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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Mean sea surface and gravity investigations using TOPEX/Poseidon altimeter data

From a broad point of view, we will be concerned with studying global ocean circulation patterns on the basis of ocean surface determinations with geoid undulation information. In addition, we will study local variations of the gravity field implied by the altimeter data. These general goals are reflected in the title of our investigation. To meet our general goal, we have defined a number of specific objectives: (1) sea surface topography representation; (2) mean sea surface determination; (3) development of local geoid models; (4) mean sea surface comparisons; (5) sea surface topographic files; and (6) gravity anomaly determination.

Rapp, Richard H.↗
NASA NTRS1984

Global mean sea surface based upon SEASAT altimeter data

A global mean sea surface based upon the SEASAT altimeter data was derived. A combination of crossing arc techniques, accurate SEASAT reference orbits, and a previously computed GOES-3/SEASAT mean sea surface were used in the computation process. This mean sea surface provides a basis for the determination of global ocean circulation patterns and for detailed analysis of the Earth's internal structure. A contour map of the global mean sea surface is presented.

Marsh, J. G.↗
NASA NTRS1994

Mean sea surface and geoid gradient comparisons with TOPEX altimeter data

Cycles 4 to 54 of TOPEX data have been analyzed through comparisons with the mean sea surface given on the disturbed geophysical data record (GDR). Two inverted barometer correction procedures were considered for the data reduction. One used a constant atmospheric pressure for all data while the one adopted for use, for most computations, introduced a cycle average pressure. The maximum difference between the two estimates was 3.0 cm with a clear annual signal. With the modified correction the TOPEX sea surface was compared to The Ohio State University (OSU) mean sea surface, given on the GDR, to estimate three translations ( delta x = -2.3 cm; delta y = 25.0 cm; delta z = -0.3 cm) and a bias (43.3 cm) between the two surfaces. The only significant translation is delta y which indicates the reference frame of the TOPEX system differs from that used in the OSU mean sea surface system. The bias between the TOPEX mean sea surface and the OSU mean sea surface was used to estimate an equatorial radius of 6,378,136.55 m based on an 18-cm biased estimate of the TOPEX altimeter. Examination of the average difference, by cycle, between the TOPEX sea surface and the OSU mean sea surface suggested a bias change of 3.1 +/- 2.2 mm/yr with a positive sign indicating the average ocean surface is rising or the altimeter measured distance is decreasing. Models were implemented that solved directly for a bias, bias rate annual/semiannual, and tide correction terms. The computations indicated that a simultaneous solution for this bias, bias rate, and annual/semiannual terms gave the most accurate results. Nonsimultaneous solutions led to slightly different bias rate values. The root mean square difference between the TOPEX sea surface and OSU sea surface, after translation and bias correction, was +/- 17 cm for a typical cycle. Some locations were indentified where the difference could reach 2.3 cm and were repeated over several cycles indicating errors in the mean sea surface. Most of the large differences occur in regions lacking altimeter data prior to the TOPEX/POSEIDON mission and/or areas of significant bathymetric signature. Geoid gradients are needed for the reduction of individual track data to a reference track. The accuracy of the determination of such gradients was determined through the comparison of predicted along-track gradients to the observed gradients. Among four mean sea surfaces tested the best agreement was found with the OSU mean sea surface placed on the TOPEX geophysical data record.

Rapp, Richard H.↗
NASA NTRS1982

Global mean sea surface computation using GEOS 3 altimeter data

A mean sea surface map has been determined for the global ocean areas between +62 deg and -62 deg latitude using GEOS 3 altimeter data. A grid of laser reference orbits computed using the GEM 10B gravity model has been used to orient the altimeter data in a center of mass coordinate system. The density of the altimeter tracks has enabled the computation of the sea surface heights above the reference ellipsoid on 1 deg x 1 deg grid in most of the oceanic areas. In the northwest Atlantic the dense coverage has enabled computations on a 0.25 deg x 0.25 deg grid. Comparisons of the global surface with an independently computed mean sea surface based upon SEASAT altimeter data indicate an rms agreement of a little over a meter. Comparisons of the regional solution in the northwest Atlantic with SEASAT profiles indicate a precision of a few decimeters in this surface. An analysis of the global crossover differences has indicated the possibility of a timing error in the altimeter data. Timing bias values of within 0.5 msec of 9.2 msec for 1975 and within 0.6 msec of 18.7 msec for 1976 have been recovered from an analysis of the altimeter data.

