There is a 210 cm long soil column that has five layers of different soil types. The topsoil layer of 15 cm has a moisture sensor in the middle. The second and third layers are of 95 and 80 cm of length and only have sensors on top and at the bottom, respectively. There are two 10-cm-long layers of sand and gravel at the end (for drainage).
So my assumption is that this network of sensors cannot give me a good estimate of the whole column water storage.
To be more specific, the (30-min) sensors are at these depths: 7.5 cm, 22.5 cm, 175 cm, and 185 cm.
A lysimeter at the bottom of last layer (beneath 20 cm of sand and gravel drainage layers) collects the percolation on an hourly basis. Also, runoff is being collected (though insignificant values, 4 mm for 2 years for instance).
The vegetation is natural growing grass. With 3 months of snow covered ground annually.
How would you suggest I estimate ETP (daily or hourly) for this column and how confident I should be about its accuracy?