Stray Light Effects Research Articles

Design of geostationary orbit ultrawide FOV long-wave infrared imaging spectrometer

The geostationary orbit imaging spectrometer offers distinct advantages for diverse applications in remote sensing. To enhance swath and data richness, there is a growing trend toward spectrometers with broader fields of view (FOV) and extended slit lengths. Optical systems equipped with these features face significant challenges in aberration correction. This paper investigates the parameters of geostationary orbits and designs a spectroscopic system capable of achieving ultrawide FOV without the need for stitching spectrograph subsystems. Additionally, it also designs a front-end telescope system that matches the spectroscopic system. The spectroscopic system features a slit length of 240 mm, employing an enhanced Offner structure for a long slit spectroscopic system, incorporating a freeform surface on the third mirror. To inhibit the effects of radiation stray light, the system's exit pupil is controlled to be positioned in front of the image plane to facilitate matching with the cold shield. The analysis indicates that the spectral resolution of the long-wave infrared imaging spectrometer system is 50 nm, with a total of 90 spectral sampling channels. The system's spatial resolution is 100 m, enabling a swath width of 400 km. Furthermore, the modulation transfer function (MTF) exceeds 0.42 at the Nyquist frequency of 8.35 lp/mm. The maximum RMS radius of the system is less than 27 μm at wavelengths ranging from 8 to 12.5 μm.

A Miniaturized and Highly Sensitive "Windmill" Three-Channel Fluorescence Detector for Simultaneous Detection of Various Mycotoxins.

A novel "windmill" three-channel light-emitting diode induced fluorescence detector (LED-IF) was proposed to maximize the excitation efficiency and fluorescence collection efficiency. Compared with the typical collinear arrangement, the fluorescence intensity of the three channels was increased by 7.85, 3.88, and 2.94 times, respectively. The compact shaping optical path was designed to obtain higher excitation efficiency and a lower background stray light effect caused by high divergence angle high-power ultraviolet (UV)-LEDs simultaneously, which increased the sensitivity of three channels by 4.6 to 5.7 times. It was found that using a photodiode (PD) with a flat window and a larger photosensitive surface can collect the Lambertian emission fluorescence in the flow cell more efficiently, increasing the signal-to-noise ratio of each channel 1.3 to 1.8 times. The limits of detection (LODs, 3 times peak-peak noise) of aflatoxin B2 (AFB2), ochratoxin (OTA), and zearalenone (ZEN) were 0.33, 1.80, and 28.2 ng/L, respectively. Finally, six mycotoxins were analyzed simultaneously by the detector coupling with HPLC. The results showed that the sensitivity of the detector was at the best level to date, which was better than that of the top commercial fluorescence detectors (FLDs). The developed detector has the advantages of having small volume, low cost, and long lifetime and being robust, which has wide application and market prospects.

Research on the background stray light suppression method of a dim target projector based on the orthogonal polarization extinction principle

Aiming at the problem of background stray light affecting the display of dim target scenes in existing projectors, a stray light suppression optical engine based on a polarizer is proposed. First, the effect of the background stray light of traditional LCOS target projectors on the display of dim targets is analyzed with simulation, and the sources of stray light in the target projector were analyzed as well. Secondly, we theoretically analyze the causes of different stray light paths and stray light polarization states, propose the method of stray light suppression based on the polarizer, and calculate the rotation angle of the polarizer. Then, we simulate and analyze the stray light suppression effect of the polarizer-based target projector model. Finally, a dim target projector test experiment system is built to verify the actual level of stray light suppression. The simulation results show that the highest stray light energy of the target projector with the polarizer-based stray light suppression optical engine has decreased by 2.37 times compared to the conventional LCOS target projector, the stray light coefficient has decreased from the previous 2.12% to 0.60%, and the simulated contrast ratio has been improved by 2.98 times. The experimental results show that the polarizer-based stray light suppression optical engine is able to reduce the peak gray level of the background stray light energy of the projected display image of the target projector by nearly 2 times, and improve the contrast of the gray level by 2.79 times. The suppression of dim target projector background stray light and the improvement of the contrast of the projected display image are realized.

