High Spectral Resolution Measurements Research Articles

High-resolution spectroscopy using a frequency magnifier

We experimentally demonstrate a spectral magnifier using an imaging system with two time-lenses based on four-wave mixing in a Si nanowaveguide. We achieve a magnification factor of 105 with a frequency resolution of 1 GHz. The system offers potential as a tool for single-shot, high resolution spectral measurements.

Surface soil moisture quantification and validation based on hyperspectral data and field measurements

Surface soil moisture information is needed for monitoring and modeling surface processes at various spatial scales. While many reflectance based soil moisture quantification models have been developed and validated in laboratories, only few were applied from remote sensing platforms and thoroughly validated in the field. This paper addresses the issues of a) quantifying surface soil moisture with very high resolution spectral measurements from remote sensors in a landscape with sandy substrates and low vegetation cover as well as b) comprehen- sively validating these results in the field. For this purpose, the recently developed Normalized Soil Moisture Index (NSMI) has been analyzed for its applicability to airborne hyperspectral remote sensing data. Three HyMap scenes from 2004 and 2005 were collected from a lignite mining area in southern Brandenburg, Germany. An NSMI model was calibrated (R 2 =0.92) and surface soil moisture maps were calculated based on this model. An in-situ surface soil mois- ture map based on a combination of Frequency Domain Reflectometry (FDR) and gravimetric data allowed for validating each image pixel (R 2 =0.82). In addition, a qualitative multitemporal comparison between two consecutive NSMI datasets from 2004 was performed and validated, showing an increase in estimated surface soil moisture corresponding with field measurements and precipitation data. The study shows that the NSMI is appropriate for modeling surface soil moisture from high spectral-resolution remote sensing data. The index leads to valid estimations of soil moisture values below field capacity in an area with sandy substrates and low vegetation cover (NDVI < 0.3). Further studies will analyze the validity of the NSMI for surface soil moisture estimation from spaceborne hyperspectral sensors like the Environmental Mapping and Analysis Program (EnMap) in different landscapes.

Comparison of solar soft X-ray irradiance from broadband photometers to a high spectral resolution rocket observation

The solar soft X-ray (XUV; 1–30 nm) radiation is highly variable on all time scales and strongly affects the ionosphere and upper atmosphere of Earth, Mars, as well as the atmospheres and surfaces of other planets and moons in the solar system; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. While there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the lack of high spectral resolution measurements in this wavelength range. The conversion of the XUV photometer signal into irradiance requires the use of a solar spectral model, but there has not been direct validation of these spectral models for the XUV range. For example, the irradiance algorithm for the XUV Photometer System (XPS) measurements uses multiple CHIANTI spectral models, but validation has been limited to other solar broadband measurements or with comparisons of the atmospheric response to solar variations. A new rocket observation of the solar XUV irradiance with 0.1 nm resolution above 6 nm was obtained on 14 April 2008, and these new results provide a first direct validation of the spectral models used in the XPS data processing. The rocket observation indicates very large differences for the spectral model for many individual emission features, but the differences are significantly smaller at lower resolution, as expected since the spectral models are scaled to match the broadband measurements. While this rocket measurement can help improve a spectral model for quiet Sun conditions, many additional measurements over a wide range of solar activity are needed to fully address the spectral model variations. Such measurements are planned with a similar instrument included on NASA’s Solar Dynamics Observatory (SDO), whose launch is expected in 2009.

