New Technique for Quantifying Air-Sea Interactions Using High Resolution SAR Imagery

Reynolds stress, drag coefficient and surface roughness are important parameters for quantifying air-sea momentum and energy exchange in the marine atmospheric boundary layer (MABL). Parameterization of these exchanges is important for climate modelling, weather forecasting, electromagnetic propagation, naval applications, monitoring bio-geo-chemical impacts and beach erosion, etc. In-situ air-sea fluxes, traditionally, are quantified using the Monin-Obukhov similarity theory (MOST). However MOST assumes horizontal uniformity of the air-sea interface. This assumption is reasonable in the open ocean but breaks down in coastal areas, which contain strong horizontal gradients. In-situ measurements from anemometers, alone, have difficulty detecting and characterizing the temporal and spatial scales very close to the sea surface. Therefore, the relationship between air sea parameters and radar returns, which provide valuable spatial information, is of interest to atmospheric, oceanic and remote sensing scientists. Synthetic Aperture Radar (SAR) images, in particular, can be utilized to extract dominant scales of ocean wavelengths using a new wavelet-based technique for deriving state-of-the-art maps of air-sea parameters, such as wave speed, roughness length, drag, stress and wave age at 5-meter resolution. With SAR’s high resolution, two features in Monterey Bay, CA during the Coastal Land Air Sea Interaction (CLASI) 2016 field campaign, a wind front and atmosphere waves, can be resolved. These features do not appear in the Coupled Ocean Atmosphere Mesoscale Predication System (COAMPS) model runs due to poor spatial resolution. The new satellite-SAR technique, applied to the entire bay, is validated against traditional coastal anemometer data and boundary layer model runs, and the results are promising. Furthermore, the technique is applied to the wind front and atmospheric waves, which are tracked at high resolution. The anemometer measurements can be used to reverse the technique to simulate SAR-derived wind speeds in Monterey Bay at different times to improve SAR algorithms. This new high resolution technique is valuable for improving models like COAMPS and can be utilized in any location where in-situ measurements are not available, including hurricane, other natural disasters, etc.