PNT Moni Monthly Report
QZSS CLAS Performance Evaluation — Free Tier
1 Revision History
| Version | Date | Notes |
|---|---|---|
| 1.0 | 2026-09-26 | Initial edition |
| 1.1 | 2026-09-27 | Appendix GNSS system notices (NAGU/NANU/NAQU) completed: previously missed notices added (Galileo from the full-year notice archive; follow-up GPS/QZSS notices reflected); satellite list now uses the snapshot nearest the month-end. No change to evaluation figures |
Rapid edition: this report uses the GSI Rapid series (R5.1 from 2026-04 onward, R5 before that) as the reference coordinates. The Rapid series is a quick-look solution published 2–3 days after observation; once the Final series (F5/F5.1, published ~3 weeks after observation) is complete a separate finalised edition will be issued.
Rapid-vs-Final differences are usually at the mm level, but can widen briefly right after events such as earthquakes or equipment changes (methodology §3.2 / §8.5).
This edition was produced and first published about 5 month(s) after the end of the reporting period, as part of completing the monthly series. The methodology, inputs and processing are the same as for the editions published on schedule.
2 Introduction
This report summarises PNT Moni’s evaluation of QZSS CLAS (Centimeter Level Augmentation Service) performance for April 2026, using publicly available data and open-source tooling.
As an independent evaluation service for GNSS augmentation, PNT Moni continuously monitors CLAS performance at higher spatial and temporal resolution than the official Service Performance Report published by the Cabinet Office / Quasi-Zenith Satellite System Services Inc. (QSS). This monthly report complements the official semi-annual report, offering monthly cadence, an independent third-party assessment, and practically useful analytical depth. This Free-tier monthly report covers national statistics only; per-station analysis is provided in the Pro tier.
The “Methodology Version Tag” at the end of this report uniquely identifies the processing configuration that produced it. For the full methodology document see [https://pntmoni.com/methodology/clas/v1.1.0](https://pntmoni.com/methodology/clas/v1.1.0).
3 Methodology
This section summarises the methodology; see the link above for the full document.
Data sources: 30-second RINEX observations from ~1,300 GEONET stations distributed by the Geospatial Information Authority of Japan (GSI) under PDL 1.0 (source: GSI GEONET data service), the CLAS L6 augmentation archive published on the web by QSS, and IGS broadcast ephemerides / Earth-rotation parameters from CDDIS.
Processing engine: pntmoni-claslib v0.8.3-pntmoni-1, PPP-RTK mode (kinematic, l1+l2+l5).
Reference coordinates: GSI daily coordinate solutions (the series matching the period — F5 era = ITRF2014, F5.1 era = ITRF2020; R5 / R5.1 when the Rapid series is used) are relativised to station 92110 (Tsukuba 1) and smoothed with a ±7-day (15 calendar-day) median filter centred on the target day \(d\) (common-mode removal, Method B). Method version: gsi-daily-median15d-1.1.
Quality control (QC): teqc 2019Feb25 for 2026–2027, with migration to MRTKLIB’s mrtk qc planned around 2027/Q4.
Statistical aggregation: 95% / 99% percentile errors are computed by pooling the epoch errors of all stations and all days in each aggregation cell (methodology §5.1, same rule as NAVIGATION 2026). TTFF uses a 15-minute reset (continuity with NAVIGATION 2026, methodology §5.2); a 60-minute reset will be added in Phase 1.
Known structural differences from official QSS figures: PNT Moni’s methodology differs structurally from the official QSS Service Performance Report in four respects — sampling rate (30 s vs 1 s), a parameter set retuned for 30 s, CLASLIB version differences, and the resulting Kalman-filter behaviour. See Shiono & Kubo (2025, 2026). These are treated as structural characteristics, not bugs; comparing absolute values or equating the numbers is not meaningful (methodology §8.3). In direction, the lower epoch density at 30 s gives filter convergence and re-convergence intervals a relatively larger weight in the pooled statistics, pushing the tail percentiles (95% / 99%) above the official evaluation. PS-QZSS standard values are accordingly used in this report as reference values only, never for compliance judgement (see the note in the Executive Summary).
