scholarly journals Interpretation of Spectral LiDAR Backscattering off the Florida Coast

2021 ◽  
Vol 13 (13) ◽  
pp. 2475
Author(s):  
Martin A. Montes ◽  
Anni K. Vuorenkoski ◽  
Ben Metzger ◽  
Brian Ramos
Keyword(s):  
Relative Size ◽  
Field Measurements ◽  
Size Composition ◽  
Spectral Slope ◽  
Dissimilarity Index ◽  
Attenuation Coefficients ◽  
Inherent Optical Properties ◽  
Multiple Collisions ◽  
Wave Glider ◽  
532 Nm

A multispectral backscattering LiDAR (Light detection and range) system (hereafter Oculus) was integrated into a wave glider and used to estimate the scattering order (i.e., single vs multiple collisions) of LIDAR backscattering, the water inherent optical properties (IOPs), the biogeo-chemical characteristics of particulate scatterers (i.e., relative size, composition) and their motion) on shelf waters of South East Florida. Oculus has a dual-wavelength configuration (473 and 532 nm) and two detection geometries (off- and on-axis). Characteristics of scatterers were investigated based on two complementary LiDAR-derived proxies (the Structural Dissimilarity Index and the spectral slope of LiDAR backscattering). In March 2017, field measurements showed a covariation between direct and diffuse backscattering contributions during morning hours and away from shore. LiDAR attenuation coefficients explained up to 57% of IOPs variability. The analysis of LiDAR-derived proxies suggested higher turbidity and larger particulates near the coast

scholarly journals Evaluation of Ocean Color Remote Sensing Algorithms for Diffuse Attenuation Coefficients and Optical Depths with Data Collected on BGC-Argo Floats

2020 ◽  
Vol 12 (15) ◽  
pp. 2367
Author(s):  
Xiaogang Xing ◽  
Emmanuel Boss ◽  
Jie Zhang ◽  
Fei Chai
Keyword(s):  
Sea Surface ◽  
Homogeneous Distribution ◽  
Photosynthetically Available Radiation ◽  
Layer Depth ◽  
Attenuation Coefficients ◽  
Argo Floats ◽  
Inherent Optical Properties ◽  
Good Consistency ◽  
The Vertical Distribution ◽  
Local Noon

The vertical distribution of irradiance in the ocean is a key input to quantify processes spanning from radiative warming, photosynthesis to photo-oxidation. Here we use a novel dataset of thousands local-noon downwelling irradiance at 490 nm (Ed(490)) and photosynthetically available radiation (PAR) profiles captured by 103 BGC-Argo floats spanning three years (from October 2012 to January 2016) in the world’s ocean, to evaluate several published algorithms and satellite products related to diffuse attenuation coefficient (Kd). Our results show: (1) MODIS-Aqua Kd(490) products derived from a blue-to-green algorithm and two semi-analytical algorithms show good consistency with the float-observed values, but the Chla-based one has overestimation in oligotrophic waters; (2) The Kd(PAR) model based on the Inherent Optical Properties (IOPs) performs well not only at sea-surface but also at depth, except for the oligotrophic waters where Kd(PAR) is underestimated below two penetration depth (2zpd), due to the model’s assumption of a homogeneous distribution of IOPs in the water column which is not true in most oligotrophic waters with deep chlorophyll-a maxima; (3) In addition, published algorithms for the 1% euphotic-layer depth and the depth of 0.415 mol photons m−2 d−1 isolume are evaluated. Algorithms based on Chla generally work well while IOPs-based ones exhibit an overestimation issue in stratified and oligotrophic waters, due to the underestimation of Kd(PAR) at depth.

The structure of plankton communities

1977 ◽  
Vol 280 (976) ◽  
pp. 485-534 ◽  
Keyword(s):  
Trophic Level ◽  
Size Structure ◽  
Food Limitation ◽  
Relative Size ◽  
Size Composition ◽  
Trophic Levels ◽  
Total Biomass ◽  
Size Dependent ◽  
First Feeding ◽  
Determining Modes

