1,721,007 research outputs found
System development for characterisation of high precision frequency standards performance for radio astronomy and industrial applications
No full textThe IRASR has many projects associated with the operation of the new AUT radio telescope station. High precision atomic clocks, oscillators regulated by the atomic properties of matter play a vitally important role in the systems operation. Like any similar device, there are errors and a limit to the precision of the behaviour of these oscillators. The Allan variance is a well-known means to characterise frequency oscillators and clocks, especially for those measurement instruments of ultra-high precision. By taking advantage of the rapid application development approach, a system has been implemented within the Matlab® development environment for the measurement of Allan variance. Three major atomic frequency standards, a Rubidium atomic clock, GPS disciplined clock, and Hydrogen Maser, were utilised as the source of references in experiments that tested the developed system. Although the system developed finally meet all project requirements, the AVAR plotting results for different atomic frequency standards show that there is uncertainty on the level for specific tau. Thus, some limitations and recommendations have been identified to assist any future experimentation in this field
Dynamic scheduling and planning parallel observations on large Radio Telescope Arrays with the Square Kilometre Array in mind
No full textScheduling, the task of producing a time table for resources and tasks, is well-known to be a difficult problem the more resources are involved (a NP-hard problem). This is about to become an issue in Radio astronomy as observatories consisting of hundreds to thousands of telescopes are planned and operated.
The Square Kilometre Array (SKA), which Australia and New Zealand bid to host, is aiming for scales where current approaches -- in construction, operation but also scheduling -- are insufficent. Although manual scheduling is common today, the problem is becoming complicated by the demand for (1) independent sub-arrays
doing simultaneous observations, which requires the scheduler to plan parallel observations and (2) dynamic re-scheduling on changed conditions. Both of these requirements apply to the SKA, especially in the construction phase.
We review the scheduling approaches taken in the astronomy literature, as well as investigate techniques from human schedulers and today's observatories. The scheduling problem is specified in general for scientific observations and in particular on radio telescope arrays. Also taken into account is the fact that the observatory may be oversubscribed, requiring the scheduling problem to be integrated with a planning process.
We solve this long-term scheduling problem using a time-based encoding that works in the very general case of observation scheduling. This research then compares algorithms from various approaches, including fast heuristics from CPU scheduling, Linear Integer Programming and Genetic algorithms, Branch-and-Bound enumeration schemes. Measures include not only goodness of the solution, but also scalability and re-scheduling capabilities.
In conclusion, we have identified a fast and good scheduling approach that allows (re-)scheduling difficult and changing problems by combining heuristics with a Genetic algorithm using block-wise mutation operations. We are able to explain and eradicate two problems in the literature: The inability of a GA to properly improve schedules and the generation of schedules with frequent interruptions.
Finally, we demonstrate the scheduling framework for several operating telescopes: (1) Dynamic re-scheduling with the AUT Warkworth 12m telescope, (2) Scheduling for the Australian Mopra 22m telescope and scheduling for the Allen Telescope Array. Furthermore, we discuss the applicability of the presented scheduling framework to the Atacama Large Millimeter/submillimeter Array (ALMA, in construction) and the SKA. In particular, during the development phase of the SKA, this dynamic, scalable scheduling framework can accommodate changing conditions
System development for characterisation of high precision frequency standards performance for radio astronomy and industrial applications
No full textThe IRASR has many projects associated with the operation of the new AUT radio telescope station. High precision atomic clocks, oscillators regulated by the atomic properties of matter play a vitally important role in the systems operation. Like any similar device, there are errors and a limit to the precision of the behaviour of these oscillators. The Allan variance is a well-known means to characterise frequency oscillators and clocks, especially for those measurement instruments of ultra-high precision. By taking advantage of the rapid application development approach, a system has been implemented within the Matlab® development environment for the measurement of Allan variance. Three major atomic frequency standards, a Rubidium atomic clock, GPS disciplined clock, and Hydrogen Maser, were utilised as the source of references in experiments that tested the developed system. Although the system developed finally meet all project requirements, the AVAR plotting results for different atomic frequency standards show that there is uncertainty on the level for specific tau. Thus, some limitations and recommendations have been identified to assist any future experimentation in this field
Analysis and Optimization of the AUT 30-metre Radio Telescope: Pointing and Surface
No full textThe purpose of this research is to analyze, evaluate and improve the current pointing performance of AUT’s 30-metre radio telescope. The telescope currently uses the "fivept" pointing procedure of the NASA Field System (used for scheduling and operation of the 30-metre) to collect pointing offsets. “pdplt”, another pro- gram in the Field System, is used to process, generate and apply a pointing model to correct for errors in pointing. The Field System pointing model allows up to 30 terms to account for various pointing errors, of which 8 terms are currently being used.
