Abstract
The observation of the polarised emission from the Cosmic Microwave Background (CMB) from
future ground-based and satellite-borne experiments holds the promise of indirectly detecting the
...elusive signal from primordial tensor fluctuations in the form of large-scale
B
-mode
polarisation. Doing so, however, requires an accurate and robust separation of the signal from
polarised Galactic foregrounds. We present a component separation method for multi-frequency CMB
observations that combines some of the advantages of map-based and power-spectrum-based
techniques, and which is direcly applicable to data in the presence of realistic foregrounds and
instrumental noise. We demonstrate that the method is able to reduce the contamination from
Galactic foregrounds below an equivalent tensor-to-scalar ratio
r
FG
≲ 5 × 10
-4
, as required for next-generation observatories, for a wide range of
foreground models with varying degrees of complexity. This bias reduction is associated with a
mild ∼20–30% increase in the final statistical uncertainties, and holds for large
sky areas, and for experiments targeting both the reionisation and recombination bumps in the
B
-mode power spectrum.
Tourists and hikers visiting glaciers all year round face hazards such as
sudden terminus collapses, typical of such a dynamically evolving
environment. In this study, we analyzed the potential of ...different survey
techniques to analyze hazards of the Forni Glacier, an important geosite
located in Stelvio Park (Italian Alps). We carried out surveys in the
2016 ablation season and compared point clouds generated from an unmanned aerial
vehicle (UAV) survey, close-range photogrammetry and terrestrial laser
scanning (TLS). To investigate the evolution of glacier hazards and evaluate
the glacier thinning rate, we also used UAV data collected in 2014 and a
digital elevation model (DEM) created from an aerial photogrammetric survey
of 2007. We found that the integration between terrestrial and UAV
photogrammetry is ideal for mapping hazards related to the glacier collapse,
while TLS is affected by occlusions and is logistically complex in glacial
terrain. Photogrammetric techniques can therefore replace TLS for glacier
studies and UAV-based DEMs hold potential for becoming a standard tool in
the investigation of glacier thickness changes. Based on our data sets, an
increase in the size of collapses was found over the study period, and the
glacier thinning rates went from 4.55 ± 0.24 m a−1 between 2007
and 2014 to 5.20 ± 1.11 m a−1 between 2014 and 2016.
The ongoing glacier shrinkage in the Alps requires frequent updates of
glacier outlines to provide an accurate database for monitoring, modelling
purposes (e.g. determination of run-off, mass ...balance, or future glacier
extent), and other applications. With the launch of the first Sentinel-2 (S2)
satellite in 2015, it became possible to create a consistent, Alpine-wide
glacier inventory with an unprecedented spatial resolution of 10 m. The first S2 images from August 2015 already provided excellent mapping conditions
for most glacierized regions in the Alps and were used as a base for the
compilation of a new Alpine-wide glacier inventory in a collaborative team
effort. In all countries, glacier outlines from the latest national
inventories have been used as a guide to compile an update consistent with
the respective previous interpretation. The automated mapping of clean
glacier ice was straightforward using the band ratio method, but the
numerous debris-covered glaciers required intense manual editing. Cloud
cover over many glaciers in Italy required also including S2 scenes from
2016. The outline uncertainty was determined with digitizing of 14
glaciers several times by all participants. Topographic information for all glaciers was
obtained from the ALOS AW3D30 digital elevation model (DEM). Overall, we derived a total glacier area
of 1806±60 km2 when considering 4395 glaciers >0.01 km2. This is 14 % (−1.2 % a−1) less than the 2100 km2 derived
from Landsat in 2003 and indicates an unabated continuation of glacier
shrinkage in the Alps since the mid-1980s. It is a lower-bound estimate, as
due to the higher spatial resolution of S2 many small glaciers were
additionally mapped or increased in size compared to 2003. Median
elevations peak around 3000 m a.s.l., with a high variability that depends on
location and aspect. The uncertainty assessment revealed locally strong
differences in interpretation of debris-covered glaciers, resulting in
limitations for change assessment when using glacier extents digitized by
different analysts. The inventory is available at https://doi.org/10.1594/PANGAEA.909133 (Paul et al., 2019).
