.8 mg m -3 ). The spectrum of the backscattering coefficient was a hyperbolic function with a slope of 1.2, often showing troughs at 440, 550 and 676 nm, due to absorption peaks of chlorophyll and phycoerythrin. The absorption spectrum computed with a specific beta correction for Trichodesmium, showed a blue to red ratio (B/R) equivalent to the one of a single colony (B/R=2), and also showed the double peak of mycosporine-like amino acids (MAA's, 330 and 360 nm). The CDOM absorption spectrum showed minor MAA peaks when cyanobacterial concentrations were above 1 mg Chl a m -3 . The chlorophyll a-specific backscattering and absorption coefficients at 442 nm were respectively 0.0126 m 2 (mg.chl a) -1 and 0.027 m 2 (mg chl a) -1 . Suspensions in tanks exhibited a high backscattering ratio at 660 nm ( b b =b bp /b p ). The above-water reflectance spectrum clearly showed troughs at the wavelength of the pigment absorption peaks. Datasets of Trichodesmium normalized absorption, backscattering and reflectance spectra will allow its detection with future hyperspectral ocean colour sensors.

- by Guillaume Dirberg
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- Geomatic Engineering, Optical Properties, Ocean Colour, Spectral Properties

Ocean colour is an "essential climate variable" needed to support carbon cycle monitoring and is globally monitored using satellite observations. In order to cover the long time span necessary for climate monitoring purposes, the required ocean colour data set can only be built by merging together observations made with different satellite systems. To ensure that different periods of the time

- by Antoine Mangin
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- Time Series, Climate variability, Carbon Cycle, Global Carbon Cycle

The relationship between inherent optical properties (IOPs), phytoplankton community structure and the abundance of suspended particles in the size range 3 -500 Am was studied near the Isles of Scilly (UK) in May 2000. Autosub, an autonomous submersible vehicle specifically designed for science missions, was used as an instrument-positioning platform. It carried a CTD system, an ac-9+ dual tube spectrophotometer, a prototype submersible flow cytometer and an Aqua-monitor water sampler. The vehicle made a 10-km transect at constant depth across a boundary between water masses with contrasting remote sensing reflectance, which was located using SeaWiFs ocean colour imagery. This boundary corresponded to a sharp (1 km) transition between one phytoplankton community consisting of coccolithophores, flagellates and dinoflagellates, and a second community dominated by diatoms and flagellates. Inherent optical properties measured along the autonomous underwater vehicle (AUV) track showed marked changes in magnitudes, ratios, spectral shapes and fine-scale spatial variability. These changes were well correlated with variations in the composition of the suspended particle assemblage measured by microscopy and in situ flow cytometry. D

- by Claire Widdicombe
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- Oceanography, Remote Sensing, Water, Flow Cytometry

This paper presents a study of the characteristics of extra-tropical oceanic Rossby waves from datasets of Sea Surface Height (SSH), Sea Surface Temperature (SST) and ocean colour. We deal in particular with the propagation speed of the waves and compare the observational results with the speeds predicted by the classical theory and by the most recent extended theory of Rossby waves. We also discuss, with an example, the additional information that can be derived by a comparison of the wave signatures in the different datasets.

- by Graham Quartly
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- Remote Sensing, Sea surface temperature, Geomatic Engineering, Wave propagation