A Vision-Based Pose Estimation of a Non-Cooperative Target Based on a Self-Supervised Transformer Network

In the realm of non-cooperative space security and on-orbit service, a significant challenge is accurately determining the pose of abandoned satellites using imaging sensors. Traditional methods for estimating the position of the target encounter problems with stray light interference in space, leading to inaccurate results. Conversely, deep learning techniques require a substantial amount of training data, which is especially difficult to obtain for on-orbit satellites. To address these issues, this paper introduces an innovative binocular pose estimation model based on a Self-supervised Transformer Network (STN) to achieve precise pose estimation for targets even under poor imaging conditions. The proposed method generated simulated training samples considering various imaging conditions. Then, by combining the concepts of convolutional neural networks (CNN) and SIFT features for each sample, the proposed method minimized the disruptive effects of stray light. Furthermore, the feedforward network in the Transformer employed in the proposed method was replaced with a global average pooling layer. This integration of CNN’s bias capabilities compensates for the limitations of the Transformer in scenarios with limited data. Comparative analysis against existing pose estimation methods highlights the superior robustness of the proposed method against variations caused by noisy sample sets. The effectiveness of the algorithm is demonstrated through simulated data, enhancing the current landscape of binocular pose estimation technology for non-cooperative targets in space.

Evaluating Landsat-9 TIRS-2 calibrations and land surface temperature retrievals against ground measurements using multi-instrument spatial and temporal sampling along transects

High-resolution TIR data are essential for a wide range of studies, e.g., in environmental monitoring, urban effects, water stress, agricultural productivity, and land/water resources. Landsat series provides high-resolution TIR data, but data accuracy must be ensured to contribute to these fields. After the calibration problems of Landsat 8 (L8) TIRS due to a stray light effect, efforts were made in the design of Landsat 9 (L9) TIRS-2 to mitigate this effect. In any case, field calibration and validation activities are necessary to evaluate the accuracy of recently launched sensors. These activities require high-quality ground TIR radiance data that are representative at satellite spatial resolution and that quantify spatial–temporal fluctuations at the experimental sites concurrently to satellite overpasses. However, these requirements are not always accomplished in the literature.This paper provides vicarious calibrations of the L9 TIRS-2 data with accurate ground measurements acquired using multi-instrument spatial and temporal sampling in a rice paddy area from December 2021 to August 2023, in order to contribute to the calibration and validation of L9 TIRS-data.In March 1, 2023 L9 TIRS-2 scenes started to be reprocessed and calibration was updated. Both the original calibration and that after reprocessing were evaluated. Close results were obtained for band 10 (b10). When comparing satellite brightness temperatures and those determined from in situ LSTs, systematic differences of −0.3 K were shown, with root-mean-square differences (RMSDs) of 0.5 K. Results for band 11 showed a bias of −0.1 K for the original data and of 0.2 K after the reprocessing, with RMSDs of 0.6 K.The L2 LST product generated operationally from b10 data was also evaluated, together with alternative single-channel (SC) algorithms. A bias (RMSD) of 0.4 K (1.1 K) was obtained for the product. However, negative biases were shown both with the radiative transfer equation used on b10 radiances and the alternative SC algorithm.Finally, we validated six types of split-window (SW) algorithms applied to L9 TIRS-2 data before and after the reprocessing. A systematic difference of about −0.6 K between SW LST biases when using the reprocessed and original data was observed. In any case, for most of the algorithms with original and reprocessed data, LST biases and standard deviations were within the recommended threshold of 1 K, which proves the good performance of L9 TIRS-2 data to monitor LST at high spatial resolution.

Fast Stray Light Performance Evaluation Based on BSDF and Radiative Transfer Theory.

Evaluating the stray light cancellation performance of an optical system is an essential step in the search for superior optical systems. However, the existing evaluation methods, such as the Monte Carlo method and the ray tracing method, suffer from the problems of vast arithmetic and cumbersome processes. In this paper, a method for a rapid stray light performance evaluation model and quantitatively determining high-magnitude stray light outside the field of view are proposed by adopting the radiative transfer theory based on the scattering property of the bidirectional scattering distribution function (BSDF). Under the global coordinates, based on the derivation of the light vector variation relationship in the near-linear system, the specific structural properties of the off-axis reflective optical system, and the specular scattering properties, a fast quantitative evaluation model of the optical system's stray light elimination capability is constructed. A loop nesting procedure was designed based on this model, and its validity was verified by an off-axis reflective optical system. It successfully fitted the point source transmittance (PST) curve in the range of specular radiation reception angles and quantitatively predicted the prominence due to incident stray light outside the field of view. This method does not require multiple software to work in concert and requires only 10-5 orders of magnitude of computing time, which is suitable for the rapid stray light assessment and structural screening of off-axis reflective optical systems with a good symmetry. The method is promising for improving imaging radiation accuracy and developing lightweight space cameras with low stray light effects.