Marsh, J. G.↗
NASA NTRS1982

The Seasat altimeter mean sea surface model

Gridding techniques are used to combine an 18-day set of Seasat altimeter data and two precisely-computed Seasat ephemerides, in order to arrive at global contour maps of the mean sea surface topography. The altimeter data have an rms agreement of 111 cm with the SS3 mean sea surface computed by means of the PGS-S3 ephemerides, and of 70 cm with the SS4 mean surface derived from the PGS-S4 ephemerides. While comparisons with the GEM 10B 1 x 1 deg gravimetric geoid have yielded rms differences of 2.8 m, those with a global mean sea surface derived from GEOS 3 altimeter data show rms differences of 1.3 m and 1.1 m for the cases of the SS3 and SS4 surfaces, respectively. An SS4 mean sea surface topograph is featured among the study findings presented. Further improvements in the representation of mean sea surface topography are expected with the development of more accurate gravity models for orbit computation.

Marsh, J. G.↗
NASA NTRS1994

Mean sea surface height of the Antarctic Circumpolar Current from Geosat data: Method and application

The mean sea surface height across the Antarctic Circumpolar Current (ACC) has been reconstructed from height variability measured by the Geosat altimeter without assuming prior knowledge of the geoid. For this study, an automated technique has been developed to estimate mean sea surface height for each satellite ground track using a meandering Gaussian jet model, and errors have been estimated using Monte Carlo simulation. The results are objectively mapped to produce a picture of the mean Subantarctic and Polar Fronts, which together comprise the major components of the Antarctic Circumpolar Current. The meandering jet model explains between 40% and 70% of the height variance along the jet axes. The results show that the fronts are substantially steered by topography and that the jets have an average Gaussian width of about 44 km in the meridional direction and meander about 75 km to either side of their mean locations. The average height difference across the Subantarctic Front (SAF) is 0.7 m and across the Polar Front (PF) 0.6 m. The mean widths of the fronts are correlated with the size of the baroclinic Rossby radius.

Gille, Sarah T.↗
NASA NTRS1985

Global mean sea surface computation based upon a combination of SEASAT and GEOS-3 satellite altimeter data

A mean sea surface map was computed for the global ocean areas between 70 deg N latitude and 62 deg S latitude based upon the 70 day SEASAT and 3.5 year GEOS-3 altimeter data sets. The mean sea surface is presented in the form of a global contour map and a 0.25 deg x 0.25 deg grid. A combination of regional adjustments based upon crossover techniques and the subsequent adjustment of the regional solutions into a global reference system was employed in order to minimize the effects of radial orbit error. A global map of the crossover residuals after the crossover adjustments are made is in good agreement with earlier mesoscale variability contour maps based upon the last month of SEASAT collinear data. This high level of agreement provides good evidence that relative orbit error was removed to the decimeter level on a regional basis. This represents a significant improvement over our previous maps which contained patterns, particularly in the central Pacific, which were due to radial orbit error. Long wavelength, basin scale errors are still present with a submeter amplitude due to errors in the PGS-S4 gravity model. Such errors can only be removed through the improvement of the Earth's gravity model and associated geodetic parameters.

Marsh, J. G.↗
NASA NTRS1992

A global mean sea surface based upon GEOS 3 and Seasat altimeter data

A mean sea surface relative to the International Union of Geodesy 1980 Geodetic Reference System reference ellipsoid has been derived from Seasat and GEOS 3 altimeter measurements. This surface, called MSS-9012, has been computed on a grid of 1/8 deg resolution. The surface covers the global ocean between 70 deg N and 72 deg S. Comparisons are made between MSS-9012 and ocean bathymetry. The eastern extent of the Chain Fracture Zone in the Gulf of Guinea is more apparent in the altimetry than in the bathymetry data, as are many other features. The combination of data from the two satellites has successfully retrieved more information about the sea surface than was previously possible using only Seasat data.