Within the eastern tropical oceans of the Atlantic and Pacific basin vast oxygen minimum zones (OMZ) exist in the depth range between 100 and 900 m. Minimum oxygen values are reached at 300-500 m depth which in the eastern Pacific become suboxic (dissolved oxygen content <4.5 lmol kg À1 ) with dissolved oxygen concentration of less than 1 lmol kg À1 . The OMZ of the eastern Atlantic is not suboxic and has relatively high oxygen minimum values of about 17 lmol kg À1 in the South Atlantic and more than 40 lmol kg À1 in the North Atlantic. About 20 (40%) of the North Pacific volume is occupied by an OMZ when using 45 lmol kg À1 (or 90 lmol kg À1 , respectively) as an upper bound for OMZ oxygen concentration for ocean densities lighter than r h < 27.2 kg m À3 . The relative volumes reduce to less than half for the South Pacific (7% and 13%, respectively). The abundance of OMZs are considerably smaller (1% and 7%) for the South Atlantic and only $0% and 5% for the North Atlantic. Thermal domes characterized by upward displacements of isotherms located in the northeastern Pacific and Atlantic and in the southeastern Atlantic are co-located with the centres of the OMZs. They seem not to be directly involved in the generation of the OMZs. OMZs are a consequence of a combination of weak ocean ventilation, which supplies oxygen, and respiration, which consumes oxygen. Oxygen consumption can be approximated by the apparent oxygen utilization (AOU). However, AOU scaled with an appropriate consumption rate (aOUR) gives a time, the oxygen age. Here we derive oxygen ages using climatological AOU data and an empirical estimate of aOUR. Averaging oxygen ages for main thermocline isopycnals of the Atlantic and Pacific Ocean exhibit an exponential increase with density without an obvious signature of the OMZs. Oxygen supply originates from a surface outcrop area and can also be approximated by the turn-over time, the ratio of ocean volume to ventilating flux. The turn-over time corresponds well to the average oxygen ages for the well ventilated waters. However, in the density ranges of the suboxic OMZs the turn-over time substantially increases. This indicates that reduced ventilation in the outcrop is directly related to the existence of suboxic OMZs, but they are not obviously related to enhanced consumption indicated by the oxygen ages. The turn-over time suggests that the lower thermocline of the North Atlantic would be suboxic but at present this is compensated by the import of water from the well ventilated South Atlantic. The turn-over time approach itself is independent of details of ocean transport pathways. Instead the geographical location of the OMZ is to first order determined by: (i) the patterns of upwelling, either through Ekman or equatorial divergence, (ii) the regions of general sluggish horizontal transport at the eastern boundaries, and (iii) to a lesser extent to regions with high productivity as indicated through ocean colour data.

- by J. Karstensen
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- Geology, Oceanography, North Atlantic, Tropical Eastern Pacific

The role and contribution of satellite data in operational oceanography is reviewed, with emphasis on northern European seas. The possibility to observe various ocean parameters and processes by existing satellite sensors, such as optical instruments, infrared radiometers, passive Ž . microwave radiometers, and active microwave systems altimeter, scatterometer, SAR is discussed. The basic parameters are: sea-surface temperature observed by infrared radiometers, ocean colour by spectrometers, sea-surface elevation by altimeters, and surface roughness by active and passive microwave systems, which can be used to derive surface wind and waves. A number of ocean processes can be derived from synoptic mapping of the basic parameters of larger sea areas, such as current patterns, fronts, eddies, water mass distribution, and various water quality Ž . parameters chlorophyll, surface slicks, suspended sediments . The suitability of existing satellite data to fulfil the operational requirements for temporal and spatial coverage, data delivery in near-real-time, and long-term access to data is discussed in light of the fact that opticalrinfrared data in northern Europe are severely hampered by frequent cloud cover, while microwave techniques can provide useful data independent of weather and light conditions. Finally, the use of data assimilation in oceanographic models is briefly summarised, indicating that this technique is under development and will soon be adopted in operational oceanography. q O.M. Johannessen . 0378-3839r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.

- by Olam Johannessen and +2
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- Civil Engineering, Geology, Coastal Engineering, Water quality

Quantitative analysis of sea surface temperature (SST) and chlorophyll improve our understanding of circulation and distribution of phytoplankton population in water masses. In this study near synchronous IRS P4 Ocean Colour Monitor (OCM)... more

- by H. Solanki and +1
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- Sea surface temperature, Quantitative analysis, Atmospheric Correction, Ocean Colour
- by Samantha Lavender
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- Remote Sensing, Multidisciplinary, Ecological Modelling, Pigment

The principal goal in early missions of satellite-borne visible spectral radiometry (ocean colour) was to create synoptic fields of phytoplankton biomass indexed as concentration of chlorophyll-a. In the context of climate change, a major application of the results has been in the modelling of primary production and the ocean carbon cycle. It is now recognised that a partition of the marine autotrophic pool into a suite of phytoplankton functional types, each type having a characteristic role in the biogeochemical cycle of the ocean, would increase our understanding of the role of phytoplankton in the global carbon cycle. At the same time, new methods have been emerging that use visible spectral radiometry to map some of the phytoplankton functional types. Here, we assess the state of the art, and suggest paths for future work.

