  We report on the measurements of telluric water vapor made with the
instrument FIFI-LS on SOFIA. Since November 2018, FIFI-LS has measured the
water vapor overburden with the same measurement setup on each science flight
with about 10 data points throughout the flight. This created a large sample of
469 measurements at different locations, flight altitudes and seasons. The
paper describes the measurement principle in detail and provides some trend
analysis on the 3 parameters. This presents the first systematic analysis with
SOFIA based on in situ observations.