3.1 Evaluation Network
CLAS divides the country into 12 networks; each station’s network is determined by the Compact Network ID assigned by CLASLIB. Stations are further classified as Inside Network or Outside Network by a point-in-polygon test against the per-network polygons defined in the ION GNSS+ 2025 / NAVIGATION 2026 papers (Shiono & Kubo) — i.e. regions where augmentation is interpolated vs extrapolated. The network polygons below are updated only when the CLAS service area changes (rarely); the polygon version is recorded in the Methodology Version Tag at the end of this report.
Figure 1: CLAS 12-network grid points and the GEONET stations evaluated this month.
The CLAS network polygons define the regions where the augmentation is intended to meet spec. Outside-Network stations receive corrections derived by extrapolation and may therefore have different error characteristics (Inside/Outside aggregate analysis is provided in the Pro tier).
4 Executive Summary
| Metric | Value | |
|---|---|---|
| 0 | Stations evaluated | 1,031 |
| 1 | Horizontal error 50% [cm] | 2.19 |
| 2 | Horizontal error 95% [cm] | 10.48 |
| 3 | Horizontal error 99% [cm] | 17.71 |
| 4 | Vertical error 95% [cm] | 17.35 |
| 5 | TTFF 50% [s, 15-min reset] | 180.0 |
| 6 | TTFF 95% [s, 15-min reset] | 300.0 |
| 7 | National fix rate (Q=4) | 97.7 % |
Highlights for April 2026:
- National horizontal error, 95th percentile: 10.48 cm
- National vertical error, 95th percentile: 17.35 cm
- TTFF (15-min reset, 95th percentile): 300.0 s
- National fix rate (Q=4): 97.67%
- L6 broadcast alerts: 0
The QZSS Performance Standard (PS-QZSS) sets the CLAS kinematic positioning-accuracy standard at horizontal 95% 12 cm / vertical 95% 24 cm. Compliance with the standard is verified by QSS’s official Service Performance Reports, whose evaluation is run under conditions that differ from this report’s (1-s sampling, a fixed evaluation station set). PNT Moni’s 30-s, ~1,100-station methodology (see Methodology) is known to produce structurally higher tail percentiles than the official evaluation (Shiono & Kubo 2026, §4.1.2). Whether a value in this report sits above or below a PS-QZSS standard value is therefore not a compliance judgement; the standard values appear in this report only as a reference scale (e.g. in the spatial distribution maps). Quantitative reconciliation against official figures is performed in the half-yearly Comparison Archive.
5 Performance
5.1 National Overview
5.1.1 Error Distribution
Figure 2: Cumulative distribution of horizontal error (epochs pooled over qualified stations).
Figure 3: Cumulative distribution of vertical error (epochs pooled over qualified stations).
| Percentile | TTFF [s] | |
|---|---|---|
| 0 | 50% | 180.0 |
| 1 | 90% | 240.0 |
| 2 | 95% | 300.0 |
| 3 | 99% | 480.0 |
April 2026: TTFF success rate 98.19 % (97,180/98,976 reset windows obtained a valid fix). At each reset the filter state is fully cleared and the solution re-initialized to standalone; TTFF is the time from that reset to the first fixed solution, recorded on the 30-second observation grid. A fix at the first epoch after reset is therefore recorded as 0 s (true TTFF ≤ 30 s), which is why P50/P95 are often 0 s; P99 reflects the convergence tail.
Figure 4: Cumulative distribution of TTFF (15-min reset, reset windows pooled nationwide over the period).
