Relative Calibration Method Research Articles

1m口径红外测量系统的辐射定标

To measure infrared radiation characteristics of air targets, the calibration system for a 1 m aperture infrared measurement system was designed. A mathematic model of calibration for the infrared measurement system was given and a radiometric calibration system was established by combinations of a cavity blackbody and a collimator as the standard radiation source. Because the spectral response of the infrared measuring system is selective, the calibration principle based on conventional radiometric calibration method has theoretical errors and reduces the precision of radiometric calibration. To solve the problem, a relative spectral calibration method based on a monochromator and a standard radiometer was proposed. The mathematical model was given and a relative spectral calibration was performed. Finally, the experiments on radiation characteristic measurement were performed in the field by using the blackbody as a simulated target. The results show that the measurement max error from the 1 m aperture infrared radiation characteristic measurement system is 9.5% and improves by an average of 8.7% as compared with that of the conventional method. These show that the proposed method meets the requirements of practical applications and is suitable for the radiometric calibration in the out-fields.

Outdoor relative radiometric calibration method using gray scale targets

The radiometric calibration of remote sensors is a basis and prerequisite of information quantification in remote sensing. This paper proposes a method for outdoor relative radiometric calibration using gray scale targets. In this method, the idea of two substitutions is adopted. Sunlight is used to replace the integrating sphere light source, and gray scale targets are used to replace the diffuser. In this way, images at different radiance levels obtained outdoors can calculate the relative radiometric calibration coefficients using the least square method. The characteristics of this method are as follows. Firstly, compared with laboratory calibration, it greatly reduces the complexity of the calibration method and the test cost. Secondly, compared with the existing outdoor relative radiometric calibration of a single radiance level, it uses test images of different radiance levels to reduce errors. Thirdly, it is easy to operate with fewer environmental requirements, has obvious advantages in the rapid calibration of airborne remote sensors before or after flight and is practical in engineering. This paper theoretically and experimentally proves the feasibility of this method. Calibration experiments were conducted on the wide-view multispectral imager (WVMI) using this method, and the precision of this method was evaluated by analyzing the corrected images of large uniform targets on ground. The experiment results have demonstrated that the new method is effective and its precision meets the requirement of the absolute radiometric calibration. relative radiometric calibration, relative radiometric correction, precision evaluation, gray scale target

Status of the SPHERE experiment

Here is presented the current state of the SPHERE-2 balloon-borne experiment. The detector is elevated up to 1 km above the snow surface and registers the reflected Vavilov-Cherenkov radiation from extensive air showers. This method has good sensitivity to the mass-composition of the primary cosmic rays due to its high resolution near the shower axis. The detector consists of a 1500 mm spherical mirror with a 109 PMT cluster in its focus. The electronics record a signal pulse profile in each PMT. In the last 2 years the detector was upgraded: time resolution of pulse registration was enhanced up to 12.5 ns, channel sensitivity was increased by a factor of 3, a new LED-based relative PMT calibration method was introduced, and new hardware and etc. was installed.

Classifying land cover based on calibrated full-waveform airborne light detection and ranging data

The capability of the parameters derived from waveform data in discriminating objects is assessed and the effect of the relative calibration of full-waveform data in discriminating land-cover classes is evaluated. Firstly, a non-linear least-squares method with the Levenberg-Marquardt algorithm is used to fit the return waveforms by a Gaussian function. Gaussian amplitude, standard deviation, and energy are extracted. Secondly, a relative calibration method using the range between the sensor and the target based on a radar equation is applied to calibrate amplitude and energy. The change in transmit pulse energy is also considered in this process. A support vector machine classifier is used to distinguish the study area into non-vegetated area (including roads, buildings, and vacant lots), grassland, needle-leaf forests, and broad-leaf forests. The overall classification accuracy ranges from 79.33% to 87.6%, with the combination of the two groups of the three studied parameters. Calibrated data classification accuracy is improved from 1.20% to 6.44%, thus resulting in better forest type discrimination. The result demonstrates that the parameters extracted from the waveforms can be applied effectively in identifying objects and that relative calibrated data can improve overall classification accuracy.

