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NASA NTRS1982

Errors in fixed and moving frame of references - Applications for conventional and Doppler radar analysis

Techniques for the correction of errors in Doppler radar scans due to advection effects are presented. A moving frame of reference is shown to be useful in least-squares estimates with stationary observations expressed in scalars or Cartesian coordinates. For non-Cartesian coordinates, such as the deduction of radial velocities from triple Doppler radar data, an integral is defined for accounting for advection effects and consequent coordinate transformations. The multiple radars are necessary for unambiguous characterization of the horizontal wind velocity. A scale analysis is employed to estimate errors with and without the error correction procedure. Improvements in correlations between scans are demonstrated when the error correction method is used.

Tzvi, G.-C.↗

NASA NTRS1983

Supersonic-nitrogen flow-field measurements with the resonant Doppler velocimeter

The application of the resonant Doppler velocimeter (RDV) for obtaining the mean velocity, temperature, and pressure measurements and flow-field visualization in a supersonic free nitrogen jet is reported. This method utilizes laser-induced fluorescence to determine the spectral absorption of an atomic or molecular species seeded into the flow. A narrow linewidth tunable laser is directed into the flow and the total fluorescence from any point is obtained as the laser is tuned. The velocity of the flow is obtained from the Doppler shifted absorption frequency, and the temperature and pressure of the gas are determined from line broadening measurements. Results are presented for the use of this technique to determine the velocity, temperature, and pressure of the flow of sodium atoms seeded into a supersonic nitrogen jet. It is concluded that the visible signal is sufficiently intense for spatially resolved flow visualization purposes.

Cheng, S.↗

NASA NTRS1983

Chung-Li, Taiwan dual mode (Doppler and spaced antenna) VHF radar: Preliminary specifications

A major unresolved question in the field of atmospheric research using VHF radar techniques is the relative merit of the two most widely used systems. These systems are the Doppler method and the spaced antenna method. It has been suggested that one radar of each type be operated side by side for a direct comparison of the two techniques. This duplication of effort is not cost effective. The major components of both systems are identical, and one radar could be operated in both modes by proper design of a suitable antenna system and by proper data analysis. The Chung-Li radar will be able to switch between modes on a time scale of seconds and is the first VHF radar to be able to directly compare the Doppler data with spaced antenna data. The system will have performance comparable with the present SOUSY spaced antenna system and will provide mesospheric data in addition to stratospheric and tropospheric data. The major specifications of the Chung-Li radar are given.

Brosnahan, J. W.↗

NASA NTRS1984

Pulmonary artery location during microgravity activity: Potential impact for chest-mounted Doppler during space travel

Doppler, or ultrasonic, monitoring for pain manifestations of decompression sickness (the bends) is accomplished by placing a sensor on the chest over the pulmonary artery and listening for bubbles. Difficulties have arisen because the technician notes that the pulmonary artery seems to move with subject movement in a one-g field and because the sensor output is influenced by only slight degrees of sensor movement. This study used two subjects and mapped the position of the pulmonary artery in one-g, microgravity, and two-g environments using ultrasound. The results showed that the pulmonary artery is fixed in location in microgravity and not affected by subject position change. The optimal position corresponded to where the Doppler signal is best heard with the subject in a supine position in a one-g environment. The impact of this result is that a proposed multiple sensor array on the chest proposed for microgravity use may not be necessary to monitor an astronaut during extravehicular activities. Instead, a single sensor of approximately 1 inch diameter and mounted in the position described above may suffice.

Hadley, A. T., III↗

NASA NTRS1983

Use of simultaneous Doppler-derived ranges in the geometric mode

A mathematical model for the use of ranges derived from integrated Doppler-shifted frequency observations in a satellite trilateration is presented. The model is tested with data taken during the Second European Doppler Observation Campaign (EDOC-2) campaign. The results of this adjustment are compared with the EDOC-2 results.

Schneeberger, R.↗

NASA NTRS1984

A comparison of satellite Doppler and gravimetric geoid undulations considering terrain-corrected gravity data

Geoid undulations derived from Doppler satellite positioning are compared with corresponding values derived from terrestrial and satellite information using three different procedures. Doppler undulations are compared with uncorrected gravimetric undulations, and systematic differences of 1.6 m and 0.4 m are found for western and eastern U.S. stations, respectively. The systematic difference of 1.6 m was reduced to 0.1 m when terrain-related corrections were applied. Undulations computed from a spherical harmonic expansion to degree 180 yielded standard deviations only slightly poorer than the combined data. A more systematic difference in the western than in the eastern stations remained.

