scholarly journals Retrieval of Particulate Backscattering Using Field and Satellite Radiometry: Assessment of the QAA Algorithm

2019 ◽  
Vol 12 (1) ◽  
pp. 77 ◽  
Author(s):  
Jaime Pitarch ◽  
Marco Bellacicco ◽  
Emanuele Organelli ◽  
Gianluca Volpe ◽  
Simone Colella ◽  
...  
Keyword(s):  
Raman Scattering ◽  
High Efficiency ◽  
Random Noise ◽  
Environmental Parameters ◽  
In Situ Data ◽  
Color Data ◽  
Oceanic Carbon ◽  
Crucial Parameter ◽  
Good Agreement

Particulate optical backscattering (bbp) is a crucial parameter for the study of ocean biology and oceanic carbon estimations. In this work, bbp retrieval, by the quasi-analytical algorithm (QAA), is assessed using a large in situ database of matched bbp and remote-sensing reflectance (Rrs). The QAA is also applied to satellite Rrs (ESA OC-CCI project) as well, after their validation against in situ Rrs. Additionally, the effect of Raman Scattering on QAA retrievals is studied. Results show negligible biases above random noise when QAA-derived bbp is compared to in situ bbp. In addition, Rrs from the CCI archive shows good agreement with in situ data. The QAA’s functional form of spectral backscattering slope, as derived from in situ radiometry, is validated. Finally, we show the importance of correcting for Raman Scattering over clear waters prior to semi-analytical retrieval. Overall, this work demonstrates the high efficiency of QAA in the bbp detection in case of both in situ and ocean color data, but it also highlights the necessity to increase the number of observations that are severely under-sampled in respect to others environmental parameters.

scholarly journals Tracer Stirring around a Meddy: The Formation of Layering

2015 ◽  
Vol 45 (2) ◽  
pp. 407-423 ◽  
Author(s):  
Thomas Meunier ◽  
Claire Ménesguen ◽  
Richard Schopp ◽  
Sylvie Le Gentil
Keyword(s):  
Vortex Core ◽  
Azimuthal Velocity ◽  
Thin Layers ◽  
Vertical Shear ◽  
In Situ Data ◽  
Simple Scaling ◽  
Diffusive Processes ◽  
Tracer Experiments ◽  
Good Agreement

AbstractThe dynamics of the formation of layering surrounding meddy-like vortex lenses is investigated using primitive equation (PE), quasigeostrophic (QG), and tracer advection models. Recent in situ data inside a meddy confirmed the formation of highly density-compensated layers in temperature and salinity at the periphery of the vortex core. Very high-resolution PE modeling of an idealized meddy showed the formation of realistic layers even in the absence of double-diffusive processes. The strong density compensation observed in the PE model, in good agreement with in situ data, suggests that stirring might be a leading process in the generation of layering. Passive tracer experiments confirmed that the vertical variance cascade in the periphery of the vortex core is triggered by the vertical shear of the azimuthal velocity, resulting in the generation of thin layers. The time evolution of this process down to scales of O(10) m is quantified, and a simple scaling is proposed and shown to describe precisely the thinning down of the layers as a function of the initial tracer column’s horizontal width and the vertical shear of the azimuthal velocity. Nonlinear QG simulations were performed and analyzed for comparison with the work of Hua et al. A step-by-step interpretation of these results on the evolution of layering is proposed in the context of tracer stirring.

CAUSAL FREQUENCY-LINEAR ATTENUATION ALGORITHM FOR TIME DOMAIN PROBLEMS

2009 ◽  
Vol 17 (04) ◽  
pp. 357-364
Author(s):  
B. EDWARD MCDONALD
Keyword(s):  
Wave Propagation ◽  
Time Domain ◽  
Fourier Transforms ◽  
Phase Speed ◽  
Sandy Sediment ◽  
Acoustic Wave Propagation ◽  
In Situ Data ◽  
Ocean Sediment ◽  
Good Agreement

Attenuation which is linear in frequency (as opposed to quadratic as for laminar viscosity) occurs in porous media wave propagation and biomedical applications. Straightforward use of Fourier transforms for frequency-linear attenuation violates causality. We give a causal time domain algorithm with numerical stability criteria and verify its accuracy. For acoustic wave propagation in ocean sediment, the algorithm results in a mild increase of phase speed with frequency as a result of the Kramers–Kronig relation. The algorithm gives results in good agreement with in situ data for sandy sediment.

