Satellite data comes with coarse resolution. For soil moisture, you can use Soil Moisture Active and Passive (SMAP) satellite data whereas for evapotranspiration (ET) you can use MODIS ET. However, if the area of interest frequently goes and under water, you need to separate measurement when area was under water. I think the measurement will not be true measurement, rather observation over the water. It will be little complicate to measure ET when part of plant is under water and other part above the water. Hope it help a little to think on this direction. Thanks.

i suggest you use satellite package such as MERRA2

What do you mean by "continuously" in your question?

Ram L. Ray Thanks for your guidance

Well,

In this question, you mean methods of calculation or measurement of ET.