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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.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Snowpack monitoring in North America and Eurasia using passive microwave satellite data

Areas of the Canadian high plains, the Montana and North Dakota high plains, and the steppes of central Russia were studied in an effort to determine the utility of spaceborne electrical scanning microwave radiometers (ESMR) for monitoring snow depths in different geographic areas. Significant regression relationships between snow depth and microwave brightness temperatures were developed for each of these homogeneous areas. In the areas investigated, Nimbus 6 (.081 cm) ESMR data produced higher correlations than Nimbus 5 (1.55 cm) ESMR data in relating microwave brightness temperature and snow depth from one area to another because different geographic areas are likely to have different snowpack conditions.

Foster, J. L.↗
NASA NTRS1980

Atmospheric corrections to passive microwave observations of the ocean

Microwave observations of the ocean surface are contaminated to a greater or lesser degree by the overlying atmosphere. The principal components of the atmosphere contributing to this contamination are molecular oxygen, water vapor, and water droplets. By means of measurements at several well-chosen frequencies, these atmospheric parameters may be removed from ocean observations and themselves retrieved as a by-product. This is the basic concept of the Scanning Multifrequency Radiometer (SMMR). These corrections may be made by quasi-linear means to useful accuracies, even in the presence of moderate rain.

Wilheit, T.↗
NASA NTRS1979

Remote sensing of atmospheric water vapor, liquid water, and wind speed at the ocean surface by passive microwave techniques from the Nimbus 5 satellite

The microwave brightness temperature measurements for Nimbus 5 electrically scanned microwave radiometer (ESMR) and Nimbus-E microwave spectrometer (NEMS) are used to retrieve the atmospheric water vapor, liquid water, and wind speed by a quasi-statistical retrieval technique. It is shown that the brightness temperature can be utilized to yield these parameters under various weather conditions. Observations at 19.35, 22.235, and 31.4 GHz were input to the regression equations. The retrieved values of these parameters for portions of two Nimbus 5 orbits are presented. Then comparison between the retrieved parameters and the available observations on the total water vapor content and the surface wind speed are made.

Chang, A. T. C.↗
NASA NTRS1980

Remote sensing of snow properties by passive microwave radiometry: GSFC truck experiment

Recent results indicate that microwave radiometry has the potential for inferring the snow depth and water equivalent information from snowpacks. In order to assess this potential for determining the water equivalent of a snowpack, it is necessary to understand the microwave emission and scattering behavior of the snow at various wavelengths under carefully controlled conditions. Truck-mounted microwave instrumentation was used to study the microwave characteristics of the snowpack in the Colorado Rocky Mountain region during the winters of 1977 to 78 and 7978 to 79. The spectral signatures of C, X, K sub u, and K sub a band radiometers with dual polarization were used, together with measurements of snowpack density, temperature an ram profiles, liquid water content, and rough characterization of the crystal sizes. These data compared favorably with calculated results based on recent microscopic scattering models.

Chang, A. T. C.↗
NASA NTRS1980

Monitoring snowpack properties by passive microwave sensors on board of aircraft and satellites

Snowpack properties such as water equivalent and snow wetness may be inferred from variations in measured microwave brightness temperatures. This is because the emerged microwave radiation interacts directly with snow crystals within the snowpack. Using vertically and horizontally polarized brightness temperatures obtained from the multifrequency microwave radiometer (MFMR) on board a NASA research aircraft and the electrical scanning microwave radiometer (ESMR) and scanning multichannel microwave radiometer (SMMR) on board the Nimbus 5, 6, and 7 satellites, linear relationships between snow depth or water equivalent and microwave brightness temperature were developed. The presence of melt water in the snowpack generally increases the brightness temperatures, which can be used to predict snowpack priming and timing of runoff.

