The Portable Satellite Laser Ranger (PSLR) is a light weight, highly portable satellite laser ranging system which employs many of the techniques and equipment types of larger fixed systems. It has a primary telescope aperture of 62 cm and uses a 150 ps pulse of 130 mJ at the second harmonic wavelength of 532 nm. The system is designed to use as little ancillary equipment as possible and only requires one small instrument rack and one PC based control computer. All of the control features of the system are based or installed in the control computer.The PSLR project at Curtin University was concerned with repairing and u p grading the PSLR to return the system to operational capacity. This involved the replacement of missing control components, repair of some hardware, modifications to the control program, and several calibration and operational tests. These tests showed that the PSLR system was capable of a ranging accuracy to fixed targets of 8.5 mm with an average accuracy of 23 mm. They showed that the PSLR was capable, in selective conditions, to track star ephemerides to less than 54. The mount error (standard deviation) over several orientations was shown to be 0.253° in elevation and 0.337° in azimuth.This dissertation will discuss; i) the operation of the equipment used with the PSLR and similar systems, the steps taken to repair or replace the necessary equipment, ii) the tests required to calibrate or evaluate various sub-systems of the PSLR and, iii) the results and conclusions drawn as a result.

One of the applications of the Satellite Laser Ranging (SLR) technique is the derivation of gravity field models; these models have various geophysical and geodynamical applications. Gravity field modelling has reached a new era where the latest satellite missions (CHAMP, GRACE and GOCE) are thought to provide significant improvement of global gravity field information in terms of quality and spatial resolution. In particular, the recent satellite missions carry on-board Global Navigation Satellite System (GNSS) receivers, accelerometers, K/Kaband microwave system (e.g. in GRACE) and gradiometers (e.g. in GOCE) allowing measurements of gravity field with unprecedented accuracy in contrast to the unsteady and fragmented orbit tracking by unevenly distributed SLR ground stations. Numerous gravity field models have been derived based on the newly available data sets by various research groups globally. Due to the availability of high quality SLR and satellite data, some of the older gravity field models are being updated as new models with higher degree and order are developed. Notwithstanding the significant progress in gravity field modelling, research focusing on assessing the accuracy and precision of the existing gravity field models has largely remained insufficient. The difference between the observed and computed satellite orbit (which is often expressed as the O-C range residuals) is used as a parameter for Precise Orbit Determination (POD) of satellites. Furthermore, O-C range residuals computed during SLR analysis are used as proxy parameters for evaluating the accuracy of gravity field models. The work presented in this thesis firstly reviewed and evaluated the accuracy of gravity field models released between 1990 and 2008. The accuracy of the gravity field models was examined by analysing the O-C residuals computed from LAGEOS 1 and 2 data analysis based on a set of twelve gravity field models. The results demonstrated that in general, there has been an improvement in the accuracy of gravity field models released between 1990 and 2008 by a factor of 2 based on improvements in the O-C residuals. Additionally, the influence of SLR tide parameterization (the IERS 2010 solid Earth and pole tide models) on the O-C residuals across five gravity field models has been assessed and results illustrate that the solid Earth and pole tides parameterization influence on the O-C residuals is dependent on the type of gravity field model. In order to ascertain the significance of mean differences in the Standard Deviations (SD) of O-C residuals based on the tide parameterization options, the student’s t-test was used. Results suggest that in general the O-C residuals derived from SLR LAGEOS 1 data have insignificant mean SD differences across the tide parameterizations. On the other hand analysis of SLR observations of LAGEOS 2 resulted in statistically significant mean SD differences in the O-C based on EIGEN-CG03C, EGM2008 and AIUB-GRACE01S gravity field models. The J2 coefficient forms part of the SLR Data Analysis Software (SDAS) package output products and was investigated in this thesis due to its role in understanding mass-redistribution within the Earth system (i.e. the equatorial bulge due to centrifugal force and rotation). In particular, the J 2 coefficient computed from SLR analysis of LAGEOS 1 and 2 data sets and based on the four selected gravity field models were compared with a priori J2 coefficients from the four models and those published in the literature. The results indicated that the J2 coefficients computed from the SDAS package were in agreement with the published coefficients. For geophysical applications, the relationship between the J2 parameter and LOD and AAM was investigated by use of data adaptive analysis methodology (the empirical mode decomposition). The results demonstrated that some degree of synchronization exists between the signal components of J2 and LOD and J2 and AAM. / Thesis (PhD)--University of Pretoria, 2013. / Geography, Geoinformatics and Meteorology / Unrestricted

Satellite laser ranging provides an opportunity to track spacecraft trajectory fluctuationsas well as contributes to study of Earth’s tectonic motions and parameters ofMoon motions. Routine operations of laser ranging are carried out during night-timewhen noise probability is low. Classical approach for distance estimation includesdistance prediction thus reflected signal is expected to arrive during known time intervalcalled gate, however this is not possible when targeted object trajectory is notknown. In these cases gateless registration mode can be applied, but this mode greatlyreduces signal-to-noise ratio. In this thesis filter for noise event reduction during gatelessor full event registration was successfully developed. The filter is applied duringthe post-processing stage to improve signal-to-noise ratio of gathered data from laserranging. Not only the application of filter resulted in reduction of noise events, butalso it provides an insight whether there is an actual useful signal being emitted fromspacecraft. Investigation of event loss during full registration showed loss probabilityof 7.6% for calculated noise rate of 19 events per 0.01 millisecond. The developedfilter in combination with gateless registration mode opens the door for precipitationaltitude determination.

An increasing number of GPS applications require a high level of accuracy. To reduce the error contributed by the GPS ephemerides, an accurate modeling of the forces acting on GPS satellites is necessary. These forces can be categorized into gravitational and non-gravitational forces. The non-gravitational forces are a significant contribution to the total force on a GPS satellite but they are still not fully understood whereas the gravitational forces are well modeled. This study focuses on two non-gravitational forces: Solar Radiation Pressure (SRP) and the y-bias force. Different SRP models are available in the University of Texas Multi-Satellite Orbit Determination Program (MSODP). The recently developed University College London model was implemented for the purpose of this study. Several techniques to compute parameters associated with SRP models and the y-bias force during an orbit prediction were examined. Using the International GNSS Service (IGS) precise ephemerides as a reference, five different models were compared in the study. Satellite Laser Ranging (SLR) residuals were also studied to validate the approach. Results showed that the analytical UCL model performed as well as a purely empirical model such as the Extended CODE model. This is important since analytical models attempt to represent the physical phenomena and thus might be better suited to separate SRP from other forces. The y-bias force was then shown to have a once per revolution effect. The time evolution of the y-bias was found to be dependent on the SRP model used, the satellite Block type, the orbital plane, and the attitude of the satellite which suggests that estimates of y-bias contain errors from other sources, particularly the SRP models. The dependency of the y-bias evolution on the orbital plane suggests that the orientation of the plane towards the Sun is important. / text