Engineering topics

Bilitza, D.

Publications and source records attributed to Bilitza, D..

At least 37 records · Page 2

NASA NTRS2004

A Correction for the IRI Topside Electron Density Model Based on Alouette/ISIS Topside Sounder Data

The topside segment of the International Reference Ionosphere (IRI) electron density model (and also of the Bent model) is based on the limited amount of topside data available at the time (40,OOO Alouette 1 profiles). Being established from such a small database it is therefore not surprising that the models have well-known shortcomings, for example, at high solar activities. Meanwhile a large data base of close to 200,000 topside profiles from Alouette 1,2, and ISIS I, 2 has become available online. A program of automated scaling and inversion of a large volume of digitized ionograms adds continuously to this data pool. We have used the currently available ISIs/Alouette topside profiles to evaluate the IRI topside model and to investigate ways of improving the model. The IRI model performs generally well at middle latitudes and shows discrepancies at low and high latitudes and these discrepancies are largest during high solar activity. In the upper topside IRI consistently overestimates the measurements. Based on averages of the data-model ratios we have established correction factors for the IRI model. These factors vary with altitude, modified dip latitude, and local time.

Bilitza, D.↗

NASA NTRS2000

International Reference Ionosphere (IRI): Task Force Activity 2000

The annual IRI Task Force Activity was held at the Abdus Salam International Center for Theoretical Physics in Trieste, Italy from July 10 to July 14. The participants included J. Adeniyi (University of Ilorin, Nigeria), D. Bilitza (NSSDC/RITSS, USA), D. Buresova (Institute of Atmospheric Physics, Czech Republic), B. Forte (ICTP, Italy), R. Leitinger (University of Graz, Austria), B. Nava (ICTP, Italy), M. Mosert (University National Tucuman, Argentina), S. Pulinets (IZMIRAN, Russia), S. Radicella (ICTP, Italy), and B. Reinisch (University of Mass. Lowell, USA). The main topic of this Task Force Activity was the modeling of the topside ionosphere and the development of strategies for modeling of ionospheric variability. Each day during the workshop week the team debated a specific modeling problem in the morning during informal presentations and round table discussions of all participants. Ways of resolving the specific modeling problem were devised and tested in the afternoon in front of the computers of the ICTP Aeronomy and Radiopropagation Laboratory using ICTP s computer networks and internet access.

Bilitza, D.↗

NASA NTRS1997

Improved IRI Predictions for the GEOSAT Time Period

Single-frequency altimeter measurements require an estimate of the signal retardation effect in the ionosphere. Ionospheric models like the International Reference Ionosphere (IRI) are being used to obtain these correction factors. Incorporation of worldwide ionosonde measurements is discussed as a way towards more accurate predictions. Using measurements of the F peak critical frequency (foF2) from more than 70 ionosondes Ac have derived (hour and month dependent) regional and global ionospheric-effective solar indices. Replacing the solar index in IRI with these new indices we could improve the IRI estimates for the GEOSAT time period (1986-1989) by a few percent.

Bilitza, D.↗

NASA NTRS1995

IRI: An international Rawer initiative

This paper was presented during the special session that was held at the 1993 International Reference Ionosphere (IRI) Workshop in honor of Karl Rawer's 80th birthday. It retraces the steps that led from the start of the IRI project to the present edition of the model highlighting the important role that the honoree played in guiding IRI from infancy to maturity. All summary view graphs are reproduced at the end of the article.

Bilitza, D.↗

NASA NTRS1995

Using IRI for the computation of ionospheric corrections for altimeter data analysis

Measurements by single-frequency satellite altimeter (Geosat, ERS-1) require a ionospheric correction to account for the signal time delay in the ionosphere. We propose using the International Reference Ionosphere (IRI) for the determination of this time delay. To investigate the effectiveness of an IRI correction, we have compared the IRI values with ionospheric corrections deduce from measurements by the dual-frequency Topex altimeter. By measuring at two frequencies, the Topex instrument can record (and thus eliminate) the ionospheric influence. We find that IRI agrees with the Topex data much better than the model that is currently used in Geosat data analysis. In particular the earlier model does not represent the equatorial double-peak (equator anomaly) clearly seen in the Topex data. Overall, the use of IRI results in a 30% improvement (over the older model) in the accuracy of ionospheric corrections computed for the first year of the Topex mission.

