In remote sensing, satellite and aerial sensors capture data from across the electromagnetic spectrum. Some parts of this spectrum - known as “bands” - may be familiar already, such as visible light captured in the red, green and blue bands, for example. Other bands vary depending on the imaging sensor and can include near-infrared, short-wave infrared and others. Because these bands are captured as independent units, they can be combined in unique ways that help us observe the earth in different ways.
One way to make the bands that are usually not visible to the human eye visible is to map them to colors that we can more easily see, such as the red, green, and blue channels of an image. If you've used Lens, you're familiar with the Truecolor layer. This maps the red band to the red image channel, the green band to the green image channel, and so on. Color infrared layers map different infrared bands to these channels, which opens up new possibilities for monitoring changes on your properties. These band combinations can be applied to imagery from a variety of sources. See our Overview of Layers in Lens article to learn about the difference between high-frequency and high-resolution sources.
There are a few ways that Color Infrared layers differ from the Index layers in Lens. First, unlike an Index layer which has numeric values, Color Infrared images cannot be graphed or quantified in the same way. Additionally, we don't mask clouds for Color Infrared imagery the way we do for Index layers. Masking clouds is important to ensure they don't impact graphs or statistics, but because Color Infrared layers are intended primarily for visual assessment, clouds are visible.
It's important to become familiar with the kinds of patterns the layers can show and how they can be used in various monitoring applications, such as those highlighted below. This work was inspired by NASA Earth Observatory's wonderful write-up on falsecolor imagery, another term for color infrared. If the first few paragraphs leave you wanting more detail - you can read more here: https://earthobservatory.nasa.gov/features/FalseColor
Blue and short wave infrared
This layer shows blue light as red, and two different short-wave infrared (SWIR) bands as green and blue. This band combination is valuable in distinguishing snow, ice, and clouds. Ice reflects more blue light than snow or clouds. Ice on the ground will be bright red in this color infrared layer, while snow is orange, and clouds range from white to dark peach.
|Use Case & Description||Visual|
|Monitoring ice - This comparison shows a wetland area before and after a big ice storm. In the second image, the bright red indicates areas where ice is present or the ground is frozen.|
|(Same as above) - This comparison shows an area with farm fields where you can see ice on the ground (shown in red) in the winter months, which then melts in the early spring.|
|(Same as above) - This comparison shows an area which was frozen in the winter months and is beginning to thaw.|
Near infrared, red, green
This layer shows near infrared (NIR) light as red, red light as green, and green light as blue. Plants reflect near infrared and green light, while absorbing red. Since they reflect more near infrared than green, plant-covered land appears deep red. Denser plant growth is darker red. Cities and exposed ground are gray or tan, and clear water is black.
Similar to NDVI, this band combination is valuable for assessing plant health. Where NDVI is a calculated index, NIR is closer to a raw value.
|Use Case & Description||Visual|
|Monitoring plant health in agricultural contexts - This comparison shows a farm field in the off-season and the same area mid-season using the NIR, red, green layer, with bright red indicating vigorous plant growth.|
|Detecting muddy water or saturated soil - Sediment reflects visible light, which appears blue in this band combination. This means muddy / sediment-laden water and saturated soil will be blue. The image on the left shows muddy water in blue and plant growth as negligible, in contrast to the other image in which plants are growing (as indicated by the red color) but the water is clear so it appears black.|
|Monitoring plant health in forested landscapes - In this comparison, we're comparing the NIR, red, green layer to the NDVI layer. The color infrared layer seems to show a bit more detail than NDVI across this forested parcel, with brighter red areas indicating more vegetation vigor or density than deeper red. In this way, NIR, red, green could be helpful in identifying more subtle variation in plant health or types of plants.|
Short wave infrared, near infrared, green
This layer shows near short-wave infrared (SWIR) light as red, NIR as green, and green light as blue. Because water and wet soil stand out in this band combination, it is valuable for monitoring floods. Saturated soil and sediment-laden water will appear blue. Ice clouds, snow, and ice are bright blue, since ice reflects visible light and absorbs infrared. Clear water will show as black. This helps distinguish water from snow and ice; it also distinguishes clouds made up mostly of liquid water or ice crystals.
Newly burned land reflects SWIR light and appears red in this combination. Hot areas like lava flows or fires are also bright red or orange. Exposed, bare earth generally reflects SWIR light and tends to have a red or pink tone. Urban areas are usually silver or purple, depending on the building material and how dense the area is.
Since plants reflect near infrared light very strongly, vegetated areas are bright green. The signal is so strong that green often dominates the scene.
|Use Case & Description||Visual|
|Monitoring snow and ice - This comparison shows the value of this layer in highlighting snow or ice in a wetland area. The first image shows areas with bright blue, which indicates snow or ice presence. This might have followed a large snow or ice storm in this area which had melted by the time the second image was captured.|
|(Same as above) - This is the same area and dates as the example above, but with the Water & Moisture layer for context. The moisture layer is picking up on the higher levels of moisture, but it is unclear if this is snow or rain. This is where the SWIR, NIR, green layer can help clarify ground conditions by adding context about the nature of the moisture.|
|Monitoring sedimentation in water or saturated soil - In this comparison, you can see a pond that appears bright blue in one image and black in the other. This blue is an indicator that the pond has lots of sediment in it, and the black image shows clear water. This could be after a rain event which washed sediment into the pond. Note that this could also be a helpful layer to use for riparian areas near farm fields to understand sediment runoff after rain events.|