Stray Light Effects Research Articles

Landsat-8 Thermal Infrared Sensor (TIRS) Vicarious Radiometric Calibration

Launched in February 2013, the Landsat-8 carries on-board the Thermal Infrared Sensor (TIRS), a two-band thermal pushbroom imager, to maintain the thermal imaging capability of the Landsat program. The TIRS bands are centered at roughly 10.9 and 12 μm (Bands 10 and 11 respectively). They have 100 m spatial resolution and image coincidently with the Operational Land Imager (OLI), also on-board Landsat-8. The TIRS instrument has an internal calibration system consisting of a variable temperature blackbody and a special viewport with which it can see deep space; a two point calibration can be performed twice an orbit. Immediately after launch, a rigorous vicarious calibration program was started to validate the absolute calibration of the system. The two vicarious calibration teams, NASA/Jet Propulsion Laboratory (JPL) and the Rochester Institute of Technology (RIT), both make use of buoys deployed on large water bodies as the primary monitoring technique. RIT took advantage of cross-calibration opportunity soon after launch when Landsat-8 and Landsat-7 were imaging the same targets within a few minutes of each other to perform a validation of the absolute calibration. Terra MODIS is also being used for regular monitoring of the TIRS absolute calibration. The buoy initial results showed a large error in both bands, 0.29 and 0.51 W/m2·sr·μm or −2.1 K and −4.4 K at 300 K in Band 10 and 11 respectively, where TIRS data was too hot. A calibration update was recommended for both bands to correct for a bias error and was implemented on 3 February 2014 in the USGS/EROS processing system, but the residual variability is still larger than desired for both bands (0.12 and 0.2 W/m2·sr·μm or 0.87 and 1.67 K at 300 K). Additional work has uncovered the source of the calibration error: out-of-field stray light. While analysis continues to characterize the stray light contribution, the vicarious calibration work proceeds. The additional data have not changed the statistical assessment but indicate that the correction (particularly in band 11) is probably only valid for a subset of data. While the stray light effect is small enough in Band 10 to make the data useful across a wide array of applications, the effect in Band 11 is larger and the vicarious results suggest that Band 11 data should not be used where absolute calibration is required.

Spectral stray light effect on high-temperature measurements using a near-infrared multi-wavelength pyrometer

The spectral stray light is a major, non-negligible error source affecting spectral intensity measurements for optical instruments. The purpose of this study is to investigate the effects of spectral stray light on high-temperature measurements using a near-infrared (1.0–1.65μm) multi-wavelength pyrometer. The spectral stray light corrections were measured for the multi-wavelength pyrometer using a pulsed tunable laser for wavelengths from 0.41μm to 2.63μm. A matrix correction method was then used for the spectral stray light for the multi-wavelength pyrometer. The spectral response characteristics of the pyrometer were calibrated using a standard high-temperature blackbody source. The experimental results show that the spectral response characteristics are approximately identical for different calibration temperatures when the spectral stray light correction is used. The corrections for the spectral stray light significantly improve the accuracy of the multi-wavelength pyrometer at a blackbody calibration temperature which gives a simplified accurate calibration procedure, unlike the temperature calibrations for general optical pyrometers. Temperature measurement tests using a multi-wavelength pyrometer for standard high-temperature source further verified the measurement accuracy of the calibrated pyrometer which also illustrates the necessity of the spectral stray light corrections for the complex optical pyrometer and the applicability of the multi-wavelength algorithm.

Radiometric Calibration Methodology of the Landsat 8 Thermal Infrared Sensor

The science-focused mission of the Landsat 8 Thermal Infrared Sensor (TIRS) requires that it have an accurate radiometric calibration. A calibration methodology was developed to convert the raw output from the instrument into an accurate at-aperture radiance. The methodology is based on measurements obtained during component-level and instrument-level characterization testing. The radiometric accuracy from the pre-flight measurements was estimated to be approximately 0.7%. The calibration parameters determined pre-flight were updated during the post-launch checkout period by utilizing the on-board calibration sources and Earth scene data. These relative corrections were made to adjust for differences between the pre-flight and the on-orbit performance of the instrument, thereby correcting large striping artifacts observed in Earth imagery. Despite this calibration correction, banding artifacts (low frequency variation in the across-track direction) have been observed in certain uniform Earth scenes, but not in other uniform scenes. In addition, the absolute calibration performance determined from vicarious measurements have revealed a time-varying error to the absolute radiance reported by TIRS. These issues were determined to not be caused by the calibration process developed for the instrument. Instead, an investigation has revealed that stray light is affecting the recorded signal from the Earth. The varying optical stray light effect is an ongoing subject of evaluation and investigation, and a correction strategy is being devised that will be added to the calibration process.

