SEARCH · Search NASA

Results for “moisture content”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6

All sources NASA NTRS DOE OSTI

NASA NTRS1991

A two-dimensional numerical investigation of the interaction between sea breezes and deep convection over the Florida peninsula

The Colorado State University Regional Atmospheric Modeling System is used to investigate the interaction between sea breezes and deep convection over the Florida peninsula, and it is shown that this model can simulate the broad features of the three characteristic types of convection systems classified by Blanchard and Lopez (1985). In sensitivity tests performed for a variety of wind and thermodynamic profiles and for different soil-moisture contents, it was found that increases in the low-level temperature and in moisture content speeded up the development of convection. It was found that the dry-soil simulation produced rapidly developing sea breezes that moved inland quickly, while the moist soil case produced a much more slowly developing sea breeze. The total rainfall over the peninsula for the dry-soil case was greater than for the moist soil; it is suggested that the enhanced surface heat fluxes for the dry soil case create stronger low-level convergence over the peninsula (than in the moist-soil case) to force the convection.

Nicholls, Melville E.↗

NASA NTRS1979

Analysis of surface moisture variations within large field sites

A statistical analysis was made on ground soils to define the general relationship and ranges of values of the field moisture relative to both the variance and coefficient of variation for a given test site and depth increment. The results of the variability study show that: (1) moisture variations within any given large field area are inherent and can either be controlled nor reduced; (2) neither a single value of the standard deviation nor coefficient of variation uniquely define the variability over the complete range of mean field moisture contents examined; and (3) using an upper bound standard deviation parameter clearly defines the maximum range of anticipated moisture variability. 87 percent of all large field moisture content standard deviations were less than 3 percent while about 96 percent of all the computed values had an upper bound of sigma=4 percent for these intensively sampled fields. The limit of accuracy curves of mean soil moisture measurements for large field sites relative to the required number of samples were determined.

Bell, K. R.↗

NASA NTRS1973

Remote monitoring of soil moisture using airborne microwave radiometers

The current status of microwave radiometry is provided. The fundamentals of the microwave radiometer are reviewed with particular reference to airborne operations, and the interpretative procedures normally used for the modeling of the apparent temperature are presented. Airborne microwave radiometer measurements were made over selected flight lines in Chickasha, Oklahoma and Weslaco, Texas. Extensive ground measurements of soil moisture were made in support of the aircraft mission over the two locations. In addition, laboratory determination of the complex permittivities of soil samples taken from the flight lines were made with varying moisture contents. The data were analyzed to determine the degree of correlation between measured apparent temperatures and soil moisture content.

Kroll, C. L.↗

NASA NTRSDate not supplied

Modeling the Worst-Case-Scenario of Soil Drydown for Agricultural Drought Monitoring in Kansas Using NASA Earth Observations and In-situ Parameters

Climatologists in Kansas have observed rapid shifts from wet to dry conditions and rapid intensification of drought conditions for the state in recent years. As a leading state in agricultural production, drought events can lead to decreased crop yields and impact the state’s economy. The exponential decay of soil moisture content is a major consequence of drought and can exacerbate these impacts on agricultural production. This study examined the rate of soil moisture drydown in Kansas to understand and monitor the worst-case-scenario of short-term soil water shortage. Soil Moisture Active Passive (SMAP) L-band Radiometer rootzone soil moisture imagery from March 2015 to June 2019 was used to estimate the minimum and maximum soil moisture capacity throughout the state. In situ soil moisture parameters, such as the exponential decay constant, were approximated from the Kansas Mesonet system. These variables were inputs into an exponential decay model that forecasted gridded rootzone soil moisture in a scenario that assumed no precipitation for a user-identified period of time. The forecasts were output on the order of weeks to capture the rapid shifts in soil moisture content. Another model was used to identify areas in Kansas currently below a given percentage of the relative soil moisture saturation, measured as a function of minimum, maximum, and current soil moisture. This model forecasted the number of days until each cell in the soil moisture grid reached the input percentage of relative soil moisture saturation. The gridded model outputs and workflow were developed in partnership with the Kansas Water Office and Kansas Office of the State Climatologist at Kansas State University, as a part of their drought monitoring efforts.

NASA DEVELOP↗

NASA NTRS1987

Oxidative processes in soybean and pea seeds: effect of light, temperature, and water content

Oxidative processes are probable determinants of longevity of seeds in storage. Measurements of actual oxygen uptake rates were made for soybean and pea seeds as a comparison of short and long lived seeds when light, temperature, and moisture contents were varied. In both peas and soybeans, the oxygen uptake was depressed at low temperatures (<16 degrees C) and low water contents (< 0.25 gram H2O per gram dry weight). Apparent activation energies under these conditions are very high, while apparent activation energies of seeds at higher water contents and at temperatures greater than 22 degrees C are much less. Light enhances the level of oxygen uptake in pea, but reduces the level of oxygen uptake in soybean. The complexities of the interactions of oxygen uptake with environmental conditions in soybean compared to pea suggest that oxidative processes occur in soybean at low water contents, but are essentially absent in pea. It is suggested that the additional oxidative processes in soybean with moisture contents between 0.10 and 0.24 gram per gram may contribute to the poorer longevity of soybean seed compared to pea seed.