Interactions of herbivorous copepods with their phytoplankton food depend on the size composition of organisms in both trophic levels. A simulation model is used to analyse these size-dependent relations with the following conclusions. 1. Relative size structure of herbivores and their food is more important than total biomass of each trophic level in determining modes of transfer from plants to herbivores. In nearly all cases, in the model, food limitation affects reproduction or the first feeding stage of the nauplii. 2. No single factor emerges as predominant in determining the size structure of both populations. 3. The nature of predation on the herbivores is at least as important in determining both phytoplankton and herbivore size composition as physical or nutrient parameters. 4. The magnitude of the population of the larger herbivores such as Calanus , important as food for fish, depends on their coexistence with the smaller copepod species which control the smaller phytoplankton. 5. Stress on the system, if it affects adversely the smaller herbivores, can lead to the breakdown of the Calanus -diatom component. 6. Prediction of the population structure for both plants and herbivores may be a more attainable objective of theory and more practically important than prediction of total biomass at each trophic level.

Optical Closure: from Theory to Measurement

Ocean Optics ◽  
1994 ◽  
Author(s):  
J. Ronald V. Zaneveld
Keyword(s):  
Optical Properties ◽  
Light Field ◽  
Vertical Structure ◽  
Spectral Radiance ◽  
Major Influence ◽  
The Sun ◽  
Attenuation Coefficients ◽  
Inherent Optical Properties ◽  
Dissolved Matter ◽  
Beam Attenuation Coefficient

The intensity and spectrum of the light in the ocean have a major influence on the biological processes. These processes in turn determine the concentrations of much of the suspended and dissolved matter in the ocean, which affect the way in which the light is scattered and absorbed. These relationships can perhaps be most easily illustrated schematically as in Fig. 3-1. At the upper boundary we have the sun and sky radiances and the surface transmission conditions that combine to provide the energy entering through the surface. The ocean itself contains the vertical structure of those optical properties that do not depend on the structure of the light field, but depend only on the properties of the suspended and dissolved materials: the absorption coefficient a(λ,z), the beam attenuation coefficient c(λ,z), and the volume scattering function β(θ,λ,z). These are known as inherent optical properties, because they do not depend on the source radiance field (Preisendorfer, 1976). They are a function only of the suspended and dissolved materials in the water, and of the water itself. How does the vertical structure of the inherent optical properties affect the vertical structure of the radiance field in the ocean itself? This is the problem of radiative transfer in which we try to predict the intensity, direction, and spectrum of the light (spectral radiance) in the ocean, based on a set of given inherent optical properties. Those properties of the light field in the ocean that depend on the radiance are known as the apparent optical properties. Radiance field integrals, such as the vector irradiance, E(λ,z), the scalar irradiance E0(λ,z), and their attenuation coefficients are also apparent optical properties.

Debris flow interaction with structures: challenges to traditional load models

2020 ◽  
Author(s):  
Alessandro Leonardi ◽  
Andrea Pasqua ◽  
Marina Pirulli
Keyword(s):  
Debris Flow ◽  
Relative Size ◽  
Nonlinear Function ◽  
Field Measurements ◽  
Italian Alps ◽  
Load Model ◽  
Flow Energy ◽  
Load Models ◽  
Maintenance Work ◽  
Flow Through

<p>Debris flow barriers often feature one or more filter elements, i.e. narrow outlets that induce deposition of the coarsest sediments, while allowing water and fines to filter through. Slit dams and steel nets are examples of this type of barriers. The design of the filter elements must balance the need to trap boulders and to dissipate the flow energy, while keeping maintenance work as low as possible.</p><p>Filter barriers elude the traditional load model prescribed by guidelines. Under some conditions, the outlets can clog with large boulders. The time necessary for this to happen mainly depends on the relative size between boulder and outlet, and is a nonlinear function of the flow composition. In any case, the main clogging mechanism is the formation of granular arches. These can induce significant load also in directions different from the main direction of the incoming flow.</p><p>Unless the barrier is specifically designed to withstand this type of load, granular arches, but also prolonged flow through the outlet, can induce deterioration and loss of functionality of the structure. In this work, we estimate these effects employing a combination of discrete- and continuum-based numerical methods. We evaluate the performance of two types of debris-resisting barriers, comparing the results with laboratory measurements and with the outcome of a monitoring campaign on a real barrier located in the Italian alps.</p><p> </p><p> </p><p>References:</p><p>Leonardi, A., Goodwin, G. R., & Pirulli, M. (2019). The force exerted by granular flows on slit dams. Acta Geotechnica, 14(6), 1949–1963.</p><p>Leonardi, A., & Pirulli, M. (2020). Analysis of the load exerted by debris flows on filter barriers : Comparison between numerical results and field measurements. Computer & Geotechnics, 118, 103311.</p>

scholarly journals Dependence of spectral distribution of inherent optical properties of lake waters on the concentrations of different water constituents