Marsh, J. G.↗
NASA NTRS1991

The mean sea surface height and geoid along the Geosat subtrack from Bermuda to Cape Cod

The mean sea-surface height and the gravitational geoid are presently estimated via near-surface velocity changes and concurrent sea-level changes along an ascending Geosat subtrack. The velocity measurements were made on three traverses, within ten days, of a Geosat subtrack, by means of an acoustic Doppler current profiler (ADCP). The mean sea-surface height was estimated as the difference between the instantaneous sea-surface height from ADCP and the Geosat residual sea level. In order to minimize mesoscale errors in the estimate, the along-track geoid estimate was computed as the difference between mean sea-level height from the Geosat Exact Repeat Mission and an estimate of the mean sea-surface height.

Kelly, Kathryn A.↗
NASA NTRS1984

Regional mean sea surfaces based on GEOS-3 and SEASAT altimeter data

Altimetric sea surfaces provide a basis for detailed analyses of the earth's gravity, crustal structure, and the oceanic surface circulation. Long-term mean surfaces have been computed for the Bering Sea, Northwest Atlantic Ocean, and Gulf of Mexico based on a combination of the entire SEASAT (three-month) and GEOS-3 (3.5-year) altimeter data sets. The number of available passes ranged from 558 in the gulf to 1396 in the Atlantic. The large amount of data in these areas, coupled with the incresed constraint provided by the combination of data from two orbital inclinations, has permited the accurate removal of the effects of radial ephemeris error through crossing arc adjustments. The precision of these regional mean sea surfaces is approximately 15 cm, with horizontal resolutions approaching 25 km.

Marsh, J. G.↗
NASA NTRS1990

Mean sea surface and variability of the Gulf of Mexico using Geosat altimetry data

Geosat Exact Repeat Mission (ERM) altimetric measurements of the sea surface height in the Gulf of Mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along Geosat ground tracks in the gulf for the time period from November 8, 1986 to November 25, 1988. A mean surface generated using the Geosat ERM along-track mean is calculated and contrasted with a previously derived mean surface determined using GEOS 3 and Seasat crossover differences. This provides a first look at the variability in the mean between the time periods of 1987-1988 and 1975-1978. In addition, the along-track mesoscale variability time series has been produced from the Geosat ERM data set by using a robust orbit-error removal algorithm to determine the variability of the sea-surface height with respect to the along-track mean. Good qualitative and quantitative agreement with previous in situ observations in the region is found. This study demonstrates the potential of satellite altimetry for oceanographic studies of the Gulf of Mexico.

Leben, Robert R.↗
NASA NTRS1992

The determination of a one year mean sea surface height track from Geosat altimeter data and ocean variability implications

Results are presented for determinations of mean sea surface along a reference Geosat altimeter tracking, using Geosat data from the first year of the exact repeat mission (ERM) and improved orbits. The results were used to study the time variability of the ocean surface, and a map was constructed of the major current structure. The data included 21 complete and one incomplete ERMs, with the sea surface heights being referenced to the single reference track through the application of geoid gradient corrections. This Geosat surface can be used as a reference surface to which other altimeter data could be incorporated; the data could then be used for the recovery of geoid undulations and gravity anomalies in the ocean areas.

Wang, Yan M.↗
NASA NTRS1979

Estimation of mean sea surfaces in the north Atlantic, the Pacific and the Indian Ocean using GEOS-3 altimeter data

