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Instrumentation

Instrumentation used by the Space and Atmospheric Physics research group are listed below:

  • Radar: Meteor

    Meter Radar LayoutThe University of Adelaide Space and Atmospheric Physics Group maintains a number of meteor radars, which are used for the measurement winds in the 70-110km height region, estimating the diffusion rate of ions (which is related to air temperature and pressure), and astronomical surveys of where meteors come from both within and outside the solar system.  Detailed studies of meteor radar detection are also leading to new insights into the density of the upper atmosphere and the composition of meteoric material that is deposited in the atmosphere.

    Meteors are narrow trails of plasma that form behind bodies entering the atmosphere.  Many objects are entering Earth’s atmosphere at any given moment, most of them about the same size or smaller than a grain of sand.  These objects, called meteoroids, travel at speeds in excess of 10 km/s and are heated by collisions with air molecules to temperatures hot enough for evaporation to occur.  The evaporated molecules and atoms are travelling fast enough that further collisions with air molecules can knock electrons off.  The mixture of free electrons and ions, called plasma, in a narrow trail behind the meteoroid reflects radio waves.  Using the right radio frequency, meteor trails are excellent targets for study with radar.

    Most meteor radars used today are comprised of a single transmitting antenna and a receive array of five antennas.  The receive antennas are arranged to form two perpendicular interferometer baselines.  The angle to returning radio waves from meteor radar echoes is determined by comparing the phase of the radio waves on the different antennas.  Our radars operate in 33-55 MHz VHF portion of the electromagnetic spectrum and can detect as many as 35,000 meteors per day.  We operate radars at Buckland Park near Adelaide, Darwin in the Northern Territory, and Davis Station in Antarctica, as well as with partner institutions at locations across the globe.

  • Radar: Boundary Layer

    Boundary Layer - Tropospheric Radar located at Adelaide AirportBuckland Park BLT Radar

    The Spaced and Atmospheric Physics Group in collaboration with Atrad operates a 20 kW, Boundary Layer - Tropospheric Radar (BLT), operating at 55 MHz, at the Buckland Park field site. This radar obtains wind measurements from 300 m up to 10 km (depending on atmospheric conditions).

    (Image shown on right is of a similar radar located at Adelaide Airport)

    Personnel

  • Radar: Medium Frequency (MF) Layer

    The Spaced and Atmospheric Physics Group operates a 64 kW Medium Frequency (VHF) radar at the Buckland Park field site. This radar obtain wind measurement from the lower ionosphere from 50 to 100 km.

    Personnel

    Medium Frequency Radar at the Buckland Park field site

  • Radar: Stratospheric-Troposperic (ST)

    55 MHz ST / all-sky meteor radar

    The Spaced and Atmospheric Physics Group operates a 80 kW VHF (55 MHz) ST / all-sky meteor radar at Buckland Park. This system is a 6 receiver channel radar operated in an interleaved mode as a Stratospheric Tropospheric (ST) radar, and as an all-sky interferometric meteor radar. A very similar system is operated at Davis Station in Antarctica and is described by Reid et al., (2006).

    In meteor mode, operation is identical to that applied to dedicated all-sky meteor systems (see e.g., Holdsworth et al., 2004) and it utilizes a single folded cross-dipole antenna for transmission and a 5-antenna interferometer for reception. The BP radar uses circularly polarized crossed dipoles for reception whereas the Davis Station radar uses linear polarization on reception. At BP, operation in meteor mode is allocated about 2/7 of the time on the radar, resulting in typical count rates of about 5,000 unambiguous meteors per day.

    In ST mode, the radar uses a single receiver channel. Beams are directed to any of five positions, four off-zenith at 15º towards the east, west, north or south, and one directed vertically. One particularly intersting feature of this radar is that it measures winds from an altitude of 400-m, much lower than comparable 50 MHz systems elsewhere to over 20 km (depending on weather conditions).

    Personnel

  • Radio Acoustic Sounding System (RASS)

    The Spaced and Atmospheric Physics Group utilizes a Radio Acoustic Sound System (RASS) in conjunction with their VHF radars to obtain temperature measurements from near ground to over 5 km. Actual coverage is very dependent on speaker placement and background winds.

    Personnel

  • Photometers

    The Space and Atmospheric Physics group's three-field photometer instrument observed atmospheric nightglow from the 557.7 nm atomic oxygen (O(1S)) and 730 nm hydroxyl (OH (8-3) Meinel) bands, at 97 and 87 km in altitude respectively, from April 1995 through to late 2010, at the Buckland Park field site about 40 km north of Adelaide. The instrument was designed initially to study the characteristics of internal gravity waves in the mesosphere with periods of up to several hours, but recently the dataset acquired by the instrument has been seen to allow the determination of some much longer-term and more fundamental atmospheric parameters on the global scale, as well as providing a useful means of comparison with the other instruments at Buckland Park studying the same region.