Low-Cost Imaging Photometer and Calibration Method for Road Tunnel Lighting

A camera-based measuring instrument for road tunnels lighting is proposed. The system is aimed at estimating the veiling luminance as it will be perceived by a driver approaching the tunnel, thus allowing the estimation of the optimum luminance level of tunnel entrances, hence increasing the driver's safety. The proposed measuring instrument and the relative calibration method are based on a low-cost commercial grade camera and a reference standard, respectively.

Principle of an in-situ relative calibration method using a double-pass beam for Thomson scattering diagnostics

In this paper, we present the detailed principles of an in-situ relative calibration method used to determine electron temperature (Te) without using optical relative transmissivity and to obtain the optical relative transmissivity. In this method, a double-pass scattering system is used and ratio between the two signals due to forward and back scattering in each spectral channel is measured. Each signal from both the scattering must be resolved using detectors with a fast response time. Statistical simulation results indicate that the method suppresses the systematic error in Te caused by chromatic degradation in optical components because of the radiation effect. The statistical error is almost the same as that of the standard method, which uses the measured wavelength spectrum to determine the electron temperature and density from a single pass. In this new method, the scattering angle (θ) and Te are considered as important parameters for evaluating its feasibility. Therefore, statistical errors for various θ were investigated. As a result, we found that the method is effective in the range of θ > 105° at Te = 10 keV. The statistical error tends to decrease for high Te measurements.

Demonstration of in-situ relative calibration method for a Thomson scattering diagnostic on TST-2

In this paper, we present the experimental results of an in-situ calibration method for Thomson scattering diagnostics in the TST-2 spherical tokamak. A double-pass scattering configuration was able to find the ratio of the output signal from the first (back scattering) pass to that from the second (forward scattering) pass; this ratio can be treated as an independent function of electron temperature. The electron temperature obtained by this new method was in good agreement with that obtained by a standard method (single pass). Relative sensitivities among spectral channels can be estimated by the new method without accessing the machines. The relative sensitivities obtained by the new method corresponded to the values obtained by direct calibration within an error of 5%, except for a spectral channel with a wide band-pass range. These results demonstrate the feasibility of applying this new in-situ calibration method to Thomson scattering diagnostics in severe radiation conditions.

Relative flux calibration for the Guoshoujing Telescope (LAMOST)

This paper presents a relative flux calibration method for the Guoshoujing Telescope (LAMOST), which may be applied to connect a blue spectrum to a red spectrum to build the whole spectrum across the total wavelength range (3700 ∼ 9000 Å). In each spectrograph, we estimate the effective temperatures of selected stars using a grid of spectral line indices in the blue spectral range and a comparison with stellar atmosphere models. For each spectrograph, stars of types A and F are selected as pseudo-standard stars, and the theoretical spectra are used to calibrate both the blue (3700 ∼ 5900 Å) and red spectrograph arms (5700 ∼ 9000 Å). Then the spectral response function for these pseudo-standard stars could be used to correct the raw spectra provided by the other fibers of the spectrograph, after a fiber efficiency function has been derived from twilight flat-field exposures. A key problem in this method is the fitting of a pseudo stellar continuum, so we also give a detailed description of this step. The method is tested by comparing a small sample of LAMOST spectra calibrated in this way on stars also observed by the Sloan Digital Sky Survey. The result shows that the Teff estimation and relative flux calibration method are adequate.

