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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Mobile Device Application for Monitoring Cyanobacteria Harmful Algal Blooms Using Sentinel-3 Satellite Ocean and Land Colour Instruments

Cyanobacterial harmful algal blooms (cyanoHAB) cause human and ecological health problems in lakes worldwide. The timely distribution of satellite-derived cyanoHAB data is necessary for adaptive water quality management and for targeted deployment of water quality monitoring resources. Software platforms that permit timely, useful, and cost-effective delivery of information from satellites are required to help managers respond to cyanoHABs. The Cyanobacteria Assessment Network (CyAN) mobile device application (app) uses data from the European Space Agency Copernicus Sentinel-3 satellite Ocean and Land Colour Instrument (OLCI) in near real-time to make initial water quality assessments and quickly alert managers to potential problems and emerging threats related to cyanobacteria. App functionality and satellite data were validated with 25 state health advisories issued in 2017. The CyAN app provides water quality managers with a user-friendly platform that reduces the complexities associated with accessing satellite data to allow fast, efficient, initial assessments across lakes.

Harmful Algal Bloom↗
NASA NTRSDate not supplied

Trends in Small Satellite Presentations from 2017-2019

As the small satellite community expands and new technologies emerge, it is important to understand and interpret these changes over time. In doing so, we observe progress and aid future development within the field. During the summer of 2020 we compiled for assessment purposes, archived presentation data for years 2017-2019 from three primary sources: the CubeSat Developers Workshop, Interplanetary Small Satellite Conference, and the Small Satellite Conference. A few examples of the information we recorded and compiled were presenter names and affiliations, presentation topic, and mission progress status. Ultimately, we reviewed roughly 600 presentations between the three conferences and the data obtained therein form the basis of our trend assessment. The paper focuses on trends interpreted through the assessment of key elements available in the content of each presentation to include: SmallSat mission developers, subsystem developments and the expanded scope for small satellite destinations. Data was generalized using various forms of analysis depending on the type of information being assessed. In the end, we achieved our goal of reducing the content to its key points and major takeaways from the conference proceedings. In this presentation, the observed trends in data and our findings will be discussed. First, we will cover changes in presentation topics by categorizing them as either: science, technology, science/technology, or other. Our next topic will be about the agencies and organizations at the forefront of small satellite research and development. The following section will explain trends in subsystem developments for telecommunications, propulsion, power, and thermal management. Further discussion will highlight how the scope of interplanetary spaceflight has expanded since 2017 as new small spacecraft missions venture beyond low-Earth orbit into deep space exploration. And finally, we will observe what information was lacking in archived presentations which included but not limited to: mission’s funding source, presentation focus area, and software used.

Small Satellite↗
NASA NTRS1995

(abstract) Satellite-Enhanced Personal Communications Experiments

As an initial step in exploring the opportunities afforded by the merger of satellite-based and land-based networks, Bellcore and JPL conducted several experiments utilizing NASA's Advanced Communications Technology Satellite (ACTS) and JPL's ACTS Mobile Terminal (AMT). Experimental goals fell into three categories: a) demonstrate personal communication applications, b) demonstrate interoperability among multiple wireless networks and the Public Switched Telecommunications Network (PSTN), and c) evaluate new protocol mechanisms for data communications using wireless links. We describe the performance of Point-of-Sale, e-mail, FAX, and call control applications, where the communication path passed through up to four networks: a wireless packet data network, the Satellite network, the PSTN, and a wireless cellular network. One important element of satellite-terrestrial interoperability is the efficiency of data communications protocols. Most protocols in use today (e.g., TCP/IP) have been optimized for wireline channels; their use over wireless networks presents significant new challenges. The characteristics of wireless channels -- increased error, longer packet delay, and limited bandwidth -- affect the design of the protocol. We describe experimental results for differing protocol mechanisms and parameters, such as acknowledgment schemes and packet sizes, that demonstrate the types of protocol needed for efficient use of wireless satellite-terrestrial networks.

