90 GHz data were intended to be combined with the other 3 frequencies and give additional information.
At this point in time separate processing of the 90 GHz data has not been done.

The png images contain raw data daily time series plots comparing 90 GHz brightness temperatures, 32 GHz liquid,
21 GHz precipitable water vapor, 170 GHz brightness temperatures, and rain rates.

ftp://ftp.etl.noaa.gov/et6/cruises/VOCALS_2008/RHB/Scientific_analysis/radiometer/90GHz/MWR90_MWR183_UMMB_TB_MMDD.png
MWR90 = Microwave radiometer 90 GHz
UMMB = Univ of Miami Mailbox
TB = biightness temperatures
MM = month  DD = Day

Univ of Miami operated radiometers at 180, 21, and 32 GHz.
PSD operated a 90 GHz radiometer

Paquita Zuidema at UM has done some processing of these data and created the nc file containing liquid water (LWP).
ftp://ftp.etl.noaa.gov/et6/cruises/VOCALS_2008/RHB/Scientific_analysis/radiometer/vocals_rhb_lwp10min_v1.nc and vocals_rhb_lwp_v1.nc