USRP Spectrum Sensing - Power in dB or dBm?


I’m a beginner working in Spectrum Sensing. I have been checking the
code given in the file in GNU Radio.

The power calculated (at line 303) is in dB as given below :

power_db = 10*math.log10([i_bin]/tb.usrp_rate) - noise_floor_db

My query is whether the power calculated in dB is in reference to 1
Can we convert this power to dBm?? What parameters are needed to be
checked or tuned in this program??

Also, how can we calculate the Power Spectral Density (PSD) from power
in dB with reference to given frequency??