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Ashley, M. D.

Publications and source records attributed to Ashley, M. D..

5 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Seasonal vegetation differences from ERTS imagery

Knowledge of the times when crop and forest vegetation experience seasonally related changes in development is important in understanding growth and yield relationships. This article describes how densitometry of earth resources technology satellite (ERTS-1) multispectral scanner (MSS) imagery can be used to identify such phenological events. Adjustments for instrument calibration, aperture size, gray-scale differences between overpasses, and normalization of changing solar elevation are considered in detail. Seasonal vegetation differences can be identified by densitometry of band 5 (0.6-0.7 microns) and band 7 (0.8-1.1 microns) MSS imagery. Band-to-band ratios of the densities depicted the changes more graphically than the individual band readings.

Ashley, M. D.↗
NASA NTRS1974

Densitometry of ERTS-1 imagery to access vegetation change

Density measurements of ERTS-1 multispectral scanner (MSS) imagery can be used to evaluate phenological changes in vegetation. It was found that the density ratios for MSS bands 5 and 7 best characterize vegetation change. The ratio increases with vegetative progression and decreases with vegetative recession. The use of a densitometer aperture as small as 0.4 mm does not adversely affect the accuracy of readings on forest sites.

Ashley, M. D.↗
NASA NTRS1973

Phenology satellite experiment

The author has identified the following significant results. The 1972 Brown Wave and 1973 Green Wave were detected at 24 sites located in four north-south corridors across the United States through analysis of ERTS-1 imagery and multispectral scanner digital tapes. Ground observations from these sites were correlated with ERTS data. These two phenological events were documented by observations from more than 3200 sites across the United States. The problem of changing atmospheric and illumination conditions were studied and corrections to ERTS data suggested. Band-to-band ratios were developed and correlated with the fall and spring phenological changes in field crops and forests. The results to date show the feasibility of developing and refining phenoclimatic models for use in characterizing crop status and as an aid to yield prediction.

Dethier, B. E.↗
NASA NTRS1973

Phenology satellite experiment

The detection of a phenological event (the brown wave-vegetation senescence) for specific forest and crop types using ERTS-1 imagery is described. Data handling techniques included computer analysis and photo interpretation procedures. Computer analysis of ERTS-1 multispectral scanner digital tapes in all bands was used to give the relative changes of spectral reflectance with time of forests and specified crops. These data were obtained for a number of the study's twenty-four sites located within four north-south corridors across the United States. Analysis of ground observation photography and ERTS-1 imagery for sites in the Appalachian Corridor and Mississippi Valley Corridor indicates that the recession of vegetation development can be detected very well. Tentative conclusions are that specific phenological events such as crop maturity or leaf fall can be mapped for specific sites and possibly for entire regions.

Dethier, B. E.↗