Spectral Radiometer Research Articles

Evaluation of the hyperspectral radiometer (HSR1) at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site

Abstract. The Peak Design Ltd hyperspectral radiometer (HSR1) was tested at the Atmospheric Radiation Measurement (ARM) user facility Southern Great Plains (SGP) site in Lamont, Oklahoma, for 2 months from May to July 2022. The HSR1 is a prototype instrument that measures total (Ftotal) and diffuse (Fdiffuse) spectral irradiance from 360 to 1100 nm with a spectral resolution of 3 nm. The HSR1 spectral irradiance measurements are compared to nearby collocated spectral radiometers, including two multifilter rotating shadowband radiometers (MFRSRs) and the Shortwave Array Spectroradiometer–Hemispheric (SASHe) radiometer. The Ftotal at 500 nm for the HSR1 compared to the MFRSRs has a mean (relative) difference of 0.01 W m−2 nm−1 (1 %–2 %). The HSR1 mean Fdiffuse at 500 nm is smaller than the MFRSRs' by 0.03–0.04 (10 %) W m−2 nm−1. The HSR1 clear-sky aerosol optical depth (AOD) is also retrieved by considering Langley regressions and compared to collocated instruments such as the Cimel sunphotometer (CSPHOT), MFRSRs, and SASHe. The mean HSR1 AOD at 500 nm is larger than the CSPHOT's by 0.010 (8 %) and larger than the MFRSRs' by 0.007–0.017 (6 %–18 %). In general, good agreement between the HSR1 and other instruments is found in terms of the Ftotal, Fdiffuse, and AODs at 500 nm. The HSR1 quantities are also compared at other wavelengths to the collocated instruments. The comparisons are within ∼ 10 % for the Ftotal and Fdiffuse, except for 940 nm, where there is relatively larger disagreement. The AOD comparisons are within ∼ 10 % at 415 and 440 nm; however, a relatively larger disagreement in the AOD comparison is found for higher wavelengths.

Optical Design and Stray Light Analysis of Underwater Spectral Radiometer

Underwater spectral detection plays an important role in the study of the underwater environment, ecology, oceanography, and environmental monitoring. A kind of underwater spectral radiometer that can observe the distribution of underwater spectral radiation bidirectionally has been developed. The flat-field concave holographic grating is used as the only optical component, the optical design parameters are optimized, and the system is miniaturized. The mechanism of stray light generation in the spectrometer is studied, and a method of suppressing stray light is proposed and simulated. The level of stray light in the system is suppressed to the order of 10−4, the signal-to-noise ratio of the system is improved, and the ability to detect weak light is enhanced. The wavelength calibration experiment was completed, and the experimental results show that the wavelength resolution of the underwater spectral radiometer is better than 3 nm. Finally, the quantitative relationship between spectral irradiance and digital output is obtained through radiation in the calibration of the system.

Wavelength calibration of a solar spectral irradiance radiometer and validation by correlation photon coincidence counting

Accurate wavelength calibration is the key to achieving accuracy observation of solar spectral irradiance. A wavelength calibration of solar spectral irradiance radiometer based on correlation photon radiation reference is proposed. The wavelengths of two channels of the solar spectral irradiance radiometer are calibrated by a Hg-Ar lamp and lasers. A collimating and focusing optics are designed to ensure that light can illuminate the slit vertically and without polarization. The optics can also keep the consistency of observing and self-calibration modes. The calibration equations of two channels are established. The wavelength deviations of two channels are −0.11 ∼ 0.07 nm and −0.085 ∼ 0.017 nm respectively. To validate the calibrated wavelength, channel 1 is selected as the inspection channel according to the spectral line number of the calibration lamp and the variation of the photon count rate. The motor position close to the calibration wavelength 763.511 nm is selected in channel 2, and the coincidence measurement is carried out to check the accuracy of wavelength calibration in channel 1. The deviation of wavelength around 408 nm is 1.139 nm. The experimental results show that the correlated photons self-calibration system can realize the calibration and validation of the system wavelength. The method can increase the number of calibration wavelengths and is suitable for both channels.

