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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Lifecycle of updrafts and mass flux in isolated deep convection over the Amazon rainforest: insights from cell tracking

Long-term observations of deep convective cloud (DCC) vertical velocity and mass flux were collected during the Observations and Modelling of the Green Ocean Amazon (GoAmazon2014/5) experiment. Precipitation echoes from a surveillance weather radar near Manaus, Brazil, are tracked to identify and evaluate the isolated DCC lifecycle evolution during the dry and wet seasons. A radar wind profiler (RWP) provides precipitation and air motion profiles to estimate the vertical velocity, mass flux, and mass transport rates within overpassing DCC cores as a function of the tracked cell lifecycle stage. The average radar reflectivity factor (Z), DCC area (A), and surface rainfall rate (R) increased with DCC lifetime as convective cells were developing, reached a peak as the cells matured, and decreased thereafter as cells dissipated. As the convective cells mature, cumulative DCC properties exhibit stronger updraft behaviors with higher upward mass flux and transport rates above the melting layer (compared with initial and later lifecycle stages). In comparison, developing DCCs have the lowest Z associated with weak updrafts, as well as negative mass flux and transport rates above the melting layer. Over the DCC lifetime, the height of the maximum downward mass flux decreased, whereas the height of the maximum net mass flux increased. During the dry season, the tracked DCCs had higher Z, propagation speed, and DCC area, and were more isolated spatially compared with the wet season. Dry season DCCs exhibit higher Z, mass flux, and mass transport rate while developing, whereas wet season DCCs exhibit higher Z, mass flux, and mass transport rates at later stages.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

tobac v1.5: introducing fast 3D tracking, splits and mergers, and other enhancements for identifying and analysing meteorological phenomena

There is a continuously increasing need for reliable feature detection and tracking tools based on objective analysis principles for use with meteorological data. Many tools have been developed over the previous 2 decades that attempt to address this need but most have limitations on the type of data they can be used with, feature computational and/or memory expenses that make them unwieldy with larger datasets, or require some form of data reduction prior to use that limits the tool's utility. The Tracking and Object-Based Analysis of Clouds (tobac) Python package is a modular, open-source tool that improves on the overall generality and utility of past tools. A number of scientific improvements (three spatial dimensions, splits and mergers of features, an internal spectral filtering tool) and procedural enhancements (increased computational efficiency, internal regridding of data, and treatments for periodic boundary conditions) have been included in tobac as a part of the tobac v1.5 update. These improvements have made tobac one of the most robust, powerful, and flexible identification and tracking tools in our field to date and expand its potential use in other fields. Future plans for tobac v2 are also discussed.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

C-SAPR2 Convective Cell Tracking Database during CACTI

The convective cell tracking database V1 using the ARM CSAPR2 radar data set at the Sierras de Córdoba (COR) AMF site in Argentina consists of individually tracked convective cells during the entire CACTI field campaign from 15 October 2018 to 3 March 2019. The cell tracking database is produced by applying an updated version of the FLEXible object TRaKeR (FLEXTRKR) (Feng et al. 2022) to the Cartesian gridded CSAPR2 PPI data set produced by the Taranis radar processing package (Hardin et al. 2020).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1960

Tracking and Orbit-Determination Program of the Jet Propulsion Laboratory

The lunar-probe tracking program at the Jet Propulsion Laboratory has two prime objectives: (1) provide real-time predictions of the direction of the probe from various observation stations; (2) establish a reliable trajectory corresponding to the actual flight path of the probe. The tracking program, although developed for use with lunar probes, can be used for interplanetary probes if certain modifications are made. The program, as developed for the IBM 704 digital computer, has two distinct phases. First, the equations of motion and the variational equations are integrated to each observation time where the elements of the equation A (sub u) equals b [linearization of the maximum likelihood equations] are computed. The second phase is concerned with the solution of a specified subset of A (sub u) equals b. Flexibility and ease of operation have been major objectives in writing the 704 program. The number of data points and tracking stations that may be used is limited only by computing time and core storage. Input formats and operating instructions are presented for utilizing the various computational options available in the program.