Effect of changes of the HITRAN database on transmittance calculations in the near-infrared region

In order to retrieve from high spectral resolution measurements with high accuracy, it is necessary to be able to evaluate the transmittance precisely. However, the uncertainty of the spectroscopic parameters is one of the most important contributions that affect the accuracy of transmittance. HITRAN is a compilation of spectroscopic parameters which has been updated several times. The transmittance calculations using the line parameters from the HITRAN’2000 database and the HITRAN’2004 database have been compared over the near infrared range from 4200 to 10,000 cm −1. The differences between calculated transmittances over this spectral range are mainly caused by changes of the line parameters for H 2O, CO 2 and CH 4. For the tropical atmosphere, the differences are very prominent. Transmittance calculations for the sub-arctic winter atmosphere are less sensitive to the changes in the HITRAN database than those for the tropical atmosphere; but, the changes of line parameters still can not be ignored when considering the relative differences. For example, the relative difference is ∼35% at 5073.3 cm −1 with 0.2 cm −1 spectral resolution. The comparisons have shown that it is important to pay attention to the changes of line parameters of the HITRAN database or to use the latest edition so as to improve the accuracy of atmospheric sounding with high spectral resolution.

Retrieval of global upper tropospheric and stratospheric formaldehyde (H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;CO) distributions from high-resolution MIPAS-Envisat spectra

Abstract. The Fourier transform spectrometer MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) on Envisat measures infrared emission of the Earth's atmosphere in a limb viewing mode. High spectral resolution measurements of MIPAS are sensitive to formaldehyde from the upper troposphere to the stratopause. Single profile retrievals of formaldehyde are dominated by a 60% noise error; however zonal mean values for 30 days of data during 8 September 2003 and 1 December 2003 reduces this error by a factor of 20 or more. The number of degrees of freedom for single profile retrieval ranges from 2 to 4.5 depending on latitude and number of cloud-free tangent altitudes. In the upper tropical troposphere zonal mean values of about 70 parts per trillion by volume (pptv) were found, which have been attributed to biomass burning emissions. In the stratosphere, formaldehyde values are determined by photochemical reactions. In the upper tropical stratosphere, formaldehyde zonal mean maximum values can reach 130 pptv. Diurnal variations in this region can be up to 50 pptv. Comparisons with other satellite instruments show generally good agreement in the region of upper troposphere and lower stratosphere as well as in the upper stratosphere.

Dual-aureole and sun spectrometer system for airborne measurements of aerosol optical properties

We have designed an airborne spectrometer system for the simultaneous measurement of the direct sun irradiance and the aureole radiance in two different solid angles. The high-resolution spectral radiation measurements are used to derive vertical profiles of aerosol optical properties. Combined measurements in two solid angles provide better information about the aerosol type without additional and elaborate measuring geometries. It is even possible to discriminate between absorbing and nonabsorbing aerosol types. Furthermore, they allow to apply additional calibration methods and simplify the detection of contaminated data (e.g., by thin cirrus clouds). For the characterization of the detected aerosol type a new index is introduced that is the slope of the aerosol phase function in the forward scattering region. The instrumentation is a flexible modular setup, which has already been successfully applied in airborne and ground-based field campaigns. We describe the setup as well as the calibration of the instrument. In addition, example vertical profiles of aerosol optical properties--including the aureole measurements--are shown and discussed.

Comparison of AIRS, MODIS, CloudSat and CALIPSO cloud top height retrievals

Knowledge of cloud properties like cloud top height (CTH) is essential to understand their impact on the earth's radiation budget and on climate change. High spectral resolution measurements from the Atmospheric Infrared Sounder (AIRS) are well suited to reveal valuable information about cloud altitude. The CTH retrievals derived from AIRS single field‐of‐view (FOV) radiance measurements are compared with the operational MODIS (Moderate Resolution Imaging Spectroradiometer) cloud product, and Level 2 products obtained from radar and lidar instruments onboard the EOS (Earth Observing System) CloudSat and the CALIPSO (Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation) satellites. Two cases containing a variety of cloud conditions have been studied, and the strengths/shortcomings of CTH products from infrared (IR) sounder radiances are discussed.