scholarly journals A method for monitoring hydrological conditions beneath herbaceous wetlands using multi-temporal ALOS PALSAR coherence data

2015 ◽  
Vol XL-7/W4 ◽  
pp. 221-226 ◽  
Author(s):  
M. Zhang ◽  
Z. Li ◽  
B. Tian ◽  
J. Zhou ◽  
J. Zeng
Keyword(s):  
Effective Area ◽  
Interferometric Synthetic Aperture Radar ◽  
Alos Palsar ◽  
Hydrological Conditions ◽  
In Situ Data ◽  
Key Indicator ◽  
Multi Temporal ◽  
First Time ◽  
Good Agreement

Reed marshes, the world’s most widespread type of wetland vegetation, are undergoing major changes as a result of climate changes and human activities. The presence or absence of water in reed marshes has a significant impact on the whole ecosystem and remains a key indicator to identify the effective area of a wetland and help estimate the degree of degeneration. Past studies have demonstrated the use of interferometric synthetic aperture radar (InSAR) to map water-level changes for flooded reeds. However, the identification of the different hydrological states of reed marshes is often poorly understood. The analysis given in this paper shows that L-band interferometric coherence is very sensitive to the water surface conditions beneath reed marshes and so can be used as classifier. A method based on a statistical analysis of the coherence distributions for wet and dry reeds using InSAR pairs was, therefore, investigated in this study. The experimental results were validated by in-situ data and showed very good agreement. This is the first time that information about the water cover under herbaceous wetlands has been derived using interferometric coherence values. This method can also effectively and easily be applied to monitor the hydrological conditions beneath other herbaceous wetlands.

scholarly journals Intercomparison of polar ozone profiles by IASI/MetOp sounder with 2010 Concordiasi ozonesonde observations

2013 ◽  
Vol 6 (3) ◽  
pp. 613-620 ◽  
Author(s):  
J. Gazeaux ◽  
C. Clerbaux ◽  
M. George ◽  
J. Hadji-Lazaro ◽  
J. Kuttippurath ◽  
...  
Keyword(s):  
Positive Bias ◽  
Satellite Measurements ◽  
Recovery Processes ◽  
In Situ Data ◽  
Vertical Range ◽  
Polar Orbiting Satellite ◽  
Polar Ozone ◽  
Good Agreement

Abstract. Validation of ozone profiles measured from a nadir looking satellite instrument over Antarctica is a challenging task due to differences in their vertical sensitivity with ozonesonde measurements. In this paper, ozone observations provided by the Infrared Atmospheric Sounding Interferometer (IASI) instrument onboard the polar-orbiting satellite MetOp are compared with ozone profiles collected between August and October 2010 at McMurdo Station, Antarctica, during the Concordiasi measurement campaign. The main objective of the campaign was the satellite data validation. With this aim 20 zero-pressure sounding balloons carrying ozonesondes were launched during this period when the MetOp satellite was passing above McMurdo. This makes the dataset relevant for comparison, especially because the balloons covered the entire altitude range of IASI profiles. The validation methodology and the collocation criteria vary according to the availability of global positioning system auxiliary data with each electro-chemical cell ozonesonde observation. The relative mean difference is shown to depend on the vertical range investigated. The analysis shows a good agreement in the troposphere (below 10 km) and middle stratosphere (25–40 km), where the differences are lower than 10%. However a significant positive bias of about 10–26% is estimated in the lower stratosphere at 10–25 km, depending on altitude. The positive bias in the 10–25 km range is consistent with previously reported studies comparing in situ data with thermal infrared satellite measurements. This study allows for a better characterization of IASI-retrieved ozone over the polar region during ozone depletion/recovery processes.

scholarly journals Comparisons of Satellite and Modeled Surface Temperature and Chlorophyll Concentrations in the Baltic Sea with In Situ Data

2021 ◽  
Vol 13 (15) ◽  
pp. 3049
Author(s):  
Malgorzata Stramska ◽  
Marta Konik ◽  
Paulina Aniskiewicz ◽  
Jaromir Jakacki ◽  
Miroslaw Darecki
Keyword(s):  
Baltic Sea ◽  
Satellite Data ◽  
In Situ Measurements ◽  
Data Sets ◽  
The Baltic Sea ◽  
Data Set ◽  
In Situ Data ◽  
The Baltic ◽  
Good Agreement

