Aerial Photography Versus Satellite Imagery: Have Satellite Imagery Replaced Aerial Photography?

September 22, 2021 0 Comments

In the last ten years we have seen spectacular developments in the clarity and availability of satellite images. Microsoft and Google are examples of companies that now offer satellite images, also known as remote sensing images, to the public. While these images are fascinating and in many cases potentially useful, some people wonder if these developments spell the end of traditional aerial photography. The resounding answer is “No, aerial photography is alive and well.”

One of the reasons aerial photography remains a valuable tool is its superior resolution. Particularly with the advent of commercial digital equipment, an aerial platform provides very high resolution images, while the resolution of satellites continues to be limited by both technology and federal law. In 1999, commercial satellites could capture a resolution of one meter in black and white, and somewhat less detail in color. This means that the smallest detail that could be captured and clearly delineated was at least one meter in size. There’s a popular rumor that military satellites can read a car’s license plate from space, and that’s probably an exaggeration, but it doesn’t matter even if it’s true. You, as a private citizen, cannot buy or use those images anyway. Current law limits the resolution of commercially available satellite images to 0.5 meters. That means the smallest detail that can be clearly delineated is at least 0.5 meters or 19.5 inches wide. An aerial photograph with the highest digital resolution taken from 1000 feet above the ground has approximately five times better resolution than the best commercially available satellite images.

Another difference between aerial photographic images and satellite images is the timeliness and availability of the images. Commercial satellites orbit the Earth from about 400 miles above mean sea level. They orbit in a pattern and speed that allows them to pass over the same point on earth about once every three days. This is fine for surveying and mapping. It generally does not allow capturing events. Generally speaking, the earth is cloudy for about 60 percent of its surface at any given time. The three-day cycle for a satellite to fly over a point can mean that it can take from a few to several dozen cycles before a clear shot is available. Air flight is also subject to weather, but planes can fly under cloud cover and are available for a photo shoot anytime between sunrise and sunset. The limitation of aerial photography due to weather conditions is usually a matter of a few days, not weeks or months.

One advantage aerial photography has over satellite imagery is the creative aspect of the composition. Satellite images are generally taken directly from above. Satellite images can be taken from an oblique angle, but this introduces additional distance from the lens and requires repositioning the angle of the satellite camera. Aerial photos, on the other hand, are generally taken from an oblique angle. This allows shooting from all sides and at different heights, introducing varied composition and improved usability. There is also the factor of light in the composition of the photograph. A satellite uses whatever light is available by the time it passes over its target. In an aerial photography session, the photographer chooses the light that best suits the composition of the target images. The amount of sunlight, the angle of the light, the shadows that the light casts, and the time of day all contribute to a photo that is useful for conveying information and aesthetically pleasing.

Satellite imagery will undoubtedly evolve in its ability to document, map and study in a variety of light spectra. It is an increasingly fascinating mode of imagery. However, aerial photography remains a superior way of capturing images from the air where direction, angle, composition and timeliness of availability are key requirements for capturing the target image.

Leave a Reply

Your email address will not be published. Required fields are marked *