122,218 research outputs found
The Use of Sentinel-3 Imagery to Monitor Cyanobacterial Blooms
Cyanobacterial harmful algal blooms (CHABs) have been a concern for aquatic systems, especially those used for water supply and recreation. Thus, the monitoring of CHABs is essential for the establishment of water governance policies. Recently, remote sensing has been used as a tool to monitor CHABs worldwide. Remote monitoring of CHABs relies on the optical properties of pigments, especially the phycocyanin (PC) and chlorophyll-a (chl-a). The goal of this study is to evaluate the potential of recent launch the Ocean and Land Color Instrument (OLCI) on-board the Sentinel-3 satellite to identify PC and chl-a. To do this, OLCI images were collected over the Western part of Lake Erie (U.S.A.) during the summer of 2016, 2017, and 2018. When comparing the use of traditional remote sensing algorithms to estimate PC and chl-a, none was able to accurately estimate both pigments. However, when single and band ratios were used to estimate these pigments, stronger correlations were found. These results indicate that spectral band selection should be re-evaluated for the development of new algorithms for OLCI images. Overall, Sentinel 3/OLCI has the potential to be used to identify PC and chl-a. However, algorithm development is needed
Ultradeep Near-Infrared ISAAC Observations of the HDF-S: Observations, Reduction, Multicolor Catalog, and Photometric Redshifts
We present deep near-infrared (NIR) Js, H, and Ks-band ISAAC imaging of the
WFPC2 field of the HDF-S. The 2.5'x 2.5' high Galactic latitude field was
observed with the VLT under the best seeing conditions with integration times
amounting to 33.6 hours in Js, 32.3 hours in H, and 35.6 hours in Ks. We reach
total AB magnitudes for point sources of 26.8, 26.2, and 26.2 respectively (3
sigma), which make it the deepest ground-based NIR observations to date, and
the deepest Ks-band data in any field. The effective seeing of the coadded
images is ~0.45" in Js, ~0.48" in H, and ~0.46" in Ks. Using published WFPC2
optical data, we constructed a Ks-limited multicolor catalog containing 833
sources down to Ks,tot ~< 26 (AB), of which 624 have seven-band optical-to-NIR
photometry. These data allow us to select normal galaxies from their rest-frame
optical properties to high redshift (z ~< 4). The observations, data reduction
and properties of the final images are discussed, and we address the detection
and photometry procedures that were used in making the catalog. In addition, we
present deep number counts, color distributions and photometric redshifts of
the HDF-S galaxies. We find that our faint Ks-band number counts are flatter
than published counts in other deep fields, which might reflect cosmic
variations or different analysis techniques. Compared to the HDF-N, we find
many galaxies with very red V-H colors at photometric redshifts 1.95 < z < 3.5.
These galaxies are bright in Ks with infrared colors redder than Js-Ks > 2.3
(in Johnson magnitudes). Because they are extremely faint in the observed
optical, they would be missed by ultraviolet-optical selection techniques, such
as the U-dropout method.Comment: LaTeX, 24 pages, 15 figures, 3 tables. Accepted for publication in
the Astronomical Journal. The paper with full resolution images and figures
is available at http://www.strw.leidenuniv.nl/~fires/papers/2002Labbe.ps.gz .
The reduced data and catalogs can be found at
http://www.strw.leidenuniv.nl/~fires/data/hdfs
Photometry using the Infrared Array Camera on the Spitzer Space Telescope
We present several corrections for point source photometry to be applied to
data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope.
These corrections are necessary because of characteristics of the IRAC arrays
and optics and the way the instrument is calibrated in-flight. When these
corrections are applied, it is possible to achieve a ~2% relative photometric
accuracy for sources of adequate signal to noise in an IRAC image.Comment: 16 pages, 13 figures. Accepted for publication in the Publications of
the Astronomical Society of the Pacifi
The First Release COSMOS Optical and Near-IR Data and Catalog
We present imaging data and photometry for the COSMOS survey in 15
photometric bands between 0.3um and 2.4um. These include data taken on the
Subaru 8.3m telescope, the KPNO and CTIO 4m telescopes, and the CFHT 3.6m
telescope. Special techniques are used to ensure that the relative photometric
calibration is better than 1% across the field of view. The absolute
photometric accuracy from standard star measurements is found to be 6%. The
absolute calibration is corrected using galaxy spectra, providing colors
accurate to 2% or better. Stellar and galaxy colors and counts agree well with
the expected values. Finally, as the first step in the scientific analysis of
these data we construct panchromatic number counts which confirm that both the
geometry of the universe and the galaxy population are evolving.Comment: 19 pages, 13 figures, 14 tables, Accepted to ApJS for COSMOS speciall
issu
The alternating least squares technique for nonuniform intensity color correction
Color correction involves mapping device RGBs to display counterparts or to corresponding XYZs. A popular methodology is to take an image of a color chart and then solve for the best 3 × 3 matrix that maps the RGBs to the corresponding known XYZs. However, this approach fails at times when the intensity of the light varies across the chart. This variation needs to be removed before estimating the correction matrix. This is typically achieved by acquiring an image of a uniform gray chart in the same location, and then dividing the color checker image by the gray-chart image. Of course, taking images of two charts doubles the complexity of color correction. In this article, we present an alternative color correction algorithm that simultaneously estimates the intensity variation and the 3 × 3 transformation matrix from a single image of a color chart. We show that the color correction problem, that is, finding the 3 × 3 correction matrix, can be solved using a simple alternating least-squares procedure. Experiments validate our approach. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 232–242, 201
Ground-based astrometry with wide field imagers. V. Application to near-infrared detectors: HAWK-I@VLT/ESO
High-precision astrometry requires accurate point-spread function modeling
and accurate geometric-distortion corrections. This paper demonstrates that it
is possible to achieve both requirements with data collected at the high acuity
wide-field K-band imager (HAWK-I), a wide-field imager installed at the Nasmyth
focus of UT4/VLT ESO 8m telescope. Our final astrometric precision reaches ~3
mas per coordinate for a well-exposed star in a single image with a systematic
error less than 0.1 mas. We constructed calibrated astro-photometric catalogs
and atlases of seven fields: the Baade's Window, NGC 6656, NGC 6121, NGC 6822,
NGC 6388, NGC 104, and the James Webb Space Telescope calibration field in the
Large Magellanic Cloud. We make these catalogs and images electronically
available to the community. Furthermore, as a demonstration of the efficacy of
our approach, we combined archival material taken with the optical wide-field
imager at the MPI/ESO 2.2m with HAWK-I observations. We showed that we are able
to achieve an excellent separation between cluster members and field objects
for NGC 6656 and NGC 6121 with a time base-line of about 8 years. Using both
HST and HAWK-I data, we also study the radial distribution of the SGB
populations in NGC 6656 and conclude that the radial trend is flat within our
uncertainty. We also provide membership probabilities for most of the stars in
NGC 6656 and NGC 6121 catalogs and estimate membership for the published
variable stars in these two fields.Comment: 36 pages (included appendix), 13 tables, 35 figures (26 in low
resolution), accepted for publication in Astronomy and Astrophysics. Online
materials will be soon available on CDS. Meanwhile, online materials can be
requested directly to the first autho
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