Digital image processing for atmospheric monitoring at Colombian Andes

ABSTRACT As an alternative to the current technologies, we explored the feasibility of using low cost and massive use of digital cameras as photometric sensors to retrieve the atmospheric total optical depth (τ) in the urban area of a city in the Colombian Andes. This study proposes a simple way to estimate τ from digital processing of images of the Sun based on the Beer-Bouguer-Lambert law Langley’s linear fitting for the colour levels in channels red, green, and blue registered by the pixels of cameras’ sensors. From February to March 2022, the τ values retrieved from the images were correlated to the retrieved values from a solar spectral radiometer (SSR). We found that τ is sensible to the featured changes in the local atmosphere and to the cameras’ exposure parameters setup. Under conditions of partly clear sky, around 80% (r > 0.8) of the τ values from cameras showed a linear correspondence to those retrieved from SSR system. Its spectral dependency (τ _red < τ _green < τ _blue) is in accordance with the physical phenomena in light-atmosphere interaction. The results suggest that the methodology applied can be used for monitoring the atmosphere at any geographical location in the world.

Evaluation of the Solar Energy Nowcasting System (SENSE) during a 12-Months Intensive Measurement Campaign in Athens, Greece

Energy nowcasting is a valuable asset in managing energy loads and having real-time information on solar irradiation availability. In this study, we evaluate the spectrally integrated outputs of the SENSE system for solar irradiance nowcasting for the period of the ASPIRE (atmospheric parameters affecting spectral solar irradiance and solar energy) campaign (December 2020–December 2021) held in Athens, Greece. For the needs of the campaign, several ground-based instruments were operating, including two pyranometers, a pyrheliometer, a cloud camera, a CIMEL sunphotometer, and a precision spectral radiometer (PSR). Global horizontal irradiance (GHI) estimations were more accurate than direct normal irradiance (DNI). SENSE estimations are provided every 15 min, but when comparing bigger time intervals (hours-days), the statistics improved. A dedicated assessment of the SENSE’s inputs is performed in respect to ground-based retrievals, considering cloud conditions (from a sky imager), AOD, and precipitable water vapor from AERONET. The factor that established the larger errors was the visibility of the solar disc, which cannot be defined by the available sources of model inputs. Additionally, there were discrepancies between the satellite estimation of the clouds and the ground picture, which caused deviations in results. AOD differences affected more the DNI.

Study on Hyperspectral Reflectance of Brown Planthopper (Nilaparvata lugens) Infestation in Rice

Background: Pest management plays crucial role in yield prediction in all crops. In Rice, Brown Planthopper (BPH) plays major role in yield reduction. Pest forewarning in agriculture is the important tool and popularly used in various countries to avoid huge fertilizer and pesticide application. In this regard, Hyperspectral remote sensing gives various information about the spectral characteristics of BPH infected plants. Methods: Investigations were carried out to assess the damage of BPH infestation at the field level using a portable Hyper spectral radiometer. The farmers field at the BPH prone area of Kuttalam block, Nagapattinam district, Tamil Nadu was chosen to analyze the spectral reflectance of BPH -infected and uninfected plants and derive certain vegetation indices for accurate forewarning. The specific spectral bands from visible to infra-red (445 nm, 550 nm, 670 nm, 760 nm, 800 nm) were utilized to detect of BPH-infested plants over the field area. Result: Among various vegetation indices, the index MCARI (Modified Chlorophyll Absorption Reflectance Index) was performed well with high accuracy from early to late infestation at the field level and considered as the most effective tool in Precision Agriculture. As a result, The specific indices were analysed over BPH infected area to prevent greater spreading of pest damage and to minimize pesticides in the field.

Improved multivariate modeling for soil organic matter content estimation using hyperspectral indexes and characteristic bands.

