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Chang, E. S.

Publications and source records attributed to Chang, E. S..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

High Excitation Rydberg Levels of Fe I from the ATMOS Solar Spectrum at 2.5 and 7 microns

The quadrupole-polarization theory has been applied to the 3d(sup 6)4S(D-6)4f and 5g subconfigurations of Fe I by a parametric fit, and the fitted parameters are used to predict levels in the 6g and 6h subconfigurations. Using the predicted values, we have computed the 4f-6g and 5g-6h transition arrays and made identifications in the ATMOS infrared solar spectrum. The newly identified 6g and 6h levels, based on ATMOS wavenumbers, are combined with the 5g levels and found to agree with the theoretical values with a root mean-squared-deviation of 0.042/ cm. Our approach yields a polarizability of 28.07 a(sub o, sup 2) and a quadrupole moment of 0.4360 +/- 0.0010 ea(sup 2, sub o) for Fe II, as well as an improved ionization potential of 63737.700 +/- 0.010/ cm for Fe I.

Schoenfeld, W. G.↗
NASA NTRS1991

Formation of the infrared emission lines of Mg I in the solar atmosphere

A non-LTE radiative transfer investigation of the emission lines is conducted at 7 and 12 microns using a realistic atomic model for neutral magnesium. An average quiet sun atmospheric model is used to calculate emission-line profiles that resemble the observed ones, i.e., broad absorption troughs with narrow central emission, and significant limb brightening. The charge exchange rates are found to be significant, but the effects of high-n coupling between Mg and Mg(+) together with radiative low-n transitions are of greater importance. It is confirmed that the emission cores are formed no higher than the temperature minimum region, and that the emission is caused by non-LTE effects rather than by the chromospheric temperature rise. It is inferred from the model calculations that the line core is sensitive to magnetic fields located almost 400 km above those measured in ordinary magnetograms; the gas pressure decreases 20-fold between these two heights.

Chang, E. S.↗
NASA NTRS1986

Rotational branch analysis of the excitation of the fundamental vibrational modes of CO2 by slow electron collisions

At 2 eV, the simultaneous rotational-vibrational cross sections for the fundamental modes are found to be well described by the Born formula with just long-range interactions. However, this result is not obtained for pure vibrational excitation (Q branch) in the Raman-active Fermi diads. At 3.8 eV, the infrared-active v2 and v3 cross sections agree with a previous theory incorporating resonant and direct scattering coherently. Measurements on the Raman-active v1 mode indicate that theories need to account for the Fermi resonance.

Antoni, TH.↗
NASA NTRS1984

Retrieval of ocean surface parameters from the scanning multifrequency microwave radiometer (SMMR) on the Nimbus-7 satellite

Sea-surface temperature retrievals have been tested on 2 months of Nimbus-7 scanning multichannel microwave radiometer data. Using the prelaunch versions of the instrument calibration and geophysical parameter retrieval algorithms the initial results were poor. Improved algorithms produced substantially better results. It appears that at least for the night-Southern Hemisphere portion of the Nimbus-7 orbit, a rms measurement accuracy of 1.45 C has been achieved. Similar tests with wind speed retrievals yield an accuracy of 2.7 m/s rms with no substantial differences between day and night measurements but limited by availability of surface observations to the Northern Hemisphere. Moreover, it appears that the retrieved wind speed is more nearly related to the square of the wind observed at the surface than to the wind itself.

Wilheit, T. T., Jr.↗
NASA NTRS1976

Detailed gravimetric geoid computations in North America

A detailed gravimetric geoid has been computed for the Eastern United States and the Northwestern Atlantic Ocean by combining the Goddard Space Flight Center GEM-8 earth gravity model with the available 15 x 15 arcmin and 1 x 1 deg mean free air surface gravity observations. The short wavelength undulations were computed by applying Stokes' formula to the 15 x 15 arcmin and 1 x 1 deg surface data. The long wavelength undulations were provided by the GEM-8 model. The gravimetric geoid has been compared with Geoceiver derived and astrogeodetically determined geoid heights in the United States and the rms agreement is on the order of 1.5 meters. Excellent agreement in shape has been found between the detailed geoid and geoidal profiles derived from GEOS-III altimeter data in the Northwest Atlantic Ocean.

Marsh, J. G.↗
NASA NTRS1975

Detailed gravimetric geoid confirmation of short wavelength features of sea surface topography detected by the Skylab S-193 altimeter in the Atlantic Ocean

A detailed gravimetric geoid was computed for the Northwest Atlantic Ocean and Caribbean Sea area in support of the calibration and evaluation of the GEOS-C altimeter. This geoid, computed on a 15 ft. x 15 ft. grid was based upon a combination of surface gravity data with the GSFC GEM-6 satellite derived gravity data. A comparison of this gravimetric geoid with 10 passes of SKYLAB altimeter data is presented. The agreement of the two data types is quite good with the differences generally less than 2 meters. Sea surface manifestations of numerous short wavelength (approximately 100 km) oceanographic features are now indicated in the gravimetric geoid and are also confirmed by the altimetry data.

Marsh, J. G.↗