Shortwave Spectrum Research Articles

Quantifying the range of the dust direct radiative effect due to source mineralogy uncertainty

Abstract. The large uncertainty in the mineral dust direct radiative effect (DRE) hinders projections of future climate change due to anthropogenic activity. Resolving modeled dust mineral speciation allows for spatially and temporally varying refractive indices consistent with dust aerosol composition. Here, for the first time, we quantify the range in dust DRE at the top of the atmosphere (TOA) due to current uncertainties in the surface soil mineralogical content using a dust mineral-resolving climate model. We propagate observed uncertainties in soil mineral abundances from two soil mineralogy atlases along with the optical properties of each mineral into the DRE and compare the resultant range with other sources of uncertainty across six climate models. The shortwave DRE responds region-specifically to the dust burden depending on the mineral speciation and underlying shortwave surface albedo: positively when the regionally averaged annual surface albedo is larger than 0.28 and negatively otherwise. Among all minerals examined, the shortwave TOA DRE and single scattering albedo at the 0.44–0.63 µm band are most sensitive to the fractional contribution of iron oxides to the total dust composition. The global net (shortwave plus longwave) TOA DRE is estimated to be within −0.23 to +0.35 W m−2. Approximately 97 % of this range relates to uncertainty in the soil abundance of iron oxides. Representing iron oxide with solely hematite optical properties leads to an overestimation of shortwave DRE by +0.10 W m−2 at the TOA, as goethite is not as absorbing as hematite in the shortwave spectrum range. Our study highlights the importance of iron oxides to the shortwave DRE: they have a disproportionally large impact on climate considering their small atmospheric mineral mass fractional burden (∼2 %). An improved description of iron oxides, such as those planned in the Earth Surface Mineral Dust Source Investigation (EMIT), is thus essential for more accurate estimates of the dust DRE.

PREDICTING INFRAGRAVITY WAVES IN HARBOURS - AN EVALUATION OF PUBLISHED EQUATIONS AND THEIR USE IN FORECASTING OPERATIONAL THRESHOLDS

Infragravity (IG) waves have received considerable study since the 1950s (Munk, 1949, Bertin, 2018), allowing their generation, propagation and impacts to be more effectively quantified. Here, we are concerned with the frequencies that directly excite motion in moored ships, thereby creating problematic and often unsafe conditions. Operational knowledge gained in surge-affected ports in Australia and New Zealand revealed IG height thresholds common to all locations (McComb, 2011), with wave periods from 25 to 120-150s being causative. A further observation that the IG spectral shapes at berths remain relatively constant regardless of the incident short wave spectra (McComb, 2014) allows robust predictive methodologies to be developed to forecast the onset and the passing of these empirically-derived values. The governing IG height thresholds are: Hsless than 0.10m is safe and manageable for a well-tendered vessel; at Hs 0.10-0.15m caution is advised and additional management is recommended, and at Hsgreater than 0.15m active management is required. Management options include shore moorings, pneumatic fendering, ShoreTension, MoorMaster etc. Without intervention, IG conditions greater than 0.20m are universally considered dangerous. Further, IG heights are strongly modulated by tide at certain locations (Thomson, 2006), which creates rapidly changing conditions that compound the difficulties ensuring safe and effective operations. We selected five published methods to predict nearshore IG height (Lara 2004, McComb 2005, Okihiro 1992, Arduin 2014 and Cuomo 2017) and undertook an evaluation of their efficacy at two energetic ports on opposite sides of the Earth. The ports of Gijon in Spain and Taranaki in New Zealand both experience problematic moored ship motions and have been subject to numerous studies of their wave dynamics over previous decades. Consequently, there is a body of knowledge, operational experience and local data to make an evaluation. The purpose of this work is to offer pragmatic guidance to the developers of operational forecasting systems on the optimal method to predict IG heights for safe mooring of ships at berth. Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/8oCRQkMdcIo

Measuring ocean total surface current velocity with the KuROS and KaRADOC airborne near-nadir Doppler radars: a multi-scale analysis in preparation for the SKIM mission