personal↗
NASA NTRSDate not supplied

Geostationary Satellite Observations Over Global Environmental Monitoring Sites

Globally, there are now hundreds of ground-based environmental monitoring stations routinely collecting data on a variety of earth-atmosphere interactions. Such observations are also being augmented with data from orbiting satellites. With the beginning of the EOS-era, the MODIS subset around flux towers has been frequently used for validating ecosystem models developed at flux towers and upscaling the observed flux data to regional scales. However, MODIS on the polar-orbiting satellites can observe target regions only once a day, while the Fluxnet eddy- covariance data are compiled as sub-hourly. Therefore, summarizing the sub-hourly flux data into daily statistics is necessary for the comparison between MODIS and Flux data. The new generation geostationary satellite sensors (GOES-16/17 ABI and Himawari-8/9 AHI) have capabilities similar to MODIS but collect data at 5-15 minute intervals. These high-frequency observations allow us to understand and scale diurnal fluxes. Some studies have already shown the effective utilization of time series of geostationary satellite data for ecosystem modeling. We are producing NEX Level-1G products, which are gridded Top-of-Atmosphere reflectance and brightness temperature data from geostationary satellite sensors. We cut out the NEX Level-1G data using the same file format with the MODIS subset except for the projection. The other data products (e.g., surface reflectance, land surface temperature, vegetation indices, and climate data) will be added upon their availability. Currently included networks are Fluxnet, PhenoCam, and AERONET. The NEX subset data will be provided through NASA NEX data portal.

Geostationary Satellites↗
NASA NTRS2021

Chapter 6: Satellite Rainfall Estimation

The measurement of precipitation (rainfall and snowfall) across the globe is important for a variety of scientific and social applications. Knowledge of the occurrence and amount of precipitation, together with its distribution and changes are crucial for improving our understanding of the global energy and water cycle, as well as for monitoring water resource availability and for hydrological modelling to help alleviate flood and drought impacts. The use of conventional instruments (gauge or radar) to map global precipitation is essentially limited to land areas and thus satellite observations must be used to provide estimates of global precipitation. Many satellite sensors operating over the last 50 years have provided data for a range of techniques, algorithms and schemes developed to generate quantitative precipitation estimates. Current satellite-based precipitation products can provide estimates at up to 4 km every 30 minutes. This chapter outlines the basis of satellite precipitation estimation, the satellites and sensors used, and the range of techniques and schemes used to generate the precipitation products.

Earth observation↗
NASA NTRSDate not supplied

Trends in Small Satellite Presentations from 2017 - 2019

As the small satellite community expands and new technologies emerge, it is important to understand and interpret these changes over time. In doing so, we observe progress and aid future development within the field. During the summer of 2020 we compiled for assessment purposes, archived presentation data for years 2017-2019 from three primary sources: the CubeSat Developers Workshop, Interplanetary Small Satellite Conference, and the Small Satellite Conference. A few examples of the information we recorded and compiled were presenter names and affiliations, presentation topic, and mission progress status. Ultimately, we reviewed roughly 600 presentations between the three conferences and the data obtained therein form the basis of our trend assessment. The paper focuses on trends interpreted through the assessment of key elements available in the content of each presentation to include: SmallSat mission developers, subsystem developments and the expanded scope for small satellite destinations. Data was generalized using various forms of analysis depending on the type of information being assessed. In the end, we achieved our goal of reducing the content to its key points and major takeaways from the conference proceedings. In this presentation, the observed trends in data and our findings will be discussed. First, we will cover changes in presentation topics by categorizing them as either: science, technology, science/technology, or other. Our next topic will be about the agencies and organizations at the forefront of small satellite research and development. The following section will explain trends in subsystem developments for telecommunications, propulsion, power, and thermal management. Further discussion will highlight how the scope of interplanetary spaceflight has expanded since 2017 as new small spacecraft missions venture beyond low-Earth orbit into deep space exploration. And finally, we will observe what information was lacking in archived presentations which included but not limited to: mission’s funding source, presentation focus area, and software used.

Small Satellites↗
NASA NTRS2022

Using commercial high-resolution satellite imagery to monitor a nuisance macroalga in the largest marine protected area in the U.S.A.

Satellite imagery is a useful tool for monitoring and mapping the distribution of invasive or nuisance algal species on coral reefs over the temporal and spatial scales needed for ecosystem management. Visual inspections of high-resolution satellite imagery were used to detect the newly discovered nuisance alga, Chondria tumulosa , at Manawai (Pearl and Hermes Atoll) in combination with ground-truthing surveys. Low-albedo (“dark”) survey sites on spur habitats were associated with mean C. tumulosa cover seven times higher than adjacent high-albedo (“light”) sites. There was an inverse relationship between C. tumulosa percent cover at ground-truthing sites and mean reflectance values. Archival satellite imagery showed that areas of high C. tumulosa cover (i.e., dark patches) were not evident on or before 2015 on the northeast backreef. This case study is the first to apply satellite imagery to target a nuisance red macroalgal bloom on a coral reef. The ability to use satellites for the detection of nuisance or invasive benthic species, such as expansive mats of C. tumulosa , provides managers with a valuable tool, especially in remote regions.

