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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Modeling of Wind Direction Signals in Polarimetric Sea Surface Brightness Temperatures

There is an increasing interest in the applications of polarimetric microwave radiometers for ocean wind remote sensing. Aircraft and spaceborne radiometers have found significant wind direction signals in sea surface brightness temperatures. It is not yet understood what physical scattering mechanisms produce the observed wind direction dependence. Some theories are examined along with the available data.

Ocean↗
NASA NTRS1992

Brightness temperature simulations for the physical interpretation of AMSU moisture channels

The use of the Advanced Microwave Sounding Unit (AMSU) moisture imagery for the dynamic, kinematic, and synoptic interpretations requires the availability of idealized 'soundings' of temperature, water vapor, and cloudiness as input to a radiative transfer model for determining how atmospheric conditions control the top-of-atmosphere brightness temperatures. This paper uses idealized vertical configurations of atmospheric water vapor and liquid cloud water to illustrate their effects on the AMSU moisture channels. Calculations with various cloud-drop size distribution functions (SDFs) showed that, at least for the specific SDFs used in this work, the Rayleigh approximation is invalid for mode radii greater than 30-40 microns, for frequencies above 89.0 GHz. It is also invalid above about 20 microns for frequencies above 157 GHz. It is concluded that AMSU moisture channels might not be suitable for detecting convective instability over land using image-based approaches.

Muller, Bradley M.↗
NASA NTRS1980

The longitudinal variation of the thermal inertia and of the 2.8 centimeter brightness temperature of Mars

The spatial variations on Mars of the surface thermal inertia and radiometric albedo are used to predict the variation with sub-earth longitude of the 2.8 cm whole-disk brightness temperature. The maximum variation predicted, about 8 K, agrees well with observations. The sub-earth longitudes at which the temperature maxima and minima are predicted to occur nearly agree with the observations. There are, however, differences in the overall form of the variation with longitude. These discrepancies can be reduced by an ad hoc assumption of spatial variations in either the fraction of the surface covered by rock or the amount of atmospheric dust.

Jakosky, B. M.↗
NASA NTRS2011

L Band Brightness Temperature Observations Over a Corn Canopy During the Entire Growth Cycle

During a field campaign covering the 2002 corn growing season, a dual polarized tower mounted L-band (1.4 GHz) radiometer (LRAD) provided brightness temperature (T(sub B)) measurements at preset intervals, incidence and azimuth angles. These radiometer measurements were supported by an extensive characterization of land surface variables including soil moisture, soil temperature, vegetation biomass, and surface roughness. During the period from May 22, 2002 to August 30, 2002 a range of vegetation water content (W) of 0.0 to 4.3 kg/square m, ten days of radiometer and ground measurements were available. Using this data set, the effects of corn vegetation on surface emissions are investigated by means of a semi-empirical radiative transfer model. Additionally, the impact of roughness on the surface emission is quantified using T(sub B) measurements over bare soil conditions. Subsequently, the estimated roughness parameters, ground measurements and horizontally (H)-polarized T(sub B) are employed to invert the H-polarized transmissivity (gamma-h) for the monitored corn growing season.

Joseph, Alicia T.↗
NASA NTRS1990

Simulation of microwave brightness temperatures of an evolving hailstorm at SSM/I frequencies

A simulation of the appearance of an intense hailstorm in the passive microwave spectrum is used to characterize the vertical sources of radiation contributing to the microwave brightness temperatures at the top of the atmosphere. The four frequencies studied correspond to those used on the USAF Special Sensor Microwave Imager. The origin and movement of the radiation are described by two vertically resolved radiative structure functions. Consideration is given to problems relating to precipitation retrieval through passive remote sensing.