Comparison of optical and psychophysical methods to measure intraocular straylight

AbstractPurpose To quantify intraocular forward scattering (straylight) by using three different methods in a group of normal subjects.Methods Intraocular straylight was measured in the dominant eye of 10 emmetropic subjects without any known ocular pathology (30±5 years).Two different, commercially available, scatter filters (Black Pro‐Mist ¼ and Black Pro‐Mist ½ from Tiffen)where used in order to recreate the effects of higher scattering. Three measurement techniques were used:a commercially available straylight meter (C‐quant, Oculus),a prototype of an optical double‐pass based method (Sigma) and a psychophysical method that we developed.We used a Bayesian method (quick‐CSF) in a range of spatial frequencies (2 to 20 cycles/degree) with 50 2‐alternative forced choice trials.Each set of trials was repeated 2 times for each condition (with and without glare).As a glare source, a fluorescent lamp was positioned concentrically to the test area where the sinusoidal gratings were projected.All tests were presented on a screen placed at 1 meter distance from the subject and the test area was covering a total of 6.4 degrees of visual field.For Sigma and C‐Quant tests,the logarithm of Scatter coefficient was determined, whereas for the q‐CSF measurements the difference between the areas below the log contrast sensitivity curves was used as scatter metrics.Results In the three methods, the effects of straylight were accordingly increasing with the addition of the scatter filters. A correlation between all three methods was verified.Conclusion These results suggest the potential use of an even simplified method based on the q‐CSF to evaluate straylight complementing other existing methods.

Iterative noise removal from temperature and density profiles in the TJ-II Thomson scattering

TJ-II Thomson Scattering diagnostic provides temperature and density profiles of plasma. The CCD camera acquires images that are corrupted with some kind of noise called stray-light. This noise degrades both image contrast and measurement accuracy, which could produce unreliable profiles of the diagnostic. So far, several approaches have been applied in order to decrease the noise in the TJ-II Thomson scattering images. Since the presence of the noise is not global but located in some particular regions of the image, advanced processing techniques are needed. However such methods require of manual fine-tuning of parameters to reach a good performance. In this contribution, an iterative image processing approach is applied in order to reduce the stray light effects in the images of the TJ-II Thomson scattering diagnostic. The proposed solution describes how the noise can be iteratively reduced in the images when a key parameter is automatically adjusted during the iterative process.

Color discrimination in individuals with light and dark irides: an evaluation of the effects of intraocular straylight and retinal illumination

To investigate the effect of induced intraocular straylight on the Farnsworth-Munsell 100-hue test performance in individuals with light and dark irides, 28 young subjects were tested both with and without a quantified light-scattering filter. The filter produced a significant increase in the total error scores (p<0.05), but no significant correlation was found between the level of straylight and error score (p>0.05). The development of a tritan-like defect in the dark-eyed participants can be attributed to the effect of light attenuation caused by filter absorption, which markedly affects S-cone mediated color discrimination. The combined effect of higher short-wavelength absorption of melanin and macular pigment in the dark eyes may be involved.

Compensating for the Effects of Stray Light in Single-Monochromator Brewer Spectrophotometer Ozone Retrieval

Spectrometers are designed to isolate particular wavebands and suppress light from wavelengths outside the band of interest. However, a small amount of undesired light will always enter the detector, not through the designed optical path, but through random scattering from the instrument optical components, housing, and dust particles. Every spectrophotometer has stray light coming from outside the nominal measurement waveband. For Dobson spectrophotometers and single monochromator Brewer spectrophotometers, which are basic instruments in the World Meteorological Organization (WMO) ozone and ultraviolet (UV) monitoring network, the error introduced by stray light is substantial when the ozone slant path becomes very large because of high solar zenith angles and a thick ozone layer. These are common conditions during Arctic spring. To study the issue, a long ozone slant path Intercomparison/Calibration campaign for Nordic Brewers and Dobsons was held at Sodankylä 8–24 March 2011 and a follow-up campaign to extend calibrations to shorter ozone slant paths took place at Izaña observatory, Tenerife, between 28 October and 18 November 2011. These campaigns were part of the Committee on Earth Observation Satellites (CEOS) Intercalibration of Ground-based Spectrometers and Lidars project funded by the European Space Agency (ESA), intended to permit the homogenization of ozone data from the European ozone ground-truthing network. During the active intercomparison periods, measurements were taken only when good conditions for sun or moon observations existed. Laboratory measurements using calibration lamps and helium-cadmium (HeCd) lasers were an essential part of both campaigns. The campaigns produced a high-quality database of total ozone and UV measurements and an accurate, up-to-date calibration and characterization of participating Brewers and Dobsons against the European standard instruments from the Regional Dobson Calibration Centre-Europe (RDCC-E) and the Regional Brewer Calibration Centre-Europe (RBCC-E). In the present work we focus on single monochromator Brewers and present a physics-based method to compensate for the stray-light effects in ozone retrieval using laboratory characterizations and radiative transfer modelling. The method was tested with independent data from the campaign.

