Direction-resolved azimuth–elevation metrics for GNSS station quality assessment

Abstract Satellite geometry and sky visibility critically influence Global Navigation Satellite System (GNSS) observation quality. Conventional quality measures such as multipath, cycle slip, SNR ratio, Position Dilution of Precision (PDOP) require sufficient valid data and time-consuming processing, whereas azimuth–elevation (Az–El) metrics can be derived directly from raw observations in RINEX files and satellite ephemeris. In this study, we propose a simple set of Az–El metrics to characterize site suitability and evaluate their ability to replicate the PDOP-based composite (baseline). We compared normalized composite scores from both approaches (Az–El composite (proposed)) using one year of GPS data from 66 continuously operating reference stations (CORS) in northern India (2024). All metrics were ECDF-scaled to [0–1], and ‘lower-is-better’ terms were flipped so higher values always indicate better quality. Agreement between Az–El and PDOP composites remained high (Spearman ρ ≈ 0.956, Kendall τ ≈ 0.831); 3-class accuracy ≈ 84.6 % with Cohen’s κ ≈ 0.769 (tertiles), with no Good↔Limited class flips. These results show that Az–El metrics provide a rapid, processing-light field-ready based QC, suitable for large-scale monitoring and national reference-frame operations. Unlike PDOP, the Az–El metrics explicitly localize direction-specific obstructions (largest blocked sector) and overall sky openness, enabling targeted field remediation and routine QC.