99 research outputs found
INTRASEASONAL VARIABILITY OF GUANO STAINS IN A REMOTELY SENSED PENGUIN COLONY USING UAV AND SATELLITE
Remote sensing of penguins gives a unique opportunity to observe ecosystem changes in the Antarctic and the Southern Ocean at a continent-wide scale. The extent of guano is the best proxy to the size of penguin populations but frequent cloud cover limits the number of available images. This study focuses on the correlation between guano coverage visible in aerial and satellite images and breeding pair numbers in the course of the breeding seasons 2016/17 and 2017/18 in a colony of Pygocelid penguins on Ardley Island (South Shetland Islands, Antarctica). Multitemporal UAV (Unmanned Aerial Vehicle) orthomosaics and high-resolution satellite images were collected of Ardley Island as well as data on breeding phenology, weather conditions and snow coverage. “Fresh” guano stains were classified using different methods of Geographical Object-based Image Analysis (GEOBIA) and differentiated from weathered guano stains. Analysis of this data shows that guano stains in an Antarctic Pygoscelid penguin colony undergo significant intraseasonal changes in extent, texture and spectral signature. Hence, the timing of image acquisition and the advance of snow melt during Antarctic spring matter when determining penguin populations and should be considered during the analysis. Our results show changes of up to 25 % of the total guano covered surface due to individual weather events and changes up to 80 % in the time between the peak of egg laying and the occurrence of the first crèche
Radial stability of a family of anisotropic Hernquist models with and without a supermassive black hole
We present a method to investigate the radial stability of a spherical
anisotropic system that hosts a central supermassive black hole (SBH). Such
systems have never been tested before for stability, although high anisotropies
have been considered in the dynamical models that were used to estimate the
masses of the central putative supermassive black holes. A family of analytical
anisotropic spherical Hernquist models with and without a black hole were
investigated by means of N-body simulations. A clear trend emerges that the
supermassive black hole has a significant effect on the overall stability of
the system, i.e. an SBH with a mass of a few percent of the total mass of the
galaxy can prevent or reduce the bar instabilities in anisotropic systems. Its
mass not only determines the strength of the instability reduction, but also
the time in which this occurs. These effects are most significant for models
with strong radial anisotropies. Furthermore, our analysis shows that unstable
systems with similar SBH but with different anisotropy radii evolve
differently: highly radial systems become oblate, while more isotropic models
tend to form into prolate structures. In addition to this study, we also
present a Monte-Carlo algorithm to generate particles in spherical anisotropic
systems.Comment: 16 pages, 12 figures, accepted for publication in MNRAS (some figures
have a lowered resolution
A critical reassessment of particle Dark Matter limits from dwarf satellites
Dwarf satellite galaxies are ideal laboratories for identifying particle Dark Matter signals. When setting limits on particle Dark Matter properties from null searches, it becomes however crucial the level at which the Dark Matter density profile within these systems is constrained by observations. In the limit in which the spherical Jeans equation is assumed to be valid for a given tracer stellar population, we study the solution of this equation having the Dark Matter mass profile as an output rather than as a trial parametric input. Within our new formulation, we address to what level dwarf spheroidal galaxies feature a reliable mass estimator. We assess then possible extrapolation of the density profiles in the inner regions and -- keeping explicit the dependence on the orbital anisotropy profile of the tracer population -- we derive general trends on the line-of-sight integral of the density profile squared, a quantity commonly dubbed J-factor and crucial to estimate fluxes from prompt Dark Matter pair annihilations. Taking Ursa Minor as a study case among Milky Way satellites, we perform Bayesian inference using the available kinematical data for this galaxy. Contrary to all previous studies, we avoid marginalization over quantities poorly constrained by observations or by theoretical arguments. We find minimal J-factors to be about 2 to 4 times smaller than commonly quoted estimates, approximately relaxing by the same amount the limit on Dark Matter pair annihilation cross section from gamma-ray surveys of Ursa Minor. At the same time, if one goes back to a fixed trial parametric form for the density, e.g. using a NFW or Burkert profile, we show that the minimal J can hardly be reduced by more than a factor of 1.5. \ua9 2016 IOP Publishing Ltd and Sissa Medialab srl
Single-subunit oligosaccharyltransferases of <i>Trypanosoma brucei </i>display different and predictable peptide acceptor specificities
A lower bound on the mass of Dark Matter particles
We discuss the bounds on the mass of Dark Matter (DM) particles, coming from
the analysis of DM phase-space distribution in dwarf spheroidal galaxies
(dSphs). After reviewing the existing approaches, we choose two methods to
derive such a bound. The first one depends on the information about the current
phase space distribution of DM particles only, while the second one uses both
the initial and final distributions. We discuss the recent data on dSphs as
well as astronomical uncertainties in relevant parameters. As an application,
we present lower bounds on the mass of DM particles, coming from various dSphs,
using both methods. The model-independent bound holds for any type of fermionic
DM. Stronger, model-dependent bounds are quoted for several DM models (thermal
relics, non-resonantly and resonantly produced sterile neutrinos, etc.). The
latter bounds rely on the assumption that baryonic feedback cannot
significantly increase the maximum of a distribution function of DM particles.
