ASRS 2280495

I was flying a LiDAR capture mission of an open field 4.5nm SW CKI (Google indicates trees but the area of operation has been cleared except for a single line of trees along the road to the immediate west). I was positioned vicinity Location X and my drone was set to follow terrain in a 25 acre area pattern at 150ft 15mph or less. At XA38 the drone was capturing data vicinity Location Y. My drone controller gave me a warning that an aircraft was in the vicinity. Within seconds I heard an approaching helicopter and within seconds identified a low flying red helicopter with a long object slung below. It flew from west to east between me and my drone. I immediately took manual control of the drone and began a descent but I don't believe it would have made much of a difference had the helicopter been slightly north. The approximate linear distance between myself and the drone was 200m. Due to my focus on flying my drone, I was not able to positively identify the type of aircraft nor the long silver object that it had in sling, it did not appear to be a saw. Issues: Unless in the performance of a mission, takeoff or landing, or in a designated lowlevel flight area manned aircraft should remain above 400ft. As a former helicopter pilot I've witnessed the effects of a bird strike; hitting a 15lb drone could be catastrophic. ADS-B should be installed in all aircraft including drones. A feature on the drone provided an indication of the approaching aircraft but if the operator is watching the drone there's not a audible indicator until roughly 2,000.