Error Analysis of Calculated Altitude:

The effect of base line length error on aircraft AGL altitude accuracy is directly proportional to the ratio of the (base length measurement error)/(base length). Because the GPS error is +/- 6 feet for each latitude and longitude site measurement the maximum base line measurement error is +/- 12 feet no matter how far away the sites are. A typical base length is 4000 feet. The maximum aircraft altitude error would be 12/4000= .3% of the aircraft's AGL of the sites. The maximum error would be +/- 1.8 feet for an aircraft actually flying at 600 feet AGL.

The effect of an error of the site's MSL altitude is added directly to the aircraft's altitude. The MSL of the site's is accurate to within 1-foot using USGS maps and Ventura County horizontal bench marks.

The effect of the aircraft not being directly inline between the two cameras will causes two types of errors. The aircraft is dropping down about 10 feet per second and the base length of the altitude calculation triangle is longer. Both of these errors are minimal because the camcorder captures pictures at a rate of about 30 frames per second. If an aircraft is moving at 100 knots then the camcorder will capture a picture of the aircraft every 5.6 feet of travel. The maximum effect of the drop error = .333 feet [(10 feet/sec)/30 frames/sec= .333 feet. The maximum effect in one frame of the base leg being longer on the altitude triangle is .000000033%. This effect on the calculation of the aircraft's altitude by a longer base length is less than .01 feet.

I give the following example to illustrate the effect of an angle measurement input error of +/- .2 degrees on an aircraft 2000 feet away. This is done by adding +/- .2 degrees to the actual elevation angle from the horizon to the aircraft and then doing the calculations for aircraft altitude. For example, if the measured angle for site A and B are both 5.710 degrees then the calculated altitude is 200 feet AGL. The effect of a +.2 degree error= TAN(5.710 + .2) * 2000= 207.0 feet AGL. The effect of a -.2 degree error= TAN(5.710 - .2) * 2000= 192.9 feet AGL. The maximum aircraft altitude error for this example caused by the +/- .2 degree measurement error is +/- 7.1 feet.

The maximum total system error on the calculations of the aircraft altitude would be the addition of all the previous described errors.

1.8 feet the effect of the altitude-triangle base length error

1.0 feet the effect of Topo map and benchmark errors

0.4 feet the effect of an aircraft not being directly inline between the cameras