Calibration Pipeline Research Articles

Automated Pipeline for Multi-LiDAR Extrinsic Calibration: Experimental Evaluation and Performance Analysis

Abstract. In recent years, 3D LiDAR (Light Detection and Ranging) has become a crucial sensor in various applications such as autonomous vehicles, robotics, object detection, precision forestry, and agriculture. However, specific LiDAR sensors, such as Velodyne VLP16, exhibit some drawbacks, such as a limited field of view and sparse data density, making them inadequate for certain specific applications. Hence, this research proposes a method for calibrating two VLP16 LiDAR sensors to improve coverage and reduce blind spots. The pipeline for performing the calibration begins with mounting LiDARs correctly in a rod at a specific orientation and distance, followed by the selection of multiple sites for data collection, then performing a registration algorithm for estimating calibration parameters, and then an accuracy assessment of the calibrated point clouds. The registration algorithm used here is a modified version of ICP (Iterative Closest Point), which overcomes the need for initialization and eliminates manual intervention in installing targets or retro-reflectors. Finally, we evaluated the accuracy of the fused point cloud collected in an open environment using two calibrated Velodyne VLP16 sensors. For accuracy assessment, we used the PCA eigenvalue and RMSE value to observe how tightly point clouds are fused. As a calibration result, we got the orientation and translation parameters, which are used to achieve the common coordinate system, and accomplished calibration accuracy up to single-digit precision from all the experimental sites. Now the system of two calibrated VLP16 sensors will provide higher coverage and increased data density and might be useful for forest applications.

Solidification and crystallographic texture modeling of laser powder bed fusion Ti-6Al-4V using finite difference-monte carlo method

Laser powder bed fusion (LPBF) additive manufacturing makes near-net-shaped parts with reduced material cost and time, rising as a promising technology to fabricate Ti-6Al-4 V, a widely used titanium alloy in aerospace and medical industries. However, LPBF Ti-6Al-4 V parts produced with 67° rotation between layers, a scan strategy commonly used to reduce microstructure and property inhomogeneity, have varying grain morphologies and weak crystallographic textures that change depending on processing parameters. This study predicts LPBF Ti-6Al-4 V solidification at three energy levels using a finite difference-Monte Carlo method and validates the simulations with large-area electron backscatter diffraction (EBSD) scans. The developed model accurately shows that a 〈001〉 texture forms at low energy and a 〈111〉 texture occurs at higher energies parallel to the build direction but with a lower strength than the textures observed from EBSD. A validated and well-established method of combining spatial correlation and general spherical harmonics representation of texture is developed to calculate a difference score between simulations and experiments. The quantitative comparison enables effective fine-tuning of nucleation density (N0) input, which shows a nonlinear relationship with increasing energy level. Future improvements in texture prediction code and a more comprehensive study of N0 with different energy levels will further advance the optimization of LPBF Ti-6Al-4 V components. These developments contribute a novel understanding of crystallographic texture formation in LPBF Ti-6Al-4 V, the development of robust model validation and calibration pipeline methodologies, and provide a platform for mechanical property prediction and process parameter optimization.

The Thermal Structure and Composition of Jupiter's Great Red Spot From JWST/MIRI

AbstractJupiter's Great Red Spot (GRS) was mapped by the James Webb Space Telescope (JWST)/Mid‐Infrared Instrument (4.9–27.9 m) in July and August 2022. These observations took place alongside a suite of visual and infrared observations from; Hubble, JWST/NIRCam, Very Large Telescope/VISIR and amateur observers which provided both spatial and temporal context across the jovian disc. The stratospheric temperature structure retrieved using the NEMESIS software revealed a series of hot‐spots above the GRS. These could be the consequence of GRS‐induced wave activity. In the troposphere, the temperature structure was used to derive the thermal wind structure of the GRS vortex. These winds were only consistent with the independently determined wind field by JWST/NIRCam at 240 mbar if the altitude of the Hubble‐derived winds were located around 1,200 mbar, considerably deeper than previously assumed. No enhancement in ammonia was found within the GRS but a link between elevated aerosol and phosphine abundances was observed within this region. North‐south asymmetries were observed in the retrieved temperature, ammonia, phosphine and aerosol structure, consistent with the GRS tilting in the north‐south direction. Finally, a small storm was captured north‐west of the GRS that displayed a considerable excess in retrieved phosphine abundance, suggestive of vigorous convection. Despite this, no ammonia ice was detected in this region. The novelty of JWST required us to develop custom‐made software to resolve challenges in calibration of the data. This involved the derivation of the “FLT‐5” wavelength calibration solution that has subsequently been integrated into the standard calibration pipeline.