Abstract. Surface currents are poorly known over most of the world's oceans. Satellite-borne Doppler wave and current scatterometers (DWaCSs) are among the proposed techniques to fill this observation gap. The Sea surface KInematics Multiscale (SKIM) proposal is the first satellite concept built on a DWaCS design at near-nadir angles and was demonstrated to be technically feasible as part of the European Space Agency Earth Explorer program. This article describes preliminary results from a field experiment performed in November 2018 off the French Atlantic coast, with sea states representative of the open ocean and a well-known tide-dominated current regime, as part of the detailed design and feasibility studies for SKIM. This experiment comprised airborne measurements performed using Ku-band and Ka-band Doppler radars looking at the sea surface at near-nadir incidence in a real-aperture mode, i.e., in a geometry and mode similar to that of SKIM, as well as an extensive set of in situ instruments. The Ku-band Radar for Observation of Surfaces (KuROS) airborne radar provided simultaneous measurements of the radar backscatter and Doppler velocity in a side-looking configuration, with a horizontal resolution of about 5 to 10 m along the line of sight and integrated in the perpendicular direction over the real-aperture 3 dB footprint diameter (about 580 m). The Ka-band RADar for Ocean Current (KaRADOC) system, also operating in the side-looking configuration, had a much narrower beam, with a circular footprint only 45 m in diameter. Results are reported for two days with contrasting conditions, a strong breeze on 22 November 2018 (wind speed 11.5 m s−1, Hs 2.6 m) and gentle breeze on 24 November 2018 (wind speed 5.5 m s−1, Hs 1.7 m). The measured line-of-sight velocity signal is analyzed to separate a non-geophysical contribution linked to the aircraft velocity, a geophysical contribution due to the intrinsic motion of surface waves and the desired surface current contribution. The surface wave contribution is found to be well predicted by Kirchhoff scattering theory using as input parameters in situ measurements of the directional spectrum of long waves, complemented by the short wave spectrum of Elfouhaily et al. (1997). It is found to be closely aligned with the wind direction, with small corrections due to the presence of swell. Its norm is found to be weakly variable with wind speed and sea state, quite stable and close to C0=2.0ms-1 at the Ka band, and more variable and close to C0=2.4ms-1 at the Ku band. These values are 10 %–20 % smaller than previous theoretical estimates. The directional spread of the short gravity waves is found to have a marked influence on this surface wave contribution. Overall, the results of this study support the feasibility of near-nadir radar Doppler remote sensing of the ocean total surface current velocity (TSCV).

Atmospheric aerosol and black carbon optical properties and associated radiative forcing under haze conditions

The optical properties and radiative forcing of atmospheric aerosol (ARF) and black carbon (BC) aerosol (BCRF) in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra were investigated under haze conditions based on the observations of the Aethalometer and sun-sky radiometer and simulations from libRadtran. The results show that the BC concentrations increased greatly from 2.73 μg/m3 under clear-air conditions to 7.95 μg/m3 under severe haze conditions, while BC aerosol optical depth (AOD) increased from 0.025 to 0.092. A high correlation (R2=0.62) was found between BC AOD and absorbing aerosol optical depth (AAOD) derived from the sun-sky radiometer. The BCRF in SW (BCRFSW) varied from -10.20 W/m2 under clear-air conditions to -25.40 W/m2 under severe hazy conditions. However, its fraction in ARF (ARFSW) decreased from 19% to 17% simultaneously, which is mainly related to the decrease of the ratio of BC AOD to AOD. The fraction of ARF in VIS in ARFSW decreased from 56.3% under clear-air conditions to 50.5% under severe haze conditions, while the fraction of BCRF in VIS in BCRFSW was much larger, and increased from 72.9% to 73.8%. The BCRF efficiency (BCRFE) was much larger than ARF efficiency (ARFE), and both of them decreased with the development of haze. The ARFE in SW decreased from -173.84 W/m2 under clear-air conditions to -112.75 W/m2 under severe haze conditions while BCRFESW varied from -482.50 W/m2 to -321.88 W/m2. The decrease of ARFE and BCRFE is related to the increase of aerosol loading and asymmetry factor (ASY). The ASY increased and the forward scattering was enhanced with the development of haze due to the hygroscopic growth of aerosol particles, which reduced the extinction efficiency of aerosols including BC on solar radiation and the cooling effect on the surface.

