Search NASA⌕ Search

SEARCH · Search NASA

Results for “hydrology”

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.

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

At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The effect of ground hydrology on climate sensitivity to solar constant variations

A zonally averaged climate model is used to investigate the effects of different evaporation parameterizations on climate sensitivity to solar constant variations. The model is based on the annual mean zonally averaged hemispheric climate model of Ohring and Adler (1978), with some modifications on the heating parameterizations. The dynamic model utilizes the two-level quasi-geostrophic potential vorticity equations. The heating processes are related to solar radiation, long-wave radiation, convection, evaporation, latent heat release, and ocean transport. Evaporation parameterization has been improved by using a nonlinear formulation in which the Bowen ratio is determined by the vertical gradients of water vapor and temperature near the earth's surface.

Chow, S.-H.↗
NASA NTRS1978

Remote sensing of snowpack with microwave radiometers for hydrologic applications

A microwave remote sensing of snowpack experiment is described and some preliminary data presented. A mobile field laboratory consisting of a four-frequency (5, 10.7, 18 and 37 GHz), all with dual linear (vertical and horizontal) polarizations, microwave radiometer system attached to a truck-mounted aerial lift was used to study the microwave emission characteristics of snowpacks in the Colorado Rocky Mountains during the winter of 1977-78. The influence of snowpack physical parameters such as water equivalent, grain size, and melt-freeze cycle on its microwave brightness temperature and its implications to the application of microwave radiometric technique to remote sensing of snowpack for runoff prediction are discussed.

Shiue, J. C.↗
NASA NTRS1980

Radar target for remotely sensing hydrological phenomena

An apparatus for remotely measuring and accessing water status relative to snow and glacial melt, surface runoff, rainfall, evaporation, flow rate, and soil moisture is described. A radar target located at a selected location on the surface of the Earth is designed to collect water and render its cross sectional area variable as a function of the height of the water level within the target. The target is remotely monitored by an orbiting or airborne synthetic aperature radar. The target appears as a bright spot embedded within the radar image. The target brightness is indicative of the height of the water level within the ground located target.

Sivertson, W. E., Jr.↗
NASA NTRS1979

Continuation of measurement of hydrologic soil-cover complex with airborne scatterometers

The author has identified the following significant results. Analysis of radar scatterometry data obtained over five flight lines in Texas by NASA C-130 aircraft demonstrated that multivariant radar data can be used to distinguish difference in land use, and hence be an indicator of surface runoff characteristics. The capability of using microwave sensors to detect flood inundation of timbered land was also determined.

Blanchard, B. J.↗
NASA NTRS1980

Estimation of effective hydrologic properties of soils from observations of vegetation density

An existing one-dimensional model of the annual water balance is reviewed. Slight improvements are made in the method of calculating the bare soil component of evaporation, and in the way surface retention is handled. A natural selection hypothesis, which specifies the equilibrium vegetation density for a given, water limited, climate-soil system, is verified through comparisons with observed data and is employed in the annual water balance of watersheds in Clinton, Ma., and Santa Paula, Ca., to estimate effective areal average soil properties. Comparison of CDF's of annual basin yield derived using these soil properties with observed CDF's provides excellent verification of the soil-selection procedure. This method of parameterization of the land surface should be useful with present global circulation models, enabling them to account for both the non-linearity in the relationship between soil moisture flux and soil moisture concentration, and the variability of soil properties from place to place over the Earth's surface.

Tellers, T. E.↗
NASA NTRS1980

Estimation of effective hydrologic properties of soils from observations of vegetation density

A one-dimensional model of the annual water balance is reviewed. Improvements are made in the method of calculating the bare soil component of evaporation, and in the way surface retention is handled. A natural selection hypothesis, which specifies the equilibrium vegetation density for a given, water limited, climate soil system, is verified through comparisons with observed data. Comparison of CDF's of annual basin yield derived using these soil properties with observed CDF's provides verification of the soil-selection procedure. This method of parameterization of the land surface is useful with global circulation models, enabling them to account for both the nonlinearity in the relationship between soil moisture flux and soil moisture concentration, and the variability of soil properties from place to place over the Earth's surface.

Tellers, T. E.↗
NASA NTRS1980

Investigation of the application of HCMM thermal data to snow hydrology

The author has identified the following significant results. Analysis of HCMM digital thermal data for daytime passes over the Salt-Verde Watershed area on five dates show a gradual depletion of snow cover in the watershed (and in the Little Colorado Watershed to the north) from a maximum on February 9th to a nearly complete disappearance of the snow pack by April 15th. Temperature contours correspond closely with the snowline observed in the visible image.

Barnes, J. C.↗
NASA NTRS1980

Investigation of the application of HCMM thermal data to snow hydrology

The author has identified the following significant results. Comparison of the thermal IR band temperatures over the rapidly melting snowcover in a number of locations in the Salt-Verde Arizona watershed by the U-2 high altitude multispectral scanner, with temperatures for these same locations measured by the corresponding HCMM pass, indicate that the U-2 temperatures are typically 5 C higher than the values analyzed from the HCMM infrared digital printout. Results tend to substantiate findings of other investigators that with the offset that has been applied to all HCMM data, the HCMM temperature values may, in fact, actually be 5 C too low. Analysis of differences between the HCMM day and night temperatures for selected snowcovered areas in the Sierra Nevada Mountains, derived from the daytime and nighttime printouts, show greater delta tau values for the sparsely vegetated higher elevations than for the lower elevation, more densely forested terrain. The differences for the 12 hour sequence are also greater in most instances than the 36 hour difference.