Chang, A. T. C.↗
NASA NTRS1981

Correlation of spacecraft passive microwave system data with soil moisture indices (API)

Electrical scanning microwave radiometer brightness temperature, meteorological data, climatological data, and winter wheat crop information were used to estimate that soil moisture content in the Great Plains region. Results over the predominant winter wheat areas indicate that the best potential to infer soil moisture occurs during fall and spring. These periods encompass the growth stages when soil moisture is most important to winter wheat yield. Other significant results are reported.

Blanchard, B. J.↗
NASA NTRS1981

Tropical cyclone rainfall characteristics as determined from a satellite passive microwave radiometer

Data from the Nimbus 5 electrically scanning microwave radiometer (ESMR-5) were used to calculate latent heat release (LHR) and other rainfall parameters for over 70 satellite observations of 21 tropical cyclones during 1973, 1974, and 1975 in the tropical North Pacific Ocean. The results indicate that the ESMR-5 measurements can be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring as well as predicting their intensity. The ESMR-5 derived total tropical cyclone rainfall estimates agree favorably with previous estimates for both the disturbance and typhoon stages. The mean typhoon rainfall rate (1.9 mm h/1) is approximately twice that of disturbances (1.1 mm h/1).

Rodgers, E. B.↗
NASA NTRS1979

Topical cyclone rainfall characteristics as determined from a satellite passive microwave radiometer

Data from the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR-5) were used to calculate latent heat release and other rainfall parameters for over 70 satellite observations of 21 tropical cyclones in the tropical North Pacific Ocean. The results indicate that the ESMR-5 measurements can be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring as well as predicting their intensity. The ESMR-5 derived total tropical cyclone rainfall estimates agree favorably with previous estimates for both the disturbance and typhoon stages. The mean typhoon rainfall rate (1.9 mm h(-1)) is approximately twice that of disturbances (1.1 mm h(-1)).

Rodgers, E. B.↗
NASA NTRS1980

Passive microwave remote sensing of soil moisture - The effect of tilled row structure

The tilled row structure in agricultural fields is one of the important factors affecting observations of microwave emission from such fields. Measurements of this effect were performed with L-band and X-band radiometers mounted on a mobile truck on a bare 40 m x 45 m row tilled field; the soil moisture content during measurements ranged from 10 to 30% by dry weight. Results showed that the variations of the antenna temperatures with incident angle changed with the azimuth angle measured from the row direction. It is found that the observed difference between horizontally and vertically polarized antenna temperatures is due to the change in the local angle of field emission within the antenna field of view caused by the large-scale row structure.

Wang, J. R.↗
NASA NTRS1980

Passive microwave sensing of coastal area waters

A technique to remotely measure sea-surface temperature and salinity was demonstrated during the 1970's with a dual-frequency microwave radiometer system developed at the NASA Langley Research Center. Accuracies in temperature of 1 C and 1 part per thousand in salinity were obtained using state-of-the-art radiometers. Several aircraft programs for the measurement of coastal area waters demonstrating the application of the microwave radiometer system are discussed. Improvements of the microwave radiometer system during the 1980's and the design and development of new radiometer systems at other frequencies are outlined and related to potential applications.

Kendall, B. M.↗
NASA NTRS1980

Radiative transfer theory for passive microwave remote sensing of a two-layer random medium with cylindrical structures

A model of the vegetation layer as a two-layer random medium with a small correlation length l sub rho in the horizontal direction, and a large correlation length l sub z in the vertical direction, is presented for fields with cylindrical structures. As l sub z approaches infinity, closed form solutions are derived for the brightness temperatures; the kernels in the scattering terms of the radiative transfer equations result in delta functions showing that forward scattering is dominant over all other directions. The results are compared with the Gaussian quadrature method data for numerical solution of the radiative transfer equations.

