M. A. Cervera

Comparison of simultaneous wind measurements using colocated VHF meteor radar and MF spaced antenna radar systems

Comparisons of wind velocities at heights from 80 to 98 km have been made using two different techniques. The first method involves the determination of winds using meteor drifts (e.g., Avery et al., 1990; Stubbs, 1973). This was done by observing meteors using the University of Adelaide VHF radar situated approximately 40 km north of Adelaide, Australia, at Buckland Park. The second method used to determine winds was the spaced antenna technique (e.g., Briggs, 1984) using an MF radar at the same site. The two radar systems are independent, the VHF radar operating at 54.1 MHz and the MF radar at 1.98 MHz. The spatial separation of the two radars is approximately 600 m. Simultaneous data obtained from September 10 to 20, 1993, are presented here. The agreement between the two techniques is good below 90 km, while above 90 km we find that the spaced antenna technique yields smaller wind speeds than the meteor drift technique. Several possible reasons for these discrepancies are discussed.

Comparison of atmospheric parameters derived from meteor observations with CIRA

In this paper we compare monthly averages of the atmospheric parameter T/ p (where T is temperature and p is pressure) derived from the decay of underdense meteor echoes with the CIRA (1986) atmospheric model. The meteor data were collected with the Buckland Park VHF radar situated ∼40km north of Adelaide, Australia. We examine the overall agreement between the meteor observations and CIRA as well as seasonal differences between the two. Comparison is made with the results of Hocking et al. [1997]. Our results are complimentary to those of Hocking et al.; our data were obtained in the Southern Hemisphere as opposed to the Northern Hemisphere. A discussion on the effect of the geomagnetic field on the diffusion of meteor trails and its effect on the measurement of atmospheric parameters is also included. We note that the geomagnetic field is a very important consideration when using meteors for the derivation of atmospheric temperatures and pressures above heights of around 92–93 km. This effect is required to be taken into account above these heights as failure to do so leads to errors in the interpretation of the data. Recent researchers have avoided this problem by restricting their data to below 90 km.

A new method for the measurement of meteor speeds: The pre-to phase technique

In this paper we describe a new technique for measuring the speeds of individual meteors based upon the variation of the phase received in specular reflections from the meteor train prior to the meteoroid reaching the point of closestapproach to the observation site. The technique is characterized by high precision, high yield, and is less subject to selection effects than the techniques used heretofore. About 75% of observed meteors are able to have a speed determined, compared with only 10% previously. It has application to the measurement of the velocities of meteoroid streams and the distribution of speeds of sporadic meteors. The latter is vital to the modeling of the response of HF/VHF radars to meteor backscatter [Elford, 1964; Thomas et al., 1988], as well as having astronomical implications. Results of observations with our narrow-beam VHF radar are presented. Data collection carried out during the epoch of the θ Ophiuchid meteor shower, whose radiant passes through the response function of the VHF radar, renders speeds which are in accord with the previously known speed for that shower. The speed distribution of sporadic meteors is determined and compared with the distributions obtained in previous radar and optical programs

A comparison of meteor radar systems at Buckland Park

This paper describes a comparison of two meteor radar systems operated simultaneously from June 29 to July 15, 1994, at the Buckland Park field station near Adelaide, Australia (35°S, 138°E). Both meteor systems operate on a narrow-beam VHF wind profiler. The first meteor system was developed by the atmospheric physics group at the University of Adelaide. The second meteor system was the University of Colorados meteor echo detection and collection (MEDAC) system. The goal of the campaign was to determine how closely the two similar meteor systems performed with regards to the detection of meteor trail echoes and the estimation of the Doppler frequencies. Classification of the signals in the resulting data set showed that a number of the echoes, including a class of echoes that appear to be from meteors traveling straight down the beam, were from sources other than under dense meteor trails. When the nonunder dense echoes were operated on by the Doppler frequency estimators, widely varying estimates between the two systems were produced. Only when taking into careful consideration the details of the detection routines, the signal composition of the data set, and performance characteristics of the Doppler estimators was the comparison satisfactory.