Soil organic matter (SOM) is a key index of soil fertility. Calculating spectral index and screening characteristic band reduce redundancy information of hyperspectral data, and improve the accuracy of SOM prediction. This study aimed to compare the improvement of model accuracy by spectral index and characteristic band. This study collected 178 samples of topsoil (0-20 cm) in the central plain of Jiangsu, East China. Firstly, visible and near-infrared (VNIR, 350-2500 nm) reflectance spectra were measured using ASD FieldSpec 4 Std-Res spectral radiometer in the laboratory, and inverse-log reflectance (LR), continuum removal (CR), first-order derivative reflectance (FDR) were applied to transform the original reflectance (R). Secondly, optimal spectral indexes (including deviation of arch, difference index, ratio index, and normalized difference index) were calculated from each type of VNIR spectra. Characteristic bands were selected from each type of spectra by the competitive adaptive reweighted sampling (CARS) algorithm, respectively. Thirdly, SOM prediction models were established based on random forest (RF), support vector regression (SVR), deep neural networks (DNN) and partial least squares regression (PLSR) methods using optimal spectral indexes, denoted here as SI-based models. Meanwhile, SOM prediction models were established using characteristic wavelengths, denoted here as CARS-based models. Finally, this research compared and assessed accuracy of SI-based models and CARS-based models, and selected optimal model. Results showed: (1) The correlation between optimal spectral indexes and SOM was enhanced, with absolute value of correlation coefficient between 0.66 and 0.83. The SI-based models predicted SOM content accurately, with the coefficient of determination (R2) and root mean square error (RMSE) values ranging from 0.80 to 0.87, 2.40 g/kg to 2.88 g/kg in validation sets, and relative percent deviation (RPD) value between 2.14 and 2.52. (2) The accuracy of CARS-based models differed with models and spectral transformations. For all spectral transformations, PLSR and SVR combined with CARS displayed the best prediction (R2 and RMSE values ranged from 0.87 to 0.92, 1.91 g/kg to 2.56 g/kg in validation sets, and RPD value ranged from 2.41 to 3.23). For FDR and CR spectra, DNN and RF models achieved more accuracy (R2 and RMSE values ranged from 0.69 to 0.91, 1.90 g/kg to 3.57 g/kg in validation sets, and RPD value ranged from 1.73 to 3.25) than LR and R spectra (R2 and RMSE values from 0.20 to 0.35, 5.08 g/kg to 6.44 g/kg in validation sets, and RPD value ranged from 0.96 to 1.21). (3) Overall, the accuracy of SI-based models was slightly lower than that of CARS-based models. But spectral index had a good adaptability to the models, and each SI-based model displayed the similar accuracy. For different spectra, the accuracy of CARS-based model differed from modeling methods. (4) The optimal CARS-based model was model CARS-CR-SVR (R2 and RMSE: 0.92 and 1.91 g/kg in validation set, RPD: 3.23). The optimal SI-based model was model SI3-SVR (R2 and RMSE: 0.87 and 2.40 g/kg in validation set, RPD: 2.57) and model SI-SVR (R2 and RMSE: 0.84 and 2.63 g/kg in validation set, RPD: 2.35).

IDENTIFICATION OF CONCENTRATIONS OF SUBSTANCES IN THE OPEN ATMOSPHERE WITH THE PROCESSED MEASUREMENT OF THE FOURIER SPECTRAL RADIOMETER

The theoretical justification was carried out and the method of operational remote non-sampling gas analysis of the atmosphere in emergency situations was selected. As a result of the analysis of the methods of non-sampling determination of substances in the open atmosphere, it was established that the most appropriate use of optical spectral methods of monitoring the composition of the atmosphere, based on the registration and subsequent analysis of the electromagnetic radiation of the object of observation. To determine the most effective method of remote monitoring, an analytical classification of all possible optical spectral methods of remote monitoring was compiled: lidar methods, acousto-optic filters, correlation spectrometers, interference light filters with reconfiguration, use of the Fabry-Pere interferometer. It has been established that to solve the problem of non-sampling analysis of substances in the open atmosphere, it is most appropriate to use an infrared Fourier spectral radiometer of medium spectral resolution, which works in passive mode in the window of atmospheric transparency of 7-14 μm and allows obtaining experimental information in real time. Algorithms for the numerical solution of the problem of identification of substances and restoration of their concentrations based on infrared spectra of medium resolution in the region of 7…14 μm obtained on an IR Fourier spectroradiometer have been developed. Algorithms make it possible to identify substances by the unit spectrum of an open atmospheric track. Instead of considering a multidimensional system of linear equations, it is proposed to solve one or several one-dimensional problems. The transition to a one-dimensional problem is carried out by methods of correlation analysis. The influence of noise in the original spectrum on errors in solving the problem of determining concentrations was studied.

