NASA space shuttle sun-glint imaging have attracted widespread attention. Outside the glint region, calmer surface areas such as slicks can be identified by changes in both brightness and color. The only potential NASA-EOS sensor is the JPL-derived multiangle imaging spectroradiometer (MISR), which is devoted principally to cloud and aerosol signal detection.

Subsurface laser scanning devices and range-gated viewing systems have been developed that have the potential for imaging of, and obtaining fundamental data on, the motions of the OBL. These systems, deployed from ROVs and able to approach and scan the OBL from below, offer a potential for active optical sensing that has been largely ignored.

Possible Role for NRL

Several NRL groups, in a combined thrust involving colleagues at different NRL sites in optics, remote sensing, acoustics, and chemistry, could develop a very strong effort in acoustical and optical oceanography as outlined below.

Oceanic Boundary Layer-Related Acoustical Oceanography

Given the Navy's interest and experience in acoustics, acoustic remote sensing is an area in which a major impact could be made. The use of acoustic techniques to study the OBL is likely to be a rewarding area of research in the next decade, and NRL is well positioned to make significant contributions at a number of levels. Such an effort would involve the acoustics groups in OBL problems.

The important topics in acoustical oceanography are the dynamics of the OBL in the bubble zone, which can be measured using active acoustics; acoustic properties of the bubbly layer using active and passive acoustics; acoustic measurements of rainfall rates; gas transfer across the air-sea interface; and adaptation of sonobuoy technology to global monitoring. Indeed, it seems that sonobuoy technology could be readily adapted to using ambient sound to monitor wave breaking and rainfall, and active sound to measure bubble cloud properties in the surface layer. NRL-S's involvement in ONR's surface reverberation project is a good beginning.

Marine Atmospheric Boundary Layer-Related Optical Oceanography

A second area that NRL should emphasize, and in which it is already strong, is passive optics for characterizing ocean optical properties. The work at NRL-S on ocean optical properties involves a good coupling of air-sea phenomenology with remote sensing. The data on ocean optical properties (e.g., that generated by SeaWIFS), and the facilities to process and manipulate the data, are resources that a research group in ocean optics can use to great advantage. NRL-E could contribute, on the actual remote sensing side, in optical instrumentation and theory. Also, NRL-W could make use of this work and these data, becoming involved in the coupling of ocean models to the optical data.

Recommendation

The panel recommends that NRL undertake a strong, coordinated research program that includes simultaneous underwater acoustic, electromagnetic, and optical measurements of the oceanic and marine atmospheric boundary layers in carefully selected coastal zone and continental shelf environments, in which different conditions of atmospheric forcing and the influence of surface slicks can also be quantitatively documented. This effort should involve active and passive electromagnetic and optical (visible and infrared) measurements from above the sea, as well as active and passive undersea probing of the ocean surface and mixed layers.



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