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(EO) EO cameras cost a few hundred to a few thousand dollars and weigh a few ounces. Lidar costs between tens of thousands of dollars and hundreds of thousands of dollars and weighs a few pounds to 15 pounds (for the lightweight aerial versions). With the relatively recent advent of installing cameras on drones, camera technology on sUAS is on a rapid rate for technological advancement. The Go Pro type camera was one of the first used. Then variations of this camera were produced at lower cost. One of the key issues with the “action” cameras let’s call them – is that they have no aperture, so the amount of light that is let into the sensor is regulated by ISO and shutter speed. With most photogrammetry operations, they are done at “high” speeds like 40 – 80 knots. This necessitates the need for a fairly high shutter speed to avoid blur due to motion. DSLR cameras were installed early on using complex and fragile gimbal systems for improved resolution. Then DSLR camera were bashed and combined with gimbal systems eliminating the viewing screen on the back of the camera to save weight and complexity not needed in a UAV. Cameras are continuing to evolve such that it is very difficult to keep up with technology as every few months a newer, better camera is on the market. For this reason, it is not possible to offer a recommendation to a specific brand or camera. However, there are some key points to keep in mind when shopping for a camera to perform surveying.
A key component of an EO camera is the lens. Some with large FOV (field of view) have very high distortions. Some software companies have come out with algorithms to reduce the effects of lens distortion, however, it’s best to avoid the distortion in the first place where possible. If you look at the imagery taken from many “action” cameras it is obvious that the horizon is quite bowed. This distortion is not the best when trying to achieve high accuracy photogrammetry. Most of the cameras coming out today have corrected this issue by not using as wide of (fisheye) lens.
Surveys consist of many photos per acre. Each photo is compared for key points by the computer to match the photos to one another. A common amount of key points is 20,000 per photo. It helps if the imagery is as good as possible to assist the computer to match up these points as quickly and easily as possible. It is the pilot’s job to obtain the best possible imagery for the computer to do its job. A better camera assists in this area.
Some off the shelf cameras which work well and are relatively inexpensive are the DJI X3, DJI X5, some point and shoot cameras, any DSLR, and 3DR Sony R10C. These are recommended primarily because they fit onto common sUAS. It is recommended that you do not use “action” type cameras with huge wide-angle fisheye lenses even though they are available. Keep in mind that it is not all about megapixels (MP). It is more about pixel size and the relative “noise” associated with the sensor. The sensor is the part inside the camera that the light activates. If the sensor is small, it typically is not as good for surveying as a camera with a large sensor. Cameras in manned planes use medium and larger format cameras which cost $50,000 or a lot more. Size does matter when it comes to sensors! A small sensor may be divided up into 12 mp, and a sensor which is ten or twenty times larger may also be 12mp, but which one do you think is better? Always go with the bigger sensor.
Site scan from 3DR has a sensor for their aircraft which is larger than the DJI X5. See below. Expect that better camera systems will be coming out quickly. The 3DR Sony 20MP APS-C sensor offers a 0.5 cm/pixel ground sampling distance at 200 feet AGL.
Cameras which are wide angle can be flown closer to the ground to increase the ground resolution, however wide angle lenses gather more oblique imagery which is difficult for the computer programs to rectify into nadir imagery, so some errors are more apparent.
A key aspect to cameras is how fast they can take (process) a photo. Many are about 1 per second at maximum resolution. This is fast enough for many applications but not all. Use the SD card that is the biggest and can be written to the fastest. This will allow a higher speed that the sUAS can operate which may significantly reduce the flight time.
It is usually not beneficial to shoot in RAW format. JPEG is usually appropriate. RAW images might be 25mb while jpeg are about 5mp. It takes far less time for the camera to process jpg images which increases the number of photos that can be taken per minute which increases the speed at which the aircraft might fly. Jpg images also upload to the data processing software much faster as well. The format used will be dependent upon the software used, so you need to follow the manufacturer’s directions.