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Weiss, H.

Publications and source records attributed to Weiss, H..

18 records
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NASA NTRS1994

Accuracy of total ozone retrieval from NOAA SBUV/2 measurements: Impact of instrument performance

The National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) has been collecting and evaluating the solar backscattered ultraviolet (SBUV/2) instrument data from NOAA 9 and NOAA 11 spacecraft since March 1985. Over 5 years (March 1985 to October 1990) of NOAA 9 (version 5.0) and over 4 years (January 1989 to June 1993) of NOAA 11 (version 6.0) reprocessed data are now available to the scientific community to study geophysical phenomena involving ozone. This paper examines the impact of the instrument performance on total ozone retrieval from the two instruments. We estimate that at the end of October 1990 the total postlaunch error for NOAA 9 due to instrument alone is -2.2%. A significant fraction of this error (-1.9%) is due to diffuser degradation which is not accounted for in the version 5 reprocessing. The estimate for NOAA 11 total postlaunch instrument error, at the end of June 1993, is -0.4%.

Ahmad, Z.↗
NASA NTRS1994

Performance evaluation of the solar backscatter ultraviolet radiometer, model 2 (SBUV/2) inflight calibration system

The Solar Backscatter Ultraviolet Radiometer, Model 2 (SBUV/2) instruments, as part of their regular operation, deploy ground aluminum reflective diffusers to deflect solar irradiance into the instrument's field-of-view. Previous SBUV instrument diffusers have shown a tendency to degrade in their reflective efficiencies. This degradation will add a trend to the ozone measurements if left uncorrected. An extensive in-flight calibration system was designed into the SBUV/2 instruments to effectively measure the degradation of the solar diffuser (Ball Aerospace Systems Division 1981). Soon after launch, the NOAA-9 SBUV/2 calibration system was unable to track the diffuser's reflectivity changes due, in part, to design flows (Frederick et al. 1986). Subsequently, the NOAA-11 SBUV/2 calibration system was redesigned and an analysis of the first 2 years of data (Weiss et al. 1991) indicated the NOAA-11 SBUV/2 onboard calibration system's performance to be exceeding preflight expectations. This paper will describe the analysis of the first three years NOAA-11 SBUV/2 calibration system data.

Weiss, H.↗
NASA NTRS1991

System characterization of positive real conditions

Necessary and sufficient conditions for positive realness in terms of state space matrices are presented under the assumption of complete controllability and complete observability of square systems with independent inputs. As an alternative to the positive real lemma and to the s-domain inequalities, these conditions provide a recursive algorithm for testing positive realness which result in a set of simple algebraic conditions. By relating the positive real property to the associated variational problem, a unified derivation of necessary and sufficient conditions for optimality of both singular and nonsingular problems is derived.

Wang, Q.↗
NASA NTRS1991

Evaluation of the NOAA-11 solar backscatter ultraviolet radiometer, Mod 2 (SBUV/2) - Inflight calibration

This paper presents an analysis both of the NOAA-11 calibration system performance and of the changes of the solar diffuser reflectivity as measured by this system. In particular, after two years of inflight operation, the NOAA-11 system's performance is either on par or exceeding preflight expectations with none of the NOAA-9 problems evident. The solar diffuser displays a wavelength dependent degradation of about 0.5 percent per year at 404 nm to about 2 percent at 185 nm which is consistent with previous diffuser reflectivity changes observed on NIMBUS-7 and NOAA-9.

Weiss, H.↗
NASA NTRS1990

System characterization of positive real conditions

Necessary and sufficient conditions for positive realness in terms of state space matrices are presented under the assumption of complete controllability and complete observability of square systems with independent inputs. As an alternative to the positive real lemma and to the s-domain inequalities, these conditions provide a recursive algorithm for testing positive realness which results in a set of simple algebraic conditions. By relating the positive real property to the associated variational problem, a unified derivation of necessary and sufficient conditions for optimality of both singular and nonsingular problems is derived.