Previous research had identified a sinusoidal pattern in the residual pointing offsets that significantly reduces pointing accuracy [1]. We develop an alternative pointing methodology that significantly improves the pointing accuracy by (a) applying a source selection method, (b) applying an outlier removal procedure and (c) using additional terms to remove the sinusoidal pattern. The “fivept” pointing procedure is used to build the pointing database. A script written in Bash is used to preprocess the offsets and the R programming language is used to process, analyze and evaluate new pointing models. Three new terms are added to the existing model that effectively suppress the sinusoidal pattern. The end result improves the pointing accuracy significantly, with the RF axis being able to point within an error ellipse that is smaller than 10% of the FWHM.
We speculate about possible reasons for the origin of the sinusoidal pattern of the pointing offsets. A major speculation was gravitational deformation in Elevation of the primary reflector surface. We use the laser scanning method to study the surface of the primary reflector. A FARO Laser scanner is used for collecting data. SCENE, an industry standard program and Matlab are used for processing and analyzing the data. We conclude that the main reflector has a good quality of surface with rms of ∼ 3 mm, and does not demonstrate any noticeable gravitational deformation when studied at different Elevation angles
Characterisation of the radio noise environment in New Zealand
No full textA methodology for the measurement of the radio frequency environment close to the radio noise floor is presented for urban, suburban and rural areas within New Zealand for the purposes of characterisation and trend monitoring by radio spectrum managers. Flux density measurements in bands within a range of frequencies from 80 MHz to 8 GHz have been made in urban, suburban and rural areas of New Zealand during 2007 and 2008. An analysis of the band occupancy is presented in summary form. These summaries are intended as a starting point for radio spectrum usage and can be used as a reference for any future measurements. A description of the computer directories and charts resulting from these measurements, using 20 MHz bandwidths have also been included. All the results for the work have been collated in a set of computer directories named “NZRFI Directories 2007 2008”, which are intended as a reference for use in the determination of local activity in particular frequency ranges. A disc with the full range measurement spectral density charts and channel occupancy charts accompanies this work. Also included on the disc are sets of 20 MHz band charts for some urban, suburban and rural location measurements
Dynamic Scheduling and Planning Parallel Observations on Large Radio Telescope Arrays With the Square Kilometre Array in Mind
No full textScheduling, the task of producing a time table for resources and tasks, is well-known to be a difficult problem the more resources are involved (a NP-hard problem). This is about to become an issue in Radio astronomy as observatories consisting of hundreds to thousands of telescopes are planned and operated.
The Square Kilometre Array (SKA), which Australia and New Zealand bid to host, is aiming for scales where current approaches -- in construction, operation but also scheduling -- are insufficent. Although manual scheduling is common today, the problem is becoming complicated by the demand for (1) independent sub-arrays doing simultaneous observations, which requires the scheduler to plan parallel observations and (2) dynamic re-scheduling on changed conditions. Both of these requirements apply to the SKA, especially in the construction phase.
We review the scheduling approaches taken in the astronomy literature, as well as investigate techniques from human schedulers and today's observatories. The scheduling problem is specified in general for scientific observations and in particular on radio telescope arrays. Also taken into account is the fact that the observatory may be oversubscribed, requiring the scheduling problem to be integrated with a planning process.
