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I spoke with one of my colleagues that worked with distribution design. He said the following:

I’m not sure about how field measurements could help with line parameters, but they do help ascertain ratings. The way we worked out the line parameters at the utility I worked for do it the following ways:

Conductor/cable impedance are obtained from the manufacturer
The impedance is calculated based on the as-builts (i.e.: line designs). The OH line impedance depends on the circuit configuration (on tower). This can be calculated by hand or can be calculated using DIgSILENT which has a OH impedance calculator based on the tower configuration. Normally what we have done in the past is that calculated it by hand and used DigSILENT to verify results. The cable impedance are also based on as-builts, and depends on the way it is buried in the soil (in trefoil or flat configuration for single core cables). There are literatures out there that shows the way to calculate the impedance. Unfortunately, DIgSILENT does not calculate the cable impedance – so no way of verifying it.
With cables however, the harder thing to work out is it’s rating. Normally, in the absence of measurements, you refer to the manufacture ratings which are based on certain conditions. The cable ratings are susceptible to soil resistivity and temperature. So where you have places of high temperature, or soil of insulating properties, you tend to do soil tests. We used to do this to ascertain the cable ratings using CYMCAP software. The ratings are also dependent on the ability to transfer heat in the trench. So you’ll have to calculate a number of things including the way it is laid out in the trench, the number of cables in the trench, the depth, backfill materials etc.