Engineering topics

Argentiero, P.

Publications and source records attributed to Argentiero, P..

At least 19 records

NASA NTRS1982

An automated approach to the design of decision tree classifiers

An automated technique is presented for designing effective decision tree classifiers predicated only on a priori class statistics. The procedure relies on linear feature extractions and Bayes table look-up decision rules. Associated error matrices are computed and utilized to provide an optimal design of the decision tree at each so-called 'node'. A by-product of this procedure is a simple algorithm for computing the global probability of correct classification assuming the statistical independence of the decision rules. Attention is given to a more precise definition of decision tree classification, the mathematical details on the technique for automated decision tree design, and an example of a simple application of the procedure using class statistics acquired from an actual Landsat scene.

Argentiero, P.↗

NASA NTRS1981

An autonomous Nimbus Doppler positioning system

A single-pass Doppler positioning system was developed at the GSFC in support of the Nimbus-6 mission. The system was designed to satisfy the following requirements: compatibility with the PDP 11/70 minicomputer; single-pass recovery of up to 250 positions with a two-sigma accuracy of 5 km; high reliability with a minimum of human interaction; and near real-time responsiveness. The system consists of a numerical integrator which includes only the J2 term (earth flattening) of the earth's gravity field, an editing routine, a first guess algorithm, a least squares position recovery program, and a routine for generating a 95% confidence circle based on a computer covariance matrix. An analysis and quantification of the following error sources that limit system accuracy are presented: orbit error, radial aliasing, computational difficulties with overhead passes, oscillator drift, and ambiguity problems. Results of system reliability tests and sample outputs are included.

Garza-Robles, R.↗

NASA NTRS1980

On extracting brightness temperature maps from scanning radiometer data

The extraction of brightness temperature maps from scanning radiometer data is described as a typical linear inverse problem. Spatial quantization and parameter estimation is described and is suggested as an advantageous approach to a solution. Since this approach takes into explicit account the multivariate nature of the problem, it permits an accurate determination of the most detailed resolution extractable from the data as well as explicitly defining the possible compromises between accuracy and resolution. To illustrate the usefulness of the method described for algorithm design and accuracy prediction, it was applied to the problem of providing brightness temperature maps during the NOSS flight segment. The most detained possible resolution was determined and a curve which displays the possible compromises between accuracy and resolution was provided.

Argentiero, P.↗

NASA NTRS1980

An automated approach to the design of decision tree classifiers

The classification of large dimensional data sets arising from the merging of remote sensing data with more traditional forms of ancillary data is considered. Decision tree classification, a popular approach to the problem, is characterized by the property that samples are subjected to a sequence of decision rules before they are assigned to a unique class. An automated technique for effective decision tree design which relies only on apriori statistics is presented. This procedure utilizes a set of two dimensional canonical transforms and Bayes table look-up decision rules. An optimal design at each node is derived based on the associated decision table. A procedure for computing the global probability of correct classfication is also provided. An example is given in which class statistics obtained from an actual LANDSAT scene are used as input to the program. The resulting decision tree design has an associated probability of correct classification of .76 compared to the theoretically optimum .79 probability of correct classification associated with a full dimensional Bayes classifier. Recommendations for future research are included.

Argentiero, P.↗

NASA NTRS1979

Results of GEOS 3/ATS 6 satellite-to-satellite tracking orbit determination experiment

The purpose of the Geos 3/ATS 6 satellite-to-satellite tracking experiment was to develop, test, and evaluate methods of deriving orbit estimates from satellite-to-satellite tracking data. The results of the form of conventional orbit overlap tests, and a comparison of a Geos 3 orbit estimate obtained from satellite-to-satellite (SST) tracking data with an orbit estimate derived form C-band data. The method recommeded for estimating orbits from SST data is a Bayesian least squares procedure utilizing independent ranging to the relay satellite.

