There is a need to develop mid-infrared (IR) spectrometers for applications in which the absorbance of only a few vibrational mode (optical) frequencies needs to be recorded; unfortunately, there are limited alternatives for the same. The key requirement is the development of a means to access discretely a small set of spectral positions from the wideband thermal sources commonly used for spectroscopy. We present here the theory, design and practical realization of a new class of filters in the mid-infrared (IR) spectral regions based on using guided mode resonances (GMR) for narrowband optical reflection. A simple, periodic surface-relief configuration is chosen to enable both a spectral response and facile fabrication. A theoretical model based on rigorous coupled wave analysis is developed, incorporating anomalous dispersion of filter materials in the mid-IR spectral region. As a proof-of-principle demonstration, a set of four filters for a spectral region around the C-H stretching mode (2600–3000 cm−1) are fabricated and responses compared to theory. The reflectance spectra were well-predicted by the developed theory and results were found to be sensitive to the angle of incidence and dispersion characteristics of the material. In summary, the work reported here forms the basis for a rational design of filters that can prove useful for IR absorption spectroscopy.

The entire set of Seasat A satellite scatterometer (SASS) wind speed observations, U,, colocated with the buoy measurements of the wind speed U b and wave height H1/3 is analyzed. The "error" Ub --U, is found to be influenced by the degree of wind-wave coupling. This coupling is quantified employing the ratio of the wave-to-wind energy densities: X .., pw•I(•2)/PaUt, 2. For the special case of a fetch-limited wave growth, X is shown to coincide with the wind fetch. It is found that when the coupling is weak, i.e., at large X, the SASS tends to overestimate the wind speed, and vice versa. The magnitude of the trend is evaluated roughly as 0.5 m/s per 100 km of X. The increased radar backscatter at large X is explained by invoking the concept (due to V. Zakharov and his collaborators) of a Kolmogorov equilibrium range appearing in wave spectra of sufficiently developed seas when the wind input is concentrated at high frequencies.In this extreme case, the surface density of steep wavelet occurrence would be at its highest owing to a pronounced cascade pattern in the surface geometry. The fractal dimension D n of such an idealized surface is estimated to be about 2.333. Further, it is suggested that D n for a general case is a function of sea maturity. Finally, it is concluded that both the probability and the surface density of steep wavelet events are increasing functions of X. A major implication with respect to the electromagnetic scattering is that the so-called spike component of the backscattering coefficient, formed from the individual radar returns caused by the steep and/or breaking wavelets, is controlled primarily by the large-scale features of surface geometry, hence by such nonlocal factors of the wave development as the wind fetch. 1317

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The algorithmic approach and expected performance for the VIIRS cloud mask, sea surface temperature and land surface temperature is presented.

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