    Atmospheric Airglow and Its Origin

    At any location, and even on the clearest and calmest of nights, the Earth's sky isn't completely dark. Many would instinctively think that a phenomenon like the Auorora Australis or Borealis may be responsible for this; this is true, but such a thing is only observed in the regions of higher latitudes. As a matter of fact, the Earth has its own natural light source ubiquitous in the upper atmosphere - a result of various chemical processes dependent on the atmosphere's temperature and dynamics. In the mesosphere-lower-thermosphere (MLT) region (altitude ~ 100 km), where the air pressure is roughly one millionth of that at the Earth's surface, the incoming solar radiation has sucient energy to dissociate (ionize) the molecules constituting the atmosphere, resulting in this region being composed mainly of free electrons and ions. Depending on the background temperature and pressure, these free electrons and ions may recombine to create neutral molecules. Given the large oscillations in temperature and pressure propagating through the atmosphere on a global scale at all altitudes (including those in the MLT) and the varying solar radiation intensity throughout a given 24-hour period, the composition of this region ends up being very dynamic.

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  • Spectrometer

    Czerny-Turner Spectrometer

    The spectrometer is a high throughput, modified Czerny-Turner spectrometer fitted with long, Fastie-type, curved entrance slits. The detector is a 1024x1024 Peltier/water cooled CCD device coupled to large aperture f/1.2 lenses. More detail is given in Sivjee and Shen (1997). The instrument's wavelength and intensity response are calibrated using a krypton reference spectrum and a reference black body emitter. Before any data analysis is carried out, a dark image is subtracted from a data image to remove intensity contributions from instrument noise.  Generally the dark image is recorded once an hour during data acquisition.

    OH Temperatures

    OH temperature estimates are calculated using the standard "ratio of lines" method from the 6-2 OH band.  The J constants for each OH line were obtained from Mies (1974), the Einstein A coefficients for each OH line from Langhoff et al. (1986), the rotational terms for each OH transition from Coxon and Foster (1982) and the nominal centre wavelengths (in nm) of each transition OH line emission were obtained from Greet et al. (1998). The "average" OH temperature uses the temperatures derived from the P1(2):P1(3) and P1(2):P1(4) ratios.

    Two different methods are used to estimate the "intensity" of the OH lines. The simplest, referred to as the "height" method, used the peak's maximum recorded value.  The alternative, dubbed the "intensity" method, used an integrated intensity under the peak.  Both methods yield similar results although the "height" method is slightly better if the spectrum is a little noisy.  The main problem with the intensity method is that it is hard to positively identify the integration bounds at times and this can lead to an incorrect integration.

    O2 Temperatures

    Unlike the OH temperatures there is no analytical method for calculating temperatures from the O2 band.  Consequently the recorded spectrum and must be compared against a temperature-dependent model spectrum.  The temperature which gives a model which is a best fit for the recorded spectrum is deemed to be the O2 temperature.

    In the case of the spectrometer data there is considerable difficulty in carrying out this process because the shape of the O2 band emission often differs from that of the model.  This can cause the software to converge on a mathematically best fit which may not be optimum.  The practical result of this is a temperature time series which is much noisier than that produced from the OH analysis.

    Both the "integrated intensity" and "peak height" properties are used separately to compare the model and recorded spectrum.  The "peak height" results tend to be the better of the two due to difficulties in identifying equivalent integration bounds in the spectra, particularly in the recorded spectrum due to bleed from nearby unrelated spectral features.

    References

    • Coxon and Foster, OH(6-2) P1{} values from Table 4, f_1f(J) column in Can. J. Phys., 60, pp41-48, 1982
    • Greet et al, Ann. Geophysicae, 17, 77-89, 1998
    • Langhoff et al., Table IV.D, J. Mol. Spectroscopy, 118, 507-529, 1986
    • Mies, F., Table C.IV, J. Mol. Spectroscopy, 53, 150-188, 1974
    • Sivjee, G.G., and D. Shen, Auroral optical emissions during the solar magnetic cloud event of October 1995, J. Geophys. Res., 102, 7431-7437, 1997
Space and Atmospheric Physics Group
Please direct any enquiries to:

School of Physical Sciences
The University of Adelaide
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AUSTRALIA

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physicalsciences@adelaide.edu.au