A physically based correction for stray light in Brewer spectrophotometer data analysis

Abstract. Brewer ozone spectrophotometers have become an integral part of the global ground-based ozone monitoring network collecting data since the early 1980s. The double-monochromator Brewer version (MkIII) was introduced in 1992. With the Brewer hardware being so robust, both single- and double-monochromator instruments are still in use. The main difference between the single Brewers and the double Brewers is the much lower stray light in the double instrument. Laser scans estimate the rejection level of the single Brewers to be 10−4.5, while the doubles improve this to 10−8, virtually eliminating the effects of stray light. For a typical single-monochromator Brewer, stray light leads to an underestimation of ozone of approximately 1 % at 1000 DU ozone slant column density (SCD) and can exceed 5 % at 2000 DU, while underestimation of sulfur dioxide reaches 30 DU when no sulfur dioxide is present. This is because even a small additional stray light contribution at shorter wavelengths significantly reduces the calculated SCD at large values. An algorithm for stray light correction based on the physics of the instrument response to stray light (PHYCS) has been developed. The simple assumption is that count rates measured at any wavelength have a contribution from stray light from longer, and thus brighter, wavelengths because of the ozone cross-section gradient leading to a rapid change in intensity as a function of wavelength. Using the longest measured wavelength (320 nm) as a proxy for the overall brightness provides an estimate of this contribution. The sole parameter, on the order of 0.2 % to 0.6 %, that describes the percentage of light at the longest wavelength to be subtracted from all channels is determined by comparing ozone calculations from single- and double-monochromator Brewers making measurements side-by-side. Removing this additional count rate from the signal mathematically before deriving ozone corrects for the extra photons scattering within the instrument that produce the stray light effect. Analyzing historical data from co-located single- and double-monochromator Brewers provides an estimate of how the stray light contribution changes over time in an instrument. The corrected count rates of the measured wavelengths can also be used to improve other calculations: the sulfur dioxide column and the aerosol optical depth, the effective temperature of the ozone layer, or any other products. A multi-platform implementation of PHYCS, rmstray, to correct the count rates for stray light and save the corrected values in a new B-file for use with any existing Brewer data analysis software is available to the global Brewer user community at https://doi.org/10.5281/zenodo.8097038 (Savastiouk and Diémoz, 2023).

Nonlinearity Measurement of Si Transferring Photodetector in the Low Radiation Flux Range

In order to establish a transferring chain from a photon flux of a single-photon source in quantum radiometry, the nonlinearity of the photodetector needs to be accurately measured. Using the flux superposition method, a nonlinearity measurement setup has been designed. The measurement setup consists of two tungsten halogen lamps, parent–child integrating spheres, an adjustable aperture, a diaphragm tube, and an optical filter. It has the advantage of low polarization error, low interference error, and low stray light effect. The Si photodiode to be measured is cooled to −40 °C to obtain a low noise level for low-flux radiation measurement. The nonlinearity of the Si photodetector is measured for photocurrent ranges from 10−12 A~10−6 A level, with a relative standard uncertainty from 0.0092~0.023%. The relative standard uncertainty of the nonlinearity correction factor ranged from 0.023~0.049%.

