The All-Sky Interferometric Meteor Radar (SKiYMET) is a scientific instrument used for observing meteors and man-made re-entrant objects as they enter the Earth's atmosphere. From these observations, a wide range of atmospheric and astronomical parameters may be measured. The radar is cost-effective and compact and is designed to run unattended for extended periods. It can be deployed with a minimum of time and effort, and is suitable for both permanent installation and for campaign use. The system software is accessed with the use of a point-and-click graphical user interface, and comprises configuration, control, detection, analysis and graphical display packages. The meteor radar has applications in a wide variety of areas including meteor astronomy, atmospheric physics, space research, space weather, space debris studies and space vehicle launch support.
SKiYMET is a joint development with MARDOC Inc.
When a meteor enters the atmosphere it rapidly vaporises leaving behind a trail of ionised gas along its path of travel.This short-lived trail can be detected by the meteor radar. The ground-based meteor radar transmits a short pulse of energy from a small antenna in the form of very-high frequency (HF/VHF) radio waves. Some of this transmitted energy is reflected back by the meteor trail and is detected on a set of receiving antennas and its characteristics recorded by the meteor radar. Various calculations are then performed on the detected meteor echoes. The results of these calculations can provide information about the nature of the meteor, such as its orbit and its speed of travel on entering the atmosphere. Further, the meteor trail so formed is subsequently carried along (advected) by the electrically-neutral atmospheric wind. By observing how the meteor trail drifts with time, deductions can be made about the speed and direction of the atmospheric wind at the altitude at which the meteor was observed. The instruments detects a sufficient number of meteor echoes throughout the day to enable a comprehensive picture of the wind field to be obtained.
Although many meteor radars have depended upon narrow-beam, large aperture arrays to measure wind velocities, the All-Sky Interferometric Meteor Radar illuminates a broad expanse of sky using a small number of antennas.When a meteor echo is detected, phase differences between the five receive antennas are used to determine an unambiguous angle-of-arrival.The interferometric approach has the advantage over the narrow-beam technique in that the complete vector wind field may be obtained over a period of time instead of only the component aligned with the Doppler radar's beam direction.In addition, narrow -beam radars operating as meteor detection systems are often only available for such use on a restricted scheduling basis - SKiYMET is a dedicated meteor detection and wind measurement instrument capable of achieving meteor count rates of over 20,000 per day.
After analysis, all detected meteor events and, optionally, all acquired raw data are stored for further off-line study. Parameters which may be calculated include:
- meteor flux
- meteor radiant source determinations
- meteor entry velocities
- atmospheric wind velocities
- atmospheric diffusion coefficients
The SKiYMET system hardware comprises two main components:The antenna system and feeders, and the radar system itself.The antenna system is typically composed of two 2-element yagis for transmission and five 2-element yagis for reception, which are light-weight and compact and may be quickly and easily assembled on-site. The complete array when deployed is sparse and typically requires an area of less than 2000 m². For the typical system a total of 6 coaxial antenna feeders are included as part of the antenna system.
Two compact instrument cabinets contain all of the remaining elements of the SKiYMET radar system.The RF components include a solid state transmitter operating in pulsed mode, 5 coherent receiver channels, gain control, and frequency synthesis units.The data acquisition system is composed of 5 coherent high-speed digitisation and buffer memory channels and miscellaneous timing and control hardware.A GPS-locked real time clock provides millisecond-accurate acquisition time stamps for the detected meteor events.
A single PC running a Unix® variant, performs all data acquisition, detection, analysis, display and system control functions in real time.All control functions and data display are accessed via graphical user interfaces with an easy-to-use point and click system.The radar system is easily configured to communicate through any available TCP/IP network point or modem, thus allowing remote control of the radar, and the facility to automatically transfer acquired data to remote hosts.
The diagram to the left shows a "screen shot" of the Raw Event (REV) Display program.This program automatically detects the arrival of new meteor event data and updates its contents accordingly.The 5 graphs on the left of the display represent the magnitude and phase recorded by the 5 receiver channels immediately before, and to about 3 seconds after the detected event (magnitude is plotted in red and phase in blue).The diagram on the top-right represents the average of all 5 channels shown on the left.Below the channel average diagram is shown one of the 5 cross correlation functions calculated between receivers 1 and 2.The phase information contained in the 5 cross correlation functions provides the data required to locate the meteor echo in azimuth and zenith.
Data analysis takes place concurrently with data acquisition and system control, and real-time graphical displays automatically update as results become available.The display mode can be changed using the graphical interface so that various statistics on the data can be shown, revealing current trends in the data quickly and easily.
- Meteor Astronomy
The meteor radar provides data for meteor astronomers.The astronomical community has interest in such things as meteor flux rates, particle size distributions, orbital statistics, the determination of meteor shower source radiants, distributions of meteors, Earth- meteor collision probabilities, and inter-stellar material. Information can be derived about such things as meteor flux rates, orbits and velocities.
- Space Research
Space vehicles, such as satellites, can be damaged by meteor impacts.On infrequent occasions, meteor showers of particular intensity occur and there is much interest in the likelihood of damage being caused to space vehicles by intense showers.The meteor radar can provide information which could lead to a better assessment of the risks posed by meteors to space vehicles.
- Space Debris
There is increasing concern about future problems that may be caused by the growing accumulation of space debris, or "space junk" as it is more commonly known.It may be possible to distinguish between the trails left by normal meteors and those left by space debris re-entering the atmosphere. Such measurements could lead to a better assessment of the problems and risks associated with space debris.
- Atmospheric Physics
The meteor radar can provide frequent measurements of the speed and direction of the winds in the upper regions of the atmosphere.These measurements could augment or replace measurements performed using other techniques which may have disadvantages associated with cost, reliability or intrusiveness.The structure and dynamics of this region of the atmosphere have application to space vehicle re-entry issues and may provide early indications of global climate change.