Relative Calibration Accuracy Research Articles

The influence of metacognition monitoring on L2 Chinese audiovisual reading comprehension.

Metacognition monitoring is the ability to evaluate the cognitive process actively. L2 learners with high metacognition monitoring ability can better monitor reading processes and outcomes consciously, thus facilitating self-regulated learning and improving reading efficiency. Previous studies mostly used offline self-reports to examine the metacognition monitoring in static text reading by L2 learners. This study investigated the effects of different indicators of metacognition monitoring on L2 Chinese audiovisual comprehension by online confidence judgment and audiovisual comprehension tasks. Target measures of metacognition monitoring included absolute calibration accuracy based on video or test and relative calibration accuracy measured by Gamma or Spearman correlation coefficient. 38 intermediate-advanced Chinese learners participated in the study. Multiple regression analysis showed three main results. First, absolute calibration accuracy can significantly predict L2 Chinese audiovisual comprehension, while relative calibration accuracy has no significant effect. Second, the predictive effect of video-based absolute calibration accuracy is affected by the video difficulty, that is, the greater the video difficulty, the greater the impact on the performance of audiovisual comprehension. Third, the predictive effect of test-based absolute calibration accuracy is influenced by the language proficiency, specifically, the higher the L2 Chinese proficiency, the stronger the prediction on the performance of audiovisual comprehension. These results support a multidimensional view of metacognition monitoring by specifying how different indicators of metacognition monitoring may predict L2 Chinese audiovisual comprehension. The findings have important pedagogical implications for strategy training of metacognition monitoring and point to the necessity to take task difficulty and individual differences among learners into full consideration.

Toward Calibration of the Global Network of Gravitational Wave Detectors with Sub-Percent Absolute and Relative Accuracy

The detection of gravitational-wave signals by the LIGO and Virgo observatories during the past few years has ushered us into the era of gravitational-wave astronomy, shifting our focus from detection to source parameter estimation. This has imposed stringent requirements on calibration in order to maximize the astrophysical information extracted from these detected signals. Current detectors rely on photon radiation pressure from auxiliary lasers to achieve required calibration accuracy. These photon calibrators have made significant improvements over the last few years, realizing fiducials displacements with sub-percent accuracy. This achieved accuracy is directly dependent on the laser power calibration. For the next observing campaign, scheduled to begin at the end of 2022, a new scheme is being implemented to achieve improved laser power calibration accuracy for all of the GW detectors in the global network. It is expected to significantly improve absolute and relative calibration accuracy for the entire network.

An integrated method to improve the GOES Imager visible radiometric calibration accuracy

A variety of vicarious calibration methods over different reference targets have been studied at National Oceanic and Atmospheric Admission (NOAA)/National Environmental Satellite, Data, and Information Service (NESDIS) to provide sensor degradation information for the GOES Imager visible channels which do not have any on-board calibration devices. To meet the increasing demand for more accurate satellite measurements, an integrated method is developed mainly to improve the relative calibration accuracy by combining the results from different vicarious methods. In this study, three commonly used vicarious calibration methods, the desert, Deep Convective Cloud (DCC) and ray-matching methods, are applied to the GOES-12 Imager visible data to describe the integrated method. The integrated method first combines the normalized observations of each individual method by anchoring the results on the first day of satellite operation, and then removes the deviated combined observations using a recursive filtering method. This integration is based on the fact that the GOES sensor trending functions from different methods are very similar within 1% difference over the 7-year study period. The trending uncertainty of the integrated method is less than that of each individual one. The absolute calibration of the integrated method can be achieved by generating the calibration coefficients using the reflectance of reference targets which are well characterized with the Aqua MODIS Collection 6 (C6) data. It is found that there is less than 1% difference between the calibration coefficients derived with the DCC and desert reference targets. It is expected that this integrated method will be a useful tool to validate the GOES-R ABI on-board radiometric calibration accuracy for the solar reflective channels.

The Herschel-PACS photometer calibration

This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ∼2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF ν = λF λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.

SCUBA-2: on-sky calibration using submillimetre standard sources

SCUBA-2 is a 10000-bolometer submillimetre camera on the James Clerk Maxwell Telescope (JCMT). The instrument commissioning was completed in September 2011, and full science operations began in October 2011. To harness the full potential of this powerful new astronomical tool, the instrument calibration must be accurate and well understood. To this end, the algorithms for calculating the line-of-sight opacity have been improved, and the derived atmospheric extinction relationships at both wavebands of the SCUBA-2 instrument are presented. The results from over 500 primary and secondary calibrator observations have allowed accurate determination of the flux conversion factors (FCF) for the 850 and 450 micron arrays. Descriptions of the instrument beam-shape and photometry methods are presented. The calibration factors are well determined, with relative calibration accuracy better than 5 per cent at 850 microns and 10 per cent at 450 microns, reflecting the success of the derived opacity relations as well as the stability of the performance of the instrument over several months. The sample-size of the calibration observations and accurate FCFs have allowed the determination of the 850 and 450 micron fluxes of several well-known submillimetre sources, and these results are compared with previous measurements from SCUBA.

