Part 107 UAS pilot reported a near miss with a low flying helicopter. The pilot put the UAS in hover mode and avoided the helicopter's flight path.

Narrative

Oblong autonomous flight at 375 ft AGL of construction site; XA:30 hours 10 mile visibility. clear skies. Flight limited to 375 ft AGL. Full VLOS (visual line of sight) of entire flight and flight area parameter. During flight; a helicopter suddenly appeared just above power lines at approximately 150 ft AGL. The adjacent area where the helicopter came from; was tree-dense corridor. Tree canopy was 112 ft AGL and power lines were 120 ft AGL. The extreme low altitude of the helicopter eliminated the ability to hear its approach in advance; while the adjacent tree corridor only allowed me to visually see it at the edge of the tree canopy; approximately 100 yards from launch/land location. No evasive action was necessary; as the sUAS was over 200 ft higher than the helicopter and approximately 30 degrees to the NW of the helicopter. I immediately went into hover mode until the helicopter was out of VLOS and outside the flight parameter of the mission. I was able to visibly see approximately 2 miles in any direction of the flight parameter; at the 375 ft AGL level. No other manned aircraft approached or breached that 2 mile radius at 375 ft AGL. I have since investigated using a COM radio; but that would only have been valuable if the helicopter had been broadcasting its position; I've been told that is generally not the case. Also; I've investigated ADS-B portable receivers but I've learned those only function at/above 500 ft AGL. The only option seems to be monitoring sites like Flightaware; realizing the latency of 30 seconds (or more) is problematic for real-time positioning.