Interannual and seasonal variations in the aerosol optical depth of the atmosphere in two regions of Spitsbergen (2002–2018)

Abstract. In this work, hourly averaged sun photometer data from Barentsburg and Ny-Ålesund, both located on Spitsbergen in the European Arctic, are compared. Our data set comprises the years from 2002 to 2018 with overlapping measurements from both sites during the period from 2011 to 2018. For more turbid periods (aerosol optical depth, AOD, τ0.5>0.1), we found that Barentsburg is typically more polluted than Ny-Ålesund, especially in the shortwave spectrum. However, the diurnal variation in the AOD is highly correlated. Next, τ was divided into a fine and coarse mode. It was found that the fine-mode aerosol optical depth generally dominates and also shows a larger interannual than seasonal variation. The fine-mode optical depth is in fact largest in spring during the Arctic haze period. Overall the aerosol optical depth seems to decrease (at 500 nm the fine-mode optical depth decreased by 0.016 over 10 years), although this is hardly statistically significant.

MEMS-based wave buoy: Towards short wind-wave sensing

Low-cost commercial micro-electro-mechanical system (MEMS)-based inertial motion unit is used for sea surface wave measurements. A buoy is developed based on the capacitive silicon-based accelerometer–gyroscope–magnetometer sensor with radically simplified architecture allowing a significant reduction of the buoy hull size down to 14-cm diameter and hence increased high-frequency sensitivity. The proposed buoy design is suitable for short-term manual wave measurements with minimal deployment–recovery efforts and/or experiments where knowledge of the high-frequency part of the spectrum is preferable. The buoy data is validated in a field experiment at the Black Sea stationary research platform using reference measurements of the six-wire resistive wave gauge. The strapped-down buoy measurements are transformed into the georeferenced buoy tilts and vertical acceleration using small wave slope approximation. The classical (Longuet-Higgins et al., 1961) approach is used for directional wave spectra estimation. Under 1 to 15 m/s wind speed, pure wind and mixed sea conditions, the significant wave height, wave peak period, wave direction, and spectral width are well reproduced by the buoy. The buoy geometric cut-off frequency, about 2.5 Hz, corresponding to wavelength twice the hull diameter, is at least 2.5 times better than that of commercially available buoys. The sub-peak low-frequency noise, typical for accelerometer-derived spectra, is wind-dependent and thus is clearly not the intrinsic sensor noise, but rather results from the buoy non-linear response to the waves. The detected high-frequency (4<f<80Hz) spectrum tail also depends on the wind speed in accord with the short-wave wind-driven wave spectrum model. The observed high-frequency sensitivity may be useful for short-wave sensing beyond the geometric cut-off frequency with MEMS-based sensors.

Features of a ZnxCd1 – xS Buffer Layer for Use in Thin-Film Solar Cells in the Context of a Literature Review

The paper presents a literature review of the latest achievements in the creation of highly efficient thin-film solar cells (SCs) based on multicomponent polycrystalline materials: semiconductors of the AIIBVI groups of the periodic table, cadmium telluride (CdTe) and a three-component compound AIBIIICVI copper–indium–gallium and selenium (Cu (In, Ga)Se2). The main criteria for the selection of the buffer layer material for thin-film SCs based on CdTe and Cu (In, Ga)Se2 are analyzed. The values of the main output parameters of the load current–voltage characteristic (short-circuit current, open-circuit voltage, fill factor of a light current–voltage characteristic, efficiency) of high-performance SCs based on CdTe and Cu(In, Ga)Se2, which have been achieved to date, are presented. The spectral photosensitivity of a SC in the short-wave region of the electromagnetic spectrum is determined by the band gap width and thickness of the p–n transition frontal–buffer layer. An increase in the photosensitivity in the short-wave spectrum part of electromagnetic radiation is achieved by an increase in the band gap of the buffer layer. In this case, it is necessary to take into account the important energy (energy of electron affinity) and crystallographic (crystal lattice parameter) parameters of the semiconductor material. As one of the promising materials for the buffer layer, semiconductor polycrystalline layers from the AIIBVI class, semiconductor chemical ternary compounds ZnxCd1 – xS, in which Eg varies from 2.4 eV (x = 0, CdS) to 3.6 eV (x = 1, ZnS) are proposed. An analysis of the compatibility of ZnxCd1 – xS layers with different x values, as a buffer layer for SCs based on CdTe and Cu(In, Ga)Se2, is carried out. Possible scenarios of variation in the main output parameters of SCs, such as short-circuit current and open-circuit voltage, are analyzed.