Among the most frequently used satellite data are surface chlorophyll concentration (Chl) and temperature (SST). These data can be degraded in some coastal areas, for example, in the Baltic Sea. Other popular sources of data are reanalysis models. Before satellite or model data can be used effectively, they should be extensively compared with in situ measurements. Herein, we present results of such comparisons. We used SST and Chl from model reanalysis and satellites, and in situ data measured at eight open Baltic Sea stations. The data cover time interval from 1 January 1998 to 31 December 2019, but some satellite data were not always available. Both the model and the satellite SST data had good agreement with in situ measurements. In contrast, satellite and model estimates of Chl concentrations presented large errors. Modeled Chl presented the lowest bias and the best correlation with in situ data from all Chl data sets evaluated. Chl estimates from a regionally tuned algorithm (SatBaltic) had smaller errors in comparison with other satellite data sets and good agreement with in situ data in summer. Statistics were not as good for the full data set. High uncertainties found in chlorophyll satellite algorithms for the Baltic Sea highlight the importance of continuous regional validation of such algorithms with in situ data.

scholarly journals Retracking Cryosat-2 Data in SARIn and LRM Modes for Plateau Lakes: A Case Study for Tibetan and Dianchi Lakes

2021 ◽  
Vol 13 (6) ◽  
pp. 1078
Author(s):  
Xiaoli Deng ◽  
Ren-Bin Wang ◽  
Fukai Peng ◽  
Yong Yang ◽  
Nan-Ming Mo
Keyword(s):  
Time Series ◽  
Lake Level ◽  
Correlation Coefficients ◽  
Dianchi Lake ◽  
The Tibetan Plateau ◽  
In Situ Data ◽  
Data Editing ◽  
Good Agreement

This paper estimates lake level variations over two small and adjacent lakes in the Tibetan plateau (TP), namely Gemang Co and Zhangnai Co, as well as the inland Dianchi Lake in China using CryoSat-2 SARIn-mode and LRM 20-Hz waveforms over the period of 2011–2018. Different retrackers and a dedicated data editing procedure have been used to process CryoSat-2 data for determining the lake level time series. The lake level estimations are indirectly validated against those from Jason-2 in TP and from in situ data in Dianchi Lake, both showing good agreement with strong correlation coefficients >0.74. The results of this paper suggest that the official ICE retracker for LRM data and APD-PPT retracker for SARIn-mode waveforms are the most appropriate retrackers over Dianchi Lake and TP lakes, respectively. The trend estimates of the time series derived by both retrackers are 61.0 ± 10.8 mm/yr for Gemang Co and Zhangnai Co in TP, and 30.9 ± 64.9 mm/yr for Dianchi Lake, indicating that the lake levels over three lakes were continuously rising over the study period. The results of this study show that CryoSat-2 SARIn-mode data can be used for monitoring many small lakes that have not been measured by other altimetry missions in TP.

scholarly journals DFT-based calculations of silicon complex structures in the KF-KCl-K2SiF6 and KF-KCl-K2SiF6-SiO2 melts

2019 ◽  
Vol 84 (10) ◽  
pp. 1129-1142 ◽  
Author(s):  
Alexey Vorob’ev ◽  
Andrey Isakov ◽  
Alexander Galashev ◽  
Yuri Zaikov
Keyword(s):  
First Principles ◽  
Potassium Ions ◽  
Complex Structures ◽  
Bond Lengths ◽  
Temperature Range ◽  
In Situ Data ◽  
The Stability ◽  
Complex Anions ◽  
Good Agreement