NASA Program Space Biology↗

NASA NTRS1981

Failure of morphology of (0 deg)8 graphite/epoxy as influenced by environments and processing

Optical and scanning electron microscopy were used to investigate the failure morphology of graphite/epoxy specimens which had been tested until tensile failure. Failure morphology was studied as a function of the quality control variables of specimen preparation technique, prepreg batch, and cure condition, and also as a function of the environmental parameters of temperature and moisture content. Defective specimens were found to exhibit a low energy failure morphology. Poor specimen edge preparation and one batch of prepreg when tested at elevated temperature or moisture content also exhibited energy failure morphology. Postcuring had no effect on strength but did slightly alter failure morphology. Temperature or moisture appeared to decrease flaw sensitivity and thus increase strength; however, moisture also appeared to increase interfacial debonding between filament and matrix. When combined moisture and temperature increased interfacial debonding and made the epoxy matrix more prone to fracture.

Clements, L. L.↗

NASA NTRS1979

Microwave and gamma radiation observations of soil moisture

The unique dielectric properties of water at microwave wavelengths afford the possibility for remotely sensing the moisture content in the surface layer of the soil. The surface emissivity and reflectivity for the soils at these wavelengths are strong functions of its moisture content. The changes in emissivity can be observed by passive microwave techniques (radiometry) and the change in reflectivity can be observed by active microwave techniques (radar). The difference in the natural terrestrial gamma ray flux measured for wet and dry soil may be used to determine soil moisture. The presence of water moisture in the soil causes an effective increase in soil density, resulting in an increased attenuation of the gamma flux for wet soil and a corresponding lower flux above the ground surface.

Schmugge, T. J.↗

NASA NTRS1974

Remote sensing of soil moisture by Skylab radiometer and scatterometer sensors

A Skylab experiment was designed to evaluate the feasibility of monitoring the moisture content of the soil from space. Data from various Skylab sensors were collected across two test sites while direct measurements of soil moisture were being made at the surface depths of soil. Correlations were obtained between the moisture content of the soil and radiometer sensors (S193 and S194) and the scatterometer instrument (S193). The high correlations obtained indicate that microwave sensors may be quite useful for such measurements in the future.-

Eagleman, J. R.↗

NASA NTRS1975

Remote sensing of soil moisture by Skylab radiometer and scatterometer sensors

Eagleman, J. R.↗

NASA NTRS1979

Time dependent deformation of a basalt at low differential stress

A detailed study of linear elastic deformation in Ralston basalt during triaxial loading has been made as a function of strain rate (8 x 10 to the -8th per sec to 5 x 10 to the -5th per sec) and moisture content under constant confining pressure (500 bars) and temperature (20 C). Young's modulus was found to be constant and independent of moisture content and strain rate; however, Poisson's ratio decreased 5.7 plus or minus 1.6% and 6.7 plus or minus 1.6% per order of magnitude increase in strain rate for two suites of dry samples and 1.4 plus or minus 1.2% per equivalent change in strain rate for one suite of wet rocks. Lateral expansion in dry rocks is therefore a more sensitive function of strain rate than it is in wet rocks. It is suggested that this strain-rate dependence is related to microcracking.

Brodsky, N.↗

NASA NTRS2011

Measuring Moisture Levels in Graphite Epoxy Composite Sandwich Structures

Graphite epoxy composite (GEC) materials are used in the construction of rocket fairings, nose cones, interstage adapters, and heat shields due to their high strength and light weight. However, they absorb moisture depending on the environmental conditions they are exposed to prior to launch. Too much moisture absorption can become a problem when temperature and pressure changes experienced during launch cause the water to vaporize. The rapid state change of the water can result in structural failure of the material. In addition, heat and moisture combine to weaken GEC structures. Diffusion models that predict the total accumulated moisture content based on the environmental conditions are one accepted method of determining if the material strength has been reduced to an unacceptable level. However, there currently doesn t exist any field measurement technique to estimate the actual moisture content of a composite structure. A multi-layer diffusion model was constructed with Mathematica to predict moisture absorption and desorption from the GEC sandwich structure. This model is used in conjunction with relative humidity/temperature sensors both on the inside and outside of the material to determine the moisture levels in the structure. Because the core materials have much higher diffusivity than the face sheets, a single relative humidity measurement will accurately reflect the moisture levels in the core. When combined with an external relative humidity measurement, the model can be used to determine the moisture levels in the face sheets. Since diffusion is temperaturedependent, the temperature measurements are used to determine the diffusivity of the face sheets for the model computations.