Pre‐Flight and In‐Flight Calibration and Performance of the Terminal Tracking Cameras (TTCams) on the NASA Lucy Mission

AbstractThe Terminal Tracking Camera (TTCam) imaging system on the NASA Lucy Discovery mission consists of a pair of cameras that are being used mainly as a navigation and target acquisition system for the mission's asteroid encounters. However, a secondary science‐focused function of the TTCam system is to provide wide‐angle broadband images over a large range of phase angles around close approach during each asteroid flyby. The scientific data acquired by TTCam can be used for shape modeling and topographic and geologic analyses. This paper describes the pre‐flight and initial in‐flight calibration and characterization of the TTCams, including the development of a radiometric calibration pipeline to convert raw TTCam images into radiance and radiance factor (I/F) images, along with their uncertainties. Details are also provided here on the specific calibration algorithms, the origin and archived location of the required ancillary calibration files, and the archived sources of the raw calibration and flight data used in this analysis.

Investigation of an irradiated CCD device: Building and testing a Charge Transfer Inefficiency correction pipeline using the Pyxel framework

Pyxel is a powerful end-to-end detector simulations framework with the aim of being reusable, reliable and help facilitate knowledge transfer between a wide range of related fields. To show how beneficial Pyxel can be, we present an investigation into the effect of Charge Transfer Inefficiency (CTI) on an irradiated CCD-273 device produced by Teledyne-e2v, the type of detector used for the Euclid VIS instrument. This requires production of two pipelines. Firstly, a calibration pipeline to search the parameter space and obtain best fitting trap parameters based upon the CTI within the detector. Secondly, a correction pipeline which aims to correct the CTI-induced data using these trap parameters to obtain a nominal efficiency of 99.5%. The following presents work conducted in building, testing and validating the correction pipeline using Pyxel and the CTI model ArCTIC. This involves data from the unirradiated portion of a CCD-273 device using the scene projection system at the labs at the European Space Agency (ESA). The images are computationally altered by varying parameters such as background levels and readout noise, and by synthetically producing CTI trails from known trap parameters. The resulting images are corrected and analysed to understand how noise affects the correction efficiency at varying image background levels.

HiFAST: An H i Data Calibration and Imaging Pipeline for FAST. II. Flux Density Calibration

Accurate flux density calibration is essential for precise analysis and interpretation of observations across different observation modes and instruments. In this research, we first introduce the flux calibration model that incorporated in HiFAST pipeline, and designed for processing H i 21 cm spectra. Furthermore, we investigate different calibration techniques and assess the dependence of the gain parameter on the time and environmental factors. A comparison is carried out in various observation modes (e.g., tracking and scanning modes) to determine the flux density gain (G), revealing insignificant discrepancies in G among different methods. Long-term monitoring data shows a linear correlation between G and atmospheric temperature. After subtracting the G–Temperature dependence, the dispersion of G is reduced to <3% over a one-year timescale. The stability of the receiver response of Five-hundred-meter Aperture Spherical radio Telescope (FAST) is considered sufficient to facilitate H i observations that can accommodate a moderate error in flux calibration (e.g., > ∼ 5%) when utilizing a constant G for calibration purposes. Our study will serve as a useful addition to the results provided by Jiang et al. Detailed measurement of G for the 19 beams of FAST, covering the frequency range 1000–1500 MHz, can be found on the HiFAST homepage: https://hifast.readthedocs.io/fluxgain.

