The true color combination for Landsat 8 imagery is achieved by using Bands 4, 3, and 2, mapped to the red, green, and blue display channels, respectively. This particular combination is designed to produce an image that closely resembles what the human eye would naturally perceive on the ground.
Understanding True Color Imagery from Landsat 8
In remote sensing, "true color" refers to an RGB (Red, Green, Blue) composite image where the displayed colors are similar to natural colors, much like a photograph taken from space. For Landsat 8's Operational Land Imager (OLI), this means selecting the bands that capture the visible light spectrum.
The choice of Bands 4, 3, and 2 is crucial because these bands correspond to the red, green, and blue wavelengths that make up the visible light spectrum. By assigning them to the respective display channels, the resulting image accurately represents the Earth's surface as seen by the human eye, showing familiar colors for landforms, water bodies, and vegetation. This specific combination is chosen because these bands capture the red, green, and blue portions of the electromagnetic spectrum that closely approximate the spectral range of vision of the human eye.
Landsat 8 True Color Band Mapping
The table below illustrates how the Landsat 8 bands are assigned to create a true color composite:
| Display Channel | Landsat 8 OLI Band | Wavelength Range (µm) | Corresponds to |
|---|---|---|---|
| Red | Band 4 (Red) | 0.636 - 0.673 | Red light |
| Green | Band 3 (Green) | 0.533 - 0.590 | Green light |
| Blue | Band 2 (Blue) | 0.452 - 0.512 | Blue light |
Interpreting True Color Images
When viewing Landsat 8 true color images (Bands 4, 3, 2), various features on the Earth's surface appear in recognizable colors:
- Vegetation: Healthy vegetation typically appears in shades of green. The vibrancy of the green can often indicate the health and type of plant life.
- Water Bodies: Water can appear in shades of blue to black, depending on its depth, clarity, and the presence of sediment or algae. Clear, deep water tends to be darker blue or black, while shallower or sediment-laden water might appear lighter blue or greenish.
- Urban Areas: Cities and developed areas often appear as varying shades of grey, brown, or white, reflecting the colors of rooftops, roads, and other man-made structures.
- Bare Soil and Deserts: These areas typically show up in shades of brown, tan, or white, depending on the soil composition and moisture content.
- Clouds and Snow/Ice: These features usually appear bright white due to their high reflectivity across the visible spectrum.
Beyond True Color: Other Landsat 8 Band Combinations
While the 4-3-2 combination is essential for true color visualization, Landsat 8's comprehensive set of spectral bands allows for many other band combinations, often called "false color composites." These combinations highlight specific features or phenomena not easily discernible in true color, such as vegetation health (using near-infrared bands), water penetration, or urban growth. Each band combination serves a unique purpose in various applications of remote sensing.
For more information on Landsat 8 and its extensive capabilities, you can explore resources from the U.S. Geological Survey (USGS).
