Engineering topics

Hartmann, G. K.

Publications and source records attributed to Hartmann, G. K..

10 records

NASA NTRS1996

A Comparison of Ozone Measurements Made by the ATMOS, MAS, and SSBUV Instruments During ATLAS 1,2, and 3

Ozone profile measurements were made by three instruments, ATMOS, MAS, and SSBUV, using distinctly different observing techniques, as part of the ATLAS Space Shuttle missions in March 1992, April 1993, and November 1994. ATMOS makes solar-occultation observations of infrared spectra using a Fourier transform interferometer. MAS uses a limb-scanning antenna to measure emission spectra at millimeter wavelengths. SSBUV is a nadir-viewing instrument measuring the transmission of scattered solar ultraviolet radiation modified by ozone absorption. A sample of zonal-mean mixing ratio profiles indicates that these three ATLAS instruments generally agree to within 10%, although a few potential biases have been noted. There are significant differences in the character of the agreement between ATLAS 1 and ATLAS 2 which will require further study.

Kriebel, D. L.↗

NASA NTRS1988

Millimeter-Wave Atmospheric Sounder (MAS)

MAS is a remote sensing instrument for passive sounding (limb sounding) of the earth's atmosphere from the Space Shuttle. The main objective of the MAS is to study the composition and dynamic structure of the stratosphere, mesosphere, and lower thermosphere in the height range 20 to 100 km, the region known as the middle atmosphere. The MAS will be flown on the Atmospheric Laboratory for Applications and Science (ATLAS 1) NASA mission scheduled for late 1990. The Millimeter-Wave Atmospheric Sounder will provide, for the first time, information obtained simultaneously on the temperature and on ozone concentrations in the 20 to 90 km altitude region. The information will cover a large area of the globe, will have high accuracy and high vertical resolution, and will cover both day and night times. Additionally, data on the two important molecules, H2O and ClO, will also be provided.

Hartmann, G. K.↗

NASA NTRS1985

Towards a Global MAP Data Base

Scientific and ecological needs call for the generation of a global data base of measured data from the Earth's atmosphere, similar but complementary to the data of the meteorological service. Right now there is a large gap between these needs and the available financial means. If this prevails, it might be prohibitive for the generation of such a data base. There must be a compromise between the needs and the means. Priorities must be set. Thus, discussions should be started on which data can be or should be stored. Newly generated data for storage in such a data base is recommended to be handled by the World Data Centers (WDCs). This brief report should help to stimulate discussions and ubsequent actions.

Hartmann, G. K.↗

NASA NTRS1984

Study of the system of middle atmosphere-ionosphere using remote-sensing data

In the present investigation, the methods of statistical spectral analysis are employed for a study of the quasi-periodic changes of state parameters of the middle atmosphere and the ionosphere, taking into account oscillations with periods of several days. The considered oscillations are typical for planetary waves. The theory and empirical findings regarding transient planetary waves are utilized as a basis for the concepts employed in the data analysis and for the interpretation of the results. The results of the investigation show a presence of coherent variations in the time series of radiation density measurements and other state parameters for the middle atmosphere and the ionosphere. The existence of presumably dynamic coupling processes can be recognized in oscillations with periods of about 16 or 5 days.

Hass, H.↗

NASA NTRS1980

Comparison of total electron content measurements made with the ATS-6 radio beacon over the U.S. and Europe

The ATS-6 radio beacon measurements made at three stations in the U.S.A. are compared and contrasted with similar measurements made in Europe the following year at two locations. It is shown that over the U.S.A. the winter plasmaspheric content reaches its maximum near 0300 LT whereas in Europe the maximum occurs near noon. The plasmaspheric content decreases with increase of magnetic activity in both continents. Winter night maxima are observed in ionospheric content in both hemispheres. Marked differences occurred in magnetic storm effects and in the day-to-night ratio of ionospheric electron content.

Davies, K.↗

NASA NTRS1979

Transionospheric propagation predictions

The current status and future prospects of the capability to make transionospheric propagation predictions are addressed, highlighting the effects of the ionized media, which dominate for frequencies below 1 to 3 GHz, depending upon the state of the ionosphere and the elevation angle through the Earth-space path. The primary concerns are the predictions of time delay of signal modulation (group path delay) and of radio wave scintillation. Progress in these areas is strongly tied to knowledge of variable structures in the ionosphere ranging from the large scale (thousands of kilometers in horizontal extent) to the fine scale (kilometer size). Ionospheric variability and the relative importance of various mechanisms responsible for the time histories observed in total electron content (TEC), proportional to signal group delay, and in irregularity formation are discussed in terms of capability to make both short and long term predictions. The data base upon which predictions are made is examined for its adequacy, and the prospects for prediction improvements by more theoretical studies as well as by increasing the available statistical data base are examined.

Klobucher, J. A.↗

NASA NTRS1977

A comparison of several methods of estimating the columnar electron content of the plasmasphere

Data from several different observation techniques are used to estimate the columnar electron content of the plasmasphere. The estimate is based upon the subtraction of the ionospheric electron content from the total content along the radio path from ground to the geostationary satellite ATS-6. The Radio Beacon Experiment on this satellite allows a very accurate determination of the total electron content up to the height of the satellite. For the ionospheric electron content (ground to appr. 2000 km) the following techniques are used: (1) Faraday effect on the ATS-6 signals, (2) differential Doppler effect on the signals of the low-orbiting NNSS satellites, (3) combination of bottomside and topside ionograms, and (4) extrapolation of bottomside ionograms. It is shown that the combination of group delay and Faraday effect data on the ATS-6 RBE signals provide the most reliable estimates of the columnar electron content of the plasmasphere. Data from low-orbiting satellites support this conclusion.

Davies, K.↗

NASA NTRS1976

Short-period fluctuations in total columnar electron content

Small sinusoidal fluctuations in the total columnar electron content of the atmosphere were found in recordings of the carrier phase of radio signals from ATS 6 received at Bozeman (Montana), Boulder (Colorado) and Dallas (Texas). Four such events are examined. A large latitudinal gradient in total electron content was found from Bozeman to Boulder. The sinusoidal oscillations have periods of 30 to 50 sec and may continue for several hours on magnetically quiet days. There is evidence that they are associated with micropulsations at ground and geostationary heights.

Davies, K.↗

NASA NTRS1976

Electron content of the ionosphere and the plasma sphere on the basis of ATS-6-Data, NNSS-data, and ionograms

The reported investigation takes into account data obtained with the aid of the geostationary satellite ATS-6, the satellites of the U.S. navy navigation system (NNSS) at an altitude between 900 and 1200 km, and the satellites ISIS 1 and ISIS 2. The altitude range between ground and ATS-6 is divided into two regions, including the 'ionosphere', involving the region with an upper limit of 2000 km, and the 'plasma sphere', involving the region above an altitude of 2000 km. Data concerning the electron content obtained from different sources are compared, taking into account discrepancies between ionogram-derived values and values computed on the basis of satellite measurements. Attention is also given to the vertical electron content of the ionosphere on the basis of a combination of data obtained with the aid of the ATS-6 and the NNSS.

Leitinger, R.↗

NASA NTRS1976

Short period oscillations in total electron content

The paper describes measurements of fluctuations in the total electron content along the propagation path of the radio beam between the ATS-6 geostationary satellite and the ground station. Short-period oscillations of the total electron content of about plus or minus 8 time 10 to the 13th electrons per sq m with a period of about 30 to 50 seconds were detected. These oscillations appear to be well correlated with the appearance of Type PC 4 micropulsations.

Davies, K.↗