The MIRI/MRS Library. I. Empirically correcting detector charge migration in unresolved sources

The James Webb Space Telescope (JWST) has been collecting scientific data for over two years now. The Medium Resolution Spectrometer (MRS) of the Mid-InfraRed Instrument (MIRI) has been one of the telescope's most popular modes, and has already produced ground-breaking results. Scientists are now looking deeper into the data for new exciting discoveries, which introduces the need to characterise and correct known systematic effects to reach the photon noise limit. Five important limiting factors for the MRS are the pointing accuracy, non-linearity, detector charge migration, detector scattering---resulting in both spatial broadening and spectral interferometric fringing---the accuracy of the point-spread function (PSF) model, and the complex interplay between these. The Cycle 2 calibration programme 3779, entitled ‘The MIRI/MRS Library', proposed a 72-point intra-pixel dither raster of the calibration star 10-Lac, which provides a unique dataset tailored for the purpose of addressing the limiting factors on the MRS data accuracy. In this first work of the paper series, we aim to address the degeneracy between the non-linearity and charge migration (brighter-fatter effect) that affect the pixel voltage integration ramps of the MRS. Due to the low flux in the longer wavelengths, we only do this in the 4.9 to 11.7 micron region (spectral channels 1 and 2). We fitted the ramps individually per pixel and dither, in order to fold in the deviations from classical non-linearity that are caused by charge migration. The ramp shapes should be repeatable depending on the part of the PSF that is sampled. By doing so, we defined both a grid-based linearity correction, and an interpolated linearity correction. Including the change in ramp shape due to charge migration yields significant improvements compared to the uniform illumination assumption that is currently used by the standard JWST calibration pipeline. The standard deviation on the pixel ramp residual non-linearity is between 70-90&lt;!PCT!&gt; smaller than the current standard pipeline when self-calibrating with the grid. We are able to interpolate these coefficients to apply to any unresolved source not on the grid points, resulting in an up to 70&lt;!PCT!&gt; smaller standard deviation on the residual deviation from linearity. After applying the correction, the full-width at half maximum is up to 20&lt;!PCT!&gt; narrower for sources that cover the full pixel dynamic range. Furthermore, the depth of the fringes is now consistent up the ramp, improving the standard deviation on the difference in fringe depth between the start and ends of integrations by sim 60&lt;!PCT!&gt;. Pointing-specific linearity corrections allow us to accurately model the pixel ramps across the PSF, and for the first time, fix the systematic deviation in the slopes. In this work we demonstrated this for unresolved sources. The discovered trends with PSF sampling suggest that, in the future, we may be able to model ramps for spatially extended and resolved illumination as well.

Towards an astronomical use of new-generation geodetic observations. I. From the correlator to full-polarization images

The current algorithms used for the calibration and analysis of very long baseline interferometry (VLBI) networks that only use linear polarizers (as is the case of the VLBI Global Observing System, VGOS) do not properly account for instrumental and source-intrinsic polarimetry, which can cause errors in geodetic and astronomical products. We aim to develop a calibration pipeline for VLBI interferometers that observe in a basis of linear polarization, as is the case of VGOS. The products from this pipeline can be used to obtain valuable full-polarization astronomical information from the observed sources, and they can be used to potentially improve the geodetic results. We used the algorithm PolConvert to write the correlation products in a basis of circular polarization that is compatible with the standard VLBI calibration procedures. In addition to this, we implemented a wide-band global fringe-fitting algorithm that accounts for dispersive effects (ionospheric delay) and allows us to perform full-polarization imaging of all the observed sources, covering the whole frequency band of VGOS. We present the outcome of our pipeline applied to a global IVS VGOS epoch of observations and show example imaging results in total intensity and polarization. We also discuss issues encountered during the analysis and suggest points of improvement in the VGOS system for an optimum geodetic and astronomical exploitation of this interferometer.

Sequence-agnostic motion-correction leveraging efficiently calibrated Pilot Tone signals.

