Search results for "WAVELENGTH"
showing 10 items of 741 documents
Surface temperature retrieval from Along Track Scanning Radiometer 2 data: Algorithms and validation
2004
[1] A study has been carried out using MODTRAN 3.5 simulations of the Along Track Scanning Radiometer 2 (ATSR-2) data at 3.7, 11, and 12 μm wavelengths to give a range of algorithms for estimating surface. Making use of the dual-angle feature of the ATSR-2, algorithms based on dual-angle, split-window, and mixed structure have been considered. The coefficients of the algorithms are derived by regression analysis using the MATLAB code. The evaluation of the sensitivity of each algorithm shows that in general, dual-angle algorithms provide smaller errors in the estimation of surface temperature than the split-window algorithms and that the algorithms with water vapor dependence give an improv…
Wavelength dependence of the effective cloud optical depth
2015
This study examines the wavelength dependence of cloud optical depth. To accomplish this task two different wavelength bands of the solar spectrum were considered in the cloud optical depth retrieval which was conducted in Valencia, Spain. The first retrieval used global irradiance measurements in the UVER range taken from a YES-UVB-1 radiometer in combination with multiple scattering model estimates; while the second retrieval was obtained in the Broadband range, with measurements of global solar surface irradiance from a CM6 pyranometer and a multiple scattering model. Whilst the dependence of the cloud optical depth (τ) on the wavelength is small, the best result was displayed by the SBD…
Optical properties of deep glacial ice at the South Pole
2006
We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ∼450 nm) varies by a fact…
Extreme, wintertime Saharan dust intrusion in the Iberian Peninsula: Lidar monitoring and evaluation of dust forecast models during the February 2017…
2019
The research leading to these results has received funding from the H2020 program from the European Union (grant agreement no. 654109, 778349) and also from the Spanish Ministry of Industry, Economy and Competitiviness (MINECO, ref. CGL2013-45410-R, CGL2016-81092-R, CGL2017-85344-R, TEC2015-63832-P), the Spanish Ministry of Science, Innovation and Universities (ref. CGL2017-90884-REDT); the CommSensLab "Maria de Maeztu" Unity of Excellence (ref. MDM-2016-0600) financed by the Spanish Agencia Estatal de Investigación. Co-funding was also provided by the European Union through the European Regional Development Fund (ref. POCI-01-0145-FEDER-007690, ALT20-03-0145-FEDER-000004, ALT20-03-0145-FED…
Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006
2009
During the Saharan Mineral Dust Experiment (SAMUM) conducted in summer 2006 in southeast Morocco, the complex refractive index of desert dust was determined from airborne measurements of particle size distributions and aerosol absorption coefficients at three different wavelengths in the blue (467 nm), green (530 nm) and red (660 nm) spectral regions. The vertical structure of the dust layers was analysed by an airborne high spectral resolution lidar (HSRL). The origin of the investigated dust layers was estimated from trajectory analyses, combined with Meteosat 2nd Generation (MSG) scenes and wind field data analyses. The real part n of the dust refractive index was found almost constant w…
A Precise Photometric Ratio via Laser Excitation of the Sodium Layer II: Two-photon Excitation Using Lasers Detuned from 589.16 nm and 819.71 nm Reso…
2020
This article is the second in a pair of articles on the topic of the generation of a two-color artificial star (which we term a "laser photometric ratio star," or LPRS) of de-excitation light from neutral sodium atoms in the mesosphere, for use in precision telescopic measurements in astronomy and atmospheric physics, and more specifically for the calibration of measurements of dark energy using type Ia supernovae. The two techniques respectively described in both this and the previous article would each generate an LPRS with a precisely 1:1 ratio of yellow (589/590 nm) photons to near-infrared (819/820 nm) photons produced in the mesosphere. Both techniques would provide novel mechanisms f…
Observation of a narrow inner-shell orbital transition in atomic erbium at 1299 nm
2021
We report on the observation and coherent excitation of atoms on the narrow inner-shell orbital transition, connecting the erbium ground state $[\mathrm{Xe}] 4f^{12} (^3\text{H}_6)6s^{2}$ to the excited state $[\mathrm{Xe}] 4f^{11}(^4\text{I}_{15/2})^05d (^5\text{D}_{3/2}) 6s^{2} (15/2,3/2)^0_7$. This transition corresponds to a wavelength of 1299 nm and is optically closed. We perform high-resolution spectroscopy to extract the $g_J$-factor of the $1299$-nm state and to determine the frequency shift for four bosonic isotopes. We further demonstrate coherent control of the atomic state and extract a lifetime of 178(19) ms which corresponds to a linewidth of 0.9(1) Hz. The experimental findi…
Influence of the filling factor on the spectral properties of plasmonic crystals
2006
Plasmonics crystals (PCs) comprised of finite-size triangular lattices of gold bumps deposited on a gold thin film are studied by means of a near-field optical microscope. The plasmonic crystals fabricated by electron-beam lithography are illuminated by an incident surface plasmon polariton excited in the Kretschmann-Raether configuration at the gold/air thin-film interface for incident free-space wavelengths in the range $740--820\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Based on the measurement of the surface plasmon polariton (SPP) damping distance in the crystals, the existence of a band gap for an incident SPP traveling along the two symmetry axes $\ensuremath{\Gamma}M$ and $\ensuremath…
Analysis of a microwave time delay line based on a perturbed uniform fiber Bragg grating operating at constant wavelength
2000
This paper presents the modeling of a new microwave time delay line based on a uniform fiber Bragg grating (FBG) with a section which period has been perturbed. The time delay can be modified by changing the position of the perturbation along the grating. Theoretical results are presented for a 5-cm long uniform grating and optical signal is modulated up to 18 GHz. Experimental setup used magnetic fields to change the period locally along the grating and a 330 ps maximum time delay is shown. Comparison between calculations and measurements show a perfect agreement. Such a delay line offers many advantages for beamforming applications in phased array antennas where the operation at a fixed w…
An optical water type framework for selecting and blending retrievals from bio-optical algorithms in lakes and coastal waters.
2014
Bio-optical models are based on relationships between the spectral remote sensing reflectance and optical properties of in-water constituents. The wavelength range where this information can be exploited changes depending on the water characteristics. In low chlorophyll-a waters, the blue/green region of the spectrum is more sensitive to changes in chlorophyll-a concentration, whereas the red/NIR region becomes more important in turbid and/or eutrophic waters. In this work we present an approach to manage the shift from blue/green ratios to red/NIR-based chlorophyll-a algorithms for optically complex waters. Based on a combined in situ data set of coastal and inland waters, measures of over…