1,720,986 research outputs found
Measuring soil bulk density profiles with a single probe gamma density gauge
Get PDFCalibrating neutron depth gauges for measuring soil water content profiles requires
soil bulk density data. In this study, the feasibility of using a single probe gamma
density gauge to measure the soil wet bulk density was investigated for use in neutron
gauge calibration. The same sites, access tubes, and conventional gravimetric soil data
used for the ASCE Neutron Gauge Calibration Study were used for the Gamma Gauge
Study. Iterative procedures were successfully developed to calibrate the gamma
density gauge, and then to convert wet bulk density to dry bulk density data for the
three soil sites studied
Why confining to vegetation indices? exploiting the potential of improved spectral observations using radiative transfer models
Get PDFVegetation indices (VI) combine mathematically a few selected spectral bands to minimize undesired effects of soil background, illumination conditions and atmospheric perturbations. In this way, the relation to vegetation biophysical variables is enhanced. Albeit numerous experiments found close relationships between vegetation indices and several important vegetation biophysical variables, well known shortcomings and drawbacks remain. Important limitations of VIs are illustrated and discussed in this paper. As most of the limitations can be overcome using physically-based radiative transfer models (RTM), advantages and limits of RTM are also presented. © 2011 SPIE
Towards an improved mapping of evapotranspiration in semi-arid regions
Get PDFIn drylands, evapotranspiration is mainly limited by soil moisture, but current surface energy balance models do not directly make use of this fact. We tested the single-source energy balance model SEBS in a semi-arid region and showed that SEBS is significantly overestimating the evaporative fraction for sparsely vegetated drylands. As an alternative for such conditions, we derived an empirical function of soil moisture, temperature gradient and NDVI, which performed significantly better. This was then integrated with the evaporative fraction output of SEBS for an improved mapping of evapotranspiration in a semi-arid region. Ground measurements of the evaporative fraction from five Bowen ratio energy balance systems were used first to test SEBS and then to calibrate the empirical equation. The resulting method uses remote sensing data and in situ air temperature measurement
Soil bulk density sampling for neutron gauge calibration
Get PDFThe ASCE Task Committee on Neutron Gauge Calibration met in Logan, Utah in July
1992 to investigate the various methods of soil sampling, installation of access tubes,
effect of various parameters on gauge readings, methods of developing field calibration
curves and comparison of neutron gauge characteristics. Details of the overall objectives
of the study are covered by Stone (1993, this volume). This paper discusses the soil
sampling methods and presents a comparative result based on bulk density, time required
for sampling and cost of sampling equipment Other papers developed from this study
describe the soils, the three sites investigated and the problems related to the tube
installation process
Polyacrylamide decreases furrow erosion
Get PDFErosion from furrow irrigated land is a serious problem in southern Idaho
and several other areas. Polyacrylamide, a very long chain polymer, increases
aggregate stability and flocculates suspended sediments. It thus can potentially
reduce furrow sediment detachment and transport. Recirculating infiltrometer
studies showed that 0.5 kg/ha/irrigation of polyacrylamide applied with the
irrigation water can dramatically reduce furrow erosion
Nongrowing season ET from irrigated fields
Get PDFThe evaporative loss of water from agricultural fields during the nongrowing
season is an important component of the annual water balance of irrigated lands.
This study was conducted to measure daily ET from clipped grass and fallow fields
from October through March and to compare the ET with precipitation received
during the same period. Two weighing lysimeters near Kimberly, Idaho, were
used to measure daily ET for six nongrowing seasons, from 1985 through 1991.
ET averaged about 1 mm/day during the 6-month season, and total El' exceeded
precipitation except for the 1985-86 period. ET from the grass lysimeter exceeded
that from the mostly fallow lysimeter in early fall while the reverse was true
during late winter. The results indicate that there is little, if any, potential for a
net increase in stored soil water during the nongrowing season when fields receive
an early or mid-fall irrigation in southern Idaho
Seasonal parameter extraction of paddy rice fields in West Java using multi-temporal MODIS imagery datasets
No full textThe potential of Sentinel-2 spectral configuration to assess rangeland quality
No full textThe European Space Agency (ESA) has embarked on the development of the Sentinel constellation. Sentinel-2 is intended to improve vegetation assessment at local to global scale. Rangeland quality assessment is crucial for planning and management of grazing areas. Well managed and improved grazing areas lead to higher livestock production, which is a pillar of the rural economy and livelihoods, especially in many parts of the African continent. Leaf nitrogen (N) is an indicator of rangeland quality, and is crucial for understanding ecosystem function and services. Today, estimation of leaf N is possible using field and imaging spectroscopy. However, a few studies based on commercially available multispectral imageries such as WorldView-2 and RapidEye have shown the potential of a red-edge band for accurately predicting and mapping leaf N at the broad landscape scale. Sentinel-2 has two red edge bands. The objective of this study was to investigate the utility of the spectral configuration of Sentinel-2 for estimating leaf N concentration in rangelands and savannas of Southern Africa. Grass canopy reflectance was measured using the FieldSpec 3, Analytical Spectral Device (ASD) in concert with leaf sample collections for leaf N chemical analysis. ASD reflectances were resampled to the spectral bands of Sentinel-2 using published spectral response functions. Random Forest (RF) technique was used to predict leaf N using all thirteen bands. Using leave-one-out cross validation, the RF model explained 90% of leaf N variation, with the root mean square error (RMSE) of 0.04 (6% of the mean). Interestingly, spectral bands centred at 705 nm (red edge) and two shortwave infrared centred at 2190 and 1610 nm were found to be the most important bands in predicting leaf N. These findings concur with previous studies based on spectroscopy, airborne hyperspectral or multispectral imagery, e.g. RapidEye, on the importance of shortwave infrared and red-edge reflectance in the estimation of leaf N. In that sense, the ESA's Sentinel-2 sampling in both spectral regions has a unique spectral configuration, and a high potential to estimate leaf N which is crucial for informing decision makers on rangeland condition monitoring.</p
The ASCE neutron probe calibration study: overview
Get PDFA workshop was held at Logan, Utah to gather field information on
neutron probe calibration and operation. Several techniques and instruments
were compared. This paper serves to establish the background information for
the work and describe the overall approaches, conditions, and equipment. Other
papers presented at this conference provide detailed procedures and results
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