Modulation Transfer Function Values Research Articles

Design of a Dual-Band Compact Integrated Remote Sensing System for Visible Light and Long-Wave Infrared

This paper presents a design of a dual-band integrated space telescope system for visible light and long-wave infrared. The system can simultaneously image the visible light band of 450–900 nm and the long-wave infrared band of 7700–10,500 nm. The dual-band integrated imaging system can freely switch the observation band to adapt to different scenes and environmental changes. The camera can also further expand its capabilities in the fields of multi-spectral observation and low-light observation by collocation with different detectors. This design is based on a coaxial reflection system, the two bands share the camera’s primary and secondary mirrors, and the separation of the two bands is achieved through a separate field of view design. After simulation, the average Modulation Transfer Function (MTF) value of the visible light band of the system at 50 lp/mm (line pairs per millimeter) reaches 0.45, and the average MTF value of the long-wave infrared band at 50 lp/mm reaches 0.36. In addition, tolerance analysis, ambient temperature analysis and transmittance analysis of the integrated system are carried out in this paper to further improve the integrated system scheme, and the feasibility of the system is further verified.

Effect of beam quality and readout direction in the edge profile on the modulation transfer function of photostimulable phosphor systems via the edge method.

Purpose: The objective of this study was to investigate the effects of (i) the difference in the beam qualities on the presampled modulation transfer function (MTF) using the edge method and (ii) the readout direction of the edge profile for the photostimulable phosphor (PSP) system. Approach: The International Electrotechnical Commission (IEC) defined a technique using the "radiation qualities based on a phantom made up of an aluminum added filter" (RQA). A general radiographic system with a tube voltage of 50kV and 9.7mm of additional aluminum filtration was used to conform the x-ray to the IEC-specified beam quality definition RQA3. Additionally, we employed two different beams with tube voltages of 60 and 70kV using a dental x-ray unit. The MTF was measured in the readout direction from low-to-high exposure regions and vice versa with respect to the scanning and subscanning directions of the PSP system. Results: The difference in the 50%MTF value for all directions between 60 and 70kV averaged less than . The 50%MTF of RQA3 was on average 0.2 lower than the value for 60kV for each direction. For all beam qualities, no difference was observed between the MTFs measured in the readout direction from the low-to-high exposure regions and vice versa. Conclusions: The MTFs, measured using the dental x-ray unit, were unaffected by the tube voltage, and they were slightly higher than those measured using the RQA3. Furthermore, the MTF was unaffected by the differences in the readout directions of the edge profile.

Modulation Transfer Function Analysis in Myopic Model Eye

Hitherto, the eye modelling is based on the emmetropic eye taken its ocular optical components value from the population-based studies. However, no studies have been done to study the effect of aberration of myopic refractive error by modelling the eye using the parameters from ocular biometrics and ray tracing method. This study aimed to determine the modulation transfer function (MTF) of myopic refractive error using eye modelling and ray tracing technique. Three eye models had been successfully modelled in Zemax software, namely, emmetropic Liou and Brennan, myopic Liou and Brennan, corrected myopic Liou and Brennan. The optical performance of the eye models were tested using the MTF. From the MTF analysis at 100 cycles/mm, the MTF value of both tangential and sagittal rays for myopic Liou and Brennan eye was the lowest compared to its emmetropic model. Also, the MTF value of the corrected myopic Liou and Brennan model was higher compared to the uncorrected myopic model. However, the corrected myopic model produced lower MTF values for both tangential and sagittal MTF compared with the emmetropic model of Liou and Brennan. In this study, the accuracy of the MTF for myopia correction and emmetropia were calculated. It was found that the accuracy of the MTF value for corrected myopia at tangential and sagittal rays was lower.

Design of a passive optical athermalization of dual-band IR seeker for precision-guided systems

The optical design of a seeker, operating in two bands of infrared (MWIR-LWIR), is performed. The dual-band design has been developed on Zemax OpticStudio. Considering the optical parameters of commercially available dual-band IR detectors, the design of the IR imaging seeker is completed for the operation within the wavelength range of 3–10 µm. The temperature dependence of the optical design is also examined for four different lens barrel materials, for the large temperature interval ranging from −40°C to 80°C. The defocusing effect caused by using different lens barrel is fixed by the passive-optical-athermalization technique. The field of view of the optical system is found to be 16°. The modulation transfer function (MTF) value of each field is higher than 0.50 when the spatial frequency takes a value of 20.8 lp/mm. The results are analyzed and discussed in terms of spot diagram, MTF.