2007 ◽  
Vol 38 (3) ◽  
pp. 265-285 ◽  
Author(s):  
Birgot Paavel ◽  
Helgi Arst ◽  
Antti Herlevi
Keyword(s):  
Organic Matter ◽  
Optical Properties ◽  
Dissolved Organic Matter ◽  
Optically Active ◽  
Total Absorption ◽  
Attenuation Coefficients ◽  
Inherent Optical Properties ◽  
Lake Waters ◽  
Active Substances ◽  
Optically Active Substances

The study focuses on the analysis of inherent optical properties of lake waters characterized by consisting of several optically active substances (OAS) (phytoplankton, suspended particles and dissolved organic matter). The results obtained can be useful for deriving the algorithms of optical remote sensing models which need the spectral data on inherent optical properties of the aquatic environment. The spectral absorption and attenuation coefficients were measured in situ using the instrument ac-9 for eight wavelengths in the range of 400–700 nm. The investigation sites were five Finnish and six Estonian lakes. The concentrations of chlorophyll a and total suspended particulate matter, as well as the absorption coefficient of coloured dissolved organic matter (at 380 nm) were determined in a laboratory from water samples taken concurrently with ac-9 measurements. There are three main objectives: (1) to calculate the values of absorption and specific absorption coefficients of tripton on the basis of ac-9 and laboratory data; (2) to estimate the contribution of pure water, chlorophyll a, dissolved organic matter and tripton to the total absorption and attenuation coefficients (results for ac-9 wavelengths and also for the PAR region, 400–700 nm); and (3) to determine the slope (and its variability) of the scattering coefficient spectrum for each measurement series and to estimate the reasons of this variability. At the wavelength of 532 nm the values of the specific absorption coefficient of tripton varied between 0.013 and 0.098 L mg−1 m−1, while the slope of its spectrum ranged from 0.0060 to 0.0109 nm−1. The contributions of different components of the aquatic medium to the total absorption/attenuation coefficients varied noticeably from lake to lake. The slope of the scattering coefficient spectrum was in the range of 0.32–2.5, the multiple regression between the slope and three main optically active substances jointly gave the determination coefficient R2(adjusted)=0.655.

scholarly journals A compilation of global bio-optical in situ data for ocean-colour satellite applications – version two

2019 ◽  
Author(s):  
André Valente ◽  
Shubha Sathyendranath ◽  
Vanda Brotas ◽  
Steve Groom ◽  
Michael Grant ◽  
...  
Keyword(s):  
Quality Control ◽  
Original Data ◽  
Ocean Colour ◽  
Attenuation Coefficients ◽  
Standard Format ◽  
Inherent Optical Properties ◽  
In Situ Data ◽  
Satellite Applications

Abstract. A global compilation of in situ data is useful to evaluate the quality of ocean-colour satellite data records. Here we describe the data compiled for the validation of the ocean-colour products from the ESA Ocean Colour Climate Change Initiative (OC-CCI). The data were acquired from several sources (including, inter alia, MOBY, BOUSSOLE, AERONET-OC, SeaBASS, NOMAD, MERMAID, AMT, ICES, HOT, GeP&CO) and span the period from 1997 to 2018. Observations of the following variables were compiled: spectral remote-sensing reflectances, concentrations of chlorophyll-a, spectral inherent optical properties, spectral diffuse attenuation coefficients and total suspended matter. The data were from multi-project archives acquired via open internet services or from individual projects, acquired directly from data providers. Methodologies were implemented for homogenisation, quality control and merging of all data. No changes were made to the original data, other than averaging of observations that were close in time and space, elimination of some points after quality control and conversion to a standard format. The final result is a merged table designed for validation of satellite-derived ocean-colour products and available in text format. Metadata of each in situ measurement (original source, cruise or experiment, principal investigator) were propagated throughout the work and made available in the final table. By making the metadata available, provenance is better documented, and it is also possible to analyse each set of data separately. This paper also describes the changes that were made to the compilation in relation to the previous version (Valente et al., 2016). The compiled data are available at https://doi.org/10.1594/PANGAEA.898188.

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