The mean surfaces of several regions of the world's oceans were estimated using GEOS-3 altimeter data. The northwest Atlantic, the northeast Pacific off the coast of California, the Indian Ocean, the southwest Pacific, and the Phillipine Sea are included. These surfaces have been oriented with respect to a common earth center-of-mass system by constraining the separate solutions to conform to precisely determined laser reference control orbits. The same reference orbits were used for all regions assuring continuity of the separate solutions. Radial accuracies of the control orbits were in the order of one meter. The altimeter measured sea surface height crossover differences were minimized by the adjustment of tilt and bias parameters for each pass with the exception of laser reference control passes. The tilt and bias adjustments removed long wavelength errors which were primarily due to orbit error. Ocean tides were evaluated. The resolution of the estimated sea surfaces varied from 0.25 degrees off the east coast of the United States to about 2 degrees in part of the Indian Ocean near Australia. The rms crossover discrepancy after adjustment varied from 30 cm to 70 cm depending upon geographic location. Comparisons of the altimeter derived mean sea surface in the North Atlantic with the 5 feet x 5 feet GEM-8 detailed gravimetric geoid indicated a relative consistency of better than a meter.

Marsh, J. G.↗
NASA NTRS1979

Estimation of mean sea surfaces in the North Atlantic, the Pacific and the Indian Ocean using GEOS-3 altimeter data

The sea surface heights above the reference ellipsoid were determined for several regions of the world's ocean using data from the radar altimeter on board the GEOS-3 satellite in conjunction with precise orbital position information derived from laser data. The resolution of the estimated sea surfaces varied from 0.25 degrees off the east coast of the United States to about 2 degrees in the Indian Ocean near Australia. The rms crossover discrepancy after adjustment varied from 30 cm to 70 cm depending on geographic location. Comparison of the altimeter derived mean sea surface in the North Atlantic with the 5 x 5 ft GEM-8 detailed gravimetric geoid indicated a relative consistency of better than one meter.

Marsh, J. G.↗
NASA NTRS2001

Observations of Sea Surface Mean Square Slope During the Southern Ocean Waves Experiment

For the Southern Ocean Waves Experiment (SOWEX), conducted in June 1992 out of Hobart, Tasmania, the NASA Scanning Radar Altimeter (SRA) was shipped to Australia and installed on a CSIRO Fokker F-27 research aircraft instrumented to make comprehensive surface layer measurements of air-sea interaction fluxes. The SRA sweeps a radar beam of P (two-way) half-power width across the aircraft ground track over a swath equal to 0.8 of the aircraft height, simultaneously measuring the backscattered power at its 36 GHz (8.3 mm) operating frequency and the range to the sea surface at 64 cross-track positions. In realtime, the slant ranges are multiplied by the cosine of the off-nadir incidence angles (including the effect of aircraft roll attitude) to determine the vertical distances from the aircraft to the sea surface. These distances are subtracted from the aircraft height to produce a sea-surface elevation map, which is displayed on a monitor in the aircraft to enable real-time assessments of data quality and wave properties. The sea surface mean square slope (mss), which is predominantly caused by the short waves, was determined from the backscattered power falloff with incidence angle measured by the SRA in the plane normal to the aircraft heading. On each flight, data were acquired at 240 m altitude while the aircraft was in a 7 degree roll attitude, interrogating off-nadir incidence angles from -15 degrees through nadir to +29 degrees. The aircraft turned azimuthally through 810 degrees in this attitude, mapping the azimuthal dependence of the backscattered power falloff with incidence angle. Two sets of turning data were acquired on each day, before and after the aircraft measured wind stress at low altitude (12 meters to 65 meters). Wave topography and backscattered power for mss were also acquired during those level flight segments whenever the aircraft altitude was above the SRA minimum range of 35 m. Data were collected over a wide range of wind and sea conditions, from quiescent to gale force winds with 9 meter wave height.

Walsh, E. J.↗
NASA NTRS1999

Observations of Sea Surface Mean Square Slope During the Southern Ocean Waves Experiment