Wang, Q.↗
NASA NTRS1981

Time and energy dependence of heavy ion abundances in solar flare energetic particle events

Examples are presented of the time and energy dependence of the abundances and spectra of the major heavy ions He, C, O and Fe during solar flare events, taken from a survey using the UMD/MPI ULET telescope on IMP-8 during 1973-1977. In some cases, time variations were found in the O/He, O/C and Fe/O ratios which appear to be inconsistent with models based solely on rigidity dependent propagation in the interplanetary medium.

Mason, G. M.↗
NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

Results of a survey of ten solar flare particle events, in which the ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe were measured, are reported. He+ was present in all events (He+/He++ approximately 0.1 to 0.25), and the mean ionization states of C, O and Fe are high. The distribution functions of He+, He++ and heavier elements are well represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between O and 1, and equal e-folding values. Results are consistent with a model whereby ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗
NASA NTRS1981

Time and energy dependence of heavy ion abundances in solar flare energetic particle events

Data from a survey of solar flare events undertaken by the UMD/MPI ULET telescope on the IMP-8 satellite during the period 1973-1977 yields examples of time and energy dependence of the abundances and spectra of the He, C, O and Fe heavy ions. Time variations are found in the O/He, O/C and Fe/O ratios which appear to be inconsistent with models based entirely on rigidity-dependent propagation in the interplanetary medium. It is speculated that such other factors as the abundance differences at the flare site on the sun, or features of the acceleration and release mechanisms, may play an important role in the variations discussed.

Mason, G. M.↗
NASA NTRS1981

Observations of the ionization states of energetic particles accelerated in solar flares

The ionization states and spectra of 0.3 to 2.4 MeV/nuc He, C, O and Fe are measured in a survey of ten solar flare particle events. He(plus) is found to be present in all events, which indicates the common presence of energetic He(plus) in the source material from which solar particles are accelerated. The distribution functions of He(plus), He(plus plus) and heavier elements are represented by simple exponentials of the particle speed times its rigidity to a power n, where n is between 0 and 1, and equal e-folding values. Results are consistent with a model where ions are accelerated in the corona by multi-dimensional shocks out of a population taken from both hot and cold coronal regions.

Gloeckler, G.↗
NASA NTRS1977

The moon's permanent magnetic field - A cratered-shell model

The possibility is considered that the properties of the larger-scale lunar magnetic field may depend in a rather straightforward manner on the geometrical properties of the distribution of larger craters. The relevant effects of cratering are analyzed in the framework of a model of a spherically symmetric shell magnetized to some specific intensity by a concentric dipolar magnetic field. The remanent dipole moment of the model is determined by calculating the dipole moment of the material removed to form craters and them computing the remanent dipole moment for three mutually orthogonal orientations of the magnetizing dipole. The resulting absolute values for the remanent dipole moment are found to be comparable to the upper limit of 10 to the -19th power G-cu cm estimated from Apollo subsatellite measurements. It is concluded that for a crust with an empirically reasonable mean magnetization, the craters can account for a dipole moment as great as that indicated by the estimated upper limit.

Weiss, H.↗
NASA NTRS1977

Geologic-magnetic correlations on the moon - Apollo subsatellite results

Comparison of the magnetic-field measurements of the Apollo subsatellite magnetometers with USGS geologic maps suggests that the ancient lunar field may have been greater during the Imbrian Period than the earlier Pre-Nectarian and Nectarian periods. Further, the field seems to have varied in direction. These data are consistent with a model in which the ancient lunar magnetizing field arises from a core dynamo which does not form until the Imbrian Period. Impacts during this period then result in magnetized crater melt and ejecta blankets. It is emphasized, however, that the area sampled by the subsatellite magnetometers is but a small fraction of the lunar surface. These results must be confirmed with studies of independent regions of the lunar surface before they can be considered conclusive.

Russell, C. T.↗