Barnes, J. C.↗
NASA NTRS1979

A hydrological analysis of east Australian floods using Nimbus-5 electrically scanning radiometer data

The chronological development and diminution of six floods in eastern Australia during January, February, and March 1974 were mapped for the first time by the Nimbus Electrically Scanning Microwave Radiometer (ESMR). Day and nighttime ESMR (19.35 GHz) coverage was analyzed for the low gradient, flooded Darling River system in New South Wales. Apparent movement of surface water as indicated by low brightness temperatures (less than 250 K, day and less than 240 K, night) was easily followed around the curved runoff basin along the northern shoreline of the flooded Darling River during this 3-month period. This pattern was in good agreement with flood crest data at selected river height gage stations, even under cloudy conditions.

Allison, L. J.↗
NASA NTRS1980

Microwave approaches in hydrology

The microwave approaches for remote sensing of soil moisture centent, snowpack properties, surface water area, and the detection of precipitation over land are discussed. Both active (radar) and passive (radiometry) approaches are considered, and the advantages of microwave sensing are pointed out, including all-weather capability, especially at the longer wavelengths, and greater penetration depth with optical or infrared sensors. Results obtained from ground-based, aircraft, and spacecraft platforms show that microwave systems can monitor the moisture content in the surface soil layer (5 cm thick), and that passive microwave systems can discriminate between light and heavy snowcover, detect the presence of liquid water in the snow, and qualitatively estimate snow water equivalent.

Schmugge, T. J.↗
NASA NTRS1980

Synergistic relationships among remote-sensing and geophysical media: Geological and hydrological applications

The synergistic relationships among LANDSAT imagery, Skylab photographs, and aerial photographs were useful for establishing areas of near surface bedrock. Lineaments were located on LANDSAT imagery and aerial photographs during 1978 and near surface water tables were to be located during 1980. Both of these subjects can be identified by remote sensing methods more reliably than individual outcrops, which are small and occur in a wide variety of environments with a wide range of responses. Bedrock outcrops themselves could not be resolved by any of the data sources used, nor did any combination of data sources specifically identify rock at the ground surface. The data sources could not simply be combined mathematically to produce a visual image of probable areas of near surface bedrock. Outcrops and near surface bedrock had to be verified visually at the site. Despite these drawbacks, a procedure for locating areas of near surface bedrock within which actual surface outcrops may occur was developed.

Goebel, J. E.↗
NASA NTRS1980

Investigation of the application of HCMM thermal data to snow hydrology

All heat capacity mapping mission (HCMM) data needed for the investigation were received, including the imagery and CCT's for the April 1979 day/night registered data set for the Sierras study area. Three sets of excellent data for the Sierras study were received. Analysis of the earlier two sets (late May and mid July 1978) was completed. Initial examination of the latest imagery received indicates that the April 1979 data are the best quality HCMM day/night registered data of the three data sets. The thermal inertia imagery is particularly outstanding, appearing to contain much more detail and information than the earlier thermal inertia images.

Barnes, J. C.↗
NASA NTRS1981

Synergistic relationships among remote-sensing and geophysical media: Geological and hydrological applications

Skylab photographs, side-looking radar imagery, published soil maps, topographic maps, conventional aerial photography as well as LANDSAT imagery under wet and dry changes for several years were analyzed over selected areas in Minnesota to test their usefulness in detecting near-surface ground water. Results show that optical density read from LANDSAT data is not a reliable discriminator of depth to shallow ground water when one band of one scene is used alone, and is little improved when several bands of several scenes are used synergistically. The method is enhanced if information from soil maps is included in the analysis, especially for discriminating boggy ground from better drained areas. It appears, however, that in areas where soil maps and good topographic maps already exist, the depth to ground water can be predicted from those media as well as (if not better than) it can be predicted from remote imagery. The LANDSAT method used demonstrated no capability for recognizing deeper categories of ground water.

Southwick, D. L.↗
NASA NTRS1981

Application of thermal model for pan evaporation to the hydrology of a defined medium, the sponge

A technique is presented which estimates pan evaporation from the commonly observed values of daily maximum and minimum air temperatures. These two variables are transformed to saturation vapor pressure equivalents which are used in a simple linear regression model. The model provides reasonably accurate estimates of pan evaporation rates over a large geographic area. The derived evaporation algorithm is combined with precipitation to obtain a simple moisture variable. A hypothetical medium with a capacity of 8 inches of water is initialized at 4 inches. The medium behaves like a sponge: it absorbs all incident precipitation, with runoff or drainage occurring only after it is saturated. Water is lost from this simple system through evaporation just as from a Class A pan, but at a rate proportional to its degree of saturation. The contents of the sponge is a moisture index calculated from only the maximum and minium temperatures and precipitation.

Trenchard, M. H.↗