Surface Reflectivity

This paper describes the first part of a series of investigations to develop algorithms for simultaneous retrieval of aerosol parameters and surface reflectance from a newly developed hyperspectral instrument, the GEOstationary Trace gas and Aerosol Sensor Optimization (GEO-TASO), by taking full advantage of available hyperspectral measurement information in the visible bands. We describe the theoretical framework of an inversion algorithm for the hyperspectral remote sensing of the aerosol optical properties, in which major principal components (PCs) for surface reflectance is assumed known, and the spectrally dependent aerosol refractive indices are assumed to follow a power-law approximation with four unknown parameters (two for real and two for imaginary part of refractive index). New capabilities for computing the Jacobians of four Stokes parameters of reflected solar radiation at the top of the atmosphere with respect to these unknown aerosol parameters and the weighting coefficients for each PC of surface reflectance are added into the UNified Linearized Vector Radiative Transfer Model (UNL-VRTM), which in turn facilitates the optimization in the inversion process. Theoretical derivations of the formulas for these new capabilities are provided, and the analytical solutions of Jacobians are validated against the finite-difference calculations with relative error less than 0.2%. Finally, self-consistency check of the inversion algorithm is conducted for the idealized green-vegetation and rangeland surfaces that were spectrally characterized by the U.S. Geological Survey digital spectral library. It shows that the first six PCs can yield the reconstruction of spectral surface reflectance with errors less than 1%. Assuming that aerosol properties can be accurately characterized, the inversion yields a retrieval of hyperspectral surface reflectance with an uncertainty of 2% (and root-mean-square error of less than 0.003), which suggests self-consistency in the inversion framework. The next step of using this framework to study the aerosol information content in GEO-TASO measurements is also discussed.

We demonstrate the importance of surface reflectivity for the radiation field in polar regions by a combination of measurements and radiative transfer calculations. Results from measurements of spectral albedo, radiance and irradiance from 280 to 1050 nm at German Neumayer Station in Antarctica in summer 2003/2004 as well as measurements of UV irradiance during summer 1997/1998 at Australian Davis Station, Antarctica are presented. The impact of surface albedo inhomogeneity is investigated by 3-D Monte Carlo modelling. We found that high surface reflectivity in the ultraviolet and visible parts of the spectrum due to the snow covered surface in Antarctica modifies the radiation field considerably compared to mid-latitudes. A change of the spectral reflectivity, which happens as a consequence of climate change will have a large impact in the radiation properties in polar regions and vice versa.

The article presents some problems of optical wireless link (OWL) reliability. The influence of atmosphere on OWL reliability is explained. There are link models from which it is possible to determine a dependability of characteristics. A summary of basic ways of its improvement is given. 15 Optical wireless links represent an alternative to optical-fibre systems for high bit rate, in particular when laying an optical-fibre cable is inconvenient or impossible (adverse terrain - valley, river, railway, historical part of city, etc.). Connection in free space is accomplished by means of a narrow optical beam with low divergence. For a successful and reliable installation of OWL it is necessary to know steady OWL parameters for standard atmosphere and statistical character of the weather in a given locality.

The transmitted power passes through the atmosphere and is reflected on the wall (reflecting surface). The incident optical power on the walls or barriers is subject to the laws of radiation and matter interaction. Reflection on the surface can have dispersive (diffused) or specular (reflective) character. The aim of this project is to create a model for the link design where power balance equation and the power level diagram are used.

A synthetic aperture acoustic imaging system with a novel inversion algorithm is described. Data is obtained by using a transducer insonifying the sample surface at a critical angle which is excited by a short electrical pulse. The critical angle is chosen for a suitable surface wave or Lamb wave mode that exists on the object. The transducer is mechanically scanned

The principle of operation, experimentation, and performance of a fiber optic displacement sensor on a tooth surface is presented. The performances of this sensor are investigated by correlating the detector output with different probe configurations and various teeth samples with different surface reflectivity properties. With a multimode plastic bundled fiber probe, the sensitivities for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.9667, 0.775, 0.5109, and 0.25 mV/mm, respectively, with a good linearity of more than 99% based on the analysis of the front slope. With a multimode plastic coupler, the sensitivities for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.3538, 0.2951, 0.2069, and 0.1579 mV/mm, respectively. This proves that the sensor is capable of discriminating between different teeth surfaces. Such results are useful as guidelines for tooth surface related research, such as tooth surface profiling and measurement of tooth surface roughness.

A synthetic aperture acoustic imaging system with a novel inversion algorithm is described. Data is obtained by using a transducer insonifying the sample surface at a critical angle which is excited by a short electrical pulse. The critical angle is chosen for a suitable surface wave or Lamb wave mode that exists on the object. The transducer is mechanically scanned

We demonstrate the importance of surface reflectivity for the radiation field in polar regions by a combination of measurements and radiative transfer calculations. Results from measurements of spectral albedo, radiance and irradiance from 280 to 1050 nm at German Neumayer Station in Antarctica in summer 2003/2004 as well as measurements of UV irradiance during summer 1997/1998 at Australian Davis Station, Antarctica are presented. The impact of surface albedo inhomogeneity is investigated by 3-D Monte Carlo modelling. We found that high surface reflectivity in the ultraviolet and visible parts of the spectrum due to the snow covered surface in Antarctica modifies the radiation field considerably compared to mid-latitudes. A change of the spectral reflectivity, which happens as a consequence of climate change will have a large impact in the radiation properties in polar regions and vice versa.

A simple fiber optic displacement sensor based on intensity modulation technique is demonstrated using a bundle multimode plastic fiber as a probe. The sensor consists of a light source, a probe, and photodiode detector. The sensor is capable of measuring displacements of mirror ranging from 0.05 to 2.2 mm using a red light source of wavelength 632.8 nm with maximum output power of 1 mW. The sensitivity of the device is found to be 168.8 mV/mm over 0.05–0.35 mm range and −29.8 mV/mm over 1.05–2.2 mm range. The sensor is highly sensitive at the front slope and very useful for close distance target. The simplicity of the design, high degree of sensitivity, dynamic range and the low cost of the fabrication make it suitable for applications in industries as position control and micro displacement measurement in the hazardous region. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 661–663, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23147