Https://journals.scholarpublishing.org/index.php/AIVP/article/view/14383

The toxicity of ultraviolet radiation in wavelength range 100-280 nm (UV-C) is well documented. UV-C irradiation can cause skin cancer, premature aging, visual problems and blindness. Prolonged exposure to UV radiation can kill both plants and animals, including entire forests. There are numerous assertions in the medical, public health, and geoscience literature that no UV-C reaches Earth’s surface, despite several studies to the contrary including one in 2007 by NASA. Naysayers blame technical problems such as stray light. Low-level UV-C measurements are difficult, if not nearly impossible, when using low integration values in the CCD Imaging Spectral Radiometers. This is due to the instrument’s internal and external atmospheric stray light issues, issues which even occur during calibration procedures that employ heated filament or gas-filled lamps. To obviate these inherent problems, one of us (RDH) designed, engineered, and constructed a Double Monochromator utilized in conjunction with the ILT950UV Spectral Radiometer operating in the raw data mode. Each of the initial measurements of solar irradiance displayed evidence of UV-C arriving at Earth’s surface, not high in the mountains, but just 176 meters above sea-level. These data were taken in the raw data mode, corrected for prism loss, with instrument noise, i.e. machine errors, subtracted. The non-zero value for relative spectral irradiance clearly shows the existence of UV-C at Earth’s surface, in the range 250-300 nm, even when measured under less than optimum atmospheric conditions. Research and development continue. We must know with certainty the condition of the stratospheric ozone layer that shields surface life from solar UV-C. Covert geoengineering atmospheric particulate pollution, in combination with industrial pollution of the atmosphere, is killing Earth’s stratospheric ozone layer. If unabated, it will sound the death knell for much of life on Earth.

The effect of a short-wave filtering contact lens on color appearance

We assessed the effect of a contact lens that filters short-wavelength (SW) visible light on color appearance. These effects were modeled and measured by direct comparison to a clear contact lens. Sixty-one subjects were enrolled, and 58 completed as cohort; 31 were 18 to 39 years old (mean ± SD, 29.6 ± 5.6), 27 were 40 to 65 years old (50.1 ± 8.1). A double-masked contralateral design was used; participants randomly wore a SW-filtering contact lens on one eye and a clear control lens on the other eye. Subjects then mixed three primaries (including a short-wave primary, strongly within the absorbance of the test lens) until a perceived perfect neutral white was achieved with each eye. Color appearance was quantified using chromaticity coordinates measured with a spectral radiometer within a custom-built tricolorimeter. Color vision in natural scenes was simulated using hyperspectral images and cone fundamentals based on a standard observer. Overall, the chromaticity coordinates of matches that were set using the SW-filtering contact lens (n = 58; x = 0.345, y = 0.325, u' = 0.222, v' = 0.470) and clear contact lens (n = 58; x = 0.344, y = 0.325, u' = 0.223, v' = 0.471) were not significantly different, regardless of age group. Simulations indicated that, for natural scenes, the SW-filtering contact lens that was evaluated changes L/(L+M) and S/(L+M) chromatic contrast by no more than -1.4% to +1.1% and -36.9% to +5.0%, respectively. Tricolorimetry was used to measure color appearance in subjects wearing a SW-filtering lens in one eye and a clear lens in the other, and the results indicate that imparting a subtle tint to a contact lens, as in the SW-filtering lens that was evaluated, does not alter color appearance for younger or older subjects. A model of color vision predicted little effect of the lens on chromatic contrast for natural scenes.