This study leverages externally generated Pilot Tone (PT) signals to perform motion-corrected brain MRI for sequences with arbitrary k-space sampling and image contrast. PT signals are promising external motion sensors due to their cost-effectiveness, easy workflow, and consistent performance across contrasts and sampling patterns. However, they lack robust calibration pipelines. This work calibrates PT signal to rigid motion parameters acquired during short blocks (˜4 s) of motion calibration (MC) acquisitions, which are short enough to unobstructively fit between acquisitions. MC acquisitions leverage self-navigated trajectories that enable state-of-the-art motion estimation methods for efficient calibration. To capture the range of patient motion occurring throughout the examination, distributed motion calibration (DMC) uses data acquired from MC scans distributed across the entire examination. After calibration, PT is used to retrospectively motion-correct sequences with arbitrary k-space sampling and image contrast. Additionally, a data-driven calibration refinement is proposed to tailor calibration models to individual acquisitions. In vivo experiments involving 12 healthy volunteers tested the DMC protocol's ability to robustly correct subject motion. The proposed calibration pipeline produces pose parameters consistent with reference values, even when distributing only six of these approximately 4-s MC blocks, resulting in a total acquisition time of 22 s. In vivo motion experiments reveal significant ( ) improved motion correction with increased signal to residual ratio for both MPRAGE and SPACE sequences with standard k-space acquisition, especially when motion is large. Additionally, results highlight the benefits of using a distributed calibration approach. This study presents a framework for performing motion-corrected brain MRI in sequences with arbitrary k-space encoding and contrast, using externally generated PT signals. The DMC protocol is introduced, promoting observation of patient motion occurring throughout the examination and providing a calibration pipeline suitable for clinical deployment. The method's application is demonstrated in standard volumetric MPRAGE and SPACE sequences.

Pushing the Limits of the Cosmic Origin Spectrograph (COS) with an Optimized Background Correction

Observations utilizing the ultraviolet capabilities of the Cosmic Origin Spectrograph (COS) onboard the Hubble Space Telescope are of unique value to the astronomy community. Spectroscopy down to 900 Å with COS has enabled new science areas. However, contrary to the situation at longer wavelengths, these observations are limited by detector background noise. The background correction currently applied by the standard calibration pipeline (CalCOS) is not optimized for faint targets, limiting the scientific value of low signal-to-noise ratio (S/N) observations. In this work we investigate a possible dependence of the variations of the dark rate in both segments of the COS far-ultraviolet detector on time, detector high voltage (HV), and solar activity. Through our analysis we identified a number of detector states (on a configuration basis, e.g., HV and segment) characterizing the spatial distribution of dark counts, and created superdarks to be used in an optimized two-dimensional (2D) background correction. We have developed and tested Another COS Dark Correction (ACDC), a dedicated pipeline to perform a 2D background correction based on statistical methods, producing background-corrected and flux-calibrated spectra. While our testing of ACDC showed an average improvement in S/N values of ∼10%, in a few cases the improvements in S/N reached 60% across the whole wavelength range of individual segments.

Mid-infrared Fine Structure Lines from the Galactic Warm Ionized Medium

The Warm Ionized Medium (WIM) hosts most of the ionized gas in the Galaxy and occupies perhaps a quarter of the volume of the Galactic disk. Decoding the spectrum of the Galactic diffuse ionizing field is of fundamental interest. This can be done via direct measurements of ionization fractions of various elements. Based on current physical models for the WIM we predicted that mid-IR fine structure lines of Ne, Ar and S would be within the grasp of the Mid-Infrared Imager-Medium Resolution Spectrometer (MIRI-MRS), an Integral Field Unit (IFU) spectrograph, aboard the James Webb Space Telescope (JWST). Motivated thus we analyzed a pair of commissioning data sets and detected [Ne ii] 12.81 μm, [S iii] 18.71 μm and possibly [S iv] 10.51 μm. The inferred emission measure for these detections is about 10 cm−6 pc, typical of the WIM. These detections are broadly consistent with expectations of physical models for the WIM. The current detections are limited by uncorrected fringing (and to a lesser extent by baseline variations). In due course, we expect, as with other IFUs, the calibration pipeline to deliver photon-noise-limited spectra. The detections reported here bode well for the study of the WIM. Along most lines-of-sight hour-long MIRI-MRS observations should detect line emission from the WIM. When combined with optical observations by modern IFUs with high spectral resolution on large ground-based telescopes, the ionization fraction and temperature of neon and sulfur can be robustly inferred. Separately, the ionization of helium in the WIM can be probed by NIRspec. Finally, joint JWST and optical IFU studies will open up a new cottage industry of studying the WIM on arcsecond scales.

