What is chop-nod mode?
Chop-nod is the standard mode of data acquisition for LWS. Chopping is performed to cancel out sky radiation and nodding of the telescope is performed to help cancel out the radiation contribution from the telescope. The LWS chop-nod style uses a nod throw equivalent to the chop throw but in opposite directions. See figure. The resulting image, after double difference process, requires no further shift and add processing. The chop-nod technique is very effective at canceling out background radiation.
