Aerial Photographs and Remote Sensing Aerial Photographs For years geographers have used aerial photographs to study the Earth’s surface. In many ways air photographs are better than maps. They provide us with a real world view of the earth’s surface, unlike a map which is a representation of the real world. Aerial photographs can be used to make the same measurements that we make on a map, as they too are a scaled image of the surface.

Air photograph of Fair Glacier, Colorado. Source: USGS North is at the top of the photograph. The glacier is easily identified by its white color. Surrounding the glacier on its western, southern, and eastern sides are the walls of a cirque in which it sits. A cirque is a bowl-shaped landscape feature common to mountainous regions which have been glaciated. The glacier formed in the area to the bottom of the picture and extended itself towards the north. The dark triangular - shaped feature to the north of the glacier is Triangle Lake.

What is remote sensing ? Remote sensing is the science and art of obtaining information about a phenomena without being in contact with it. Remote sensing deals with the detection and measurement of phenomena with devices sensitive to electromagnetic energy such as: Light (cameras and scanners) Heat (thermal scanners) Radio Waves (radar) How is remote sensing useful? It provides a unique perspective from which to observe large regions. Sensors can measure energy at wavelengths which are beyond the range of human vision (ultra-violet, infrared, microwave). Global monitoring is possible from nearly any site on earth.

Typical Remote Sensing Platforms used today

Sample Landsat TM image along Missouri River

Landsat TM image of San Francisco Bay

Remote Sensing of the Global Environment (AVHRR Satellite Composite: 26 Aug 1993) (Image from SSEC: UW-Madison)

Remote Sensing and Satellite Imagery Remote Sensing and Satellite Imagery Figure EG.30 SIR-C/X-SAR image of the Mississippi River (Source: NASA Jet Propulsion Lab) To get a much larger view of the earth’s surface features, geographers have turned to using remotely sensed data from satellites. Satellites do not use conventional film like that used for air photographs. Satellite sensors scan the surface and break it down into picture elements or pixels like those displayed on your computer monitor. Each pixel is identified by coordinates known as lines (horizontal rows), and samples (vertical columns). As the satellite scans the ground, it transmits this information to earth-based receivers, the same way a television broadcasts a signal to your television. The digital data received is processed in a variety of ways: simulated natural color, "false" color, signal filtering, enhanced contrast, etc.

Much of the area in purple is agricultural land. Areas occupied by water appear in black while the bright green areas are forested. The long narrow lakes bordering the river are called oxbow lakes and are created when the river changes course, abandoning the old channel for a new one.