Radar reflectivity plots - Digital method.
Digital method to produce radar reflectivity from analog audio frequency Doppler data extracted from terrain echo signal of CW scatterometer radar
Oherren, D. H.↗
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A range-rate extraction unit for determining Doppler effect
Active ranging technique devised for VHF or S-band radar systems divides target Doppler frequency by counter-generated number that is proportional to transmitting frequency, thus producing target velocity data in terms of speed and distance relative to target transponder.
Source record↗
Protonospheric electron concentration profiles
Electron density profiles along OGO 1 orbit portions calculated by measuring harmonic radio beacon transmissions differential Doppler frequencies and Faraday polarization rotation angle
Da Rosa, A. V.↗
Determination of the columnar electron content and the layer shape factor of the plasmasphere up to the plasmapause
Plasmaspheric columnar electron content determination up to plasmapause by ATS-3 beacon transmitter and combining differential Doppler frequency and Faraday rotation angle methods
Almeida, O. G.↗
Bistatic-radar observation of long-period, directional ocean-wave spectra with loran A
Ocean wave spectra from bistatic radar scatter data, using time delay Doppler-frequency map
Peterson, A. M.↗
Application of laser Doppler systems to vortex measurement and detection
Laser system for atmospheric wind velocity and turbulence, using Doppler frequency shift undergone by radiation beam scattered by particles suspended in flows
Huffaker, R. M.↗
Convective amplification of Type 1 irregularities in the equatorial electrojet
Wave propagation and refraction of Type 1 irregularities in the equatorial electrojet were investigated. Quantitative calculation of wave refraction in a model electrojet showed that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upwards in the upper electrojet and downwards in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray-path integrated wave growth shows that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. It was concluded that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic speed.
Lee, K.↗
Convective amplification of type I irregularities in the equatorial electrojet.
Wave propagation and refraction of 'type I' irregularities in the equatorial electrojet are investigated. Quantitative calculation of wave refraction in a model electrojet shows that the direction of wave refraction must change sign at one altitude. Waves propagating with the electrons rotate their wave vectors upward in the upper electrojet and downward in the lower electrojet during the day, and vice versa at night. Furthermore, the altitude region of largest linear growth rate is also the one with the weakest refraction rate. Consequently, computations of the ray-path integrated wave growth show that this region would dominate the backscatter spectrum from the electrojet if linear theory were valid, and it is further noted that the maximum amplitude wave should have phase velocities exceeding the ion acoustic speed. It is therefore concluded that propagation alone, without inclusion of nonlinear effects, cannot explain backscatter observations of a constant Doppler frequency shift given by the ion acoustic speed.
Lee, K.↗
Propeller modulation effects on a scanning beam microwave landing system
An investigation to assess the modulation effects on microwave signals transmitted through rotating propeller blades. Interruption of the antenna line-of-sight signal by the rotating propeller causes a variation of path loss, which produces essentially an amplitude modulation of the received signal. This interruption or blockage effect is generally only partial because of edge diffraction around the particular interfering propeller blade. Signals reflected from the rotating propeller will also cause Doppler frequency shifts to be present in the received signals. A scanning beam microwave landing system (MLS) known as MODILS (modular instrument landing system) was used to process the received signals for display. The effects of propeller modulation were studied by varying the following parameters: (1) spacing between propeller and receiving antenna, (2) propeller dimensions, (3) propeller speed (rpm), (4) number of propeller blades, (5) system data rate, (6) receiver response time, and (7) receiver antenna aperture.
Pope, J. M.↗
The O I 1304 and 1356 emissions in aurorae
An altitude profile of the 3914 emission of N2+ measured in an aurora by two rocket-borne spectrometers has been used to compute height-intensity profiles of the O I radiations at 1304 and 1356. Comparison of predictions with observations shows that the shape of the altitude profiles can better be reproduced by assuming a Doppler frequency profile rather than a Voigt profile in the radiative transfer computations. There are serious discrepancies between the observed and predicted intensity maxima for both oxygen features that could be due to the particular value for the cross sections we have adopted for excitation of oxygen by electron impact.
Strickland, D. J.↗
Distribution and size of elements of Saturn's rings as inferred from 12-cm radar observations
A 64m radar antenna was used to observe Saturn's rings at 12.6 cm wavelength, with reduced Doppler spread. The results show a positive radar return corresponding to about a 60 percent return from an isotropic scatterer with the projected area of the rings, allowing for the Cassini division. A radar spectrogram of the rings is shown with power density plotted against Doppler frequency shift.
