Measuring heat flux with differential absorption techniques

Since the heat passing between ocean and atmosphere is controlled by the temperature gradient in the air/water interface (except for breaking waves and high wind conditions), measurement of these interface gradients constitutes a new measurement of air/sea heat flux. Such measurements have been implemented in laboratory experiments using the differential absorption characteristics of water in the 3 - 5 micron infrared region. The inherent radiometric characteristics of the water molecule cause frequency variations of absorption which allow emerging radiation to originate beneath the interface. This radiation carries information about subsurface temperature and is sensitive down to the optical depth (~ 0.4 mm at 2.2 microns). Radiance variations with frequency bring information about temperature variations with depth. A well-calibrated instrument that is radiometrically stable with low instrument noise is required to measure the radiance variations. Laboratory evidence using both FTIR and two-color camera techniques indicate that interface gradients can be accurately measured. This technique allows detailed examination of this previously unobserved and crucial zone for air/sea interactions.