Models and parameters for Swarm multi-GNSS observation simulation. Individual signals are identified by RINEX (IGS/RTCM, 2019) observation codes
| Item | Description |
|---|---|
| GNSS constellation | |
| Orbits and clock offsets | GFZ0MGXRAP rapid multi-GNSS product with 5 m orbit and 30 s clock sampling (CDDIS, 2020) |
| Attitude | Models of rate-limited yaw-steering (Dilssner, 2010; Dilssner et al., 2018; GSC, 2019; Kouba, 2009) |
| Antenna offsets & phase variations | igs14.atx (week 2118) |
| Code biases | CAS0MGRAP differential code bias product (CDDIS, 2020) |
| LEO satellite | |
| Spacecraft center of mass | Swarm-C precise science orbit (ESA, 2020) |
| Attitude | Star sensor based attitude quaternions (ESA, 2020) |
| Center of mass | (-1.9540 m, +0.0010 m, -0.3340 m) ESA (2020) |
| Antenna reference point | (-1.6502 m, +0.0010 m, -0.8055 m) ESA (2020) |
| Link model | |
| GNSS gain patterns | Marquis and Reigh (2015), Monjas et al. (2010), Valle et al. (2006), Zhan et al. (2013) |
| Transmit power | Steigenberger et al. (2018), Steigenberger et al. (2019) |
| Receiver antenna gain pattern | RUAG PEC antenna (Wettergren et al., 2009) |
| Losses | 4.5 dB for LNA noise figure and A/D conversion losses (Moreau et al., 2002) |
| Receiver model | |
| Clock | Linear drift, controlled within ±0.5 ms |
| Channels | 2×8 per constellation (GPS, Galileo, BeiDou-3) |
| Signals | GPS: semi-codeless P(Y) (1W, 2W), or L1 C/A + L2C (1C, 2L), or L1 C/A + L5 pilot (1C, 5Q) |
| GAL: E1 O/S & E5a pilot (1C, 5Q) | |
| BDS-3: B1C & B2a pilot (1P, 5P) | |
| Early-late correlator spacing | GPS 1C: 0.14 chips; GPS 1W, 2W: 0.5 chips; GPS 2L: 0.28 chips; GAL 1C, BDS-3 1P: 0.07 chips; GPS 5Q, GAL 5Q, BDS-3 5P: 0.7 chips |
| DLL bandwidth | GPS 1W, 2W: 0.10 Hz; GPS 2L: 0.25 Hz; GPS 5Q, GAL 5Q, BDS-3 5P: 1 Hz; others 0.5 Hz |
| PLL bandwidth | GPS 1W, 2W: 1 Hz; others: 15 Hz |
| Elevation mask | 0° |
| Acquisition/tracking threshold | 15 dBHz / 10 dBHz for GPS P(Y), all others 35 dBHz / 30 dBHz |
| Observation model | |
| Light-time | Modeled (iterative solution) |
| Relativity | Modeled (periodic clock variation, Shapiro effect) |
| Phase wind-up | Modeled (Wu et al., 1993) |
| Ionospheric path delay | Constant vertical TEC (10 TECU) and thick-layer mapping function (Lear, 1989) |
| Receiver antenna phase center offset | Zero (GPS L1/L2 offset included in antenna reference point; same value assumed for other signals) |
| Receiver antenna phase variations | GPS L1/L2 phase variations from in-flight calibration; applied for all signals |
| Receiver antenna multipath | Phase multipath included in phase pattern; in-flight calibration of GPS L1 and L2 pseudorange multipath applied for signals in L1/E1/B1 and L2/E5a/B2a frequency bands, respectively |