Amplitude Calibration for Pulse Amplitude Modulated (PAM) Infrared (IR) Link with Relative Motion Between Emitter and Receiver
Maybe use a discrete ring of IR emitters and possibly this IR Rx, but you don't have enough system specs to choose anything yet.

https://www.digikey.ca/product-detail/en/vishay-semiconductor-opto-division/TFDU8108-TR3/751-1087-2-ND/1681221

But these are rapidly going or are obsolete.

A bigger picture of the actual measurement problem might be helpful.