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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Partitioning Evapotranspiration in Semiarid Grassland and Shrubland Ecosystems Using Diurnal Surface Temperature Variation

The encroachment of woody plants in grasslands across the Western U.S. will affect soil water availability by altering the contributions of evaporation (E) and transpiration (T) to total evapotranspiration (ET). To study this phenomenon, a network of flux stations is in place to measure ET in grass- and shrub-dominated ecosystems throughout the Western U.S. A method is described and tested here to partition the daily measurements of ET into E and T based on diurnal surface temperature variations of the soil and standard energy balance theory. The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (I(sub A)), was used to identify days when E was negligible, and thus, ET=T. For other days, a three-step procedure based on energy balance equations was used to estimate Qe contributions of daily E and T to total daily ET. The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona based on Bowen ratio estimates of ET and continuous measurements of surface temperature with an infrared thermometer (IRT) from 2004- 2005, and a second dataset of Bowen ratio, IRT and stem-flow gage measurements in 2003. Results showed that reasonable estimates of daily T were obtained for a multi-year period with ease of operation and minimal cost. With known season-long daily T, E and ET, it is possible to determine the soil water availability associated with grass- and shrub-dominated sites and better understand the hydrologic impact of regional woody plant encroachment.

Moran, M. Susan↗
NASA NTRS2008

Comparison of Satellite-Derived and In-Situ Observations of Ice and Snow Surface Temperatures over Greenland

The most practical way to get a spatially broad and continuous measurements of the surface temperature in the data-sparse cryosphere is by satellite remote sensing. The uncertainties in satellite-derived LSTs must be understood to develop internally-consistent decade-scale land-surface temperature (LST) records needed for climate studies. In this work we assess satellite-derived "clear-sky" LST products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and LSTs derived from the Enhanced Thematic Mapper Plus (ETM+) over snow and ice on Greenland. When possible, we compare satellite-derived LSTs with in-situ air-temperature observations from Greenland Climate Network (GC-Net) automatic-weather stations (AWS). We find that MODIS, ASTER and ETM+ provide reliable and consistent LSTs under clear-sky conditions and relatively-flat terrain over snow and ice targets over a range of temperatures from -40 to 0 C. The satellite-derived LSTs agree within a relative RMS uncertainty of approx.0.5 C. The good agreement among the LSTs derived from the various satellite instruments is especially notable since different spectral channels and different retrieval algorithms are used to calculate LST from the raw satellite data. The AWS record in-situ data at a "point" while the satellite instruments record data over an area varying in size from: 57 X 57 m (ETM+), 90 X 90 m (ASTER), or to 1 X 1 km (MODIS). Surface topography and other factors contribute to variability of LST within a pixel, thus the AWS measurements may not be representative of the LST of the pixel. Without more information on the local spatial patterns of LST, the AWS LST cannot be considered valid ground truth for the satellite measurements, with RMS uncertainty approx.2 C. Despite the relatively large AWS-derived uncertainty, we find LST data are characterized by high accuracy but have uncertain absolute precision.

Hall, Dorothy K.↗
NASA NTRS1981

Heat flux estimates over vegetation derived using radiometric surface temperatures and a boundary layer model in comparison with sodar-derived values

An attempt was made to validate a method that uses radiometric surface temperatures and a boundary layer model to estimate surface energy budgets and characteristics. Surface temperatures from a hand-held radiometer and sodar data were collected simultaneously on seven days between mid-July and mid-October 1980. The comparison of the RDMS and sodar heat fluxes proved disappointing. Free convection conditions, required to produce sodar-derived heat fluxes, were inhibited by a terrain-induced low level inversion. Only three out of seven cases produced meaningful sodar heat fluxes. Of those three cases, one had good agreement and the other two had sodar heat fluxes 15 to 45 w/sq m lower than the RDMS values. Since the RDMS method is relatively untested, it was impossible to conclusively determine its validity from the results. There was evidence that the true heat flux was not underestimated by the RDMS, so it could be concluded that the Bowen ratios over well-watered vegetation were likely to be quite small.

