Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “microwave radiometry”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Remote sensing of the Chesapeake Bay plume salinity via microwave radiometry

The NASA-Langley-developed L-Band microwave radiometer was used to remotely measure sea surface salinity during the Chesapeake Bay plume studies. Obtained measurements of microwave brightness temperatures of the sea surface were combined with measurements of sea surface temperature obtained with an infrared radiometer and inverted to produce corresponding values of sea surface salinity. Results from the plume measurements, which indicate the southward extent of the plume along the Virginia-North Carolina coast, are presented and discussed. Additional measurements obtained for the Delaware Bay Mouth flight, and the James River-Shelf flight, are also discussed.

Kendall, B. M.↗
NASA NTRS1983

Microwave radiometry as a probe of precipitation physics

The Advanced Microwave Moisture Sounder (AMMS) is a passive airborne microwave imager operating at 92 GHz and three frequencies near the 183 GHz water vapor line. Attention is presently given to AMMS measurements conducted during the Cooperative Convection Precipitation Experiment of 1981. The simple model of Nieman (1982), which consists of an imperfect mirror reflecting the downwelling radiation from the atmosphere above its surface while screening from view the upwelling radiation that reaches it from below, has been applied to these measurements. Mirror altitude and emissivity values are retrieved by an algorithm, using observations near the water vapor line.

Szejwach, G.↗
NASA NTRS1989

Diurnal variations of mesospheric ozone obtained by ground-based microwave radiometry

From December 1986 until April 1987 ground-based microwave observations of the diurnal variation of mesospheric ozone were made over Bern, Switzerland. These data were of sufficient quality to define the characteristics diurnal behavior of the ozone mixing ratio during winter and equinoctial conditions. The observed diurnal variation of ozone peaks at about 74 km, where its amplitude is about a factor of 6. At 65 km the observed diurnal variation is a factor of 3, whereas at 55 km it is only a factor of 1.4. One-dimensional model calculations accurately reproduce the relative diurnal variation of ozone at equinox, suggesting that the model value of the ozone photolysis rate coefficient is accurate to better that 10 percent. For winter conditions, however, the model underpredicts the observed relative diurnal variation by a factor of 2; a major part of this discrepancy is due to an observed postmidnight increase in ozone. Various suggested changes in model parameters to better produce the ozone abundance vertical profile result in only small differences in the relative diurnal variation, indicating that these observations do not provide a sensitive test of the mesospheric chemistry controlling the abundance of odd oxygen.

Zommerfelds, W. C.↗
NASA NTRS1994

Atmospheric Remote Sensing by Microwave Radiometry

The Earth's atmosphere is a puzzle and a concern. Its unpredictable weather has always been a force to be recokoned with, but until recent times, our trust was implicit in the robustness of the atmospheric system as the foundation of our biosphere. Now we are not so sure.

microwave↗
NASA NTRS1978

A review of applications of microwave radiometry to oceanography

Following a review of the essential physics of microwave radiative transfer, oceanographic applications of this background physics are discussed using data from electrically scanning microwave radiometers on the Nimbus 5 and 6 satellites operating at 1.55-cm and 8-mm wavelengths, respectively. These data are interpreted in terms of rain rate, ice coverage, and first-year versus multiyear ice determination. It is shown that multifrequency radiometer measurements make it possible to separate the surface and atmospheric effects and to obtain useful measurements of sea surface temperature, surface wind speed, and atmospheric parameters along with improved measurements of rain and ice.

Wilheit, T. T., Jr.↗
NASA NTRS1980

Microwave radiometry as a tool to calibrate tropospheric water-vapor delay

Microwave radiometers were used to measure the emission line due to the water vapor molecules of atmospheric emission. Four separate field tests were completed which compared radiometers to other techniques which measure water vapor. It is shown that water vapor induced delay can be estimated with an accuracy of plus or minus 2 cm for elevation angles above 17 degrees.

Resch, G. M.↗
NASA NTRS1997

Airborne Microwave Radiometry on a Semi-Arid Area During HAPEX-Sahel

Airborne microwave radiometric measurements in the framework of the HAPEX-Sahel Experiment were performed by the Push Broom Microwave Radiometer (PBMR) and the PORTOS radiometer. The flights of both radiometers produced an original set of data covering the 1.4-90 GHz range of frequency. The East and West Central Super Sites were the areas most intensively observed by the microwave radiometers. Over those sites, several brightness temperature (TB) maps are available at seven dates distributed over a 1 month period in the middle of the rainy season. A comparison of the two radiometers demonstrates their radiometric quality and the precision of the localization of the microwave observations. At 1.4 GHz, the vegetation had very little effect on the soil microwave emission. Maps of soil moisture were developed using a single linear relationship between TB and the surface soil moisture. There is an important spatial heterogeneity in the soil moisture distribution, which is explained by both the soil moisture hydrodynamic properties and the localization of the precipitation fields. At 5.05 GHz, the vegetation must be accounted for to infer soil moisture from the microwave observations. A method based on a simple radiative transfer model and on microwave data has shown encouraging results.