Ammonium abundance and short-wave infrared absorption spectra of altered rocks

Rhyolitic rocks hosting the El Zapote epithermal Ag deposit are pervasively altered and contain ammonium ranging from 290 to 1750 ppm. High ammonium values are found in samples containing abundant fine-grained illite. This fine-grained illite shows overall low ratios of K/(Al + Fe), likely due to ammonium substituting K + . Samples containing high ammonium, greater than 1000 ppm in the proximity of Ag-bearing veins, show distinct absorption features of ammonium in short-wave infrared (SWIR) absorption spectra. Samples containing ammonium ranging from 500 to 1000 ppm show mixed absorption signatures; some show prominent absorption features related to ammonium, whereas others have no recognizable features. There is no discernible absorption feature related to ammonium for samples containing less than 500 ppm NH 4 . The data suggest that SWIR spectroscopy is useful in locating the proximal areas to mineralization, but the extent of ammonium alteration is much larger than that identified by SWIR spectroscopy. Nitrogen isotope compositions of ammonium are similar to those of sedimentary rocks, suggesting that the source of ammonium in altered rhyolite is sedimentary basement rocks in the area. Supplementary material : bulk rock composition is available at https://doi.org/10.6084/m9.figshare.c.5015663

Organic Carbon and Total Iron Effect on Soil Vis-SWNIR Spectraand Quantification of Their Contents Using PLS R Models

ABSTRACT Many factors could influence simultaneously soil spectra. We aimed to study the single effect of organic carbon and total iron in soil visible and short-wave near-infrared spectra and to quantify their contents. Two datasets of soil mixture samples were prepared by mixing, in various fractions, an organic carbon-rich material with a total iron-rich material and then with a total iron-poor material. For these two datasets, contents in organic carbon are quite similar but contents in total iron are significantly different. Results show that samples of the same dataset have the same overall spectral shape. Organic carbon has a decreasing effect that affects the whole spectral range without showing any specific absorption peaks. By contrast, total iron has specific absorption peaks. Spectra of the second dataset characterized by soil mixtures with higher total iron contents were more compact within the spectral bands 400–440 and 920–950 nm. Besides, continuum removal enables to exaggerate absorption peaks of wavelengths linked to total iron content. Partial Least Squares Regression (PLS R) models of both total organic carbon and total iron assign high coefficients to the wavelengths that are considered relevant and conversely low coefficients to those that are considered irrelevant. Both organic carbon content and total iron content were well predicted. For these models, coefficients of determination were superior to 0.9 and RMSE was closed to zero. The global models calibrated on all the samples demonstrated that PLS R was able to integrate sample heterogeneity.

The Influence of Short-Wave and Long-Wave Radiation Spectrum on the Photostability of Sunscreens

Background: Sunscreen products aim to help protect the skin against UV radiation and consequently reduce the risk of early skin ageing and skin cancer. However, it is well known that some sunscreen ingredients are not photostable, but this usually refers to irradiation with UV light. Moreover, it has to be mentioned that a relative cumulative erythema effectiveness compliant light source is used for the in vivo sun protection factor (SPF) testing. Here, UV simulators equipped with a xenon arc lamp use filters such as WG320 and UG11 (thickness 1 mm) to minimize infrared (IR) radiation and wavelength below 300 nm. However, under practical conditions, the sunscreen product is not only exposed to UVA/B light, but also to visible light (VIS) and IR light. In fact, the spectrum of solar radiation is composed of approximately 7% UV, 39% VIS and 54% IR. Aims: To investigate the influence of short-wave and long-wave radiation on the photostability of sunscreens. Methods: Irradiation was performed with the Suntest CPS+ that is considered to closely imitate solar radiation. The filter UG11 (thickness 1 mm), which absorbs much of the VIS and IR light, and the glass filter WG320 (thickness 2 mm), which effectively absorbs radiation of wavelengths less than 300 nm, were used in the Suntest CPS+ both individually and in combination and were inserted between the light source and the samples. The following transmission measurements were carried out with Labsphere’s UV-2000s device. Here, the effectiveness (percentage change of SPF before irradiation to SPF after irradiation) as a measure of the photostability was calculated. Results:As expected after total solar spectrum irradiation, the effectiveness in all tested sunscreens is lower compared to relative cumulative erythema effectiveness light used for in vitro testing of SPF. In the reference sunscreen formula S2 as well as in the two different sunscreen products, especially long-wave radiation (>400 nm) had an effect on photostability, whereas short-wave radiation had only a minor impact. In contrast, in the BASF sun care gel line only short-wave radiation below 300 nm had an effect on photostability, and blocking VIS and IR light had no effect at all. Conclusion:Based on these data, we can conclude that short waves and/or VIS + IR light have an influence on the photostability of sunscreens.

