Table.1: The standard deviations obtained in X, Y & Z using different ionospheric models provided in SKI –GPS observations processing software.
| Sr. No. | Baseline Identification | Ionospheric Model Used | Standard Deviation (geodetic coordinates) in m |
| | SX | SY | SZ |
| 1 | Ref._10 | No model | 0.0108 | 0.0474 | 0.0644 |
| | | Standard | 0.0108 | 0.0474 | 0.0645 |
| | | Computed | 0.0107 | 0.0471 | 0.0641 |
| | | Global/Regional | 0.0108 | 0.0474 | 0.0644 |
| | | Klobuchar | 0.0108 | 0.0474 | 0.0644 |
| 2 | Ref._01 | No model | 0.0030 | 0.0124 | 0.0031 |
| | | Standard | 0.0030 | 0.0123 | 0.0032 |
| | | Computed | 0.0031 | 0.0122 | 0.0032 |
| | | Global/Regional | 0.0030 | 0.0124 | 0.0031 |
| | | Klobuchar | 0.0030 | 0.0124 | 0.0031 |
| 3 | Ref._07 | No model | 0.0011 | 0.0040 | 0.0029 |
| | | Standard | 0.0011 | 0.0042 | 0.0030 |
| | | Computed | 0.0011 | 0.0041 | 0.0029 |
| | | Global/Regional | 0.0011 | 0.0040 | 0.0029 |
| | | Klobuchar | 0.0011 | 0.0040 | 0.0029 |
| 4 | Ref._08 | No model | 0.0035 | 0.0105 | 0.0062 |
| | | Standard | 0.0035 | 0.0105 | 0.0062 |
| | | Computed | 0.0035 | 0.0105 | 0.0062 |
| | | Global/Regional | 0.0035 | 0.0105 | 0.0062 |
| | | Klobuchar | 0.0035 | 0.0105 | 0.0062 |
| 5 | Ref._09 | No model | 0.0032 | 0.0087 | 0.0053 |
| | | Standard | 0.0031 | 0.0084 | 0.0051 |
| | | Computed | 0.0032 | 0.0086 | 0.0053 |
| | | Global/Regional | 0.0032 | 0.0087 | 0.0053 |
| | | Klobuchar | 0.0032 | 0.0087 | 0.0053 |
| 6 | Ref._02 | No model | 0.0028 | 0.0075 | 0.0078 |
| | | Standard | 0.0028 | 0.0074 | 0.0077 |
| | | Computed | 0.0026 | 0.0071 | 0.0074 |
| | | Global/Regional | 0.0028 | 0.0075 | 0.0078 |
| | | Klobuchar | 0.0028 | 0.0074 | 0.0077 |
| 7 | Ref._03 | No model | 0.0005 | 0.0006 | 0.0014 |
| | | Standard | 0.0013 | 0.0016 | 0.0043 |
| | | Computed | 0.0013 | 0.0045 | 0.0019 |
| | | Global/Regional | 0.0005 | 0.0006 | 0.0014 |
| | | Klobuchar | 0.0039 | 0.0051 | 0.0126 |
| 8 | Ref._04 | No model | 0.0026 | 0.0066 | 0.0051 |
| | | Standard | 0.0025 | 0.0066 | 0.0050 |
| | | Computed | 0.0026 | 0.0067 | 0.0051 |
| | | Global/Regional | 0.0026 | 0.0066 | 0.0051 |
| | | Klobuchar | 0.0026 | 0.0067 | 0.0050 |
| Parameters | - | Selected input |
| Cut-off angle (deg.) | - | 10 |
| Tropospheric model | - | Hopfield |
| Ionospheric model | - | Computed |
| Solution type | - | Standard |
| Ephemeris | - | Broadcast |
|
Accuracy evaluation of the measurement of the same points using single and dual frequency receivers
The GPS observation data with single frequency and dual frequency were processed using SKI processing software version 2.3.1. Baselines were computed between the reference and respective rovers for single and dual frequency observations and results are shown in the Table- 2. In processing following specification were selected.
Table. 2: Difference between Dual & Single Frequency observations
| Baseline Station | Residuals (Difference between Dual & Single Frequency observations ) |
| | lat (cm) | long (cm) | height(cm) |
| Ref. – 01 | -46.83 | 9.78 | -68.44 |
| Ref. – 02 | -44.13 | -22.47 | -68.08 |
| Ref. – 03 | -42.69 | -24.57 | -76.84 |
| Ref. – 04 | -42.42 | -13.14 | -72.26 |
| Ref. – 07 | -34.59 | -15.96 | -92.97 |
| Ref. – 08 | -15.96 | -15.93 | -83.1 |
It is found that considering the offset of placing the single frequency receiver away from the dual frequency and comparing the baseline distance in terms of geodetic coordinates, it gives difference less than one metre in all the three latitude, longitude and height values.
The difference between the reference and the rover point coordinates are computed without considering the offset part in setting the GPS receivers. The differences in the distances are shown in the Table 3.1, 3.2 and 3.3.
Validation of results
Validation of results was carried out by baseline distance verification and computing the triangle closing error methods.
Baseline distance verification
Baseline distances were calculated from positional coordinates obtained using both single and dual frequency observations. These baseline distances were compared with that from actual ground measurements. Details of the comparisons is given in tables 3.1