noise yopt

In theory,the noise of a 2 ports network can be defined by NF and Yopt(3 variables totally). The NF can be measured. But how to measure the YOPT? Could I calcualte it out with the output noise measured with the RFinput be open and short?

Added after 1 hours 4 minutes:

I'm waiting. :)
In some books. 4 variables are needed: Vn, In and Yopt., (The Yopt is a complex and has 2 variables). I think The Vn and In can be measured out with open and short terminal at the input. So can I get the Yopt from Vn, In, and NF ( which is the matched case).

I guess it is determined by the measurement.