Model-Based Decomposition of Low-Altitude Infrared Radiance Using Dual-Band MWIR Observations

Infrared image radiance combines surface and atmospheric thermal emission with solar contributions, making agreement in total radiance insufficient to assess individual components. This study presents a model-based decomposition method using two mid-wave infrared (MWIR) bands with contrasting atmospheric absorption and solar sensitivity. Viewing geometry recovered from imagery and terrain data is combined with meteorological inputs. Ground-target temperatures retrieved from the longer-wavelength band are held fixed in shorter-wavelength predictions, without further target fitting. Observations on two days test these predictions across different atmospheric and surface contributions. For forests at 280 and 1080 m, spanning modeled surface-dominated and path-dominated conditions, shorter-band radiance predicted using longer-band temperatures differs from observations by at most 0.056 W m−2 sr−1 (maximum absolute residual across 12 comparisons at six times). Independently retrieved long-wave infrared forest temperatures agree with MWIR estimates within 2.6 °C. In two comparison frames, using observation-constrained atmospheric inputs reduces the root-mean-square (RMS) difference between observed and predicted longer-band sky radiance to 1/10.9 and 1/15.4 of the values obtained with an unmodified standard atmosphere, with the same offset retained across profiles within each frame. Greenhouse observations extend the analysis to diffuse solar reflection and localized brightening consistent with specular reflection. These results demonstrate how cross-band comparisons can assess the modeled radiance composition of field imagery beyond agreement in total signal.