Complex refractive indices and single-scattering albedo of global dust aerosols in the shortwave spectrum and relationship to size and iron content

Abstract. The optical properties of airborne mineral dust depend on its mineralogy, size distribution, and shape, and they might vary between different source regions. To date, large differences in refractive index values found in the literature have not been fully explained. In this paper we present a new dataset of complex refractive indices (m=n-ik) and single-scattering albedos (SSAs) for 19 mineral dust aerosols over the 370–950 nm range in dry conditions. Dust aerosols were generated from natural parent soils from eight source regions (northern Africa, Sahel, Middle East, eastern Asia, North and South America, southern Africa, and Australia). They were selected to represent the global-scale variability of the dust mineralogy. Dust was resuspended into a 4.2 m3 smog chamber where its spectral shortwave scattering (βsca) and absorption (βabs) coefficients, number size distribution, and bulk composition were measured. The complex refractive index was estimated by Mie calculations combining optical and size data, while the spectral SSA was directly retrieved from βsca and βabs measurements. Dust is assumed to be spherical in the whole data treatment, which introduces a potential source of uncertainty. Our results show that the imaginary part of the refractive index (k) and the SSA vary widely from sample to sample, with values for k in the range 0.0011 to 0.0088 at 370 nm, 0.0006 to 0.0048 at 520 nm, and 0.0003 to 0.0021 at 950 nm, as well as values for SSA in the range 0.70 to 0.96 at 370 nm, 0.85 to 0.98 at 520 nm, and 0.95 to 0.99 at 950 nm. In contrast, the real part of the refractive index (n) is mostly source (and wavelength) independent, with an average value between 1.48 and 1.55. The sample-to-sample variability in our dataset of k and SSA is mostly related to differences in the dust iron content. In particular, a wavelength-dependent linear relationship is found between the magnitude of k and SSA and the mass concentrations of both iron oxide and total elemental iron, with iron oxide better correlated than total elemental iron with both k and SSA. The value of k was found to be independent of size. When the iron oxide content exceeds 3 %, the SSA linearly decreases with an increasing fraction of coarse particles at short wavelengths (&lt; 600 nm). Compared to the literature, our values for the real part of the refractive index and SSA are in line with past results, while we found lower values of k compared to most of the literature values currently used in climate models. We recommend that source-dependent values of the SW spectral refractive index and SSA be used in models and remote sensing retrievals instead of generic values. In particular, the close relationships found between k or SSA and the iron content in dust enable the establishment of predictive rules for spectrally resolved SW absorption based on particle composition.

Non-Destructive Soluble Solids Content Determination for 'Rocha' Pear Based on VIS-SWNIR Spectroscopy under 'Real World' Sorting Facility Conditions.

In this paper we report a method to determine the soluble solids content (SSC) of ‘Rocha’ pear (Pyrus communis L. cv. Rocha) based on their short-wave NIR reflectance spectra (500–1100 nm) measured in conditions similar to those found in packinghouse fruit sorting facilities. We obtained 3300 reflectance spectra from pears acquired from different lots, producers and with diverse storage times and ripening stages. The macroscopic properties of the pears, such as size, temperature and SSC were measured under controlled laboratory conditions. For the spectral analysis, we implemented a computational pipeline that incorporates multiple pre-processing techniques including a feature selection procedure, various multivariate regression models and three different validation strategies. This benchmark allowed us to find the best model/preproccesing procedure for SSC prediction from our data. From the several calibration models tested, we have found that Support Vector Machines provides the best predictions metrics with an RMSEP of around 0.82 Brix and 1.09 Brix for internal and external validation strategies respectively. The latter validation was implemented to assess the prediction accuracy of this calibration method under more ‘real world-like’ conditions. We also show that incorporating information about the fruit temperature and size to the calibration models improves SSC predictability. Our results indicate that the methodology presented here could be implemented in existing packinghouse facilities for single fruit SSC characterization.

