Research On PRARE And Its Application To Precise ERS-2 Orbit Determination

PRARE (Precise Range And Range-rate Equipment) is a space-borne, two-way, two-frequency microwave satellite tracking system developed by Germany in 1990's. PRARE canautomatically provide precise range and range-rate measurements under all weather condi-tions, with full-rate precision 2.5 - 6.5 cm for range and 0.1 mm/s for Doppler, normal-pointprecision 1 cm and 0.015 mm/s, respectively. Its space segment has been carried by the 2ndEuropean Remote Sensing satellite ERS-2 since April, 1995 and works normally up to now.This dissertation analyzed the tracking data provided by PRARE, and applied the datato precision orbit determination (POD) for ERS-2. In summary, the main contents are asfollow:1. Introducing the system composition and measurement principle of PRARE. Presentingmeasurement models for PRARE observations, especially the space-based two-way range-rate model.2. Analyzing the surface geometric model and attitude transformation characteristics ofERS-2. Presenting the computational formula of cross-sectional area in any direction forthe satellite.3. Introducing dynamic models used in ERS-2 POD, analyzing surface force models inemphasis, including atmospheric drag and lift, solar radiation pressure, Earth albedoand emissivity. Some proper modifications on the models were made. Based on themagnitude estimation of each perturbing factors, made a choice among the perturbationmodels.4. Analyzing the corrections of PRARE observations, and tropospheric delay corrections inemphasis. The comparisons among several mapping functions with high nominal preci-sion showed, that the mapping functions are all similar in accuracy above 5°elevation.5. Analyzing the effect of horizontal station displacement due to ocean loading on PODcWutation, conc1uded that the horizontal station disp1acement caused by ocean loadingshould not be neglected in current computational accuxacy.6. Updating the constants and models in the POD software SHORDE according to IERSConvention (1996). Adding PRARE and ERS-2 models into SHORDE, made the com-bination of SLR and PRARE data for ERS-2 POD possible.7. Editing the PRARE data carefully by using data-edit program PASEDT and DATEDT.8. App1ying the Relmert method of variance-comPonent-estimation to POD comPutationconsidering Givens-Gentleman orthogonal transfOrmation method simultaneous1y. Thismade the data-weighting moe prOPer in POD comPutation while combiaing severalkinds of observations. Moreover, based on the deep analysis of Helmert VCE method,we brought forward a the improved Helinert VCE method n which remove the possiblenegative variance esthaation by using the a priori infOrmation of solved-for parameters.The experAnenis showed that the twroved method was effective in avoiding the negativevariance. The probIems about the strength of a priori constraints and noninteger degreeof freedom were discussed.9. Detendning the scheme fOr ERS-2 POD computation according to experimental com-putations and comPuting ERS-2 orbits in 1997. According to the accuracy assessmentfrom several aspects, the accuracy estAnation of 3 -- 5 cm in radial direction and 10 -- 20cm in normal direction are given. This precision can comP1etely satisfy the requlrementof ocean surface research by using altAnetry, and basically satisfy the requlrement ofInSAR measuxement.