For week 3, I found myself falling falling behind the rest of the class.
I was having a hard time understanding which unique frequncies and color bands of light energy produce certain spectral images.
Fortunately, in my Fundamentals of Remote Sensing class, the I was directed to a particular website. This website, provided a wide range of pre-made images using the RGB color guns. In addition, it was set up to mimic real satellites, Landsat being one of them. I spent at least an hour experimenting when I decided to hand copy the entire list of Bands and their associated traits. I copied it on to my phone, and refer to it whenever I am using Landsat imagery (or equilivant).
Band 1 (0.45-0.52um, blue-green):
Since this short wavelength of light penetrates better than the other bands, it is often the band of choice for aquatic ecosystems. It is used to monitor sediment in water, mapping coral reefs, and water depth. Unfortunately, this is the noisiest of the Landsat bands since short wavelength blue light is scattered more than the other bands. For this reason, it is rarely used for “pretty picture” type images.
Band 2 (0.52-0.60um, green):
This has similar qualities to band 1, but not as extreme. This band is often selected because it matches the wavelength for the green we seen when looking at vegetation.
Band 3 (0.63-0.69um, red):
Since vegetation absorbs nearly all red light (it is often referred to as the “Chlorophyll absorption” band), this band can be useful for distinguishing between vegetation, soil, and with monitoring vegetation health.
Band 4 (0.76-0.90um, near infrared):
Since water absorbs nearly all light at this wavelength, bodies of water appear very dark. This contrast with bright reflectance for soil and vegetation, making it a good band for defining the water/land interface.
Band 5 (1.55-1.75um, mid-infrared):
This band is very sensitive to moisture, and therefore is used to monitor vegetation and soil moisture. It is also good at differentiating between clouds and snow.
Band 6 (10.40-12.50um, thermal infrared):
This is a thermal band, which means it can be used to measure surface temperature. This is primarily used for geological applications, but it is sometimes used to measure plant heat stress. This is also used to differentiate clouds from bright spots, since clouds tend to be very cold. One other difference between this band and the other multispectral ETM bands, it that the resolution is half the of the other bands (60m instead of 30m).
Band 7 (2.08-2.35um, mid infrared)
This band is also used for vegetation moisture, although generally band 5 is preferred for that application, as well as for soil and geology mapping.
Landsat Band Combinations (Suggestions)
R=3 G=2 B=1 or 321
This color composition s as close to true that can be obtained with Landsat. Very useful for studying aquatic habitats. Downside is that images can be hazy.
R=4 G=3 B=2 or 432
This has similar qualities to the image with bands 3,2,1,-- however, since this includes the near infrared channel (band 4), land—water boundaries are clearer and different types of vegetation are more apparent. This was a popular band combination for Landsat MSS data since that it did not have a mid-infrared band
R=4 G=5 B=3 or 453
This is crisper than the previous two images because the two shortest wavelength bands (bands 1 and 2) are not included. Different vegetation types can be more clearly defined and the land/water interface is very clear. Variations in moisture content are evident with this set of bands. Very popular.
R=7 G=4 B=2 or 742
This has similar properties to the 453 combo, but the biggest difference is that vegetation is green.
I also wanted to memorize the Electromagnetic Spectrum, so I developed a quick story.
Blue to red are growing lengths
NIR-- -- -- - 1.2µm
Red-- -- -- - 0.7µm
Green-- -- 0.6µm
Blue-- -- -- 0.4µm
Story to memorize EMS
Violet was years 3 old when she started
picking BLUE flowers at 4 in the morning.
Green with envy, 6 girls teased her. Her face
Red, she shouted 7 times at them. NIR by, a
clock struck 12.