In spite of the quite abundant literature focusing on fine debris deposition over glacier accumulation areas, less attention has been paid to the glacier melting surface. Accordingly, we proposed a ...novel method based on semi-automatic image analysis to estimate ice albedo from fine debris coverage (d). Our procedure was tested on the surface of a wide Alpine valley glacier (the Forni Glacier, Italy), in summer 2011, 2012 and 2013, acquiring parallel data sets of in situ measurements of ice albedo and high-resolution surface images. Analysis of 51 images yielded d values ranging from 0.01 to 0.63 and albedo was found to vary from 0.06 to 0.32. The estimated d values are in a linear relation with the natural logarithm of measured ice albedo (R = −0.84). The robustness of our approach in evaluating d was analyzed through five sensitivity tests, and we found that it is largely replicable. On the Forni Glacier, we also quantified a mean debris coverage rate (Cr) equal to 6 g m−2 per day during the ablation season of 2013, thus supporting previous studies that describe ongoing darkening phenomena at Alpine debris-free glaciers surface. In addition to debris coverage, we also considered the impact of water (both from melt and rainfall) as a factor that tunes albedo: meltwater occurs during the central hours of the day, decreasing the albedo due to its lower reflectivity; instead, rainfall causes a subsequent mean daily albedo increase slightly higher than 20 %, although it is short-lasting (from 1 to 4 days).
Abstract
LiteBIRD, the Lite (Light) satellite for the study of B-mode polarization and Inflation from cosmic background Radiation Detection, is a space mission for primordial cosmology and ...fundamental physics. The Japan Aerospace Exploration Agency (JAXA) selected LiteBIRD in May 2019 as a strategic large-class (L-class) mission, with an expected launch in the late 2020s using JAXA’s H3 rocket. LiteBIRD is planned to orbit the Sun–Earth Lagrangian point L2, where it will map the cosmic microwave background polarization over the entire sky for three years, with three telescopes in 15 frequency bands between 34 and 448 GHz, to achieve an unprecedented total sensitivity of $2.2\, \mu$K-arcmin, with a typical angular resolution of 0.5○ at 100 GHz. The primary scientific objective of LiteBIRD is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models. The measurements of LiteBIRD will also provide us with insight into the quantum nature of gravity and other new physics beyond the standard models of particle physics and cosmology. We provide an overview of the LiteBIRD project, including scientific objectives, mission and system requirements, operation concept, spacecraft and payload module design, expected scientific outcomes, potential design extensions, and synergies with other projects.
QUBIC I: Overview and science program Mousset, L.; Battistelli, E.S.; de Bernardis, P. ...
Journal of cosmology and astroparticle physics,
04/2022, Letnik:
2022, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
The Q & U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind of polarimeter optimized for the measurement of the B-mode polarization of the Cosmic Microwave Background (CMB), ...which is one of the major challenges of observational cosmology. The signal is expected to be of the order of a few tens of nK, prone to instrumental systematic effects and polluted by various astrophysical foregrounds which can only be controlled through multichroic observations. QUBIC is designed to address these observational issues with a novel approach that combines the advantages of interferometry in terms of control of instrumental systematic effects with those of bolometric detectors in terms of wide-band, background-limited sensitivity. The QUBIC synthesized beam has a frequency-dependent shape that results in the ability to produce maps of the CMB polarization in multiple sub-bands within the two physical bands of the instrument (150 and 220 GHz). These features make QUBIC complementary to other instruments and makes it particularly well suited to characterize and remove Galactic foreground contamination. In this article, first of a series of eight, we give an overview of the QUBIC instrument design, the main results of the calibration campaign, and present the scientific program of QUBIC including not only the measurement of primordial B-modes, but also the measurement of Galactic foregrounds.
We give forecasts for typical observations and measurements: with three years of integration on the sky and assuming perfect foreground removal as well as stable atmospheric conditions from our site in Argentina, our simulations show that we can achieve a statistical sensitivity to the effective tensor-to-scalar ratio (including primordial and foreground B-modes)
σ
(
r
)=0.015.
We present and compare 11 years of snow data (snow depth and
snow water equivalent, SWE) measured by an automatic weather station (AWS) and
corroborated by data from field campaigns on the Forni ...Glacier in Italy. The
aim of the analysis is to estimate the SWE of new snowfall and the annual SWE
peak based on the average density of the new snow at the site (corresponding
to the snowfall during the standard observation period of 24 h) and
automated snow depth measurements. The results indicate that the daily SR50
sonic ranger measurements and the available snow pit data can be used to estimate
the mean new snow density value at the site, with an error of
±6 kg m−3. Once the new snow density is known, the sonic ranger
makes it possible to derive SWE values with an RMSE of 45 mm water equivalent
(if compared with snow pillow measurements), which turns out to be about
8 % of the total SWE yearly average. Therefore, the methodology we
present is interesting for remote locations such as glaciers or high alpine
regions, as it makes it possible to estimate the total SWE using a relatively inexpensive, low-power, low-maintenance, and
reliable instrument such as the sonic ranger.