- by Liane Guild
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- Remote Sensing, Climate Change, Carbon Cycle, Global Carbon Cycle

- by Marie-hélène Forget and +1
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- Remote Sensing, Climate Change, Carbon Cycle, Global Carbon Cycle

An algorithm is presented for estimating near-surface SPM concentrations in the turbid Case 2 waters of the southern North Sea. The single band algorithm, named POWERS, was derived by parameterising Gordon's approximation of the radiative transfer model with measurements of Belgian and Dutch inherent optical properties. The algorithm was used to calculate near-surface SPM concentration from 491 SeaWiFS datasets for 2001. It was shown to be a robust algorithm for estimating SPM in the southern North Sea. Regression of annual geometric mean SPM concentration derived from remote sensing (SPM rs ), against in situ (SPM is ) data from 19 Dutch monitoring stations was highly significant with an r 2 of 0.87. Further comparison and statistical testing against independent datasets for 2000 confirmed the consistency of this relationship. Moreover, time series of SPM rs concentrations derived from the POWERS algorithm, were shown to follow the same temporal trends as individual SPM is data recorded during 2001. Composites of annual, winter and summer SPM rs for 2001 highlight the three dominant water masses in the southern North Sea, as well as their winter-fall and spring-summer variability. The results indicate that wind induced wave action and mixing cause high surface SPM signals in winter in regions where the water column becomes well mixed, whereas in summer stratification leads to a lower SPM surface signal. The presented algorithm gives accurate near-surface SPM concentrations and could easily be adapted for other water masses and seas.

- by Reinold Pasterkamp and +1
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- Earth Sciences, Remote Sensing, Time Series, Stratification

Estuary is challenging for ocean-colour retrieval algorithms. The Changjiang Estuary is characterized by suspended-sediment-dominated waters in the mouth and optically complex case 2 waters offshore of the mouth. Satellite ocean-colour products show that high-sediment loads of estuarine waters can cause overestimations or invalid flags of Chl-a concentration. A synthetic chlorophyll index (SCI) was designed for extracting chlorophyll information and for minimizing the influence of sediments on the remote-sensing reflectance spectrum. An SCI algorithm, a quadratic polynomial function of the SCI versus Chl-a concentration, was applied to the estimation of Chl-a concentration from Medium Resolution Imaging Spectrometer (MERIS) images. The overestimation of Chl-a concentration was corrected. The SCI algorithm has applications for MERIS estimation of Chl-a concentration in turbid waters with a moderate to high suspended-sediment concentration.

- by Mhd. Suhyb Salama
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- Oceanography, Remote Sensing, Climate Change, Time Series
- by Medhavy Thankappan
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- Remote Sensing, Satellite remote sensing, Level Of Detail (LOD), Forest fire

Chromophoric dissolved organic matter (CDOM) is a key parameter in the biogeochemical cycles affecting the oceans' contribution to the carbon budget of the Earth system. Despite its importance, important ocean colour satellite radiometers... more

- by Luigi Lazzara
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- Southern Ocean, Data Collection, Satellite Imagery, Ocean Colour

The Agulhas Current with its retroflection and attendant eddy-shedding is the cause of some of the greatest mesoscale variability in the ocean. This paper considers the area to the south and east of Madagascar, which provides some of the source waters of the Agulhas Current, and examines the propagating sea surface height signals in altimetry and output from a numerical model, OCCAM. Both show bands of variability along the axis of the East Madagascar Current (EMC) and along a zonal band near 25˚S. Sequences of images plus associated temperature data suggest that a number of westward-propagating eddies are present in this zonal band. The paper then focuses on the region to the south of the island, where ocean colour and infra-red imagery are evocative of an East Madagascar Retroflection. The synthesis of data analysed in this paper, however, show that remotely observed features in this area can be explained by anticyclonic eddies moving westward through the region, and this explanation is consistent with numerical model output and the trajectories of drifting buoys.

- by Graham Quartly
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- Oceanography, Ocean Colour, Marine Systems, Numerical Model

