No abstract

[1] Surf zone bore celerities and swash zone surface currents were measured on a shallow sloping, low-energy beach using two remote sensing methods that differ fundamentally in their imaging mechanisms. Microwave Doppler radar measures electromagnetic backscatter from small-scale ocean surface roughness while video-based particle image velocimetry (PIV) relies on image texture resulting from variations in light reflectivity from the ocean surface. Imagery from the two methods showed high correlation, in which regions of high radar backscatter corresponded to visibly identifiable waves and bores propagating across the surf zone. Correlation coefficients between radial velocity time series sampled using the two methods at multiple locations across the surf zone were typically greater than 0.5 for frequencies less than a noise cutoff of 0.25 Hz. Similarly, spectra were found to be coherent at the 95% level with a nearly zero phase shift between the two signals near the broad spectral peak between 0.02 and 0.25 Hz. However, some significant differences were evident. PIV was capable of estimating both cross-shore and alongshore surface velocities while the use of one microwave Doppler radar system restricted surface velocity estimates from that technique to line of sight (radial) only. PIV was found to be more capable of estimating swash zone (uprush and backwash) surface velocities as a smoother water surface in the swash zone adversely affected radar reflectivity. In contrast, microwave Doppler radar was found to be more capable of estimating the surface velocity between bores when insufficient image texture was recorded in the video imagery. Both techniques were capable of measuring surf zone bore celerities through comparison to a shallow water model and to independent celerity estimates extracted from the slope of individual bore trajectories. Typical normalized errors were roughly 25% for radar and 15% for PIV.

Abstract-Radiometric measurements of the microwave emissivity of foam were conducted during May 2000 at the Naval Research Laboratory's Chesapeake Bay Detachment using radiometers operating at 10.8 and 36.5 GHz. Horizontal and vertical polarization measurements were performed at 36.5 GHz; horizontal, vertical, +45 , 45 , left-circular, and right-circular polarization measurements were obtained at 10.8 GHz. These measurements were carried out over a range of incidence angles from 30 to 60 . Surface foam was generated by blowing compressed air through a matrix of gas-permeable tubing supported by an aluminum frame and floats. Video micrographs of the foam were used to measure bubble size distribution and foam layer thickness. A video camera was boresighted with the radiometers to determine the beam-fill fraction of the foam generator. Results show emissivities that were greater than 0.9 and approximately constant in value over the range of incidence angles for vertically polarized radiation at both 10.8 and 36.5 GHz, while emissivities of horizontally polarized radiation showed a gradual decrease in value as incidence angle increased. Emissivities at +45 , 45 , left-circular, and right-circular polarizations were all very nearly equal to each other and were in turn approximately equal to the average values of the horizontal and vertical emissivities in each case.

Abstract-Radiometric measurements of the microwave emissivity of foam were conducted during May 2000 at the Naval Research Laboratory's Chesapeake Bay Detachment using radiometers operating at 10.8 and 36.5 GHz. Horizontal and vertical polarization measurements were performed at 36.5 GHz; horizontal, vertical, +45 , 45 , left-circular, and right-circular polarization measurements were obtained at 10.8 GHz. These measurements were carried out over a range of incidence angles from 30 to 60 . Surface foam was generated by blowing compressed air through a matrix of gas-permeable tubing supported by an aluminum frame and floats. Video micrographs of the foam were used to measure bubble size distribution and foam layer thickness. A video camera was boresighted with the radiometers to determine the beam-fill fraction of the foam generator. Results show emissivities that were greater than 0.9 and approximately constant in value over the range of incidence angles for vertically polarized radiation at both 10.8 and 36.5 GHz, while emissivities of horizontally polarized radiation showed a gradual decrease in value as incidence angle increased. Emissivities at +45 , 45 , left-circular, and right-circular polarizations were all very nearly equal to each other and were in turn approximately equal to the average values of the horizontal and vertical emissivities in each case.

Two distinct phases of island-are evolution are recognized in late Mesozoic sedimentary rocks of the northern Antarctic Peninsula. During late Jurassic (Kimmeridgian-Tithonian) times, alternating radiolaria-rich mudstones and ash-fall tuffs were deposited under shallow marine euxinic conditions in association with restricted volcanic centres. The name Nordenskjöld Formation is proposed for this lithostratigraphic unit. Subsequently, during the early Cretaceous, a major episode of volcanism and uplift led to the construction of an emergent are-terrane. Simultaneous development of a retro-arc basin resulted in the accumulation of coarse volcaniclastic detritus along the eastern side of the arc. Retro-are sedimentation and intermittent volcanism continued into the late Cretaceous and early Tertiary. Although the pattern of sedimentation in the northern Antarctic Peninsula is broadly comparable to that of the southern Andes, an active marginal basin has not been recognized in the former area. Interbedded mudstones and tuffs, identical to those of the Nordenskjöld Formation, were deposited in the southern Andes and South Georgia during the late Jurassic - early Cretaceous.