Cloud-Target Calibration for Fengyun-3D MERSI-II Solar Reflectance Bands: Model Development and Instrument Stability

Radiative calibration of satellite spectral radiometers is essential for their downstream applications. The Medium Resolution Spectral Imager (MERSI-II) is a key instrument of the Chinese polar orbit Fengyun-3D satellite. However, its calibration performance has not been sufficiently studied, which limits its broad application. This study revealed the feasibility of an cloud-target method for assessing the MERSI-II calibration performance in solar bands. The top-of-atmosphere reflectances for six MERSI-II reflective solar bands were numerically simulated using a rigorous forward radiative transfer method and cloud properties from well-collocated and well-calibrated MODIS operational cloud products with strict constraints. Only ice cloud targets were examined in the collocation due to their better homogeneity. The excellent agreement between our simulated reflectance and the MODIS reflectance (relative differences (RDs) of over 90% are within a 5% uncertainty range in six bands) validates our models. The simulated results in MERSI-II bands 1-4 showed reasonable agreements with the MERSI-II operational reflectance, i.e., mean RDs <3%, while the RDs in bands 6 and 7 reaches 12% and 6%, respectively. Our systematic cloud-target-calibration results over three years (2019-2021) indicated clear seasonal calibration biases and signal degradation of the MERSI-II solar bands, and those in the two cloud-absorbing bands, which reached ~15% and ~12% (in the three years), respectively. More importantly, we removed these seasonal and degradation biases to improve the current calibration accuracy to a stable value within 3%. Due to its robust performance, our cloud-target-based calibration method can be applied to future MERSI-II sensors to monitor the solar band stability.

Validation of Remote-Sensing Algorithms for Diffuse Attenuation of Downward Irradiance Using BGC-Argo Floats

Estimates of the diffuse attenuation coefficient (Kd) at two different wavelengths and band-integrated (PAR) were obtained using different published algorithms developed for open ocean waters spanning in type from explicit-empirical, semi-analytical and implicit-empirical and applied to data from spectral radiometers on board six different satellites (MODIS-Aqua, MODIS-Terra, VIIRS–SNPP, VIIRS-JPSS, OLCI-Sentinel 3A and OLCI-Sentinel 3B). The resultant Kds were compared to those inferred from measurements of radiometry from sensors on board autonomous profiling floats (BGC-Argo). Advantages of BGC-Argo measurements compared to ship-based ones include: 1. uniform sampling in time throughout the year, 2. large spatial coverage, and 3. lack of shading by platform. Over 5000 quality-controlled matchups between Kds derived from float and from satellite sensors were found with values ranging from 0.01 to 0.67 m−1. Our results show that although all three algorithm types provided similarly ranging values of Kd to those of the floats, for most sensors, a given algorithm produced statistically different Kd distributions from the two others. Algorithm results diverged the most for low Kd (clearest waters). Algorithm biases were traced to the limitations of the datasets the algorithms were developed and trained with, as well as the neglect of sun angle in some algorithms. This study highlights: 1. the importance of using comprehensive field-based datasets (such as BGC-Argo) for algorithm development, 2. the limitation of using radiative-transfer model simulations only for algorithm development, and 3. the potential for improvement if sun angle is taken into account explicitly to improve empirical Kd algorithms. Recent augmentation of profiling floats with hyper-spectral radiometers should be encouraged as they will provide additional constraints to develop algorithms for upcoming missions such as NASA’s PACE and SBG and ESA’s CHIME, all of which will include a hyper-spectral radiometer.

Optical amplification enables a huge sensitivity improvement to laser heterodyne radiometers for high-resolution measurements of atmospheric gases.

A novel, to the best of our knowledge, performance-enhanced laser heterodyne radiometer has been developed by utilizing a semiconductor optical amplifier to amplify the collected weak solar radiation in an optical fiber. High-spectral-resolution measurements of atmospheric carbon dioxide column absorption are used to validate the technique and performance of the developed instrument. The implementation of optical amplification led to a 9-times improvement in sensitivity according to the Allan variance analysis for noise fluctuations, and resulted in a 7.7-times enhancement in measurement precision for atmospheric carbon dioxide. The promising results showed the great potential of employing this type of compact fiber-optics-based spectral radiometer for applications such as atmospheric greenhouse gas sensing.

