Government UAS pilot reported a near miss with another UAS that was experiencing a malfunction during a night flight. There was no collision and both UAS landed safely.

Narrative

On the night of Day 0 the fire district was requested to assist law-enforcement in a search.Upon receiving the request; and determining the area of operation and knowing that there would probably be multiple aircraft operating at the same time; deconfliction between the multiple uncrewed aircraft; would require us to fly higher than 400 feet and utilize our COA. As part of the mission planning; a phone call was placed to Dispatch to notify them of the area of operation in the event a crewed aircraft operated by them; had to fly in the area; and a NOTAM was posted for the operating area as added precaution; and as required by our COA.While in route to the incident location; the pilot and visual observer started going through the incident checklist and discussed the various configurations for operations that evening. This would've been the first nighttime operation for the visual observer and we wanted to make sure all checklist items were covered. Upon arrival on the gravel road in the middle of the woods; with some patchy area; fog; hugging the ground. The temperature was about 36-38 throughout the operation. Wind was slight with gusts of 5mph. The take-off area was slightly crowded with tall fir trees of over 100 feet. The only place we could take off was in between two police cars. This provided ample light for the take-off area; but required the pilots to manipulate the aircraft precariously after taking off. Meaning; the aircraft could ascend to about eight feet off the ground; pitch forward over the road about 12 feet; then climb and pitch forward more towards a clear cut where we had an open view of the sky and surrounding area. At that point we could ascend to cruising altitude. Based on previous incident operations and incident management practices; the team; checked in with various law-enforcement officials to determine situational awareness; scope of the mission and how we could assist with our uncrewed aircraft.Since there was no air operations branch identified for this incident; the three different agencies piloting aircraft had a conversation about areas of operation and deconfliction. Ultimately; it was determined that vertical separation made the most sense in the event. Multiple cameras. Angles of the same area were needed; and we were operating in the same vicinity. Vertical separation consisted of more than 100 feet. Everyone agreed to have strobes on.We completed our Flight Risk Assessment Tool (FRAT) and our score put us in the yellow category (Green; Amber; Red model). Everything that could be mitigated was mitigated. We were yellow due to limited experience of the VO in night settings; the cramped take-off and landing area; multiple aircraft and frequencies.Our standard preflight check was completed and our 20 and 20 (flight control characteristics) check was completed. This includes; pitch forward; pitch back; roll right; roll left; yaw right; yaw left; climb and descend. Everything checked out as normal and we continued with the mission. Two complete battery cycles were completed before the near miss which occurred on the third battery cycle. With the cold and stress of the environment; the lead pilot and VO traded off at battery cycles to prevent fatigue and to allow the newer pilot (VO) and opportunity to gain mission experience. About nine minutes into the third battery; was when the near miss occurred. At this point in the mission; we were asked to provide overwatch. The overwatch was necessary to protect the pilot who had limited night vision to protect himself since they were looking at a video screen.At about the nine-minute mark; we heard over the radio; which was in the possession of the liaison; a request from the pilot who said tell the aircraft that's over me to get out of the way I think I may hit them. I think it's important to point out that had we not been in the vicinity of the liaison we never would've heard that request from the pilot.Upon hearing that request; I took evasive action by climbing and rolling to the right; which was in the west direction. My altitude at the time was 520 feet. At this point I climbed up to 650 feet and scanned the sky for any other UAS aircraft. I could see the other aircraft flying about half a mile from where I was; but never saw a strobe from the other aircraft. I then continued searching; using various patterns away from the area where I was providing over watch until the battery timed out. I was able to land without incident.A couple of days later; after the mission was complete; and; after action review was completed with the other pilot. The other pilot was experiencing a battery malfunction which caused their aircraft to execute an immediate return to home. Because my aircraft had strobes; they could see me; but I informed them I could not see them at all. Because of the dark in the in ability to accurately determine altitudes; they made the call for the other aircraft in the vicinity to vacate the area.One of the epiphanies that occurred during this After-Action Review (AAR) was one of the errors that all of us made that evening. Generally; when operating uncrewed aircraft altitude is referred to as Above Ground Level (AGL). In most situations; this makes sense. However; have we been communicating in Mean Sea Level (MSL); this never would've happened. What we didn't realize was that; even though we deconflicted at the beginning of the incident; the takeoff and landing area and altitudes ended up being different. Because of the dark; and being in the woods; it was hard to tell. In this case the other pilot was taking off at an altitude of about 100 to 120 feet higher than my takeoff and landing area. This accounted for the assumption of the potential near mess and the request for the other aircraft to vacate the area. Some things that are now lessons learned include; when more than three aircraft are operating and if more than two aircraft are operating at the same incident but from different locations; someone dedicated to managing air operations is necessary; common operating frequency for all pilots on the incident; having a better understanding from the Incident Commander (IC) what the exact mission that is needed for air operations); a check of strobes with positive verification from all the pilots flying (to make sure they see each other); Potentially using thermal tape on the aircraft so that other aircraft can see each other in the thermal IR spectrum; communicate in MSL when operations occur in varied terrain; contacting the FAA to obtain more clearance vertically; continue to push the manufacturers to figure out how to incorporate the ability to capture the Remote ID from other aircraft and see them on the GCS.