Engineering Papers⌕ Search

Engineering topics

Carter, D. A.

Publications and source records attributed to Carter, D. A..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Climatology of tropospheric vertical velocity spectra

Vertical velocity power spectra obtained from Poker Flat, Alaska; Platteville, Colorado; Rhone Delta, France; and Ponape, East Caroline Islands using 50-MHz clear-air radars with vertical beams are given. The spectra were obtained by analyzing the quietest periods from the one-minute-resolution time series for each site. The lengths of available vertical records ranged from as long as 6 months at Poker Flat to about 1 month at Platteville. The quiet-time vertical velocity spectra are shown. Spectral period ranging from 2 minutes to 4 hours is shown on the abscissa and power spectral density is given on the ordinate. The Brunt-Vaisala (B-V) periods (determined from nearby sounding balloons) are indicated. All spectra (except the one from Platteville) exhibit a peak at periods slightly longer than the B-V period, are flat at longer periods, and fall rapidly at periods less than the B-V period. This behavior is expected for a spectrum of internal waves and is very similar to what is observed in the ocean (Eriksen, 1978). The spectral amplitudes vary by only a factor of 2 or 3 about the mean, and show that under quiet conditions vertical velocity spectra from the troposphere are very similar at widely different locations.

Ecklund, W. L.↗
NASA NTRS1986

Continuous wind measurement in the tropical Pacific using VHF radars

Very High Frequency (VHF) Radar Wind Profilers are being installed on Ponape, East Caroline Islands and Christmas Island, Republic of Kiribati to continuously monitor winds aloft. The purpose of this experiment is to study wind fluctuations on time scales between minutes and days, to determine the longitudinal character of these fluctuations, and to examine their relationship to climate variability. Six-hourly wind profiles will be provided via satellite to the scientific community for Project TOGA (Tropical Ocean Global Atmosphere).

Balsley, B. B.↗
NASA NTRS1986

The NOAA TOGA antenna array

The Aeronomy Laboratory recently installed a 100 x 100 meter array antenna with limited beam steering on Christmas Island as a part of the TOGA (Tropical Ocean and Global Atmosphere) program. The array and the associated beam steering and indicating hardware are described.

Ecklund, W. L.↗
NASA NTRS1986

A single-board preprocessor and pulse generator

The Aeronomy Lab. of NOAA has designed and built a single board, programmable radar controller for use with VHF ST (stratosphere troposphere) radars. The controller consists of a coherent integrator preprocessor and a radar pulse generator, both of which are described, as well as interfaces to an antenna beam switch and a receiver bandwidth switch. The controller occupies a single slot in a Data General Nova of Eclipse computer. The integrator and pulse generator take advantage of high density, dual port FIFO chips such as the 512 x 9 Mostek MK 4501. These FIFOs have separate input and output ports and independent read and write cycles with cycle times of less than 200 ns, making them very fast and easy to interface. A simple block diagram of the coherent integrator is shown. The integrator is designed to handle inputs from one receiver (2 channels) with 1 sec sample spacing. The pulse generator is based on controllers designed by R. F. Woodman for the Arecibo and SOUSY radars us a recirculating memory scheme.

Carter, D. A.↗
NASA NTRS1985

Tropospheric gravity waves observed by three closely-spaced ST radars

During a 6 week period in 1982, 3 ST (Stratosphere-Troposphere) radars measured horizontal and vertical wavelengths of small scale tropospheric gravity waves. These 50 MHz, vertically-directed radars were located in a trianglar network with approximately 5 km spacing on the southern coast of France at the mouth of the Rhone River during the ALPEX (Alpine Experiment) program.

Carter, D. A.↗
NASA NTRS1984

Tropospheric gravity waves observed by three closely spaced ST radars

Clear-air radar experiments were carried out on the southern coast of France during the (ALPEX) Alpine experiment program vertically directed stratosphere-troposphere-radars were set up with spacings of about 5 to 6 km. The temporal and spectral characteristics of the vertical velocity fluctuations were examined. The horizontal and vertical properties of gravity waves in the lower atmosphere were analyzed. The techniques used and the first results from this wave study are described.

Carter, D. A.↗
NASA NTRS1984

The Ponape ST radar

In May, 1984, a 50-MHz ST radar was installed on the island of Ponape in the western equatorial Pacific (7 deg N, 158 deg E) by the Aeronomy Laboratory of NOAA. The radar consists of a 100 m x 100 m array with a single, vertically directed, beam and is initially transmitting micro sec. (2.25 km) pulses. The radar is operating continuously, with Doppler spectra being recorded at approximately 1 1/2 minute intervals and sent to Boulder for later analysis. One of the principal goals of the radar is to measure vertical motions in the troposphere and lower stratosphere at a location which is within the intertropical convergence zone during part of the year. First results, during generally fair weather conditions, show detectable echoes up to about 21 km with the tropopause at 17-18 km. Once daily balloon soundings are available locally from a NOAA Weather Service Office on the island, it is planned that this radar will be joined in the coming year by two others with oblique as well as vertical beams on two yet-to-be-selected equatorial islands as part of the TOGA (Tropical Oceans Global Atmosphere) program.

