Changes between Version 5 and Version 6 of Processing/LeverArmOffset


Ignore:
Timestamp:
Dec 18, 2008, 3:24:23 PM (15 years ago)
Author:
benj
Comment:

Updated due to previous incorrect information about direction of gamma angle

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  • Processing/LeverArmOffset

    v5 v6  
    77The distance is from the phase centre of the master (rear) antenna to each sensor's "prime" point; so for the ATM it is the scan mirror centre, for the Eagle, Hawk and CASI ideally the focus point of the lens.
    88
    9 The angles (as used in aznav) are:  gamma is the positive angle from the horizontal through the antenna to the sensor prime point and delta is positive to starboard from the centre line direction of the aircraft.
     9The angles (as used in aznav) are:  gamma is the positive angle from the vertical through the antenna to the sensor prime point and delta is positive to starboard from the centre line direction of the aircraft.
    1010
    1111Initially it is necessary to make sure you have the correct sensor prime point coords as observed.
    … …  
    1414
    1515----
    16 Jan 2008 numbers:
     1618th Dec. 2008: Due to confusion about angle directions, the originally computed gamma angles are incorrect. The error caused should be of similar magnitude to the previous, similar error (ie ~1.5m along-track for ATM, other sensors will have a smaller error). Because the error will be partially compensated for by boresight angles depending on flight altitude, the "wrong" numbers should be used anyway unless you re-calculate the boresight angles.
     17
     18Jan 2008 numbers (Wrong but use anyway):
    1719||       ||  Gam   ||   Del   ||  Dst   ||
    1820|| ATM   || 1.2258 ||  0.0051 || 1.7380 ||
    … …  
    2022|| Hawk  || 0.9705 || -0.0049 || 1.7985 ||
    2123
     24Jan 2008 numbers (Corrected for reference but use "wrong" numbers above):
     25||       ||  Gam   ||   Del   ||  Dst   ||
     26|| ATM   || 0.3450 ||  0.0051 || 1.7380 ||
     27|| Eagle || 0.4960 || -0.0036 || 1.7441 ||
     28|| Hawk  || 0.6003 || -0.0049 || 1.7985 ||
     29
    2230----
    23312006 obs and results as follows:
    24 
    25 11th Mar. 2008: Note that the email below contains the numbers as originally received, but calculation of the Gamma angle contains an error - "gam = acos( abs(dz) / dst )" should use asin, not acos. Del and Dst are unaffected. Investigation of this suggests this causes an along-track error of approx. 1.5m in all 2006/2007 delivered data for ATM, which may be partially corrected by boresight correction (since these numbers were computed using the incorrect lever-arm numbers) depending on flight altitude. Other sensors have smaller errors, since the effect of the original calculation error is smaller for the offset angles of these sensors. Correct lever-arm numbers are below for reference, new boresight numbers would need to be computed to use these.
    26 
    27 Corrected 2006/7 lever-arm numbers (use "wrong" numbers below unless you recompute boresight correction)
    28 ||       ||  Gam  ||   Del     ||  Dst  ||
    29 || ATM   || 1.306 ||  0.006353 || 1.741 ||
    30 || Casi  || 1.098 ||  0.007934 || 1.702 ||
    31 || Eagle || 0.873 ||  0.000781 || 1.994 ||
    32 || Hawk  || 0.806 ||  0.000682 || 2.117 ||
    3332
    3433{{{