Dr. GarverGEO 420

Radiation that

reaches that surface

interacts with targets

in 3 ways:

Absorption(A),

transmission(T),

reflection (R).

Absorption(A)

Transmission(T)

Reflection (R).

Proportions of each

depends on of

energy and what the

target is.

Reflection (R) - radiation "bounces" off target and is redirected.

Radiation reflected from targets is what we are most interested in.

Two types - Specular reflection and Diffuse reflection.

Represents the two extreme ends of the way in which energy is

reflected from a target.

Smooth surface (road) - specular or mirror-like reflection where all (or

almost all) of energy is directed away from surface in a single direction.

Rough surface (tree) - diffuse reflection occurs, energy is reflected

almost uniformly in all directions.

Most earth surface features lie somewhere between, depends on the

surface roughness of the feature in comparison to the wavelength of

the incoming radiation.

Electromagnetic Spectrum: Spectral Signatures

For any material, the amount of solar radiation that it

reflects, absorbs, transmits, or emits varies with

wavelength.

When that amount (usually represented as a %)

coming from the material is plotted over a range of

wavelengths, the connected points produce a curve

called the material's spectral signature (spectral

response curve).

 Spectral Signatures

Plot variations of reflected EMR as

a function of wavelength.

Identify and separate different

materials using multispectral data.

Short wave ir

Visible (Vis) 0.4. – 0.7 m

Near Infrared (NIR) 0.7 – 1.3 m

Shortwave Infrared (SWIR) 1.3 – 3.0 m

LK 2 handoutEqn 1.6 pg. 12

EI = ER + EA + ET

Fig. 1.6

LK 2 handoutEqn 1.8 pg. 14Energy of reflected from object x 100 = ______%Energy of incident from object

Fig. 1.8, 1.9, 1.10 (1.10 is similar to graphs in this ppt)

*Important to know typical spectral signatures for vegetation, water and soil!

Fig. 1.8 L&K 2

General example of a reflectance plot for some (unspecified) vegetation type with the dominating factor influencing each interval of the curve indicated:

Vegetation – LK2Visible - Chlorophyll absorption in blue

and red, reflection in green.Near IR (0.7 – 1.3 um) – reflectance

increases dramatically, plant leaf reflects 40 – 50%, absorption is minimal so remainder is transmitted.Reflection is due to the internal structure of

plants.Allows discrimination of speciesPlant stresses – alters reflection

Vegetation – LK2

SWIR (1.3 – 3.0m) - incident energy is absorbed or reflected, little is transmitted.

Water absorption bands in this range

Soil – LK2Considerably less peak and valley variations

in reflectance.Factors that influence soil reflectance act

over less specific spectral bands.Factors – moisture, soil texture, organic

matter, iron oxide.

Short wave ir

Water – LK2Most distinctive characteristic is absorption

at near IR and beyond.Delineate water bodies using near IR But look at water quality/clarity/biology in

the visible

Water: Longervisible and near IR absorbed, reflectance of blue or blue-green

Water and vegetation may reflect somewhat similarly in the visible wavelengths but are almostalways separable in the infrared.

Short wave ir

Landsat Bands

The spectral

response for

inorganic

materials is

distinct from

vegetation types.

Gradual rise in

reflectance with

increasing

wavelengths.

Concrete, light-

colored and bright,

has higher % refl

than dark asphalt.

Refl for veg. rises

abruptly at ~0.7 µm,

followed by a

gradual drop at

about 1.1 µm.

0.3 - 0.5 µm - most veg. types similar in response

0.5 - 0.6 µm moderate variations

0.7 - 0.9 µm - maximum variability

(optimum discrimination)

Sensors

operating in

green, red, and

near IR can

discriminate

absorption and

reflectance of

vegetation.

GR

EE

N

RE

DN

IR

BL

UE

RE

FL

GR

EE

N

HIG

HL

Y R

EF

L N

IR

SUN

SENSO

R

Absorption in red & blue by chlorophyll

pigments.

Reflectance concentrated in the green.

Thus, most vegetation has a green-leafy

color.

Strong reflectance between 0.7 and 1.0

µm (near IR) in cells located in the

interior or back of a leaf.

Intensity of this reflectance is greater

than from most inorganic materials.

So, vegetation appears bright in the near-

IR

Near Infrared Composite (4,3,2) 

Adding near

infrared (NIR)

band, drop

visible blue

band

Landsat Bands

Landsat Thematic Mapper BLUE (0.45-0.52 µm): water penetration, soil/veg.

discrimination.

GREEN (0.52-0.60 µm): green reflectance peak for

discrimination and vigor assessment.

RED (0.63-0.69 µm): chlorophyll absorption for species differentiation.

NEAR IR (0.76-0.90 µm): determining vegetation types, vigor, and

biomass content, delineating water bodies, soil moisture.

One of the most successful applications of

multispectral space imagery is monitoring

the state of the world's agricultural

production.

Major crops: wheat, barley, millet, oats,

corn, soybeans, rice.

4 spectral curves

Variations in depths of absorption bands.

If the spectral curves are so similar, how can we

hope to distinguish them in the field?

Characteristic leaf or frond shape will differ

geometrically from most other types.

Oat hay and potato as crops are clearly

dissimilar in the way they look in bulk.

Combination of spectral response and diversity

of shape produce slightly different signatures,

mainly in the depth of any absorption features.

Some crops distinguishable by separations in 0.56 to 0.66 µm interval.

San Joaquin Valley –

July 1972 - barley,

alfalfa, sugar beets,

beans, tomatoes,

cotton.

Yellow-brown and

blue areas flanking

Valley crops are

grasslands and

chapparal.

Blue areas –

Stockton/Modesto.

Spectral signatures for healthy, stressed, and severely

stressed vegetation.

Visible-spectral signatures similar.

Near-infrared -spectral signatures very different.

Healthy vegetation - highest reflectance

Severely stressed vegetation - lowest reflectance.

Which region of the spectrum shows

the greatest reflectance for;

grasslands

pinewoods

red sand

silty water

Spectral Signatures of 4 MaterialsBand 1 = 0.55 um Band 2 = 0.85 um

Vis 0.4. – 0.7 mNIR 0.7 – 1.3 mSWIR 1.3 – 3.0 m

Different materials,

amount of solar radiation that it reflects,

absorbs, or transmits varies with

wavelength.

Important property of matter,

makes it possible to identify different

substances, or classes, and separate them

by their spectral signatures.

Method for measuring differences

Use reflectance differences to distinguish

the four common surface materials

Plot the reflectance percentages of the 4

classes at two wavelengths where there is

maximum differences observed in the

spectral signatures.

Spectral Signatures of 4 MaterialsBand 1 = 0.55 um Band 2 = 0.85 um

Vis 0.4. – 0.7 mNIR 0.7 – 1.3 mSWIR 1.3 – 3.0 m

GL = grasslands PW = pinewoods RS = red sand SW = silty water