Mugnai, Alberto↗
NASA NTRS2006

The Aquarius Scatterometer: An Active System for Measuring Surface Roughness for Sea-Surface Brightness Temperature Correction

The Aquarius scatterometer is a total-power L-band radar system for estimating ocean surface roughness. Its measurements will enable the removal of wind effects from the Aquarius radiometer ocean-surface brightness temperature measurements being used to retrieve ocean salinity. The Aquarius scatterometer is a relatively simple, low-spatial resolution power-detecting radar, without ranging capability. But to meet its science requirement, it must be very stable, with repeatability on the order of 0.1 dB over several days, and calibrated accuracy to this level over several months. Data from this instrument over land as well as ocean areas will be available for a variety of geophysical applications.

scatterometers↗
NASA NTRS1985

Mercury - Thermal emission at radio wavelengths. I - 3.3- and 28-mm observed brightness temperatures and periodicities therein

The thermal radio emission from Mercury at 3.3 mm and 28 mm was measured over a period of several years, and the results of a statistical analysis of the data are reported. The disk-average brightness temperature is reported as a function of longitude, and other periodicities are reported. The range of values of the thermophysical parameters is constrained by comparing the data with models.

Epstein, E. E.↗
NASA NTRS2012

Retrieval of Ocean Surface Windspeed and Rainrate from the Hurricane Imaging Radiometer (HIRAD) Brightness Temperature Observations

The Hurricane Imaging Radiometer (HIRAD) is a new airborne synthetic aperture passive microwave radiometer capable of wide swath imaging of the ocean surface wind speed under heavy precipitation e.g. in tropical cyclones. It uses interferometric signal processing to produce upwelling brightness temperature (Tb) images at its four operating frequencies 4, 5, 6 and 6.6 GHz [1,2]. HIRAD participated in NASA s Genesis and Rapid Intensification Processes (GRIP) mission during 2010 as its first science field campaign. It produced Tb images with ~70 km swath width and 3 km resolution from a ~ 20 km altitude. From this, ocean surface wind speed and column averaged atmospheric liquid water content can be retrieved across the swath. The column averaged liquid water then could be related to an average rain rate. The retrieval algorithm (and the HIRAD instrument itself) is a direct descendant of the nadir-only Stepped Frequency Microwave Radiometer that is used operationally by the NOAA Hurricane Research Division to monitor tropical cyclones [3,4]. However, due to HIRAD s slant viewing geometry (compared to nadir viewing SFMR) a major modification is required in the algorithm. Results based on the modified algorithm from the GRIP campaign will be presented in the paper.

Biswas, Sayak K.↗
NASA NTRS2019

Global Assimilation of L-Band Brightness Temperature Observations from SMAP and SMOS into the Catchment Land Surface Model and Contribution to the Skill of Soil Moisture Estimates

The Soil Moisture Active Passive (SMAP) and Soil Moisture Ocean Salinity (SMOS) missions provide global observations of L-band (1.4 GHz) passive microwave brightness temperature (Tb) observations at a resolution of ~40 km every 2-3 days. These observations have been available since 2015 from SMAP and since 2010 from SMOS.Soil moisture estimates from the separate assimilation of SMAP and SMOS Tb observations into land surface models were previously shown to improve over model-only estimates, thereby demonstrating the value of assimilating L-band Tb observations for soil moisture estimation. The assimilation experiments documented in the literature do not, however, establish whether the joint assimilation of SMAP and SMOS Tbs improves the skill of the resulting soil moisture estimates beyond what can be achieved with either set of observations alone. Moreover, because the published SMAP and SMOS results used different assimilation systems and configurations and applied different evaluation data and procedures, it is unclear whether the assimilation of SMAP-only or SMOS-only Tbs results in better soil moisture skill. In this presentation, we compare the results of three separate assimilation experiments for the period from April 2015 to present. The experiments utilize the SMAP Level-4 Soil Moisture (L4_SM) algorithm, which assimilates L-band Tb observations into the NASA Catchment land surface model using a spatially distributed ensemble Kalman filter. Specifically, the three experiments presented here assimilate (i) SMAP Tbs only, as in the L4_SM product, (ii) SMOS Tbs only, after interpolation of 40° incidence angle, and (iii) both SMAP and SMOS Tbs. In all other respects, the configuration of three experiments is identical, as is the validation of the output. Preliminary results suggest that the joint assimilation of SMAP and SMOS Tbs yields the most skillful soil moisture estimates when compared to independent in situ measurements. Moreover, the skill of the SMAP-only assimilation exceeds that of the SMOS-only assimilation. The presentation provides an in-depth evaluation of the skill of the assimilation estimates vs. independent in situ and satellite measurements and in terms of statistics of the observation-minus-forecast residuals and analysis increments.