Design of Refractive/Diffractive Hybrid Projection Lens for DMD-Based Maskless Lithography

The projection lens is the core component of DMD-based maskless lithography and its imaging quality directly affects the transferal of exposure pattern. Based on the traditional projection lens system, we have designed diffractive optical element (DOE) and aspheric surfaces to optimize the refractive/diffractive hybrid projection lens system to improve its imaging quality. We found that the best effect is obtained when DOE is very close to the front lens group before the diaphragm of the hybrid system. Compared with the traditional projection lens system, this hybrid projection lens system has lower wave aberration with the help of DOE, and higher image quality owing to the modulation transfer function (MTF) value being improved. Finally, a hybrid projection lens system with working distance of 29.07 mm, image Space NA of 0.45, and total length of 196.97 mm is designed. We found that the maximum distortion and field curvature are 1.36 × 10−5% and 0.91 μm, respectively.

Laboratory analysis and ray visualization of diffractive optics with enhanced intermediate vision

BackgroundTo assess the optical behavior of a new diffractive intraocular lens (IOL) and compare its performance to that of an established extended-depth-of-focus (EDOF) IOL.MethodsThis study assessed the Proming EDOF Multifocal AM2UX [Eyebright Medical Technology (Beijing) Co., Ltd., China] and the AT LARA 829MP [Carl Zeiss Meditec, Germany]. An experimental set-up with 0.01% fluorescein solution and monochromatic light (532 nm) was used to visualize the IOLs’ ray propagation. In addition, the optical quality of the IOLs was assessed by measuring the modulation transfer function (MTF) values at 50lp/mm and 3.0 and 4.5 mm apertures on the optical bench OptiSpheric® IOL PRO II [Trioptics GmbH, Germany].ResultsThe ray propagation of the two IOLs showed two distinct foci. Light intensity assessment revealed that both IOLs allocate more energy to primary than secondary focus. At 3.0 mm pupil, the MTF values at 50lp/mm for the primary focus were 0.39 and 0.37, and for the secondary focus, 0.29 and 0.26 for the AT LARA and Proming IOLs, respectively. At 4.5 mm pupil, the single-frequency MTF for the primary focus was 0.51 and 0.24 and for the secondary focus 0.21 and 0.15 for the AT LARA and Proming IOLs, respectively.ConclusionsWhen tested with an aberration-free model cornea under monochromatic conditions, the Proming behaved as a low-add bifocal lens; however, its properties did not differ much from the well-established AT LARA EDOF IOL. The AT LARA outperformed the Proming at low defocus (up to 2D), while the latter demonstrated better image quality in the 2-3D range.

Fast full-field modulation transfer function analysis for photographic lens quality assessment.

Full-field modulation transfer function (MTF) data based on the slanted-edge method can give useful insights on the performance of a photographic lens sample and its shortcomings. Decentering and other out-of-tolerance states are recognized easily. A process to derive accurate lens MTF from slanted-edge spatial frequency response measurements is presented, covering chart design and alignment, data capture by standard digital cameras, slanted-edge algorithm implementation requirements, sensor and chart MTF corrections, and also visualization of the results. It is demonstrated that the reliability of the measured MTF values is by far good enough to support automated quality assessment with a measurement accuracy of ≈0.02 MTF and repeatability of ≲0.005 up to 100 c/mm. The measured full-field MTF values provide an unambiguous numerical criterion for comparison with expectations based on lens design.

