learning objectives nature of light color & spectroscopy alta spectrophotometer spectral...

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