5.1.2 Spatial Distribution
Performance is visualised on hexagonal cells sized to the CLAS augmentation grid spacing (~60 km). Each cell’s value is the 95th percentile computed over all stations and all epochs pooled within that cell (same rule as methodology §5.1). Cells with no stations remain blank. Cells backed by fewer than 3 distinct stations are drawn with a dotted inner ring — a reliability marking: with so few stations the cell’s percentile is statistically thin and station-local effects (multipath environment, antenna snow accretion) can colour the whole cell, so read those cells as indicative rather than representative (methodology §5.1, 2026-07-18 revision). Southern-island stations outside the CLAS service area (out_of_service) are excluded from cell evaluation.
Colour encodes error magnitude on a perceptually-uniform continuous colormap (purple = smaller error → yellow = larger error), with no discrete boundaries — the map shows the spatial gradient of performance, not a pass/fail classification. The scale spans a fixed range (0–40 cm horizontal, 0–60 cm vertical) set from PNT Moni’s own historical error range, so maps stay comparable month to month; this range is not a Performance-Standard threshold and the colouring is not a compliance judgement (see Methodology and the Executive Summary note). Cells exceeding the range render at the top colour (colorbar top arrow).
Figure 5: Spatial distribution of the horizontal-error 95th percentile (60 km hex cells, epochs pooled). Dotted ring = cell backed by fewer than 3 stations (indicative).
Figure 6: Spatial distribution of the vertical-error 95th percentile (60 km hex cells, epochs pooled). Dotted ring = cell backed by fewer than 3 stations (indicative).
5.1.3 Recent-Month Trend
Coming Soon. This section will show the past 13 months of national 95th-percentile horizontal/vertical error, with the current month highlighted and a comparison marker for the same month last year. The trend view becomes meaningful once the Phase 0 / Phase 1 backfill has filled in everything from April 2025 onward; until then the table above shows the current month’s values only.
5.2 Cross-Validation
Coming Soon (Phase 1+)
Cross-validation will report agreement statistics between the primary CLASLIB-based processing and the parallel evaluation engine MRTKLIB on a sample of ~100 stations. It demonstrates that PNT Moni’s evaluation agrees across independent OSS implementations, in preparation for making MRTKLIB primary in 2027/Q4.
Phase 1 goal: publish cross-validation on the parallel sample stations. Phase 2 goal (2027/Q4): role reversal — MRTKLIB primary, CLASLIB as historical reference.
6 Data Availability
6.1 Overview
Figure 7: Distribution of data availability across stations.
National-statistics availability for April 2026: 97.7%.
GEONET maintenance events affecting availability: no major maintenance events are recorded for April 2026.
For the latest GEONET maintenance notices see GSI’s official notices page (https://terras.gsi.go.jp/).
7 Anomaly Detection
7.1 L6 Broadcast Alerts
The L6 broadcast Alert flag, carried in the CLAS augmentation stream (CSSR data part), signals a known issue detected on the generation side. This section aggregates it monthly to surface the broadcaster’s self-reported health.
April 2026: 0 alerts across all L6 broadcasts (no message had the Alert flag set).
7.2 Crustal Deformation Events
An earthquake large enough to displace a GEONET station breaks the continuity of that station’s GSI daily-solution series. Because the reference coordinate is the denominator of every error metric in this report, the affected station-days are withheld rather than reported against a reference that straddles the discontinuity. Events are identified from JMA earthquake information and confirmed on the daily solutions themselves; a candidate is an event with only a few displaced stations, or an aftershock whose step estimate carries postseismic motion — it is excluded all the same and re-examined when the Final edition is produced.
April 2026: 3 co-seismic offset event(s) catalogued (2 candidate). Events are identified from JMA earthquake information (M ≥ 6.0 or seismic intensity ≥ 5-lower) and confirmed on the GSI daily solutions (station step > 1 cm horizontal or > 2 cm vertical near the epicentre). Per the methodology, a displaced station has an undefined reference coordinate on the event day and is excluded from that day’s error metrics; the reference on neighbouring days is computed without spanning the event. Source: Japan Meteorological Agency website (edited).