Carr, Russell E.↗
NASA NTRS1962

Analysis of the Range and Range Rate Tracking System

The "range and range rate"' (r(sub i) + r(sub i)) system in its very simplest form is described. In particular, the errors in position and velocity are treated using pessimistic values of the measured quantities r(sub i) and r(sub i). Thus, a realistic evaluation of tracking qualities can be made for different orbits over certain tracking stations. The range and range rate system briefly described in this paper is a high-precision tracking system. Knowledge of the uncertainty in position δ(sub xi) is important, but knowledge of the uncertainty of the velocity vector δ(sub xi) is of the utmost importance. Thus the use of coherent Doppler measurements to determine the velocity has a great advantage over any pulsed system and, in addition, permits extremely narrow frequency bandwidths (in the order of 10 to 100 cps) to be employed, reducing the power requirements considerably. The basis for using range r(sub i) and range rate r(sub i) only is the fact that r(sub i) and r(sub i) can be measured to very high precision, thus furnishing r and r with low errors. The nature of these errors is discussed.

Vonbun, F. O.↗
NASA NTRS1971

The accuracy of laser tracking

A brief discussion of the actual laser tracking performance of geodetic satellites is followed by a discussion of the errors inherent in the laser system. An estimate is made of the capability expected within the next few years for the tracking of a heliocentric probe. The GEOS 1, GRARR, and GEOS 2 systems are considered. Errors in the tracking of a heliocentric probe are noted. These include errors due to the earth's atmosphere, (beam bending, atmospheric absorption, atmospheric turbulence, and atmospheric distortion of short laser pulses), and errors due to coronal effects.

Blamont, J. E.↗
NASA NTRS1972

A Markov chain technique for determining the acquisition behavior of a digital tracking loop

An iterative procedure is presented for determining the acquisition behavior of discrete or digital implementations of a tracking loop. The technique is based on the theory of Markov chains and provides the cumulative probability of acquisition in the loop as a function of time in the presence of noise and a given set of initial condition probabilities. A digital second-order tracking loop to be used in the Viking command receiver for continuous tracking of the command subcarrier phase was analyzed using this technique, and the results agree closely with experimental data.

Chadwick, H. D.↗
NASA NTRS1970

GEOS satellite tracking corrections for refraction in the ionosphere

The analytic formulations at different elevation angles and at a frequency of 2-GHz for the ionospheric refraction corrections used on the GEOS satellite tracking data are compared. The formulas and ray trace results for elevations greater than 10 deg, where most satellite tracking is done, differ in elevation, range, and range rate by less than 0.4 millidegrees (1.4 arc-seconds), 12 meters, and 12 cm/sec, respectively. In comparison to most operational requirements, this is insignificant. However, for the GEOS Observation Systems Intercomparison Investigation, these differences are equivalent in size to observed differences in system biases for some of the best electronic geodetic tracking systems and are probably contributing to the observed biases. The ray trace results and most of the more detailed analytic correction formulas show that the ionospheric refraction correction for range rate on an overhead pass is a maximum for elevation angles between 15 deg and 30 deg and falls off rapidly for both higher and lower elevation angles, contrary to the effect of the troposphere and to some reports in the literature.

Berbert, J. H.↗
NASA NTRS1969

Tracking system study

A digital computer program was generated which mathematically describes an optimal estimator-controller technique as applied to the control of antenna tracking systems used by NASA. Simulation studies utilizing this program were conducted using the IBM 360/91 computer. The basic ideas of applying optimal estimator-controller techniques to antenna tracking systems are discussed. A survey of existing tracking methods is given along with shortcomings and inherent errors. It is explained how these errors can be considerably reduced if optimal estimation and control are used. The modified programs generated in this project are described and the simulation results are summarized. The new algorithms for direct synthesis and stabilization of the systems including nonlinearities, are presented.

