3,921 research outputs found
Comparisons among a new soil index and other two- and four-dimensional vegetation indices
The 2-D difference vegetation index (DVI) and perpendicular vegetation index (PVI), and the 4-D green vegetation index (GVI) are compared in LANDSAT MSS data from grain sorghum (Sorghum bicolor, L. Moench) fields for the years 1973 to 1977. PVI and DVI were more closely related to LAI than was GVI. A new 2-D soil line index (SLI), the vector distance from the soil line origin to the point of intersection of PVI with the soil line, is defined and compared with the 4-D soil brightness index, SBI. SLI (based on MSS and MSS7) and SL16 (based on MSS 5 and MSS 6) were smaller in magnitude than SBI but contained similar information about the soil background. These findings indicate that vegetation and soil indices calculated from the single visible and reflective infrared band sensor systems, such as the AVHRR of the TIROS-N polar orbiting series of satellites, will be meaningful for synoptic monitoring of renewable vegetation
Estimating total standing herbaceous biomass production with LANDSAT MSS digital data
Rangeland biomass data were correlated with spectral vegetation indices, derived from LANDSAT MSS data. LANDSAT data from five range and three other land use sites in Willacv and Cameron Counties were collected on October 17 and December 10, 1975, and on July 31 and September 23, 1976. The overall linear correlation of total standing herbaceous biomass with the LANDSAT derived perpendicular vegetation index was highly significant (r = 0.90**) for these four dates. The standard error of estimate was 722 kg/ha. Biomass data were recorded for two of these range sites for 8 months (March through October) during the 1976 growing season. Standing green biomass accounted for most of the increase in herbage, starting in June and ending about September and October. These results indicate that satellite data may be useful for the estimation of total standing herbaceous biomass production that could aid range managers in assessing range condition and animal carrying capacities of large and inaccessible range holdings
Spectral reflectance from plant canopies and optimum spectral channels in the near infrared
Theoretical and experimental aspects of the interaction of light with a typical plant canopy are considered. Both theoretical and experimental results are used to establish optimum electromagnetic wavelength channels for remote sensing in agriculture. The spectral range considered includes half of the visible and much of the near-infrared regions
Brauer-Thrall for totally reflexive modules
Let R be a commutative noetherian local ring that is not Gorenstein. It is
known that the category of totally reflexive modules over R is representation
infinite, provided that it contains a non-free module. The main goal of this
paper is to understand how complex the category of totally reflexive modules
can be in this situation.
Local rings (R,m) with m^3=0 are commonly regarded as the structurally
simplest rings to admit diverse categorical and homological characteristics.
For such rings we obtain conclusive results about the category of totally
reflexive modules, modeled on the Brauer-Thrall conjectures. Starting from a
non-free cyclic totally reflexive module, we construct a family of
indecomposable totally reflexive R-modules that contains, for every n in N, a
module that is minimally generated by n elements. Moreover, if the residue
field R/m is algebraically closed, then we construct for every n in N an
infinite family of indecomposable and pairwise non-isomorphic totally reflexive
R-modules, that are all minimally generated by n elements. The modules in both
families have periodic minimal free resolutions of period at most 2.Comment: Final version; 34 pp. To appear in J. Algebr
Vegetation density as deduced from ERTS-1 MSS response
Reflectance from vegetation increases with increasing vegetation density in the 0.75- to 1.35 micron wavelength interval. Therefore, ERTS-1 bands 6 (0.7 to 0.8 micron) and 7 (0.8 to 1.1 micron) contain information that should relate to the probable yield of crops and the animal carrying capacity of rangeland. The results of an experiment designed specifically to test the relations among leaf area index (LAI), plant population, plant cover and plant height, and the ERTS-1 MSS responses for 3 corn, 10 sorghum, and 10 cotton fields are given. Plant population was as useful as LAI for characterizing the sorghum and corn fields, and plant height was as good as LAI for characterizing cotton fields. These findings generally support the utility of ERTS-1 data for explaining variability in green biomass, harvestable forage and other indicators of productivity
- …