John B. Schutt

Directional Reflectance Distributions of a Hardwood and Pine Forest Canopy

The directional reflectance distributions for both a hardwood and pine forest canopy at Beltsville, Maryland, were measured in June as a function of sun angle from a helicopter platform using a hand-held radiometer with AVHRR band 1 (0.58-0.68 ¿m) and band 2 (0.73-1.1 ¿m). Canopy characteristics were measured on the ground. The reflectance distributions are reported and compared to the scattering behavior of agricultural and natural grassland canopies. In addition, the three-dimensional radiative transfer model of Kimes was used to document the unique radiant transfers that take place in forest canopies due to their special geometric structure. Measurements and model simulations showed that the scattering behavior of relatively dense forest canopies is similar to the scattering behavior of agricultural crops and natural grasslands. Only in more sparse forest canopies with significant spacing between the tree crowns (or clumps of tree crowns) does the scattering behavior deviate from homogeneous agricultural and natural grassland canopies. This clumping of vegetation material has two effects on the radiant transfers within the canopy: A) it increases the probability of gap to the understory and/or soil layers that increases the influence of the scattering properties of these lower layers; and B) it increases the number of low transmitting clumps of vegetation within the scene causing increased backscatter and decreased forward scatter to occur relative to the homogeneous case. Both effects, referred to as phenomenon A and B, respectively, tend to increase backscatter relative to forward scatter.

Directional reflectance factor distributions of a cotton row crop

Abstract The directional reflectance factor distribution spanning the entire exitance hemisphere was measured for a cotton row crop ( 39 per cent ground cover) as a function of the solar azimuth and zenith angles. Two spectral bands NOAA 7 AVHRR bands 1 ( 0.57-0.69 μ ) and 2 (0.71-0.99 μ ) were measured. Ancillary data consisted of leaf orientation distribution measurements, structural and agronomic measurements, as well as optical measurements of leaves and soil. Polar co-ordinate system plots of directional reflectance factor distributions and three-dimensional computer graphic plots of scattered flux were created from the radiometric data. These plots were used to study the dynamics of the directional reflectance factor distribution as a function of spectral band, geometric structure of the scene, solar zenith and azimuth angles and optical properties of the leaves and soil The polymodal nature of the directional reflectance factor distribution for incomplete row crop canopies was evident from these da...

Leaf water stress detection utilizing thematic mapper bands 3, 4 and 5 in soybean plants

Abstract Foliar water stress in a mature soybean canopy, manifested as wilt rather than as a reflectance shift, was studied using reflectance measurements for Thematic Mapper bands 3 (0.63-0.69 μm), 4 (0.76-0.90 μm) and 5 (1.55-1.75μm). Diffuse and total reflectances were determined using polarization measurements and compared statistically at a variety of look angles at 15min intervals from about 09.00 until 14.00 hours EST. Plots of the data from unstressed canopy show that the behaviour of both the diffuse and total reflectances mimics that of the solar radiance curve with time of day, whereas the stressed canopy reflectance data revealed a nearly linear behaviour with a small negative slope. For both the diffuse and total reflectances measured in the nadir position, TM4 was found to be the most responsive spectral band for foliar water stress detection when the water deficit was sufficient to cause wilting, implying that substantial changes in canopy leaf geometry can best be monitored by TM4. TM3 was...

Highly Reflecting Stable White Paint for the Detection of Ultraviolet and Visible Radiations

The use of polyvinyl alcohol polymer as a binder for barium sulfate does not allow the intrinsically high reflectance of barium sulfate in the 200-300-nm range to be optimally employed. In an effort to better utilize this property, totally inorganic coating systems are described. Potassium sulfate turns out to be the preferred binder for reflectance enhancement. Compositions, formulating procedures, and application techniques are included. For completeness, absolute and relative reflectance data are included for intrasystem and intersystem comparisons.