Comparation of aerosol optical properties and associated radiative effects of air pollution events between summer and winter: A case study in January and July 2014 over Wuhan, Central China

Differences in aerosol optical properties and associated radiative effects at ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra during haze periods between winter and summer of 2014 in Wuhan were compared in this study. With the development of haze, the average aerosol optical depth increased from 0.371 to 0.769 in winter and from 0.602 to 1.163 in summer. A positive correlation was found between absorbing aerosol optical depth and black carbon, only in winter. The mean fine mode effective radius of aerosols increased from 0.128 μm to 0.166 μm in winter and from 0.179 μm to 0.229 μm in summer, due to hygroscopic growth under high humidity conditions during haze periods. The fine mode particles were more dominant in summer than in winter. The single scattering albedo (SSA) increased significantly in both seasons as a result of the emergence of numerous non-absorbent aerosols when haze occurred. The aerosol radiative effect (ARE) increased from −73.46 W/m2 to −115.38 W/m2 (−96.01 W/m2 to −135.67 W/m2) at the earth's surface, and from −15.09 W/m2 to −32.91 W/m2 (−20.49 W/m2 to −49.13 W/m2) at the top of the atmosphere because of the change from clear air conditions to haze periods in winter (summer). Unusual increases in aerosol radiative effect efficiency (AREE) from −40.78 W/m2 to −43.57 W/m2 and AREE fraction of UV in SW spectrum from 1.9% to 3.3% were found at the top of atmosphere in winter. This exception was probably due to dust aerosols with iron components, which had a strong UV absorption ability. The AREE dependence showed a high dependence on particle size in winter but a greater dependence on the SSA in summer. Back trajectory analysis with active fire areas from Moderate Resolution Imaging Spectroradiometer indicated that the black carbon originated from the North in summer, while active fires in winter were rare.

Automatic determination of shoreline at maximum retreating

Coastal zones are the most influenced areas by global sea level rising. One of the important coastal zones in Egypt is the Red Sea. Red Sea coastal area is an attractive touristic area, which still under development. For the high value of such areas, the position of the set-back construction line is required for well planning and development. This position influenced greatly by the position of the shoreline at the maximum retreating. This paper introduces an automatic approach for determining the shoreline at the maximum retreating. This approach depends on three types of information; 1) the location of the current shoreline, 2) the mean higher high-water level (MHHWL), and 3) the topography of the coastal area.A study area North of Hurghada, is selected to apply the introduced approach. The shoreline is extracted out of Landsat-8 images based on a combination of three factors; a modified normal difference water index, the reflectance values of the water bodies in specific bands within the shortwave infra-red spectrum, and the relation of the reflectance values of water bodies in the Green, Red, NIR, and SWIR bands. The higher high-water level is determined from near tidal gauge station that has collected data each 30 min since 2008, and the topography of the coastal area is determined by the Kinematic GPS technique. The extracted shoreline was assessed by comparing it to actual shoreline traced on the ground. The results show that the accuracy of the extracted shoreline is within 15 m of the actual shoreline.

Importance-driven approach for reducing urban radiative exchange computations

In the context of large scale urban heat transfer simulation, the prediction of radiative flux at short and long wave spectra is a step necessary to obtain accurate results. From a computational perspective, this task is expensive because realistic conditions require calculations in many sensors, considering multiple radiation bounces, and evaluating many hundred daylighting conditions. Radiosity-based approaches are adequate methods for processing the large number of diffuse surfaces that are usually present in city models. However, the high memory consumption of these algorithms turns them inefficient for handling big geometries, and therefore ray tracing techniques are commonly used. In this article we present a study on using the importance concept to improve the performance of radiosity calculations at the urban scale. The algorithm is able to consider diffuse and specular materials, and it proves to be a viable alternative to ray tracing. Since most of the information contained in big city models is not needed for simulating a selected zone of interest, the computational requirements can be reduced drastically. Several experiments are conducted to test the approach, and promising results are reported.