Calibrating Deep Learning Classifiers for Patient-Independent Electroencephalogram Seizure Forecasting.

The recent scientific literature abounds in proposals of seizure forecasting methods that exploit machine learning to automatically analyze electroencephalogram (EEG) signals. Deep learning algorithms seem to achieve a particularly remarkable performance, suggesting that the implementation of clinical devices for seizure prediction might be within reach. However, most of the research evaluated the robustness of automatic forecasting methods through randomized cross-validation techniques, while clinical applications require much more stringent validation based on patient-independent testing. In this study, we show that automatic seizure forecasting can be performed, to some extent, even on independent patients who have never been seen during the training phase, thanks to the implementation of a simple calibration pipeline that can fine-tune deep learning models, even on a single epileptic event recorded from a new patient. We evaluate our calibration procedure using two datasets containing EEG signals recorded from a large cohort of epileptic subjects, demonstrating that the forecast accuracy of deep learning methods can increase on average by more than 20%, and that performance improves systematically in all independent patients. We further show that our calibration procedure works best for deep learning models, but can also be successfully applied to machine learning algorithms based on engineered signal features. Although our method still requires at least one epileptic event per patient to calibrate the forecasting model, we conclude that focusing on realistic validation methods allows to more reliably compare different machine learning approaches for seizure prediction, enabling the implementation of robust and effective forecasting systems that can be used in daily healthcare practice.

HiFAST: An Hi data calibration and imaging pipeline for FAST

HiFAST: An Hi data calibration and imaging pipeline for FAST

Cosmic evolution of FRI and FRII sources out to z = 2.5

Context. Radio-loud active galactic nuclei (RLAGN) play an important role in the evolution of galaxies through the effects on their environment. The two major morphological classes are core-bright (FRI) and edge-bright (FRII) sources. With the LOw-Frequency ARray (LOFAR), we can now compare the FRI and FRII evolution down to lower flux densities and with larger samples than before. Aims. Our aim is to examine the cosmic space density evolution for FRIs and FRIIs by analyzing their space density evolution between L150 ∼ 1024.5 W Hz−1 and L150 ∼ 1028.5 W Hz−1 and up to z = 2.5. In particular, we look at the space density enhancements and compare the FRI and FRII evolution with the total RLAGN evolution. Methods. We constructed radio luminosity functions (RLFs) from FRI and FRII catalogues based on recent data from LOFAR at 150 MHz to study the space densities as a function of radio luminosity and redshift. These catalogues contain over 100 times the number of FRIs with associated redshifts greater than z = 0.3, compared to the most recent FRI/FRII RLF study. To derive the maximum distance according to which a source can be classified and to correct for detection limits, we conducted simulations of how sources appear across a range of redshifts. Results. Our RLFs do not show any sharp transitions between the space density evolution of FRI and FRII sources as a function of radio luminosity and redshift. We report a space density enhancement from low to high redshift for FRI and FRII sources brighter than L150 ∼ 1027 W Hz−1. Furthermore, while we observe a tentative decrease in the space densities of FRIs with luminosities below L150 ∼ 1026 W Hz−1 and at redshifts beyond z = 0.8, this may be due to residual selection biases. The FRI/FRII space density ratio does not appear to evolve strongly as a function of radio luminosity and redshift. Conclusions. We argue that the measured space density enhancements above L150 ∼ 1027 W Hz−1 are related to the higher gas availability in the earlier, denser universe. The constant FRI/FRII space density ratio evolution as a function of radio luminosity and redshift suggests that the jet-disruption of FRIs might be primarily caused by events occurring on scales within the host galaxy, rather than being driven by changes in the overall large-scale environment. The remaining selection biases in our results also highlight the need to resolve more sources at angular scales below 40″, thereby strengthening the motivation for further developing and automating the calibration and imaging pipeline of LOFAR data to produce images at a sub-arcsecond resolution.