Rapp, R. H.↗

NASA NTRS1984

Measurements of Doppler shifts by gas correlation spectroscopy

IR gas correlation spectroscopy is a sensitive technique for the measurement of small Doppler shifts in spectra. This technique also exhibits several important advantages over alternative methods in the remote sensing of stratospheric and mesospheric winds from spacecraft. Attention is presently given to laboratory tests demonstrating gas correlation spectroscopy's quantitative measurement of small Doppler shifts in spectra, whose close agreement with theoretical predictions suggests that measurements of the change in the radiant flux through a gas correlation spectrometer can be used to measure the relative velocity between gas and instrument for a moving parcel of gas.

Mccleese, D. J.↗

NASA NTRS1984

Doppler radiation sensing of Shuttle angle of attack and TAS during entry

Space Shuttle true airspeed, angle of attack, and sideslip angle are currently derived from inertial guidance information. A new method is proposed which offers a potential improvement in Shuttle safety during entry. Angle of attack, sideslip angle and true airspeed could be measured directly at heights from 120 km down to 20 km by Doppler sensing three independent true airspeeds along the Shuttle body axes. Two types of Doppler measurement sensors, employing either passive detection of atmospheric radiation or coherent detection of scattered laser light are discussed. The proposed technique is essentially solid-state and robust, and is well suited for use in future small hypersonic vehicles that require flight control in the Upper Atmosphere of the earth or in probes destined for the other planets.

Foale, C. M.↗

NASA NTRS1984

Ionospheric electron density irregularities observed by satellite-to-satellite, dual-frequency, low-low Doppler tracking link

A low-low, satellite-to-satellite, dual-frequency, Doppler tracking experiment was performed. The data are analyzed here for irregularities in electron density at the altitude of 212 km. The differential Doppler data with the relative motion term removed are integrated to obtain a representation of the electron density variation along the satellite path. Well-known large-scale features such as the equatorial geomagnetic anomaly and day/night ionization level differences are clearly observed in the integrated data. The larger crest of the morning geomagnetic anomaly is seen to occur in the southern (winter) hemisphere in agreement with previous observations. In addition, a sharp peak in the electron density at the day-to-night transition point is observed in two consecutive revolutions. This effect may be due to the previously postulated atmospheric shock wave generated by supersonic motion of the terminator.

Estes, R. D.↗

NASA NTRS1985

Convective storm downdraft outflows detected by NASA/MSFC's Airborne 10.6 micron pulsed Doppler Lidar System

The capability of a unique Airborne Doppler Lidar System to measure the horizontal winds in the vicinity of severe storm activity is demonstrated. The Airborne Doppler Lidar System (ADLS), developed at NASA/MSFC, was flown on a CV990 research aircraft during the CCOPE (Cooperative Convective Precipitation Experiments, Montana, Summer 1981). Flown between 400 and 600 m AGL, the lidar probed the subcloud regions of several deep convection storms. ADLS data collected near storms on 21 and 23 July 1981 are presented along with satellite imagery, radar echo maps and surface station measurements. These case studies are evidence of the successful performance of an airborne remote wind sensing system and the advantages of two dimension flow visualization of storm outflow structures and interactions.

Emmitt, G. D.↗

NASA NTRS1985

Development of a new laser Doppler velocimeter for the Ames High Reynolds Channel No. 2

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. 2 is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to position the laser beams in the channel flow. Techniques used to seed the flow with 0.5-micron-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.

Seegmiller, H. L.↗

NASA NTRS1985

The structure of the convective atmospheric boundary layer as revealed by lidar and Doppler radars

Results on the structure of the convective atmospheric boundary layer based on the analyses of data from the instrumented NSSL-KTVY tower, airborne Doppler lidar, and ground-based Doppler radars are presented. The vertically averaged wind over the boundary layer was found to be insensitive to baroclinicity, supporting the hypothesis of Arya and Wyngaard (1975). The computed momentum flux profiles were affected by baroclinicity. Horizontal wind spectra from lidar, radar, and tower data compared well with each other both in shape and magnitude. A consistent peak found near 4 km in all the computed spectra might have been caused by horizontally symmetric cells with horizontal wavelength 4 times the boundary-layer height as shown in Kuettner (1971) for the case of weak wind shear.