Estimation of Modulation Transfer Function (MTF) of VNREDSat-1 satellite for image quality assessment by using the permanent test site

MTF is a factor in evaluating image quality with respect to the contrast and sharpness of the payload, thus directly related to spatial resolution. Therefore, ensuring image quality is an important task, especially for small satellites with high spatial resolution. This study uses the slanted-edge method for the artificial permanent test site and VNREDSat-1 image data with spatial resolution of panchromatic band as 2.5 m to make an MTF value estimate. The MTF value during 5 years of operation averages about 0.2 compared to the threshold as 0.08 (for the test site at Salon de Provence, France, the MTF value ranged from 0.16÷0.27 in across-track direction and 0.16÷0.25 in along-track direction; and at the Buon Ma Thuot test site, these values were 0.16÷0.23 and 0.20÷0.24, the reflectivity of these two test sites are similar), proving that image quality is guaranteed throughout the design life of the satellite; moreover, they are also the basis for Vietnam to finalize regulations on validation and calibration of optical satellite systems in the future when we have own test site.

Innovative monochromatic x-ray source for high-quality and low-dose medical imaging.

An estimated 377 million diagnostic and interventional radiological exams are performed annually in the United States and approximately 4 to 5 billion globally. All use x-ray tubes that emit x-rays over a broad energy band, a technology that is more than a century old. Only a small fraction of the radiation is useful for imaging while the remaining fraction either increases the radiation dose received by the patient or degrades the image. Monochromatic x-rays can provide lower dose images in many of these radiological applications while maintaining or improving image quality. We report the development of the first monochromatic x-ray source suitable for low-dose, high-quality imaging in the clinic and demonstrate its first application and performance with mammography phantoms. X-ray fluorescence was used to generate monochromatic x-rays with selectable energies from 18 to 60keV. This patented technology was incorporated into a laboratory prototype of a monochromatic x-ray mammography system. Image quality was evaluated as a function of radiation dose in standard breast phantoms using the signal-to-noise ratio (SNR) measured for high and low contrast masses and microcalcifications. Spatial imaging properties were assessed from these images as well as from modulation transfer function (MTF) analysis. Measurements using an iodine contrast agent were also performed. The results were compared to those obtained using a commercially available, conventional x-ray mammography system. Our prototype system reduced radiation dose by factors of five to ten times for the same SNRs as obtained from the conventional system. This performance was demonstrated in phantoms simulating a wide range of lesion sizes and microcalcifications in a variety of breast thicknesses. The high SNRs for very thick breast phantoms provide evidence that screening with less breast compression is possible while maintaining image quality. Contrast-enhanced digital mammography (CEDM) with monochromatic x-rays was shown to provide a simpler and more effective technique at substantially lower radiation dose. The MTF value at 20% was 9lp/mm. The monochromatic x-ray system is more sensitive for imaging a wide range of breast sizes and compositions than conventional broadband mammography. High image quality and lower dose are its hallmarks. It also makes CEDM much more effective than current methods developed for use with conventional broadband mammography systems.

Error analysis and optimal design of reduction relay lens for field of view stitching applications

Purpose FOV splicing optical remote sensing instruments have a strict requirement for the focal length consistency of the lens. In conventional optical-mechanical structure design, each optical element is equally distributed with high accuracy and everyone must have a high machining and assembly accuracy. For optical remote sensors with a large number of optical elements, this design brings great difficulties to lens manufacture and alignment. Design/methodology/approach Taking the relay lens in an optical remote sensing instrument with the field of view splicing as an example, errors of the system are redistributed to optical elements. Two optical elements, which have the greatest influence on modulation transfer function (MTF) of the system are mounted with high accuracy centering and the other elements are fixed by gland ring with common machining accuracy. The reduction ratio consistency difference among lenses is compensated by adjusting the optical spacing between the two elements. Findings Based on optical system simulation analysis, the optimized structure can compensate for the difference of reduction ratio among lens by grinding the washer thickness in the range of ±0.37 mm. The test data for the image quality of the lens show that the MTF value declined 0.043 within ±0.4 mm of space change between two barrels. The results indicate that the reduction ratio can be corrected by adjusting the washer thickness and the image quality will not obviously decline. Originality/value This paper confirms that this work is original and has not been published elsewhere nor is it currently under consideration for publication elsewhere. In this paper, the optimum structural design of the reduction relay lens for the field of view stitching applications is reported. The method of adjusting washer thickness is applied to compensate for the reduction ratio consistency difference of lenses. The optimized structure also greatly reduces the difficulty of lenses manufacture, alignment and improves the efficiency of assembly.

