月船三号任务宜居地球光谱偏振测量仪（SHAPE）：仪器特性、校准与在轨性能
Spectro-polarimetry of HAbitable Planet Earth (SHAPE) on Chandrayaan-3: Instrument characteristics, calibration and onboard performance
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- Space Astronomy Group, ISITE-Campus, U. R. Rao Satellite Centre（空间天文组，ISITE校园，U.R. Rao卫星中心）
- U. R. Rao Satellite Centre（U.R. Rao卫星中心）
- Laboratory for Electro-Optics Systems（光电系统实验室）
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中文总结 AI 辅助
本文介绍月船三号SHAPE载荷（近红外光谱偏振计）的仪器特性、校准与在轨性能，通过月球观测和理论模型验证其测量波段偏振的能力，最大偏差小于1%。
中文摘要 AI 辅助
印度空间研究组织（ISRO）的月船三号（Chandrayaan-3）任务轨道器搭载了一项实验性有效载荷，名为SHAPE（宜居地球光谱偏振测量仪）。该载荷从月球以及高海拔地球轨道对地球进行盘积分观测，将地球视为一颗系外行星。该仪器由基于声光可调滤光器（AOTF）的近红外光谱偏振计组成，使用一对铟镓砷（InGaAs）探测器在两个正交偏振方向上进行测量。仪器飞行模型的实验室表征包括对仪器两个通道响应的相对测量。仪器的外场测量揭示了视场响应的不均匀性。鉴于两个通道响应不完全一致以及视场响应的不均匀性，开发了此类偏振计的理论模型，以深入了解偏振计的性能。对SHAPE视场内获得的月球观测数据的分析表明，两个偏振通道之间的透射比处于0.8至1.2的范围内。这种与1的偏差可导致所测偏振引入高达约10%的偏移。研究了SHAPE用于研究波段偏振（定义为光谱吸收带内的相对偏振）的适用性。利用月球观测数据和理论仪器模型，证明了测量相对波段偏振的可行性。对波段偏振中系统性偏差的研究表明，所测波段偏振值的最大偏移小于1%。此外，还讨论了地球观测的初步结果、不同相位角下的光谱和通量测量，以及从这些观测中提取波段偏振的方法。
英文摘要
The orbiter of the Chandrayaan-3 mission of the Indian Space Research Organisation (ISRO) carries an experimental payload called SHAPE (Spectro-polarimetry of HAbitable Planet Earth). This payload makes disc-integrated observations of Earth as an exoplanet, from the Moon as well as from the high altitude Earth orbit. The instrument consists of an Acousto-Optic Tunable Filter (AOTF) based near-infrared spectro-polarimeter making the measurements in the two orthogonally polarized directions using a pair of Indium-Gallium-Arsenide (InGaAs) detectors. The laboratory characterization of the flight model of the instrument included a relative measurement of the response of the two channels of the instrument. The field measurements of the instrument revealed a non-uniformity in the field response. In the light of non-identical response of the two channels and the non-uniformity of the field response, a theoretical model of such a polarimeter is developed to gain insights into the performance of a polarimeter. Analysis of lunar observations obtained within the SHAPE field of view indicates that the transmission ratio between the two polarized channels lies in the range 0.8-1.2. Such deviations from unity can introduce offsets in the measured polarization of up to about 10%. The suitability of SHAPE for studying the band polarization, defined as the relative polarization within a spectral absorption band, is studied. Using the Moon observations and the theoretical instrumental model, the suitability of measuring the relative band polarization is demonstrated. A study of systematic biases in the band polarization demonstrates a maximum offset of less than 1% in the measured value of the band polarization. The initial results of Earth observations, spectra and flux measurements across phase angles, and the methodology for retrieving the band polarization from these observations are also discussed.
