## 7 Conclusions  
Multipaths have remained one of the dominant sources of errors that limit site position accuracy and the atmospheric propagation delays estimated from GNSS receivers that employ carrier phase and code observables. No standard model or technique has been developed yet. In this study, we devised a _in situ_ strategy that avoids any complex modelling of the multipath effect but rather limits the impact of multipath in the first place, contaminating the carrier phase and code observables. We have established two close-by, continuously observing multi-GNSS stations under challenging conditions, with different metal frames, poles, various sizes and shapes, ensuing a complex multipath environment. The two configurations were used: one with and one without Eccosorb AN-W-79--a specialized electromagnetic signal absorption material--placed around the antenna. The station with the _in situ_ microwave-absorbing material has shown a significant improvement in the accuracy of the single-point positioning that depends on the code measurements. The reductions in the standard error are between 4% and 45% for all four GNSSs (BeiDou, GLONASS, Galileo and GPS). In addition, we computed the combined GPS + GLONASS + Galileo + BeiDou single-point positioning solution with a reduction in the standard error of up to 15%. Furthermore, the code multipath linear combinations using the various frequencies from the GNSS, on average, show an improvement from 20% to 70%. All the GPS-based code multipaths, i.e., \(GPSM1C\), \(GPSM1X\), \(GPSM2W\), \(GPSM2X\) and \(GPSM5X\), show an improvement of 20-40%. In particular, the improve  
Figure 15: The wavelet power spectrum of residual SNR time series for station KBG1 (**left**) as depicted in Figure 14a with light green solid line and for station KBG2 (**right**) as depicted in Figure 14c with a light red solid line as observed for KBG1 and KBG2 on 1 March 2021 (DoY 60), as the satellite GPS PRN27 ascends, subtending the angles between 255 and 275\({}^{\circ}\) in azimuth. The Morlet wavelet is used to create a wavelet spectrum. The left axis is the period in seconds that corresponds to wavelet scales with base 2. The horizontal axes represent time (seconds). The representations of the Morlet wavelet spectrum show a significant power for KBG2 for the periods 30–64 and 64–128 s, spanning approximately 100 and 850 s, respectively. However, for the station KBG1, only a short-lived power is observed for the period 60–100 s. The thick contour encloses areas of higher than 95% confidence. The cross-hatched portions represent the cone of influence, where the edge effects become substantial. ment of \(GPS\)\(S\)\(S\)\(X\) with the C5 code using the I + Q channel reaches more than 40%. For GLONASS, the same pictures appear. The linear code combinations, such as \(G\)\(LOM\)1C, \(G\)\(LOM\)2C, \(G\)\(LOM\)2C and \(G\)\(LOM\)3X, show improvements of between 20% and 55%; for Galileo, the code multipath combinations \(GAL\)\(M\)1X, \(GAL\)\(S\)\(X\), \(GAL\)\(M\)6X, \(GAL\)\(M\)7X, and \(GAL\)\(M\)8X show the largest improvement, reaching 60-70%; and for BeiDou, combinations \(BD\)\(M\)1X, \(BD\)\(M\)2I, \(BD\)\(S\)\(X\), \(BD\)\(M\)6I, and \(BD\)\(M\)7I reaches 30-40%. The cycle slip detection and subsequent repair, particularly in a dynamic scenario, are complex, impending the full exploitation of the otherwise precise carrier phase measurements, and this study shows a nearly 20-60% improvement for BeiDou GLONASS and GPS. The Galileo signal shows no improvement. The use of _in situ_ microwave-absorbing material shows convincing results in reducing the code multipath noise level and in carrier phase cycle slip. The quality of code measurements will thus lead to shrinking the search space in resolving the carrier phase ambiguity [15]. Furthermore, multipath has shown to severely impact the attitude determination of spacecraft [18]. While the _in situ_ method was evaluated with a static antenna, microwave-absorbing material can be used for kinematic applications as well.