Search results for "optical depth"

2021

Abstract. Sustainable aviation fuels can reduce contrail ice numbers and radiative forcing by contrail cirrus. We measured apparent ice emission indices for fuels with varying aromatic content at altitude ranges of 9.1–9.8 and 11.4–11.6 km. Measurement data were collected during the ECLIF II/NDMAX flight experiment in January 2018. The fuels varied in both aromatic quantity and type. Between a sustainable aviation fuel blend and a reference fuel Jet A-1, a maximum reduction in apparent ice emission indices of 40 % was found. We show vertical ice number and extinction distributions for three different fuels and calculate representative contrail optical depths. Optical depths of contrails (0.…

Remote sensing of vegetation dynamics in agro-ecosystems using smap vegetation optical depth and optical vegetation indices

2017

The ESA's SMOS and the NASA's SMAP missions, launched in 2009 and 2015, respectively, are the first two missions having on-board L-band microwave sensors, which are very sensitive to the water content in soils and vegetation. Focusing on the vegetation signal at L-band, we have implemented an inversion approach for SMAP that allows deriving vegetation optical depth (VOD, a microwave parameter related to biomass and plant water content) alongside soil moisture, without reliance on ancillary optical information on vegetation. This work aims at using this new observational data to monitor the phenology of crops in major global agro-ecosystems and enhance present agricultural monitoring and pre…

EARLINET observations of the 14-22-may long-range dust transport event during SAMUM 2006: validation of results from dust transport modelling

2009

We observed a long-range transport event of mineral dust from North Africa to South Europe during the Saharan Mineral Dust Experiment (SAMUM) 2006. Geometrical and optical properties of that dust plume were determined with Sun photometer of the Aerosol Robotic Network (AERONET) and Raman lidar near the North African source region, and with Sun photometers of AERONET and lidars of the European Aerosol Research Lidar Network (EARLINET) in the far field in Europe. Extinction-to-backscatter ratios of the dust plume over Morocco and Southern Europe do not differ. Ångstr¨om exponents increase with distance from Morocco. We simulated the transport, and geometrical and optical properties of the dus…

First evaluation of the simultaneous SMOS and ELBARA-II observations in the Mediterranean region

2012

Abstract The SMOS (Soil Moisture and Ocean Salinity) mission was launched on November 2, 2009. Over the land surfaces, simultaneous retrievals of surface soil moisture (SM) and vegetation characteristics made from the multi-angular and dual polarization SMOS observations are now available from Level-2 (L2) products delivered by the European Space Agency (ESA). Therefore, first analyses evaluating the SMOS observations in terms of Brightness Temperatures (TB) and L2 products (SM and vegetation optical depth TAU) can be carried out over several calibration/validation (cal/val) sites selected by ESA over all continents. This study is based on SMOS observations and in situ measurements carried …

Relationship between vegetation microwave optical depth and cross-polarized backscatter from multiyear Aquarius observations

2017

Soil moisture retrieval algorithms based on passive microwave remote sensing observations need to account for vegetation attenuation and emission, which is generally parameterized as vegetation optical depth (VOD). This multisensor study tests a new method to retrieve VOD from cross-polarized radar backscattering coefficients. Three years of Aquarius/SAC-D data were used to establish a relationship between the cross-polarized backscattering coefficient σ HV and VOD derived from a multitemporal passive dual-channel algorithm (VODMT). The dependence of the correspondence is analyzed for different land use classes. There are no systematic differences in the slope for woody versus nonwoody vege…

Fe K α and Fe K β line detection in the NuSTAR spectrum of the ultra-bright Z source Scorpius X-1

2021

Context.Low-mass X-ray binaries hosting a low-magnetised neutron star, which accretes matter via Roche-lobe overflow, are generally grouped into two classes called Atoll and Z sources after the path described in their X-ray colour-colour diagrams. Scorpius X–1 is the brightest persistent low-mass X-ray binary known so far, and it is the prototype of the Z sources.Aims.We analysed the firstNuSTARobservation of this source to study its spectral emission, exploiting the high-statistics data collected by this satellite. The colour-colour diagram shows that the source was probably observed during the lower normal and flaring branches of its Z track. We separated the data from the two branches in…

The Cosmological Evolution of Light Dark Photon Dark Matter

2020

Light dark photons are subject to various plasma effects, such as Debye screening and resonant oscillations, which can lead to a more complex cosmological evolution than is experienced by conventional cold dark matter candidates. Maintaining a consistent history of dark photon dark matter requires ensuring that the super-thermal abundance present in the early Universe $\textit{(i)}$ does not deviate significantly after the formation of the CMB, and $\textit{(ii)}$ does not excessively leak into the Standard Model plasma after BBN. We point out that the role of non-resonant absorption, which has previously been neglected in cosmological studies of this dark matter candidate, produces strong …

Was there an early reionization component in our universe?

2017

A deep understanding of the Epoch of Reionization is still missing in our knowledge of the universe. While future probes will allow us to test the precise evolution of the free electron fraction from redshifts between $z\simeq 6$ and $z\simeq 20$, at present one could ask what kind of reionization processes are allowed by present Cosmic Microwave Background temperature and polarization measurements. An early contribution to reionization could imply a departure from the standard picture where star formation determines the reionization onset. BBy considering a broad class of possible reionization parameterizations, we find that current data do not require an early reionization component in ou…

Comprehensive formulation of temperature-dependent dispersion of optical materials: illustration with case of temperature tuning of a mid-IR HgGa_2S_…

2009

The temperature dependence of refractive indices of optical materials is characterized in this work by what we call their normalized thermo-optic coefficients. These are determined experimentally through interferometric measurements of thermal expansion and of changes in optical thickness at a few laser wavelengths as function of temperature. A suitable vectorial formalism applied to these data allows predicting the thermal evolution of the refractive index all over the useful range of transparency. The validity and reliability of our methodology is demonstrated through temperature tuning of a mid-IR HgGa2S4 optical parametric oscillator (OPO) pumped at 1.0642 μm by a Nd:YAG laser. Measured…

Impact of Crystal Habit on Cirrus Radiative Properties

2007

The impact of assumed ice crystal morphology of subtropical cirrus on the solar and thermal infrared (IR) radiative field above, within, and below the cirrus is quantified. For this purpose airborne measurements of ice crystal size distribution from the CRYSTAL-FACE campaign and a library of optical properties of nonspherical ice crystal habits are implemented into radiative transfer simulations.Two cirrus cases are studied in detail: a high (cold) cirrus cloud with small visible optical thickness (τ≈1), and a lower (warmer) cirrus cloud of relatively large visible optical thickness (τ≈7). For t+he solar wavelength range the impact of shape characteristics of the crystals was important for …