Visual Quality and Subjective Satisfaction in Ultrathin Descemet Stripping Automated Endothelial Keratoplasty (UT-DSAEK) versus Descemet Membrane Endothelial Keratoplasty (DMEK): A Fellow-Eye Comparison.

Background: To analyze objective and subjective visual quality differences between descemet membrane endothelial keratoplasty (DMEK) and ultra-thin descemet stripping automated endothelial keratoplasty (UT-DSAEK) with a paired contralateral-eye design. Methods: A cross-sectional, comparative, and observational case series study between DMEK and UT-DSAEK were presented. Visual acuity, refractive status and corneal quality assessment were compared between both endothelial keratoplasty techniques. The sample consisted of 20 eyes (10 patients) diagnosed with Fuchs endothelial corneal dystrophy. All measurements were performed preoperatively and at six months after surgery. Analyzed data included the measurement of objective scattering index, modulation transfer function, Strehl ratio, and optical quality assessment (OQAS) values. Contrast sensitivity, subjective patient satisfaction, visual acuity, tomography, pachymetry, endothelial cell count, and refraction status were also analyzed. Results: Objective and subjective visual quality variables had similar results among UT-DSAEK and DMEK procedures. Statistically significant differences favoring DMEK against UT-DSAEK were found in endothelial cell density (658.80 ± 139.33 and 1059.00 ± 421.84 cells/mm2, respectively), pachymetry (621.20 ± 33.74 and 529.70 ± 30.00 µm, respectively), and follow-up (45.50 ± 24.76 and 15.50 ± 8.43 months, respectively). Conclusions: UT-DSAEK and DMEK revealed no differences in terms of objective and subjective visual quality. However, DMEK showed a faster recovery during the follow-up, increased endothelial cell density, lower pachymetry, and a more anatomical posterior keratometry against UT-DSAEK in this case series paired-eye study.

Comparison of early visual quality in patients with moderate myopia using different optical zones in small incision lenticule extraction (SMILE)

BackgroundThe early visual qualities of patients with moderate myopia were evaluated after small incision lenticule extraction (SMILE) using different optical zones.MethodsIn this retrospective case study, 27 cases (51 eyes) were selected, including 10 cases in Group A (19 eyes), 6.6–6.8 mm in the optical zone, 10 cases in Group B (19 eyes), 6.4–6.5 mm in the optical zone, and 7 cases in Group C (13 eyes),6.1–6.3 mm in the optical zone. The following items were examined preoperatively and 1 month postoperatively: uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), spherical, cylinder, central corneal thickness (CCT), corneal mean curvature (CMC), total ocular aberrations (TA), total low order aberrations (tLOAs), defocus, astigmatism and total high order aberrations (tHOAs), spherical, coma, trefoil, modulation transfer function (MTF), MTFcutoff, SR, objective scatter index (OSI), point scatter function at 50 and 10% (PSF50%, PSF10%), and contrast visual acuity of 100, 20, and 9% (VA100%, VA20%, and VA9%). We compared the three groups by Kruskal-Wallis test. Wilcoxon signed ranks test was used for each group before and 1 month after surgeries. P< 0.05 was considered statistically significant.ResultsThere was no significant difference in UCVA, BCVA, CCT, cylinder, and CMC in three groups preoperatively and 1 month postoperatively (P> 0.05). Comparison of the aberrations of the three groups showed statistically significant difference only in TA, tLOA, defocus, astigmatism and SA preoperatively, and trefoil 1 month postoperatively(P< 0.05). The postoperative TA, tLOAs, defocus, astigmatism and trefoil of the three groups were lower than those before surgeries (P< 0.05). The postoperative tHOAs of Group B and C was lower than those before surgeries (P< 0.05). The MTF results showed that before surgeries, there were significant differences in three groups (P< 0.05) in spatial frequencies 5~15 cycles per degree (cpd), and no differences in 20~30 cpd(P> 0.05), while no difference were observed in all spatial frequencies postoperatively (P> 0.05). Comparing the preoperative and postoperative MTF values for each group, the results showed that there was a significant difference in Group C at 5~20 cpd after surgeries(P< 0.05). There was no significant difference in MTFcutoff, SR, OSI, PSF50%, PSF10%, VA100%, VA20%, and VA9% in the three groups preoperatively (P> 0.05). One month after surgeries, higher VA9% values were measured for Group C compared to Group A and B (P < 0.05). There was no significant difference in each group before and after surgeries (P> 0.05).ConclusionSMILE could improve the visual qualities of patients with moderate myopia. Reducing the surgical optical zone will only affect night vision slightly.