The length and energy of bonds in the complex anions of silicon formed in KF?KCl?K2SiF6 and KF?KCl?K2SiF6?SiO2 melts were evaluated using the method of first-principles molecular dynamics, accomplished by means of the Siesta program. The effect of K+ (from the second coordination sphere) on the stability of these complexes was studied. The bond lengths in the silicon complexes was found to change with increasing amount of the potassium ions. It was established that the following complexes [SiO4]4-, [SiO3F]3- and [SiF6]2- are the most stable in KF?KCl?K2SiF6 and KF?KCl? ?K2SiF6?SiO2 melts. The [SiO4]4- and [SiF6]2- complexes are thermally stable in the molten salt in the temperature range of 923?1073 K, whereas the [SiF7]3- structure, which is typical for the lattice of crystalline K3SiF7, is unstable in this temperature range. In the KF?KCl?K2SiF6?SiO2 melts, conditions above 1043 K were created allowing the transformation of [Si?3F]3- into [SiO4]4-. Within the studied temperature mode, the Si?F bond length is in the range 1.5? ?1.9 ? and the Si?O bond lengths is 1.5?1.7 ?. The obtained results are in a good agreement with in situ data of Raman spectroscopy for the KF?KCl?K2SiF6 and KF?KCl?K2SiF6?SiO2 melts.

scholarly journals BIODIVERSITY OF MARINE TUNICATES IN SAMALONA WATERS, SANGKARANG ARCHIPELAGO, INDONESIA

2018 ◽  
Vol 4 (1) ◽  
Author(s):  
Magdalena Litaay ◽  
Slamet Santosa ◽  
Eva Johannes ◽  
Rosana Agus ◽  
Willem Moka ◽  
...  
Keyword(s):  
Species Diversity ◽  
Dominant Species ◽  
Good Condition ◽  
Environmental Parameters ◽  
Marine Resources ◽  
Line Transect ◽  
Sample Collection ◽  
Ecological Analysis ◽  
In Situ Data

The study aims to know the biodiversity and community structure of marine tunicate in Samalona waters. The present study is part of biodiversity assessment for marine resources of Sangkarang Archipelago SW Makassar Indonesia. Field campaign was conducted from October to November 2016. Sample collection was done at 3 and 7 m depth by using Line Intersection Transect (LIT) method combined with a quadrat (plot). Two 50 m transects were placed parallel to a shore line at three stations (sta.) at Samalona waters. A quadrat (plot) (2.5 m x 2.5 m) was placed side by side of the line transect and all tunicates in the transect was recorded, identified, counted and photographed. Samples were collected by using SCUBA and under water camera. Environmental parameters including water temperatue, salinity, dissolved oxygen, clarity, current and wind speed, were measured in situ. Data were analysed using ecological indices including species composition and density, Shanon Wienner species diversity, Evenness, and Morisita Indices. The result indicates that there are 18 species of tunicates present at 3 m as well as 7 m depth of Samalona waters.. Result of the ecological analysis shows that species diversity can be categorized as moderate and there were no dominant species. Environmental parameters indicates that water quality at Samalona waters was in good condition to support tunicates.

scholarly journals In situ autonomous optical radiometry measurements for satellite ocean color validation in the Western Black Sea

2014 ◽  
Vol 11 (6) ◽  
pp. 3003-3034 ◽  
Author(s):  
G. Zibordi ◽  
F. Mélin ◽  
J.-F. Berthon ◽  
M. Talone
Keyword(s):  
Black Sea ◽  
Ocean Color ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
In Situ Data ◽  
Infrared Imager ◽  
Color Data ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Satellite Ocean Color

Abstract. The accuracy of primary satellite ocean color data products from the Moderate Resolution Imaging Spectroradiometer on-board Aqua (MODIS-A) and the Visible/Infrared Imager/Radiometer Suite (VIIRS), is investigated in the Western Black Sea using in situ measurements from the Gloria site included in the Ocean Color component of the Aerosol Robotic Network (AERONET-OC). The analysis is also extended to an additional well-established AERONET-OC site in the northern Adriatic Sea characterized by optically complex coastal waters exhibiting similarities with those observed at the Gloria site. Results from the comparison of normalized-water leaving radiance LWN indicate biases of a few percent between satellite derived and in situ data at the center-wavelengths relevant for the determination of chlorophyll a concentration (443–547 nm, or equivalent). Remarkable is the consistency among the annual cycle determined with time series of satellite-derived and in situ LWN ratios at these center-wavelengths. Contrarily, the differences between in situ and satellite-derived LWN are pronounced at the blue (i.e., 412 nm) and red (i.e., 667 nm, or equivalent) center-wavelengths, suggesting difficulties in confidently applying satellite-derived radiometric data from these spectral regions for quantitative analysis in optically complex waters.

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