Carter, D. A.↗
NASA NTRS1983

The effects of pulse rate, power, width and coding on signal detectability

The effects on the signal detectability of varying the pulse repetition rate (PRF), peak pulse power (p(pk)) and pulse width (tau(p)) (tp) are examined. Both coded and uncoded pulses are considered. The following quantities are assumed to be constant; (1) antenna area, (z)echo reflectivity, (3) Doppler shift, (4) spectral width, (5) spectral resolution, (6) effective sampling rate, and (7) total incoherent spectral averagaing time. The detectability is computed for two types of targets.

Carter, D. A.↗
NASA NTRS1983

Discrimination against interfering signals at the Poker Flat MST radar

Several on line and off line data processing techniques are used to remove interfering signals due to ground clutter, aircraft, instrumental effects, and external transmissions from the desired atmospheric echoes of Mesosphere Stratosphere, Troposphere (MST) radar. The on line, real time techniques are necessarily simple in order to minimize processing delays. This algorithm examines the individual Doppler spectra which are computed every two to four seconds (for oblique antenna beams). The total spectral power in each individual spectrum is computed by summing all the spectral points. If this integrated power increases from one spectrum to the next by a factor greater than a preselected threshold, then that spectrum is not added to the spectral sum. Succeeding spectra are compared to the last acceptable spectrum. Only a certain maximum number of spectra are allowed to be rejected in succession.

Carter, D. A.↗
NASA NTRS1983

Techniques for studying gravity waves and turbulence: Horizontal, vertical and temporal resolution needed

One of the most important atmospheric measurements that is needed is a measure of the gravity-wave spectrum. The MST radar has been investigated as means to measure the temporal resolution required to determine gravity-wave oscillations. The required vertical and horizontal resolution is dependent on the particular part of the gravity wave spectrum that is analyzed. Horizontal spacing is also discussed.

Avery, S. K.↗
NASA NTRS1983

Techniques for studying gravity waves and turbulence: Vertical wind speed power spectra from the troposphere and stratosphere obtained under light wind conditions

A joint France/U.S. experiment was conducted near the mouth of the Rhone river in southern France as part of the ALPEX program. This experiment used 3 vertically directed 50 MHz radars separated by 4 to 6 km. The main purpose of this experiment was to study the spatial characteristics of gravity waves. The good height resolution (750 meters) and time resolution (1 minute) and the continuous operation over many weeks have yielded high resolution vertical wind speed power spectra under a variety of synoptic conditions. Vertical spectra obtained during very quiet (low wind) conditions in the troposphere and lower stratosphere from a single site are presented.

Ecklund, W. L.↗
NASA NTRS1983

Capabilities and limitations of existing MST radars: Poker Flat

Designed as a prototype system to continuously monitor the atmosphere up to approximately 100 km, the Poker Flat MST radar began operating in 1979 at a relatively low sensitivity. In almost continuous operation since then, the system is steadily increasing in sensitivity to its ultimate design characteristics. Current and final parameters are listed. The advantages of its modular design, which uses 64 transmitting modules distributed through the 200 mx 200 m antenna array include: easy maintenance, beam switching using very low power switching, air cooled transmitting tubes, lower feedline costs, and no moving parts. Continuous, uninterrupted operation ( 4 years) and less man-made interference because of the remote location) are other assets. Most disadvantages are related to its not-yet-finished status, climate, moose excursions, and operating expenses.

Balsley, B. B.↗
NASA NTRS1983

Signal processing at the Poker Flat MST radar

Signal processing for Mesosphere-Stratosphere-Troposphere (MST) radar is carried out by a combination of hardware in high-speed, special-purpose devices and software in a general-purpose, minicomputer/array processor. A block diagram of the signal processing system is presented, and the steps in the processing pathway are described. The current processing capabilities are given, and a system offering greater coherent integration speed is advanced which hinges upon a high speed preprocessor.

Carter, D. A.↗
NASA NTRS1976

Evidence for a Rayleigh-Taylor type instability and upwelling of depleted density regions during equatorial spread F

Recent rocket probe, barium cloud and radar measurements conducted during equatorial spread F conditions are interpreted in terms of a Rayleigh-Taylor gravitational instability operating on the bottomside of the F peak. The persistent theoretical problems associated with strong radar echoes typically observed in patch-like structures at high altitudes are explained in terms of regions of depleted plasma density which buoyantly rise against the gravitational field.

Kelley, M. C.↗