|
|
||||||
| PCV Calibration of GPS Antennas Absolute PCV Field Calibration Discussion of Absolute PCV Absolute PCV Calibration of AOAD/M_T Absolute PCV Results of AOAD/M_T Summary Publications (including pdf-downloads) |
||||||
| Absolute PCV Field Calibration - Basics and
Procedure Starting point for the development of this procedure was, that existing field calibrations were only relative (refering to a reference antenna) and correlated with the site (multipath influence and satellite constellation, i.e. northern hole). The goals were
The realization has two features to handle the problems "relative" and "multipath influence". First of all, in order to get the absolute PCV information, the test antennas are rotated AND inclined. Secondly, differences between observations with identical multipath effects are used to eliminate site correlations. Antenna Mount |
||||||
|
||||||
| During
the first development phase of the project we used the two mounts shown above
(a, b). In order to achieve a better stability and precision, the current
procedure makes use of a robot (c). Considerable efforts were necessary to
develop an error model for the robot. The observations for this modell are
derived from a tachymetric measurement system (TMS). Beside an exactly known
position due to the precise robot and the high number of possible rotations and
tilts, another advantage is the possibility of an automation of the calibration
procedure. Multipath Elimination and PCV Estimation The satellite constellation repeats after a mean sidereal day. In case of identical conditions (geometry, weather, surfaces ...), also multipath effects repeat with the same period. Thus, with the pre-conditions fulfilled, day time differences eliminate the multipath influence. Since the PCV information is elimated also, the antenna has to be rotated and tilted on one of the two measurement days. The difference of the PCV between the rotated/tilted position and the fixed position will be the observable for the PCV determination. - NEW - The multipath elimination approach has been improved within the second phase of the project. The current calibrations are a real-time procedure without a static reference day. The multipath conditions between close measurement epochs are identical. Therefore, the difference between epochs can eliminate the effects (the realization within the software uses the correlation in time of the multipath). Finally, with both possibilities for the multipath elimination/reduction, spherical harmonic functions serve for the PCV estimation.
The high resolution of the PCV and the possibility to estimate reliable and repeatable azimuthal PCV is based on the automation of the measurement program. With the help of the robot, there are between 4000 and 7000 different positions (standard procedure) of the antenna. The measurement program changes with the actual satellite constellation. Thus, a total coverage of the whole antenna hemisphere is reached. Furthermore, a dynamical elevation mask is used (only satellites in high elevations) within the observation procedure. With the presented procedure (especially through the use of a highly precise and calibrated robot and the automation of the measurements), very precise and reliable PCV corrections can be derived (e.g. see AOAD/M_T results), even down to elevation zero and also for azimuthal PCV. The results have been independently confirmed through measurements
More detailed information can be found in several publications. |
||||||
  |
||||||
| last change
25.02.2008 by webmaster Institute of Geodesy |
 |
| Schneiderberg 50 · D-30167 Hannover · Tel.: (++ 49) 511 762 2795 · Fax.: (++ 49) 511 762 4006 |
| email: office · email: webmaster |