Invasive↗
NASA NTRSDate not supplied

Machine Learning Application for Improving Cloud Detection and Phase Determination Over Sunglint Regions for Geostationary Satellites

Cloud detection and phase determination over sunglint regions has been a challenge, especially for geostationary (GEO) satellites. Sunglint is observed when the sunlight specular reflection is at the same viewing angle of the satellite sensor. This intense reflection in the visible channels (VIS) is often comparable to that from optically thick clouds. It also contaminates the shortwave infrared channels (SWIR). Consequently, VIS and SWIR channels become less useful - or not useful- when they are saturated, hampering the detection of cloudy and clear-sky pixels. Sunglint contamination happens frequently and exists nearly in every daytime GEO full disk satellite images. However, sunglint intensity and region are difficult to model due to variable viewing geometry and ocean surface conditions. Moreover, existing physical models do not meet the accuracy required for operational GEO satellite cloud detection. We developed a machine learning algorithm to improve cloud detection in sunglint conditions for the NASA Langley’s Satellite ClOud and radiation Property retrieval System (SatCORPS). This poster presents our recent progress in the algorithm development, validation and applications. The algorithm is validated using collocated SatCORPS GOES-East and GOES-West cloud products. We demonstrate that the machine learning cloud detection in sunglint regions is superior to the traditional approach by improving temporal consistency between sunglint and non-sunglint conditions.

Machine Learning, Cloud detection, Sunglint, SatCO↗
NASA NTRS1971

Examination of the anomalous behavior of three gravity gradient satellites

The anomalous oscillatory behavior of three satellites was examined. The satellites were all hinged, two-body, gravity gradient configurations passively stabilized about their three principal axes by gravity gradient and damper torques. Two basic behavior patterns were observed. Either the satellites were stable with attitude perturbations less than + or - 5 deg or their behavior tended towards a low frequency rigid body oscillation dominated by large yaw motions and in some cases by yaw inversions. A causal relationship between sun angle and the character of satellite behavior was observed which appears to indicate that thermal distortion is a critical factor in a gravity gradient satellite's dynamic behavior. The behavior appeared to be futher modified by the existence of response frequencies that were higher than anticipated values.

Goldman, R. L.↗
NASA NTRS1971

The Smithsonian Earth Physics Satellite (SEPS) definition study, volumes 1 through 4

A limited Phase B study was undertaken to determine the merit and feasibility of launching a proposed earth physics satellite with Apollo-type hardware. The study revealed that it would be feasible to launch this satellite using a S-IB stage, a S-IVB with restart capability, an instrument unit, a SLA for the satellite shroud, and a nose cone (AS-204 configuration). A definition of the proposed satellite is provided, which is specifically designed to satisfy the fundamental requirement of providing an orbiting benchmark of maximum accuracy. The satellite is a completely passive, solid 3628-kg sphere of 38.1-cm radius and very high mass-to-area ratio (7980 kg sq mi). In the suggested orbit of 55 degrees inclination, 3720 km altitude, and low eccentricity, the orbital lifetime is extremely long, so many decades of operation can be expected.

Source record↗
NASA NTRS1972

STADAN and data relay satellite simulation (emphasis on the scheduler)

A set of computer programs was developed which can be used to simulate the operation of NASA's Satellite Tracking and Data Acquisition Network (STADAN). The simulation consists of two major modules, a computerized algorithmic satellite scheduler (CASS) and a generalized evaluation model simulator (GEMS). CASS generates in-view time intervals of satellites over ground stations, and using these candidate passes, produces a schedule of service times for specific satellites to be serviced by specific ground stations in an attempt to fulfill certain inputted service requirements. GEMS than examines how well STADAN fulfills this schedule in terms of the availability and dependability of different (inputted) complements of equipment at the ground stations. The simulation was modified to allow for the introduction of one or more tracking and data relay satellites, which can serve as orbital receiving and command stations.

Kerne, B.↗
NASA NTRS1972

Future techniques for tracking of synchronous satellites

A tracking system error analysis computer program is reported to study the feasibility of using range sum and range-rate sum measurements through a synchronous satellite to a user satellite, and range sum and range-rate sum measurements through a synchronous satellite to a ground based transponder for tracking of synchronous satellites. Error analysis transformed noise, bias, ground station location and orbit uncertainties into expected uncertainties in each of the orbits after tracking. Results show that both of the proposed measurement methods are feasible for determining and refining the orbits of future synchronous satellites.