LiteBIRD is a planned JAXA-led cosmic microwave background (CMB)
B
-mode satellite experiment aiming for launch in the late 2020s, with a primary goal of detecting the imprint of primordial ...inflationary gravitational waves. Its current baseline focal-plane configuration includes 15 frequency bands between 40 and 402 GHz, fulfilling the mission requirements to detect the amplitude of gravitational waves with the total uncertainty on the tensor-to-scalar ratio,
δr
, down to
δr
< 0.001. A key aspect of this performance is accurate astrophysical component separation, and the ability to remove polarized thermal dust emission is particularly important. In this paper we note that the CMB frequency spectrum falls off nearly exponentially above 300 GHz relative to the thermal dust spectral energy distribution, and a relatively minor high frequency extension can therefore result in even lower uncertainties and better model reconstructions. Specifically, we compared the baseline design with five extended configurations, while varying the underlying dust modeling, in each of which the High-Frequency Telescope (HFT) frequency range was shifted logarithmically toward higher frequencies, with an upper cutoff ranging between 400 and 600 GHz. In each case, we measured the tensor-to-scalar ratio
r
uncertainty and bias using both parametric and minimum-variance component-separation algorithms. When the thermal dust sky model includes a spatially varying spectral index and temperature, we find that the statistical uncertainty on
r
after foreground cleaning may be reduced by as much as 30–50% by extending the upper limit of the frequency range from 400 to 600 GHz, with most of the improvement already gained at 500 GHz. We also note that a broader frequency range leads to higher residuals when fitting an incorrect dust model, but also it is easier to discriminate between models through higher
χ
2
sensitivity. Even in the case in which the fitting procedure does not correspond to the underlying dust model in the sky, and when the highest frequency data cannot be modeled with sufficient fidelity and must be excluded from the analysis, the uncertainty on
r
increases by only about 5% for a 500 GHz configuration compared to the baseline.
Abstract
Setting an upper limit or detection of B-mode polarization
imprinted by gravitational waves from Inflation is one goal of
modern large angular scale cosmic microwave background (CMB)
...experiments around the world. A great effort is being made in the
deployment of many ground-based, balloon-borne and satellite
experiments, using different methods to separate this faint
polarized component from the incoming radiation. QUBIC exploits one
of the most widely-used techniques to extract the input Stokes
parameters, consisting in a rotating half-wave plate (HWP) and a
linear polarizer to separate and modulate polarization
components. QUBIC uses a step-by-step rotating HWP, with 15°
steps, combined with a 0.4°s
-1
azimuth sky scan
speed. The rotation is driven by a stepper motor mounted on the
cryostat outer shell to avoid heat load at internal cryogenic
stages. The design of this optical element is an engineering
challenge due to its large 370 mm diameter and the
8 K operation temperature that are unique features of
the QUBIC experiment. We present the design for a modulator
mechanism for up to 370 mm, and the first optical
tests by using the prototype of QUBIC HWP (180 mm
diameter). The tests and results presented in this work show that
the QUBIC HWP rotator can achieve a precision of 0.15°
in position by using the stepper motor and custom-made optical
encoder. The rotation induces <5.0 mW (95% C.L) of
power load on the 4 K stage, resulting in no thermal
issues on this stage during measurements. We measure a temperature
settle-down characteristic time of 28 s after a rotation
through a 15° step, compatible with the scanning
strategy, and we estimate a maximum temperature gradient within the
HWP of ≤ 10 mK. This was calculated by setting
up finite element thermal simulations that include the temperature
profiles measured during the rotator operations. We report
polarization modulation measurements performed at
150 GHz, showing a polarization efficiency >99%
(68% C.L.) and a median cross-polarization χ
Pol
of 0.12%, with 71% of detectors showing a
χ
Pol
+ 2
σ
upper limit <1%, measured using
selected detectors that had the best signal-to-noise ratio.
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