Ultraviolet Emission Spectra of Sunbeds¶

It is well known that UV radiation contributes to the development of skin cancer. Exposure to solar radiation is predominantly responsible for the high incidence rate of skin cancer, but there are also indications that sunbeds are involved. The aim of the present investigation was to determine the UV emission spectra of sunbeds. It included the most common sunbed models, which cover more than 50% of the Swiss market. The UV emission spectra of sunbeds have special characteristics and are different from the sun spectrum, which can be seen in high-resolution spectral measurements. Sunbed emission spectra are similar to the sun spectrum in the UVB (280–320 nm) range but reach values 10 to 15 times higher in the UVA (320–400 nm) range. An average erythema-effective irradiance of 0.33 W/m2 was determined for sunbeds. This corresponds to a UV index of 13, which is significantly higher than the UV index of 8.5 of the high summer sun at noon at intermediate latitudes. The measurements were spread over the whole effective area of the sunbeds, and an inhomogeneous distribution of the irradiances with variations of up to 30% from the average value was found.

Directional effects consideration to improve out-doors emissivity retrieval in the 3-13 μm domain

This work analyses and solves for issues encountered when retrieving surface emissivity in LWIR (750 to 1250 cm(-1)) and MWIR (2000 to 3500 cm(-1)) bands under outdoor conditions. The Spectral Smoothness method, which takes advantage of high spectral resolution measurements to solve for temperature emissivity separation, and which has already proven its efficiency in the LWIR domain, was applied in an experimental campaign to assess its ability to operate both in the LWIR and MWIR domains. In the MWIR band, directional behaviour of surface emissivity is shown to be a source of systematic errors in the retrieved emissivity and a new method, called SmaC (SMoothness And Continuity), corrects for this error by providing quantitative estimates on the deviation of the surface from Lambertian behavior.

TargetK-vacancy production by2.5to25MeV∕amuAr, Kr, and Xe ions

Cross sections have been measured for $K\ensuremath{\alpha}$ x-ray production in targets of Al, Ti, Cu, Zr, Ag, Sm, and Ta by Ar, Kr, and Xe ions ranging in energy from $2.5\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}25\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{amu}$. In addition, the degree of simultaneous $L$-shell ionization and the enhancement of the $K\ensuremath{\alpha}$ diagram lines due to secondary ionization processes were assessed by performing high-resolution spectral measurements on Al, Ti, V, Co, and Cu targets. This information was used to correct for the $K\ensuremath{\alpha}$ x-ray yield produced by electron bombardment and photoionization, and to calculate the fluorescence yields needed to convert the $K\ensuremath{\alpha}$ x-ray production cross sections into $K$-vacancy production cross sections. The resulting cross sections were compared with the predictions of the perturbed stationary state approximation with corrections for projectile energy loss, Coulomb deflection, and relativistic effects (ECPSSR theory). Also, the scaling properties of the $K\ensuremath{\alpha}$ x-ray production cross sections were examined and a semiempirical (universal) curve was deduced that reproduces the measured cross sections to within $\ifmmode\pm\else\textpm\fi{}30%$ on average.

Spectral and spatial dynamics in InGaN blue-violet lasers

An angular differential analysis of the longitudinal modes associated with successive spectral substructures in InGaN lasers demonstrates a large increase in the mode widths towards the red side of the spectra because of the antiguiding lens effects occurring in such gain-guided lasers. A simple model predicts the growing asymmetrical triangular-shape spectral envelope with much higher powers in the red substructures with increasing excitation, in agreement with the high-resolution spectral measurements. Moreover, the observed 20% mode-width variations imply a critical stripe-width limitation of the active medium that would prevent oscillation of higher-order modes on the blue side of the laser spectrum.

Radioactive 26Al from massive stars in the Galaxy

Gamma-rays from radioactive 26Al (half-life approximately 7.2 x 10(5) years) provide a 'snapshot' view of continuing nucleosynthesis in the Galaxy. The Galaxy is relatively transparent to such gamma-rays, and emission has been found concentrated along its plane. This led to the conclusion that massive stars throughout the Galaxy dominate the production of 26Al. On the other hand, meteoritic data show evidence for locally produced 26Al, perhaps from spallation reactions in the protosolar disk. Furthermore, prominent gamma-ray emission from the Cygnus region suggests that a substantial fraction of Galactic 26Al could originate in localized star-forming regions. Here we report high spectral resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide origin. We determine a present-day equilibrium mass of 2.8 (+/- 0.8) solar masses of 26Al. We use this to determine that the frequency of core collapse (that is, type Ib/c and type II) supernovae is 1.9 (+/- 1.1) events per century.

