Thesis / Master of Science (MS)

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography : leaves 78-84. / by Lucy-Ann A. McFadden. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Includes bibliographies. / by Robert Bennett Singer. / Ph.D.

Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Dale J. Bremer / Radiometric methods may provide more objective and quantitative assessments of turf quality and density than visual ratings and may be useful in measuring green leaf area index (LAI), aboveground biomass, and chlorophyll concentration. This three-year study was conducted near Manhattan, KS to examine: 1) relationships between canopy reflectance and visual quality and density ratings in four cool-season grasses tall fescue (Festuca arundinacea Schreb.), Kentucky bluegrass (Poa pratensis L.) and two hybrid bluegrasses (HBG); 2) effects of species, mowing height, and irrigation deficit on relationships between visual quality and reflectance; 3) comparisons of visual quality with reflectance and digital images of individual plots; and 4) relationships of LAI, aboveground biomass, and chlorophyll concentration with canopy reflectance in the same four grasses and in perennial ryegrass (Lolium perenne), zoysiagrass (Zoysia japonica Stued.), and bermudagrass [Cynodon dactylon (L.) Pers.]. Reflectance was strongly correlated with visual ratings in the normalized difference vegetation index (NDVI, [935-661]/[935+661] nm, r = 0.88), the near infrared to red (NIR/R [935/661] nm, r = 0.83), Stress1 (706/760 nm, r= 0.84), and Stress2 (706/813 nm, r= 0.70) ratios and at wavelengths 613 (r= 0.74) and 661 nm (r = 0.80), but correlations varied among years at each wavelength and vegetation index. For density, highest correlations were in NDVI (r=0.86), R661 (r=-0.84), and Stress2 (r=-0.82). Regressions between reflectance and quality and density ratings indicated cultivar- and mowing height-specific models. Irrigation-deficit strongly affected reflectance in KBG and both HBG but not in TF, indicating greater sensitivity to drought of bluegrasses than TF. Digital images indicated strong correlations between percentage green cover and visual quality (r=0.89). However, wide ranges in visual quality were observed in plots with similar green cover or NDVI for reasons that are not apparent. Correlations of LAI, aboveground biomass, and chlorophyll concentration with reflectance were strong in some species at different wavelengths and ratios. Results indicated both potential and limitations in using spectral reflectance to estimate turfgrass canopy characteristics.

published_or_final_version / Physics / Master / Master of Philosophy

Three applications of Smith's model of magneto-optical effects in stratified magnetic media are presented. Each application involves the incident-angle dependence of magneto-optical effects which Smith's model treats explicitly. In addition. the three applications address current issues in magnetic and magneto-optical recording. The first problem considered is that of nonmagnetic surface layers which form on magnetic recording heads. The second is a theoretical treatment of effects which arise in magneto-optical recording when high numerical-aperture optical systems are combined with media exhibiting interference-enhanced optical properties. The final application is a novel technique for determining the entire dielectric tensor of materials used for magneto-optical recording. The incident-angle dependence of the longitudinal Kerr effect is employed to study nonmagnetic surface layers which form on ferrite recording heads. Calculations based on the Smith model show a correlation between the inert-layer thickness and the incident-angle dependence of the longitudinal Kerr effect. Experimental results confirm the shift in the angular position of the signal peak. in agreement with the theory for finite inert-layer thickness. An unambiguous determination of the inert-layer thickness for ferrite materials is prevented because of a periodic dependence of the peak angle on the inert-layer thickness. Jones-matrix algebra is used with the Smith model to quantitatively determine the effects of obliquely-incident rays on the reflectance and magneto-optical readout signals for various magneto-optical media structures. The most antireflective structure is found to be very sensitive to incident-angle effects. Structures with moderate reflectance (>10%). however. are not significantly affected by incident-angle effects. Finally. a technique for the determination of the optical and magneto-optical constants from multiple incident-angle measurements of reflectance and Kerr rotation is presented. The experimental system employs a Helium-Neon laser and a rotating differential detection system. The technique is used to investigate the optical properties of a series of Cu/Co multilayers and a comparison with a model based on the bulk optical. constants of Cu and Co is made. Anomalous behavior is observed for multilayers with very thin periods.

No description available.

No description available.

Yellow avian plumage is a direct result of carotenoid pigments obtained in a bird’s diet and may act as an indicator for individual health, parasite resistance, and status. This study describes breast feather reflectance of adult Prothonotary Warblers (Protonotaria citrea) (n=169), insectivorous Neotropical migrant passerines, throughout the Ultraviolet (UV) and human visible light spectra and examines the relationship between Haemosporidia (pathogen causing Avian Malaria) infection and feather reflectance (n=41). Reflectance was characterized using a Principle Component Analysis evaluating Intensity, Brightness, Hue, UV Intensity, UV Brightness, and UV Chroma. UV and visible light reflectance was higher in birds sampled earlier in the field season (early clutch) (p=0.0017 and p=0.0743 respectively). There was no relationship between infection and either visible light or hue. However, UV reflectance was lower in infected birds (p=0.0843). This study suggests that UV reflectance is an important indicator for the infection status of a Neotropical migrant passerine.

Master of Science / Department of Chemical Engineering / John Schlup / This study investigated the specular reflectance properties of 6061-T6 aluminum alloy anodized in accordance with military specification MIL-A-8625 as a function of both etch process time and anodization process potential. Both process parameters affect the specular reflectance characteristics when measured using a 660 nm, collimated diode laser source. The etch process time, when varied between 0.5 to 20 minutes, resulted in a decrease in specular reflectivity with increasing time. The anodization process potential was varied between 10 and 21 volts, with a 15 volt condition producing samples with the greatest specular reflectivity. Between the two parameters, the etch time had the greater effect. Additionally, the dependence of the incident beam angle on specular reflectivity was shown not to have a significant effect when compared to the etch process time and process potential.