# Aerial Survey w/Laser? **URL:** \ **Category:** Factual Questions\ **Created:** [July 2, 2013, 12:43pm UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438 "2013-07-02T12:43:10Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [July 2, 2013, 12:43pm UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438/1 "2013-07-02T12:43:10Z")
I was sitting on my porch the other day when I noticed a twin engine prop plan flying relatively low (1500’?) overhead. I’d seen it earlier flying a low circle and assumed he was looking at something on the ground. This time he flew almost directly overhead and I could see a large black square on the bottom of the fuselage. I could also see what I assume was green laser “sparkling” from the center of the box. No beam or anything (it was mid-day) just a green dot. So, what was he doing and how does it work? Using a laser to aim a camera? Nothing blew up so I guess no drone strike was in the works. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [July 2, 2013, 12:54pm UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438/2 "2013-07-02T12:54:53Z")
It may have been LIDAR. > **[Lidar](https://en.wikipedia.org/wiki/LIDAR)** > > Lidar (/ˈlaɪdɑːr/, also LIDAR, or LiDAR; sometimes LADAR) is an acronym of "light detection and ranging" or "laser imaging, detection, and ranging". It is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It is sometimes called 3-D laser scanning, a special combination of 3-D scanning and laser scanning. LIDAR has terrestrial, airborne, and mobile applications. > Lidar is commonly used to make ... ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [July 2, 2013, 12:57pm UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438/3 "2013-07-02T12:57:34Z")
Probably [lidar](http://en.wikipedia.org/wiki/Lidar). Planes fly over areas and shoot rapid pulses of laser to measure changes in terrain height by calculating the time it takes the laser to bounce back. This data gets made into a [point cloud](http://facility.unavco.org/software/idv/IDV_datasource_point_cloud.html) and a [digital elevation model](http://commons.wikimedia.org/wiki/File:Dem.jpg). Scientists, foresters, government agencies, etc. use this data for all sorts of land-use decisions. The government does a lot of this work and makes it available for free. You can [download their data](http://ned.usgs.gov/) and use open-source software like [Quantum GIS](http://www.qgis.org/) to play with it. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [July 2, 2013, 6:56pm UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438/4 "2013-07-02T18:56:54Z")
That make sense. We were impacted by Superstorm Sandy and flood maps are being revised (although I thought this was already completed). How wide of a swath can be covered in one sweep? ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [July 3, 2013, 1:57am UTC](https://boards.straightdope.com/t/aerial-survey-w-laser/662438/5 "2013-07-03T01:57:27Z")
This kind of data is also used in conjunction with modeling software to plan cell phone base station locations.