61 research outputs found
Introduction to special section on Recent Advances in the Study of Optical Variability in the Near-Surface and Upper Ocean
Optical variability occurs in the near-surface and upper ocean on very short time and space scales (e.g., milliseconds and millimeters and less) as well as greater scales. This variability is caused by solar, meteorological, and other physical forcing as well as biological and chemical processes that affect optical properties and their distributions, which in turn control the propagation of light across the air-sea interface and within the upper ocean. Recent developments in several technologies and modeling capabilities have enabled the investigation of a variety of fundamental and applied problems related to upper ocean physics, chemistry, and light propagation and utilization in the dynamic near-surface ocean. The purpose here is to provide background for and an introduction to a collection of papers devoted to new technologies and observational results as well as model simulations, which are facilitating new insights into optical variability and light propagation in the ocean as they are affected by changing atmospheric and oceanic conditions
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CoastColour Round Robin data sets: a database to evaluate the performance of algorithms for the retrieval of water quality parameters in coastal waters
The use of in situ measurements is essential in the validation and evaluation of the algorithms that provide coastal water quality data products from ocean colour satellite remote sensing. Over the past decade, various types of ocean colour algorithms have been developed to deal with the optical complexity of coastal waters. Yet there is a lack of a comprehensive intercomparison due to the availability of quality checked in situ databases. The CoastColour Round Robin (CCRR) project, funded by the European Space Agency (ESA), was designed to bring together three reference data sets using these to test algorithms and to assess their accuracy for retrieving water quality parameters. This paper provides a detailed description of these reference data sets, which include the Medium Resolution Imaging Spectrometer (MERIS) level 2 match-ups, in situ reflectance measurements, and synthetic data generated by a radiative transfer model (HydroLight). These data sets, representing mainly coastal waters, are available from doi:10.1594/PANGAEA.841950.
The data sets mainly consist of 6484 marine reflectance (either multispectral or hyperspectral) associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: total suspended matter (TSM) and chlorophyll a (CHL) concentrations, and the absorption of coloured dissolved organic matter (CDOM). Inherent optical properties are also provided in the simulated data sets (5000 simulations) and from 3054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three data sets are compared. Match-up and in situ sites where deviations occur are identified. The distributions of the three reflectance data sets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications. The published article can be found at: http://www.earth-system-science-data.net
The evolution of metallicity and metallicity gradients from z = 2.7 to 0.6 with KMOS<sup>3D</sup>
We present measurements of the [NII]/Ha ratio as a probe of gas-phase oxygen
abundance for a sample of 419 star-forming galaxies at z=0.6-2.7 from the
KMOS3D near-IR multi-IFU survey. The mass-metallicity relation (MZR) is
determined consistently with the same sample selection, metallicity tracer, and
methodology over the wide redshift range probed by the survey. We find good
agreement with long-slit surveys in the literature, except for the low-mass
slope of the relation at z~2.3, where this sample is less biased than previous
samples based on optical spectroscopic redshifts. In this regime we measure a
steeper slope than some literature results. Excluding the AGN contribution from
the MZR reduces sensitivity at the high mass end, but produces otherwise
consistent results. There is no significant dependence of the [NII]/Ha ratio on
SFR or environment at fixed redshift and stellar mass. The IFU data allow
spatially resolved measurements of [NII]/Ha, from which we can infer abundance
gradients for 180 galaxies, thus tripling the current sample in the literature.
The observed gradients are on average flat, with only 15 gradients
statistically offset from zero at >3sigma. We have modelled the effect of
beam-smearing, assuming a smooth intrinsic radial gradient and known seeing,
inclination and effective radius for each galaxy. Our seeing-limited
observations can recover up to 70% of the intrinsic gradient for the largest,
face-on disks, but only 30% for the smaller, more inclined galaxies. We do not
find significant trends between observed or corrected gradients and any stellar
population, dynamical or structural galaxy parameters, mostly in agreement with
existing studies with much smaller sample sizes. In cosmological simulations,
strong feedback is generally required to produce flat gradients at high
redshift.Comment: submitted to Ap
A compilation of global bio-optical in situ data for ocean colour satellite applications – version three
A global in situ data set for validation of ocean colour products from the ESA Ocean Colour Climate
Change Initiative (OC-CCI) is presented. This version of the compilation, starting in 1997, now extends to
2021, which is important for the validation of the most recent satellite optical sensors such as Sentinel 3B
OLCI and NOAA-20 VIIRS. The data set comprises in situ observations of the following variables: spectral remote-sensing reflectance, concentration of chlorophyll-a, spectral inherent optical properties, spectral diffuse
attenuation coefficient, and total suspended matter. Data were obtained from multi-project archives acquired via
open internet services or from individual projects acquired directly from data providers. Methodologies were
implemented for homogenization, quality control, and merging of all data. Minimal changes were made on the
original data, other than conversion to a standard format, elimination of some points, after quality control and
averaging of observations that were close in time and space. The result is a merged table available in text format.
Overall, the size of the data set grew with 148 432 rows, with each row representing a unique station in space
and time (cf. 136 250 rows in previous version; Valente et al., 2019). Observations of remote-sensing reflectance
increased to 68 641 (cf. 59 781 in previous version; Valente et al., 2019). There was also a near tenfold increase
in chlorophyll data since 2016. Metadata of each in situ measurement (original source, cruise or experiment,
principal investigator) are included 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. The compiled data are available at
https://doi.org/10.1594/PANGAEA.941318 (Valente et al., 2022)
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