Licor Li-190 quantum sensors measure up-welling and down-welling PAR.
Two Li-190 sensors are employed; one downward pointing (mounted to the rear of the left hand pod) and one upward poiting (mounted on the Skyward Sensor Mount, in the rear cabin). These are broad band sensors sensitive to 'Photosythetically Active Radiation' (PAR).
Logging for both is accomplished on the MET-CR3 datalogger (Note: the upward point sensor data is initially logged on the Central Services Module's CSM-CR1A datalogger and then passed on to the MET-CR3, so there is a lag of approximately one cycle in this data).
Both sensor mounts are angled to provide vertical alignment, as far as practically possible, during normal sampling flight. It will be necessary to apply further corrections during manoeuvring flight.