Separation of O/X polarization modes on oblique ionospheric soundings†

The oblique-incidence sounder (OIS) is a well-established instrument for determining the state of the ionosphere, with several advantages over vertical-incidence sounders (VIS). However, the processing and interpretation of OIS ionograms is more complicated than that of VIS ionograms. Due to the Earths magnetic field, the ionosphere is birefringent at radio frequencies and a VIS or OIS will typically see two distinct ionospheric returns, known as the O- and X-modes. The separation of these two modes on a VIS, using a polarimetric receive antenna, is a well-established technique. However, this process is more complicated on an OIS due to a variable phase separation in the phase difference between the two modes, as measured between the two arms of a polarimetric antenna. Using a polarimetric antenna that can be rotated and tilted, we show that this variation in phase separation within an ionogram is caused by the variation in incidence angle, with some configurations leading to greater variation in phase separation. We then develop an algorithm for separating O- and X-modes in oblique ionograms which can account for the variation in phase separation and we demonstrate successful separation even in relatively difficult cases. The variation in phase separation can also be exploited to estimate the incident elevation, a technique which may be useful for other applications of HF radio.

Climatological model of over-the-horizon radar (CMOR)

Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependant on their purpose; for instance microwave radar models which are designed to be integrated into existing wargaming simulation frameworks will often be low-fidelity models. The development of similar models of over-the-horizon radar is particulary challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The “base level” environmental modelling required to accurately characterise OTH radar performance is the climatology, i.e. diurnal, seasonal and solar cycle variations. In this paper we detail a climatological model of OTH radar (CMOR) developed using high frequency (HF) radio wave raytracing techniques. We discuss how this model may be integrated into low-fidelity wargaming simulations, used to provide initial assessments of the viability of candidate OTH radar networks to meet particular missions and how it may be used in highly sophisticated radar network design methodologies. The last example is the subject of a companion paper presented in this forum.

Performance prediction of a network of skywave over-the-horizon radars

We introduce a radar network design methodology to address the challenge of designing a network of skywave overt-he-horizon radar (OTHR). The approach can be used to optimise the number of radars, the location of each radar, the sensitivity of each radar, and the total network system cost, based on the chosen mission objectives. The approach postulates these parameters and evaluates radar performance based on ionospheric propagation and noise models and a model of the radar detection and tracking sensitivity. We demonstrate the method with a stylised example of a three radar network directed at the eastern region of Australia from radars located in New Zealand, Norfolk Island and New Caledonia. The network is evaluated for performance with respect to commercial aircraft flights operating between several major Australian cities and Sydney.

Climatological Model of Over‐the‐Horizon Radar

Models of radar systems are required for a variety of reasons. The sophistication of these models is highly dependent on their purpose; for instance, microwave radar models, which are designed to be integrated into existing wargaming simulation frameworks, will often be low-fidelity models. The development of similar models of over-the-horizon (OTH) radar is particularly challenging. This is due to the highly variable propagation environment in which such systems are required to operate: even the lowest fidelity model of an OTH radar must model the environmental conditions appropriately. The base level environmental modeling required to accurately characterize OTH radar performance is the climatology, that is, diurnal, seasonal, and solar cycle variations. In this paper we detail a climatological model of OTH radar developed using high-frequency radio wave ray tracing techniques. We discuss how this model may be used to provide initial assessments of the viability of candidate OTH radar networks to meet particular missions and how it may be used in sophisticated radar network design methodologies.

Radar sensitivity budget analysis for a network of skywave over-the-horizon radars

We introduce a performance prediction methodology to address the challenge of designing a network of skywave over-the-horizon radar (OTHR). The approach can be used to optimise the number of radars, the location of each radar, the sensitivity of each radar, and the total network system cost, based on the chosen mission objectives. We demonstrate the method with a stylised example of a three radar network directed at the eastern region of Australia from radars located in New Zealand, Norfolk Island and New Caledonia. The network is evaluated for performance with respect to commercial aircraft flights operating between several major Australian cities and Sydney.

Observations and modeling of traveling ionospheric disturbance signatures from an Australian network of oblique angle-of-arrival sounders

An Australian network of oblique angle-of-arrival (AoA) ionosondes was installed as part of the ELOISE experimental campaign in September 2015, aimed at an improved understanding of the spatial and temporal structure of traveling ionospheric disturbances (TIDs) at mid-latitudes. In this paper, the array design and signal processing for the AoA sounder is described, along with a sample of results showing typical disturbance signatures. Realistic parameterized models of electron density perturbations, along with geometric ray tracing, were used to synthesize the effects of medium to large scale TIDs on the sounder observables and aid in classifying the measurements.