Search

We present two methods for improved calibration of multi-point electron density measurements from incoherent scatter radars (ISR). They are based on the well-established Flatfield correction method used in imaging and photography, where we exploit the analogy between independent measurements in separate pixels in one image sensor and multi-beam radar measurements. Applying these correction methods adds to the current efforts of estimating the magic constant or system constant made for the calibration of multi-point radars, increasing data quality and usability by correcting for variable, unaccounted, and unpredictable variations in system gain. This second-level calibration is especially valuable for studies of plasma patches, irregularities, turbulence, and other research where inter-beam changes and fluctuations of electron density are of interest. The methods are strictly based on electron density data measured by the individual radar and require no external input. This is of particular interest when independent measurements of electron densities for calibration are available only in one pointing direction or not at all. A correction factor is estimated in both methods, which is subsequently used to scale the electron density measurements of a multi-beam ISR experiment run on a phased array radar such as RISR-N, RISR-C, PFISR, or the future EISCAT3D radar. This procedure could improve overall data quality if used as part of the data-processing chain for multi-beam ISRs, both for existing data and for future experiments on new multi-beam radars. [ABSTRACT FROM AUTHOR]

A novel approach in addressing cyclone global navigation satellite system (CyGNSS) intersatellite and GPS-related calibration issues is proposed, based on a track-wise $\sigma ^{o}$ bias correction method. This method makes use of both ancillary data from numerical weather prediction models and a semiempirical geophysical model function. Care is taken, so the track-wise $\sigma ^{o}$ bias correction maintains CyGNSS signal sensitivity. Both intersatellite and GPS-related calibration issues are removed after correction. Long-term $\sigma ^{o}$ downward trend, observed throughout the CyGNSS mission, is greatly reduced. Using the corrected $\sigma ^{o}$ measurements, a wind retrieval method is also presented and its product thoroughly assessed for a three-year period against European Centre for Medium-Range Weather Forecasts (ECMWFs), Advanced Scatterometer (ASCAT) A/B, Advanced Microwave Scanning Radiometer (AMSR)-2, GMI, WindSat, hurricane weather research and forecasting (HWRF) model, and the stepped frequency microwave radiometer (SFMR) winds. The overall wind speed bias and standard deviation of the error (stde) against ECMWF are 0.16 and 1.19 m/s, while these are −0.11 and 1.12 m/s against ASCAT A/B, respectively. The same metrics against AMSR-2/GMI/WindSat (combined) are −0.19 and 1.11 m/s, respectively. The bias and stde against soil moisture active passive (SMAP) are −0.38 and 1.90 m/s, respectively. In the tropical cyclone environment, the bias and stde against HWRF are −0.54 and 2.90 m/s, and −4.71 and 5.88 m/s with SFMR. Finally, CyGNSS wind performance is gauged in the presence of rain. Below 10 m/s, the bias between CyGNSS and ECMWF increases as the rain rate increases. Between 10 and 15 m/s, biases are mostly absent. Above 15 m/s, results are inconclusive due to the low number of collocated rain samples. Overall, the presented CyGNSS wind speed product both exhibits consistency and reliability, showing promise of using GNSS-R derived winds for operational purposes. [ABSTRACT FROM AUTHOR]

The characteristic frequencies of a system provide important information on the phenomena that govern its physical properties. In this framework, there has recently been renewed interest in cryogenic microwave characterization for condensed matter systems since it allows to probe energy scales of the order of a few μeV. However, broadband measurements of the absolute value of a sample response in this frequency range are extremely sensitive to its environment and require a careful calibration. In this paper, we present an in situ calibration method for cryogenic broadband microwave reflectometry experiments that is both simple to implement and through which the effect of the sample electromagnetic environment can be minimized. The calibration references are provided here by the sample itself, at three reference temperatures where its impedance is assumed or measured, and not by external standards as is usual. We compare the frequency-dependent complex impedance (0.1–2 GHz) of an a-Nb15Si85 superconducting thin film obtained through this Sample-Based Calibration (SBC) and through an Open-Short-Load Standard Calibration (SC) when working at a very low temperature (0.02–4 K) and show that the SBC allows us to obtain the absolute response of the sample. This method brings the calibration planes as close as possible to the sample, so that the environment electrodynamic response does not affect the measurement, provided it is temperature independent. This results in a heightened sensitivity, for a given experimental set–up. [ABSTRACT FROM AUTHOR]