Cooper, J. N.↗
NASA NTRS1985

Surface temperature distribution along a thin liquid layer due to thermocapillary convection

The surface temperature distributions due to thermocapillary convections in a thin liquid layer with heat fluxes imposed on the free surface were investigated. The nondimensional analysis predicts that, when convection is important, the characteristics length scale in the flow direction L, and the characteristic temperature difference delta T sub o can be represented by L and delta T sub o approx. (A2Ma)/1/4 delta T sub R, respectively, where L sub R and delta sub R are the reference scales used in the conduction dominant situations with A denoting the aspect ratio and Ma the Marangoni number. Having L and delta sub o defined, the global surface temperature gradient delta sub o/L, the global thermocapillary driving force, and other interesting features can be determined. Numerical calculations involving a Gaussian heat flux distribution are presented to justify these two relations.

Lai, C. L.↗
NASA NTRS1985

Surface temperature distribution along a thin liquid layer due to thermocapillary convection

The surface temperature distributions due to thermocapillary convections in a thin liquid layer with heat fluxes imposed on the free surface were investigated. The nondimensional analysis predicts that, when convection is important, the characteristics length scale in the flow direction L, and the characteristic temperature difference delta T sub o can be represented by L and delta T sub o approx. (A2Ma)/1/4 delta T sub R, respectively, where L sub R and delta sub R are the reference scales used in the conduction dominant situations with A denoting the aspect ratio and Ma the Marangoni number. Having L and delta sub o defined, the global surface temperature gradient delta sub o/L, the global thermocapillary driving force, and other interesting features can be determined. Numerical calculations involving a Gaussian heat flux distribution are presented to justify these two relations.

Lai, C.-L.↗
NASA NTRS1988

Simulation studies of the influence of sea-surface temperature anomalies on the Sahelian circulation and rainfall

An investigation was conducted to find out if sea surface temperature (SST) - African rainfall relationships could be simulated in a global climate model (GCM). If indeed that were possible, researchers generated useful diagnostics that can enable them to understand the physical mechanisms which lead to rainfall fluctuations over Africa in response to sea surface temperature anomalies over global ocean.

Sud, Y. C.↗
NASA NTRS2012

A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet

We have developed a climate-quality data record of the clear-sky surface temperature of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) ice-surface temperature (1ST) algorithm. A climate-data record (CDR) is a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change. We present daily and monthly MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 at 6.25-km spatial resolution on a polar stereographic grid. This record will be elevated in status to a CDR when at least nine more years of data become available either from MODIS Terra or Aqua, or from the Visible Infrared Imager Radiometer Suite (VIIRS) to be launched in October 2011. Our ultimate goal is to develop a CDR that starts in 1981 with the Advanced Very High Resolution (AVHRR) Polar Pathfinder (APP) dataset and continues with MODIS data from 2000 to the present, and into the VIIRS era. Differences in the APP and MODIS cloud masks have so far precluded the current 1ST records from spanning both the APP and MODIS time series in a seamless manner though this will be revisited when the APP dataset has been reprocessed. The complete MODIS 1ST daily and monthly data record is available online.

Hall, Dorothy K.↗
NASA NTRS2008

Titan's Surface Temperatures Measured by Cassini CIRS

A large fraction of 19-micron thermal radiation from the surface of Titan reaches space through a spectral window of low atmospheric opacity. The emergent radiance, after removing the effect of the atmosphere, gives the brightness temperature of the surface. This atmospheric window is covered by the far-infrared channel of the Composite Infrared spectrometer1 (CIRS) on Cassini. In mapping Titan surface temperatures, CIRS is able to improve upon results of Voyager IRIS, by taking advantage of improved latitude coverage and a much larger dataset. Observations are from a wide range of emission angles and thereby provide constraints on the atmospheric opacity and radiance that are used to derive the surface temperature. CIRS finds an average equatorial surface brightness temperature of 93.7+/-0.6 K, virtually identical to the HASI temperature at the Huygens landing site. Mapping in latitude shows that the surface temperature decreases toward the poles by about 2 K in the south and 3 K in the north. This surface temperature distribution is consistent with the formation of lakes seen at high latitudes on Titan.