Modeling of surface spectra with and without dust from Martian infrared data: new aspects

PurposeThis paper aims to characterize the mineral composition of Martian surfaces based on Thermal Emission Spectrometer (TES; Mars Global Surveyor) as measured in the infrared thermal range. It presents modeling and interpreting of TES spectral data from selected Martian regions from which the atmospheric influences had been removed using radiative transfer algorithm and deconvolution algorithm. The spectra from the dark area of Cimmeria Terra and the bright Isidis Planitia were developed in Philip Christensen’s and Joshua Bandfield’s publications, where these spectra were subjected to spectral deconvolution to estimate the mineral composition of the Martian surface. The results of the analyses of these spectra were used for the modeling of dusty and non-dusty surface of Mars. As an additional source, the mineral compositions of Polish basalts and mafic rocks were used for these surfaces as well as for modeling Martian meteorites Shergottites, Nakhlites and Chassignites. Finally, the spectra for the modeling of the Hellas region were obtained from the Planetary Fourier Spectrometer (PFS) – (Mars Express) and the mineralogical compositions of basalts from the southern part of Poland were used for this purpose. The Hellas region was modeled also using simulated Martian soil samples Phyllosilicatic Mars Regolith Simulant and Sulfatic Mars Regolith Simulant, showing as a result that the composition of this selected area has a high content of sulfates. Linear spectral combination was chosen as the best modeling method. The modeling was performed using PFSLook software written in the Space Research Centre of the Polish Academy of Sciences. Additional measurements were made with an infrared spectrometer in thermal infrared spectroscopy, for comparison with the measurements of PFS and TES. The research uses a kind of modeling that successfully matches mineralogical composition to the measured spectrum from the surface of Mars, which is the main goal of the publication. This method is used for areas where sample collection is not yet possible. The areas have been chosen based on public availability of the data.Design/methodology/approachThe infrared spectra of the Martian surface were modeled by applying the linear combination of the spectra of selected minerals, which then are normalized against the measured surface area with previously separated atmosphere. The minerals for modeling are selected based on the expected composition of the Martian rocks, such as basalt. The software used for this purpose was PFSLook, a program written in C++ at the Space Research Centre of the Polish Academy of Sciences, which is based on adding the spectra of minerals in the relevant percentage, resulting in a final spectrum containing 100 per cent of the minerals.FindingsThe results of this work confirmed that there is a relationship between the modeled, altered and unaltered, basaltic surface and the measured spectrum from Martian instruments. Spectral deconvolution makes it possible to interpret the measured spectra from areas that are potentially difficult to explore or to choose interesting areas to explore on site. The method is described for mid-infrared because of software availability, but it can be successfully applied to shortwave spectra in near-infrared (NIR) band for data from the currently functioning Martian spectroscopes.Originality/valueThis work is the only one attempting modeling the spectra of the surface of Mars with a separated atmosphere and to determine the mineralogical composition.

Factors affecting air temperature in Bulgaria

The research period is 1984–2007 and includes data for air temperatures at 20 Bulgarian and Serbian stations. Also, data for four radiation fluxes and cloud fraction were used in the study. Atmospheric circulation is represented by six different circulation patterns and indices. Statistical methods such as principal component analysis, trend analysis, and correlation were employed in order to solve different problems. The main factor that affects air temperature in Bulgaria is solar radiation. Among different radiation fluxes, the most important is Surface Longwave Upward Flux followed by Surface Shortwave Downward Flux and radiation balance. Circulation factors also contribute to the values of air temperature in Bulgaria. The most significant is East Atlantic teleconnection pattern. Local physical geographical conditions such as relief and large water bodies are also important, especially by modeling and modifying the temperature field over Bulgaria. Average annual and most of average monthly air temperatures have increased in the period 1984–2007. The only exceptions are months of September and December. The observed increase in air temperature is due mainly to the increase in Surface Shortwave Downward Flux, which in turn is due to the decrease in cloudiness. The decrease in cloudiness leads to redistribution of radiation fluxes, increasing the net balance in shortwave spectrum and decreasing the net balance in longwave spectrum. The latter suggests a decreasing greenhouse effect in the studied period over the territory of Bulgaria.

Toward an on-line characterization of kaolin calcination process using short-wave infrared spectroscopy

ABSTRACTIn the production of calcined kaolin, the on-line monitoring of the calcination reaction is becoming more relevant for the generation of optimal products. In this context, this study aimed to assess the suitability of using infrared (IR) spectroscopy as a potential technique for the on-line characterization of the calcination of kaolin. The transformation of kaolin samples calcined at different temperatures were characterized in the short-wave (SWIR) spectra using the kaolinite crystallinity (Kx) index and the depth of the water spectral feature (1900D). A high correlation between the standard operational procedure for the quality control of calcined kaolin and the Kx index was observed (r = -0.89), as well as with the 1900D parameter (r = -0.96). This study offers a new conceptual approach to the use of SWIR spectroscopy for the characterization the calcination of kaolin, withdrawing the need of using extensive laboratory techniques.

