Engineering topics

Wu, L. K.

Publications and source records attributed to Wu, L. K..

5 records

NASA NTRS1987

Estimation of X-band scattering properties of tree components

An X-band FM-CW very fine range resolution scatterometer was used to acquire backscattering data for a number of tree species. Using a model to describe the scattering source function and an experimental procedure for selected removal of plant parts allows the estimation of the volume backscatter coefficient and the volume extinction coefficient. It is found that: (1) leaves are strong attenuators as well as scatterers; (2) the albedo at a given angle of incidence is nearly independent of the tree type; (3) the tree limbs are good attenuators but rather poor scatterers; and (4) the albedo changes as a function of the angle of incidence and for deciduous trees is also a function of the season.

Pitts, D. E.↗

NASA NTRS1986

Identification of major backscattering sources in trees and shrubs at 10 GHz

A short-range very-fine-resolution FM-CW radar scatterometer has been used to identify the primary contributors to 10-GHz radar backscatter from pine, pin oak, American sycamore and sugar maple trees, and from creeping juniper shrubs. This system provided a range resolution of 11 cm and gave a 16-cm diameter illumination area at the target range of about 4 m. For a pine tree, the needles caused the strongest backscatter as well as the strongest attenuation in the radar signal. Cones, although insignificant contributors to the total backscatter, were more important for backscattering than for attenuation. For the rest of the trees, leaves were the strongest cause of backscattering and attenuation. However, in the absence of leaves, the petioles, small twigs, and branches gave relatively strong backscatter. For American sycamore and sugar maple trees, the fruits did not affect the total backscatter unless they were packed in clusters. For creeping juniper the backscattered energy and attenuation in the radar signal were mainly due to the top two layers of the evergreen scales. The contribution of the tree trunks was not determined.

Zoughi, R.↗

NASA NTRS1985

Determination of Backscattering Sources in Various Targets

The objectives of this research are to identify the primary contributors to 10 GHz radar backscatter from various natural and man-made surfaces and objects, and to use this information in developing new and better models for the scatter. When the true sources are known for the scattering that leads to variation in intensity on radar images, the images (and sets of them) may be interpreted more meaningfully in terms of the variation of parameters of interest for science or application. For example, better interpretation of vegetation images may be possible for yield forecasting and stress detection.

Moore, R. K.↗

NASA NTRS1984

Determination of the Sources of Radar Scattering

The sources of radar backscattering sources in vegetation canopies and surface targets were determined. The fundamental questions were, how much of backscattering is due to direct volume backscatter by the canopy, the soil, and indirect backscatter by soil/vegetation, and what are the relative roles in terms of scattering. The results for crops, milo plant, wheat plant, soybean plant, and surface targets are reported.

Moore, R. K.↗

NASA NTRS1983

Focusing the parabolic antenna

The focused parabolic antenna has far field pattern characteristics in the radiating near field region. Therefore, it can provide fine resolutions in the across range dimensions. The technique of focusing the parabolic antenna is discussed and applied to a 2-1/2 foot parabolic antenna at X-band. The results of the pattern measurements at various ranges from 2.8 m to 5 m are provided.

Wu, L. K.↗