Small Format Aerial Photography

Aerial Images of Quivira National Wildlife Refuge
Lori Bird, July 2006
Link to ES555 class

Table of Contents
Introduction Acquiring the Image
Aerial Photography Processing the Images
Final Images References

Introduction

Aerial photos can be effectively taken using various platforms. These platforms include manned and unmanned, tethered and free flying. Each platform has its advantages and disadvantages. Unmanned platforms include kites, blimps, balloons and drones. Kites, blimps and balloon are relatively inexpensive and can be tethered during the image acquiring process. Tethering provides a stable platform from which the images can be gathered from a relatively fixed axis. The camera can be rotated and pivoted for different views of the surrounding countryside. However, the camera for the most part is stationary about an axis perpendicular to the Earth.

Drones can capture aerial pictures as it flies over the area of interest. Real-time video is trasnmited back to the pilot, enabling him to steer the drone via a remote control link and obtain the required images. Drones can be costly and require training to operate. Satellites provide remote images from space. The images are limited to the area covered by the satellite's orbit and are often not very recent.

Manned platforms include airplanes, balloons, the shuttle and various other manned vehicles. The advantage of a manned vehicle is the ability to have a human eye behind the camera. The human can determine which pictures are of interest and can be flexible. Most manned platform are very expensive. They require a vehicle, trained pilot and often, expensive camera equipment. This reports deals with amateur aerial photography from a small plane.

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Acquiring the Images

The actual process of acquiring images taken from a small plane platform was divided into several tasks:

  • Determining locale and obtaining required permissions.
  • Obtaining suitable camera, pilot and plane.
  • Coordinating the schedule of photographer and pilot along with weather.
  • Selecting representative images from those obtained.
  • Processing the images.

    The Quivira National Wildlife Refuge in Stafford County, Kansas was selected as the locale for the pictures. The Federal Aviation Administration requires special permission to overfly a national wildlife area below 2500 feet. The FAA and the Quivira park ranger were contacted. They granted permission to overfly the wildlife area since it was not during a migration period. Both permissions were easily obtained, but as the wildlife ranger remarked "Its better to get permission first. Let me know when you will fly over so I don't have to file a report with the FAA for an unauthorized flight."

    The second task was to obtain a suitable camera for taking aerial pictures. Three cameras were available to the photographer: a digital Polaroid 5380, a Zonica Minolta Z10 and a Cannon Rebel SLR 35 mm. The Z10 was selected because it was manually adjustable, had a single relex lens like view finder, and was digital. A digital camera would allow the photographer to take numerous images without film and processing cost concerns.

    Two planes were available for this task. One was a single place Cessna 188 airplane. This plane was unsuitable because it had a low wing that obstructed the view below. Also, the pilot had to multitask: fly as well as take the pictures. Basically, he just pointed the camera, pressed the button and hoped for the best. The results were not acceptable. The second plane was a Tripacer owned, restored, and piloted by Steve Stacey of Hutchinson, KS. This plane could carry several people and had a high wing that allowed the photographer to take unobstructed pictures of the ground. The plane did not have a window that could be opened, so all images were taken "through the window". This introduced some glare and reflection, especially in images towards the West.

    View of Flint Hill of Kansas, June 2006 Tripacer owned by Steve Stacey, Hutchinson, KS. Image taken by Bird, J. Oct. 2005. Quivira Image out the window, June 2006. J. Bird.  Notice glare towards the west.

    The weather was another factor that required coordination. The ideal weather would be a calm, clear day, preferably during the early afternoon, before the glare and shadows became a factor. When the air is calm, it is much easier to maintain a stable flight platform from which to take the pictures. Unfortunately, the optimum time was not possible. The pictures were taken in the early evening. Notice the glare and shadows in the pictures. TOP

    Aerial Photography

    The photographer and pilot took off from a private airstrip in Nickerson, KS aprroximately 7:00 p.m. on June 14, 2006. Several passes were made over the wildlife refuge. The images were take at altitudes of 4200 and 2400 feet. The camera shutter speed was set to 1/125 second, and f/stop was set at 3.2. The focal length was set to 36 mm. The pictures were taken at 1.3 frames/second. When taking the pictures, the usefulness of the digital camera soon became apparent. The photographer basically shot continuous images as the plane overflew the salt marshes. Several images out of the 150 taken were selected for processing. The plane banked (turned) as some of the images in the chosen sequence were taken. Notice the attitude (the angle at which the airplane is at in relationship to objects on the ground) changed, resulting in a change in the position of objects in the photographs. This is especially noticable in the road in images PICT1405 - PICT1402. This change in attitude was even more pronounced when the images were processed and were being joined together.

    1405 1404 1403 1402 1401 1400
    Sequence of pictures of Quivira, PICT1412 - PICT1400 (left to right). Pictures taken by J. Bird, June 2006
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    Processing the Images

    The Gimp (an image processing software package) allowed the student to crop out undesirable obstructions from the images (airplane strut) and sharpen the images. Several images were then stitched using PTGui software. A trial PTGui version was used; hence the watermark on the images. To create a stitched image, several photos were selected. The photos were examined and several (at least 3) reference points were identified in each image. By identifying common points in each photo, the images were linked together. Several stitched images were attempted. A good fit was produced when the pictures were taken from the same attitude or angle to the ground.
    Good fit.   Images 1400-1403, created by L. Bird July 2006 Bad fit.  Images 1402-1405.
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    Final Image

    In the case of images 1400 through 03, many common reference points were discovered. Evidently the plane held the same attitude for these pictures, which produced a very good fit. The stitched image was processed with The Gimp software. It was rotated, cropped and the borders were painted grey to blend in with the image.

    The next step was to somehow quantify the image to determine its scale and resolution. An image of Quivira National Wildlife was obtained from Google Earth and compared to the stitched image. A rough scale was calculated and added with the aid of IDRISI Andes software. The title and North arrow were also added. The final result is displayed below.

    Scaled and annotated stitched image of Quivira National WIldlife Area facing East-southeast.  Photo taken byJ. Bird, July 2006. Image created by L. Bird, July 2006

    This adventure into aerial photography was intriguing and quite illuminating. It has given the student a greater appreciation of aerial photography and a better understanding of the nuances involved in producing a good, usable image. The stitched fit of the images 1400 -1403 was especially gratifying. Calculating a scale based upon the Google Earth image was very challenging due to the oblique angle of the student's image and the resolution of the Google Earth image. Many thanks to John Bird who agreed to take these pictures if he could be the one who took the plane ride. Thank also to Brian Bird and Steve Stacey who volunteered their planes, time and piloting skill for this project.

    References

    Bird, Brian A. Hutchinson, KS June, 2006.

    Bird, John J. Hutchinson, KS. June 2006.

    www.earth.google.com, accessed July 2006.

    IDRISI, The Andes Edition, Clark Labs, Clark University, Worcester, MA. July 2006.

    Quivira National Wildlife Area Park Ranger, Stafford County, Kansas, June 2006.

    PTGui Software Company, July 2006

    Stacey, Steve. Hutchinson, KS, June 2006.

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