A Coupled Evaluation of Operational MODIS and Model Aerosol Products for Maritime Environments Using Sun Photometry: Evaluation of the Fine and Coarse Mode

Although satellite retrievals and data assimilation have progressed to where there is a good skill for monitoring maritime Aerosol Optical Depth (AOD), there remains uncertainty in achieving further degrees of freedom, such as distinguishing fine and coarse mode dominated species in maritime environments (e.g., coarse mode sea salt and dust versus fine mode terrestrial anthropogenic emissions, biomass burning, and maritime secondary production). For the years 2016 through 2019, we performed an analysis of 550 nm total AOD550, fine mode AOD (FAOD550; also known as FM AOD in the literature), coarse mode AOD (CAOD550), and fine mode fraction (η550) between Moderate Resolution Spectral Imaging Radiometer (MODIS) V6.1 MOD/MYD04 dark target aerosol retrievals and the International Cooperative for Aerosol Prediction (ICAP) core four multi-model consensus (C4C) of analyses/short term forecasts that assimilate total MODIS AOD550. Differences were adjudicated by the global shipboard Maritime Aerosol Network (MAN) and selected island AERONET sun photometer observations with the application of the spectral deconvolution algorithm (SDA). Through a series of conditional and regional analyses, we found divergence included regions of terrestrial influence and latitudinal dependencies in the remote oceans. Notably, MODIS and the C4C and its members, while having good correlations overall, have a persistent +0.04 to +0.02 biases relative to MAN and AERONET for typical AOD550 values (84th% &lt; 0.28), with the C4C underestimating significant events thereafter. Second, high biases in AOD550 are largely associated with the attribution of the fine mode in satellites and models alike. Thus, both MODIS and C4C members are systematically overestimating AOD550 and FAOD550 but perform better in characterizing the CAOD550. Third, for MODIS, findings are consistent with previous reports of a high bias in the retrieved Ångström Exponent, and we diagnosed both the optical model and cloud masking as likely causal factors for the AOD550 and FAOD550 high bias, whereas for the C4C, it is likely from secondary overproduction and perhaps numerical diffusion. Fourth, while there is no wind-speed-dependent bias for surface winds &lt;12 m s−1, the C4C and MODIS AOD550s also overestimate CAOD550 and FAOD550, respectively, for wind speeds above 12 m/s. Finally, sampling bias inherent in MAN, as well as other circumstantial evidence, suggests biases in MODIS are likely even larger than what was diagnosed here. We conclude with a discussion on how MODIS and the C4C products have their own strengths and challenges for a given climate application and discuss needed research.

Above-aircraft cirrus cloud and aerosol optical depth from hyperspectral irradiances measured by a total-diffuse radiometer

Abstract. This study develops the use of spectral total and diffuse irradiance measurements, made from a prototype hyperspectral total-diffuse sunshine pyranometer (SPN-S), to retrieve layer fine-mode aerosol (τaer) and total optical depths from airborne platforms. Additionally, we use spectral analysis in an attempt to partition the total optical depth into its τaer and cirrus cloud optical depth (τcld) components in the absence of coarse-mode aerosols. Two retrieval methods are developed: one leveraging information in the diffuse irradiance and the other using spectral characteristics of the transmitted direct beam, with each approach best suited for specific cloud and aerosol conditions. The SPN-S has advantages over traditional sun photometer systems, including no moving parts and a low cost. However, a significant drawback of the instrument is that it is unable to measure the direct-beam irradiance as accurately as sun photometers. To compensate for the greater measurement uncertainty in the radiometric irradiances, these retrieval techniques employ ratioed inputs or spectral information to reduce output uncertainty. This analysis uses irradiance measurements from the SPN-S and the solar spectral flux radiometer (SSFR) aboard the National Aeronautics and Space Administration's (NASA) P-3 aircraft during the 2018 deployment of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign and the 2019 Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) mission to quantify above-aircraft cirrus τcld and derive vertical profiles of layer τaer. Validation of the τaer retrieval is accomplished by comparison with co-located measurements of direct solar irradiance made by the Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) and in situ measurements of aerosol optical depth. For the aggregated 2018 ORACLES results, regression between the SPN-S-based method and sun photometer τaer values yields a slope of 0.96 with an R2 of 0.96, while the root mean square error (RMSE) is 3.0×10-2. When comparing the retrieved τaer to profiles of integrated in situ measurements of optical extinction, the slope, R2, and RMSE values for ORACLES are 0.90, 0.96, and 3.4×10-2, and for CAMP2Ex they are 0.94, 0.97, and 3.4×10-2, respectively. This paper is a demonstration of methods for deriving cloud and aerosol optical properties in environments where both atmospheric constituents may be present. With improvements to the low-cost SPN-S radiometer instrument, it may be possible to extend these methods to a broader set of sampling applications, such as ground-based settings.

