An astronomy invited talk by Bhavesh Jaiswal (U. R. Rao Satellite Center, ISRO) exploring spectro-polarimetric signatures of (exo)planetary atmospheres, combining theoretical modeling, instrumental development, and observational validation.

Abstract
Spectro-polarimetry provides a powerful and largely untapped diagnostic of planetary atmospheres, offering sensitivity to atmospheric composition, cloud and aerosol properties that are difficult to access with intensity-only measurements. This talk will discuss radiative transfer modeling of polarized light in planetary atmospheres with examples of Venus, Mars, and Earth. The cloud-induced polarization across optical and near-infrared wavelengths caused due to single and multiple scattering is discussed. These models are used to predict disk-integrated spectro-polarimetric signals for Earth-like planets under a range of atmospheric and viewing geometries, and to identify observables that are robust tracers of atmospheric structure and planetary surface. The development of SHAPE (Spectropolarimetry of HAbitable Planet Earth), a near-infrared spectro-polarimeter aboard the Chandrayaan-3 orbiter, is presented. Designed for high polarimetric sensitivity and spectral resolution, SHAPE observes Earth as an unresolved exoplanet analog. Instrument design, calibration strategies, and in-flight performance are discussed, with emphasis on mitigating instrumental polarization and systematic effects. The first spectro-polarimetric observations of Earth as an unresolved planet are also discussed, providing a critical benchmark for exoplanet studies and demonstrating the potential of spectro-polarimetry for future characterization of habitable exoplanets.