Atmospheric correction under cloud edge effects for Geostationary Ocean Color Imager through deep learning

The Geostationary Ocean Color Imager (GOCI) is widely employed in tracking diurnal dynamics of oceanic conditions. However, the current atmospheric correction (AC) algorithms for GOCI often mask pixels around cloud edges to exclude pixels contaminated by cloud edge effects (CEEs; including stray light, cloud shadows, and cloud adjacent effects (AEs)), which results in massive data loss. In this paper, we propose a novel AC algorithm to correct these CEE-affected pixels based on deep learning (namely, DLACC) to achieve a comparable quality level to those pixels far away from cloud edges. We used the standard near-infrared iterative AC algorithm in SeaDAS (namely, NIR) to obtain Rayleigh-corrected reflectance (Rrc) and remote sensing reflectance (Rrs). Then, high-quality Rrs values were extracted using a quality assurance (QA) algorithm. Next, we obtained 2,821,668 matchups by matching CEE-free noontime Rrs values with CEE-affected Rrc values in a time window of 1 h. These matchups were used to develop DLACC. Validations using in situ data from Aerosol Robotic Network-Ocean Color (AERONET-OC) stations showed that more matchups were obtained with the DLACC model than with the NIR algorithm and Korea Ocean Satellite Center standard AC algorithm in GDPS 2.0 (KOSC), and the accuracies were similar. More importantly, the DLACC algorithm is more tolerant of AEs and reduces AEs in a 2-pixel distance from cloud edges by 10% in the blue bands and by 50% in the green band. As a result, more valid observations are obtained with the DLACC algorithm, with the daily percentage of valid observations (DPVOs) increasing by 71% and 62% over those with the NIR algorithm and the KOSC algorithm, respectively. These increases in valid observations could further result in more consistent patterns in terms of space and time. Our DLACC algorithm can not only be used to process GOCI images but also provide an open framework to develop corresponding deep-learning models for other geostationary satellites.

Balloon-borne FIREBall-2 ultraviolet spectrograph stray light control based on nonsequential reverse modeling of on-sky data

We present a comprehensive stray light analysis and mitigation strategy for the FIREBall-2 ultraviolet balloon telescope. Using nonsequential optical modeling, we identified the most problematic stray light paths, which impacted telescope performance during the 2018 flight campaign. After confirming the correspondence between the simulation results and postflight calibration measurements of stray light contributions, a system of baffles was designed to minimize stray light contamination. The baffles were fabricated and coated to maximize stray light collection ability. Once completed, the baffles will be integrated into FIREBall-2 and tested for performance preceding the upcoming flight campaign. Given our analysis results, we anticipate a substantial reduction in the effects of stray light.

Multiprojector Interreflection Compensation Using a Deep Convolution Network

The aim of multiprojector interreflection compensation is to modify input images to remove complex physical stray-light effects (interreflection) from a multiprojector immersive system. This is an important but often ignored problem, which can lead to degradation of a projection image. Traditional methods usually address this problem by computing a matrix inversion. These traditional methods often ignore issue of the clarity of the generated images. In this paper, we describe a method for learning the inversion using a deep convolutional neural network (CNN), named Superresolution Compensation Net (SRCN). SRCN consists of four convolution layers to learn interactions of global light, six convolution layers, and two transposed convolution layers to extract multilevel features and generate compensation images. We also used a subpixel convolution layer to increase the resolution. To make compensation images more consistent with human visual perception, we used a perceptual loss, which compares the differences between feature maps on the VGG16 network. We implemented an immersive projector-camera display prototype (Pro-Cam) and calculated the quality index of the compensation images and the projection results. Our method achieved better results than previous methods in both objective evaluations and subjective visual perception.

3D Printing of a PDMS Cylindrical Microlens Array with 100% Fill-Factor.

Cylindrical microlens arrays (CMLAs) play a key role in many optoelectronic devices, and 100% fill-factor CMLAs also have the advantage of improving the signal-to-noise ratio and avoiding stray-light effects. However, the existing preparation technologies are complicated and costly, which are not suitable for mass production. Herein, we propose a simple, efficient, and low-cost manufacturing method for CMLAs with a high fill-factor via the electric-field-driven (EFD) microscale 3D printing of polydimethylsiloxane (PDMS). By adjusting the printing parameters, the profile and the fill-factor of the CMLAs can be controlled to improve their optical performance. The optical performance test results show that the printed PDMS CMLAs have good image-projecting and light-diffraction properties. Using the two printing modes of this EFD microscale 3D-printing technology, a cylindrical dual-microlens array with a double-focusing function is simply prepared. At the same time, we print a series of specially shaped microlenses, proving the flexible manufacturing capabilities of this technology. The results show that the prepared CMLAs have good morphology and optical properties. The proposed method may provide a viable route for manufacturing large-area CMLAs with 100% fill-factor in a very simple, efficient, and low-cost manner.

