Evaluating junction temperature from thermal imaging data
@mkeith is correct. If you measure the Vf with very short 1A pulses, to avoid self heating, whilst controlling the ambient temperature with an oven, you will be able to get the Vf @ 1A over the temperature range. If short pulses can not be acheived, steps between 0A and 1A are acceptable if you take the measurement very quickly and obviously keep the duty cycle very low; this can be done with a scope and preferrably also a current probe to see when the current has settled.

I have done a similar experiment in the past to characterise the temperature dependance of the Vf of various LEDs over a range of currents in order to calculate the junction temperatures in normal operation.