1. What is light and how do we describe it? 2. What are the physical units that we use to describe light? 1. Be able to convert between them and use scientific notation! 3. How do we calculate wavelength, frequency, and energy?
4. What is the electromagnetic spectrum, and how do we describe it for RS? 5. What are the additive primary colors, how do they combine, and why is this important? 6. How does the atmosphere affect light, and why does this matter? 7. How do clouds affect RS data?
From Wikipedia What is light? Direction of Electromagnetic Wave Propagation Maxwell’s Equations describe light as perpendicular electrical and magnetic waves. The changing magnetic wave creates the electrical wave, and vice versa.
All objects warmer than absolute zero emit EMR Temperature of an object determines the quality (wavelength distribution) of emitted light Objects reflect EMR emitted by other objects Key basis of remote sensing because earth’s surface materials reflect light in unique ways.
Wavelengths that dominate radiation given off by the sun Most animals evolved to “see” these wavelengths In fact, eyes only sensitive to red, green, and blue (using “cones”) Captured by your personal multi- spectral sensor (= digital camera)
Red + Blue = Magenta Red + Green = Yellow Blue + Green = Cyan Red + Blue + Green = White Additive Primaries (Color Theory) (Can add together in different proportions to make all other colors we see) Do all of these colors have their own wavelength??
Your computer screen uses the 3 additive primaries to display all possible colors To interpret remotely sensed imagery you must be able to interpret color
Computer monitor uses red, green, and blue to create color images You choose 3 satellite bands and color each with one of the 3 primary colors Brightness of each color is determined by each pixel value (DN) in in the band to which the color is assigned, and the three colors mix. Result is a color image with each pixel’s color determined by combination of RGB of different brightness.
All of this is important because it determines in part how objects of interest interact with EMR which is what we use in remote sensing. The better we understand these interactions, the better we are at using the remote sensing tool!