Jennings, Donald E.↗
NASA NTRS1988

The relationship between large-scale vertical motion, highly reflective cloud, and sea surface temperature in the tropical Pacific region

Vertical motion fields at 850 mbar over the tropical Pacific region are calculated from the 1963-1973 mean wind fields for 4 months of the year and for October 1972, the peak month in the 1972-1973 El Nino event. These vertical motion fields are derived using the projective separation technique, which has the unique property of separating vertical motion into components due to meridional wind convergence and zonal wind convergence. This separation permits investigation of the response of the Hadley and Walker circulations to annual and interannual variation of the sea surface temperature in the tropical Pacific. The large-scale features of the computed vertical motion fields are in agreement with those of highly reflective clouds, which indicate the locations of deep convection. Examination of the annual cycle of the vertical motion and its components shows no strong variation of the Walker circulation with the east-west gradient of sea surface temperature. On the other hand, a strong correlation is found between meridional overturning in the eastern Pacific and the local equatorial sea surface temperature: during El Nino events, the eastern and central Pacific contribution to the Hadley circulation tends to increase.

Zimmermann, Peter H.↗
NASA NTRS1985

A surface temperature and moisture parameterization for use in mesoscale numerical models

A modified multi-level soil moisture and surface temperature model is presented for use as in defining lower boundary conditions in mesoscale weather models. Account is taken of the hydraulic and thermal diffusion properties of the soil, their variations with soil type, and the mixing ratio at the surface. Techniques are defined for integrating the surface input into the multi-level scheme. Sample simulation runs were performed with the modified model and the original model defined by Pielke, et al. (1977, 1981). The models were applied to regional weather forecasting over soils composed of sand and clay loam. The new form of the model avoided iterations necessary in the earlier version of the model and achieved convergence at reasonable profiles for surface temperature and moisture in regions where the earlier version of the model failed.

Tremback, C. J.↗
NASA NTRS2009

Titan Surface Temperatures as Measured by Cassini CIRS

Thermal radiation from the surface of Titan reaches space through a spectral window of low opacity at 19-microns wavelength. This radiance gives a measure of the brightness temperature of the surface. Composite Infrared Spectrometer' (CIRS) observations from Cassini during its first four years at Saturn have permitted latitude mapping of zonally averaged surface temperatures. The measurements are corrected for atmospheric opacity using the dependence of radiance on emission angle. With the more complete latitude coverage and much larger dataset of CIRS we have improved upon the original results from Voyager IRIS. CIRS measures the equatorial surface brightness temperature to be 93.7+/-0.6 K, the same as the temperature measured at the Huygens landing site. The surface brightness temperature decreases by 2 K toward the south pole and by 3 K toward the north pole. The drop in surface temperature between equator and north pole implies a 50% decrease in methane saturation vapor pressure and relative humidity; this may help explain the large northern lakes. The H2 mole fraction is derived as a by-product of our analysis and agrees with previous results. Evidence of seasonal variation in surface and atmospheric temperatures is emerging from CIRS measurements over the Cassini mission.

Jennings, Donald E.↗
NASA NTRS1994

Development of practical multiband algorithms for estimating land-surface temperature from EOS/MODIS data

A practical multiband, hierarchical algorithm for estimating land-surface temperature from NASA's future Earth Observing System (EOS) instruments Moderate Resolution Imaging Spectroradiometer (MODIS) and Advance Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is developed through comprehensive, accurate, radiative transfer simulations at moderate spectral steps of 1-5/cm for wide ranges of atmospheric and surface conditions. The algorithm will accept empirical or estimated information about the surface emissivity and reflectivity and the atmospheric temperature and water-vapor profiles. Ground-based and aircraft measurements are necessary to validate and improve the algorithm and to establish its quality. Its accuracy depends on the calibration accuracy of thermal infrared data, uncertainties in surface heterogeneity, and temperature-dependent atmospheric absorption coefficients. Better knowledge of land-surface spectral emissivities and more accurate coefficients for atmospheric molecular band absorption and water vapor continuum absorption are needed to develop global land-surface temperature algorithms accurate to 1-2 K.

Dozier, J.↗