Intereses de los pescadores organizados - Objetivo específico 3.5

5. RESULTADOS

5.5 Objetivo específico 3.5

5.5.3 Intereses de los pescadores organizados

Following the ZBL trials made in November and December 1999, a series of combined ZBL and SBL trials were made in year 2000 using CRS1000 receivers and the IESSG facilities. During these trials, two receivers were connected to the same antenna at a known point to form a ZBL and a third receiver was attached to a separate chokering antenna at another known point (Fig. 3.38). With such a receiver configuration, one ZBL and two SBLs can be formed. In this section the focus will be on the data analysis of SBL trials.

Ashtech Receiver Two Leica CRS 1000 Receivers Leica CRS 1000 Receiver Mini Network of ZBL&SBL

IESSG Turret

Fig. 3.38. Facility used for ZBL and SBL tests

Partial SBL trials are listed in Appendix A4. The results of the highlighted trials are presented in this thesis. A one-hour SBL trial at sampling rate of 10 Hz on 1 February 2000 is illustrated first, followed by the discussion of the results obtained from a lower sampling rate from long-term SBL trials made from 5 to 7 June 2000. For longer-term SBL trials, precise and broadcast ephemerides are used in the data processing. The results show no differences in positioning solutions due to such a close distance between the two known points of 1.032m apart. The data gathered in

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three consecutive days shows significant multipath signatures. SDs of the 3D positioning solutions are also illustrated with coordinate residuals. The baseline residuals calculated are illustrated separately.

Unlike ZBL tests, which can be used to quantify the noise levels of the GPS receivers, the positioning solutions of SBL tests include many similar error sources that are encountered in the actual surveying. Fig. 3.39 to Fig. 3.42 are the X, Y, Z and baseline residual time series from a SBL trial on 1 February 2000. Within one-hour data collection trial, apparent movements caused by multipath make the rover look like a moving point. The 99.7% probability error ranges of X, Y and Z residuals are 1.26cm, 0.76cm and 1.37cm. The maximum baseline residual could reach 1.7cm.

Epoch by epoch SD of 3D coordinate residuals are depicted by Fig. 3.43, 3.44, and 3.45. Sub-centimetre positioning solution can be obtained in this trial, with roughly equivalent precisions in X and Z coordinate and the best precision in Y coordinate. Simulations of the GPS satellite geometry reveals that in the high latitude areas, the horizontal accuracy could degrade to the same level as that of vertical component. This will be further explored in Chapter 6. Fig. 3.46 illustrates the changes of the time lags of the autocorrelation coefficient of X coordinate residual. Recall the autocorrelation time lag is about 1 second for ZBL using CRS1000 dual frequency receivers. The time lag for the SBL test consists of two parts, one caused by receiver noise due to the internal filtering algorithm and another one caused by the slow changing multipath signatures with a cycle period of several minutes, governed by the reflectors in the surveying environment. In this example, the total cycle period identified from autocorrelation time lag is about 480 seconds (8 minutes), mainly caused by multipath signature. It is worth pointing out the autocorrelation coefficients are determined by the instruments used, including antenna type and receiver noise. Different antenna design has different multipath rejection pattern, internal filtering algorithm, and behaves different in the same reflection environment.

Fig. 3.39. X coordinate residual (CRS1000)

Fig. 3.40. Y coordinate residual (CRS1000)

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Fig. 3.42. Baseline residual (CRS1000)

Fig. 3.43. Each epoch SD of X coordinate

Fig. 3.45. Each epoch SD of Z coordinate

Fig. 3.46. Autocorrelation lags of X residual (CRS1000)

To further study the possible pattern of multipath on the turret of the IESSG building, two 24-hour SBL trials were carried out at a sampling rate of 30 seconds on 5, 6 and 7 June 2000. Fig. 3.47 to Fig. 3.54 are the residual time series of the corresponding coordinates and baselines. Comparing each coordinate and baseline pair, it can be found that the time series patterns are identical. The cross-correlation coefficients of X, Y and Z coordinates for the two data sets are 0.43, 0.46 and 0.47 and demonstrate high level multipath signature in the positioning solutions.

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X Coordinate Residuals of SBL from 5 to 6 June 2000

-0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 130000 140000 150000 160000 170000 180000 190000 200000 210000