Differential absorption techniques and radiometric satellite calibration for measuring air-sea interactions

The transfer of heat and gas between ocean and atmosphere is a critical parameter for coupled climate models. Surface measurements of these transfers are difficult, expensive, prone to large errors, and based on parameters measured alongside the interface. Although temperature profiles inside the interface itself (topmost millimeter) control air-sea heat flux, measurement of these gradients with fine-wire thermistors is difficult and therefore rare. Recent research has shown that interface temperature profiles can be examined in detail with infrared interferometry by using the frequency variation of water´s absorption in the 3.0-5.0 μm region. Separate theoretical work indicates that sensing a linear interface temperature profile´s vertical thickness may be used for remote sensing of gas flux. Naval Research Laboratory (NRL), Washington, D.C., experiments show that a two-frequency camera technique can map heat flux variations on waves with root mean square error (RMSE) <3.1 W/m² if a linear interface gradient is assumed. The U.S. Navy is funding the GOES Air-Sea Interaction Project (GASIP) to radiometrically calibrate the multichannel sea surface temperature (MCSST) using accurate surface radiometry. Scatterometer winds will be added to estimate the skin-bulk temperature difference ΔT. Since ΔT correlates closely with heat flux, improved spatial and temporal heat flux inputs will go into coupled Naval models