Engineering topics

Demarcke, J. S.

Publications and source records attributed to Demarcke, J. S..

3 records

NASA NTRS1981

Look direction dependence of radar backscattering cross section for agricultural fields

Analysis of multifrequency-multipolarization scatterometer data acquired by NASA Johnson Space Center during the 1978 Colby Agricultural Soil Moisture Experiment provides evidence that the effects of row orientation remain quite severe for relatively bare fields over a wide range of radar frequencies. In addition, Seasat satellite radar imagery from areas in Louisiana shows dominant row orientation effects even beneath substantial amounts of vegetation cover. The multiparameter nature of the Colby data set, and the continuous angular change in field patterns observed in the Louisiana test area provide much finer definition of microwave sensitivity to row orientation than has been possible in the past.

Waite, W. P.↗

NASA NTRS1981

Use of Seasat satellite radar imagery for the detection of standing water beneath forest vegetation

The Seasat synthetic aperture radar, operating at a 23-cm, L-band wavelength, detected anomalous tonal patterns in areas having relatively uniform vegetable canopy. These anomalously high radar returns were shown to be related more to the underlying terrain (areas of standing water) than to the vegetation canopy. These results show that L-band radars, imaging forested terrain in a Seasat configuration, are sensitive to gross changes in vegetation, and may even penetrate the vegetation canopy, providing an unmistakable radar signature. Properly designed space imaging radar shuttle experiments, using multiple frequency and polarization radars of various depression angles, may provide documentation for a flood-monitoring capability. Height, configuration, and density of the biomass in conjunction with frequency and incidence angle of the imaging system are shown to be important factors in formulating a backscatter model, but the relative significance of each is yet to be determined.

Macdonald, H. C.↗

NASA NTRS1981

Wetland mapping with imaging radar

An analysis of Seasat radar imagery is presented to identify the radar signature of vegetation-covered water surfaces. Imagery taken on Aug. 21, 1978 displayed anomalously high returns over swamp lands near Lafayette, LA. Landsat scans of the area two days later revealed uniform vegetation cover in the area, and ground examination found the area to be filled with cypress trees in swamps. Similar results were obtained during an overflight above a region of southeast Arkansas. Mechanisms producing the high degree of reflectance are explored, and the possibility that the strong return is due to an interaction of the vegetation cover and the specular water surface underneath is mentioned. Further studies to identify the exact mechanisms producing the anomalous returns are recommended, as well as optimization of the viewing angle for general classes of vegetation density.

Waite, W. P.↗