The uncertainty codes used by the HITRAN database are described in Table 2 of the HITRAN2020 paper [1], which is reproduced here. There are two types of uncertainty code corresponding to absolute uncertainty in cm-1 (used for the line position and air pressure-induced line shift parameters) and relative uncertainty in % (used for the line intensity and broadening parameters).
| Code | Absolute Uncertainty range | Code | Relative Uncertainty range |
|---|---|---|---|
| 0 | ≥ 1 or Unreported | 0 | Unreported or unavailable |
| 1 | ≥ 0.1 and < 1 | 1 | Default or constant |
| 2 | ≥ 0.01 and < 0.1 | 2 | Average or estimate |
| 3 | ≥ 0.001 and < 0.01 | 3 | ≥ 20 % |
| 4 | ≥ 0.0001 and < 0.001 | 4 | ≥ 10 % and < 20 % |
| 5 | ≥ 0.00001 and < 0.0001 | 5 | ≥ 5 % and < 10 % |
| 6 | ≥ 0.000001 and < 0.00001 | 6 | ≥ 2 % and < 5 % |
| 7 | ≥ 0.0000001 and < 0.000001 | 7 | ≥ 1 % and < 2 % |
| 8 | ≥ 0.00000001 and < 0.0000001 | 8 | < 1 % |
| 9 | ≥ 0.000000001 and < 0.00000001 |
[1] I. E. Gordon, L. S. Rothman, R. J. Hargreaves, R. Hashemi, E. V. Karlovets, F. M. Skinner, et al., "The HITRAN2020 molecular spectroscopic database", J. Quant. Spectrosc. Radiat. Transfer 277, 107949 (2022).