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Triangulation and Orbit Determination

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Analysis Techniques

Meteor Capture

Most cameras of the NEMETODE network reside in wall / post mounted CCTV housings with internal heaters. To protect them from direct sunlight falling onto the sensors the cameras and their auto-iris lenses are activated by electronic time-switches. Each camera is connected to its own dedicated desktop PC running UFO Capture software. Video capture (nominally 720 x 576 pixels at 25 frames per second) is performed either by an internal video card or a USB 2.0 capture device, with a resultant CPU loading of <20%. The Operating Systems in use are Windows Vista and XP.

UFO Capture was installed and configured as described in SonotaCo’s Night Sky Observation Guide and the UFO Capture Manual.


Technical Notes

One of the longstanding objectives of the team has been to share knowledge / expertise with respect to meteor videography techniques. As sufficient details become available, this information is consolidated into Technical Notes.

Technical Note #1
Technical Note #2
Technical Note #3
Technical Note #4


Hints & Tips

From our experiences (the school of hard knocks) we recommend the following PC settings and maintenance schedule:

Disable Hard Disk Drive Power Saving. This avoids the loss of meteor captures if the HDD has been spun down by a Power Saving setting.

Schedule automatic Windows Updates and security scans to occur during daylight hours or run them manually, otherwise they will slow down your PC and might reboot it during the night when it should be detecting meteors!

Reboot the PC at least once per week to ensure that any cumulative memory issues don’t lead to problems during the observing runs.

Check that the PC's air inlets are unobstructed, clean and dust free. Keep the cable runs neat and tidy to avoid restricting the airflow.

Consider a separate HDD for UFO Capture. The Leeds PC uses the same HDD as the OS, but a dedicated HDD might improve performance in some cases.

Synchronise the PC clock with an SNTP time service. The timestamp for each meteor video is taken from the PC’s internal clock. The default Windows Time Service is not accurate enough. The NEMETODE PCs are synchronised every 15 minutes with an Internet time server using Dimension4 software. This software saves a text file of the timing corrections that have been applied to the PC’s internal clock. This data is reviewed prior to each analysis to ascertain if large (>0.5 s) changes occurred during observing runs (and could therefore have affected the timing data).

When running more than one capture PC it is recommended to stagger their synchronisation requests or set up one PC as a time server for the other PCs.

Set the PC clock to GMT and disable the “Automatically Adjust to Daylight Savings Time” feature. The timestamps for each meteor will then always be in UTC and won’t suddenly jump by one hour twice per year when daylight savings starts / finishes. This is particularly useful when analysing meteors captured by multiple stations.

Anti-virus and Firewall protection. Auto-synching the PC clock and installing Windows updates require a permanent Internet connection. Make sure that each PC is protected by up to date anti-virus software.

Use a large HDD (>100GB). NEMETODE’s systems are configured with high sensitivity settings to maximise the meteor captures, which also include cosmic ray hits, electronic blips, flights of ‘planes, birds, insects, etc, consuming several GB of disk space per night. On a regular basis (typically daily) the video clips from the previous night are reviewed and non-meteor events are deleted.

Defragment the HDD every week. Creating and deleting very large files can lead to portions of the same file being located on different sections of the HDD as opposed to all in the same place. This can cause problems with UFO Capture as the write heads on the HDD search for clear sections of disk to write to.

Data backups. Copy meteor captures to separate hard-drives and flash drives for safety backups and later analysis.

Cable runs. A combined video / power cable can be used between the CCTV housing and the PC though separate dedicated cables for power and video are highly recommended as they are often of much better quality.

Uninterruptible Power Supply (UPS). If a PC and/or CCTV housing are at risk from mains power cuts a UPS can protect them for up to about 30 minutes. It is also recommended to connect the equipment to a mains surge protector.

Some users have reported "banding" interference in the video signal - and have been able to correct it by fitting a "Coaxial Video Ground Loop Isolator" in line with the video feed from the camera. Normal practice is to place it next to the camera but good results (from a location suffering from extensive background electronic noise and where it was suspected the video cable was acting as a receiving antenna) have been obtained by fitting it just before the video capture input on the PC.

The videos associated with each capture are typically too large to email and can be compressed to more manageable sizes (circa 4MB) using software loaded as standard with a Windows Operating System - see instructions for Windows XP and Windows 7.

NEW: Much of the above, together with additonal information, was discussed at the BAA/NEMETODE Meteor Section Workshop Meeting held in Birmingham on the 27th September 2014. The main slide deck provides an overview of what was used to initiate much of the discussion and in addition we have the slides from Alex on UFO Capture and UFO Analyser. The MS Excel template for analysing the output from Dimension 4 (commonly used for applying time corrections to PCs) is available here.


Meteor Analysis

The capture files are copied to other computers (e.g. Windows 7 laptop) where they are processed as described in the UFO Analyser Manual.

In addition, a number of custom NEMETODE checklists and spreadsheets are used to confirm the quality of the profile used, to analyse any timing corrections, to provide an independent check of concurrence of event start times and to perform orbital parameter analysis. The main checklist is the Profiles Checks and Adjustments (PCA) Quality Checklist.

Each month, the NTP history.txt file from Dimension 4 is checked for any timing corrections > 1.0s. A spreadsheet to aid analysis is available here.

The SonotaCo website and BBSForum are checked for any new software updates (e.g. updated software versions, leap second correction files). If a new version is available, the NEMETODE team schedule an upgrade.

For each night’s events the following checks are applied in UFO Analyser:

Is there good overlay and registration of the reference stars and the scintillation masks? If not, a new profile is created and logged in the PCA file.

Does the computed meteor trajectory match the trail on the video? If not, the Mask Editor and Profile/Analyse tabs are used to modify the ‘ddl’ and ‘leap’ settings until a best match is achieved. Any misalignment is recorded in the PCA Quality Checklist. (The NEMETODE team has found that in about 10% of cases the assigned meteor trajectory is slightly misaligned and has to be reanalysed).

Does the meteor appear within the first second of the clip? If it occurs later, (perhaps because the capture was triggered by an aeroplane within the field of view), then a timing correction is applied. The correct start time is noted by stepping through the clip, frame by frame, then the M*.XML is edited with the corrected time and the clip is reprocessed through UFO Analyser. Modifying the frame range parameters ‘f1’ and ‘f2’ can help in the re-analysis.

The resultant M*.CSV files are then shared between the members of the NEMETODE team. A custom spreadsheet lists how many events have a common start time (±1.0 s) and thus may be multi-station captures of the same event. These are compared against UFO Orbit’s automated matching feature at the quality levels Q1, Q2 and Q3. Another spreadsheet records the efficiency of the NEMETODE network.

A further spreadsheet logs the time, Q-level, magnitude, radiant point, geocentric velocity and orbital parameters of multi-station meteors.

Finally, if sufficient good quality data have been obtained, a report is prepared for submission as a formal paper to a journal.

Archived data will be made publicly available on the NEMETODE website.

All these stages of meteor analysis are summarised in the NEMETODE Workflow flowchart.