Design and Analysis of a Compact Airborne Hyperspectral Imager for Vegetation Photosynthesis and Stress Monitoring

Solar-induced chlorophyll fluorescence (SIF) provides a direct proxy for vegetation photosynthesis-related information; however, under stress conditions, its relationship with photosynthesis should be interpreted together with absorbed photosynthetically active radiation by chlorophyll (APARchl) and non-photochemical quenching (NPQ). This study presents a conceptual design of a compact dual-channel airborne imaging spectrometer for synchronous observation of SIF-related spectral radiance and broadband vegetation-canopy spectral reflectance (BR). A self-collimating shared-optical-path configuration is proposed to reduce the system volume, yielding a simulated optical envelope of 205 × 150 × 120 mm3. Optical simulations predict spectral resolutions better than 0.3 nm over 670–780 nm for the SIF channel and better than 2 nm over 400–780 nm for the BR channel. An asymmetric double Babinet depolarizer is incorporated to reduce polarization-related errors, and the simulated system polarization sensitivity is below 1%. The calculated stray-light ratios of the SIF and BR channels are 0.553% and 0.287%, respectively. LightTools was used to simulate the radiative transfer performance of the instrument under realistic scenes. Furthermore, an end-to-end SIF retrieval simulation was performed to evaluate the retrieval capability of the proposed system. The results indicate that the proposed concept is theoretically feasible and may support future quantitative SIF retrieval and the interpretation of vegetation photosynthetic and stress-related processes.