Absolute molecular weight determination of hypromellose acetate succinate by size exclusion chromatography: Use of a multi angle laser light scattering detector and a mixed solvent

Molecular weight distribution is an important quality attribute for hypromellose acetate succinate (HPMCAS), a pharmaceutical excipient used in spray-dried dispersions. Our previous study showed that neither relative nor universal calibration method of size exclusion chromatography (SEC) works for HPMCAS polymers. We here report our effort to develop a SEC method using a mass sensitive multi angle laser light scattering detector (MALLS) to determine molecular weight distributions of HPMCAS polymers. A solvent screen study reveals that a mixed solvent (60:40%, v/v 50 mM NaH 2PO 4 with 0.1 M NaNO 3 buffer: acetonitrile, pH* 8.0) is the best for HPMCAS-LF and MF sub-classes. Use of a mixed solvent creates a challenging condition for the method that uses refractive index detector. Therefore, we thoroughly evaluated the method performance and robustness. The mean weight average molecular weight of a polyethylene oxide standard has a 95% confidence interval of (28,443–28,793) g/mol vs. 28,700 g/mol from the Certificate of Analysis. The relative standard deviations of average molecular weights for all polymers are 3–6%. These results and the Design of Experiments study demonstrate that the method is accurate and robust.

A relative calibration method for a valve leakage rate measurement system

This paper presents a relative calibration method for an internal valve leakage rate measurement system using both microcontroller and acoustic emission (AE) methods. An air jet was selected to calibrate because it provides a frequency spectrum similar to the AE spectrum obtained from the valve leak, especially in the frequency range of 100–300 kHz. Three AE sensors mounted on a valve were used to validate the system calibration. Ratios between the average energy (AErms) were obtained from each pair of sensors, and these ratios were used to transfer the leakage AErms value. Subsequence, its performance to predict the leakage rate in the laboratory and in the field was tested. The error is less than 5% in almost cases. Its benefit is to reduce the recalibration time when a part of measurement system is changed. Accordingly, inexpensive equipment including an AE sensor was built, and its system performance was revealed.

Quantification of polychlorinated dibenzo- p-dioxins and dibenzofurans by direct injection of sample extract into the comprehensive multidimensional gas chromatograph/high-resolution time-of-flight mass spectrometer

Polychlorinated dibenzo- p-dioxins and dibenzofurans in crude extracts of fly ash and flue gas from municipal waste incinerators were quantified using a comprehensive multidimensional gas chromatograph (GC × GC) coupled to a high-resolution time-of-flight mass spectrometer (HR-TOFMS). For identification and quantification, we developed our own program to prepare 3D chromatograms of selected mass numbers from the data of the GC × GC/HR-TOFMS. Isolation of all congeners with a TCDD toxic equivalency factor from the other isomers by only one injection was confirmed. The instrumental detection limit of TCDD on the GC × GC/HR-TOFMS was 0.9 pg by the relative calibration method. Quantification of these substances in the crude extracts was achieved by direct injection to the GC × GC/HR-TOFMS. The results agree with the values obtained using a generic gas chromatography/high-resolution mass spectrometry (GC/HRMS) system. It was confirmed that measurement by high-resolution TOFMS and GC × GC effectively reduces interference from other chemicals.

New Thomson scattering diagnostic on RFX-mod

This article describes the completely renovated Thomson scattering (TS) diagnostic employed in the modified Reversed Field eXperiment (RFX-mod) since it restarted operation in 2005. The system measures plasma electron temperature and density profiles along an equatorial diameter, measuring in 84 positions with 7 mm spatial resolution. The custom built Nd:YLF laser produces a burst of 10 pulses at 50 Hz with energy of 3 J, providing ten profile measurements in a plasma discharge of about 300 ms duration. An optical delay system accommodates three scattering volumes in each of the 28 interference filter spectrometers. Avalanche photodiodes detect the Thomson scattering signals and allow them to be recorded by means of waveform digitizers. Electron temperature is obtained using an alternative relative calibration method, based on the use of a supercontinuum light source. Rotational Raman scattering in nitrogen has supplied the absolute calibration for the electron density measurements. During RFX-mod experimental campaigns in 2005, the TS diagnostic has demonstrated its performance, routinely providing reliable high resolution profiles.

