scholarly journals Chlorophyll-a concentrations inversion based on the modified Quasi-Analytical Algorithm and Sentinel-3 OLCI in Daihai Lake, China

2021 ◽  
Author(s):  
Zhao Lu ◽  
Huajie Duan ◽  
Daqing Wang ◽  
Jianwu Cao ◽  
Guoli Du ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Chlorophyll A ◽  
Spectral Reflectance ◽  
Absorption Coefficients ◽  
Chl A ◽  
The North ◽  
Daihai Lake ◽  
Analytical Algorithm ◽  
Measured Absorption ◽  
Particle Backscattering

Abstract The Quasi-Analytical Algorithm (QAA) is effective in retrieving water inherent optical properties (IOPs) from remote sensing spectral reflectance and has wider applications in studies of the open ocean and coastal waters than of inland waters. This research aimed to modify the QAA model based on measured field spectral reflectance and absorption coefficients to render it applicable to studies of Daihai Lake, China. The improvements mainly included the reference wavelength selection, the power index of the particle backscattering coefficient and the exponential slope of the absorption coefficient of the colored detrital matter estimation. The average relative error between the inversed and measured absorption coefficients was less than 20%. A linear model was established between the phytoplankton absorption coefficient at a wavelength of 674 nm (aph(674)) and the chlorophyll-a (Chl-a) concentration, with a determination coefficient of 0.88. Additionally, the modified Quasi-Analytical Algorithm (MQAA) model was applied to the Ocean and Land Color Instrument (OLCI) data aboard the Sentinel-3 satellite. Finally, a spatial distribution map for the Chl-a concentrations in Daihai Lake on August 10, 2017 was drawn and the mid-eutrophication area was found to occur in the north and border.

scholarly journals Microwave Absorption in Compressed Carbon Monoxide and Nitrous Oxide

1972 ◽  
Vol 25 (3) ◽  
pp. 283 ◽  
Author(s):  
JC Andrews
Keyword(s):  
Carbon Monoxide ◽  
Nitrous Oxide ◽  
Absorption Coefficient ◽  
Microwave Absorption ◽  
Resonant Cavity ◽  
Absorption Coefficients ◽  
Power Absorption ◽  
Measured Absorption ◽  
Van Vleck ◽  
Resonant Contribution

The absorption of microwaves by both CO and N2O has been measured at a frequency of 9�75 GHz using a resonant cavity technique. The power absorption coefficients were measured at pressures up to 670 bars for CO at 20�5�C, 54 bars for 20 at 25�C, and 121 bars for N2O at 40�C. In all cases the power absorption coefficient was found to increase with density up to the highest pressures reached. The theory of Van Vleck and Weisskopf fails to account for the measured absorption except at low densities. At higher densities the measured absorption was in excess of that predicted by this theory and the discrepancy increased with increasing density. The theory of Ben-Reuven accounts for the absorption up to intermediate densities but at high densities it also predicts values which are smaller than the measured ones. However, it is possible to account for the measured absorption by considering it to be the sum of a resonant contribution, which is assumed to be given by the Van Vleck-Weisskopf theory, and a nonresonant collision-induced contribution which increases with density and is assumed to be the result of collisions so strong that rotation of the molecules is quenched.

scholarly journals Seasonal variability of vertical patterns in chlorophyll-a fluorescence in the coastal waters off Kimbiji, Tanzania

2021 ◽  
Vol 20 (1) ◽  
pp. 21-33
Author(s):  
Nyamisi Peter ◽  
Masumbuko Semba ◽  
Charles Lugomela ◽  
Margareth Kyewalyanga
Keyword(s):  
Chlorophyll A ◽  
Coastal Waters ◽  
Mixed Layer Depth ◽  
Northeast Monsoon ◽  
Nutrient Input ◽  
Layer Depth ◽  
Chl A ◽  
The North ◽  
A Value ◽  
Chl A Fluorescence

