Message Board Thread - "Information on fly overs"

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Information on fly overs David Campbell 2/24/2008
I have a customer that I have serviced for the last 10 or 12 years doing electrical inspections. As part of the inspection I inspect his power lines (14,400). The line is 30KM long and I use either a snowmible or an ATV and do it in the winter. The area is very rugged with lots of streams and woods and no roads. I have a friend who offered his plane (fixed wing) if I wanted to use it. Because I haven't done an inspection this way before I would like to give it a try for my own self-satisfaction . Here is the problem - I am using a Flir P65HS camera with a normal 36mm lens. I know that I can get my flight speed down to around 60KM/Hr and a height of 400-600 feet but will that work? Since this is probably a 1 shot deal and the system I use now works OK, I really don't want to spend a lot of money to gear up. Any comments would be appreciated.

Dave Campbell
9393@nbnet.nb.ca
 
Re:Information on fly overs Doctir bob 2/25/2008
You need to know your IR camera spot size ratio (SSR), the ratio of the distance between camera and target to the size of the spot you wish to measure. Typical P65HS SSR is about 250:1 with standard optics. You can measure a 1 inch target at 250 inches (~21ft). For non-temperature measuring surveys, you can probably see a hot spot at a distance defined by the camera's IFOV (instantaneous field of view). For the P65HS this is 1.1 mrad (milliradian). Providing the radiance contrast is high enough, this means you should be able to see a hot spot of 1 inch size at about 900 inches (75 ft). A 3X telescope triples these distances.

The camera does not see through plexiglass or any normal aircraft window material. You will need to have an open window to shoot from. You will need to hand hold your camera which will eventually get tiring. I did this once from a Bell jet ranger helicopter. We flew 80 feet above the ground and 40 to 60 feet off the power line, viewing more or less horizontally. In fixed wing, I don’t think you’ll be able to do that. You need to calculate the actual working distance and play that off the numbers above to see if you have a chance at success.

An InfraMation 2005 Conference technical paper by Derrick Brydges of HydroOne gives good information about aerial IR surveys of transmission lines. They use a helicopter and a gimbal mounted IR system for surveying 30,000 km of transmission lines.
 
Re:Information on fly overs Derrick 3/11/2008
Doctir bob wrote:
d to know your IR camera spot size ratio (SSR), the ratio of the distance between camera and target to the size of the spot you wish to measure. Typical P65HS SSR is about 250:1 with standard optics. You can measure a 1 inch target at 250 inches (~21ft). For non-temperature measuring surveys, you can probably see a hot spot at a distance defined by the camera's IFOV (instantaneous field of view). For the P65HS this is 1.1 mrad (milliradian). Providing the radiance contrast is high enough, this means you should be able to see a hot spot of 1 inch size at about 900 inches (75 ft). A 3X telescope triples these distances.

The camera does not see through plexiglass or any normal aircraft window material. You will need to have an open window to shoot from. You will need to hand hold your camera which will eventually get tiring. I did this once from a Bell jet ranger helicopter. We flew 80 feet above the ground and 40 to 60 feet off the power line, viewing more or less horizontally. In fixed wing, I don’t think you’ll be able to do that. You need to calculate the actual working distance and play that off the numbers above to see if you have a chance at success.

An InfraMation 2005 Conference technical paper by Derrick Brydges of HydroOne gives good information about aerial IR surveys of transmission lines. They use a helicopter and a gimbal mounted IR system for surveying 30,000 km of transmission lines.
I agree with Bob on the spot size issue.Prior to utilizing our external gimbal I had a wind sock placed where the sliding glass was in the back seat of the Jet Ranger helicopter as per winter conditions. I utilized a pistol grip attached to the bottom of the camera and held the unit with my left hand. I have a remote attached to the camera to adjust all the parameters. I then relayed the image into a monitor which was placed in a mount to my right on the floor. Distance and speed will gauge your success. With a fixed wing plane it will be task consuming especially on lower voltage power lines where the spans are possibly 200 feet.
Any questions please do not hesitate to contact me and good luck.
 


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