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Results for “Geostationary satellites”

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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

A Satellite-Derived Upper-Tropospheric Water Vapor Transport Index for Climate Studies

A new approach is presented to quantify upper-level moisture transport from geostationary satellite data. Daily time sequences of GOES-7 water vapor imagery were used to produce estimates of winds and water vapor mixing ratio in the upper-troposphere sensed by the 6.7-microns water vapor channel. The winds and mixing ratio values were gridded and then combined to produce a parameter called the Water Vapor Transport Index (WVTI) which represents the magnitude of the two dimensional transport of water vapor in the upper troposphere. Daily grids of WVTI, meridional moisture transport, mixing ratio, pressure and other associated parameters were averaged to produce monthly fields for June, July and August of 1987 and 1988 over the Americas and surrounding oceanic regions. The WVTI was used to compare upper-tropospheric moisture transport between the summers of 1987 and 1988, contrasting the latter part of the 1986/87 El Nino event and the La Nina period of 1988. A similar product derived from the NCEP reanalysis was used to help validate the index and understand interannual variability of moisture transport from the modeling perspective. Both datasets showed large upper-level water vapor transport associated with synoptic features over the Americas and with outflow from tropical convective systems. Minimal transport occurred over tropical and subtropical high pressure regions where winds were light. Index values from NCEP were 2-3 times larger than that determined from the GOES satellite This difference resulted from an over estimate of the zonal winds and upper-tropospheric moisture in the reanalysis model. A comparison of the satellite-derived monthly values between the summers of 1987 and 1988 provided some insight into the impact of the ENSO event on upper-level moisture and its transport during the period. During July 1987, a large portion of the tropics in the eastern Pacific Ocean and Caribbean Sea was dominated by strong vapor transport in excess of 5 g/kg/ms with relatively small amounts in the other months. In contrast, JJA 1988 showed an opposite trend with July 1988 being less dominated by tropical water vapor transport. The meridional transport of upper-level water vapor indicated significant poleward transport from the tropics to the higher latitudes. This transport favored the Southern Hemisphere with large transport occurring south of the ITCZ which extended across the eastern Pacific and northern South America. Zonally-averaged monthly transport values were shown to provide a simple way to quantify the monthly and interannual changes in water vapor transport. Zonally-averaged WVTI values peaked in the Southern Hemisphere subtropics during both Austral winters. In the tropics a single more pronounced peak located over the equator and south latitudes occurred in 1988 as opposed to a dual peak in 1987. The second peak around 20 deg.N latitude is consistent with findings of others where upper-tropospheric winds were noted to be stronger in this region during warm ENSO events. Zonally-averaged meridional transport was southward for all summer months and stronger in 1988. The asymmetric nature of the zonally-averaged meridional transport (more southerly water vapor transport) was enhanced during JJA 1998 thus indicating a stronger upper-level branch of the Hadley circulation during this notable strong La Nina period.

Jedlovec, Gary J.↗
NASA NTRSDate not supplied

TPSAS-NF1676L-32467-DND

With the launch of a new generation of Geostationary satellites (GEO) such as Himawari and GOES-16 & 17, cloud detection using satellite imager data has been greatly enhanced with increased spectral bands, and higher temporal and spatial resolutions. A concern for all geostationary sensors, however, are changes in instrument sensitivity and algorithm performance at different viewing for daytime and nighttime. CALIPSO lidar observations provide a valuable reference for assessing these impacts as the satellite flies in a sun-synchronous orbit and crosses a wide range of GEO viewing angles each day. This paper will present the cloud mask results using the imager data from Himawari (AHI) and GOES-16&17 (ABI). The detection algorithms have been adapted from the Cloud and Earth’s Radiant Energy System (CERES) MODIS Edition 4 cloud mask, and adjusted and tuned to geo-satellites. They are used operationally for the CERES Time and Space Averaging (TISA) gridded cloud products and for near-real-time retrievals for weather and nowcasting applications.