Identification of lipid-based biomarkers in the high-resolution pyrolysis/mass spectrum of Brucella neotomae

High-resolution (HR) mass spectral measurements were performed on pyrolysis products from Brucella neotomae at masses corresponding to low-resolution mass spectral peaks known to be of statistical and biological importance for the identification of diverse bacteria. The high-resolution capabilities allowed the separation of the nominal mass peaks into mass spectral clusters. Empirical formulas were calculated for each peak. Selected standards representing the composition of the bacterial membrane and total bacterial lipid extract were analyzed under identical conditions. High-resolution mass spectral peaks that were found in the whole bacterial cell spectra, in the standards, and total lipid extract were assigned as having originated from lipid-based molecules. Using precursor- and product-ion scans, the electron ionization fragmentation pathways were proposed for most of the peaks. The results from the HR identification of the selected peaks provide biochemical factors leading to the use of the peaks for differentiating bacterial samples.

Virtual sensors: using data mining techniques to efficiently estimate remote sensing spectra

Various instruments are used to create images of the earth and other objects the universe a diverse set of wavelength bands with the aim of understanding natural phenomena. Sometimes these instruments are built a phased approach, with additional measurement capabilities added later phases. In other cases, technology may mature to the point that the instrument offers new measurement capabilities that were not planned the original design of the instrument. In still other cases, high-resolution spectral measurements may be too costly to perform on a large sample, and therefore, lower resolution spectral instruments are used to take the majority of measurements. Many applied science questions that are relevant to the earth science remote sensing community require analysis of enormous amounts of data that were generated by instruments with disparate measurement capabilities. This work addresses this problem using virtual sensors: a method that uses models trained on spectrally rich (high spectral resolution) data to fill in unmeasured spectral channels spectrally poor (low spectral resolution) data. The models we use Are multilayer perceptrons, support vector machines (SVMs) with radial basis function kernels, and SVMs with mixture density Mercer kernels. We demonstrate this method by using models trained on the high spectral resolution Terra Moderate Resolution Imaging Spectrometer (MODIS) instrument to estimate what the equivalent of the MODIS 1.6-/spl mu/m channel would be for the National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (AVHRR/2) instrument. The scientific motivation for the simulation of the 1.6-/spl mu/m channel is to improve the ability of the AVHRR/2 sensor to detect clouds over snow and ice.

Piperidinyl Amides with Insecticidal Activity from the Maritime Plant Otanthus maritimus

Two new piperidine amides, N-[(2E,4E,8Z)-tetradecatrienoyl]piperidine (1) and N-[(2E,4E,8Z,11Z)-tetradecatetrenoyl]piperidine (2), along with the known metabolites N-[(2E,4E)-tetradecadienoyl]piperidine (3), N-isobutyl-(2E,4E,)-tetradecadienamide (4), N-isobutyl-(2E,4E,8Z)-tetradecatrienamide (5), N-isobutyl-(2E,4E,8Z,11Z)-tetradecatetraenamide (6), sesamine (7), pinoresinol (8), and espeletone (9), were isolated from the dichloromethane/methanol extracts of the plant Otanthus maritimus Hoffman & Link collected from coastal areas in Greece. Pinoresinol (8) and espeletone (9) are reported for the first time as metabolites of O. maritimus. The structures of the new natural products were elucidated by interpretation of their NMR and high-resolution mass spectral measurements. The insecticidal properties of the crude extracts, essential oil, and isolated metabolites 1-9 were evaluated on Crematogaster scutellaris (Olivier) ants and Reticulitermes balkanensis (Clement) termites, showing significant levels of activity.