A broadband spherical prism imaging spectrometer based on a single integrated module

The application range of hyperspectral imaging is subject to the operational system platform especially relies on the core imaging spectrometer. With a rising practical requirement of extensive remote sensing recently, the traditional method of two or multiple separate imaging submodules combined has obviously brought inevitable shortages in certain cases such as mineral detection or environmental monitoring, etc. Not only is the whole imaging system somewhat so large in physical size and so high in weight that it has an objective influence on convenience as well as flexibility in actual operation, but also each independent instrument has unique optical parameters and assembling matrices after fabrication and alignment which is against the image consistency. Instead of common image correction and data processing, the essential solution is to set up a broadband integrative system platform. This paper introduces a new prototype of imaging spectrometer in the visible and near-infrared (VNIR) to short-wave infrared (SWIR) region. Different from most existing research-based and commercial VNIR to SWIR imaging spectrometers, it is designed as broadband integration of a single core module. The main optical system consists of a collimating mirror, a central dispersive spherical prism, a converging mirror and two plane mirrors on the sides, which is similar to the normal convex grating spectrometer of three-concentric-mirror (Offner) configuration. The imaging spectrometer has relatively high imaging quality and satisfactory instantaneous field of view (IFOV) with a fairly compact internal structure benefiting from the integrated design and conscientious fabrication. The approach not only avoids extra expense and alignment complexities of multiple spectrometers but also enhances radiometric stability and reduces stray light and polarization effects. Relative performance tests are performed in various specific environment and validating imaging experiments are represented on schedule to demonstrate the expectant effectiveness of the whole system.

Calibration of a CubeSat spectroradiometer with a narrow-band widely tunable radiance source.

We have developed an SI-traceable narrow-band tunable radiance source based on an optical parametric oscillator (OPO) and an integrating sphere for the calibration of spectroradiometers. The source is calibrated with a reference detector over the ultraviolet/visible spectral range with an uncertainty of <1%. As a case study, a CubeSat spectroradiometer has been calibrated for radiance over its operating range from 370 nm to 480 nm. To validate the results, the instrument has also been calibrated with a traditional setup based on a diffuser and an FEL lamp. Both routes show good agreement within the combined measurement uncertainty. The OPO-based approach could be an interesting alternative to the traditional method, not only because of reduced measurement uncertainty, but also because it directly allows for wavelength calibration and characterization of the instrumental spectral response function and stray light effects, which could reduce calibration time and cost.

The effect of the stimulus eccentricity on the main component of the steady‐state visual evoked potential

PurposeFor electrophysiological functional diagnostics, the main component of steady‐state visual evoked potentials (SSVEP) at stimulation frequency (SF) is mainly used. However, some studies reported the main component at the second harmonic of the SF. A possible cause are signal components of the single responses that differ from the SF when the responses overlap during steady‐state stimulations, but the origin is not fully understood. The aim of our study was to investigate the effect of the stimulus eccentricity on the occurrence of the main component of SSVEP.MethodsWe studied 14 healthy subjects (5 m, 28 ± 5.0 years) using a circular layout (r1 = 0–1.6°, r2 = 1.6–3.5°, r3 = 3.5–6.4°, r4 = 6.4–10.9°, r5 = 10.9–18°). The dimensions of the stimuli were scaled according to the cortical magnification. The stimuli (luminance: 350 cd/m2, contrast: 99%) were presented in a random order at 7.5Hz for 75 cycles for each eccentricity. This procedure was repeated 10 times in total (750 cycles per eccentricity). A background luminance of 30 cd/m2 was added to supress foveal stray light effects. The electrodes were placed at Oz (active), FCz (reference) and FPz (ground). The recorded SSVEP were transformed using Fourier analysis. The medians (M) of the normalized amplitude ratios for amplitudes at first and second harmonic were calculated. Friedman's test (α = 0.05) and the probability of the occurrence of the main component at the second harmonic (P(MCSH)) were used for statistical analysis.ResultsThe normalized amplitude ratios showed a significant difference for the 5 stimulus eccentricities (Mr1 = 0.45, Mr2 = 0.41, Mr3 = 0.72, Mr4 = 0.72 Mr5 = 0.67; p = 0.0002*). P(MCSH) showed an increase for stimulus eccentricities for ≥r3 (P(MCSH)r1 = 0.07, P(MCSH)r2 = 0.07, P(MCSH)r3 = 0.36, P(MCSH)r4 = 0.29, P(MCSH)r5 = 0.36).ConclusionsThe stimulus eccentricity has an influence on the main component of SSVEP. An increase in stimulus eccentricity leads to an increased occurrence of the main component at second harmonic.