Cooley, J. L.↗
NASA NTRS1973

Saturn satellite encounter opportunities for Mariner Jupiter-Saturn 1977

The opportunities for close satellite encounters which meet the planetary constraints at Saturn that are imposed by science value return and environmental conditions are investigated. Since the satellites travel at various speeds in their orbits, Saturn arrival time is critical and was chosen as the design parameter. Arrival times are recommended which afford close satellite encounters and also meet important mission constraints. A design chart illustrates the satellite opportunities as a function of Saturn arrival date. Through the use of such a design chart, the Saturn encounter design process, which will take place according to recommendations by the selected science investigators over the next several years, will be considerably streamlined. Potential applications are given to illustrate the use of the Saturn satellite opportunity chart in encounter design.

Wallace, R. A.↗
NASA NTRS1972

Satellite networks for education.

Consideration of satellite-based educational networking. The characteristics and structure of networks are reviewed, and pressures within the educational establishment that are providing motivation for various types of networks are discussed. A number of studies are cited in which networking needs for educational sectors and services are defined. The current status of educational networking for educational radio and television, instructional television fixed services, inter- and intrastate educational communication networks, computer networks, cable television for education, and continuing and proposed educational experiments using NASA's Applications Technology Satellites is reviewed. Possible satellite-based educational telecommunication services and three alternatives for implementing educational satellite systems are described. Some remarks are made concerning public policy aspects of future educational satellite system development.

Singh, J. P.↗
NASA NTRS1973

Dynamic passivation of a spinning and tumbling satellite using free-flying teleoperators.

A satellite will generally have some initial angular motion. Before the satellite can be retrieved, it will be necessary to null its angular rates. A method is presented for nulling the simultaneous angular rates for cylindrical and near-cylindrical satellites. It is assumed that there are no external torques acting on the satellite initially. A model is being fabricated to verify the analysis. The analysis shows that it is feasible to null the spin and tumble rates for cylindrical and near-cylindrical satellites with an arm attached to a remote manipulator unit.

Faile, G. C.↗
NASA NTRS1973

Orbital design strategy for domestic communication satellite systems.

Review of some of the considerations pertinent to efficient orbit utilization in the design of domestic communications satellite systems. A strategy is developed to efficiently locate a heterogeneous system of satellites within the available arc and provide room for future growth. A practical design is illustrated, using a computer simulation model, for the placement of 25 satellites within 73% of the available arc employing frequency and polarization coordination techniques. A number of widely variable factors that influence satellite spacing are examined. These factors include such critical system elements as telephony and television interference noise limits, frequency plan coordination, polarization plan coordination, ground antenna diameter, signal protection ratio, and satellite station keeping.

Ramji, S.↗
NASA NTRS1974

Radiation pressure and air drag effects on the orbit of the balloon satellite 1963 30D

Computed orbits of the balloon satellite 1963 30D are given every 2 days over an interval of 456 days near the beginning of the satellite's lifetime and an interval of 824 days near the end of its lifetime. The effects of radiation pressure on the satellite are examined in some detail. It is found that the variations in all the elements can be represented by use of a single parameter to specify the effect of diffuse reflection from the satellite's surface, and that this parameter remains constant, or nearly so, during the entire 7-year lifetime. Success in obtaining a consistent representation of the radiation-pressure effects is ascribed to the inclusion of the effects of terrestrial radiation pressure, using a model for the earth's albedo that includes seasonal and latitudinal variations. Anomalous effects in the orbital acceleration, as well as in the other elements, are represented quite well by including a small force at right angle to the solar direction and by allowing this to rotate about the solar direction. This implies that the satellite is aspherical, that it is rotating, and that the axis of rotation precesses.

Slowey, J. W.↗
NASA NTRS1974

Contributions of satellite-determined gravity results in geodesy

Different forms of the theoretical gravity formula are summarized and methods of standardization of gravity anomalies obtained from satellite gravity and terrestrial gravity data are discussed in the context of three most commonly used reference figures, e.g., International Reference Ellipsoid, Reference Ellipsoid 1967, and Equilibrium Reference Ellipsoid. These methods are important in the comparison and combination of satellite gravity and gravimetric data as well as the integration of surface gravity data, collected with different objectives, in a single reference system. For ready reference, tables for such reductions are computed. Nature of the satellite gravity anomalies is examined to aid the geophysical and geodetic interpretation of these anomalies in terms of the tectonic features of the earth and the structure of the earth's crust and mantle. Computation of the Potsdam correction from satellite-determined geopotential is reviewed. The contribution of the satellite gravity results in decomposing the total observed gravity anomaly into components of geophysical interest is discussed. Recent work on the possible temporal variations in the geogravity field is briefly reviewed.

Khan, M. A.↗