A cyclone global navigation satellite system (CYGNSS) $\sigma _o$ calibration analysis is presented using version 2.0 of the Level 1 dataset available on PO.DAAC. Three separate analyzes are conducted, namely, an examination of the specular bin location (in delay) and $\sigma _o$ relationship, an investigation of the impact of recently improved characterizations of the GPS effective isotropically radiated power on CYGNSS $\sigma _o$ , and an intersatellite $\sigma _o$ calibration analysis. We first noted a correlation between the specular delay bin location and $\sigma _o$ , where an increase in the specular delay bin resulted in an increase in $\sigma _o$ regardless of the wind speed level; a specular delay bin location ranging from 4.75 to 5.00 and from 7.00 to 7.25 resulted in a 14.74 and 17.72 dB median $\sigma _o$ , respectively. Noticeable improvements in the median $\sigma _o$ were present in the version 2.0 dataset, when separating the data by GPS block type: for blocks IIR, IIF, and IIR-M, median $\sigma _o$ were 15.39, 15.42, and 15.10 dB, respectively (compared to 19.38, 20.53, and 21.38 dB in version 1.1). Finally, an unexpected correlation between the instrument noise floor and $\sigma _o$ was observed for all eight observatories while conducting the intersatellite $\sigma _o$ calibration analysis. Approximately 0–1 dB absolute $\sigma _o$ difference biases (with up to $\sim$ 1 dB standard deviation) between spacecrafts were observed. A report of this analysis was presented to CYGNSS scientists and engineers, who eventually found an issue with the D/A DDM scaling algorithm. We expect better statistical performances in future releases of the data. [ABSTRACT FROM AUTHOR]

Most optical scanners work based on a fix resolution and, thus, produce a huge number of points, many of which are usually redundant. Therefore, an intensive post-processing step is required to simplify the resulting point cloud. In this paper, a novel technique is proposed that does not require the post-measurement calculations; instead, it reduces the scanned points at the data-acquisition phase. For this, the surface curvatures of object points are determined using the photometric stereo. Then, the curvature values are classified based on an adaptive sampling interval which is defined through an innovative calibration process. Once the curvature ranges are identified as such, a simplification mask is created. The mask is a binary image that is used to show points in the image space the optical scanner requires to decide if the 3D coordinates of an object point need to be computed. Having evaluated the proposed method using a fringe scanner, we observed that, although the data acquisition time is slightly increased, the number of redundant points is notably reduced. Therefore, not only the production of unnecessary data is prevented by 71–90% (depending on the surface complexity), but also carrying out the intensive post-processing simplification step is totally avoided. [ABSTRACT FROM AUTHOR]

We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia. [ABSTRACT FROM AUTHOR]

We aim to present the photometric calibration of T40 telescope system at Ankara University Kreiken Observatory(AUKR) in the Johnson BVRI bands system through CCD observations of selected Landolt stars on the clearest 11 nights. Ten more stars with a magnitude of $V< 11$ were also observed in order to check up on standard transformation coefficients. Using these coefficients, we present standard brightness and color magnitudes for these 10 selected stars. These standard brightness values of these 10 stars are also compared with the previously published ones. It is clearly seen that the calibration results are sufficiently reliable. [ABSTRACT FROM AUTHOR]

We present a software application for the calibration of stellar magnitudes in the absence of standard stars. It uses an existing algorithm to match stars in the target's field of view to catalogue entries and computes the average offset between the two sets of magnitudes using a weighted least-squares approach. This offset is used to calibrate the target's instrumental magnitude. The software application was used to calibrate magnitudes for six Be/X-ray binary sources in the Small Magellanic Cloud and the results were compared with published results for these sources. Where comparisons were possible, our results agreed with those results within the uncertainties specified. Infrared variability was found for all six of the sources tested. The interactive outlier removal that was made possible by our software allowed for smaller uncertainties to be reported for our results. [ABSTRACT FROM AUTHOR]

Out-of-field stray-light spots of the Herschel telescope optics relative to the PACS and SPIRE instrument apertures were modeled by ray tracing simulations with the Advanced Systems Analysis Program (ASAP, by Breault Research Organization) prior to launch. The predicted stray-light behaviour was verified by dedicated stray-light calibration observations in-flight. This resulted in a special feature of the Herschel Science Mission Planning Software, marking the sky positions of stray-light spots by the very bright infrared planetary sources Venus, Mars, Jupiter, and Saturn, as well as the Moon, thus avoiding contamination of scientific photometric observations by out-of-field stray-light of these sources. [ABSTRACT FROM AUTHOR]

Interfaces based on projection screens have become increasingly popular in recent years, mainly due to the large screen size and resolution that they provide, as well as their stereo-vision capabilities. This work shows a local method for real-time detection of non-stationary photometric perturbations in projected images by means of computer vision techniques. The method is based on the computation of differences between the images in the projector's frame buffer and the corresponding images on the projection screen observed by the camera. It is robust under spatial variations in the intensity of light emitted by the projector on the projection surface and also robust under stationary photometric perturbations caused by external factors. Moreover, we describe the experiments carried out to show the reliability of the method. [ABSTRACT FROM AUTHOR]