抑制眼内杂散光提高视网膜成像质量方法研究

Using the liquid crystal spatial light modulator and Shack-Hartmann wave front sensor as the core components, an adaptive optics (AO) system for retinal imaging in vivo is constructed. Based on the modulation transfer function, quantitative analysis of the effects of the intraocular stray light on retinal imaging is carried out. The result demonstrates that the ocular stray light degrades the quality of the retinal images. According to the change characteristic of the polarization state of intraocular stray light. The fundus is illuminated by the polarized light. With the help of trial lens and sighting target with focal length of 1 m, the light source can be precisely focused on the capillary layer of the retina. Adopting the above mentioned methods, the effect of the ocular stray light is inhibited and the quality of retinal images is improved. Four volunteers participates in the experiments. The clear capillary images are obtained.

Attention to the effect of intraocular straylight in pseudophakic eyes on visual quality

As ophthalmic science develops,the expectations of the patients undergoing cataract also advance.Good Snellen visual acuity is not always an indicator for patient's satisfaction,and the visual quality is much more important.The intraocular straylight is one of the important parameters to analyze the vision quality after surgery.The pseudophakic photic phenomena,such as dysphotopsia,is closely related to the intraocular straylight.The posterior capsular opacification,the material and the edge design of the intraocular lens (IOL),the diameter of IOL optical component are the important influential factors that cause the dysphotopsia.Great attention must be paid to it,which make us to understand the straylight deeply in order to improve postoperative visual quality. Key words: Straylight; Visual quality; Intraocular lens

Detecting Light Outages After Severe Storms Using the S-NPP/VIIRS Day/Night Band Radiances

Power outages after a major storm affect the lives of millions of people and cause massive light outages. The launch of the Suomi National Polar-orbiting Partnership satellite with the Visible Infrared Imaging Radiometer Suite (VIIRS) significantly enhances our capability to monitor and detect light outages with the well-calibrated day/night band (DNB) and to use light loss signatures as indication of regional power outages. This study explores the use of the DNB in quantifying light outages due to the derecho storm in the Washington DC metropolitan area in June 2012 and Hurricane Sandy at the end of October 2012 on the East Coast of U.S. The results show that the DNB data are very useful in detecting power outages by quantifying light loss, but it also has some challenges due to clouds, lunar illumination, and straylight effect. Comparison of light outage and recovery trend determined from DNB data with power company survey shows reasonable agreement, demonstrating the usefulness of DNB in independently verifying and complementing the statistics from power companies.

Simulation and assessment of stray light effects in infrared cameras using non-sequential ray tracing

In this article, we have evaluated the stray light effects in infrared cameras operating in the 3–5μm waveband having cooled focal plane array detectors. A non-sequential ray tracing method is used to model the multiple reflections from polished lens surfaces as well as diffused scattering from rough mechanical surfaces inside the camera housing. The flux signature on the detector surface due to the self-emission of in-band radiation from the lenses and camera housing is calculated. The flux signature due to sources beyond the nominal field-of-view of the camera is also calculated. Light splitting into multiple diffraction orders from diffractive lens surfaces is taken into account both in the transmission and the reflection paths. The wavelength and angle dependent reflection coefficient of the anti-reflection coatings on the polished lens surfaces is taken into account. The effect of local heating of camera mounts on the stray light signature on the detector surface is also evaluated. The results show that using the non-sequential ray tracing method, useful predictions can be made for the stray light signature in the infrared cameras. Such calculations can be used to identify areas in the camera housing which need to be temperature stabilized to reduce their detrimental stray-light signature.