- 2026-04-01 — 茨城県南部 M5.0 (茨城県南部, M5.0, max. intensity 5弱): 1 station(s) excluded for that day — candidate, to be reviewed for the Final edition (JMA)
- 2026-04-10 — Uncatalogued step (step detected on the daily solutions with no JMA trigger): 5 station(s) excluded for that day — candidate, to be reviewed for the Final edition
- 2026-04-20 — 三陸沖 M7.7 (三陸沖, M7.7, max. intensity 5強): 58 station(s) excluded for that day — confirmed (JMA)
8 Appendix
8.1 GNSS System Notices: NAGU / NANU / NAQU
Notices issued against GNSS constellation operations during April 2026, recorded for cross-referencing against anomaly events and signal availability.
| Date | Satellite | Notice | Type | Severity | |
|---|---|---|---|---|---|
| 0 | 2026-04-02 02:10 UTC | GAL | NAGU 2026020, NAGU 2026023 | scheduled_maintenance | informational |
| 1 | 2026-04-07 11:35 UTC | GAL | NAGU 2026022, NAGU 2026024 | scheduled_maintenance | informational |
| 2 | 2026-04-09 22:45 UTC | GPS PRN2 | NANU 2026030, NANU 2026031 | scheduled_maintenance | total |
| 3 | 2026-04-13 17:59 UTC | QZS PRN199 | NAQU 2026120, NAQU 2026128 | scheduled_maintenance | total |
| 4 | 2026-04-15 01:55 UTC | GAL | NAGU 2026025, NAGU 2026026 | scheduled_maintenance | informational |
| 5 | 2026-04-17 02:15 UTC | GPS PRN20 | NANU 2026032, NANU 2026033 | scheduled_maintenance | total |
| 6 | 2026-04-13 01:27 UTC | QZS PRN194 | NAQU 2026121, NAQU 2026124 | other | partial |
| 7 | 2026-04-13 01:27 UTC | QZS PRN205 | NAQU 2026122, NAQU 2026125 | other | partial |
| 8 | 2026-04-13 01:28 UTC | QZS PRN204 | NAQU 2026123, NAQU 2026126 | other | partial |
| 9 | 2026-04-23 16:59 UTC | QZS PRN200 | NAQU 2026127, NAQU 2026144 | scheduled_maintenance | total |
| 10 | 2026-04-15 08:53 UTC | QZS PRN209 | NAQU 2026130, NAQU 2026132 | other | partial |
| 11 | 2026-04-15 08:53 UTC | QZS PRN199 | NAQU 2026129, NAQU 2026131 | other | partial |
| 12 | 2026-04-24 02:00 UTC | GPS PRN22 | NANU 2026034, NANU 2026036 | scheduled_maintenance | total |
| 13 | 2026-04-26 18:59 UTC | QZS PRN194 | NAQU 2026133, NAQU 2026147 | scheduled_maintenance | total |
| 14 | 2026-04-21 14:10 UTC | QZS PRN185 | NAQU 2026135, NAQU 2026139 | other | partial |
| 15 | 2026-04-21 14:10 UTC | QZS PRN185 | NAQU 2026136, NAQU 2026138 | other | partial |
| 16 | 2026-04-21 14:10 UTC | QZS PRN185 | NAQU 2026134, NAQU 2026137 | other | partial |
| 17 | 2026-04-21 14:10 UTC | QZS PRN195 | NAQU 2026140, NAQU 2026142 | other | partial |
| 18 | 2026-04-21 14:10 UTC | QZS PRN205 | NAQU 2026141, NAQU 2026143 | other | partial |
| 19 | 2026-04-24 16:00 UTC | GPS PRN13 | NANU 2026035, NANU 2026038 | scheduled_maintenance | total |
| 20 | 2026-04-28 10:54 UTC | GAL | NAGU 2026027, NAGU 2026028 | scheduled_maintenance | informational |
| 21 | 2026-04-30 15:45 UTC | GPS PRN21 | NANU 2026037, NANU 2026040 | scheduled_maintenance | total |
| 22 | 2026-04-29 19:27 UTC | GPS PRN13 | NANU 2026039 | other | total |
April 2026: 23 notice(s) detected. Collected from the official NAGU (Galileo), NANU (GPS) and NAQU (QZSS) notices.