We solve this long-term scheduling problem using a time-based encoding that works in the very general case of observation scheduling. This research then compares algorithms from various approaches, including fast heuristics from CPU scheduling, Linear Integer Programming and Genetic algorithms, Branch-and-Bound enumeration schemes. Measures include not only goodness of the solution, but also scalability and re-scheduling capabilities.
In conclusion, we have identified a fast and good scheduling approach that allows (re-)scheduling difficult and changing problems by combining heuristics with a Genetic algorithm using block-wise mutation operations. We are able to explain and eradicate two problems in the literature: The inability of a GA to properly improve schedules and the generation of schedules with frequent interruptions.
Finally, we demonstrate the scheduling framework for several operating telescopes: (1) Dynamic re-scheduling with the AUT Warkworth 12m telescope, (2) Scheduling for the Australian Mopra 22m telescope and scheduling for the Allen Telescope Array. Furthermore, we discuss the applicability of the presented scheduling framework to the Atacama Large Millimeter/submillimeter Array (ALMA, in construction) and the SKA. In particular, during the development phase of the SKA, this dynamic, scalable scheduling framework can accommodate changing conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analysis and Optimization of the AUT 30-metre Radio Telescope: Pointing and Surface
No full textThe purpose of this research is to analyze, evaluate and improve the current pointing performance of AUT’s 30-metre radio telescope. The telescope currently uses the "fivept" pointing procedure of the NASA Field System (used for scheduling and operation of the 30-metre) to collect pointing offsets. “pdplt”, another pro- gram in the Field System, is used to process, generate and apply a pointing model to correct for errors in pointing. The Field System pointing model allows up to 30 terms to account for various pointing errors, of which 8 terms are currently being used.
Previous research had identified a sinusoidal pattern in the residual pointing offsets that significantly reduces pointing accuracy [1]. We develop an alternative pointing methodology that significantly improves the pointing accuracy by (a) applying a source selection method, (b) applying an outlier removal procedure and (c) using additional terms to remove the sinusoidal pattern. The “fivept” pointing procedure is used to build the pointing database. A script written in Bash is used to preprocess the offsets and the R programming language is used to process, analyze and evaluate new pointing models. Three new terms are added to the existing model that effectively suppress the sinusoidal pattern. The end result improves the pointing accuracy significantly, with the RF axis being able to point within an error ellipse that is smaller than 10% of the FWHM.
We speculate about possible reasons for the origin of the sinusoidal pattern of the pointing offsets. A major speculation was gravitational deformation in Elevation of the primary reflector surface. We use the laser scanning method to study the surface of the primary reflector. A FARO Laser scanner is used for collecting data. SCENE, an industry standard program and Matlab are used for processing and analyzing the data. We conclude that the main reflector has a good quality of surface with rms of ∼ 3 mm, and does not demonstrate any noticeable gravitational deformation when studied at different Elevation angles
Characterisation of the Radio Noise Environment in New Zealand
No full textA methodology for the measurement of the radio frequency environment close to the radio noise floor is presented for urban, suburban and rural areas within New Zealand for the purposes of characterisation and trend monitoring by radio spectrum managers. Flux density measurements in bands within a range of frequencies from 80 MHz to 8 GHz have been made in urban, suburban and rural areas of New Zealand during 2007 and 2008. An analysis of the band occupancy is presented in summary form. These summaries are intended as a starting point for radio spectrum usage and can be used as a reference for any future measurements. A description of the computer directories and charts resulting from these measurements, using 20 MHz bandwidths have also been included. All the results for the work have been collated in a set of computer directories named “NZRFI Directories 2007 2008”, which are intended as a reference for use in the determination of local activity in particular frequency ranges. A disc with the full range measurement spectral density charts and channel occupancy charts accompanies this work. Also included on the disc are sets of 20 MHz band charts for some urban, suburban and rural location measurements
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