Bilitza, D.↗

NASA NTRS1995

The High Latitudes in the International Reference Ionosphere; Meeting C4 of Commission C, COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994

An international conference on high-latitude ionospheric modeling produced 27 papers in the areas of ionospheric mapping, electron density and distribution, ion density and distribution, ionospheric storems, ionospheric composition, and ionospheric sounding techniques. Upgrades to the International Reference Ionosphere (IRI) model were proposed in several papers.

Rawer, K.↗

NASA NTRS1993

International Reference Ionosphere: Past, present, and future. I - Electron density. II - Plasma temperatures, ion composition and ion drift

The most important investigations leading to the International Reference Ionosphere 1990 (IRI-90) are overviewed, and the latest version of the model is described. The shortcomings and limitations of the IRI-90 are pointed out, together with the ways of overcoming them. The list of studies that the IRI group has yet to carry out includes the investigations of magnetic storm effects as the highest priority. This paper discusses determinations of and the available data on the electron density, plasma temperatures, ion composition, and ion drift in the ionosphere, together with future improvements needed on these parameters.

Bilitza, D.↗

NASA NTRS1992

Solar-terrestrial models and application software

The empirical models related to solar-terrestrial sciences are listed and described which are available in the form of computer programs. Also included are programs that use one or more of these models for application specific purposes. The entries are grouped according to the region of their solar-terrestrial environment to which they belong and according to the parameter which they describe. Regions considered include the ionosphere, atmosphere, magnetosphere, planets, interplanetary space, and heliosphere. Also provided is the information on the accessibility for solar-terrestrial models to specify the magnetic and solar activity conditions.

Bilitza, D.↗

NASA NTRS1991

Solar-terrestrial models at the National Space Science Data Center

The National Space Science Data Center (NSSDC) and World Data Center A for Rockets and Satellites (WDC-A-R&S) has a long record of participation in the worldwide efforts to establish and improve empirical models for the different regions of the solar-terrestrial environment. The center maintains a unique archive of solar-terrestrial models and related applications software, described in a recently published models catalog. The software packages are distributed on tape, diskette, and on-line on the Space Physics Analysis Network (SPAN). Four of the most frequently requested models (IRI, MSIS/CIRA, IGRF, AE-8/AP-8) can also be accessed and run on the NSSDC Online Documentation and Information Service (NODIS) account, which can be reached from any SPAN node.

Bilitza, D.↗

NASA NTRS1990

International Reference Ionosphere: Plasma densities - Status 1988

An account is given of the changes proposed in 1988 for the International Reference Ionosphere electron density profile, as well as the status of their implementation. The fully analytical profile function under development for the entire ionosphere can be achieved with a linear combination of several LAY functions. Although four LAY functions are required to describe the density features of the middle ionosphere, three LAY functions suffice to reproduce electron densities in both the topside ionosphere and lower ionosphere. Attention is given to the way in which the LAY parameters are computationally derivable from characteristic profile points.

Rawer, K.↗

NASA NTRS1990

Solar activity variation of ionospheric plasma temperatures

The present status of understanding and modeling of the variation of electron and ion temperatures with solar activity is reviewed. All atmospheric and ionospheric densities and temperatures are positively correlated with solar activity except the electron temperature, which exhibits a rather complex variation pattern during a solar cycle. The ion temperature at low altitudes closely follows the variation patterns of the neutral temperature. The electron temperature at high altitudes increases with increasing solar activity; the increase is larger during day than during night and exhibits a latitudinal variation. At low altitudes during daytime, tha amplitude of the seasonal variation of the electron temperature increases toward the solar maximum. At 400 km during daytime, the summer electron temperatures for Millstone Hill increase slightly toward higher solar activities, whereas the winter temperatures decrease distinctly. For Arecibo, an opposite trend is noticeable.