Simulation of modulation transfer function using a rendering method

We propose a novel simulation method based on rendering to evaluate the modulation transfer function (MTF) of optical imaging systems. The new simulation method corresponds to an experimental measurement of the MTF using imaging resolution test charts, and therefore allows an analysis of the resolving power of shift-variant optical systems that are difficult to evaluate with conventional methods based on the point spread function (PSF). Furthermore, the effects of stray light, such as from reflection or scattering, on the imaging performance can be analyzed. In contrast to methods based on illumination optics using Monte Carlo methods, the proposed method calculates the intensities on an image surface with rendering techniques used in three-dimensional computer graphics (3D CG), which results in calculations that are faster and have a higher precision. The proposed method is highly effective in analyzing the MTF of optical imaging systems through simulations.

Clinical relevance of straylight in patients with retinitis pigmentosa

AbstractPurpose The importance of straylight derives from the fact that it reduces retinal sensitivity. This may be particularly relevant in conditions with retinal dysfunction, such as Retinitis Pigmentosa (RP). Moreover in RP often early in life PSC cataract develops. The question of this study is whether straylight substantially contributes to visual disability in RP patients, potentially aggravated due to the combination of retinal degradation and increased straylight from cataract formation. In addition, straylight was used to predict possible benefit of (early) cataract surgery.Methods Twenty‐five RP patients scheduled for cataract extraction (CE) participated. Before and after CE, best corrected visual acuity (BCVA) in logMAR, contrast sensitivity (CS) in log(CS), temporal contrast sensitivity (TCS) in log(TCS), and straylight (log of the straylight parameter s, log[s]) were tested. TCS, or flicker sensitivity, was tested with a new test, using the C‐Quant hardware. TCS measurement was performed to assess foveal function isolated from the eye’s optical quality.Results Average pre CE log(s) value was 1.72, corresponding to a factor 6 straylight increase as compared to a healthy, young eye. Functionally significant improvement defined as &gt;0.2 log, was only found for log(s). Only log(s) improvement was related to pre CE values. LogMAR and log(TCS) were correlated (pre CE r(19)= .57, p&lt; .01; post CE ρ(19)= .47, p&lt; .05). Pre and post CE log(TCS) values were similar (p= .14).Conclusion Straylight effects of cataract may substantially aggravate visual disability in RP patients, whereas BCVA may (not yet) be affected. Loss of BCVA may reflect foveal function rather than cataract. For proper CE referral straylight must be assessed.

Variation in sunspot properties between 1999 and 2011 as observed with the Tenerife Infrared Polarimeter

We study the variation in the magnetic field strength and the umbral intensity of sunspots during the declining phase of the solar cycle no.23 and in the beginning of cycle no.24. We analyze a sample of 183 sunspots observed from 1999 until 2011 with the Tenerife Infrared Polarimeter at the German Vacuum Tower Telescope. The magnetic field strength is derived from the Zeeman splitting of the Stokes-V signal in one near-infrared spectral line, either Fe I 1564.8 nm, Fe I 1089.6 nm, or Si I 1082.7 nm. This avoids the effects of the unpolarized stray light from the field-free quiet Sun surroundings. The minimum umbral continuum intensity and umbral area are also measured. We find that there is a systematic trend for sunspots in the late stage of the solar cycle no.23 to be weaker, i.e., to have a smaller maximum magnetic field strength than those at the start of the cycle. The decrease in the field strength with time of about 94 G/yr is well beyond the statistical fluctuations that would be expected because of the larger number of sunspots close to cycle maximum (14 G/yr). In the same time interval, the continuum intensity of the umbra increases with a rate of 1.3 (+- 0.4)% of Ic/yr, while the umbral area does not show any trend above the statistical variance. Sunspots in the new cycle no.24 show higher field strengths and lower continuum intensities than those at the end of cycle no.23, interrupting the trend. Sunspots have an intrinsically weaker field strength and brighter umbrae at the late stages of solar cycles compared to their initial stages, without any significant change in their area. The abrupt increase in field strength in sunspots of the new cycle suggests that the cyclic variations are dominating over any long-term trend that continues across cycles. We find a slight decrease in field strength and an increase in intensity as a long-term trend across the cycles.

