Analysis on applicability of nonlinearity coefficients derived from prelaunch calibration tests to onboard calibration of Microwave Humidity Sounder （MWHS-Ⅲ） on FY-3E satellite

WANG Zhenzhan; XIAO Yuwei; ZHANG Shengwei; HE Jieying; GU Songyan

doi:10.11834/jrs.20221447

Common Technology of Historical data Re-Calibration of Domestic Remote Sensing Satellite | Views : 0 下载量: 1216 CSCD: 3

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Analysis on applicability of nonlinearity coefficients derived from prelaunch calibration tests to onboard calibration of Microwave Humidity Sounder （MWHS-Ⅲ） on FY-3E satellite
Vol. 27, Issue 10, Pages: 2327-2336(2023)
Received：08 July 2021，

Published：07 October 2023
DOI： 10.11834/jrs.20221447
稿件说明：

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王振占，肖雨伟，张升伟，何杰颖，谷松岩.2023.FY-3E微波湿度计发射前定标的非线性系数在星上定标中的适用性分析.遥感学报，27（10）： 2327-2336 DOI： 10.11834/jrs.20221447.

Wang Z Z，Xiao Y W，Zhang S W，He J Y and Gu S Y. 2023. Analysis on applicability of nonlinearity coefficients derived from prelaunch calibration tests to onboard calibration of Microwave Humidity Sounder （MWHS-Ⅲ） on FY-3E satellite. National Remote Sensing Bulletin， 27（10）：2327-2336 DOI： 10.11834/jrs.20221447.

摘要

星载微波湿度计发射前定标和在轨定标的最大不同是冷源的使用：在轨定标的冷源是宇宙冷空背景温度，通常为2.7 K，而发射前定标的冷源通常控制在80—100 K。这样通过发射前定标得到的非线性系数是否可以用于在轨定标一直是一个非常关心和值得研究的问题。本文通过在FY-3E微波湿度计发射前热真空定标中除了传统需要的冷热、变温定标源之外，另外设计了一个独立的位于180—200 K附近的定标源。利用该验证源，本文提出了三点定标公式，基于冷空不变性并通过外推到冷空亮温的模拟观测计算非线性系数。随后通过比较传统和新型非线性系数推导方法的结果，并将两组系数带入同一组数据中分析两组发射前定标系数用于在轨定标的适用性。结论表明，通过对传统方法和新方法的计算结果比较，发现将两组非线性方法应用于同一数据集的结果存在差异，说明传统方法得到的发射前系数存在误差。并且该方法简化了发射前标定过程，提高了非线性系数用于星上标定的精度。

Abstract

Nonlinearity is one of the most important errors in calibrating a microwave radiometer. It cannot be corrected in orbit through direct measurements

and its correction usually uses a set of coefficients derived from prelaunch calibration tests

namely

thermal vacuum test. The main difference between prelaunch and on-board calibration of a microwave radiometer is that of the cold calibration target used in two-point calibration. On board calibration usually uses the cold sky

which is also called cosmic background temperature of 2.7 K

as the lower end in the response of a microwave radiometer

whereas in the prelaunch calibration

a blackbody at a temperature between 80 K and 100 K is used in the calibration practice. Therefore

the applicability of the nonlinear coefficients derived from the prelaunch calibration test for on-board calibration is a long-standing concern that has never been validated. In this study

a special program of prelaunch calibration was designed

adding a validation blackbody target

which works at ambient temperature of 180—200 K in the thermal vacuum chamber

in addition to the traditional cold blackbody target

a warm blackbody target

and a varied-temperature blackbody target. This validation target provides an opportunity to compute nonlinear coefficients directly through three-point calibration and to evaluate the errors in applying the nonlinear coefficients by the traditional calibration method. Furthermore

a novel method is invented through extrapolating the measurements to the cold sky temperature by the equation of three-point calibration during a scan. It serves as a virtual on-board calibration target to calibrate the radiometer and to produce nonlinear coefficients combined with three other calibration targets. The nonlinear coefficients of the traditional and novel methods are compared

and the two groups of nonlinearities are applied to the same data sets. Thus

the errors in applying the nonlinear coefficients by the traditional calibration method can be evaluated. The results show a deviation between the two group of nonlinear coefficients; the greater absolute value of the nonlinear coefficients indicates greater error. The nonlinear coefficients of the traditional and novel methods are compared

and discrepancies are found in applying the two groups of nonlinearities to the same data sets. The finding implies that errors exist in the prelaunch coefficients when using the traditional method. The novel method simplifies the procedure of prelaunch calibration and improves the accuracy of nonlinear coefficients using for on-board calibration.

关键词

Keywords

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