We argue that geophysical and geographical ® elds are generally characterised by wide range scaling implying systematic, strong (power law) resolution dependencies when they are remotely sensed. The corresponding geometric structures are fractal sets; the corresponding ® elds are multifractals. Mathematically, multifractals are measures that are singular with respect to the standard Lebesgue measures; therefore, they are outside the scope of many of the methods of classical geostatistics. Because the resolution of a measurement is generally (due to technical constraints) much larger than the inner scale of the variability/scaling, the observations will be fundamentally observer dependent; hence, standard remote sensing algorithms that do not explicitly take this dependence into account will depend on subjective resolution-dependent parameters. We argue that, on the contrary, the resolution dependence must be systematically removed so that scale-invariant algorithms independent of the observer can be produced. We illustrate these ideas in various ways with the help of eight-channel, 7 m resolution remote ocean colour data (from the MIES II sensor) over the St Lawrence estuary. First, we show that the data is indeed multiscaling over nearly four orders of magnitude in scale, and we quantify this using universal multifractal parameters. With the help of conditional multifractal statistics, we then show how to use multifractals in various practical ways such as for extrapolating from one resolution to another or from one location to another, or to correcting biases introduced when studying extreme, rare phenomena. We also show how the scaling interrelationship of surrogate and in situ data can be handled using vector multifractals and examine the resolution dependence of principle components in dual wavelength analyses. Finally, we indicate why the standard ocean colour algorithms have hidden resolution dependencies, and we show how they can (at least in principle) be removed.

- by Shaun Lovejoy
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- Computer Science, Remote Sensing, Geomatic Engineering, Lebesgue measure

A method of blending of a specific satellite ocean colour algorithm in the Southern Ocean (SO) with a generic algorithm elsewhere is proposed. The SO is known to have bio-optical properties that require a different bio-optical algorithm for retrieving chlorophyll-a concentration. Merging data retrieved with a specific algorithm in one area with data retrieved with another algorithm elsewhere has remained a problem. We use a blending scheme that uses both bio-optical properties and the location of the pixel relative to the mean position of the Subtropical Front to create a smooth transition from one algorithm to another. The method can be applied to other regions or variables after modification.

- by B. Greg Mitchell
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- Earth Sciences, Southern Ocean, Ocean Colour
- by Irene Schloss
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- Remote Sensing, Geomatic Engineering, Continental shelf, Ocean Colour

This chapter focuses on recent advances in water quality monitoring of the Baltic Sea using remote sensing techniques in combination with optical in situ measurements. Here the Baltic Sea ecosystem is observed through its bio-optical properties, which are defined by the concentration of optical in-water constituents governing the spectral attenuation of light. In the introduction, typical geograph-ical patterns and seasonal variations of optical properties and the cause of the mass occurrence of cyanobacterial blooms in summer are discussed. The optical characteristic of Baltic Sea waters is clearly dominated by a relatively high load of dissolved organic matter and, during the productive season, by phytoplankton growth, stimulated by nutrients mostly originating from land. In the coastal zone, inorganic suspended matter also has a significant effect on the light attenuation, which increases with proximity to land. The ecological status of the coastal zone may be synthesized using a...

- by Kai Sørensen
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- Remote Sensing, Water quality, Satellite remote sensing, Continuous Improvement
- by Marcel Wernand and +2
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- Geology, Oceanography, Remote Sensing, Seasonality

The present study emphasizes on the impact of cyclone on the coastal environment of Orissa, using the IRS-P4 (OCM) satellite data. The study includes the analysis of IRS-P4 (OCM) data to generate chlorophyll, suspended sediment concentration (SSC) images for the coastal water and normalized difference vegetation index (NDVI) images for coastal vegetation in the pre and post-cyclonic stages. The effect on mangroves and change in distribution pattern of water constituents like chlorophyll and suspended sediments are brought out.

- by Qian Yu
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- Remote Sensing, Hyperspectral remote sensing, Multidisciplinary, Optical Sensor
- by Chris Mannaerts
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- Water quality, Case Study, Geomatic Engineering, Inverse Problem

Ocean colour features like chlorophyll fronts are widely used for the prediction of Potential Fishery Zones (PFZs). These mesoscale features are dynamic since ocean surface is always in motion. They tend to drift because of surface advective movements. The present study is an attempt to understand the relationship between wind speed and drift of ocean colour features, which can be used to update the location of PFZ mesoscale features. Ocean colour images from IRS-P4 Ocean Colour Monitor (OCM) were atmospherically corrected and Ocean Chlorophyll-2 bio-optical algorithm was applied to derive the sea surface chlorophyll. QuikSCAT (NASA) scatterometer wind data was obtained from the global 25 km 2 gridded dataset. A mathematical relationship between wind speed and drift was derived. The relation was validated on a second set of time series images. Results show that the relation can be used for updating the location of PFZ features in the northeast Arabian Sea for up to 96 hr within an error of 12%.