Eilts, M. D.↗

NASA NTRS1983

Weighted least squares formulas for multiple Doppler radar analysis

An algorithm is developed for the analysis of multiple Doppler radar data in meteorological applications. The algorithm is based on the least squares linear solutions for the variable parameters of a local particle velocity field. The computational sequence for the algorithm is described, and some factors influencing the covariance of Doppler measurement errors are discussed.

Wilson, F. W., Jr.↗

NASA NTRS1983

Dual Doppler lidar measurements of winds in the JAWS experiment

Differences are noted in the operations of Doppler lidar and radar for the case of a thunderstorm outflow observed during the Joint Airport Weather Studies project field experiments. Calculated wind fields agreed with surface wind observations made routinely by the Portable Automated Mesonet stations. The lidar data are found to complement Doppler radar observations; while the latter is superior for the measurement of wind fields within convective storms, the former is more useful in examinations of dynamical processes in regions outside storm.

Rothermel, J.↗

NASA NTRS1983

The structure of a microburst - As observed by ground-based and airborne Doppler radar

Attention is given to the microburst observed near Denver, CO, on June 29, 1982, in the course of the Joint Airport Weather Study (JAWS). The JAWS ground radar network was specifically established to furnish high spatial and temporal resolution multiple Doppler data for microburst observations. The data, which were collected from directly above the microburst, permitted direct measurements of vertical velocities to be made. P-3 surveillance aircraft Doppler data was also available for this microburst, whose considerable complexity is noted.

Mueller, C. K.↗

NASA NTRS1985

Evaluation of data obtained from atmospheric laser Doppler velocimeter

The Doppler lidar velocimeter produces a variety of kinds of data. Besides the line of sight velocity components, there are the reflected amplitudes and the Doppler widths. Computer graphics software for displaying these data was produced. Different methods of presentation are needed for the various items. A picture was produced as pictures are often the best way to gain understanding. The individual lidar scans form a crosshatch pattern. Thus one-dimensional measurements fit together to form a two-dimensional whole. A pair of velocity measurements at a point combine to form a wind measurement with direction and magnitude. This gives a forest of wind vectors. The goal is to find a recognizable pattern to these trees. Often it is necessary to show only part of the information. That is, show only the wind direction not its magnitude or reduce the wind to streamlines of air flow. In other cases data are reduced to contour plots. Just enough contour lines are included to show the picture described.

Keck, T. S.↗

NASA NTRS1985

HF Doppler observations of acoustic waves excited by the earthquake

Ionospheric disturbances caused by the earthquake of a relatively small and large epicentral distance have been detected by a network of HF-Doppler sounders in central Japan and Kyoto station, respectively. The HF-Doppler data of a small epicentral distance, together with the seismic data, have been used to formulate a mechanism whereby ionospheric disturbances are produced by the Urakawa-Oki earthquake in Japan. Comparison of the dynamic spectra of these data has revealed experimentally that the atmosphere acts as a low-pass filter for upward-propagating acoustic waves. By surveying the earthquakes for which the magnitude M is larger than 6.0, researchers found the ionospheric effect in 16 cases of 82 seismic events. As almost all these effects have occurred in the daytime, it is considered that it may result from the filtering effect of the upward-propagating acoustic waves.

Ichinose, T.↗

NASA NTRS1986

Users Guide to the JPL Doppler Gravity Database

Local gravity accelerations and gravimetry have been determined directly from spacecraft Doppler tracking data near the Moon and various planets by the Jet Propulsion Laboratory. Researchers in many fields have an interest in planet-wide global gravimetric mapping and its applications. Many of them use their own computers in support of their studies and would benefit from being able to directly manipulate these gravity data for inclusion in their own modeling computations. Pubication of some 150 Apollo 15 subsatellite low-altitude, high-resolution, single-orbit data sets is covered. The doppler residuals with a determination of the derivative function providing line-of-sight-gravity are both listed and plotted (on microfilm), and can be ordered in computer readable forms (tape and floppy disk). The form and format of this database as well as the methods of data reduction are explained and referenced. A skeleton computer program is provided which can be modified to support re-reductions and re-formatted presentations suitable to a wide variety of research needs undertaken on mainframe or PC class microcomputers.

Muller, P. M.↗