Chuang, S. L.↗
NASA NTRS1981

Tropical cyclone rainfall characteristics as determined from a satellite passive microwave radiometer

Data from the Electrically Scanning Microwave Radiometer on Nimbus-5 (ESMR-5) have been used to calculate total tropical cyclone Latent Heat Release (LHR) and rainfall parameters for over 70 satellite observations of 21 tropical cyclones during 1973, 1974, and 1975 in the North Pacific tropical ocean. The data were found to be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring and making short-term prediction of their intensity. Case studies as well as composite studies indicate that the increase in the ESMR-5 derived LHR corresponds to storm intensification. It also appears that the ESMR-5 derived rainfall parameters can be used to detect the beginning of tropical cyclone intensification.

Rodgers, E. B.↗
NASA NTRS1981

Passive microwave sensing of snow characteristics over land

Truck-mounted, airborne, and spaceborne systems with various radiometers ranging in wavelength from 0.8 to 21 cm were used to measure the brightness temperatures of snow-covered areas at test sites near Steamboat Springs and Walden, Colorado. The brightness temperature at a short wavelength (0.8 cm) was found to decrease more rapidly with increasing snow depth than the brightness temperature at a longer wavelength (6 cm). More scattering of the shorter-wavelength radiation by the snow crystals results in a lower brightness temperature. The longer-wavelength (6 cm) radiation penetrates through meters of dry snowpack and is useful for the assessment of the underlying ground conditions.

Chang, A. T. C.↗
NASA NTRS1981

Freshwater ice thickness observations using passive microwave sensors

Walden Reservoir, a freshwater lake in north-central Colorado, was overflown six times by a NASA C-130 aircraft between January 1977 and April 1980. The aircraft was equipped with four microwave radiometers operating between 0.81 and 6.0 cm in wavelength (37.0 to 5.0 GHz). The 6.0-cm radiometer data showed a good relationship with ice thickness based on a sample of four ice thickness values. The 1.67- and 1.35-cm radiometer data showed weaker relationships with ice thickness. The 0.81-cm sensor data showed no positive relationship with ice thickness. None of the relationships was statistically significant because of the small sample size. The 6.0-cm sensor data in the nadir-viewing mode was found to have the most potential of all the wavelengths studied, for use in remotely determining ice thickness. The 6.0-cm radiometer probably sensed the entire thickness of the ice on the reservoir (ranging from 25.4 to 67.3 cm in thickness) and was apparently not significantly affected by the snow overlying the ice. The shorter wavelengths are scattered by the snow overlying the ice and are more suitable for snow studies than for ice thickness studies.

Hall, D. K.↗
NASA NTRS1981

Antarctic sea ice cover from satellite passive microwave

The 3-day images from the Nimbus 5 electrically scanning microwave radiometer were combined to form monthly average maps and contour plots. These show clearly the yearly cycle from minimum ice extent in February to maximum ice extent from August to September and the spatial distribution of ice 15 to 50 percent concentrated, 50 to 85 percent concentrated, and 85 to 100 percent concentrated. The yearly cycle of the monthly extent of ice is plotted for each of the four years (1973-76). The total 4-year range in monthly mean concentrations (over the 30 km x 30 km grid elements with ice present) is 50 to 80 percent, and the yearly cycle is far less distinct than that for the ice areas.

Zwally, H. J.↗
NASA NTRS1980

Snowpack monitoring in North America and Eurasia using passive microwave satellite data

Areas of the Canadian high plains, the Montana and North Dakota high plains, and the steppes of central Russia have been studied in an effort to determine the utility of spaceborne microwave radiometers for monitoring snow depths in different geographic areas. Significant regression relationships between snow depth and microwave brightness temperatures were developed for each of these homogeneous areas. In each of the study areas investigated in this paper, Nimbus-6 (0.81 cm) ESMR data produced higher correlations than Nimbus-5 (1.55 cm) ESMR data in relating microwave brightness temperature to snow depth. It is difficult to extrapolate relationships between microwave brightness temperature and snow depth from one area to another because different geographic areas are likely to have different snowpack conditions.

Foster, J. L.↗