Using Alt Az Distance to find position of satellite in ICRF

[sgboakes]

Hi all,

I am currently using Skyfield for calculating visibility of Earth satellites from a ground-based sensor. I followed the example for finding the altitude, azimuth and distance of the satellite from the sensor (https://rhodesmill.org/skyfield/earth-satellites.html#satellite-altitude-azimuth-and-distance), which provides me with good results.

However, I now need a function that will compute the reverse function, to transform a measurement in altitude azimuth and distance into an ICRF position. I'm not sure how to leverage Skyfield to do this using only the AzAlDist vector and the ECEF/LLA position of the sensor on the Earth. Has anyone been successful in doing this before? I've tried searching through the repository but I can't see how I would find even the transform matrices.

Thanks in advance :)