One of her first tasks was field measurements of potential evapotranspiration using a Thornthwaite-designed evapotranspirometer. After successful experiments in Mount Pleasant Cemetery, Toronto, Thornthwaite was keen to see further experiments conducted in the NWT.
Two evapotranspirometers were installed, and 65 days of readings were obtained in the summer of 1949--the first climate experiment in the NWT.
There are several methods for in situ measurement of ET including pan evaporation (large/small), atmometers, evapotranspirometers
tanks, lysimeters, Bowen ratio  based on meteorological data, the eddy covariance method using flux tower measurements, and scintillometers .