Qing Z. Trepte↗
DOE OSTI2022

Deep Neural Network High Spatiotemporal Resolution Precipitation Estimation (Deep-STEP) Using Passive Microwave and Infrared Data

Recent developments in “headline-making” deep neural networks (DNNs), specifically convolutional neural networks (CNNs), along with advancements in computational power, open great opportunities to integrate massive amounts of real-time observations to characterize spatiotemporal structures of surface precipitation. This study aims to develop a CNN algorithm, named Deep Neural Network High Spatiotemporal Resolution Precipitation Estimation (Deep-STEP), that ingests direct satellite passive microwave (PMW) brightness temperatures (Tbs) at emission and scattering frequencies combined with infrared (IR) Tbs from geostationary satellites and surface information to automatically extract geospatial features related to the precipitable clouds. These features allow the end-to-end Deep-STEP algorithm to instantaneously map surface precipitation intensities with a spatial resolution of 4 km. The main advantages of Deep-STEP, as compared to current state-of-the-art techniques, are 1) it learns and estimates complex precipitation systems directly from raw measurements in near–real time, 2) it uses the automatic spatial neighborhood feature extraction approach, and 3) it fuses coarse-resolution PMW footprints with IR images to reliably retrieve surface precipitation at a high spatial resolution. We anticipate our proposed DNN algorithm to be a starting point for more sophisticated and efficient precipitation retrieval systems in terms of accuracy, fine spatial pattern detection skills, and computational costs.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1975

The plasma sheet boundary and Kp

The paper studies data obtained by the suprathermal ion detector aboard the ATS-1 geostationary satellite in order to establish a relation between the local time occurrence of the plasma sheet at the geostationary orbit (6.6 earth radii) and the Kp index. This relation is then used along with Alfven and Falthammer's (1963) equation for the drift path of an electron moving under the combined influence of a homogeneous electric field and a dipole magnetic field to derive an expression that shows the manner in which the inner boundary of the plasma sheet can be expected to vary radially with Kp along the midnight meridian for Kp less than about 4.

Freeman, J. W.↗
NASA NTRS1987

An expert system that performs a satellite station keepimg maneuver

The development and characteristics of a prototype expert system, Expert System for Satellite Orbit Control (ESSOC), capable of providing real-time spacecraft system analysis and command generation for a geostationary satellite are described. The ESSOC recommends appropriate commands that reflect both the changing spacecraft condition and previous procedural action. An internal knowledge base stores satellite status information and is updated with processed spacecraft telemetry. Procedural structure data are encoded in production rules. Structural methods of knowledge acquisition and the design and performance-enhancing techniques that enable ESSOC to operate in real time are also considered.

Linesbrowning, M. Kate↗
NASA NTRS1971

VHF ranging and position fixing experiment using ATS satellites: Executive summary of final report on phases 1 and 2, 25 November - 1 May 1971

The VHF transponders of the ATS-1 and ATS-3 geostationary satellites were used in ranging and position fixing experiments. An interrogation signal was transmitted from a ground terminal to ATS-3, which relayed it to the vehicle transponders. The vehicle that was addressed repeated the signal and its response was relayed back through both satellites to the ground terminal, where propagation times were measured; lines-of-position and fixes were computed. The 0.43 second tone-code ranging signal contained a single audio tone frequency. Ambiguity was resolved and user craft identified by a simple digital code. Seven vehicles were used in the test: three aircraft, two ships, an oceanographic buoy, and a truck. Ionospheric and multipath effects were studied. It is concluded that a VHF system could have an accuracy of + or - one nautical mile for ships and aircraft if calibration transponders are used to monitor the ionosphere.

Source record↗
NASA NTRS1995

Tropopause Structure as Revealed by the Satellite Water Vapor Channel During STRAT: The Relationship to Small and Mesoscale Structure as Shown in Aircraft Measurements

This paper examines the use of 6.5 micron geostationary satellite imagery during the Stratospheric Radiation And Transport (STRAT) field mission, the first pha:ie of which is during May, 1995. The 6.5 micron imagery is being us4!d to define the horizontal structure of areas where the tropopause is particularly low. Regions of high PV on, say, a 350K surface have been shown to coincide roughly with regions of enhanced radiance. These regions of enhanced 6.5 micron radiance coincide with dryness in the 5-10 km region, since the dryness enables radiation from lower (and warmer) levels to penetrate through the atmosphere into space. Such dryness is associated with downward penetrations of dry stratospheric, high potential vorticity air. We explore the extent to which such regions of high radiance are related to stratospheric intrusions into the troposphere as observed by aircraft data.

Pfister, Leonhard↗
NASA NTRS2014

Q-Band (37 to 41 GHz) Satellite Beacon Architecture for RF Propagation Experiments

In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37 to 41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cutparaboloidal reflector.

Simons, Rainee N.↗
NASA NTRS2012

Q-Band (37-41 GHz) Satellite Beacon Architecture for RF Propagation Experiments

In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37-41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cut-paraboloidal reflector.