Quantum radio astronomy: Quantum linear solvers for redundant baseline calibration

The computational requirements of future large scale radio telescopes are expected to scale well beyond the capabilities of conventional digital resources. Current and planned telescopes are generally limited in their scientific potential by their ability to efficiently process the vast volumes of generated data. To mitigate this problem, we investigate the viability of emerging quantum computers for radio astronomy applications. In this a paper we demonstrate the potential use of variational quantum linear solvers in Noisy Intermediate Scale Quantum (NISQ) computers and combinatorial solvers in quantum annealers for a radio astronomy calibration pipeline. While we demonstrate that these approaches can lead to satisfying results when integrated in calibration pipelines, we show that current restrictions of quantum hardware limit their applicability and performance.

An Algorithm to Mitigate Charge Migration Effects in Data from the Near Infrared Imager and Slitless Spectrograph on the James Webb Space Telescope* *This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association

We present an algorithm that mitigates the effects of charge migration due to the “brighter-fatter effect” (BFE) that occurs for highly illuminated stars in the Teledyne HAWAII-2RG detectors used in the NIRCam, NIRISS, and NIRSpec science instruments aboard the James Webb Space Telescope (JWST). The impact of this effect is most significant for photometry and spectrophotometry of bright stars in data for which the point-spread function (PSF) is undersampled, which is the case for several observing modes of the NIRISS instrument. The main impact of BFE to NIRISS data is incorrect count rate determinations for pixels in the central regions of PSFs of bright stars due to jump detections that are caused by charge migration from peak pixels to surrounding pixels. The effect is especially significant for bright compact sources in resampled, distortion-free images produced by the drizzle algorithm: quantitatively, apparent flux losses of >50% can occur in such images due to BFE. We describe the algorithm of the “charge_migration” mitigation step that has been implemented in version 10.0 of the operational JWST calibration pipeline as of 2023 December 5. We illustrate the impact of this step in terms of the resulting improvements of the precision of imaging photometry of point sources. The algorithm renders the effects of BFE on photometry and surface brightness measurements to stay within 1%.

Vision-aided precise positioning for long-reach robotic manipulators using local calibration

A vision-based guidance methodology is proposed for precise positioning of the tool center point (TCP) of heavy-duty, long-reach (HDLR) manipulators. HDLR manipulators are non-rigid structures with many nonlinearities. Therefore, conventional rigid-body–based modeling and control methods issue challenges for accurate TCP positioning. To compensate for these errors, we compute the pose error between the TCP and an object of interest (OOI) directly in the camera frame, while using motion-based local calibration to find the extrinsic sensor-to-robot correspondence. The proposed pipeline for local calibration is twofold: first, the detected tool is oriented perpendicularly with respect to the OOI. Second, range adjustment is performed in the local planar plane by exploiting the visual measurements. Two methods for adjusting the range were examined: a line equation–based method and a trajectory matching–based method. Real-time experiments were conducted using a HDLR manipulator with a 5 m reach, and visual fiducial markers were used as detectable objects for the visual sensor. The experimental results demonstrated that the proposed methodology can provide sub-centimeter positioning accuracy, which is very challenging to achieve with HDLR manipulators due to their characteristic uncertainties.

Investigating focal spot position drift in a mobile imaging system equipped with a monobloc-based x-ray generator.

