• Assessment of biomass dynamics of a semidesert grassland by remote sensing techniques.

      Huete, Alfredo R.; Lumbuenamo, Sinsi Dianza.; Dutt, Gordon R.; Marsh, Stuart E.; Jackson, Ray D.; Post, Donald F. (The University of Arizona., 1990)
      In order to study the effect of standing dead biomass on vegetation canopy spectral response, the normalized difference, the soil-adjusted vegetation index, the green vegetation index and the perpendicular vegetation index were used to examine and compare the spectral behavior of a mostly green (regrowth after burning) vegetation canopy to a perennial vegetation stand. Results showed all greenness indicators to be strongly affected by the presence of standing dead vegetation. The burned plots which had less green biomass in the first growing season (February-June) exhibited higher vegetation index values through the entire growing season. The observed discrepancies in the vegetation indices seem to stem from the attenuation of the near-infrared flux combined with a lack of responsivity of the red channel. Overall, there was no correlation between green biomass and greenness measures in the perennial stand. Furthermore, in the perennial environment, a steady increase in "greenness" was observed while the green biomass was actually decreasing. The problem seems to be more of visibility than quantity of green biomass present.
    • Spectral and spatial variability of the soils on the Maricopa Agricultural Center, Arizona.

      Post, Donald F.; Suliman, Ahmed Saeid Ahmed.; Jackson, Ray D.; Huete, Alfredo; Hendricks, David M.; Tucker, Thomas C. (The University of Arizona., 1989)
      Dry and wet fine earth spectral measurements were made on the Ap soil surface horizons on the Maricopa Agricultural Center by using a Barnes Modular Multiband Radiometer. Three subsets were used in the analyses 552, 101 and 11. There were three soil series, Casa Grande, Shontik and Trix, four soil mapping units, and three texture classes identified on the farm. The wet soil condition reduced the amplitude of the spectral curves over the entire spectrum range (0.45 to 2.35 μm). The spectral curves were statistically related to the soil mapping units to determine if the soil mapping units and texture classes could be separated. The wet soil condition and the smaller sample size increased the correct classification percentages for soil mapping units and texture classes. LSD tests showed there were significant differences between these groups. Simple- and Multiple-linear regression analysis were used to relate some soil physical (sand, silt and clay contents and color components) and chemical (iron oxide, organic carbon and calcium carbonate contents) to soil spectral responses in the seven bands under dry and wet conditions. There were high correlations levels among the spectral bands showing an overlap of spectral information. Generally, the red (MMR3) and near-infrared (MMR4) bands had the highest correlations with the studied soil properties under dry and wet conditions. Usually, the wet soil condition resulted in higher correlations than that for the dry soil condition over the total spectrum range. The predictive equations for sand, silt and clay and iron oxide contents were satisfactory. For organic carbon and color components, the greatest success was achieved when variation in spectral response within individual samples are smaller than that between soil mapping unit group averages. There was a poor relation between calcium carbonate and spectral response. A comparison of multi-level remotely sensed data collected by SPOT, aircraft, and ground instruments showed a strong agreement among the data sets, which correlated well to fine earth data, except for the SPOT data. Rough soil surfaces showed a reduction in reflectance altitude compared to laser level, and it appears to be directly proportional to the percent shadow in the viewing area measured by SPOT satellite and aircraft.
    • Temporal and spatial relationships of canopy spectral measurements

      Bamatraf, Abdurhman Mohamed.; Matthias, Allan D.; Warrick, Arthur W.; Jackson, Ray D.; Post, Donald F.; Huete, Alfredo R.; Fangmeier, Delmar D. (The University of Arizona., 1986)
      Ground-based, remotely sensed reflectance and temperature data were collected over differentially irrigated, developing cotton and sorghum canopies in order to investigate interrelations of these parameters; to monitor their temporal changes ; to understand their spatial structure ; and to estimate crop coefficient (KO from canopy reflectance. Spectral reflectance and derived vegetation indices showed ability to significantly discriminate among differential irrigation levels of sorghum canopies, starting the fourth week of growth. All vegetation indices increased as a result of crop development, with the perpendicular vegetation index (PVI ) demonstrating the greatest potential for assessing water stress conditions, whereas, soil indices behaved independently of crop development and water stress. Canopy temperature and derived water stress indices, on the other hand, were in high concordance and were able to detect crop water stress with variable degrees of sensitivity. Experimental variograms revealed that cotton reflectance and temperature were not spatially dependent when all water treatments were included. For the moisture stress treatments, only canopy temperature exhibited spatial dependence early in the period of stress. Sorghum canopy reflectance and temperature demonstrated some spatial structure; however, a drift was suspected due to regularity in the data spatial distribution. Normalized difference (ND), normalized perpendicular vegetation index (NPVI) and normalized green vegetation index (NGVI), for fifty days covering the period from planting to heading, were fitted with a complementary error function equation with minor adjustment. Both NPVI and NGVI displayed a 1:1 relation with interpolated tabular values of basal Kc, whereas ND deviated from the 1:1 relation for the period beyond 30 days after planting. The model was also found to be valid for estimating K(c) for moderately deficit irrigation conditions.