Joint analysis and modeling of the hot spot effect from the diurnal reflectance and temperature cycles observed by SEVIRI
Authors
Pinnepalli C., Jean-Louis R., Rajasekaran E., Vidal T., Bian Z., Hu T., Irvine M., Cao B., Gamet P.
Reference
Science of Remote Sensing, vol. 12, art. no. 100309, 2025
Description
This study evaluates the influence of the hot spot effect, i.e. when the solar and viewing angles coincide, producing a radiance peak on the diurnal reflectance and temperature cycles (DRC and DTC, respectively) observed by the SEVIRI (Spinning Enhanced Visible and InfraRed Imager) sensor aboard the Meteosat Second Generation (MSG) satellite. Focusing on clear-sky conditions and multiple land cover types, we assess the directional impact on both spectral brightness temperature (Tb) and land surface temperature (LST). A four-parameter DTC model is coupled with a directional kernel-driven model (KDM), including a hot spot term, to create Time-Evolving KDMs. The models are applied to six diverse sites to evaluate whether optical BRDF characteristics can inform thermal BRDF (Bidirectional Reflectance Distribution Function) behavior, and to what extent directional effects distort DTC profiles. Findings indicate a clear hot spot signature in the DRC, while in the DTC, it subtly alters the bell-shaped curve, resulting in Tb deviations up to 3 K and LST differences up to 4 °C. The results underscore the need to correct for angular effects when comparing DTCs across sites or seasons. Moreover, visual inspections show that optical BRDF peaks align closely with cosine peaks for two satellites, whereas thermal peaks diverge—highlighting mismatches and the challenges of modeling mixed land cover. Present findings underscore the need for improved models and multi-sensor validation to support a full exploitation of thermal remote sensing.