- by rashmin dwivedi
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- Indian, Ocean Colour

Global standard ocean colour algorithms may be inefficient to estimate the concentration of seawater constituents in the Mediterranean Sea. Local overestimation or underestimation of chlorophyll, suspended sediments and yellow substance are in fact quite common. To avoid this problem, our research group works on the local calibration of empirical or semianalytical algorithms through comparison to in situ measured data. The spectral features of chlorophyll, suspended sediments and yellow substance were found for a number of samples near the coast of Tuscany (Italy). An unconventional algorithm was then developed and applied to satellite data (MODIS) for the retrieval of water constituent concentrations. This inversion algorithm is based on the minimization of the spectral angle between simulated and measured remote sensing reflectances. The estimated concentrations show a lower error with respect to that obtained by a standard error minimization criterion. Monthly maps of seawater constituent concentrations obtained by applying the proposed algorithm to numerous satellite images confirm the oligotrophic nature of the Tuscany Sea, where high values of these concentrations can be found only in early spring near the mouths of the main rivers.

- by luca massi
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- Algorithms, Remote Sensing, Water, Physical Oceanography

Suspended Particulate Matter (SPM) is an important environmental parameter in coastal seas such as the North Sea. Our description and understanding of the complex dynamical SPM transport system can be much improved by means of an integration of remote sensing data and numerical modelling. SPM data products retrieved from MERIS RR ocean colour by VU-IVM, which include information on the uncertainty in the data, are very suitable to be used to update the Delft3D-WAQ sediment transport model in an Ensemble Kalman Filtering approach. The sediment transport model proper is provided with information on water motion from the Delft3D-Flow hydrodynamic model and with surface wave parameters from a combination of SWAN wave model data and wave buoy observations, such that a robust modelling system results. The robustness of both data and model are prerequisites for a successful Kalman Filtering. Eventually, the assimilation of the mostly daily MERIS observations enables to overcome the limitations of cloud cover and restriction to the sea surface layer inherent to space borne ocean colour observations.

- by Ghada Serafy
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- Numerical Modelling, Kalman Filter, Sediment transport, Data Model

- by Shailesh Nayak
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- Remote Sensing, Indian Remote Sensing Satellites, Marine Environment, Ocean Colour
- by Samantha Lavender
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- Remote Sensing, Near Infrared, Surface Water, Geomatic Engineering

This study compares spatial and temporal variability in net primary productivity (PP) and particulate organic carbon (POC) export production (EP) from three different coupled climate carbon cycle models (IPSL, MPIM, NCAR) with... more

- by Fortunat Joos
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- Climate Change, Carbon Cycle, Stratification, Biogeosciences

This study presents the application of a semi-empirical approach, based on the Kubelka–Munk (K-M) model, to retrieve the total suspended matter (TSM) concentration of water bodies from ocean colour remote sensing. This approach is validated with in situ data sets compiled from the tropical waters of Berau estuary, Indonesia. Compared to a purely empirical approach, the K-M model provides better results in the retrieval of TSM concentration on both data sets (in situ and Medium Resolution Imaging Spectrometer (MERIS)). In this study, the K-M model was calibrated with in situ measurements of remote-sensing reflectance (R rs) and TSM concentration. Next, the inverse K-M model was successfully applied to images taken by the MERIS instrument by generating regional maps of TSM concentration. MERIS top-of-atmosphere radiances were atmospherically corrected using the Moderate Spectral Resolution Atmospheric Transmittance (MODTRAN) radiative transfer model. The best correlation between R rs measured in situ and R rs MERIS was found to be at a wavelength of 620 nm. The TSM concentrations retrieved using the K-M model showed a lower root mean square error (RMSE), a higher coefficient of determination and a smaller relative error than those retrieved by the purely empirical approach.

- by Suhyb Salama
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- Remote Sensing, Geomatic Engineering, Atmospheric Correction, Root-Mean Square Error

Remotely sensed data on ocean colour of waters surrounding Sri Lanka received from the Coastal Zone Colour Scanner (CZCS) are processed and analyzed. Raw data of 1 km resolution on relatively cloud free days during 1978--1986 are processed to produce sea surface chlorophyll maps within latitudes 4.5N--11N and longitudes 78E--85E, a region in the Indian Ocean surrounding Sri Lanka. The processed data include about 110 single day maps and composite averages for each month and season. The months of July, August and September are omitted in the calculation of averages due to insufficient data. The waters in the Gulf of Mannar and Palk Bay areas show high chlorophyll-a concentrations throughout the year. However, these high values may represent other suspended particles and dissolved organic matter besides chlorophyll-a as this region is shallow (< 100 m). Regions with high chlorophyll concentrations (> 0:5 mg m À3 ) along the coast and western ocean region can be seen in the months of October and November, after the southwest monsoon period. As high surface chlorophyll concentrations may indicate high productivity, these regions need extensive measurements of primary production and also continuous monitoring of fish catches, during and after the southwest monsoon. Studies of particle composition in shallow water areas, in particular waters in Palk Bay and Gulf of Mannar, should be carried out in order to elucidate the effect of non-phytogenic.

