An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils

For a practical superconducting quantum interference device（SQUID） based measurement system,the Tesla/volt coefficient must be accurately calibrated.In this paper,we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils.The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil.By applying magnetic fields through a three-dimensional Helmholtz coil,the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields.Calibration with alternating current（AC） field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current（DC） calibration to avoid possible effects due to eddy current.In our experiment,a calibration relative error of about 6.89 × 10-4is obtained,and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils.The method does not need precise alignment of the magnetometer inside the Helmholtz coil.It can be used for the multichannel magnetometer system calibration effectively and accurately.

Method study and uncertainty analysis of calibration coefficients validation based on the Inner Mongolia test site

Calibration coefficients validation is the foundation for ascertaining the sensor performance and carrying out the quantitative application.Based on the analysis of the differences between the calibration and validation,two calibration coefficients validation methods were introduced in this paper.Taking the HJ-1A satellite CCD1 camera as an example,the uncertainties of calibration coefficients validation were analyzed.The calibration coefficients validation errors were simulated based on the measured data at an Inner Mongolia test site.The result showed that in the large view angle,the ground directional reflectance variation and the atmospheric path variation were the main error sources in calibration coefficients validation.The ground directional reflectance correction and atmospheric observation angle normalization should be carried out to improve the validation accuracy of calibration coefficients.

Dual-calibration coefficient:a more accurate protocol for simultaneous determination of superoxide and hydrogen peroxide in human Hep G2 cell extracts

We present a more accurate method for the quantification of superoxide anion （02-） and hydrogen peroxide （H202） simulta- neously in human HepG2 cell extracts. After the xanthine/xanthine oxidase system was added into cell extract which was devoid of O2＊- and H202, steady-state and in-situ produced O2＊- and H202 by xanthine/xanthine oxidase system was labeled by fluorescent probes and subsequently separated by microchip electrophoresis. Based on this method, two differential equations with the calibration coefficients were established for O2 and H202, respectively. Using the established dual-calibration coefficients, we obtained the calibrated concentrations of 02＊ and H202 that produced in human HepG2 cells, which were lower （0.66±0.03 and 0.82±0.04 lamol/L for 02＊-and H202, respectively） than that （0.85±0.03 and 0.96±0.03 gmol/L for O. and H202, respectively） obtained from statutory working curve. The proposed dual-calibration coefficient protocol takes into account both the complex matrix effect of the biological system and real time decaying of O2 ＊- and H202, providing a method with higher accuracy.

Monthly calibration and optimization of Ångstrom-Prescott equation coefficients for comprehensive agricultural divisions in China

Angstrom-Prescott equation(AP)is the algorithm recommended by the Food and Agriculture Organization(FAO)of the United Nations for calculating the surface solar radiation(R_(s))to support the estimation of crop evapotranspiration.Thus,the a_(s) and b_(s) coefficients in the AP are vital.This study aims to obtain coefficients a_(s) and b_(s) in the AP,which are optimized for Chinas comprehensive agricultural divisions.The average monthly solar radiation and relative sunshine duration data at 121 stations from 1957-2016 were collected.Using data from 1957 to 2010,we calculated the monthly a_(s) and b_(s) coefficients for each subregion by least-squares regression.Then,taking the observation values of R_(s) from 2011 to 2016 as the true values,we estimated and compared the relative accuracy of R_(s) calculated using the regression values of coefficients a_(s) and b_(s) and that calculated with the FAO recommended coefficients.The monthly coefficients,a_(s) and b_(s),of each subregion are significantly different,both temporally and spatially,from the FAO recommended coefficients.The relative error range(0-54%)of R_(s) calculated via the regression values of the a_(s) and b_(s) coefficients is better than the relative error range(0-77%)of R_(s) calculated using the FAO suggested coefficients.The station-mean relative error was reduced by 1% to 6%.However,the regression values of the a_(s) and b_(s) coefficients performed worse in certain months and agricultural subregions during verification.Therefore,we selected the a_(s) and b_(s) coefficients with the minimum R_(s) estimation error as the final coefficients and constructed a coefficient recommendation table for 36 agricultural production and management subregions in China.These coefficient recommendations enrich the case study of coefficient calibration for the AP in China and can improve the accuracy of calculating R_(s) and crop evapotranspiration based on existing data.

VICARIOUS RADIOMETRIC CALIBRATION OF SATELLITE FY-ID SENSORS AT VISIBLE AND NEAR INFRARED CHANNELS

For the problem of in-flight test site radiometric calibration for the FY-1D Meteorological Satellite onboard sensor's visible and near infrared channels,this paper described the calibration method,satellite-ground synchronous observation data acquired at China Dunhuang Calibration Test Site,parameter derivation and radiative transfer computation during the calibration,and the calibration result analysis.At FY-1D seven channels (with central wavelength at Channels 1:630 nm,2:865 nm;6:1610 nm;7:455 nm,8:505 nm;9:555 nm;10:932 nm),calibration coefficients obtained during the ground site calibration were compared with that respectively of pre- launch calibration.It is demonstrated that results of FY-1D onboard two sensors' (A and B) at channels 1,2,6 and 10 were close to pre-calibration,and the absolute difference of Gobi desert reflectance computed using test site and pre-launch calibration coefficients was no more than 2%. At other channels,large pre-launch calibration errors resulted in a poor consistency between the test site and pre-launch calibration.The errors can be corrected by the test site calibration results. Based on a rough estimation,the overall error of the calibration was about 6%. The paper also presented the in-flight vicarious calibration at the visible and near infrared channels of FY-1C sensor A which was launched in 1999 and has been put into operational mode since 2002.The results exhibit that FY-1C sensor's response has 23% attenuation at Channels 7 and 8,while only minor degradation at the other channels was found. During the mission,calibrations were also conducted at NOAA-17's Channels 1 and 2 (1:430 -830 nm,2:500--1072 nm).A very good consistency has been achieved between the test site and pre-launched calibration results.