IOSEE: An efficient and flexible infrared ocean surface effective emissivity package for remote sensing, numerical weather prediction, and climate modeling applications

This study presents the Infrared Ocean Surface Effective Emissivity (IOSEE) package for computing infrared effective ocean surface emissivity (OSE) across the infrared spectrum. IOSEE builds on the conventional surface-emitted surface-reflected (SESR) physical model, which captures the fundamental spectral emission-reflection physics of the ocean surface. It employs the effective viewing zenith angle (VZA) formulation that implicitly accounts for the angular treatment of reflected downwelling atmospheric radiation by the wind-roughened surface, together with an updated water complex refractive index (CRI) and salinity correction. This combined framework mitigates the systematic underestimation of unpolarized OSE that the conventional SESR model produces at moderate-to-large geometric VZAs under the specular approximation. Validation against independent shipborne and ground-based retrievals shows that effective OSEs calculated by IOSEE agree closely with instrument-derived values within the thermal infrared window. A decomposition analysis attributes the improvement in accuracy over the conventional SESR model primarily to the effective VZA implementation rather than to the updated CRI and salinity correction. Evaluations outside the thermal window, against independent observations and a reference effective OSE model, are consistent with the working hypothesis that the effective VZA derived within the window applies across the broader spectral range without introducing a systematic bias in the effective OSEs. The IOSEE package is released as an open-source tool. Multithreaded parallelization makes it efficient enough to generate infrared effective OSE look-up tables for remote sensing, numerical weather prediction, and climate modeling applications.