Reichle, Rolf↗
NASA NTRS2021

The benefit of brightness temperature assimilation for the SMAP Level-4 surface and root-zone soil moisture analysis

The Soil Moisture Active Passive (SMAP) Level-4 (L4) product provides global estimates of surface soil moisture (SSM) and root-zone soil moisture (RZSM) via the assimilation of SMAP brightness temperature (Tb) observations into the NASA Catchment Land Surface Model (CLSM). Here, using in situ measurements from 2474 sites in China, we evaluate the performance of soil moisture estimates from the L4 data assimilation (DA) system and from a baseline “open-loop” (OL) simulation of CLSM without Tb assimilation. Using random forest regression, the efficiency of the L4 DA system (i.e., the performance improvement in DA relative to OL) is attributed to eight control factors related to the CLSM as well as τ–ω radiative transfer model (RTM) components of the L4 system. Results show that the Spearman rank correlation (R) for L4 SSM with in situ measurements increases for 77 % of the in situ measurement locations (relative to that of OL), with an average R increase of approximately 14 % (ΔR=0.056). RZSM skill is improved for about 74 % of the in situ measurement locations, but the average R increase for RZSM is only 7 % (ΔR=0.034). Results further show that the SSM DA skill improvement is most strongly related to the difference between the RTM-simulated Tb and the SMAP Tb observation, followed by the error in precipitation forcing data and estimated microwave soil roughness parameter h. For the RZSM DA skill improvement, these three dominant control factors remain the same, although the importance of soil roughness exceeds that of the Tb simulation error, as the soil roughness strongly affects the ingestion of DA increments and further propagation to the subsurface. For the skill of the L4 and OL estimates themselves, the top two control factors are the precipitation error and the SSM–RZSM coupling strength error, both of which are related to the CLSM component of the L4 system. Finally, we find that the L4 system can effectively filter out errors in precipitation. Therefore, future development of the L4 system should focus on improving the characterization of the SSM–RZSM coupling strength.

Jianxiu Qiu↗
NASA NTRS2016

A New Operational Snow Retrieval Algorithm Applied to Historical AMSR-E Brightness Temperatures

Snow is a key element of the water and energy cycles and the knowledge of spatio-temporal distribution of snow depth and snow water equivalent (SWE) is fundamental for hydrological and climatological applications. SWE and snow depth estimates can be obtained from spaceborne microwave brightness temperatures at global scale and high temporal resolution (daily). In this regard, the data recorded by the Advanced Microwave Scanning Radiometer-Earth Orbiting System (EOS) (AMSR-E) onboard the National Aeronautics and Space Administration's (NASA) AQUA spacecraft have been used to generate operational estimates of SWE and snow depth, complementing estimates generated with other microwave sensors flying on other platforms. In this study, we report the results concerning the development and assessment of a new operational algorithm applied to historical AMSR-E data. The new algorithm here proposed makes use of climatological data, electromagnetic modeling and artificial neural networks for estimating snow depth as well as a spatio-temporal dynamic density scheme to convert snow depth to SWE. The outputs of the new algorithm are compared with those of the current AMSR-E operational algorithm as well as in-situ measurements and other operational snow products, specifically the Canadian Meteorological Center (CMC) and GlobSnow datasets. Our results show that the AMSR-E algorithm here proposed generally performs better than the operational one and addresses some major issues identified in the spatial distribution of snow depth fields associated with the evolution of effective grain size.

passive microwave↗
NASA NTRS2018

Accounting for Static and Dynamic Open Water in the Modeling of SMAP Brightness Temperatures over Peatlands