Chanzy, A↗
NASA NTRS1979

Improved microwave radiometry for remote sensing

Significant improvements in the gain stability and overall performance of microwave radiometers have been achieved with the use of a self-balancing gain modulation technique. This technique, in combination with automatic thermal calibration, is particularly well suited for remote sensing radiometric applications. The essential features of such a radiometer, including typical data obtained from a spaceborne satellite, is presented to show the instrument's utility.

Leber, A.↗
NASA NTRS1987

Severe storm identification with satellite microwave radiometry - An initial investigation with Nimbus-7 SMMR data

The use of satellite passive microwave observations for the detection of severe thunderstorms is investigated. Nimbus 7 SMMR data obtained from 1979 to 1980 over the U.S. east of 105 deg W are analyzed. The relative temperature brightnesses of the severe storms are examined; it is observed that temperature brightness decreases as the storm severity increases. The temperature brightness data were transformed into a quantitative measure of storm detection ability using the critical success index of Donaldson et al. (1975). Critical success indices of 0.32, 0.48, and 0.38 were obtained for the low-brightness-temperature thresholding of severe versus nonsevere storms during 1979, 1980, and 1979 and 1980 combined, respectively. The data reveal that the geostationary passive microwave imaging capability at 37 GHz is applicable to the detection and monitoring of severe convective storms.

Howland, Michael R.↗
NASA NTRS2006

Precipitation and Latent Heating Distributions from Satellite Passive Microwave Radiometry. Part II: Evaluation of Estimates Using Independent Data

Rainfall rate estimates from spaceborne microwave radiometers are generally accepted as reliable by a majority of the atmospheric science community. One of the Tropical Rainfall Measuring Mission (TRMM) facility rain-rate algorithms is based upon passive microwave observations from the TRMM Microwave Imager (TMI). In Part I of this series, improvements of the TMI algorithm that are required to introduce latent heating as an additional algorithm product are described. Here, estimates of surface rain rate, convective proportion, and latent heating are evaluated using independent ground-based estimates and satellite products. Instantaneous, 0.5 deg. -resolution estimates of surface rain rate over ocean from the improved TMI algorithm are well correlated with independent radar estimates (r approx. 0.88 over the Tropics), but bias reduction is the most significant improvement over earlier algorithms. The bias reduction is attributed to the greater breadth of cloud-resolving model simulations that support the improved algorithm and the more consistent and specific convective/stratiform rain separation method utilized. The bias of monthly 2.5 -resolution estimates is similarly reduced, with comparable correlations to radar estimates. Although the amount of independent latent heating data is limited, TMI-estimated latent heating profiles compare favorably with instantaneous estimates based upon dual-Doppler radar observations, and time series of surface rain-rate and heating profiles are generally consistent with those derived from rawinsonde analyses. Still, some biases in profile shape are evident, and these may be resolved with (a) additional contextual information brought to the estimation problem and/or (b) physically consistent and representative databases supporting the algorithm. A model of the random error in instantaneous 0.5 deg. -resolution rain-rate estimates appears to be consistent with the levels of error determined from TMI comparisons with collocated radar. Error model modifications for nonraining situations will be required, however. Sampling error represents only a portion of the total error in monthly 2.5 -resolution TMI estimates; the remaining error is attributed to random and systematic algorithm errors arising from the physical inconsistency and/or nonrepresentativeness of cloud-resolving-model-simulated profiles that support the algorithm.

Yang, Song↗
NASA NTRS1992

Microwave radiometry for monitoring the diverse cloudiness regimes on Earth: A review

Recent work concerning the use of microwave radiometers in space to provide views of the water content of clouds is reported. Recently, theoretical algorithms were refined and the sampling by microwave radiometers for polar orbiting satellite became more commensurate in resolution and coverage with the scale of the meteorological phenomena. Parameters available from the Special Sensor Microwave/Imager (SSM/I) include total integrated water vapor (kg/sq m), integrated cloud liquid water (kg/sq m), rain rate (mm/hr), and an index for the presence and concentration of large ice particles; this so called scattering index can also be converted to a rain rate, although conversion is still rather uncertain. The hydrologic aspects of climatically important cloud systems on the Earth such as subtropical stratus decks, tropical convection, and midlatitude and polar cyclone can thus be monitored with the SSM/I parameters. The diagnostic as well as prognostic potential of these satellite derived water content properties of cloud systems are also discussed.