First ground‐based measurements of OI 6300 Å daytime aurora over Boston in response to the 30 October 2003 geomagnetic storm

High spectral resolution measurements of OI 6300 Å emissions during daytime on 30 October 2003 from Boston revealed prolonged auroral activity from 1415–1900 LT. The solar zenith angles varied from 70°–115° during that interval. Intense enhancement in brightness of 38 Kilo Rayleighs were observed at 1509 LT, which were six times larger than the normal daytime emission rates for that day. During this event the solar zenith angle was 74° and the solar background continuum was 4 × 106 Rayleighs Å−1. Such large enhancement in brightness were due to the daytime aurora generated in response to an X‐class Coronal Mass Ejection on the Sun. The measured daytime airglow emissions show good agreement, both, in the magnitudes and in the temporal variability with the emissions modeled by using as inputs the Ne, Te and Ti profiles that were measured by the Millstone Hill Incoherent Scatter Radar (ISR) located approximately 60 km away from the spectrograph.

Retrieval of stratospheric and mesospheric O 3 from high resolution MIPAS spectra at 15 and 10 μm

In this work, we deal with the retrieval of O 3 from the upper atmosphere data from 20 to 100 km using the high spectral resolution measurements of MIPAS in the regions of 14 and 10 μm. Non-LTE modelling of the O 3 levels is included. Quality parameters of the retrievals and sensitivity tests for tuning the retrieval processor are presented. Day and nighttime O 3 profiles and zonal O 3 distribution for solstice conditions are shown to demonstrate the robustness and quality of the method. Finally a preliminary error assessment on the random and systematic errors, including non-LTE sources, is presented.

Chamuvarinin, an acetogenin bearing a tetrahydropyran ring from the roots of Uvaria chamae.

A new cytotoxic acetogenin, chamuvarinin (1), containing a tetrahydropyran ring with an adjacent bis-tetrahydrofuran ring, which corresponds to a novel carbon skeleton in this series, was isolated from the roots of Uvaria chamae, together with the previously reported acetogenins squamocin (2), desacetyluvaricin (3), and neoannonin (4). The structure determination of chamuvarinin (1) was based on extensive NMR studies and high-resolution mass spectral measurements. This new compound shows significant cytotoxicity toward the KB 3-1 cell line (IC50 = 8 x 10(-10) M). In addition, a biosynthetic relationship between 1 and 2 is briefly discussed.

BIOACTIVE PRINCIPLES OF THE FLOWERS OF PANCRATIUM MARITIMUM

Bioactive-guided fractionation and purification of the ethyl acetate fraction of anethanolic extract of fresh flowers of Pancratium maritimum (Amaryllidaceae)cultivated in Egypt yielded an alkaloid, pancratistatin (1), together with 3-caffeoylquinic acid methyl ester (2). Their structures were determined on the basis ofextensive 1D (1H and 13C) and 2D (COSY, HMQC, HMBC, and NOESY) NMR studiesand high-resolution mass spectral measurements. Both compounds showed potentcytotoxic activity against HeLa cells and moderate anti-tuberculosis activity againstMycobacterium tuberculosis H37Rv. This is the first report of pancratistatin inPancratium maritimum and the first report of 3-caffeoylquinic acid methyl ester in thefamily Amaryllidaceae.

Physical Implications of RHESSI Neutron-Capture Line Measurements

We report high spectral resolution measurements of the 2.223 MeV neutron-capture line obtained with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) from the 2002 July 23 solar flare. The time history of this line is affected by both the photospheric 3He abundance and the angular distribution of the interacting flare-accelerated particles producing the neutrons. The measured time history is compared with predicted time histories calculated using a magnetic loop model with a magnetic field perpendicular to the solar surface at the footpoints. The model includes energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tube, and MHD pitch-angle scattering in the corona. This is the first analysis of the neutron-capture line using such a physically based model. The derived constraints on the interacting angular distribution require that the accelerated particles had to suffer pitch-angle scattering during their transport through the coronal portion of the loop. The derived photospheric 3He/H ratio was not well constrained, primarily because of uncertainties associated with the measured nuclear de-excitation line flux used to represent the neutron-production time profile.