For the scenario in which all the DM is made of sterile neutrinos produced via
non-resonant mixing with the active neutrinos (NRP) this gives m_nrp > 1.7 keV.
Combining these results in their most conservative form with the X-ray bounds
of DM decay lines, we conclude that the NRP scenario remains allowed in a very
narrow parameter window only. This conclusion is independent of the results of
the Lyman-alpha analysis. The DM model in which sterile neutrinos are
resonantly produced in the presence of lepton asymmetry remains viable. Within
the minimal neutrino extension of the Standard Model (the nuMSM), both mass and
the mixing angle of the DM sterile neutrino are bounded from above and below,
which suggests the possibility for its experimental search.Comment: 20 pages, published in JCA
CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z
MULTISEASONAL TREE CROWN STRUCTURE MAPPING WITH POINT CLOUDS FROM OTS QUADROCOPTER SYSTEMS
OTF (Off The Shelf) quadro copter systems provide a cost effective (below 2000 Euro), flexible and mobile platform for high
resolution point cloud mapping. Various studies showed the full potential of these small and flexible platforms. Especially in very
tight and complex 3D environments the automatic obstacle avoidance, low copter weight, long flight times and precise maneuvering
are important advantages of these small OTS systems in comparison with larger octocopter systems. This study examines the
potential of the DJI Phantom 4 pro series and the Phantom 3A series for within-stand and forest tree crown 3D point cloud mapping
using both within stand oblique imaging in different altitude levels and data captured from a nadir perspective. On a test site in
Brandenburg/Germany a beach crown was selected and measured with 3 different altitude levels in Point Of Interest (POI) mode
with oblique data capturing and deriving one nadir mosaic created with 85/85 % overlap using Drone Deploy automatic mapping
software. Three different flight campaigns were performed, one in September 2016 (leaf-on), one in March 2017 (leaf-off) and one in
May 2017 (leaf-on) to derive point clouds from different crown structure and phenological situations – covering the leaf-on and leafoff
status of the tree crown. After height correction, the point clouds where used with GPS geo referencing to calculate voxel based
densities on 50 × 10 × 10 cm voxel definitions using a topological network of chessboard image objects in 0,5 m height steps in an
object based image processing environment. Comparison between leaf-off and leaf-on status was done on volume pixel definitions
comparing the attributed point densities per volume and plotting the resulting values as a function of distance to the crown center.
In the leaf-off status SFM (structure from motion) algorithms clearly identified the central stem and also secondary branch systems.
While the penetration into the crown structure is limited in the leaf-on status (the point cloud is a mainly a description of the
interpolated crown surface) – the visibility of the internal crown structure in leaf-off status allows to map also the internal tree
structure up to and stopping at the secondary branch level system. When combined the leaf-on and leaf-off point clouds generate a
comprehensive tree crown structure description that allows a low cost and detailed 3D crown structure mapping and potentially
precise biomass mapping and/or internal structural differentiation of deciduous tree species types. Compared to TLS (Terrestrial
Laser Scanning) based measurements the costs are neglectable and in the range of 1500–2500 €. This suggests the approach for low
cost but fine scale in-situ applications and/or projects where TLS measurements cannot be derived and for less dense forest stands
where POI flights can be performed. This study used the in-copter GPS measurements for geo referencing. Better absolute geo
referencing results will be obtained with DGPS reference points. The study however clearly demonstrates the potential of OTS very
low cost copter systems and the image attributed GPS measurements of the copter for the automatic calculation of complex 3D point
clouds in a multi temporal tree crown mapping context
- …