Engineering topics

Lang, Roger H.

Publications and source records attributed to Lang, Roger H..

22 records · Page 2

NASA NTRS1991

Discrete random media techniques for microwave modeling of vegetated terrain

Microwave remote sensing models of vegetated terrain are investigated. The problem is to determine canopy characteristics such as biomass, canopy height, and the moisture of the underlying soil. The report describes a discrete scatter model which has been employed to model backscatter in the active (radar) case and to model brightness temperature in the passive (radiometric) case. The acquisition of ground truth data is discussed, as well as the comparison of theory and experiment. The overall conclusion of the work has been that the discrete scatter model in conjunction with efficient scatter algorithms and the distorted Born approximation is a most appropriate methodology to use for modeling purposes in the microwave region.

Lang, Roger H.↗

NASA NTRS1991

Radar modeling of a boreal forest

Microwave modeling, ground truth, and SAR data are used to investigate the characteristics of forest stands. A mixed coniferous forest stand has been modeled at P, L, and C bands. Extensive measurements of ground truth and canopy geometry parameters were performed in a 200-m-square hemlock-dominated forest plot. About 10 percent of the trees were sampled to determine a distribution of diameter at breast height (DBH). Hemlock trees in the forest are modeled by characterizing tree trunks, branches, and needles as randomly oriented lossy dielectric cylinders whose area and orientation distributions are prescribed. The distorted Born approximation is used to compute the backscatter at P, L, and C bands. The theoretical results are found to be lower than the calibrated ground-truth data. The experiment and model results agree quite closely, however, when the ratios of VV to HH and HV to HH are compared.

Chauhan, Narinder S.↗

NASA NTRS1991

Microwave backscattering and emission model for grass canopies

A two-layer model is developed that treats the grass canopy as a collection of randomly oriented elliptical dielectric discs over a layer of thatch with underlying soil surface. The distorted Born approximation in conjunction with the Peake formulation is used to calculate the backscattering coefficient and the emissivity from the canopy. Two particular features of this model which are unique for grass canopies are the variation of the canopy structure and the presence of the thatch layer. The basic parameters in the model such as the size and orientation of grass blades, dielectric constant of soil and vegetation, and thickness and water content of the thatch layer have been obtained from ground truth data. To interpret the available experimental observations of grasslands, numerical results from both passive and active models at L-band (1.4 GHz) are generated and various scattering and emission properties of the grass canopies are discussed.

Saatchi, Sasan S.↗

NASA NTRS1990

Average reflected power from a one-dimensional slab of discrete scatterers

Reflection from a one-dimensional random medium of discrete scatterers is considered. The discrete scattering medium is modeled by a Poisson impulse process with concentration lambda. By employing the Markov property of the Poisson impulse process, an exact functional integro-differential equation of the Kolmogorov-Feller type is found for the average reflected power. Approximate solutions to this equation are obtained by regular perturbation and two variable expansion techniques in the limit of small lambda. The regular perturbation results is valid for small slab thicknesses, while the two-variable result is uniformly valid for any thickness. The two-variable result shows that as the slab size becomes infinite all of the incident power is reflected on the average.

Saatchi, Sasan S.↗