Nurge, Mark↗

NASA NTRS1979

The use of microwave approaches in hydrology

Passive (radiometry) and active (radar) microwave approaches and their application to the study of the earth's hydrologic problem are examined and parameters including soil moisture content, snowpack properties, surface water area and the detection of precipitation overland are studied. Results show that these methods are capable of monitoring the moisture content in the surface layer of the soil in 5 cm thickness, detecting the presence of liquid water in snow and observing oil slicks. In addition, the methods make it possible to determine the water equivalent of snow packs and to delineate areas of rainfall over land.

Schmugge, T. J.↗

NASA NTRS1998

Ultrasonic Velocity Variations with Soil Composition for Moisture Measurement

Soil moisture content may be measured by many methods, but the presently available techniques all have drawbacks when used in ground truth measurements for remote sensing. Ultrasonic velocity varies with soil moisture content, and may be used as the basis of a new measurement technique. In order to characterize a sensor capable of field use, soil particle size distribution data are compared to ultrasonic velocity in a variety of soils over a wide moisture range.

Metzl, R.↗

NASA NTRS2005

A comparison of soil moisture sensors for space flight applications

Plants will be an important part of future long-term space missions. Automated plant growth systems require accurate and reliable methods of monitoring soil moisture levels. There are a number of different methods to accomplish this task. This study evaluated sensors using the capacitance method (ECH2O), the heat-pulse method (TMAS), and tensiometers, compared to soil water loss measured gravimetrically in a side-by-side test. The experiment monitored evaporative losses from substrate compartments filled with 1- to 2-mm baked calcinated clay media. The ECH2O data correlated well with the gravimetric measurements, but over a limited range of soil moisture. The averaged TMAS sensor data overstated soil moisture content levels. The tensiometer data appeared to track evaporative losses in the 0.5- to 2.5-kPa range of matric potential that corresponds to the water content needed to grow plants. This small range is characteristic of large particle media, and thus high-resolution tensiometers are required to distinguish changing moisture contents in this range.

NASA Center KSC↗

NASA NTRS1981

Radar reflectivity of bare and vegetation-covered soil

Radar sensitivity to soil moisture content has been investigated experimentally for bare and vegetation-covered soil using detailed spectral measurements obtained by a truck-mounted radar spectrometer in the 1-8 GHz band and by airborne scatterometer observations at 1.6, 4.75, and 13.3 GHz. It is shown that radar can provide quantitative information on the soil moisture content of both bare and vegetation-covered soil. The observed soil moisture is in the form of the soil matric potential or a related quantity such as the percent of field capacity. The depth of the monitored layer varies from 1 cm for very wet soil to about 15 cm for very dry soil.

Ulaby, F. T.↗

NASA NTRS2001

Radar Attenuation by Sand: Laboratory Measurement of Radar Transmission

Under certain conditions, radar is able to penetrate loose sand to reveal subsurface geology in arid areas. However, backscatter from the subsurface is modified by signal attenuation by the sand, To quantify the amount of radar transmission as a function of radar frequency and sand moisture. The frequency range covers P-through X-bands (0.5 - 12.6 GHz), and the moisture contents of the sand were 0.3, 4.7, and 10.7% by volume. Results show that addition of the sand causes a small decrease in transmission at low frequencies for all three moisture levels, but the sand causes a large decrease in transmission at higher frequencies. The transmission measurements were also used to calculate values for attenuation, The dry sand resulted in attenuations of less than 6 dB/m over the entire frequency range. Sand with moisture contents of 4.7 and 10.7% volume caused by attenuations greater than 150 dB/m at the highest frequencies, but the attenuation values calculated for P-and L-band frequencies were less than 10 dB/m even at these relatively high moisture levels. THese results challenge previous restrictions that sand must be extremely dry for radar penetration to occur.

Williams, Kevin K.↗

NASA NTRS1979

Predicting the wet strength of laminates

Graphite/epoxy strengths at various moisture contents are estimated by extrapolating from small data base. With procedure, massive testing is unnecessary because advantage is taken of large data base already available for moisture content in laminates.

Bohlman, R. E.↗

NASA NTRS2009

Prediction of Material Properties of Nanostructured Polymer Composites Using Atomistic Simulations

Atomistic models of epoxy polymers were built in order to assess the effect of structure at the nanometer scale on the resulting bulk properties such as elastic modulus and thermal conductivity. Atomistic models of both bulk polymer and carbon nanotube polymer composites were built. For the bulk models, the effect of moisture content and temperature on the resulting elastic constants was calculated. A relatively consistent decrease in modulus was seen with increasing temperature. The dependence of modulus on moisture content was less consistent. This behavior was seen for two different epoxy systems, one containing a difunctional epoxy molecule and the other a tetrafunctional epoxy molecule. Both epoxy structures were crosslinked with diamine curing agents. Multifunctional properties were calculated with the nanocomposite models. Molecular dynamics simulation was used to estimate the interfacial thermal (Kapitza) resistance between the carbon nanotube and the surrounding epoxy matrix. These estimated values were used in a multiscale model in order to predict the thermal conductivity of a nanocomposite as a function of the nanometer scaled molecular structure.

Hinkley, J.A.↗