Spectro-polarimetry of HAbitable Planet Earth (SHAPE) on Chandrayaan-3: Instrument characteristics, calibration and onboard performance

@misc{jaiswal2026spectropolarimetry,
  title = {{Spectro-polarimetry of HAbitable Planet Earth (SHAPE) on Chandrayaan-3: Instrument characteristics, calibration and onboard performance}},
  author = {Bhavesh Jaiswal and Swapnil Singh and Ravishankar B T and Anand Jain and Smrati Verma and Reenu Palawat and Brajpal Singh and Bijoy Raha and Sathyanarayana Raju and Bhavesh Mendhekar and Srinivasa Rao Kondapi and Priyanka Das and Rahul Waghmare and Supratik Bose and Supriya Verma and Yogesh Prasad K R and Praloy Karmakar and Abhishek Kumar Singh and Honey Gupta and Balaraman Prabakaran and Motamarri Srikanth and Sankarasubramanian Kasiviswanathan and Anuj Nandi},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.13107},
  eprint = {2609.13107},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.13107},
}

TY  - UNPB
TI  - Spectro-polarimetry of HAbitable Planet Earth (SHAPE) on Chandrayaan-3: Instrument characteristics, calibration and onboard performance
AU  - Bhavesh Jaiswal
AU  - Swapnil Singh
AU  - Ravishankar B T
AU  - Anand Jain
AU  - Smrati Verma
AU  - Reenu Palawat
AU  - Brajpal Singh
AU  - Bijoy Raha
AU  - Sathyanarayana Raju
AU  - Bhavesh Mendhekar
AU  - Srinivasa Rao Kondapi
AU  - Priyanka Das
AU  - Rahul Waghmare
AU  - Supratik Bose
AU  - Supriya Verma
AU  - Yogesh Prasad K R
AU  - Praloy Karmakar
AU  - Abhishek Kumar Singh
AU  - Honey Gupta
AU  - Balaraman Prabakaran
AU  - Motamarri Srikanth
AU  - Sankarasubramanian Kasiviswanathan
AU  - Anuj Nandi
PY  - 2026
DA  - 2026/09/11
PB  - arXiv
DO  - 10.48550/arxiv.2609.13107
UR  - https://arxiv.org/abs/2609.13107
AB  - 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.
ER  -