CALIBRAÇÃO DE ANTENAS GPS EM DIFERENTES ESTAÇÕES

The goal of this paper is to investigate the modelling of geodetic GPS antenna phase center through the relative field calibration method. Two geodetic GPS antenna models were investigated. Field measurements were carried out at two calibration pillars in order to estimate azimuth and elevation dependent phase center variations. Significant differences between the modellings due to antenna interchange between the pillars are rather evident and can be attributed to different multipath conditions.

Relative Calibration of Multitemporal Landsat Data for Forest Cover Change Detection

The aim is to investigate how well old Landsat data can be calibrated and utilized for monitoring past changes in forest cover status. The material consists of three MSS images and a TM image covering a period of 19 years. The classes of interest were 1) no change, 2) deforestation, and 3) reforestation. Various relative calibration methods are first compared and their effects on the results of interpreting the “change image” are then studied. As it is sometimes impossible to locate unchanged areas for calibration, the use of both unchanged and changed training areas for calibration purposes is tested here. The change detection method is fixed to parametric supervised change image classification. The longest time difference between image pairs was 19 years and R 2 with a time span of this order was around 40%. R 2 for the models increased about 10% when time span was reduced from 11 years to 3 years. Smoothing methods can predict band-by-band regression very well, and R 2 values are 10–15% higher than with the robust regression technique used. RMSE was slightly larger when multiple band models were used than with smoothing methods. When general calibration models were applied to unchanged data, the differences between the calibration errors were not statistically significant. Thus it was satisfactory to use an entire target area for image calibration and include changed areas in the training data for calibration models. Models created from multiple occasions did not perform well in classification. A fair agreement with estimates and the ground truth was possible using four images. The best result was obtained when using three image pairs and multiple band robust regression calibration. Classification with calibration was only slightly better than without calibration, the difference not being statistically significant.

Indirect calibration of visible channel data

To provide quantitative measurements for Earth studies accurate and comprehensive calibration of satellite radiometers is critically needed. The recent increase in the use of satellite data for climate studies calls for the retrieval of physical parameters from the measured radiances and therefore for absolute calibrations that are known over long time periods. However, even the use of classification or “index” type analyses of satellite data to monitor changes in climate requires that the relative stability of the satellite radiometers be known for long-term data sets. Moreover, plans to collect global satellite data over decadal periods, to monitor changes in surface conditions and in climate, require a calibration standard that can be transferred from one satellite to another in a series. Although most instruments undergo a thorough calibration prior to their launch on a satellite, there appears to be no predictable relationship between these pre-launch calibrations and the post-launch performance. Thus, comprehensive, well-documented post-launch calibrations are needed. Because the solar channels used for imaging on most operational satellites do not have onboard calibration capabilities, a number of indirect approaches have been developed using the Earths surface as a target. A variety of earth targets have been used in calibration ranging from a single target (such as White Sands, NM) to multiple targets covering the entire globe. The use of such targets to monitor the relative calibration of satellite instruments over long time periods introduces a number of uncertainties such as diurnal and seasonal changes in the radiation from the target as seen by the satellite. These temporal changes arise from variations in viewing and illumination geometry, changes in the atmosphere, navigation errors, changes in the surface characteristics (such as soil moisture and vegetation), and cloud variations. Relative calibration methods require periodic absolute calibration checks. There is a demonstrated need for routine aircraft calibration flights to validate the various approaches.

A Method of Self Calibration for Molecular Weight Distribution Determinations for Liquid Crystalline Polymers

Abstract A method of molecular weight calibration was devised for various substituted liquid crystalline polymers with substantial molecular weight repeat units. With the use of gel permeation chromatography, oligomer peak separation was achieved offering a method for self calibration for molecular weight distribution determinations. Employing an overlay of a low molecular weight polystyrene standard, a retention time marker was utilized as a source from which to mark an oligomer peak. The calibration plot produced using this technique showed much better correlation coefficients than that of the polystyrene calibration plot. In addition, molecular weight determinations made from the two techniques yielded two distinct molecular weight averages and distributions, indicating polystyrene to be a poor relative calibration method for the liquid crystalline polymers tested. The technique illustrates the utility of alternative calibration methods when samples show certain physical characteristics.