Most perimeter assessments are conducted at eye level by someone walking the fence with a clipboard, which means most perimeter assessments share a blind spot: everything the site looks like from above eye level. Camera fields of view are guessed from the ground. Mast-top mounting hardware hasn’t been inspected since the lift left on install day. The fence line gets sampled where it’s walkable and assumed where it isn’t.
I fly a drone on assessments as a certified RPAS pilot, and the aerial pass has become the part of the survey that changes findings rather than confirming them.
What the flight actually produces
The flight produces specific evidence, not a pretty site photo:
- True sightline verification. An orthographic pass at camera height along the perimeter shows what each camera can see, including the dead zones created by that shipping container someone parked in year two. Comparing this against the coverage map in the O&M manual is reliably humbling.
- Mounting and cable condition at height. Corroded banding on a pole mount, a drip loop that’s become a water feed, conduit pulled away from a mast, a junction box missing its cover: all invisible from the ground, all photographed in ten minutes without a lift rental.
- Fence-line continuity in sequence. A low pass along the full perimeter produces a continuous, timestamped record. Wash-outs under the fabric, vegetation defeating the clear zone, sagging fabric between posts, and the informal path worn to the exact spot where the fence is climbable all show up without anyone bushwhacking the back 40.
- Lighting and approach documentation. Dusk flights map real illumination against the photometric plan, and approach routes an intruder would actually use read differently from 60 metres up than they do from the guard shack.
- As-built truth for the drawing set. Roof-mounted equipment, antenna farms, and pathway routing get documented as they are, which matters when the drawings are three revisions behind the building.
The part people skip: flying it legally
An RPAS survey of an industrial or critical infrastructure site isn’t a hobby flight. In Canada that means Part IX of the Canadian Aviation Regulations: registration for anything over 250 grams, a pilot certificate, and an advanced operations certificate plus air traffic control authorization before flying in controlled airspace, which covers a good share of the industrial sites worth assessing because they sit near an aerodrome. Client property doesn’t exempt you from any of it, and a security consultant generating regulatory violations while auditing someone’s risk posture is a story that writes its own ending.
Build the flight into the assessment scope like any other task: airspace check, site notification, weather window, flight log retained with the deliverable. The photos go into the report with coordinates and timestamps, which is also what makes them defensible when a finding gets disputed.
Where this fits in an assessment
The aerial pass covers the axis the walk-down can’t reach, and it doesn’t replace the ground work. Ninety minutes of flying on a mid-size site typically produces three or four findings that would otherwise have needed a lift rental or plain luck. On one survey the aerial pass settled in an afternoon a camera-coverage dispute that had run for months on the ground, because a photograph from the camera’s actual mounting height ends arguments that diagrams start.
If your assessor isn’t looking at your site from above, part of your site isn’t being assessed.
Perimeter and CCTV assessments, with the aerial pass in scope, are described under independent review.