Image Motion of Remote Sensing Camera With Wide Field of View Over the Antarctic and Arctic

Imaging by the remote sensing camera with a wide field of view (WFV) is of great significance in the issue of polar environment. However, the instability of the image motion velocity poses a huge challenge to the observation task since the direction of the earth's rotation velocity keeps changing in the polar regions. The edge blur of polar image by the camera with the WFV is usually ignored. Therefore, a specific theoretical model that the camera images over the polar region is supposed to describe the instability distinctly. Mathematical expressions of the image motion velocity field are obtained with a novel method of velocity projection and coordinate transformation. The quantitative analysis of simulation reveals that the increasing anisotropy of the instantaneous image motion velocity field gets most significant near the poles. The value of modulation transfer function at the edge of the field of view decreased by 0.33%, which results in a discrepancy of sharpness in an image. The model is capable of explaining the edge blur, of the image from BNU-1, which provides a theoretical basis for the image motion compensation strategy of cameras with the WFV.

Assessment of Uncertainty Depending on Various Conditions in Modulation Transfer Function Calculation Using the Edge Method.

In medical X-ray imaging, to perform optimal operations, it is essential for the user to understand whether a required image quality level which depends on a diagnostic task can be achieved with the imaging system used. This study focuses on the effects of noise on the modulation transfer function (MTF) using the edge method, the most widely used to evaluate the task dependence property. The purpose is to verify the uncertainty of the MTF value at each spatial frequency and examine the conditions under which the accuracy is ensured. By using a Monte Carlo simulation, edge images with various contrast-to-noise ratio (CNR) are acquired. MTFs are then calculated with different edge spread function (ESF) lengths. The uncertainties for each spatial frequency are estimated based on the independent MTF calculations obtained from the five edge data. The uncertainty of the MTF is inversely proportional to the CNR. In the frequency range up to the Nyquist frequency, the uncertainty in five calculations is <0.01 when the CNR is more than 60. In addition, it is observed that the uncertainty increases as the ESF length increases. This relationship depends on the frequency range, but it is proportional to the 0.3–0.5 power of the ESF length. The results in which the uncertainty is most likely to be large in the MTF calculation are clearly shown. Therefore, it is expected to provide an important barometer and useful insights for a proper image quality measurement.

Comparison between Variance and Edge Methods for Measuring Image Resolution Properties in Digital Mammography

We studied the image resolution properties in digital mammography using the variance and edge response function methods. The associated measurements were made using a polymethylmethacrylate phantom of 0-40 mm thickness while maintaining the incident dose to the detector constant, as well as with and without using the phantom but by varying the level of exposure to the detector. The results obtained using the two methods were compared on the object plane of the mammography unit with compensation for the magnification and rejection of the scattered radiation. In this unit, the imaging process of resolution enhancement may be performed according to the phantom thickness, shape of test device, exposure level, and so on. The modulation transfer function values of the variance method were slightly higher than those of the edge method, approximately 6% at 2 cycles/mm and 8% at 4 cycles/mm without resolution enhancement processing. We concluded that the variance method is more suitable than the edge method for the constancy test or quality control because of its lower coefficient of variation.

Misalignment and tilt effect on aspheric intraocular lens designs after a corneal refractive surgery.