Bilitza, D.↗

NASA NTRS1990

N(h) profile data at World Data Centers

The data base for ionospheric electron density profiles at the World Data Centers is assessed. Past and future N(h) profiling from ionograms and profiles from incoherent scatter radar measurements are considered.

Allen, J. H.↗

NASA NTRS1990

The NSSDC trapped radiation model facility

The National Space Science Data Center (NSSDC) trapped radiation models calculate the integral and differential electron and proton flux for given values of the particle energy E, drift shell parameter L, and magnetic field strength B for either solar maximum or solar minimum. The most recent versions of the series of models, which have been developed and continuously improved over several decades by Dr. James Vette and coworkers at NSSDC, are AE-8 for electrons and AP-8 for protons. The present status of the NSSDC trapped particle models is discussed. The limits of validity of the models are described.

Gaffey, John D., Jr.↗

NASA NTRS1989

Electron density profile description in the international reference ionosphere

Problems encountered during efforts to reformulate the IRI description of the electron density profile are examined. Consideration is given to Booker's (1979) proposal that the unique, analytic profile functions should cover the entire ionospheric height range. The IRI topside model is reviewed and the electron density profile of the middle and lower ionosphere are discussed. Rawer's (1983) procedure for combining the topside, middle, and lower ionospheric profiles into one analytic profile is reviewed.

Rawer, K.↗

NASA NTRS1989

Trapped particle flux models at NSSDC/WDC-A-R/S

The data needed in the future for trapped particle modeling are summarized. A short summary of past and future modeling activities and a list of satellite data that have not yet been considered in the modeling efforts is included.

Bilitza, D.↗

NASA NTRS1988

Study of ionospheric models for satellite orbit determination

Means of improving the accuracy of the ionospheric correction of two empirical ionospheric models, the Bent (Schmid et al. 1973) and international reference ionosphere (IRI) models, have been evaluated. An improved IRI topside formula is found to minimize the tendency for the electron density profile to decrease too sharply with increasing altitude, and is shown to produce results which compare well with satellite data and ground-based incoherent scatter measurements. A model for the effective parabolic thickness is proposed for the bottomside. Comparison with results from a Meteosat tracking exercise demonstrates that the present changes improve the overall accuracy of ionospheric delays calculated using the two models.

Bilitza, D.↗

NASA NTRS1988

National Space Science Data Center and World Data Center A for Rockets and Satellites - Ionospheric data holdings and services

The activities and services of the National Space Science data Center (NSSDC) and the World Data Center A for Rockets and Satellites (WDC-A-R and S) are described with special emphasis on ionospheric physics. The present catalog/archive system is explained and future developments are indicated. In addition to the basic data acquisition, archiving, and dissemination functions, ongoing activities include the Central Online Data Directory (CODD), the Coordinated Data Analysis Workshopps (CDAW), the Space Physics Analysis Network (SPAN), advanced data management systems (CD/DIS, NCDS, PLDS), and publication of the NSSDC News, the SPACEWARN Bulletin, and several NSSD reports.

Bilitza, D.↗

NASA NTRS1988

Evaluation of the international reference ionosphere with the large AE-C and DE2 data bases

Empirical models such as the International Reference Ionosphere (IRI) are synthesized from large data bases. They can be viewed as analytical tools to facilitate accessing information stored in the data banks. However, in establishing the models, one has to apply smoothing and averaging procedures that in effect reduce the original information content. This study evaluates the agreement between the data base and the model at two opposite extremes of time resolution. Electron densities and temperatures in the altitude range of 300 to 400 km predicted by the IRI and measured by the AE-C and DE 2 satellites on the level of individual orbits as well as on the level of mission averages are compared. Whereas the averages show excellent agreement, the comparison for individual measurements indicates the limitations of empirical models.

Bilitza, D.↗