Characterization and effectiveness of a violet LED light for in-office whitening.

This study characterized a violet LED light (V-LED; bright max whitening) tooth whitening device and evaluated its efficacy on stained enamel compared to hydrogen peroxide (HP). Characterization of the V-LED beam profile was performed using a laser beam-profiler. The irradiance was measured throughout an exposure cycle at 0- and 8-mm distances using an integrating sphere and a spectral radiometer. Bovine enamel/dentin blocks stained with black tea (BT), cigarette smoke (CS), or without staining (CONT) were subjected to V-LED or 40% HP (n = 10/group). Color parameters (ΔL, Δa, Δb, and ΔE00) were measured using a digital spectrophotometer. Light transmission was estimated through 1-mm-thick bovine enamel slices (n = 5). ΔL, Δb, ΔE00, and irradiance were analyzed by two-way ANOVAs and Tukey's tests, Δa by Kruskal-Wallis and Mann-Whitney tests, and light transmission by t-test (α = 5%). Heterogeneous beam distribution was observed for the emitting V-LED chips. After 20 sequential exposures, irradiance levels were reduced 25-50%, regardless of the distance from V-LED. Localized irradiance values were statistically different between beam locations and different distances from the target. V-LED produced lower ΔE00, ΔL, Δa, and Δb values than HP for CONT and BT, with no differences for CS. Light transmittance decreased approximately 98% through 1-mm thick enamel. V-LED irradiance was heterogeneous and decreased throughout the exposure cycles and was also greatly reduced with increasing tip distance. V-LED produced a significantly lower whitening effect on BT and control teeth. This study contributes to the knowledge of V-LED and its clinical use.

Evaluation of local measurement-driven adjustments of modelled cloud-free atmospheric photolysis rate coefficients

Using time series of spectral radiometer measurements we reveal three sets of photolysis reactions that group together according to the adjustments required to their modelled j-values for local solar flux conditions.

The Effects of a Blue-Light Filtering Versus Clear Intraocular Implant on Color Appearance.

PurposeMore than a dozen studies have investigated whether blue-light filtering (BLF) intraocular lens (IOL) implants influence color vision, generally finding they do not. These studies have not tested color vision per se; rather, they have measured color vision deficiencies or chromatic discrimination. Here, we used additive trichromatic colorimetry to assess color appearance in participants with BLF and clear IOL.MethodsSeventy-six participants were recruited from two populations: older participants (n = 52) with BLF and clear IOL (n = 98 eyes; M = 67.33 ± 7.48 years; 58.8% female; 25.5% non-White), and young adult control participants (n = 24; M = 21.0 ± 5.13 years; 70.8% female; 41.5% non-White). Participants used a custom-built tricolorimeter to mix three primaries until a perceived perfect neutral white was achieved. Color appearance, expressed as chromaticity coordinates, was measured with a spectral radiometer (ILS950).ResultsBetween subjects, the BLF IOL chromaticity coordinates (x = 0.34, y = 0.35, u′ = 0.21, v′ = 0.48) were not significantly different from the clear IOL (x = 0.34, y = 0.33, u′ = 0.22, v′ = 0.48). BLF and clear IOL were also not different within-contralateral subjects (n = 21; BLF x = 0.34, y = 0.33, u′ = 0.22, v′ = 0.47; clear x = 0.34, y = 0.33, u′ = 0.21, v′ = 0.48). Both IOL groups differed from young adults (v′[0.45; P = 0.001], x[0.31; P = 0.008], and y[ 0.30, P < 0.000], but not u′[0.21]).ConclusionsOne advantage of geometric representation of color space is the ability to specify the appearance (rather than spectral composition) of any light mixture by specific coordinates. Using this system, only minor differences in color appearance were found between a BLF, clear IOL, and young natural lens.Translational RelevanceWhen color perception is directly measured, the BLF and clear IOL are not meaningfully different.

