43 research outputs found
Satellite-Derived Bathymetry Using Multiple Images: The Alaska North Slope Case Study
Currently, charting data in much of the U.S. Arctic North Slope is inadequate or nonexistent and most of its areas have not been updated since the early-1950s. Although the charting infrastructure is out of date, ship transportation (such as, fishing and transit between the towns) has increased. NOAA conducted a preliminary multibeam survey in 2013 that reached Point Barrow, AK. However, all the Arctic North Slope remained untouched. Previous studies have shown that satellite-derived bathymetry (SDB) is a useful reconnaissance tool in tropical and sub-tropical waters in clear water conditions, especially over sandy seafloor. However, it is very difficult to extract good information over the Arctic using a single satellite image, especially over the U.S. North Slope. The glacial powder from land reduces the water clarity that limits the light penetration depth. Also, this turbidity is not uniform along the coast line and may affect the calculations. In this paper, a new SDB approach was developed that compiles multiple satellite images to extract only areas that were identified clear by comparison (i.e., minimum water clarity change between two satellite images). Preliminary results using Landsat 7 imagery from 1999-2002 and Landsat 8 imagery from 2013 are presented
Monitoring Near-Shore Bathymetry Using a Multi-Image Satellite-Derived Bathymetry Approach
ABSTRACT Two advanced survey systems for hydrographic surveying are multi-beam echsounder (MBES) and airborne lidar bathymetry (ALB). Compared to more traditional hydrographic surveying methods, these systems provide both highly accurate and a dense coverage of depth measurements. However, high cost and logistic challenges that are required for either type of hydrographic survey operation limit the number of surveys and coverage area that can be conducted. As a result, most survey efforts primarily focus on updating existing chart information, and do not provide more enhanced charting capabilities, such as identifying dynamic seafloor areas or monitoring changes due to natural disasters (e.g., hurricanes, floods, or tsunamis) along the charted coastlines. An alternative reconnaissance approach is the use of Satellite Derived Bathymetry (SDB). Although SDB provide bathymetry products at a coarser spatial resolution compared to MBES or ALB, satellite imagery can be repeatedly collected over the same area. In addition, some of the multi-spectral satellite imagery is publically-available, and at low at no cost. In this paper, we describe a practical approach that is based on a multitemporal analysis of the SDB using Landsat 8 imagery. The study results presented here are based on a time series of two sites (Barnegat Bay Inlet, NJ and Nantucket Sound, MA). Preliminary results indicate that it is possible to identify both stable and dynamic seafloor areas that have implications for charting and coastal zone management application
Noncommutative vector bundles over fuzzy CP^N and their covariant derivatives
We generalise the construction of fuzzy CP^N in a manner that allows us to
access all noncommutative equivariant complex vector bundles over this space.
We give a simplified construction of polarization tensors on S^2 that
generalizes to complex projective space, identify Laplacians and natural
noncommutative covariant derivative operators that map between the modules that
describe noncommuative sections. In the process we find a natural
generalization of the Schwinger-Jordan construction to su(n) and identify
composite oscillators that obey a Heisenberg algebra on an appropriate Fock
space.Comment: 34 pages, v2 contains minor corrections to the published versio
The Extragalactic Distance Scale without Cepheids IV
The Cepheid period-luminosity relation is the primary distance indicator used
in most determinations of the Hubble constant. The tip of the red giant branch
(TRGB) is an alternative basis. Using the new ANU SkyMapper Telescope, we
calibrate the Tully Fisher relation in the I band. We find that the TRGB and
Cepheid distance scales are consistent.Comment: ApJ in press 201
The On-Orbit Performance of the Galaxy Evolution Explorer
We report the first year on-orbit performance results for the Galaxy
Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey
of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter
modified Ritchey-Chretien telescope with a 1.25 degree field of view,
selectable imaging and objective grism spectroscopic modes, and an innovative
optical system with a thin-film multilayer dichroic beam splitter that enables
simultaneous imaging by a pair of photon counting, microchannel plate, delay
line readout detectors. Initial measurements demonstrate that GALEX is
performing well, meeting its requirements for resolution, efficiency,
astrometry, bandpass definition and survey sensitivity.Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issu
Matrix Models on the Fuzzy Sphere and their Continuum Limits
We demonstrate that the UV/IR mixing problems found recently for a scalar
theory on the fuzzy sphere are localized to tadpole diagrams and can
be overcome by a suitable modification of the action. This modification is
equivalent to normal ordering the vertex. In the limit of the
commutative sphere, the perturbation theory of this modified action matches
that of the commutative theory.Comment: 19 pages of LaTeX, with 3 figure
SN 2005bf: A possible transition event between type Ib/c supernovae and gamma-ray bursts
We present u′g′r′i′BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ∼100 days following discovery. The u′g′BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 × 1042 ergs s -1 at maximum light and a total of 2.1 × 1049 ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u′g′BV was accompanied by the presence in the spectrum of high-velocity (>14,000 km s-1) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s-1, which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 × 1051 ergs), asymmetric explosion of a massive (8.3 M⊙) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of (1) a polar explosion containing a small fraction of the total mass and moving at high velocity and (2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and γ-ray bursts.Facultad de Ciencias Astronómicas y Geofísica
SN 2005bf: A Possible Transition Event Between Type Ib/c Supernovae and Gamma Ray Bursts
We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic
SN 2005bf covering the first ~100 days following discovery. The u'g'BV light
curves displayed a double-peaked morphology, which is among Type Ib/Ic
supernovae. The bolometric light curve indicates that SN 2005bf was a
remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique
transformation from a Type Ic-like event at early times to a typical Type Ib
supernova at later phases. The initial maximum in u'g'BV was accompanied by the
presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and
H I. The photospheric velocity derived from spectra at early epochs was
unusually low compared with ordinary Type Ib supernovae. We describe
one-dimensional computer simulations which attempt to account for these
remarkable properties. The most favored model is that of a very energetic (2 x
10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star
that had lost most of its hydrogen envelope. We speculate that an unobserved
relativistic jet was launched producing a two-component explosion consisting of
1) a polar explosion containing a small fraction of the total mass and moving
at high velocity, and 2) the explosion of the rest of the star. At first, only
the polar explosion is observed, producing the initial maximum and the high
velocity absorption-line spectrum resembling a Type Ic event. At late times,
this fast-moving component becomes optically-thin, revealing the slower-moving
explosion of the rest of the star and transforming the observed spectrum to
that of a typical Type Ib supernova. If this scenario is correct, then SN
2005bf is the best example to date of a transition object between normal Type
Ib/Ic supernovae and gamma ray bursts.Comment: Accepted ApJ on 15 December 2005, 37 pages, 11 figures; minor changes
after refereeing proces
SN 2005bf: A possible transition event between type Ib/c supernovae and gamma-ray bursts
We present u′g′r′i′BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ∼100 days following discovery. The u′g′BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 × 1042 ergs s -1 at maximum light and a total of 2.1 × 1049 ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u′g′BV was accompanied by the presence in the spectrum of high-velocity (>14,000 km s-1) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s-1, which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 × 1051 ergs), asymmetric explosion of a massive (8.3 M⊙) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of (1) a polar explosion containing a small fraction of the total mass and moving at high velocity and (2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and γ-ray bursts.Facultad de Ciencias Astronómicas y Geofísica