Water vapor correction to improve the operational calibration for NOAA AVHRR/3 channel 2 (0.85 µm) over a desert target

The Advanced Very High Resolution Radiometers (AVHRRs) flown on the National Oceanic and Atmospheric Administration (NOAA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) polar satellites have been providing invaluable data for Earth system science and global change studies. However, the use of AVHRR solar reflectance products (e.g., normalized difference vegetation index (NDVI)) is constrained by calibration uncertainty, largely owing to the lack of an on-orbit calibration device for solar reflectance channels. Since the mid-1990s, NOAA has been applying operational calibration to these channels using the time series of top-of-atmosphere (TOA) measurements of the Libyan Desert site. However, the assumed radiometric stability of Libyan Desert TOA measurements can be disrupted by short-term variations in atmospheric components, especially for AVHRR channel 2, which has a spectral response function covering water vapor absorption lines in the near-infrared (NIR) spectra. This study aims to improve the calibration accuracy of AVHRR channel 2 data by applying water vapor correction over the homogeneous desert target surface using the water vapor content (W) derived from the linear relationships between the AVHRR split-window temperature difference (ΔT) and the Moderate Resolution Imaging Spectroradiometer (MODIS) NIR water vapor product. Results show that the linear ΔT–W relationship is affected by the temperature lapse rate at the satellite over-passing time and the spectral response functions of AVHRR split-window channels. Water vapor correction reduces the calibration uncertainty from 2.6%–3.5% to 1.7%–1.8%, and about 1.0% surface-based relative calibration accuracy is independent of the water vapor uncertainty introduced by the ΔT–W regression. Furthermore, the short-term variations in the channel 2 operational degradation rate are largely reduced after water vapor correction. Thus, implementing water vapor correction can improve the operational calibration accuracy for AVHRR channel 2.

Prelaunch instrument calibration in the real world: The GOES example

The pre-launch ground infrared calibration of the Geostationary Operational Environmental Satellite (GOES) N-Q Imager and Sounder is presented. Ground calibration provides information necessary to the accurate on-orbit calibration of these radiometers. Infrared channels are calibrated in a thermal vacuum environment, under minimum and maximum mission operation temperatures, using a variable-temperature warm target to simulate the Earth scene and a cold target to simulate the space scene. Brightness temperatures derived from observation of the instrument internal calibration target, used for on-orbit calibration, are compared to brightness temperatures of the external calibration target as a check of relative accuracy using these two sources. Changes to the GOES N-Q specification from GOES I-M are highlighted, as well as results of noise, relative calibration accuracy, and spectral response performance to date. For completeness, results of spatial and pointing performance will be presented. Enhancements to test methodology and data processing techniques are highlighted throughout.

Comparisons of Rain Rate and Reflectivity Factor Derived from the TRMM Precipitation Radar and the WSR-88D over the Melbourne, Florida, Site

Abstract Validating the results from the spaceborne Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) requires comparisons with well-calibrated ground-based radar measurements. At altitudes near the storm top, where effects of PR signal attenuation are small, the data are used to check the relative calibration accuracy of the radars. Near the surface, where attenuation effects at the PR frequency of 13.8 GHz can be significant, the data provide an assessment of the performance of the PR attenuation correction algorithm. The ground-based data are taken from the Doppler Weather Surveillance (WSR-88D) radar located at Melbourne, Florida. In 1998, 24 overpasses of the TRMM satellite over the Melbourne site occurred during times when significant precipitation was present in the overlap region of the PR and WSR-88D. Resampling the ground-based and spaceborne datasets to a common grid provides a means by which the radar reflectivity factors (dBZ) can be compared at different heights and for dif...

Precipitable Water Estimation from High-Resolution Split Window Radiance Measurements

A technique that uses the spatial variance of image brightness temperature to derive total column precipitable water is applied to high-resolution multispectral aircraft scanner data for the June 19, 1986 COHMEX day. The technique has several advantages over other approaches in that it requires only relative calibration accuracy, is less susceptible to instrument error, and does not directly use a priori information. Results indicate significant horizontal variability of precipitable water at the mesoscale. Precipitable water gradients of 6 mm per 10 km are not uncommon. The results verify well against special rawinsonde measurements and the ensuing cloud field development. While only applied to this specialized aircraft data, the applicability of the technique to operational AVHRR and VAS data is discussed.