Hydrological change in peatlands due to anthropogenic disturbance and global warming can release enormous amounts of greenhouse gas emissions. Passive microwave satellite observations are an opportunity to globally monitor these changes. Abundant static and dynamic open water surfaces in peatlands strongly affect observed brightness temperatures (Tb). Here, we account for these contributions in radiative transfer modeling using NASA's Goddard Earth Observing System Model version 5 (GEOS-5) static open water mask and, for the dynamic open water fraction, the simulated inundated area using a version of the GEOS-5 Catchment land surface model that has been modified for peatland areas (PEAT-CLSM). Modeled Tb is compared against two years of SMAP L-band Tb. Preliminary results indicate: (i) a bias reduction when including the static open water fraction in a simple RTM mixing model, and ii) significantly improved correlation between modeled and observed Tb when using land surface output from PEAT-CLSM instead of the operational CLSM.

passive microwave↗
NASA NTRS2018

Utilizing Brightness Temperature Histograms for Microwave Radiometer High Frequency (150-183 Ghz) Calibration

Spaceborne microwave radiometers with high frequency channels (150-183 GHz) are important for retrieving many geophysical parameters such as snowfall, ice water path, and atmospheric water vapor profiles. In order to obtain accurate retrievals from the brightness temperature measurements, the radiometers must be properly calibrated. Several methods have been developed to analyze the on-orbit calibration, including comparisons with radiative transfer models, comparisons with radiosonde profiles, and cross-calibration with similar radiometers. This paper introduces a new method to calibrate high frequency channels that utilizes TB histograms. This new method gives an independent approach that can be used by itself to analyze radiometer calibration or in conjunction with other methods to corroborate results.

microwave radiometry↗
NASA NTRS1982

Evaluation of atmospheric attenuation from SMMR brightness temperature for the Seasat satellite scatterometer

The effect of attenuation in precipitation regions of the sea, which must be considered in order to measure the radar backscatter from the ocean with sufficient accuracy to allow determination of the wind vector, can be ascertained from a knowledge of the brightness temperature observed by a microwave radiometer such as the Seasat multifrequency scanning radiometer. Two algorithms relating radiometric measurements and attenuation, and thereby correcting measured scattering coefficient values, were compared with wind vectors reported by surface observers and those determined by the Seasat scatterometer measurements with and without correction for atmospheric attenuation. Although the attenuation correction yields some improvements, it is constrained by both radiometer footprint differences and different scan patterns.

Moore, R. K.↗
NASA NTRS1974

Variations in the infrared brightness temperature of Saturn's rings

After adjusting for the decreased Sun-Saturn distance and adjusting all measurements to B ring values only, it is shown that the temperature variations are not as large as was thought. Various models of the multilayer agglomerate of particles of Saturn's rings are evaluated. It is recommended that the difference between the 11 and 20 micron brightness temperatures should be explained by a satisfactory model.

Murphy, R. E.↗
NASA NTRS1986

Zonal wave number variance spectra of stratospheric microwave brightness temperatures

Well-known theoretical predictions suggest that variances of large-scale atmospheric fluctuations, for scales somewhat shorter than those of the forcing mechanisms, should obey a power law, k exp -b, where k is the horizontal wave number. The invariance of the exponent b with season, hemisphere, and latitude is tested using satellite-measured brightness temperatures. Global grids of Tiros-N Microwave Sounding Unit channel 4 measurements, which closely approximate the 30- to 150-mbar layer mean temperature, are constructed for January, March, and August 1979. These grids are zonally Fourier-transformed, and the resulting spectra are averaged over four 18 deg-wide latitude bands. Fits of a power law to these spectra over wave numbers 10-36 and 10-26 give values of b which are independent of season, hemisphere, and latitude band, to within statistical uncertainties. The observed values of b are about 3.6, as compared to theoretical predictions of 3.

Martin, Russell L.↗
NASA NTRS1984

Interpretation of the lunar microwave brightness temperature spectrum - Feasibility of orbital heat flow mapping

The feasibility of an orbital mapping of heat flow by means of microwave radiometers is examined on the basis of a detailed model of the lunar regolith. The results obtained are discussed in terms of contributions of physical properties and regolith structure to the spectral signature of lunation-averaged brightness temperatures. Even for regions for which remote heat flow detection is not feasible, detailed interpretations of remote measurements in terms of physical properties and regolith structure could be made by means of the model presented. Surface and subsurface scattering effects are considered in evaluating possible wavelength dependencies of the microwave emissivity.

Keihm, S. J.↗