Spatiotemporal Heterogeneity of Aerosol and Cloud Properties Over the Southeast Atlantic: An Observational Analysis

AbstractThe southeast Atlantic has expansive aerosol plumes overlying clouds for a third of each year. Aerosol optical depths (AODs) were measured from the airborne Sun photometer and lidar during the 2016 NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign. We compare these measurements with one another and with collocated Moderate Resolution Imaging Spectroradiometer (MODIS) observations at native spatial resolutions using &lt;15‐min and 3‐h temporal collocation criteria. We find better statistical relationships for the &lt;15‐min temporal resolution, indicating that AODs in the southeast Atlantic commonly vary below three‐hourly temporal scales over MODIS spatial resolutions. We also use the airborne Solar Spectral Flux Radiometer (SSFR) to conduct the first comprehensive evaluation of attenuation‐corrected below‐aerosol cloud optical depths (CODs) from MODIS and the Spinning Enhanced Visible and Infrared Imager (SEVIRI). MODIS COD retrievals improve their agreement with the SSFR when accounting for overlying aerosol attenuation whereas SEVIRI CODs are mostly underestimated.

The effect of low-level thin arctic clouds on shortwave irradiance: evaluation of estimates from spaceborne passive imagery with aircraft observations

Abstract. Cloud optical properties such as optical thickness along with surface albedo are important inputs for deriving the shortwave radiative effects of clouds from spaceborne remote sensing. Owing to insufficient knowledge about the snow or ice surface in the Arctic, cloud detection and the retrieval products derived from passive remote sensing, such as from the Moderate Resolution Imaging Spectroradiometer (MODIS), are difficult to obtain with adequate accuracy – especially for low-level thin clouds, which are ubiquitous in the Arctic. This study aims at evaluating the spectral and broadband irradiance calculated from MODIS-derived cloud properties in the Arctic using aircraft measurements collected during the Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE), specifically using the upwelling and downwelling shortwave spectral and broadband irradiance measured by the Solar Spectral Flux Radiometer (SSFR) and the BroadBand Radiometer system (BBR). This starts with the derivation of surface albedo from SSFR and BBR, accounting for the heterogeneous surface in the marginal ice zone (MIZ) with aircraft camera imagery, followed by subsequent intercomparisons of irradiance measurements and radiative transfer calculations in the presence of thin clouds. It ends with an attribution of any biases we found to causes, based on the spectral dependence and the variations in the measured and calculated irradiance along the flight track. The spectral surface albedo derived from the airborne radiometers is consistent with prior ground-based and airborne measurements and adequately represents the surface variability for the study region and time period. Somewhat surprisingly, the primary error in MODIS-derived irradiance fields for this study stems from undetected clouds, rather than from the retrieved cloud properties. In our case study, about 27 % of clouds remained undetected, which is attributable to clouds with an optical thickness of less than 0.5. We conclude that passive imagery has the potential to accurately predict shortwave irradiances in the region if the detection of thin clouds is improved. Of at least equal importance, however, is the need for an operational imagery-based surface albedo product for the polar regions that adequately captures its temporal, spatial, and spectral variability to estimate cloud radiative effects from spaceborne remote sensing.