Abstract: Quality control of vegetable oils is becoming more stringent, and strict laws are being enforced, especially for avoiding adulteration. The public bodies that are responsible for the prevention of the adulteration of foodstuffs necessitate methods of analysis that could facilitate large-scale in situ controls. Similarly, oil producers constantly strive to speed up internal quality control. As a direct consequence, there is an increasing demand for innovative methods of analysis that could guarantee real-time in situ monitoring and provide adequate accuracy. On such bases, the present work addresses the possibility of monitoring qualitative characteristics of vegetable oils through microwave dielectric spectroscopy. To this purpose, the Cole–Cole dielectric parameters of different vegetable oils are evaluated through an innovative automatable procedure that suitably combines traditional TDR measurements, SOL calibration, frequency domain processing, TL modelling and, finally, a minimization routine. The proposed procedure is carried out first on different “pure” oils and, secondly, on some oil mixtures. The obtained results confirm that different dielectric characteristics are associated with different oils, thus confirming the considerable potential of dielectric spectroscopy for quality and anti-adulteration control purposes, especially in view of practical applications. [Copyright &y& Elsevier]

We present a 3-12 GHz compact mixer-based reflectometer (CMR) and horn antenna system, and demonstrate its use in detecting backscatter signals with a free space calibration procedure. We evaluate the frequency-domain performance of the CMR-antenna system for measuring the complex reflection coefficient of a dielectric slab and compare it with that of a commercial vector network analyzer (VNA)-antenna setup. Time-domain responses are also investigated, and show the effectiveness of this calibration method. This low-cost, compact system eliminates the need for traditional mechanical standards and a VNA, is effective in reducing reflection artifacts, and allows for flexibility in the placement of reference planes; thus it is well suited for array-based imaging applications [ABSTRACT FROM PUBLISHER]

We present the largest high-redshift (3 < z < 6.85) sample of X-ray-selected active galactic nuclei (AGNs) on a contiguous field, using sources detected in the Chandra COSMOS-Legacy survey. The sample contains 174 sources, 87 with spectroscopic redshift and the other 87 with photometric redshift (zphot). In this work, we treat zphot as a probability-weighted sum of contributions, adding to our sample the contribution of sources with zphot < 3 but zphot probability distribution >0 at z > 3. We compute the number counts in the observed 0.5–2 keV band, finding a decline in the number of sources at z > 3 and constraining phenomenological models of the X-ray background. We compute the AGN space density at z > 3 in two different luminosity bins. At higher luminosities (logL(2–10 keV) > 44.1 erg s−1), the space density declines exponentially, dropping by a factor of ∼20 from z ∼ 3 to z ∼ 6. The observed decline is ∼80% steeper at lower luminosities (43.55 erg s−1 < logL(2–10 keV) < 44.1 erg s−1) from z ∼ 3 to z ∼ 4.5. We study the space density evolution dividing our sample into optically classified Type 1 and Type 2 AGNs. At logL(2–10 keV) > 44.1 erg s−1, unobscured and obscured objects may have different evolution with redshift, with the obscured component being three times higher at z ∼ 5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGNs. These models significantly overpredict the number of expected AGNs at logL (2–10 keV) > 44.1 erg s−1 with respect to our data. [ABSTRACT FROM AUTHOR]

We present custom-processed ultraviolet, optical, and near-infrared photometry for the REsolved Spectroscopy of a Local VolumE (RESOLVE) survey, a volume-limited census of stellar, gas, and dynamical mass within two subvolumes of the nearby universe (RESOLVE-A and RESOLVE-B). RESOLVE is complete down to baryonic mass , probing the upper end of the dwarf galaxy regime. In contrast to standard pipeline photometry (e.g., SDSS), our photometry uses optimal background subtraction, avoids suppressing color gradients, and employs multiple flux extrapolation routines to estimate systematic errors. With these improvements, we measure brighter magnitudes, larger radii, bluer colors, and a real increase in scatter around the red sequence. Combining stellar mass estimates based on our optimized photometry with the nearly complete H i mass census for RESOLVE-A, we create new z = 0 volume-limited calibrations of the photometric gas fractions (PGF) technique, which predicts gas-to-stellar mass ratios (G/S) from galaxy colors and optional additional parameters. We analyze G/S-color residuals versus potential third parameters, finding that axial ratio is the best independent and physically meaningful third parameter. We define a “modified color” from planar fits to G/S as a function of both color and axial ratio. In the complete galaxy population, upper limits on G/S bias linear and planar fits. We therefore model the entire PGF probability density field, enabling iterative statistical modeling of upper limits and prediction of full G/S probability distributions for individual galaxies. These distributions have two-component structure in the red color regime. Finally, we use the RESOLVE-B 21 cm census to test several PGF calibrations, finding that most systematically under- or overestimate gas masses, but the full probability density method performs well. [ABSTRACT FROM AUTHOR]