8.2 List of Satellites
A snapshot of the constellation operators’ official pages (state at fetch time). Sources: GPS = USCG NAVCEN, QZSS = QSS DoD, Galileo = GSC Europa.
Fetched at: 2026-06-02 02:42 UTC
This snapshot was taken 33 days after the end of the reporting period; no snapshot closer to the period exists. Satellite status may have differed during the period — see the NAGU / NANU / NAQU notices above.
8.2.1 GPS
| PRN | SVN | Block | Slot | Clock | Status | Notice | |
|---|---|---|---|---|---|---|---|
| 0 | G16 | 56 | IIR | B1 | RB | Operational | FCSTSUMM |
| 1 | G29 | 57 | IIR-M | C1 | RB | Operational | FCSTSUMM |
| 2 | G02 | 61 | IIR | D1 | RB | Operational | FCSTSUMM |
| 3 | G24 | 65 | IIF | A1 | RB | Unusable | UNUSABLE |
| 4 | G03 | 69 | IIF | E1 | RB | Operational | FCSTSUMM |
| 5 | G32 | 70 | IIF | F1 | RB | Unusable | UNUSABLE |
| 6 | G31 | 52 | IIR-M | A2 | RB | Operational | FCSTSUMM |
| 7 | G15 | 55 | IIR-M | F2 | RB | Operational | FCSTSUMM |
| 8 | G25 | 62 | IIF | B2 | RB | Operational | FCSTSUMM |
| 9 | G27 | 66 | IIF | C2 | RB | Operational | FCSTSUMM |
| 10 | G10 | 73 | IIF | E2 | RB | Operational | FCSTSUMM |
| 11 | G01 | 80 | III | D2 | RB | Unusable | UNUSABLE |
| 12 | G22 | 44 | IIR | B3 | RB | Operational | FCSTSUMM |
| 13 | G05 | 50 | IIR-M | E3 | RB | Operational | FCSTSUMM |
| 14 | G30 | 64 | IIF | A3 | RB | Operational | FCSTSUMM |
| 15 | G09 | 68 | IIF | F3 | RB | Operational | FCSTSUMM |
| 16 | G08 | 72 | IIF | C3 | RB | Operational | FCSTSUMM |
| 17 | G07 | 48 | IIR-M | A4 | RB | Operational | FCSTSUMM |
| 18 | G17 | 53 | IIR-M | C4 | RB | Operational | FCSTMX |
| 19 | G12 | 58 | IIR-M | B4 | RB | Operational | FCSTSUMM |
| 20 | G06 | 67 | IIF | D4 | RB | Operational | FCSTDV |
| 21 | G04 | 74 | III | F4 | RB | Operational | FCSTDV |
| 22 | G13 | 43 | IIR | A5 | RB | Decommissioned | DECOM |
| 23 | G20 | 82 | III | F5 | RB | Operational | FCSTSUMM |
| 24 | G19 | 59 | IIR | C5 | RB | Operational | FCSTSUMM |
| 25 | G26 | 71 | IIF | B5 | RB | Operational | FCSTSUMM |
| 26 | G23 | 76 | III | E5 | RB | Operational | FCSTSUMM |
| 27 | G11 | 78 | III | D5 | RB | Operational | FCSTSUMM |
| 28 | G21 | 81 | III | E6 | RB | Operational | FCSTSUMM |
| 29 | G18 | 75 | III | D6 | RB | Operational | FCSTSUMM |
| 30 | G14 | 77 | III | B6 | RB | Operational | FCSTSUMM |
| 31 | G28 | 79 | III | A6 | RB | Unusable | UNUSABLE |
8.2.2 QZSS (Michibiki)
| PRN | SVN | Block | Signals | Status | Notice | |
|---|---|---|---|---|---|---|
| 0 | J194 | 002 | Ⅱ-Q | L1C/A, L1C, L2C, L5, L1S, L5S, L6D, L6E | Operational | |
