Abstract. Low-grazing angle (LGA) radar sea spikes were observed with a highresolution, dual-polarization, X band imaging radar deployed on the floating instrument platform (FLIP) during the Marine Boundary Layer Experiment (MBLEX) held off the California coast during April-May 1995. Spatiotemporal statistics of observed sea spike events are presented, including duration, velocity, and directional distributions. The dependence of these parameters on wind and wave conditions is compared to theoretical predictions and to similar measurements of breaking wave signatures obtained with passive acoustic techniques by Ding and Farmer [1994]. The density of sea spikes (events per unit time per unit area) and the fractional surface coverage are estimated as a function of friction velocity and compared to theoretical predictions. Though we find consistency between the dynamical aspects of sea spike events and of acoustic wavebreaking signatures, we do not observe a predicted cubic u, dependence of sea spike density. Differences may be a consequence of the specific nature of low-grazing angle scattering at X band (and higher) frequencies. We observe an approximately quadratic dependence on u, of sea spike fractional surface coverage which is insensitive to the choice of backscattered power threshold over a 9 dB range. IntroductionBreaking waves on the ocean surface are believed to be an important part of air-sea interactions. They limit the height of ocean waves, mix surface waters, transfer energy from the wave field to currents, and enhance the fluxes of heat, mass, and momentum through the generation of turbulence and entrainment of air [Melville, 1996]. Because wave breaking is a nonlinear and intermittent process, direct measurement of wave breaking in the field is extremely difficult. For this reason the development of optical, acoustical, and microwave remote sensing methods is desirable.Breaking events have long been attributed as a source for microwave backscatter, especially for horizontally polarized radiation at near-grazing angles [Wetzel, 1990]. "Sea spikes," the colloquial term for high-intensity bursts of radar backscatter typically observed at low grazing angles, are attributable both to actively breaking waves and to scattering features (i.e., wedges, bores, plumes) bound near the crests of steep waves. A number of radar studies of wave breaking in the laboratory have attempted to identify the specific mechanisms for scattering and to measure the dependence of the microwave signature on breaking strength. Kwoh and Lake [1984] attributed discrete bursts of backscatter from short gravity waves at moderate to high incidence angles to "gentle" breaking. Banner and Fooks [1990, 1991a, b] used a CW scatterometer and boresighted video to study both the detection of breaking waves and the dependence on environmental parameters. They found an approximately cubic relation between u, and the number of sea spikes observed at moderate incidence attributable to breaking, in agreement with theoretical predictions by ...

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Breath analysis is a noninvasive diagnostic method that profiles a person's physical state by volatile organic compounds in the breath. It has huge potential in the field of disease diagnosis. In order to offer opportunities for practical applications, various GC-based techniques have been investigated for on-line breath analysis since GC is the most preferred technique for mixed gas separation. This article reviews the development of breath analysis and GC-based techniques in basic breath research, involving sampling methods, preconcentration methods, conventional GC-based techniques, and newly developed GC techniques for breath analysis. The combination of GC and newly developed detection techniques takes advantages of the virtues of each. In addition, portable GC or micro GC are poised to become field GC-based techniques in breath analysis. Challenges faced in GC-based techniques for breath analysis are discussed candidly. Effective cooperation of experts from different fields is urgent to promote the development of breath analysis.

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