A laboratory investigation of a physical rnechanisim for the extended infrared absorption (‘red shift‘) in wheat

Abstract Laboratory spectral measurements, on the components of both greenhouse and field grown winter wheat, were performed to identify the component and its appropriate response which gave rise to the extended infrared absorption or ‘red shift’ reported by Collins. Results of this study indicated that inherent intraplant adaxial (upper) leaf reflectances were of sufficient variability to suggest that an admixture of mechanisms may have utility on identifying the booting and head emergence stages in the life cycle of wheat. The physical mechanism for the shift was found to be relatively independent of the inherent variability in leaf spectra, and to be dependent upon the difference in the mode of deposition of cuticle upon the abaxial (lower) surface relative to that of the adaxial (upper) surface, ihe position of the flag leaf, and thus the surface exposed to the incident light during heading and after emergence of the head.

Estimation of emittances and surface temperatures from avhrr data

An approach to the estimation of surface temperatures and emissivities using AVHRR (Advanced Very High Resolution Radiometer) data acquired near noon is presented. Thermal data in channels 3, 4, and 5 were used to estimate the reflective component in 3. For three water bodies in Oregon the average emittances found for channels 3 and 4 were 0.979 and 0.991, respectively. Also studied were agricultural sites and forests, comprising both primary (PF) and secondary (SF) types. For the agricultural sites, the average emittances were 0.919 and 0.943 for channels 3 and 4. For the PF and SF the results were 0.976 and 0.983 for channel 3 and 0.988 and 0.995 for channel 4.

Comparison of the reflectance characteristics of polytetrafluoroethylene and barium sulfate paints.

Preliminary results are presented of the directional reflectance measurements taken on two tetrafluorethylene (TFE) paints formulated with silicone binders. Both paints are found to be more Lambertian than barium sulfate paint and pressed powder, although the pigment to binder ratios for barium sulfate and TFE paints are about 133 and 3.3 to 1, respectively. The TFE paints exhibit total visible reflectances above 90 percent and offer surfaces that are not significantly affected by water.

Effect of heliotropism on the bidirectional reflectance of irrigated cotton

Abstract The dynamic movement of cotton leaves in the presence of sunlight has been described using gyroscopic coordinates. These coordinates were used to calculate the position of leaf normals with respect to the sun on an individual basis. A sensitivity analysis established that the angle between a leaf normal and the sun was most affected by changes in pitch and roll. Averaging leaf normals by quadrant (as established by the direction of the compass) showed the pronounced heliotropic behavior of cotton leaves and the differential behavior of cotton leaves relative to the quadrant of the sun. These results were subsequently applied to the estimation of the phase angle γ between the canopy normals and sun from cross sections of bidirectional reflectance curves obtained for a band spanning 0.57–0.69 μm. From the cross section determined by the principal plane at 6:07 MST, which turned out to be concave and nearly symmetrical, the canopy averaged value for γ was estimated to be about 90°, while the calculated value from the leaf angle data was 85°. At 12:08 MST the same cross section was convex and asymmetrical with respect to rotation about the nadir direction, indicating distinguishable forescattered and backscattered components. For the forescattered component the estimated value for γ was 15°, and the calculated value 20°. For the backscattered component the estimated value for γ was 12°, and the calculated value 21°. These results suggested that bidirectional reflectance information analyzed sequentially using a visible band for which the optical transmission is nearly zero can be used to monitor leaf movement and hence moisture availability.

Optical coatings formulations containing tetrafluoroethylene

Two optical reference coatings containing tetrafluorethylene have been formulated using silicone binders. One of the silicones used is an oligomer of methyl silanol supplied at 48 percent solids in a mixture of butanol and ethanol. The other silicone is a proprietory silicone tethered ethyl silicate based colloidal silica binder supplied at 22 and 36 percent solids in a mixture of low molecular weight aliphatic alcohols. The coatins are characterized by high durability and have an overall reflectance in the visible part of the spectrum of about 90 percent. The substrate preparation and application procedures are described.

Cerenkov Light Collection in the High Energy Astronomical Observatory a Cosmic Ray Experiment

An improved Cerenkov counter for the High Energy Cosmic Ray Experiment on the first High Energy Astronomy Observatory will make the resolution between different nuclei much better. A more UV reflecting paint and improved radiator and PMT positioning should give us hoped for results.