P.504 Targeting nitric oxide synthase 1 adaptor protein interactions as a possible treatment for schizophrenia: an initial proof-of-concept study in mice

Nonporous, submicrometer spherical particles can be fabricated by pulsed laser melting in liquid. In this process, particles dispersed in liquid absorb laser light, instantaneously heated above melting point, and quenched to form submicrometer spherical particles. The dispersed raw particles can only be heated from the laser beam direction, and thus the surface layer facing laser beam is reaction zone. Two automated iterative batch processing apparatuses with different cell sizes were developed to fabricate large quantities of submicrometer spherical particles by efficient use of liquid surface layer. Model calculations indicated that the formation rate will be higher when smaller cells and frequent cell exchange are adopted. This is experimentally confirmed with the fabrication of submicrometer spherical silver particles. The overall production rate of the iterative process with smaller cells was 5.15 mg h−1. However, the smaller cells imposed several limitations, including difficult sample agitation and stray light effects.

The Influence of the Stimulus Design on the Harmonic Components of the Steady-State Visual Evoked Potential

Steady-state visual evoked potentials (ssVEPs) are commonly used for functional objective diagnostics. In general, the main response at the stimulation frequency is used. However, some studies reported the main response at the second harmonic of the stimulation frequency. The aim of our study was to analyze the influence of the stimulus design on the harmonic components of ssVEPs. We studied 22 subjects (8 males, mean age ± SD = 27 ± 4.8 years) using a circular layout (r1 = 0–1.6°, r2 = 1.6–3.5°, r3 = 3.5–6.4°, r4 = 6.4–10.9°, and r5 = 10.9–18°). At a given eccentricity, the stimulus was presented according to a 7.5 Hz square wave with 50% duty cycle. To analyze the influence of the stimulus eccentricity, a background luminance of 30 cd/m2 was added to suppress foveal stray light effects; to analyze the influence of simultaneous foveal and peripheral stimulations, stimulations are performed without stray light suppression. For statistical analysis, medians M of the amplitude ratios for amplitudes at the second harmonic to the first harmonic and the probability of the occurrence of the main response at the second harmonic P(MCSH) are calculated. For stimulations with foveal stray light suppression, the medians were M0–1.6° = 0.45, M1.6–3.5° = 0.45, M3.5–6.4° = 0.76, M6.4–10.9° = 0.72, and M10.9–18° = 0.48, and the probabilities were P0–1.6°(MCSH) = 0.05, P1.6–3.5°(MCSH) = 0.05, P3.5–6.4°(MCSH) = 0.32, P6.4–10.9°(MCSH) = 0.29, and P10.9–18°(MCSH) = 0.30. For stimulations without foveal stray light suppression, the medians M were M0–1.6° = 0.29, M1.6–3.5° = 0.37, M3.5–6.4° = 0.98, M6.4–10.9° = 1.08, and M10.9–18° = 1.24, and the probabilities were P0–1.6°(MCSH) = 0.09, P1.6–3.5°(MCSH) = 0.05, P3.5–6.4°(MCSH) = 0.50, P6.4–10.9°(MCSH) = 0.55, and P10.9–18°(MCSH) = 0.55. In conclusion, the stimulus design has an influence on the harmonic components of ssVEPs. An increase in stimulation eccentricity during extrafoveal stimulation leads to a transition of the main response to the second harmonic. The effect is enhanced by a simultaneous foveal stimulation.