PurposeTo numerically evaluate and compare the tolerance to misalignment and tilt of aspheric intraocular lenses (IOLs) designed for three eyes: with standard cornea and with simulated corneas after myopic and hyperopic laser ablation surgery.MethodsThree aspheric IOLs of +20.00 diopter (D) with different spherical aberration (SA) () values have been designed using a theoretical model eye. Drastic changes on the theoretical eye anterior corneal asphericity have been performed to simulate myopic and hyperopic refractive surgeries. The effect of IOL misalignment and tilt on the image quality has been evaluated using a commercial optical software design for the three eye models. Image quality was assessed from the modulation transfer function (MTF), root mean square (RMS) values of defocus, astigmatism, coma and spherical aberration (), and retinal images obtained from a visual simulator using an aleatory optotype of 0.00 LogMar visual acuity (VA).ResultsIOL misalignment and tilt reduced MTF values in general, and increased wavefront aberrations errors. Aberration-free IOLs maintained best the MTF values when misalignments were applied, together with good on-axis optical quality. IOLs with negative SA () correction decreased the MTF value under 0.43 for misalignments values higher than 0.50 mm with the three corneas. The effect of misalignment on RMS astigmatism and coma was correlated with the IOL SA () and with the three corneas.ConclusionsThis theoretical study shows that the largest degradation in image quality arises for the IOL with the highest amount of spherical aberration (). Moreover, it has been found that the aspherical design has a more influential role in misalignment tolerance than in tilt tolerance.

Multizonal Design Multifocal Intraocular Lens-Induced Astigmatism According to Orientation.

To evaluate the differences in intraocular lens (IOL)-induced astigmatism according to differences in orientation of a multizonal multifocal IOL, the Precizon Presbyopic NVA IOL (Ophtec BV). The clinical study reviewed 80 eyes from 40 patients with cataracts who underwent Precizon Presbyopic IOL implantation. Residual astigmatism, as measured by autorefraction and manifest refraction, was investigated using vector analysis of eyes implanted with vertical (90 ± 30 degrees) and horizontal (180 ± 30 degrees) orientations of the first near segment of the IOL. In the ray-tracing simulation study, pseudophakic eyes with the Precizon Presbyopic IOL were modeled. The modulation transfer function (MTF) of each case was compared with respect to the amount of corneal astigmatism of the model eyes and the orientation of the first near segment. The mean IOL-induced astigmatism measured by autorefraction was 0.68 ± 0.58 diopters (D) at 1 degree in the vertical orientation of the first near segment (n = 52) and 1.05 ± 0.81 D at 96 degrees in the horizontal orientation (n = 28). However, the mean IOL-induced astigmatism measured by manifest refraction was 0.14 ± 0.44 D at 171 degrees and 0.46 ± 0.40 D at 95 degrees. The MTF analysis showed that the highest MTF values were measured in eyes without corneal astigmatism in both the vertically and horizontally implanted IOLs. Autorefraction measurement indicates induction of with-the-rule astigmatism by the Precizon Presbyopic IOL when implanted vertically with respect to the first near segment, and against-the-rule astigmatism when implanted horizontally. However, this astigmatism is clinically insignificant according to manifest refraction and ray-tracing simulation. [J Refract Surg. 2020;36(11):740-748.].

In vitro optical quality assessment of a monofocal IOL sutured to an artificial iris.

To assess whether the combined implantation of a monofocal IOL and an artificial iris had an effect on the IOL's optical performance. David J. Apple International Laboratory for Ocular Pathology, Heidelberg, Germany. In vitro laboratory study. IOL optical quality was assessed using an OptiSpheric IOL Pro II to measure the IOL's modulation transfer function (MTF) at 3.0 mm pupil size and spatial frequency of 100 lp/mm. Three ASPIRA-aAY IOLs with different base powers, 10.0 diopter (D) (IOL A), 20.0 D (IOL B), and 30.0 D (IOL C) were measured before and after suturing the IOL to an ArtificialIris (AI). The degree of IOL decentration about the center of the AI was also evaluated. The mean MTF values prior to suturing were 0.57, 0.65, and 0.63 for IOLs A, B, and C, respectively. After suturing to the AI, the mean MTF values were 0.52, 0.54, and 0.55 for IOLs A, B, and C, respectively. The decentration values in vertical direction were 0.20 mm, 0.00 mm, and 0.02 mm for IOLs A, B, and C, respectively. In horizontal direction, the decentration values were 0.42 mm, 0.10 mm, and 0.03 mm for IOLs A, B, and C, respectively. The MTF decreased slightly in all 3 IOLs after they were sutured to the AI. The small differences, however, should be clinically irrelevant. This laboratory assessment showed that suturing of the IOL to the AI can be performed in a reliable and reproducible manner without deteriorating optical quality.