- by kanthi yapa
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- Geology, Sri Lanka, Earth System Science, Indian Ocean

Baroclinic Rossby waves are long wavelength oceanic processes that can affect the whole of the water column. During the past decade they have been detected in sea surface height data from altimetry, with clear signals in all ocean basins. More recently they have been observed globally in datasets of sea surface temperature too. Because of their effect on the mixed layer, they may also produce an effect on the development of phytoplankton, and thus produce a signal in ocean colour data. We show westwardpropagating features in chlorophyll-a data from two different spaceborne sensors and compare their characteristics with the signals in sea surface height.

- by Graham Quartly
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- Sea surface temperature, Ocean Colour, Chlorophyll a, Mixed layer

Ocean colour varies as an inverse function of the absorption coefficient. In Case 1 waters, phytoplankton are known to be the principal agents responsible for variations in the total absorption coefficient. The concentration and composition of pigments present have a strong influence on phytoplankton absorption spectra. Empirical (regression) algorithms exist to recover the wavelength-specific absorption coefficient of phytoplankton from the concentration of the main pigment, chlorophyll-a. However, to explain the residuals about such regressions remains a major challenge. We have analysed a set of over 1,600 absorption spectra of phytoplankton collected from various oceanographic provinces. In parallel, we examined the corresponding pigment complexes, as revealed by High Performance Liquid Chromatography (HPLC). We have uncovered broad trends in the shapes of the absorption spectra and in the pigment complexes, consequent upon changes in the pigment biomass, with clear implications...

- by Venetia Stuart
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- Remote Sensing, Indian, High Performance Liquid Chromatography, Ocean Colour

- by Shailesh Nayak
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- Remote Sensing, Indian Remote Sensing Satellites, Marine Environment, Ocean Colour

In-situ bio-optical measurements were collected during six ship campaigns in the north eastern Arabian Sea using SeaWiFS Multi-channel Profiling Radiometer (SPMR). An artificial neural network (ANN) based algorithms were constructed to... more

- by Shailesh Nayak
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- Remote Sensing, Ocean Colour, Arabian Sea, Correlation coefficient

A diatom-detection algorithm was parametrized for the Humboldt upwelling system using local cruise data that were first validated, then used to create monthly composites of diatom distribution from 0 to 408S and 90 to 708W for both normal and El Niño conditions. There was a 50% reduction in the areal extent of diatom-dominated waters during the peak of the 1997 El Niño. The extent of the coastward contraction in the diatom-dominated area varied along the South American coastline. These regional shifts in phytoand zooplankton communities would have increased food stress on local anchovy (Engraulis ringens) populations and could have contributed to diminished larval survival and landings the following year. A region of strong upwelling over the wide Peruvian continental shelf around 158S was the only area that maintained a strong diatom population throughout the El Niño; the area may require special protection from fishing pressure in years following an El Niño event.

- by Jerlando F.L. Jackson
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- Business, Remote Sensing, Political Science, Fisheries

The confidence level of oil spill detections in satellite Synthetic Aperture Radar (SAR) imagery requires the analysis of many different factors. Unfortunately, oil slicks are not the only phenomena which can appear as a dark feature in a SAR image. These include a number of parameters like wind speed, currents, internal waves, upwelling sea areas, algae bloom, mixing water areas, et cetera. These phenomena are called look-alikes. The largest challenge in detecting oil spills in SAR images remains in the accurate discrimination between oil spills and look-alikes. This study introduces the vantages of using geospatial analysis of various metocean data (e.g. wind speed and direction, sea surface temperature, wave direction, ocean colour data) and environmental ancillary data (e.g. vessel traffic, port locations) as a supplementary information source for the oil spill probability assessment in SAR imagery. The analysed data exists in different formats with different value scales. In ad...

- by Marko Perkovic
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- Remote Sensing, Water, Data Analysis, Sea surface temperature

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.

- by Richard Mantoura
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- Geochemistry, Oceanography, Ecology, Southern Ocean