gps英文论文翻译

gps英文论文翻译内容摘要：

s for the noise of the observables can easily be found from an assessment of the measurement precision. In our case, the carrier phase observables have been assigned a measurement noise of 2 cm.The process noise of the state vector elements is in general more difficult to determine. For simplicity, it is assumed to result from an integrated white noise process,which means that the process noise increases linear in time. It is denoted qi for the filter state element i and is characterized with the standard deviation σ and τ time constant s. The process noise matrix has diagonal structure and the elements of the main diagonal are found from qi =σi2Δt/τi. The time difference Δt denotes the time between the consecutive epochs.For the process noise settings of the satellite clock states, no distinction is made between the individual clock types. Instead, the process noise settings are the same for all GPS satellites. The clock offsets have a process noise with a standard deviation of 3 cm and a timeconstant of 600 s. The clock drift process noise has a standard deviation of m/s (amp。 1012 s/s) over 900 s. Though these simplified assumptions do not strictly reflect the selected twostate clockmodel, they are favored for a realtime capable process pared to more elaborated clock models with characteristic process noise settings depending on the satellite block type (Senior et ) or even on the individual satellite clocks (Hutsell1996) adds more plexity, since changes of the used onboard frequency standard or untypical clock behavior must be detected to adjust the process noise , the benefits of the model would not be fully exploited. Adapting the settings in realtime from recent data significantly increases the putational load and has therefore not been attempted. However, a rigor assessment of the benefits different clock models deems helpful to identify possible enhancements. The differential zenith path delay of the ground stations are assumed to vary only marginally over time. Consequently,only a small amount of process noise with a standard deviation of 2 mm over 1 h is assigned. On the contrary, the ground station clock offset will exhibit noiselike behavior with deviations in the order of tens of meters due to the ‘‘clockjump’’ elimination procedure mentioned previously. Therefore, the parably large process noise has been chosen to pensate for these deviations. The ambiguities of the carrier phase measurements are assumed to be constant parameters and therefore no process noise is introduced. Upon filter initialization, the initial covariance matrix is set up as a diagonal matrix with the square of the initial standard deviation on the main diagonal. Table 1 provides an overview of the filter settings. In the next step, the filter state is propagated towards the first epoch where measurements are available. During preprocessing in the following step, the ground station clock jumps are eliminated from the data as previously explained. Additionally, the observables are screened for missing data and satellites, which have dropped below an elevation cutoff angle of 10. The core part of the data screening is an integrity monitoring which is performed on the pseudo range and the carrier phase measurements in order to detect and remove outliers. During this monitoring,the orbits and clocks of the predicted IGU product are used together with the known station position to pute the residuals of the ionospherefree observations for each satellite. Since the position is known, only the station clock offset, which is mon for all measurements, must be puted and removed from the residuals. If the RMS of the pseudo ranges exceeds a predefined threshold, the residuals are recursively reputed with a single satellite excluded at a time. The bination, which yields the lowest residual, identifies the satellite with the outlier in the pseudo range measurement. This satellite is excluded from the filter at this epoch. If the residualthreshold is still exceeded, the procedure of recursively excluding satellite is repeated until the threshold is met or the number of valid satellites drops to two. In the latter case, all remaining satellites are rejected as well, since the monitoring procedure cannot further be performed. A similar approach has been chosen for the monitoring and screening of the carrier phase measurements, but instead time differences of the carrier phases between the current and the previous epoch are used, in order to avoid the plication of estimating ambiguities at this step. With this monitoring procedure,measurement outliers and cycle slips can be detected and the associated satellites are excluded from the measurement u。