Argentiero, P.↗

NASA NTRS1979

Ambiguity resolution for satellite Doppler positioning systems

The implementation of satellite-based Doppler positioning systems frequently requires the recovery of transmitter position from a single pass of Doppler data. The least-squares approach to the problem yields conjugate solutions on either side of the satellite subtrack. It is important to develop a procedure for choosing the proper solution which is correct in a high percentage of cases. A test for ambiguity resolution which is the most powerful in the sense that it maximizes the probability of a correct decision is derived. When systematic error sources are properly included in the least-squares reduction process to yield an optimal solution the test reduces to choosing the solution which provides the smaller valuation of the least-squares loss function. When systematic error sources are ignored in the least-squares reduction, the most powerful test is a quadratic form comparison with the weighting matrix of the quadratic form obtained by computing the pseudoinverse of a reduced-rank square matrix. A formula for computing the power of the most powerful test is provided. Numerical examples are included in which the power of the test is computed for situations that are relevant to the design of a satellite-aided search and rescue system.

Argentiero, P.↗

NASA NTRS1978

A comparison of satellite systems for gravity field measurements

A detailed and accurate earth gravity field model is important both to geophysical progress and to the precise tracking necessary for interpretation of geophysical experiments. Various satellite techniques which may be used to determine the earth's gravity field are compared and their ability to recover the long wavelength and short wavelength features of the field are described. A high-low configuration satellite-to-satellite tracking mission is recommended for the determination of the long wavelength portion of the gravity field. Satellite altimetry and satellite gradiometry experiments are recommended for determination of the short wavelength portion of the gravity field.

Argentiero, P.↗

NASA NTRS1977

Efficient estimation algorithms for a satellite-aided search and rescue mission

It has been suggested to establish a search and rescue orbiting satellite system as a means for locating distress signals from downed aircraft, small boats, and overland expeditions. Emissions from Emergency Locator Transmitters (ELT), now available in most U.S. aircraft are to be utilized in the positioning procedure. A description is presented of a set of Doppler navigation algorithms for extracting ELT position coordinates from Doppler data. The algorithms have been programmed for a small computing machine and the resulting system has successfully processed both real and simulated Doppler data. A software system for solving the Doppler navigation problem must include an orbit propagator, a first guess algorithm, and an algorithm for estimating longitude and latitude from Doppler data. Each of these components is considered.

Argentiero, P.↗

NASA NTRS1977

Interpolation schemes for orbit determination with the global positioning system

This paper demonstrates that the Global Positioning System (GPS) and simple interpolation schemes can be utilized to satisfy typical orbit determination demands of applications satellites. The complete GPS consists of 24 satellites and permits a position fix of a user satellite at any arbitrary instant. The interpolation formulae used in this report fit generalized Keplerian orbits through a number of position fixes. For a given accuracy level the telemetry requirements as measured by the time intervals between position fixes and the computational load of an interpolation as measured by the number of points through which a generalized Keplerian orbit is fitted vary inversely. A set of possible compromises between these two factors is presented. The Phase I GPS consists of 6 satellites and permits a position fix of a user satellite just 36% of the time. It is shown that with this system more sophisticated interpolation schemes which model atmospheric drag and higher degree terms of the earth's gravity field must be employed to obtain accurate orbits.

Argentiero, P.↗

NASA NTRS1977

Orbit determination with the tracking data relay satellite system

The possibility of employing the tracking data relay satellite system to satisfy the orbit determination demands of future applications missions is investigated. It is shown that when the relay satellites are continuously and independently tracked from ground stations it is possible, using six hour data arcs, to recover user satellite state with an average error of about 25 m radially, 260 m along track, and 20 m cross track. For this arc length, range sum data and range sum rate data are equally useful in determining orbits. For shorter arc lengths (20 min), range sum rate data is more useful than range sum data. When relay satellites are not continuously tracked, user satellite state can be recovered with an average error of about 140 m radially, 515 m along track, and 110 m cross track. These results indicate that the TDRS system can be employed to satisfy the orbit determination demands of applications missions, such as the MAGSAT and potential gradiometer missions, provided the relay satellites are continuously and independently tracked.

