field level

https://doi.org/10.1351/goldbook.F02361
Logarithm of the ratio of two values of a field quantity, usually amplitude. Levels are expressed in different ways: LF=ln(FF0) Np, where Np is the symbol for the unit
neper
coherent with the SI, or LF=20 log10(FF0) dB, where dB is the symbol for the unit
decibel
.
Source:
Green Book, 2nd ed., p. 79 [Terms] [Book]