A study on the vertical pattern of chlorophyll-a (Chl-a) fluorescence was undertaken in the Mafia Channel offKimbiji, Tanzania. Data was collected during the Southeast Monsoon (SEM) and Northeast Monsoon (NEM) seasons. There was higher Chl-a concentration of 0.1 to 1.1 mgm-3 in the surface layer off Kimbiji to about 50 m depth due to the presence of mixed layer depth (MLD) which allowed water mixing in the layer. A deep Chl-a maximum was recorded at around 40 m depth during the NEM and between 40 and 70 m in the SEM. Surface water between longitude 39.9°E and 40.2°E had low Chl-a from the surface to about 50 m depth due to poor nutrient input. The NEM had an insignificantly higher Chl-a value than the SEM (p > 0.05) which differed from other studies in which Chl-a was higher during the SEM than the NEM, than, the Chl-a concentration was higher at the surface during the SEM than during the NEM. Satellite data showed higher Chl-a in the SEM than NEM, localized along the Mafia Channel. During the SEM season the wind pushes higher Chl-a water from the Mafia Channel towards the north and leads to a higher concentration at Kimbiji.

scholarly journals A Semi-Empirical Chlorophyll-a Retrieval Algorithm Considering the Effects of Sun Glint, Bottom Reflectance, and Non-Algal Particles in the Optically Shallow Water Zones of Sanya Bay Using SPOT6 Data

2020 ◽  
Vol 12 (17) ◽  
pp. 2765
Author(s):  
Yan Yu ◽  
Shengbo Chen ◽  
Wenhan Qin ◽  
Tianqi Lu ◽  
Jian Li ◽  
...  
Keyword(s):  
Optical Properties ◽  
Absorption Coefficient ◽  
Chlorophyll A ◽  
Coastal Waters ◽  
Green Band ◽  
Chl A ◽  
Inherent Optical Properties ◽  
Sanya Bay ◽  
Semi Empirical ◽  
Empirical Algorithms

Chlorophyll-a (Chl-a) concentration retrieval is essential for water quality monitoring, aquaculture, and guiding coastline infrastructure construction. Compared with common ocean color satellites, land observation satellites have the advantage of a higher resolution and more data sources for retrieving the concentration of Chl-a from optically shallow waters. However, the sun glint (Rsg), bottom reflectance (Rb), and non-algal particle (NAP) derived from terrigenous matter affect the accuracy of Chl-a concentration retrieval using land observation satellite image data. In this paper, we propose a semi-empirical algorithm based on the remote sensing reflectance (Rrs) of SPOT6 to retrieve the Chl-a concentration in Sanya Bay (SYB), considering the effect of Rsg, Rb, and NAP. In this semi-empirical algorithm, the Cox–Munk anisotropic model and radiative transfer model (RTM) were used to reduce the effects of Rsg and Rb on Rrs, and the Chl-a concentration was retrieved by the Chl-a absorption coefficient at 490 nm (aphy(490)) to remove the effect of NAP. The semi-empirical algorithm was in the form of Chl-a = 43.3[aphy(490)]1.454, where aphy (490) was calculated by the total absorption coefficient and the absorption coefficients of each component by empirical algorithms. The results of the Chl-a concentration retrieval show the following: (1) SPOT6 data are available for Chl-a retrieval using this semi-empirical algorithm in oligotrophic or mesotrophic coastal waters, and the accuracy of the algorithm can be improved by removing the effects of Rsg, Rb, and NAP (R2 from 0.71 to 0.93 and root mean square error (RMSE) from 0.23 to 0.11 ug/L); (2) empirical algorithms based on the blue-green band are suitable for oligotrophic or mesotrophic coastal waters, and the algorithm based on the blue-green band difference Chl-a index (DCI) has stronger anti-interference in terms of the effects of sun glint and bottom reflectance than the algorithm based on the blue-green ratio (BGr); (3) in the case of ignoring Rsg unrelated to inherent optical properties (IOPs), NAP is the biggest interference factor when >9.5 mg/L and the effect of bottom reflectance should be considered when the water depth (H) <5 m in SYB; and (4) the inherent optical properties of the waters in SYB are dominated by NAP (Chl-a = 0.2–2.6 ug/L and NAP = 2.2–30.1 mg/L), and the nutrients are concentrated by enclosed terrain and southeast current. This semi-empirical algorithm for Chl-a concentration retrieval has the potential to monitor Chl-a in oligotrophic and mesotrophic coastal waters using other land observation satellites (e.g., Landsat8 OLI, ASTER, and GaoFen2).

scholarly journals Analysis of chlorophyll a concentration along the Galician coast: seasonal variability and trends