Argentiero, P.↗

NASA NTRS1977

On estimating gravity anomalies - A comparison of least squares collocation with conventional least squares techniques

The least squares collocation algorithm for estimating gravity anomalies from geodetic data is shown to be an application of the well known regression equations which provide the mean and covariance of a random vector (gravity anomalies) given a realization of a correlated random vector (geodetic data). It is also shown that the collocation solution for gravity anomalies is equivalent to the conventional least-squares-Stokes' function solution when the conventional solution utilizes properly weighted zero a priori estimates. The mathematical and physical assumptions underlying the least squares collocation estimator are described.

Argentiero, P.↗

NASA NTRS1976

A spacecraft-borne gradiometer mission analysis

Numerical simulations were performed to obtain the orbit- and attitude-determination requirements of a spacecraft-borne gradiometer mission. Results demonstrated that position determination of 300 meters in the along-track and cross-track directions and 50 meters in the radial direction are mission requirements. The optimal orientation of the gradiometer sensing plane is achieved when the spin vector elevation is 0 degrees. The attitude-determination requirements are 5 degrees resolution for spin-vector azimuth and 0.2 degree resolution for spin-vector elevation. When these requirements are met, 3-degree gravity anomalies can be recovered globally with an accuracy of 0.025/mm/sq s (2.5 mgals). The Appendix documents the mathematical procedures for estimating detailed gravity fields from gradiometer data.

Argentiero, P.↗

NASA NTRS1976

On estimating gravity anomalies from gradiometer data

The Gravsat-gradiometer mission involves flying a gradiometer on a gravity satellite (Gravsat) which is in a low, polar, and circular orbit. Results are presented of a numerical simulation of the mission which demonstrates that, if the satellite is in a 250-km orbit, 3- and 5-degree gravity anomalies may be estimated with accuracies of 0.03 and 0.01 mm/square second (3 and 1 mgal), respectively. At an altitude of 350 km, the results are 0.07 and 0.025 mm.square second (7 and 2.5 mgal), respectively. These results assume a rotating type gradiometer with a 0.1 -etvos unit accuracy. The results can readily be scaled to reflect another accuracy level.

Argentiero, P.↗

NASA NTRS1976

Strategies for estimating the marine geoid from altimeter data

Altimeter data from a spacecraft borne altimeter was processed to estimate the fine structure of the marine geoid. Simulation studies show that, among several competing parameterizations, the mean free air gravity anomaly model exhibited promising geoid recovery characteristics. Using covariance analysis techniques, quantitative measures of the orthogonality properties are investigated.

Argentiero, P.↗

NASA NTRS1976

On estimating gravity anomalies: A comparison of least squares collocation with least squares techniques

Argentiero, P.↗

NASA NTRS1975

Applications of satellite technology to gravity field determination

Various techniques for using satellite technology to determine the earth's gravity field are analyzed and compared. A high-low configuration satellite to satellite tracking mission is recommended for the determination of the long wavelength portion of the gravity field. Satellite altimetry and satellite gradiometry experiments are recommended for determination of the short wavelength portion of the gravity field. The recently developed least squares collocation method for estimating the gravity field from satellite derived data is analyzed and its equivalence to conventional methods is demonstrated.

Argentiero, P.↗

NASA NTRS1975

GEOS-C orbit determination with Satellite to Satellite Tracking

This report studies the feasibility of employing satellite to satellite tracking in lieu of ground based tracking to satisfy the orbit determination requirements of the GEOS-C mission. It is shown that with proper estimation procedures it is possible to obtain from Satellite to Satellite Tracking data a GEOS-C orbit whose altitude error averages about 1 meter. The usefulness of this data type for geopotential recovery is also indicated.

Argentiero, P.↗

NASA NTRS1975

Applications of satellite-to-satellite tracking to orbit determination and geopotential recovery

Recent simulations have demonstrated the applicability of satellite-to-satellite tracking data to the related problems of orbit determination and geopotential recovery. Specifically, satellite-to-satellite tracking between an earth orbiting satellite and a satellite at geosynchronous altitude (36000 km) produces long continuous data arcs which are not available by means of ground-based tracking. This facility, in conjunction with correct estimation techniques, yields exceptional orbit determination accuracy. The data type also has considerable applicability to geopotential determination when the low satellite has a high inclination.

Argentiero, P.↗