Abstract: A FMCW radar tank level gauge (14) that measures a level (13) in a tank (10) by obtaining a set of phase shift data points of mixed transmitted waves and received waves. The set of spectral data phase shift values has a received target marker indicating the level. An adaptive set of masking threshold phase shift values corresponding to at least a portion of the spectral data phase shift values are calculated. The adaptive set of masking threshold values are compared with the corresponding spectral data values to identify at least one spectral data value associated with the level. The level of the tank is calculated from at least one spectral data value and the level of the tank is reported.