2012 ◽  
Vol 69 (5) ◽  
pp. 728-738 ◽  
Author(s):  
I. Alvarez ◽  
M. N. Lorenzo ◽  
M. deCastro
Keyword(s):  
Chlorophyll A ◽  
Seasonal Variability ◽  
Temporal Distribution ◽  
Ekman Transport ◽  
North Coast ◽  
Chlorophyll A Concentration ◽  
Chl A ◽  
Galician Coast ◽  
The North ◽  
Run Off

Abstract Alvarez, I., Lorenzo, M. N., and deCastro, M. 2012. Analysis of chlorophyll a concentration along the Galician coast: seasonal variability and trends. – ICES Journal of Marine Science, 69: 728–738. The spatial and temporal distribution of chlorophyll a (Chl a) concentration was analysed along the Galician coast from 1998 to 2007. Sea surface temperature and Ekman transport data were also used to investigate the relationship between the ocean–atmosphere conditions and Chl a formation and variability. The west coast showed the highest Chl a concentration, with three peaks of maximum values (February, April–May, and July–September). Along the central coast, the pattern was similar, with the highest concentrations measured during spring and summer, but with lower values. The north coast was the least productive, with much lower values. The high seasonal variability of Chl a was mainly related to upwelling events during spring and summer. During autumn and winter, Chl a variations depended on other factors such as the input of nutrients from land run-off. There was no clear seasonal trend in Chl a.

scholarly journals Variations of chlorophyll-a and particulate organic carbon in the Yellow-Bohai Sea: in response to the Typhoon Lekima event

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Xiaowen Wang ◽  
Xiujun Wang ◽  
Zai-Jin You
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Chlorophyll A ◽  
Yellow Sea ◽  
Bohai Sea ◽  
Sediment Resuspension ◽  
Chl A ◽  
Marginal Seas ◽  
Terrigenous Input ◽  
The North

AbstractTyphoon events have large impacts on marginal seas’ environmental conditions with implications for biological processes and carbon cycling. However, little is known about the responses of phytoplankton and particulate organic carbon (POC) to typhoon events in the Yellow-Bohai Sea (YBS). In this study, we utilized satellite-derived datasets of chlorophyll-a (Chl-a) and POC, together with key physical parameters, to analyze their responses to the Typhoon Lekima event induced heavy rainfall and strong winds. Overall, there were enhanced upwelling, strengthened currents, and increased terrestrial runoff during weakened Typhoon Lekima in the YBS. The basin-scale response of Chl-a showed large differences post the Typhoon Lekima event, with a decrease in the Bohai Sea (BS, 0.34 ± 3.0 mg m−3) but an increase in Yellow Sea (YS, 0.23 ± 1.7 mg m−3 in the south YS and 0.54 ± 0.8 mg m−3 in the north YS). The increase of Chl-a in the YS was attributed to increased nutrients, whereas the reduction of Chl-a in the BS was caused by dilution and water exchange with the North Yellow Sea. However, there was an overall increase in POC post-Typhoon Lekima in both BS and YS. The increase of POC in the majority of BS resulted largely from enhanced sediment resuspension and terrigenous input. The increase of POC in the nearshore waters of YS was attributable to enhanced biological production, sediment resuspension, and terrigenous input of POC, whereas the increase of POC in the central YS was partly due to transportation of high-POC waters from nearshore to offshore via strengthened current. Our study highlights the complex impacts of typhoon events on the carbon cycle in marginal seas.

Estimation of chlorophyll content by absorption spectra of native Spirulina platensis cells

2020 ◽  
pp. 25-33
Author(s):  
Leonid E. Paramonov
Keyword(s):  
Chlorophyll Content ◽  
Chlorophyll A ◽  
Absorption Spectra ◽  
Spirulina Platensis ◽  
Intracellular Concentration ◽  
Absorption Coefficients

A method for retrieving the absorption coefficients of Spirulina platensis pigments using absorption spectra of native cells and excluding the use of extracts is considered. Estimates of the intracellular concentration of chlorophyll a, С-phycoerythrin, С- phycocyanin and allophycocyanin in native cells are discussed.

Spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean

2018 ◽  
Vol 612 ◽  
pp. 1141-1148 ◽  
Author(s):  
Min Zhang ◽  
Yuanling Zhang ◽  
Qi Shu ◽  
Chang Zhao ◽  
Gang Wang ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Chlorophyll A ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Spatiotemporal Evolution ◽  
The North ◽  
The North Atlantic

scholarly journals Spatiotemporal Variability of Surface Phytoplankton Carbon and Carbon-to-Chlorophyll a Ratio in the South China Sea Based on Satellite Data

2020 ◽  
Vol 13 (1) ◽  
pp. 30
Author(s):  
Wenlong Xu ◽  
Guifen Wang ◽  
Long Jiang ◽  
Xuhua Cheng ◽  
Wen Zhou ◽  
...  
Keyword(s):  
South China Sea ◽  
Chlorophyll A ◽  
South China ◽  
Satellite Data ◽  
Phytoplankton Biomass ◽  
The South China Sea ◽  
Spatiotemporal Variability ◽  
The South ◽  
Chl A ◽  
China Sea

The spatiotemporal variability of phytoplankton biomass has been widely studied because of its importance in biogeochemical cycles. Chlorophyll a (Chl-a)—an essential pigment present in photoautotrophic organisms—is widely used as an indicator for oceanic phytoplankton biomass because it could be easily measured with calibrated optical sensors. However, the intracellular Chl-a content varies with light, nutrient levels, and temperature and could misrepresent phytoplankton biomass. In this study, we estimated the concentration of phytoplankton carbon—a more suitable indicator for phytoplankton biomass—using a regionally adjusted bio-optical algorithm with satellite data in the South China Sea (SCS). Phytoplankton carbon and the carbon-to-Chl-a ratio (θ) exhibited considerable variability spatially and seasonally. Generally, phytoplankton carbon in the northern SCS was higher than that in the western and central parts. The regional monthly mean phytoplankton carbon in the northern SCS showed a prominent peak during December and January. A similar pattern was shown in the central part of SCS, but its peak was weaker. Besides the winter peak, the western part of SCS had a secondary maximum of phytoplankton carbon during summer. θ exhibited significant seasonal variability in the northern SCS, but a relatively weak seasonal change in the western and central parts. θ had a peak in September and a trough in January in the northern and central parts of SCS, whereas in the western SCS the minimum and maximum θ was found in August and during October–April of the following year, respectively. Overall, θ ranged from 26.06 to 123.99 in the SCS, which implies that the carbon content could vary up to four times given a specific Chl-a value. The variations in θ were found to be related to changing phytoplankton community composition, as well as dynamic phytoplankton physiological activities in response to environmental influences; which also exhibit much spatial differences in the SCS. Our results imply that the spatiotemporal variability of θ should be considered, rather than simply used a single value when converting Chl-a to phytoplankton carbon biomass in the SCS, especially, when verifying the simulation results of biogeochemical models.

scholarly journals Detecting Climate Driven Changes in Chlorophyll-a in Deep Subalpine Lakes Using Long Term Satellite Data

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 866
Author(s):  
Gary Free ◽  
Mariano Bresciani ◽  
Monica Pinardi ◽  
Nicola Ghirardi ◽  
Giulia Luciani ◽  
...  
Keyword(s):  
Climate Change ◽  
Chlorophyll A ◽  
Nutrient Dynamics ◽  
Cascading Effects ◽  
The North ◽  
Subalpine Lakes ◽  
Winter Temperatures ◽  
Decadal Climate ◽  
The North Atlantic Oscillation ◽  
Traditional Pattern

Climate change has increased the temperature and altered the mixing regime of high-value lakes in the subalpine region of Northern Italy. Remote sensing of chlorophyll-a can help provide a time series to allow an assessment of the ecological implications of this. Non-parametric multiplicative regression (NPMR) was used to visualize and understand the changes that have occurred between 2003–2018 in Lakes Garda, Como, Iseo, and Maggiore. In all four deep subalpine lakes, there has been a disruption from a traditional pattern of a significant spring chlorophyll-a peak followed by a clear water phase and summer/autumn peaks. This was replaced after 2010–2012, with lower spring peaks and a tendency for annual maxima to occur in summer. There was a tendency for this switch to be interspersed by a two-year period of low chlorophyll-a. Variables that were significant in NPMR included time, air temperature, total phosphorus, winter temperature, and winter values for the North Atlantic Oscillation. The change from spring to summer chlorophyll-a maxima, relatively sudden in an ecological context, could be interpreted as a regime shift. The cause was probably cascading effects from increased winter temperatures, reduced winter mixing, and altered nutrient dynamics. Future trends will depend on climate change and inter-decadal climate drivers.

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