Aerial photogrammetry

Figure 65 Aerial image of Niagara Falls
Figure 65 Aerial image of Niagara Falls (Hexagon Geosystems)

Aerial photogrammetry refers to the recording of images of the ground (photographs, for example) from an elevated position, such as an aircraft. Systems of this type are now more generally referred to as “remote sensing” since the images can be taken from aircraft or from satellites.

In the past, images would have to be manually corrected for orientation, perspective, height and location of the camera and manually “stitched” together. This manual process would be based on the accurate alignment of known points in adjacent pictures.

By integrating the camera with GNSS+INS, it is now possible to automate the process in real-time or post-mission to “transfer” the location accuracy of the aircraft determined from GNSS to the image.

Aerial photographs are used in online map systems such as Google Earth. Many of us have found our houses, and perhaps even our cars, through these applications.

GNSS technology has also been integrated with LiDAR (Light Detection and Ranging), an optical remote sensing technology used to measure the range to distant targets. It is possible to detect and image a feature or object down to the wavelength, which at LiDAR frequencies is less than a millionth of a metre.

Mapping wildfires

To battle wildfires, firefighters need to know the locations of the fires and any hotspots. Using an airplane equipped with an infrared imaging sensor and a GNSS+INS system, locations of fires and hotspots can be projected on topographical or 3D terrain maps.

An article (Custom Airborne Mapping Solutions) about how GNSS is used in aerial mapping is in the 2014 Velocity magazine available at:

Chapter 9: GNSS applications and equipment