Multipath induced errors in meteorological Doppler/interferometer location systems

One application of an RF interferometer aboard a low-orbiting spacecraft to determine the location of ground-based transmitters is in tracking high-altitude balloons for meteorological studies. A source of error in this application is reflection of the signal from the sea surface. Through propagating and signal analysis, the magnitude of the reflection-induced error in both Doppler frequency measurements and interferometer phase measurements was estimated. The theory of diffuse scattering from random surfaces was applied to obtain the power spectral density of the reflected signal. The processing of the combined direct and reflected signals was then analyzed to find the statistics of the measurement error. It was found that the error varies greatly during the satellite overpass and attains its maximum value at closest approach. The maximum values of interferometer phase error and Doppler frequency error found for the system configuration considered were comparable to thermal noise-induced error

Pre-emphasis determination for an S-band constant bandwidth FM/FM station

Telemetry bands are being reassigned to UHF at 1500 and 2200 MHz. Conversion primarily requires changes in equipment used in RF link, while many of same subcarrier oscillators, mixer amplifiers, and frequency discriminators can be used

Did Neoliberalizing West African Forests Produce a New Niche for Ebola?

A recent study introduced a vaccine that controls Ebola Makona, the Zaire ebolavirus variant that has infected 28,000 people in West Africa. We propose that even such successful advances are insufficient for many emergent diseases. We review work hypothesizing that Makona, phenotypically similar to much smaller outbreaks, emerged out of shifts in land use brought about by neoliberal economics. The epidemiological consequences demand a new science that explicitly addresses the foundational processes underlying multispecies health, including the deep-time histories, cultural infrastructure, and global economic geographies driving disease emergence. The approach, for instance, reverses the standard public health practice of segregating emergency responses and the structural context from which outbreaks originate. In Ebola's case, regional neoliberalism may affix the stochastic "friction" of ecological relationships imposed by the forest across populations, which, when above a threshold, keeps the virus from lining up transmission above replacement. Export-led logging, mining, and intensive agriculture may depress such functional noise, permitting novel spillovers larger forces of infection. Mature outbreaks, meanwhile, can continue to circulate even in the face of efficient vaccines. More research on these integral explanations is required, but the narrow albeit welcome success of the vaccine may be used to limit support of such a program.SCOPUS: re.jinfo:eu-repo/semantics/publishe

Effects of spacecraft reflections on RF interferometer position location accuracy

This report describes one of three study tasks related to the application of an RF interferometer aboard a low-orbiting spacecraft to determine the location of ground-based transmitters. Computer modeling was used to estimate the error in the measured signal angle-of-arrival caused by reflection and diffraction off the spacecraft. Existing computer codes (NEC-BSC) were modified and used to determine the perturbation, due to the spacecraft, in the phase difference between two interferometer antennas, suspended on either side of the spacecraft. This phase perturbation was found as a function of the angle-of-arrival of the signal from a far-field source. The spacecraft antennas were assumed to be circularly polarized with a cardioid pattern. It was found that the perturbation was as much 12.4 deg within the + or - 60 deg field-of-view. This suggests that phase calibration and correction of phase measurements are essential for precision position location using this technique

NOSS/ALDCS analysis and system requirements definition

The results of system analyses and implementation studies of an advanced location and data collection system (ALDCS) , proposed for inclusion on the National Oceanic Satellite System (NOSS) spacecraft are reported. The system applies Doppler processing and radiofrequency interferometer position location technqiues both alone and in combination. Aspects analyzed include: the constraints imposed by random access to the system by platforms, the RF link parameters, geometric concepts of position and velocity estimation by the two techniques considered, and the effects of electrical measurement errors, spacecraft attitude errors, and geometric parameters on estimation accuracy. Hardware techniques and trade-offs for interferometric phase measurement, ambiguity resolution and calibration are considered. A combined Doppler-interferometer ALDCS intended to fulfill the NOSS data validation and oceanic research support mission is also described

Analysis of Meteorological Satellite location and data collection system concepts

A satellite system that employs a spaceborne RF interferometer to determine the location and velocity of data collection platforms attached to meteorological balloons is proposed. This meteorological advanced location and data collection system (MALDCS) is intended to fly aboard a low polar orbiting satellite. The flight instrument configuration includes antennas supported on long deployable booms. The platform location and velocity estimation errors introduced by the dynamic and thermal behavior of the antenna booms and the effects of the presence of the booms on the performance of the spacecraft's attitude control system, and the control system design considerations critical to stable operations are examined. The physical parameters of the Astromast type of deployable boom were used in the dynamic and thermal boom analysis, and the TIROS N system was assumed for the attitude control analysis. Velocity estimation error versus boom length was determined. There was an optimum, minimum error, antenna separation distance. A description of the proposed MALDCS system and a discussion of ambiguity resolution are included

Pseudo-noise test set for communication system evaluation

A test set for communications systems is described which includes a pseudo noise sequence generator providing a test signal that is fed to a pair of signal channels. The first channel includes a spectrum shaping filter and a conditioning amplifier. The second channel includes a variable delay circuit, a spectrum shaping filter matched to the first filter, and an amplifier. The output of the first channel was applied to the system under test. The output of the system and the output of the second channel are compared to determine the degree of distortion suffered by the test signal due to the communications system

Method of and means for testing a tape record/playback system

A tape record/playback system was tested by first deriving an analog test signal and a band-limited digital reference signal from a pseudo-noise sequence generator driven by a clock signal. It recorded the signals on respective tracks of the system during operation in a record mode. During the playback mode of operation of the system, a delayed analog reference signal without time base variations was reconstructed from the played back reference signal. It was compared with the played back test signal in order to obtain an error signal that was a measure of the performance of the system

Strainrange partitioning behavior of an automotive turbine alloy

This report addresses Strainrange Partitioning, an advanced life prediction analysis procedure, as applied to CA-101 (cast IN 792 + Hf), an alloy proposed for turbine disks in automotive gas turbine engines. The methodology was successful in predicting specimen life under thermal-mechanical cycling, to within a factor of + or - 2

Distal occurrence of mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and potential for cryptotephra studies

The Whakatane Tephra, a rhyolitic tephra erupted ca. 5500 cal. BP from Okataina Volcanic Centre, central North Island, has been identified on the Chatham Islands which lie ˜900 km east of Christchurch, New Zealand. The visible tephra layer, ˜5 mm in thickness and preserved within peat on Pitt Island, was identified using both radiocarbon dating and analysis of glass shards by electron microprobe. Whakatane Tephra is the first Holocene tephra to be identified on the Chatham Islands, and it is the most distal Holocene tephra yet recorded in the New Zealand region, being ˜850 km from source. The Pitt Island occurrence extends the tephra's dispersal area markedly, by an order of magnitude, possibly to ˜300,000 km2. An estimated dispersal index (D) of approximately 105 km2 indicates that the eruption generated a very high plinian column, possibly exceeding ˜30 km in height, with strong winds blowing the ash plume southeastwards. This new discovery of distal Whakatane Tephra as a thin but visible layer strongly implies that cryptotephras are likely to be preserved on the Chatham Islands and within adjacent ocean floor sediments. Therefore the potential exists to develop enhanced cryptotephrostratigraphic records from these distal areas, which in turn would help facilitate precise correlation via tephrochronology of palaeoenvironmental records (such as NZ-INTIMATE) from mainland New Zealand, the southwest Pacific Ocean, and the Chatham Islands