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Bernese GPS Software Version 5.0 - Bernese GNSS Software

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7.7 Special Applications<br />

(8) The screening procedure should be performed iteratively repeating the processing<br />

steps (5) to (7).<br />

Introduce the improved orbit from the previous iteration to MAUPRP. You may now<br />

reduce the screening level for the zero-difference observations. Make sure that you<br />

reset the marking flags in the observation files from the previous run (disable the<br />

option “Mark if marking flags in observation file”).<br />

Due to technical reasons, <strong>GPS</strong>EST can handle standard orbit and radiation pressure<br />

files only if no stochastic pulse parameters are included. For that reason, the LEO a<br />

priori orbit for <strong>GPS</strong>EST has to be the initial orbit (from processing step (4)) together<br />

with the corresponding radiation pressure file for all iterations.<br />

Usually, after the second iteration the screening is finalized.<br />

(9) The reduced-dynamic orbit resulting from the last update from ORBGEN is already of<br />

good quality. In order to generate a reduced-dynamic orbit with a shorter interval for<br />

the stochastic pulse parameters, it is necessary to run <strong>GPS</strong>EST again with an increased<br />

“Number of parameter sets per day”. It is important to pay attention that the interval<br />

between subsequent pulses is a multiple of the integration step size for the equation<br />

of motion previously specified in ORBGEN.<br />

The determination of a kinematic trajectory works in an analogue way as for a roving<br />

ground station (see Section 10.4). The reduced-dynamic orbit generated with the procedure<br />

described above may be selected as a priori information and the screened phase observation<br />

files may also be used for the determination of the kinematic trajectory.<br />

7.7.1.3 Import of LEO Attitude Files<br />

Each LEO has its own attitude characteristics and in most cases the real attitude behavior is<br />

measured with star cameras onboard the satellite. These measurements are then distributed<br />

in special attitude files with different file formats for each satellite mission. Besides the<br />

<strong>Bernese</strong> attitude file format (description in Section 22.7.13) the <strong>Bernese</strong> <strong>GPS</strong> <strong>Software</strong>,<br />

<strong>Version</strong> <strong>5.0</strong> supports at the moment the CHAMP (auxiliary) data format and the JASON<br />

format from CNES (Centre Nationale d’ Études Spatiales).<br />

All attitudes files have the default extension ATT. The files in CHAMP data format may<br />

also be transformed to the <strong>Bernese</strong> attitude file format with the program LEOAUX (using<br />

the RUN<strong>GPS</strong> command, see Section 18.8). This makes sense, e.g., if you would like to extract<br />

the accelerometer and maneuver data from the CHAMP auxiliary files.<br />

If you have attitude files available for other LEOs you would like to process, you have to<br />

implement these new attitude file formats in the subroutine ${LG}/READATT.f90. Within<br />

this subroutine you find two sections corresponding to each of the supported formats.<br />

The first section is to distinguish between the supported formats looking at the first line of<br />

the attitude file. The variable iAuxFlg(if) is set according to the decision (for the <strong>Bernese</strong><br />

attitude format called ”pre-preprocessed attitude” this flag stays zero). In addition, the<br />

number of lines in the file are counted for the allocation of the corresponding variables later<br />

in the subroutine.<br />

<strong>Bernese</strong> <strong>GPS</strong> <strong>Software</strong> <strong>Version</strong> <strong>5.0</strong> Page 159

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