Changes In Viewing Angle Research Articles

Directional Thermal Infrared Exitance Distributions from a Leafless Deciduous Forest

The directional thermal infrared exitance distributions of a 21.5-m-tall leafless deciduous forest were measured using a rotating 7-detector array suspended 33 m above the forest floor. These distributions are presented for several illumination conditions. Strong directional thermal infrared distributions were observed at high solar elevations on a clear day. Temperature gradients frequently exceeded 3°C per 10-degree change of view angle. At low sun angles and the early evening, change of observed temperature with nadir angle was more moderate and was negligible with azimuth angle. At night and on a cloudy morning, uniform temperature distributions were observed. An interpretation of these directional temperature distributions is given.

Dynamics of directional reflectance factor distributions for vegetation canopies

Directional reflectance factors that span the entire exitance hemisphere were measured for vegetation canopies and bare soils with different geometric structures. Two spectral bands were used—NOAA 6/7 AVHRR bands 1 (0.58–0.68 μm) and 2 (0.73–1.1 μm). Geometric measurements of leaf orientation distributions were taken when possible, and other structural and agronomic measurements were collected. For each cover type, these data were taken several different times on a clear day. Polar coordinate system plots of directional reflectance factors, along with 3-D computer graphic plots of scattered flux, were created. These field data were used in conjunction with literature data to study the dynamics of the directional reflectance factor distribution as a function of the geometric structure of the scene, solar zenith angle, and optical properties of the leaves and soil. Physical mechanisms causing the observed dynamics were proposed and were supported by a number of field and modeling studies. For complete homogeneous vegetation canopies, the major trend observed at all sun angles and spectral bands was a minimum reflectance near nadir and increasing reflectance with increasing off-nadir view angle for all azimuth directions. This trend is well known in the experimental and theoretical literature and is caused by the shading of lower canopy layers by components in the upper layers and by viewing different proportions of the layer components as the sensor view angle changes. In some cases the reflectance minimum was shifted slightly off-nadir in the foward scattering direction. The reflectance distributions tended to be azimuthally symmetric because the leaf transmittance was nearly equal to the leaf reflectance for most wavelengths. For sparse homogeneous canopies the anisotropic scattering properties of the soil significantly influenced the observed directional reflectance in the visible band. Soils have strong backscattering characteristics which can dominate the observed reflectance distribution for sparse canopies and small solar zenith angles. This knowledge is important in interpreting aircraft and satellite data, where the scan angle varies widely and can have different orientations with respect to the sun. Finally, the measured data and knowledge of the mechanics of the observed dynamics of the data can provide rigorous validation and verification tests for theoretical radiative transfer models.

Trends in aluminium paint finishes

It appears that the demand for metallic coat finishes will be maintained at a high level in the foreseeable future. Over the years these finishes have had their detractors who saw it as a passing phase, but they now have a well established share of the automarket. The market for metallic coats started mainly in the United States to attract the younger drivers of the larger automobiles. However, it transpired that they were to have an appeal to all age groups. They convey a feeling of freshness as the viewing angle changes and the colours of gold and silver psychologically convey value.

The Potential of Location within a Room in Producing Equivalent Sphere Illumination

A method is shown whereby ESI may be calculated. The value of ESI, produced by a light source located at a ceiling or wall surface, is mapped onto the ceiling or wall surface for various conditions of polarization and viewing angle. These maps indicate optimum positions for light source locations, and the optimum areas of walls and ceilings to be illuminated for maximum effect of reflected light on ESI. The effect of viewing angle change is also depicted. The actual ESI is calculated by using two charts, a table, an isolux curve, and a calculator capable of raising sums to nonintegral powers.