Simmons, Rainee N.↗
NASA NTRSDate not supplied

Development of a Consistent GEOsat Cloud Property Dataset for the CERES Climate Data Record

Cloud properties are critical for understanding the Earth’s radiation budget and cloud feedbacks. At NASA Langley Research Center, the Satellite ClOud and Radiative Property retrieval System (SatCORPS) provides real-time and historical analyses of clouds derived from Geostationary satellite (GEOsat) data for weather and climate applications. For the Clouds and the Earth’s Radiant Energy System (CERES) program, the global constellation of GEOsats has been analyzed since 2000 to help characterize and account for the diurnal cycle of clouds and their radiative impacts in the CERES climate data record. Obtaining consistent cloud properties over the GEOsat data record during the CERES era is a major objective but a significant challenge considering the diversity of imaging capabilities deployed during that time. The GEOsat data analysis approach for the current CERES Edition-4 (Ed4) data products was focused on accuracy and consistency with MODIS by employing as much spectral information as possible from each satellite. However, the inconsistent use of spectral information across GEOsats led to marked discontinuities in the spatial and temporal record of cloud properties that had to be accounted for post facto in downstream CERES processing. This paper reports progress in developing a new GEOsat analysis system for the next CERES edition (Ed5) that has potential to improve cross-platform consistency and continuity. In this approach, the spectral channel complement is limited to just 3-channels during daytime, ~0.65 µm (VIS), ~3.9 µm (NIR), and ~10.8 µm (IR), common to nearly all of the satellites in the record. At night, a 2-channel approach is taken with the NIR and IR, and ~6.7 µm bands that includes a machine learning approach for optically thick cloud properties. A tradeoff is the potential for reduced accuracy particularly using data from the more advanced satellites that have more spectral channels (e.g. SEVIRI, AHI and ABI) that are known to help improve thin cirrus detection, cloud-aerosol discrimination and estimates in other difficult conditions that challenge cloud remote sensing. The new continuity approach is applied to one month of global GEOSat data for each year of the CERES record since 2000 and compared with the Ed4 GEO and MODIS cloud property time series in order to evaluate the level of improved consistency in the GEOsat record and to assess the accuracy impacts. Cloud fraction will also be assessed with CALIPSO data. Outstanding issues and challenges will be discussed. The results are expected to guide future work needed to develop a more robust GEOsat cloud data record for CERES.

CERES CDR↗
NASA NTRS1980

Geostationary platform systems concepts definition study. Volume 1: Executive summary

The results of a geostationary platform concept analysis are summarized. Mission and payloads definition, concept selection, the requirements of an experimental platform, supporting research and technology, and the Space Transportation System interface requirements are addressed. It is concluded that platforms represent a logical extension of current trends toward larger, more complex, multifrequency satellites. Geostationary platforms offer significant cost savings compared to individual satellites, with the majority of these economies being realized with single Shuttle launched platforms. Further cost savings can be realized, however, by having larger platforms. Platforms accommodating communications equipment that operates at multiple frequencies and which provide larger scale frequency reuse through the use of large aperture multibeam antennas and onboard switching maximize the useful capacity of the orbital arc and frequency spectrum. Projections of market demand indicate that such conservation measures are clearly essential if orderly growth is to be provided for. In addition, it is pointed out that a NASA experimental platform is required to demonstrate the technologies necessary for operational geostationary platforms of the 1990's.

Source record↗
NASA NTRS1979

Error analysis of a satellite interferometer navigation system

An error analysis is performed for a global positioning and navigation system which relies on an orthogonal array of interferometry baselines on board a geostationary satellite. The error analysis involves linearization of a mathematical model which is based on the relationship between the measured phase differences, the known transmitter positions, and other systematic error parameters. According to the error analysis, position accuracy is critically dependent on the baseline length and the magnitude of the random component of the measuring errors. It is shown that a satellite interferometry system with baselines of about 50 m can yield position accuracies on the order of 20 m.

Gopalapillai, G. S.↗
NASA NTRSDate not supplied

A Principal Component and Machine Learning Approach to Spatially Gap Fill Hyperspectral Ocean Color Satellite Retrievals

