ASGARD All-Sky

The ASGARD software was first designed to detect very bright meteors in all-sky imagery from multiple recording sites.

Importance

There are many reasons as to why meteor observations in this size range are important:
  • Flux measurements of centimetre sized meteoroids
  • Detection of meteor shower outbursts
  • Better understanding of the ablation process through multi-instrument comparisons with other instruments (radar, infrasound, VLF, etc...)
  • Comparisons also provide contraints for numerical entry models
  • Deceleration measurements allow for density determinations
  • Being able to pinpoint a meteorite fall, should one occur
  • Tracing out pre-fall meteorite orbits
Camera Hardware

ASGARD typically runs on low-light black and white video cameras with all-sky lenses, however there are many different types of cameras and lenses that can be used. On the Western network (which is part of the Southern Ontario Meteor Network (SOMN) run by Peter Brown), this is the equipment currently used:
  • HiCam HB-710E CCD camera
  • Rainbow L163VDC4 1.6-3.4 mm f/1.4 lens
  • Brooktree 878A framegrabber
  • US GlobalSat BU-353 USB GPS
The GPS is used to ensure the clock is accurate enough to compare to other instruments, such as the Canadian Meteor Orbit Radar (CMOR).

The camera and lens are enclosed in a weather proof enclosure, which was constructed by Zbyszek Krzeminski, and is pictured here:



The SOMN currently consists of 13 cameras, located throughout South Western Ontario, and in Ohio (USA). Some are located at:
  • Elginfield Observatory, north of London
  • McMaster University, in Hamilton Ontario
  • CMOR, near Tavistock Ontario
  • The RASC Carr Astronomical Observatory, near Collingwood Ontario
  • RoboSky, near Orangeville Ontario
  • various RASC member's homes
Each camera will produce a stacked image similar to the following to be used for calibration purposes (both astrometric and photometric):



In this image, the constellation Orion is easily visible. There are some hot pixels with these cameras, but these are present in most SONY HAD CCD chips due to the way that they are manufactured. The white arrow in the upper right corner of the image indicates how the camera is rotated, and points towards North. East is measured counter-clockwise from North, and there are some clouds visible in the South East.

This camera is sensitive to meteors down to about magnitude zero, and can see much fainter stars (through frame stacking, as shown in the above image).

Detection Algorithm

When running in all-sky mode, ASGARD detects meteors by counting the number of neighbouring pixels that have increased in intensity from a previous frame by a configured threshold. Regions of the image that should not be triggered on can be masked out, although the software is also capable of dynamically masking out constant triggers, such as smoke stacks or lights on the horizon.

In the following two figures:

 


You can see the grouping of pixels that would be detected. For such a grouping, the position is determined through a centre-of-mass weighted by the intensity. This position is then converted to a zenith and azimuth angle pair through the use of a plate calibration file (determined from visible stars in a stacked image).

Photometric measurements are also measured, which gives an estimate of the meteoroid mass. The entire process is completely automated.