Comparison of the Sentinel-3A and B SLSTR Tandem Phase Data Using Metrological Principles

The Sentinel-3 mission is part of the Copernicus programme space segment and has the objective of making global operational observations of ocean, land and atmospheric parameters with its four on-board sensors. Two Sentinel-3 satellites are currently on orbit, providing near-daily global coverage. Sentinel-3A was launched on 16 February 2016 and Sentinel-3B on 25 April 2018. For the early part of its operation, Sentinel-3B flew in tandem with Sentinel-3A, flying 30 s ahead of its twin mission. This provided a unique opportunity to compare the instruments on the two satellites, and to test the per pixel uncertainty values in a metrologically-robust manner. In this work, we consider the tandem-phase data from the infrared channels of one of the on-board instruments: the Sea and Land Surface Temperature Radiometer, SLSTR. A direct comparison was made of both the Level 1 radiance values and the Level 2 sea surface temperature values derived from those radiances. At Level 1, the distribution of differences between the sensor values were compared to the declared uncertainties for data gridded on to a regular latitude-longitude grid with propagated pixel uncertainties. The results showed good overall radiometric agreement between the two sensors, with mean differences of ∼0.06 K, although there was a scene-temperature dependent difference for the oblique view that was consistent with what was expected from a stray light effect observed pre-flight. We propose a means to correct for this effect based on the tandem data. Level 1 uncertainties were found to be representative of the variance of the data, expect in those channels affected by the stray light effect. The sea surface temperature results show a very small difference between the sensors that could be in part due to the fact that the Sentinel-3A retrieval coefficients were also applied to the Sentinel-3B retrieval because the Sentinel-3B coefficients are not currently available. This will lead to small errors between the S3A and S3B retrievals. The comparison also suggests that the retrieval uncertainties may need updating for two of the retrieval processes that there are extra components of uncertainty related the quality level and the probability of cloud that should be included. Finally, a study of the quality flags assigned to sea surface temperature pixel values provided valuable insight into the origin of those quality levels and highlighted possible uncertainties in the defined quality level.

Comparison of Above-Water Seabird and TriOS Radiometers along an Atlantic Meridional Transect

The Fiducial Reference Measurements for Satellite Ocean Color (FRM4SOC) project has carried out a range of activities to evaluate and improve the state-of-the-art in ocean color radiometry. This paper described the results from a ship-based intercomparison conducted on the Atlantic Meridional Transect 27 from 23rd September to 5th November 2017. Two different radiometric systems, TriOS-Radiation Measurement Sensor with Enhanced Spectral resolution (RAMSES) and Seabird-Hyperspectral Surface Acquisition System (HyperSAS), were compared and operated side-by-side over a wide range of Atlantic provinces and environmental conditions. Both systems were calibrated for traceability to SI (Système international) units at the same optical laboratory under uniform conditions before and after the field campaign. The in situ results and their accompanying uncertainties were evaluated using the same data handling protocols. The field data revealed variability in the responsivity between TRiOS and Seabird sensors, which is dependent on the ambient environmental and illumination conditions. The straylight effects for individual sensors were mostly within ±3%. A near infra-red (NIR) similarity correction changed the water-leaving reflectance (ρw) and water-leaving radiance (Lw) spectra significantly, bringing also a convergence in outliers. For improving the estimates of in situ uncertainty, it is recommended that additional characterization of radiometers and environmental ancillary measurements are undertaken. In general, the comparison of radiometric systems showed agreement within the evaluated uncertainty limits. Consistency of in situ results with the available Sentinel-3A Ocean and Land Color Instrument (OLCI) data in the range from (400…560) nm was also satisfactory (−8% &lt; Mean Percentage Difference (MPD) &lt; 15%) and showed good agreement in terms of the shape of the spectra and absolute values.

A silicon‐organic hybrid platform for quantum microwave-to-optical transduction

Low-loss fiber optic links have the potential to connect superconducting quantum processors together over long distances to form large scale quantum networks. A key component of these future networks is a quantum transducer that coherently and bidirectionally converts photons from microwave frequencies to optical frequencies. We present a platform for electro-optic photon conversion based on silicon‐organic hybrid photonics. Our device combines high quality factor microwave and optical resonators with an electro-optic polymer cladding to perform microwave-to-optical photon conversion from 6.7 GHz to 193 THz (1558 nm). The device achieves an electro-optic coupling rate of 590 Hz in a millikelvin dilution refrigerator environment. We use an optical heterodyne measurement technique to demonstrate the single-sideband nature of the conversion with a selectivity of approximately 10 dB. We analyze the effects of stray light in our device and suggest ways in which this can be mitigated. Finally, we present initial results on high-impedance spiral resonators designed to increase the electro-optic coupling.