Aerial photography is one of the oldest and simplest methods used in remote sensing to capture images of the Earth’s surface. Think of it like using your smartphone camera but on a much larger scale, from aircraft or satellites, to take pictures of land, cities, forests, or farmlands. These images help in mapping, environmental studies, disaster management, urban planning, and many other fields.
Aerial Photography and Its Components
Aerial cameras use either photographic films or digital sensors to capture images. Traditional photographic films are sensitive to light ranging from 0.3 µm to 0.9 µm, covering ultraviolet (UV), visible, and near-infrared (NIR) wavelengths. This is similar to how different filters in a mobile camera allow you to capture specific light conditions, such as night mode or infrared mode.
Types of Aerial Photography Films
1. Panchromatic Film (Black and White Photography)
- Sensitive to UV and visible light.
- Produces black and white images.
- Commonly used in topographic mapping and land surveys.
- Example: If a city needs to map out its road network, panchromatic images can provide clear contrast between roads and buildings.
2. UV Photography
- Uses panchromatic film with a UV filter to block visible light.
- Captures only UV reflectance from objects.
- Not widely used because UV rays are scattered in the atmosphere, making it hard to get clear images.
- Example: Scientists sometimes use UV photography to detect air pollution levels or oil spills on water.
3. Black & White Infrared Photography
- Sensitive to the entire 0.3 – 0.9 µm wavelength range.
- Very useful for vegetation studies because healthy plants reflect more infrared light.
- Example: A farmer can use infrared aerial images to check which parts of their crop fields are growing well and which need more water or fertilizer.
4. Color and False Color Infrared (CIR) Photography
- Uses a three-layer film, similar to the RGB filters in digital cameras.
- Normal Color Photography: Captures blue, green, and red light, just like our human eyes see colors.
- False Color Infrared (CIR) Photography: Captures green, red, and near-infrared light but displays them as blue, green, and red.
- Example: A CIR image of a forest can show healthy trees in bright red, while unhealthy or dry trees appear in dull red or yellow. This helps in forest conservation and wildfire prevention.
Platforms for Aerial Photography
Aerial cameras can be mounted on different platforms, depending on the purpose:
- Ground-based setups: Used for close-range studies such as photographing buildings, archaeological sites, or soil erosion.
- Helicopters and aircraft: Used for capturing detailed aerial images over cities, mountains, or disaster zones.
- Satellites and spacecraft: Used for large-scale remote sensing, such as monitoring deforestation, tracking ocean currents, or mapping global climate changes.
Example
Imagine Google Earth – the high-resolution images of your city or even your home are taken using aerial cameras from satellites or aircraft. These images help in navigation, urban planning, and environmental monitoring.
Factors Affecting Aerial Photographs
Several factors influence how much detail and area an aerial photograph covers:
1. Focal Length of Lens
- The focal length of a camera lens determines how much area is captured in one photo.
- Common focal lengths: 90mm, 152mm, 210mm.
- Short focal length: Covers a larger area but with less detail.
- Long focal length: Covers a smaller area but with greater detail.
- Example: A 90mm lens on a drone can capture a large part of a city, but if you want to zoom into a single street or a specific building, you’ll need a 210mm lens.
2. Altitude of Platform
- Higher altitude = wider coverage but less detail.
- Lower altitude = smaller coverage but high detail.
- Example: If an aircraft flies at 5000 meters, it captures an entire village, but if it flies at 500 meters, it captures individual farms, roads, and even vehicles.
3. Spatial Resolution
- Spatial resolution refers to the level of detail in an image.
- High-resolution images can detect objects as small as 50 cm.
- Example: If a city planner wants to map traffic congestion, high-resolution images can show individual cars and pedestrians.
Types of Aerial Photographs
1. Oblique Aerial Photographs
- Taken at an angle from the aircraft.
- High oblique: Includes the horizon (good for panoramic views).
- Low oblique: No horizon, focuses on details.
- Example: Oblique photos are used in tourism promotions and landscape photography, like aerial shots of mountains or coastal cities.
2. Vertical Aerial Photographs
- Taken directly downward (90° angle).
- Most commonly used for mapping and remote sensing.
- Helps in accurate measurement of distance, area, and elevation.
- Example: Google Maps uses vertical aerial images to create satellite maps.
How Aerial Photographs Are Captured
- Aircraft fly in a planned flight path, capturing images in a sequence.
- Each image overlaps 50-60% with the next one.
- Stereoscopic viewing: When two overlapping images are viewed together, they create a 3D effect.
- Example: 3D city models used in real estate apps and navigation systems use this technique.
Photogrammetry: Extracting Data from Aerial Photos
Photogrammetry is the process of measuring distances, elevations, and landforms from aerial images.
- Used in urban planning, forest mapping, disaster management.
- Example: After a flood or earthquake, photogrammetry helps in damage assessment and rescue planning.
Digital Cameras in Aerial Photography
Modern aerial photography uses digital cameras instead of film.
- Digital cameras use CCD sensors to convert light into digital numbers (DNs).
- Provide faster data processing, higher resolution, and better storage options.
- Example: Drones with digital cameras are used for traffic monitoring, real estate surveys, and precision farming.
Multiband Photography: Enhancing Feature Detection
Some aerial cameras use multiple lenses and filters to capture different wavelengths of light.
- Helps in better feature identification (e.g., soil moisture, pollution levels).
- Example: NASA uses multiband photography for planetary exploration and environmental monitoring.
Conclusion
Aerial photography is a powerful tool that helps in mapping, land-use planning, environmental monitoring, and disaster management. With the advancement of digital imaging and drone technology, aerial photography is becoming more accessible and efficient for daily applications, from agriculture to urban development.
