METAL Event Analysis

I wrote a companion program, called METAL (Meteor Analyser) which can perform complete event reductions, although this program has no automated analysis.

Astrometric Plate Calibration

The first function of METAL is to be able to calibrate the pixel locations against zenith and azimuth angles. This is done using the camera latitude and longitude as well as the SKY2000v4 catalogue. The equatorial position for each visible star from the catalogue is converted to a local coordinate, and then a centre-of-mass function is applied to a stacked calibration image to obtain the pixel position to sub-pixel precision.

For all-sky images, a non-linear fit to an eight parameter set of equations is made.

However, for 'regular' images, two ten-parameter fits are made. The yellow error arrows ("errows") show the resulting fit residuals. In the above images, the errows are drawn at ten times their true size, while for the images below, they are 100 times their true size.

Event Reduction

After astrometric plates have been made, a multi-station event can be reduced to determine its trajectory in the atmosphere. This includes its speed, radiant, and both the beginning and ending heights.

For each video frame, a point must be selected along the leading edge of the meteor that represents where the meteor was at that time. Care must be taken as blooming that occurs when the meteor brightens may introduce an artificial acceleration in the trajectory solution, and this acceleration does not actually happen.

All pixels that correspond to the meteor must then be masked out. This allows the total light emitted in each frame to be found, and the result when plotted as a function of frame number (or time of each frame) gives a light curve.

The magnitude values that are measured are in an arbitrary instrumental scale, but can be converted to the 'standard' scales by calibrating the brightness of the stars against their standard magnitudes from the star catalogue used.

With this calibration, the light curve can be mathematically integrated to give a photometric mass estimate. Of course, if any of the pixels saturate, then the mass will be an under-estimate, however work is on-going to correct this effect. Saturation is indicated in METAL by drawing that part of the light curve in a magenta colour.