’50 in 50′ Series: Aerial Photography – A Picture is Worth A Thousand Words (1993)

50in50

Lower Trent Conservation is celebrating its 50th anniversary! To commemorate this milestone occasion, we have released our ’50 in 50′ historical blog series. This special series features 50 articles highlighting some of the achievements, milestones and events of the past 50 years. We hope you enjoy them!

Much of the mapping information we use at Lower Trent Conservation is gleaned from aerial photographs. Whoever said that a picture is worth a thousand words was onto something! From early black and white photos to modern digital orthophotography, Lower Trent Conservation retains all of this information.

1993.jpg

Before 1993, aerial photos were collected about once every 10 to 15 years using black and white film. These photos were extremely valuable to staff but relatively expensive to acquire.  Due to cost, these photos were taken at high altitude. This resulted in greater coverage in each photo but less detail. By 1993, improving technology permitted photos to be collected in colour and at slightly larger scales, which made significant improvements in the ability to interpret.

Lower Trent Conservation retains all photos collected over the years in a historical archive. These photos are like a time capsule which allows us to see what the landscape looked like in snapshots back to the 1950s. We can easily see where old woodlands once stood and where wetlands flooded the landscape.

1993-2.jpg

Trained analysts could observe apparent flood plains and areas at risk of erosion from a photo.  They did this by using stereoscopic imagery. Photos were collected as duplicate pairs where the same area was photographed from two slightly different angles. Using an apparatus called a stereoscope, the analyst could view the images in 3D. This illustrated a new dimension in the imagery allowing the analyst to observe differences in topography and vegetation.

In 2002, Lower Trent Conservation participated in the south-central Ontario orthophotography project. This was a partnership between federal, provincial, municipal, and private sector organizations to acquire a consistent digital photographic map.

What is the difference between an aerial photograph and a digital orthophoto? Regular aerial photos represent an image of the earth’s surface as observed from a single point (central projection) – this results in image displacements caused by tilting of the camera and changes in topography. Areas near the centre of the photo appear at a larger scale than areas at the edge of the photo. It does not have a uniform scale and you cannot measure precise distances like you can on a map.

1993-3.png

Through a rectification procedure, an aerial photo can be converted into an orthogonal photo (orthophoto) by taking into account information on topography and the orientation of the camera. This results in the terrain being displayed in a unified scale and may serve as a base map onto which other map information can be overlaid. Additionally, orthophotos can be mosaicked together to create a seamless base map of the watershed.

Lower Trent Conservation continues to collect digital orthophotos about every five years in partnership with other agencies. The latest acquisition coincides with our 50th anniversary in 2018. These images are invaluable to the work that we do – key tools for our watershed science and services and conservation lands programs.

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s