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GT-1 Data Files A significant amount of data is collected from both the gravimeter for post-processing, as indicated by the following file description. Together with this information, the data gathered from the GPS receivers on board the aircraft and at the base stations(s) is used during post-processing to generate values of delta-g for the survey. Gravimetric data (G-file)
This file contains measurements from the gravimetric sensing element (GSE) and the horizontal accelerometers as shown in Table 1.
Table 1
Where: Top time from initialization of the gravimeter Tgps Greenwich time (hh, mm, ss) received from GPS Tsynh time interval (sec) from the beginning of the Greenwich second (defined by the sync pulse received from GPS) up to the end of the referenced interval Wz Wxh, Wxa, Wya average values of the components of apparent acceleration of the fine and coarse channels along axes of the azimuth-free coordinate system at the time interval [ti -dt, ti] (dt = 16/300 sec). Wz and Wzh are smoothed by an a-periodic filter of the first order with a time constant of 2 sec. oWz, oWzh, oWxa, oWya average values of the components of apparent acceleration along axes of the azimuth-free coordinate system averaged over the previous time interval dt text, tkpl, tkwz, tkoe increments in normalized temperatures: external, gyro-platform, gravimetric SE, gravimetric SE resistor Nh number of 1/300s measurements of Wz in excess of 0.25 g (N1 or fine) range and Wzh 0.5g (N2 or coarse) range for the previous interval of 1/9 sec. Nh = N1 + N2 x 1000 GV data file (S-file)Each line in this file contains the parameters presented in Table 2. Table 2
Where: Top time from initialization of the gravimeter Tgps Greenwich time (hh, mm, ss) received from GPS Tsynh time interval (s) from the beginning of the Greenwich second (defined by the sync pulse received from GPS) up to the end of the mentioned interval vxa, vya values of the normalized projections of the relative angular velocity at current Greenwich time ti qN the value of the North component of absolute angular velocity Aghk the value of the azimuth-free co-ordinate system heading; calculated clockwise C the value of the azimuth angle between the instrument and the azimuth-free co-ordinate systems; calculated clockwise dvxa, dvya values of the corresponding normalized damping signals tdp, tdq values of the corresponding damping algorithm estimations DUx, DUy, DUz values of the rotation angle of the internal gimbal window, external gimbal window and the gravimeter body relative to the base, respectively. When axis Y of the platform is parallel to the longitudinal axis of the aircraft, positive values of DUx and DUy correspond to nose-up and left-wing up, respectively. DUz is positive when the aircraft is rotating anti-clockwise. SY status of GPS hardware and data readiness in hex-format. Values of the SY bits are given in Table 3. Transfer to linear velocity values is provided by the formula V = v · R, where R = the Earths radius. Table 3
Header file (H-file) The header file includes service information on the flight plus various constants:
F = 55o4835.5 geographical latitude of the starting point (reference point) L = 35o4214.6 geographical longitude of the starting point (reference point) H = 157.123 m altitude of the starting point above the reference ellipsoid G = 9.812345 m/s2 gravity force acceleration at the starting point. If data is not available, G = 9.810000 m/s2 is recorded D = 13:04:2001 date of flight Xant X coordinate (lateral axis of the aircraft) of the GPS antenna Yant Y coordinate (longitudinal axis of the aircraft) of the GPS antenna Zant Z coordinate (vertical axis of the aircraft) of the GPS antenna Kwx correction to the scale factor of accelerometer X Kwy correction to the scale factor of accelerometer Y Kwzm correction to the GSE scale factor, small range Kwzb correction to the GSE scale factor, large range Kp correction to the scale factor of gyro X Kq correction to the scale factor of gyro Y Kr correction to the FOG scale factor dp gyro drift along X axis dq gyro drift along Y axis dr FOG drift along Z axis dWx zero drift of accelerometer X dWy zero drift of accelerometer Y Awx nonalignment of accelerometer X Awy nonalignment of accelerometer Y Ay non-orthogonality of gyro axes Betz non alignment of GSE about X axis Gamz non-alignment of GSE about Y axis dDUx zero signal of angular-data transmitter X dDUy zero signal of angular-data transmitter Y dDUz zero signal of angular-data transmitter Z Kwxq scale factor of GSE root-mean-square correction Kwyq scale factor of GSE root-mean-square correction Down-load the above information together with the Technical Description (pdf 312 KB). |
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Canadian Micro Gravity Ltd
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