A novel method for destriping of OCM-2 data and radiometric performance analysis for improved ocean color data products

Despite the capability of Ocean Color Monitor aboard Oceansat-2 satellite to provide frequent, high-spatial resolution, visible and near-infrared images for scientific research on coastal zones and climate data records over the global ocean, the generation of science quality ocean color products from OCM-2 data has been hampered by serious vertical striping artifacts and poor calibration of detectors. These along-track stripes are the results of variations in the relative response of the individual detectors of the OCM-2 CCD array. The random unsystematic stripes and bandings on the scene edges affect both visual interpretation and radiometric integrity of remotely sensed data, contribute to confusion in the aerosol correction process, and multiply and propagate into higher level ocean color products generated by atmospheric correction and bio-optical algorithms. Despite a number of destriping algorithms reported in the literature, complete removal of stripes without residual effects and signal distortion in both low- and high-level products is still challenging. Here, a new operational algorithm has been developed that employs an inverted gaussian function to estimate error fraction parameters, which are uncorrelated and vary in spatial, spectral and temporal domains. The algorithm is tested on a large number of OCM-2 scenes from Arabian Sea and Bay of Bengal waters contaminated with severe stripes. The destriping effectiveness of this approach is then evaluated by means of various qualitative and quantitative analyses, and by comparison with the results of the previously reported method. Clearly, the present method is more effective in terms of removing the stripe noise while preserving the radiometric integrity of the destriped OCM-2 data. Furthermore, a preliminary time-dependent calibration of the OCM-2 sensor is performed with several match-up in-situ data to evaluate its radiometric performance for ocean color applications. OCM-2 derived water-leaving radiance products obtained after calibration show a good consistency with in-situ and MODIS-Aqua observations, with errors less than the validated uncertainties of ±5% and ±35% endorsed for the remote-sensing measurements of water-leaving radiance and retrieval of chlorophyll concentrations respectively. The calibration results show a declining trend in detector sensitivity of the OCM-2 sensor, with a maximum effect in the shortwave spectrum, which provides evidence of sensor degradation and its profound effect on the striping artifacts in the OCM-2 data products.

Aerosol optical properties and radiative effects: Assessment of urban aerosols in central China using 10-year observations

Poor air quality episodes are common in central China. Here, based on 10 years of ground-based sun-photometric observations, aerosol optical and radiative forcing characteristics were analyzed in Wuhan, the biggest metropolis in central China. Aerosol optical depth (AOD) in the last decade declined significantly, while the Ångström exponent (AE) showed slight growth. Single scattering albedo (SSA) at 440 nm reached the lowest value (0.87) in winter and highest value (0.93) in summer. Aerosol parameters derived from sun-photometric observations were used as input in a radiative transfer model to calculate aerosol radiative forcing (ARF) on the surface in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra. ARFSW sustained decreases (the absolute values) over the last 10 years. In terms of seasonal variability, due to the increases in multiple scattering effects and attenuation of the transmitted radiation as AOD increased, ARF in summer displayed the largest value (−73.94 W/m2). After eliminating the influence of aerosol loading, the maximum aerosol radiative forcing efficiency in SW range (ARFESW) achieved a value of −64.5 W/m2/AOD in April. The ARFE change in each sub-interval spectrum was related to the change in SSA and effective radius of fine mode particles (Refff), that is, ARFE increased with the decreases in SSA and Refff. The smallest contribution of ARFENIR to ARFESW was 34.11% under strong absorbing and fine particle conditions, and opposite results were found for the VIS range, whose values were always over 51.82%. Finally, due to the serious air pollution and frequency of haze day, aerosol characteristics in haze and clear days were analyzed. The percentage of ARFENIR increased from 35.71% on clear-air days to 37.63% during haze periods, while both the percentage of ARFEUV and ARFENIR in ARFESW kept decreasing. The results of this paper should help us to better understand the effect of aerosols on solar spectral radiation and to develop improved the aerosol models over central China.