For the Southern Ocean Waves Experiment (SOWEX), conducted in June 1992 out of Hobart, Tasmania, the 36 GHz (8.3 mm) NASA Scanning Radar Altimeter (SRA) was shipped to Australia and installed on a CSIRO Fokker F-27 research aircraft instrumented to make comprehensive surface layer measurements of air-sea interaction fluxes. The sea surface mean square slope (mss), which is predominantly caused by the short waves, was determined from the backscattered power falloff with incidence angle measured by the SRA in the plane normal to the aircraft heading. On each flight, data were acquired at 240 m altitude while the aircraft was in a 7 deg roll attitude, interrogating off-nadir incidence angles from -15 deg through nadir to +29 deg. The aircraft turned azimuthally through 810 deg in this attitude, mapping the azimuthal dependence of the backscattered power falloff with incidence angle. Two sets of turning data were acquired on each day, before and after the aircraft measured wind stress at low altitude (12 m to 65 m). Wave topography and backscattered power for mss were also acquired during those level flight segments whenever the aircraft altitude was above the SRA minimum range of 35 m. A unique feature of this experiment was the use of a nadir-directed low-gain horn antenna (35 deg beamwidth) to acquire azimuthally integrated backscattered power data versus incidence angle before and after the turn data.

Walsh, E. J.↗
NASA NTRSDate not supplied

Synergy of Satellite Radiation, Precipitation, and Other Meteorological Variable Observations for Global Mean Sea Surface Turbulent Heat Flux Estimation

Sea surface turbulent heat flux is one of the key components in global freshwater and energy balances and plays an important role in atmospheric dynamics, thermodynamics and general circulation. This turbulent heat flux is dominantly decided by sea surface latent heat release with some contribution from sensible heat exchange. The flux and its anomaly could significantly affect ocean heat storage and ocean circulation. They are part of and have great impacts on climate variability. Though the turbulent heat flux is extremely important for the climate and weather systems, only very limited ship and buoy observations of the flux are available over open oceans. There are no global, operational, direct measurements of this crucial meteorological variable. Global estimates are, basically, indirectly calculated from bulk turbulent flux parameterization with a combination of satellite column water vapor, sea surface water temperature, and wind speed observations. Critical parameters such as sea surface air temperature and humidity are estimated from empirical relations of theses variables with the water vapor and sea surface water temperature, respectively. Lacking accurate knowledge on surface air temperature and humidity, uncertainties in the parameterization and potential changes in the non-linear turbulent processes with long-term climate variations could cause large errors in estimated long-term turbulent fluxes from the indirect method as shown in current global sea surface turbulent flux datasets. This study uses synergized data of satellite global radiation, precipitation, and other meteorological variable observations to estimate sea surface turbulent heat fluxes. The radiation observations are made by the satellite Clouds and the Earth’s Radiant Energy System (CERES) sensors, while the global precipitation data is from NASA’s satellite Global Precipitation Climatology Project (GPCP). Other data includes satellite sea surface water temperature and wind speed observations. These datasets are obtained from a wide range of space sensors from passive to active instruments and from visible and near infrared to thermal infrared and microwave spectral sounders. One significant feature of these datasets is that they have multi-decades long climate records. Top-of-atmosphere (TOA) radiation and its anomaly represents the net heat energy input to the climate system, and the oceanic precipitation and ocean-land moisture transport can be used to quantify sea surface latent heat release. Based on the synergized datasets and the principle of global water and energy balances, global mean turbulent heat fluxes are estimated. The turbulent heat anomalies for the first two decades of the 21st century are, then, obtained mainly from global CERES radiation and GPCP precipitation anomalies, along with CERES derived ocean-land heat transports. Analysis indicates that the uncertainties in the estimated turbulent flux anomalies may be reduced considerably. The results suggest a strong needs in synchronized and synergized observations of atmospheric radiation, precipitation, and oceanic meteorological variables for long-term climate studies.

Bing Lin↗
NASA NTRS1972

Use of a spacecraft borne altimeter for determining the mean sea surface and the geopotential

An experiment is proposed to test a first generation spacecraft-borne radar altimeter's capability to measure the topography of the sea surface. The initial radar altimeter will have an instrumental error of one meter and an overall accuracy to two to five meters. This instrument will thus improve the accuracy of the geoid from the present 10 to 20 meters to better than 5 meters. In order to detect storm surges, tidal forces, and ocean currents, an altimeter with an overall accuracy of at least ?1 meter will be required. The overall accuracy of the initial radar altimeter will thus primarily provide geodetic information and possible oceanographic information such as sea state.

Kahn, W. D.↗