You can explore the way different band combinations highlight different features by using a browse tool called Worldview, which displays data from many different imagers, including Aqua and Terra MODIS. Click on “add layers” and then select one of the alternate band combinations (1-2-1, 3-6-7, or 7-2-1). The site also provides descriptions of common MODIS band combinations.
How to create a red hue by combining
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Though there are many possible combinations of wavelength bands, the Earth Observatory typically selects one of four combinations based on the event or feature we want to illustrate. For instance, floods are best viewed in shortwave infrared, near infrared, and green light because muddy water blends with brown land in a natural color image. Shortwave infrared light highlights the difference between clouds, ice, and snow, all of which are white in visible light.
Our four most common false-color band combinations are:
- Near infrared (red), green (blue), red (green). This is a traditional band combination useful in seeing changes in plant health.
- Shortwave infrared (red), near infrared (green), and green (blue), often used to show floods or newly burned land.
- Blue (red), two different shortwave infrared bands (green and blue). We use this to differentiate between snow, ice, and clouds.
- Thermal infrared, usually shown in tones of gray to illustrate temperature.
Near infrared, red, green
One of our most frequently published combinations uses near infrared light as red, red light as green, and green light as blue. In this case, plants reflect near infrared and green light, while absorbing red. Since they reflect more near infrared than green, plant-covered land appears deep red. The signal from plants is so strong that red dominates the false-color view of Algeria below. Denser plant growth is darker red. This band combination is valuable for gauging plant health.
Cities and exposed ground are gray or tan, and clear water is black. In the image below, the water is muddy, and the sediment reflects light. This makes the water look blue. Images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and from the early Landsats are often shown in this band combination because that’s what the instruments measured.
Near infrared, red, and green light were used to create this false-color image of Algeria. Red, plant-covered land dominates the scene. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)
Shortwave infrared, near infrared, and green
The most common false-color band combination on the Earth Observatory uses the shortwave infrared (shown as red), the near infrared (green), and the green visible band (shown as blue).
Water absorbs all three wavelengths, so it is black in this band combination. In the below false-color image of Algeria, however, water is blue because it is full of sediment. Sediment reflects visible light, which is assigned to look blue in this band combination. This means that both sediment-laden water and saturated soil will appear blue. Because water and wet soil stand out in this band combination, it is valuable for monitoring floods. Saturated soil will also appear blue. Ice clouds, snow, and ice are bright blue, since ice reflects visible light and absorbs infrared. This helps distinguish water from snow and ice; it also distinguishes clouds made up mostly of liquid water or ice crystals.
The shortwave infrared, near infrared, and green light version of the Algeria scene highlights the presence of water and wet soil in an otherwise dry landscape. (NASA image by Robert Simmon with Landsat 8 data from the USGS Earth Explorer.)
Newly burned land reflects shortwave infrared 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 shortwave infrared 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. Even the sparse vegetation in Algeria’s desert landscape stands out as bright green spots in the above image.
Hue:
Hue is a term that seems more complicated than it is. A hue is just a color. More specifically, a hue is any color on the color wheel. Hopefully, you’re familiar with the color wheel, but let’s go over it quickly if you need a refresher.
There are three primary colors, red, blue and yellow. Most of us also know that combining any two of those primary colors will give you one of the secondary colors: red and blue make violet, yellow and blue make green, and red and yellow make orange. A third set of colors, the tertiary colors, fill in the six gaps between the primary and secondary colors — red-orange, blue-green, red-violet and so on. Tertiary colors are pretty simple to figure out based on their names, so we won’t cover them here.
Colors on exact opposites of the color wheel are known as complementary colors. Mixing a color with its complement will give you a muddy brown.
You might have noticed that black and white are not colors on the color wheel, and thus are not hues. So where do they fit in when it comes to mixing colors?
Tints, tones, and shades are variations of the hues found on the basic color wheel when white, black or both are mixed in. To illustrate this, I painted a Tint, Tone and Shade color wheel using Liquitex Basics acrylic paint for each of the 6 primary and secondary colors.
At the center of the wheel, I have painted the six primary and secondary hues, just as in the color wheel shown above. Paints straight out of the tube vary by manufacturer and can skew towards cool (having qualities of the blue side of the color spectrum) or warm (having qualities of the red and yellow sides of the spectrum). Compare the hues below to the color wheel I noticed here that the Liquitex Basics “Primary Red” hue skews cool, as you’ll see.
Let’s break down the other rings of the wheel:
Tints are created when you add white to any hue on the color wheel. This will lighten and desaturate the hue, making it less intense. Tints are often referred to as pastel colors, and many feel they are calmer quieter colors. To make the tints below, I used equal parts white and the hue straight from the bottle. Again, the amounts needed will vary by manufacturer and paint variety, depending on the intensity of the pigment in a given paint.
Tones
Tones are created when you add both black and white to a hue. You could also say grey has been added. Depending on the proportions of black, white and the original hue used, tones can be darker or lighter than the original hue, and will also appear less saturated or intense than the original hue. Tones can reveal subtle and complex qualities in a hue or combination of hues, and are more true to the way we see colors in the real world.