Retrievals of ocean color properties from space are important for monitoring the health of the ocean ecosystem but such retrievals tend to be limited in spatial coverage due to conditions such as clouds, aerosols, and sun glint. Gap filling of ocean color retrievals is typically performed by combining retrievals from multiple satellites or temporally averaging multiple days of retrievals but despite these techniques large gaps still exist posing challenges for near real time monitoring of events like harmful algae blooms. To address these limitations, we propose a spatial gap filling approach using machine learning to learn how to perform an atmospheric correction under challenging retrieval conditions. In this approach a principal component analysis is used to decompose the hyperspectral measurements into spectral features that describe the scattering and absorption of the atmosphere as well as the underlying surface. The coefficients of the principal components are then used to train a neural network to predict ocean color properties derived from a standard ocean color algorithm such as the MODIS atmospheric correction algorithm. This machine learning approach is independent of a priori information and does not rely on any radiative transfer modeling. We apply the approach to two hyperspectral UV/VIS instruments, the Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) to show that it can be used to estimate ocean color properties such as chlorophyll, remote sensing reflectance, and fluorescence line height. This method could be used as a gap-filling technique for the future Ocean Color Instrument (OCI) which will be onboard NASA's Plankton, Aerosol Cloud, ocean Ecosystem (PACE) ocean color satellite to provide additional information for monitoring the health of our global oceans. Additionally, it could be applied to the geostationary satellite Tropospheric Emissions: Monitoring of Pollution (TEMPO) to better understand diurnal variability in ocean ecology.

MODIS atmospheric correction algorithm↗
NASA NTRS1971

VLBI clock synchronization tests performed via the ATS-1 and ATS-3 satellites

Clock synchronization experiments were carried out May 10 to June 10, 1971, by the NASA/Goddard Space Flight Center and the Smithsonian Astrophysical Observatory via the ATS-1 and 3 geostationary satellites at the NASA tracking stations Rosman and Mojave, during a VLBI (Very Long Baseline Interferometer) experiment in order to determine the clock-offset between the two stations. Ten microsecond pulses at C-band with very sharp risetime were exchanged by the two stations through the dual transponders of the satellites. At each station, a time-interval counter was started by the transmitted pulse and stopped by the received pulse. The probable error of the difference in the mean values of the clock-offset is 10 nanoseconds.

Ramasastry, J.↗
NASA NTRS1974

Orbit-spectrum sharing between the fixed-satellite and broadcasting-satellite services with applications to 12 GHz domestic systems

A systematic, tutorial analysis of the general problem of orbit-spectrum sharing among inhomogeneous satellite system is presented. Emphasis is placed on extrapolating and applying the available data on rain attenuation and on reconciling differences in the results of various measurements of the subjective effects of interference on television picture quality. An analytic method is presented for determining the approximate values of the intersatellite spacings required to keep mutual interference levels within prescribed limits when many dissimilar satellites share the orbit. A computer model was developed for assessing the interference compatibility of arbitrary configurations of large numbers of geostationary satellite systems. It is concluded that the band from 11.7 c GHz can be shared effectively by broadcasting-satellite and fixed-satellite systems. Recommendations for future study are included.

Reinhart, E. E.↗
NASA NTRS1984

Navigation system and method

In a global positioning system (GPS), such as the NAVSTAR/GPS system, wherein the position coordinates of user terminals are obtained by processing multiple signals transmitted by a constellation of orbiting satellites, an acquisition-aiding signal generated by an earth-based control station is relayed to user terminals via a geostationary satellite to simplify user equipment. The aiding signal is FSK modulated on a reference channel slightly offset from the standard GPS channel. The aiding signal identifies satellites in view having best geometry and includes Doppler prediction data as well as GPS satellite coordinates and identification data associated with user terminals within an area being served by the control station and relay satellite. The aiding signal significantly reduces user equipment by simplifying spread spectrum signal demodulation and reducing data processing functions previously carried out at the user terminals.

Taylor, R. E.↗
NASA NTRS1987

Precipitation factors leading to arc cloud formation

The combined efforts of three graduate students and the principal investigator are presented. Satellite observations and interpretation have become increasingly important in the areas of weather research and operational forecasting. One reason is that geostationary satellite imagery is the only meteorological observing tool that can follow the evolution of clouds from the synoptic scale down to the cumulas scale. Therefore, it can depict atmospheric activity which is up to two orders of magnitude smaller than can be resolved by conventional meteorological observations. This unique ability of the satellite provides the meteorologist a mechanism to infer weather events down to the mesoscale. This evolution is the subject of this report.

Brundidge, Kenneth C.↗
NASA NTRS1990

An overview of results derived from mobile-satellite propagation experiments

During the period 1983-1988, a series of Land Mobile Satellite Service (LMSS) propagation experiments were performed. These experiments were implemented with transmitters on stratospheric balloons, remotely piloted aircraft, helicopters, and geostationary satellites. The earlier experiments were performed at UHF (870 mega-Hz) and the latter at both L band (1.5 giga-Hz) and UHF. The general objective of the above tests was to assess the impairment to propagation caused by trees and terrain for predominantly suburban and rural regions where cellular communication services are impractical. This paper presents an overview of the results derived from the above experiments.

Goldhirsh, Julius↗