Comparative Resilience of Clinical Perimetric Tests to Induced Levels of Intraocular Straylight

PURPOSE To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT). METHODS Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument. RESULTS SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss. CONCLUSIONS The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Comparative Resilience of Clinical Perimetric Tests to Induced Levels of Intraocular Straylight

To investigate the effect of intraocular straylight (IOS) induced by white opacity filters (WOF) on threshold measurements for stimuli employed in three perimeters: standard automated perimetry (SAP), pulsar perimetry (PP) and the Moorfields motion displacement test (MDT). Four healthy young (24-28 years old) observers were tested six times with each perimeter, each time with one of five different WOFs and once without, inducing various levels of IOS (from 10% to 200%). An increase in IOS was measured with a straylight meter. The change in sensitivity from baseline was normalized, allowing comparison of standardized (z) scores (change divided by the SD of normative values) for each instrument. SAP and PP thresholds were significantly affected (P < 0.001) by moderate to large increases in IOS (50%-200%). The drop in motion displacement (MD) from baseline with WOF 5, was approximately 5 dB, in both SAP and PP which represents a clinically significant loss; in contrast the change in MD with MDT was on average 1 minute of arc, which is not likely to indicate a clinically significant loss. The Moorfields MDT is more robust to the effects of additional straylight in comparison with SAP or PP.

Simultaneous correction of bandpass and stray-light effects in array spectroradiometer data

A method for the simultaneous correction of bandpass and stray-light effects in array spectroradiometer data is presented. The method is based on the inversion of the instrument matrix of a device determined with the help of tuneable lasers. By applying the Tikhonov regularization technique, a straightforward correction of the measurement results is possible.

Non-Contact Vibration Sensor Using Bifurcated Bundle Fiber for Real Time Monitoring of Diesel Engine

A non-contact vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic reflective intensity modulation for monitoring the health condition of the diesel engine. An IR-source is used along with glass fibers to avoid the effect of stray light in sensing. The encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10µm, enough to monitor the vibrations generated in heavy machines like diesel engine.

不同线宽结构杂散光Kirk模型分析

The Kirks stray light simulation model is adopted to study the variation of stray light on different line structures, and the effects of stray light on imaging of different line structures are analyzed according to be image contrast. The simulation based on in-house image processing software written in Matlab indicates that, imaging of a sparser line structure has a lower image contrast and is more susceptible to stray light when the critical dimension is fixed. When the ratio of line width and space is fixed, a smaller critical dimension will lead to a lower image contrast and stronger effect of stray light on image pattern. Therefore, the stray light has great influence on the image pattern of narrow and sparse line structure.

Sensitivity of Dobson and Brewer Umkehr ozone profile retrievals to ozone cross-sections and stray light effects

Abstract. Remote sounding methods are used to derive ozone profile and column information from various ground-based and satellite measurements. Vertical ozone profiles measured in Dobson units (DU) are currently retrieved based on laboratory measurements of the ozone absorption cross-section spectrum between 270 and 400 nm published in 1985 by Bass and Paur (BP). Recently, the US National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) proposed using the set of ozone cross-section measurements made at the Daumont laboratory in 1992 (BDM) for revising the Aura Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment (GOME) satellite ozone profiles and total ozone column retrievals. Dobson Umkehr zenith sky data have been collected by NOAA ground-based stations at Boulder, CO (BDR) and Mauna Loa Observatory, HI (MLO) since the 1980s. The UMK04 algorithm is based on the BP ozone cross-section data. It is currently used for all Dobson Umkehr data processing submitted to the World Ozone and Ultraviolet radiation Data Centre (WOUDC) under the Global Atmosphere Watch (GAW) program of the World Meteorological Organization (WMO). Ozone profiles are also retrieved from measurements by the Mark IV Brewers operated by the NOAA-EPA Brewer Spectrophotometer UV and Ozone Network (NEUBrew) using a modified UMK04 algorithm (O3BUmkehr v.2.6, Martin Stanek). This paper describes the sensitivity of the Umkehr retrievals with respect to the proposed ozone cross-section changes. It is found that the ozone cross-section choice only minimally (within the retrieval accuracy) affects the Dobson and the Brewer Umkehr retrievals. On the other hand, significantly larger errors were found in the MLO and Boulder Umkehr ozone data (−8 and +5% bias in stratosphere and troposphere respectively) when the out-of-band (OOB) stray light contribution to the Umkehr measurement is not taken into account (correction is currently not included in the UMK04). The vertical distribution of OOB effect in the retrieved profile can be related to the local ozone climatology, instrument degradation, and optical characteristics of the instrument. Nonetheless, recurring OOB errors do not contribute to the long-term ozone trends.