## 4 Results and Validation
### Assessment of Heterogeneous Receivers  
We first performed UPD estimation using the 18 base stations in the second network. The quality of the UPD products was first checked by examining the a posteriori residuals of the float WL and NL ambiguities, the statistical histogram for which is shown in Figure 11. For the WL ambiguity, 94.6% of GPS residuals are within 0.15 cycles, whereas only 88.9% of GLONASS residuals are within 0.15 cycles. However, 97.9% of GLONASS WL residuals are within 0.25 cycles. For the NL residuals, more than 97% and 98% are within 0.1 and 0.15 cycles for GPS and GLONASS, respectively. The UPD products, therefore, have the same quality as those calculated using Trimble NetR8 receivers. Figure 12 shows a histogram of the residuals of the WL and NL ambiguities in the WL IFCB estimation. We deleted the WL residuals for satellites that have only one arc. The figure shows that 73.1% of the NL residuals are within 0.1 cycles, while and 95.1% within 0.2 cycles. For the WL ambiguity, 89.9% and 99.0% of residuals are within 0.1 and 0.2 cycles, respectively. These statistics reveal that the proposed IFCB calibration method works well for heterogeneous receiver types. Figure 11: Distribution of a posteriori residuals of WL (**a,b**) and NL (**c,d**) float ambiguities for GPS and GLONASS ((**a,c**) to (**b,d**)) in UPD estimation using reference stations. Figure 12: Distribution of a posteriori residuals of WL and NL float ambiguities in GLONASS WL IFCB calibration. Receivers with heterogeneous types are used rover sites. To validate the quality of the IFCB corrections, we processed GPS + GLONASS daily static PPP-IAR for each rover station. The processing strategy is the same as that shown in Figure 5. The average daily fixing percentage for each station is shown in Figure 13, and the over-manufacturer-averaged daily fixing percentage is summarized in Table 3. The fixing percentages of the GPS exceed 92.2% for all stations and average 96.6%, 97.3% and 97.1% for Leica, TPS, and Trimble receivers, respectively. For GLONASS without IFCB corrections, the fixing percentage is below 66% for the 17 Leica and TPS receivers, and over 89.9% for the 12 Trimble receivers. Upon applying the IFCB corrections, they exceed 91.9% for all 29 receivers and average 95.9%, 94.5% and 95.5% for Leica, TPS, and Trimble receivers. Kinematic precise point positioning-integer ambiguity resolution (PPP-IAR) was also performed for all hourly datasets of the 29 rover stations using the three models. The fixing percentage of all hourly solutions for different observation durations was calculated and is shown in Figure 14, and typical values for observation durations of 5, 10 and 15 min are given in Table 4. The fixing percentages for GPS-only for observation durations 5, 10 and 15 min are very small. Upon adding GLONASS without considering IFCB corrections, the fixing percentages are even lower than that of the GPS-only solution when the observation durations exceeded 17 min. The fixing percentage improves significantly by considering IFCB corrections. The fixing percentage in Figure 14 is smaller than that in Figure 8. We believe this may be attributed to the data quality in the network being lower than that corresponding to Figure 7. This can be inferred by two findings. First, the fixing percentage of GPS-only for observation durations 5, 10 and 15 min is lower than that obtained from the first network, by 5.8%, 15.5%, and 17.1%, respectively. Second, a comparison of Figures 6 and 13 shows that the fixing percentage of static PPP is lower than that for the first network. To further validate our speculation, we applied kinematic PPP-IAR to the 18 base stations and calculated the fixing percentage as shown in Figure 15. Since there is no \"base station\" to calculate the P1 and P2 IFCBs, we only calculated WL IFCB for the base stations. It is seen that the fixing percentage for the base stations is similar to that calculated using the rover stations.