Morris, G. A., Jr.↗
Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity
A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.
Hung, R. J.↗
Ionization effects due to solar flare on terrestrial ionosphere
Sudden frequency deviation ionospheric disturbances related to the flares of May 18 and 19, 1973 were observed from the NASA/MSFC high frequency Doppler sounder array system in Huntsville, Alabama. The results are compared with those observed at Table Mountain near Boulder, Colorado and at the University of Hawaii.
Wu, S. T.↗
System measurements of a CO2 laser communications link
Measurements were made under simulated operating conditions to establish the capability of a CO2 laser transmitting heterodyne receiver link to acquire weak laser transmitter beams and maintain spatial tracking during communications. For the case of a synchronous satellite-to-earth station link, analysis and laboratory measurements indicate that the infrared heterodyne receiver subsystem is capable of performing the acquisition, acquisition confirm, and spatial tracking functions at IF signal-to-noise ratio of -17 dB. For the case of a low-altitude satellite-to-earth station link, the laser transmit signal is Doppler-shifted due to the difference in relative velocity of the two stations. The resultant Doppler frequency shift varies with time and must be spectrally acquired and tracked.
Peyton, B. J.↗
DSN radio science system Mark III-78 real-time display capability
The current plane to provide radio science real-time display capability in response to multimission radio science requirements is described. Topics discussed include the display of Doppler frequency and high-resolution graphical display of all closed-loop radio metric parameters, and spectrum displays of open-loop receiver output.
Berman, A. L.↗
CO2 laser communication systems for near-earth space applications
Projections of the growth of earth-sensing systems for the latter half of the 1980's show a data-transmission requirement of 300 Mbit/s and above. The most efficient technique to return the data from a sensing satellite to a ground station is through a geosynchronous data relay satellite. A laser system is most attractive for the space-to-space link. A five-year program was conducted which has shown the basic technical feasibility of accomplishing this link with a CO2 laser system operating at a wavelength near 10 microns. The system uses a mercury-cadmium-telluride infrared mixer cooled to approximately 100 K by a radiative cooler. The laser local oscillator and coupling-modulated laser transmitter use conductively cooled beryllium oxide construction. The optical antenna for transmission and reception has a gain of nominally 92 dB with a 3-dB beamwidth of 80 microrad. Tracking jitter is less than ten microrad, and signal acquisition occurs in less than 1 min. The receiver subsystem has a sensitivity of 10 to the -19th power W/Hz, accommodates a 300-Mbit/s data rate, and can track Doppler frequency variations over a + or - 700-MHz range.
Mcelroy, J. H.↗
Lunar gravity - A long-term Keplerian rate method
Nearside tracking data from Apollo subsatellites and Lunar Orbiter 5 are used to construct a model of the farside lunar gravity field. An indirect method of calculating the average effect of all the gravity anomalies which affect spacecraft orbits is reduced to a linear estimation problem by eliminating the integration of spacecraft dynamics. Doppler frequency shifts between the lunar satellite and earth-based tracking station are used to measure the line of sight velocity component between the orbiter and the tracker; gravity determination is then performed in a weighted least squares estimator which employs the orbital rates as data and formulates the normal equations using the associated Keplerian state. Simulations performed demonstrate that farside gravity features can be economically determined by use of gravity estimates obtained from long-period models of nearside orbiting tracks.
Ferrari, A. J.↗
Improvements in search and rescue distress alerting and locating using satellites
This paper describes a system concept for search and rescue which is capable of making a major contribution to saving lives and reducing the search time for downed aircraft. In addition, a beacon location experiment is described using the Amateur Radio Satellite Corporation Oscar-6 and Oscar-7 spacecraft. The purpose of this experiment was to demonstrate the system concept above by determining the geographical location of a low power 'distress beacon' via satellite based on a single pass of Doppler frequency measurements. Preliminary results are presented showing beacon location recovery on the order of 10 km with indications that an order of magnitude improvement is entirely possible. This experiment is in support of NASA's current exploration into the role satellites might play in providing much needed improvements in the reliability, coverage and accuracy of present search and rescue procedures.
Brandel, D. L.↗