Misalignment or double-contouring artifacts can appear in high-resolution 3D cone beam computed tomography (CBCT) images, potentially indicating geometric accuracy issues in the projection data. Such artifacts may go unnoticed in low-resolution images and could be associated with changes in the focal spot (FS)position. High-resolution 3D-CBCT imaging by a mobile imaging device with a large gantry clearance offers more versatility for clinical workflows in image-guided brachytherapy (IGBT), intraoperative radiation therapy (IORT), and spinal, as well as maxillofacial surgery. However, misalignment or double-contouring artifacts hinder workflow advancements in these domains. This paper introduces intrinsic calibration and geometrical correction methods as extensions to a well-established technique for addressing geometrical deviations resulting from factors such as gravity or mechanical inconsistencies. These extensions cover shifts and drifts of the FS depending on FS size selection, temperature, tube current, and tube potential. The proposed methods effectively mitigate artifacts in high-resolution CBCT images stemming from geometrical inaccuracies in projection data, without requiring additional equipment like a pinholedevice. Geometrical offsets and drifts of the x-ray tube FS were characterized on a mobile multi-purpose imaging system, the ImagingRing-m. A pinhole-like experiment was simulated by adjusting the movable collimation unit to a small rectangular aperture within the FS size range. The influence of filament selection, that is, FS size, temperature, the relatively low tube currents, as well as tube potential settings have been studied on two different monobloc types sharing the same x-ray tube insert. The Catphan 504 and an Alderson head phantom were used to assess resulting imageartifacts. Switching the FS size to one different from what was used for geometrical (gravitation, mechanical variations) calibration induced the most notable position changes of the x-ray FS, resulting in double-contouring artifacts and blurring of high-resolution 3D-CBCT images. Incorporating these shifts into a geometrical correction method effectively minimized these artifacts. Thermal drifts exhibited the second largest geometrical changes, comparable to FS size shifts across the thermal operating conditions of the x-ray system. The proposed thermal drift compensation markedly reduced thermal drift effects. Tube current and potential had little impact within the range of available tube currents, eliminating the need for compensation in currentapplications. Augmenting the geometrical calibration pipeline with proposed FS drift compensations yielded significant enhancements in image quality for high-resolution reconstructions. While compensation for thermal effects posed challenges, it proved achievable. The roles of tube current and potential were found to benegligible.

An improved spectral extraction method for JWST/NIRSpec fixed slit observations

The James Webb Space Telescope is performing beyond our expectations. Its Near Infrared Spectrograph (NIRSpec) provides versatile spectroscopic capabilities in the 0.6–5.3 µm wavelength range, where a new window is opening for studying Trans-Neptunian objects in particular. We propose a spectral extraction method for NIRSpec fixed slit observations, with the aim of meeting the superior performance on the instrument with the most advanced data processing. We applied this method on the fixed slit dataset of the guaranteed-time observation program 1231, which targets Plutino 2003 AZ84. We compared the spectra we extracted with those from the calibration pipeline.

Calibrating VLBI Polarization Data Using GPCAL. I. Frequency-dependent Calibration

In this series of papers, we present new methods of frequency- and time-dependent instrumental polarization calibration for very long baseline interferometry (VLBI). In most existing calibration tools and pipelines, it has been assumed that instrumental polarization is constant over frequency within the instrument bandwidth and over time. The assumption is not always true and may prevent an accurate calibration, which can result in degradation of the quality of linear polarization images. In this paper, we present a method of frequency-dependent instrumental polarization calibration that is implemented in GPCAL, a recently developed polarization calibration pipeline. The method is tested using simulated data sets generated from real Very Long Baseline Array (VLBA) data. We present the results of applying the method to real VLBA data sets observed at 15 and 43 GHz. We were able to eliminate significant variability in cross-hand visibilities over frequency that is caused by frequency-dependent instrumental polarization. As a result of the calibration, linear polarization images were slightly to modestly improved as compared to those obtained without frequency-dependent instrumental polarization calibration. We discuss the reason for the minor impact of frequency-dependent instrumental polarization calibration on existing VLBA data sets and prospects for applying the method to future VLBI data sets, which are expected to provide very large bandwidths.