Sharpening the Sentinel-2 10 and 20 m Bands to Planetscope-0 3 m Resolution

Combination of near daily 3 m red, green, blue, and near infrared (NIR) Planetscope reflectance with lower temporal resolution 10 m and 20 m red, green, blue, NIR, red-edge, and shortwave infrared (SWIR) Sentinel-2 reflectance provides potential for improved global monitoring. Sharpening the Sentinel-2 reflectance with the Planetscope reflectance may enable near-daily 3 m monitoring in the visible, red-edge, NIR, and SWIR. However, there are two major issues, namely the different and spectrally nonoverlapping bands between the two sensors and surface changes that may occur in the period between the different sensor acquisitions. They are examined in this study that considers Sentinel-2 and Planetscope imagery acquired one day apart over three sites where land surface changes due to biomass burning occurred. Two well-established sharpening methods, high pass modulation (HPM) and Model 3 (M3), were used as they are multiresolution analysis methods that preserve the spectral properties of the low spatial resolution Sentinel-2 imagery (that are better radiometrically calibrated than Planetscope) and are relatively computationally efficient so that they can be applied at large scale. The Sentinel-2 point spread function (PSF) needed for the sharpening was derived analytically from published modulation transfer function (MTF) values. Synthetic Planetscope red-edge and SWIR bands were derived by linear regression of the Planetscope visible and NIR bands with the Sentinel-2 red-edge and SWIR bands. The HPM and M3 sharpening results were evaluated visually and quantitatively using the Q2n metric that quantifies spectral and spatial distortion. The HPM and M3 sharpening methods provided visually coherent and spatially detailed visible and NIR wavelength sharpened results with low distortion (Q2n values &gt; 0.91). The sharpened red-edge and SWIR results were also coherent but had greater distortion (Q2n values &gt; 0.76). Detailed examination at locations where surface changes between the Sentinel-2 and the Planetscope acquisitions occurred revealed that the HPM method, unlike the M3 method, could reliably sharpen the bands affected by the change. This is because HPM sharpening uses a per-pixel reflectance ratio in the spatial detail modulation which is relatively stable to reflectance changes. The paper concludes with a discussion of the implications of this research and the recommendation that the HPM sharpening be used considering its better performance when there are surface changes.

Physical characterization of a novel wireless DRX Plus 3543C using both a carbon nano tube (CNT) mobile x-ray system and a traditional x-ray system

This work aims to characterize the novel DRX Plus 3543C detector in terms of detective quantum efficiency (DQE) using both a mobile x-ray system called Carestream DRX Revolution Nano and a traditional x-ray system (Carestream DRX Evolution). We used the commercial system DRX Revolution Nano, equipped with a new x-ray source based on CNT technology and field emission (FE) as the electron emitter (cathode). An innovative aspect of this device is its intrinsic selection of the focal spot size. We tested the system using three IEC-specified beam qualities (RQA3, 5 and 7) in terms of modulation transfer function (MTF), normalized noise power spectra (NNPS) and DQE as defined in the IEC 62220-1-1:2015. We compared the results obtained using DRX Revolution Nano and DRX Evolution with correlation and with Bland–Altman plots to study their agreement. RQA3 MTF is slightly lower than the RQA5 and 7 curves between 0.5 and 2.5 cycles mm−1. We measured MTF values of about 0.6 at 1 lp mm−1 and about 0.28 lp mm−1 at 2 lp mm−1. The NNPS curves show a decreasing trend with the energy regarding the DRX Revolution Nano. On the other hand, the DRX Evolution NNPS curve at RQA3 is greater than the one at RQA5, but the one at RQA5 is less than the one at RQA7. The DQE(0) ranged between about 0.82 (DRX Evolution at RQA3) and 0.54 (DRX Evolution at RQA7). As expected, the squared Pearson’s correlation coefficients between the two x-ray tubes were always in an optimal agreement, and Bland–Altman plots confirmed a substantial equivalence between the two physical characterizations of the wireless detector. In conclusion, we can show that the dynamic focal selection of the system equipped with CNT does not play a substantial role in image quality compared to a traditional system in terms of physical characterisation of the detector in our measurement conditions.