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.

 Wavelength  Frequency  Energy

 Meters (m)  Centimeters (cm)  Millimeters (mm)  Micrometers (µm)  Nanometers (nm)  Angstroms (Ǻ)

 The number of waves (cycles) that pass through an imaginary plane in a specific amount of time ( e.g., 1 second)

 Hertz (Hz) = 1 wave cycle/second  Kilohertz (KHz)  Megahertz (MHz)  Gigahertz (GHz)  Etc.

 c = wavelength x frequency ( x )  c = 2.98 x 10 8 m/sec (the speed of light) = 186,000 miles/sec So…what happens to wavelength as frequency increases?

The EMR Spectrum

 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.

Infrared Portion of the Spectrum

 Near Infrared (NIR) 720 – 1300 nm  Mid Infrared (MIR or SWIR) 1300 – 3000 nm  Far Infrared (FIR or Thermal) > 3000 nm

Other parts of the Spectrum Radar UV

 Absorption (and transmittance)  Scattering (will discuss later in the semester)

 Prevention or attenuation of the transmission of radiant energy through the atmosphere  Especially important: Ozone (O 3 ), Carbon Dioxide (CO 2 ), Water vapor (H 2 O)

 Transmittance (t) = Transmitted/Incident  Varies with wavelength  Atmospheric transmittance varies depending on atmospheric conditions for each wavelength

Thermal IR – Greenhouse Effect Ozone Hole

 Absorbs strongly in the UV (short wavelengths)  Protects us from skin cancer!

 Absorbs in mid and far infrared  Greenhouse effect!

 Very strong absorber in um range  Very strong absorber > 27 um  Variable in time and space

 Most EMR wavelengths can’t penetrate clouds  Big problem in remotely sensed imagery— tropics especially  Temporal compositing to get rid of clouds  Cloud shadows a problem too

Riverton Landsat Image July Cloudy!

 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!