Dennis, A. R.↗
NASA NTRS1972

Satellite height determination using satellite-to-satellite tracking and ground laser systems

The height of the GEOS-C spacecraft was utilized as measured by the onboard radar altimeter, for an improved determination of the earth's gravitational field and for the determination of the variation of the physical surface of the oceans. Two tracking system approaches to accurately determine the spacecraft height (orbit) are described and their results stated. These are satellite-to-satellite tracking (SST) and ground laser tracking (GLT). Height variations can be observed in the dm-regions using SST and in the m-region using present GLT.

Vonbun, F. O.↗
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 NTRS1972

Human operator dynamics for aural compensatory tracking

The human operator's ability to control using aural information only and using combined aural and visual displays was investigated for a simple tracking task. Tracking error was presented to the test subjects using one- and two-ear displays. For both displays the pitch of the tone represented the magnitude of the tracking error. The operator's aural control characteristics were modeled as a describing function plus a remnant. The effects on the measured describing function and remnant of different system dynamics, changes in the frequency content of the input and different displays were determined during the study. The describing function and remnant data indicate that humans can control as well with aural cues as with visual cues for the task considered. However, the reduction in operator time delays, expected because of the generally faster human response to aural stimuli, was not evident in the results. It was also determined that the operators could control equally well with either the one- or two-ear display.

Vinje, E. W.↗
NASA NTRS1972

Synchronization using pulsed edge tracking in optical PPM communication system

A pulse position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge tracking method of maintaining the necessary timing. The edge tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to pure synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal to noise ratio.

Gagliardi, R.↗
NASA NTRS1972

Satellite (IRLS) tracking of elk

The practicability of tracking free roaming animals in natural environments by satellite systems is reported. Satellite systems combine continuous tracking with simultaneous monitoring of physiological and environmental parameters through a combination of radio tracking and biotelemetric ground systems that lead to a better understanding of animal behavior and migration patterns.

Buechner, H. K.↗
NASA NTRS1972

Satellite height determination using satellite-to-satellite tracking and ground laser systems

An attempt was made to use GEOS-C spacecraft height, as measured by the onboard radar altimeter, for an improved determination of the earth's gravitational field and for the determination of the variation of the physical surface of the oceans. Two tracking system approaches to accurately determine the spacecraft height (orbit) are described and their results stated. These are satellite-to-satellite tracking (SST) and ground-laser tracking (GLT). Height variations can be observed in the dm-regions using SST and in the m-region using present GLT.

Vonbun, F. O.↗
NASA NTRS1972

An experiment to determine the relative positions of two collocated laser tracking stations

Two Goddard Space Flight Center laser tracking stations were collocated for a short time towards the end of 1971 for the purposes of comparing their tracking performance and quality. The lasers, only 25 meters apart, obtained simultaneous tracking data on eighteen passes of the Beacon Explorer C spacecraft. These data have now been used to determine the location of one laser with respect to the other with the result that the computed position of the second laser agrees with the surveyed position to 4 centimeters in latitude and height, and 1 centimeter in longitude.

Dunn, P. J.↗
NASA NTRS1971

An error analysis of the recovery capability of the relative sea-surface profile over the Puerto Rican trench from multi-station and ship tracking of GEOS-2

Error analyses were performed to examine the height error in a relative sea-surface profile as determined by a combination of land-based multistation C-band radars and optical lasers and one ship-based radar tracking the GEOS 2 satellite. It was shown that two relative profiles can be obtained: one using available south-to-north passes of the satellite and one using available north-to-south type passes. An analysis of multi-station tracking capability determined that only Antigua and Grand Turk radars are required to provide satisfactory orbits for south-to-north type satellite passes, while a combination of Merritt Island, Bermuda, and Wallops radars provide secondary orbits for north-to-south passes. Analysis of ship tracking capabilities shows that high elevation single pass range-only solutions are necessary to give only moderate sensitivity to systematic error effects.

Stanley, H. R.↗