Katsaros, Kristina B.↗
NASA NTRS1974

Satellite microwave radiometry

Recent technological developments have enabled application of the techniques of radio astronomy to problems of earth and ocean physics. To illustrate these applications, we review results from the 19.35 GHz Electrically Scanned Microwave Radiometer (ESMR) now in operation on Nimbus 5. A composite image of the earth made from ESMR observations taken between January 12 and January 16, 1973 illustrates the wide range of physical effects in single channel microwave observations. Multi-frequency observations made from aircraft have demonstrated an even greater potential for satellite radiometry when several frequencies and polarizations are used simultaneously. As an illustration of the considerations required in multi-channel radiometry, we discuss the choice of frequencies for the Scanning Multichannel Microwave Radiometer (SMMR) planned for the Nimbus G satellite.

Webster, W. J., Jr.↗
NASA NTRS1988

Vertical resolution of middle atmospheric measurements by ground-based microwave radiometry

The vertical resolution obtainable through measurement of trace constituents in the middle atmosphere by ground-based microwave spectroscopy has remained somewhat ambiguous. In order to explore this question, the Backus-Gilbert (1967, 1968, 1970) inversion technique, which automatically yields quantitative estimates of the inversion spatial resolution was applied to this particular inverse problem. This indicated that the optimum resolution of Backus-Gilbert inversions of microwave spectroscopic measurements is about 10 km. A general technique, based on inversion of delta function simulated profiles, was then developed, for evaluating the resolution of any inversion technique and applied to the Chahine (1970) inversion technique. These results indicated that the optimum resolution of the Chahine technique is about 6 or 7 km, or nearly a factor of 2 better than the equivalent Backus-Gilbert results.

Bevilacqua, Richard M.↗
NASA NTRS1984

Comments on 'Inference of cloud temperature and thickness by microwave radiometry from space'

The method proposed by Pandey et al. (1983) for estimating the temperature differential and thickness of clouds from microwave data obtained with the scanning multichannel microwave radiometers of the Seasat and Nimbus-7 satellites is examined critically. It is pointed out that both the thicknesses and the temperature differentials derived from them may not be meaningful unless accurate measurements of cloud-top height (from IR radiometry) and reliable data on liquid-water content are available. It is suggested that the good fits obtained in generating regression coefficients for the proposed method may be artifacts of the fixed or limited-range liquid-water densities of the cloud models used. With respect to cloud-top height, the need to quantify and account for differences in the fields of view and spatial resolutions of the IR and microwave radiometers, as undertaken for the case of precipitating clouds by Yeh and Liou (1983), is stressed.

Yeh, H.-Y. M.↗
NASA NTRS1977

Microwave radiometry for soil moisture sensing

Investigations have been conducted with truck-mounted radiometers to study the variation of microwave emissivity from a soil. It was found that the longer wavelength radiometers, (21 cm), are preferable for the remote sensing of soil moisture. Aircraft observations indicated a nonlinear dependence of microwave brightness temperature on soil moisture. The dielectric constants of soils are considered along with the radiative transfer in soils, and soil water characteristics. A description is presented of test flights conducted with a NASA aircraft, taking into account soil moisture measurements and instrumentation. The obtained results show that the surface emissivity of a soil is determined by the dielectric properties of the surface soil layer a few tenths of a wavelength thick while the thermal sampling depths are much greater. The capability of the 21-cm radiometer to sense soil-moisture variations through a moderate vegetation canopy, and the promising Skylab results encourage consideration of a radiometer operating at this wavelength for routine soil moisture observations.

Schmugge, T.↗
NASA NTRS1985

Measuring the global distribution of intense convection over land with passive microwave radiometry

The global distribution of intense convective activity over land is shown to be measurable with satellite passive-microwave methods through a comparison of an empirical rain rate algorithm with a climatology of thunderstorm days for the months of June-August. With the 18 and 37 GHz channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR), the strong volume scattering effects of precipitation can be measured. Even though a single frequency (37 GHz) is responsive to the scattering signature, two frequencies are needed to remove most of the effect that variations in thermometric temperatures and soil moisture have on the brightness temperatures. Because snow cover is also a volume scatterer of microwave energy at these microwavelengths, a discrimination procedure involving four of the SMMR channels is employed to separate the rain and snow classes, based upon their differences in average thermometric temperature.

Spencer, R. W.↗