Remote sensing techniques

Remote sensing of ocean currents is becoming an operational tool in many countries. Wyatt reviews phased-array HF radar systems, with examples of wave, wind and current measurements from operational systems, and she provides an assessment of their accuracy. Observations from HF radar on board an oil platform in the Gulf of Mexico, as described by Barrick et al., show tremendous strides forward when working in this difficult environment, where only one system may be feasible and the structure of the rig distorts the antenna pattern. In contrast, Kohut et al. describe results from a "triple nested HF radar array" that combines lower frequency long-range systems with high-resolution radars and several other techniques to map the plume of the Hudson River in New York Bight. Advances in theory continue to be made, which may lead to future improvements in practical current and wave radars. Wang and colleagues describe new ideas on nonlinear polarisation vector translation. Dugan and Piotrowski argue that aircraft remote sensing is advantageous for rivers and estuaries where currents may change rapidly in time and space. Using images of light scattered by near surface sediment, mean flow vectors have been derived and compared with ADCP data. Terray and colleagues report on their assessment of the feasibility of studying horizontal dispersion and vertical mixing on metre to kilometre space scales using measurements of dye dispersion from an airborne lidar.