κ computed from ERA5 measured data — not assumed.
Every surveyor, engineer, and scientist working with line-of-sight has been using κ = 0.13 — an empirical average from the 1960s. KAPPA replaces that assumption with the actual measured atmosphere from ERA5 reanalysis at 137 model levels, for any location, any date, any time.
The difference between an assumed κ and a measured κ is the difference between a survey that closes and one that does not.
An empirical average from 1960s European observations. Applied uniformly regardless of location, season, humidity, or elevation. Wrong by 15–40% in most real conditions.
Derived from ERA5 reanalysis at 137 vertical levels using the full ITU-R P.453 wet-term formula. Location-specific, date-specific, time-specific. Correct.
Unmodelled refraction error in a first-order levelling network. Enough to fail closure tolerances and require expensive re-observation.
Real atmospheric correction applied per session. Network closures that meet first-order tolerances on the first attempt.
Every computation is traceable to published scientific standards. No black boxes. No empirical shortcuts.
KAPPA serves every professional who needs to know what the atmosphere was actually doing at a specific place, on a specific date, at a specific time.
ERA5 is ECMWF's fifth-generation global atmospheric reanalysis. It is the only freely available dataset with sufficient vertical resolution to compute a path-specific refraction coefficient from real measured data. KAPPA is the first operational tool to connect ERA5 directly to geodetic practice.
Contains modified Copernicus Climate Change Service information 2024. Neither the European Commission nor ECMWF is responsible for any use that may be made of this information.
KAPPA is currently being validated against real-world professional survey observations and documented long-range photographic records. Results will be published here and in a peer-reviewed FIG Commission 5 technical paper.
First-order levelling network comparison. KAPPA-computed κ versus standard assumed κ = 0.13 over measured traverses. Network closure analysis.
ERA5-predicted κ compared against documented extreme long-distance photographic observations. Blind prediction of visibility windows versus photographic record.
Full scientific validation paper submitted to FIG Working Week 2026, Commission 5 — Positioning and Measurement. Peer-reviewed publication of methodology and field results.
We are looking for professional surveyors and long-range observation specialists to validate KAPPA against real field data. Early collaborators receive complimentary Professional access and co-authorship on the FIG paper.
Every surveyor, engineer, and scientist working with line-of-sight deserves the correct κ — not a 60-year-old guess. KAPPA gives you the real atmosphere, for any location, any date, any time.