| 1 | J199 | 003 | Ⅱ-G | L1C/A, L1C, L2C, L5, L1S, L5S, L1Sb, L6D, L6E,... | Operational | |
| 2 | J195 | 004 | Ⅱ-Q | L1C/A, L1C, L2C, L5, L1S, L5S, L6D, L6E | Operational | |
| 3 | J196 | 005 | ⅡA-Q | L1C, L2C, L5, L1C/B, L1S, L5S, L6D, L6E | Operational | |
| 4 | J200 | 007 | Ⅲ-G | L1C, L5, L1C/B, L5S, L1Sb, L6D, L6E | Operational |
8.2.3 Galileo
| E# | GSAT | Clock | Status | Notice | |
|---|---|---|---|---|---|
| 0 | E11 | GSAT0101 | RAFS | Operational | |
| 1 | E12 | GSAT0102 | RAFS | Operational | |
| 2 | E19 | GSAT0103 | RAFS | Operational | |
| 3 | E18 | GSAT0201 | PHM | Unusable | GENERAL 2021008 |
| 4 | E14 | GSAT0202 | RAFS | Unusable | GENERAL 2021008 |
| 5 | E26 | GSAT0203 | PHM | Operational | |
| 6 | E22 | GSAT0204 | RAFS | Unusable | GENERAL 2017045 |
| 7 | E30 | GSAT0206 | PHM | Operational | |
| 8 | E07 | GSAT0207 | PHM | Operational | |
| 9 | E08 | GSAT0208 | PHM | Operational | |
| 10 | E09 | GSAT0209 | RAFS | Operational | |
| 11 | E01 | GSAT0210 | RAFS | Unusable | GENERAL 2023048 |
| 12 | E02 | GSAT0211 | PHM | Operational | |
| 13 | E03 | GSAT0212 | PHM | Operational | |
| 14 | E04 | GSAT0213 | PHM | Operational | |
| 15 | E05 | GSAT0214 | PHM | Operational | |
| 16 | E21 | GSAT0215 | PHM | Operational | |
| 17 | E25 | GSAT0216 | PHM | Operational | |
| 18 | E27 | GSAT0217 | PHM | Operational | |
| 19 | E31 | GSAT0218 | PHM | Operational | |
| 20 | E36 | GSAT0219 | PHM | Operational | |
| 21 | E13 | GSAT0220 | PHM | Operational | |
| 22 | E15 | GSAT0221 | PHM | Operational | |
| 23 | E33 | GSAT0222 | PHM | Operational | |
| 24 | E34 | GSAT0223 | PHM | Operational | |
| 25 | E10 | GSAT0224 | PHM | Operational | |
| 26 | E29 | GSAT0225 | PHM | Operational | |
| 27 | E23 | GSAT0226 | PHM | Operational | |
| 28 | E06 | GSAT0227 | PHM | Operational | |
| 29 | E16 | GSAT0232 | PHM | Operational | |
| 30 | E28 | GSAT0233 | PHM | Operational | USABINIT 2026033 |
| 31 | E32 | GSAT0234 | Commissioning | LAUNCH 2025061 |
PNT Moni’s evaluation also covers the Galileo signals received at GEONET stations.
8.3 Methodology Version Tag
| Item | Value |
|---|---|
| Methodology version | 1.1.0 |
| Pipeline config hash | 8f6422e9b5b433ec |
| Engine | pntmoni-claslib v0.8.3-pntmoni-1 |
| QC tool | teqc 2019Feb25 |
| Reference-coordinate method version | gsi-daily-median15d-1.1 |
| Evaluation stream | rapid |
| Reporting period | April 2026 |
| Data mode | live |
For the full methodology document see [https://pntmoni.com/methodology/clas/v1.1.0](https://pntmoni.com/methodology/clas/v1.1.0).