learning objectives nature of light color & spectroscopy alta spectrophotometer spectral...
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Learning Objectives
• Nature of Light• Color & Spectroscopy• ALTA Spectrophotometer• Spectral Signature of Substances• Interpretation of Satellite Images
Satellites Observe the Earth
• Resulting images yield valuable information about natural resources
and the environment
• Special sensors are like sensitive cameras that can “see” invisible light
Light Has a Dual Nature
• Particles called photons• Waves that can travel through the vacuum
of space• Einstein’s photoelectric effect
demonstrates dual nature
What is Color?
• What color is the sky?• What color is water?• The color an object appears depends on the
color of the light source and the pigments in object.
• How does sunlight shining through water droplets cause a rainbow?
Color Spectrum Light through a Prism
• Each wavelength band bends differently through prism
Electromagnetic Radiation
• Energy traveling outward, as in rays
• Waves through space
– Periodic disturbances to electric and magnetic fields
• Speed of Light
– C= 186,000 mi/sec or 300,000 km/sec
Electromagnetic Spectrum
• Visible bands (colors)are small portion of spectrum• Long wavelengths to left are lower energy• Short wavelengths to right are higher energy
What happens when light strikes matter?
Red
Red
Orange
Orange
Yellow
Yellow
Green
Green
Blue
Blue
Violet
Violet
Reflec
ted
White Light
Absorbed
Tran
smitt
ed
Why do we see object as blue?
Spectroscopy: Science of Making & Studying Spectra
• Spectroscope: device that produces color spectrum
• Spectrometer: instrument that measures the intensity of light
ALTA II Reflectance Spectrometer
• Measures intensity of
reflected light • Provides its own light
sources - Light Emitting Diodes (LEDs)• Provides results comparable to data
gathered from satellite spectroscopy
Spectral Signature
Blu
e Gre
en
Yel
low
Yel
low
Ora
nge
Red D
eep R
ed
Near Infrared
Cya
nCya
n
Example of a Graph of Data Collected From a Leaf With the ALTA
Remote Sensing
• Gathering information about something without actually touching it.
• Human eye acts as a remote sensor.
Remote Sensing
• Satellites remotely sense the Earth using spectroscopy
• Provides a wealth of information applying to many users including:– Agriculture– Environment– Natural Resources– Telecommunications– Utilities
False Color Image of Orlando, Fla.; Courtesy of NASA.
Ground Truth
• Reference data collected on Earth– Aids in interpretation, analysis,
and validation of remotely sensed data
– Expensive and time consuming
Key for False Color Image
Red: Healthy VegetationPink: Less Densely Vegetated AreasTanTan, Brown, Green With Patches of Red: ForestDark Blue: Rivers, Lakes, StreamsLight BlueLight Blue and Gray: Urban Areas, Cities, TownsWhiteWhite: Bare Land, Fields, Soils
Remotely Sensed Image
• Image is composed of small dots, called picture elements (pixels)• Scientist can extract information from every pixel
Operating the Alta
• On/Off• LEDs & Detector• Dark Voltage• Standard White Card Reading
Data Table
Green Leaf & Roofing Shingle
Sample Data Set
Green Leaf & Roofing Shingle
Calculating Percent Reflectance
For Green Leaf
Perform the following steps for each ALTA data point (wavelength)
• Step 1 - Subtract dark voltage from standard white card reading and leaf reading.
• Step 2 - Divide resulting leaf reading by resulting standard white card reading.
• Step 3 - Multiply result of Step 2 by 100
Repeat Steps 1-3 for roofing shingle
Graph Template
Sample Graph