spectral signatures passive sensors (receive reflected or emitted signals from the surface,...

Spectral Signatures

Passive Sensors(receive reflected or emitted signals

from the surface, including optical, thermal and microwave sensors )

Active Sensors(generate and emit radiation to the surface

and receive the returned signals,Including RADAR, Laser, etc.)

Reflectance (reflectivity)Ratio of total reflected radiation divided

by the total incoming radiation

Spectral ReflectanceReflectance for a given range of wavelength

Bi-Directional Reflectance

Albedo

Reflectance for a fixed view-target-sun geometry

Reflectance for total incoming radiation in all directionfor wavelength ranging from 0.3 to 4.0 m

128

Radiance and Reflectance of a Pixel

192 51

Red Near-Infrared Mid-Infrared

Each band has its own sensor calibration (gain and offset)which must be considered in the image interpretation

128:1 192:2 51:3

From DN to Radiance to Reflectance

1 G=(-3.58E-05)*D+1.376 0.4863 1959.22 G=(-2.10E-05)*D+0.737 0.5706 1827.43 G=(-1.04E-05)*D+0.932 0.6607 1550.04 G=(-3.20E-06)*D+1.075 0.8382 1040.85 G=(-2.64E-05)*D+7.329 1.677 220.757 G=(-3.81E-04)*D+16.02 2.223 74.960

Source:CCRS Web site

LANDSAT TM Spectral Band

Calibration GainCoefficient

(counts/(W/m2/sr/m))

CharacteristicWavelength

(m)

SolarIrradiance

(W/m2/m)

Radiance = (DN - Offset)/Gain

Reflectance = Radiance/Solar Irradiance

D = days since launch

If the input signal exceeds the amount for which the sensor was designed, the system response will become non-linear or reach the saturation level.

This is a common occurrence in land remote sensing systems when they image bright clouds and/or snow cover, for example.

Linear Region y = a.x + b (DN = gain*Radiance + offset)

Non-Linear Region

Saturation

Offset b

Input Value x (radiance)

Source:CCRS Web site

y (D

N)

Spectral Reflectance of Vegetationin the visible

Visible

BLUE GREEN RED

RE

FL

EC

TA

NC

E

Low

High

16.4

Time variation of Vegetation Spectral Reflectance

BLUE GREEN RED

RE

FL

EC

TA

NC

E

Low

High Fall

Fall

Summer

Summer

Sugar MapleAspen

16.4

Vegetation Spectral Reflectance

BLUE GREEN RED

RE

FL

EC

TA

NC

E

Low

High

NORMAL LEAF

LEAF INFILTRATED WITH WATER

NEAR-INFRARED

16.4

0

5

10

15

20

25

30

35

40

45

50

350 600 850 1100 1350 1600

Wavelength (nm)

Nad

ir R

efle

ctan

ce (

%)

3.41g/g

2.13 g/g

1/66 g/g

1.25 g/g

0.0 g/g

SWIR

Spectral Response to Wetness of Feather Moss And the Utility of Shortwave Infrared (SWIR)

dry

wet

0

0.2

0.4

0.6

350 550 750 950 1150 1350 1550 1750Wavelength (nm)

Ref

lect

ance

(%

)whea

t

moss

lichen

forest soil

farm soil

Spectral Reflectivity of Vegetation

Black Spruce Needle

Moss

BLUE GREEN RED

16.4

Vegetation Spectral Reflectance

BLUE GREEN RED

RE

FL

EC

TA

NC

E

Low

High

WHITE LEAF

NEAR-INFRARED

GREEN LEAF

16.4

Summery for plant leaves

Visible reflectance controlled by pigments

B G R

Near Infraredreflectancecontrolled bycell structure

Mid Infraredreflectancecontrolled bywater content

Ref

lect

anc

e

720 1300 2500 nm380

Other factors affecting the spectral signature ofvegetation

Age (0.7 m)

diseases (e.g. yellow discoloration 0.55-0.75 m)

16.417.4

Spectral signature for plant canopiesA plant canopy is the whole layer of vegetation of considerablehorizontal extent (In case of forests, it is not just a tree crown, but consists of many tree crowns )

Canopy

Vegetation Spectral Reflectivity

BLUE GREEN RED

RE

FL

EC

TA

NC

E

Low

HighASPEN

NEAR-INFRARED

SPRUCE

16.4

Vegetation Spectral Reflectivity

BLUE GREEN RED

RE

FL

EC

TA

NC

E (

%)

BROADLEAF FORESTS

NEAR-INFRARED

CONIFEROUS FORESTS

GRASS

0

20

40

60

80

100

16.4

Water Spectral Reflectance

18.2

BLUE GREEN RED NEAR-INFRARED

Clear Water

Moderate Turbidity

High Turbidity

RE

FL

EC

TA

NC

E

Low

High

VISIBLE NEAR-IR MID-INFRARED

RE

FL

EC

TA

NC

E

Low

High

Clouds

Snow

Spectral Reflectance of Clouds versus Snow

Soil Spectral Reflectivity

VISIBLE NEAR-IR MID-INFRARED

RE

FL

EC

TA

NC

E

Low

High

Dry Soil

Moist Soil

LANDSAT TM

SPOT-HRVSPOT- PAN

JERS-OPS

AVHRR

AtmosphericAbsorption Bands

Vegetation

Sandstone

Limestone

Shale

Reflected IR Wavelength

0.50 1.00 1.50 2.00 2.50

Blu

e

Gre

en

Red

Wavelength (m)

17.5

1 2 3 4 5 7

1 2 3

1 2 3,4 5 7 8 9

1 2

Spectral Reflectivity of Minerals

Wavelength (m)2.00 2.10 2.20 2.30 2.40

RE

FL

EC

TA

NC

E

Kaolinite

Alunite

Buddingtonite

AVIRIS

Laboratory Spectrometer

Kaolinite: Al4Si4O10(OH)8

Alunite: (K,Na)Al3(SO4)2(OH)6

Thermal Signatures

Emissivity 8.6

Wavelength (m)7 8 9 10 11 12 13

Leucogranite

Granodiorite

Quartz Monzonite

Granodiorite

Diorite

Anorthosite

SiO2% Quartz%

70.8 29.5

67.8 31.9

64.0 23.7

60.4 18.8

49.7 0.0

54.7 2.2

EM

ISS

SIV

ITY

Thermal Remote Sensing

LANDSAT TM 6 DIGITAL VALUE

SU

RF

AC

E W

AT

ER

TE

MP

ER

AT

UR

E

110 135

Thermal Diurnal Signature

8.8

SAND

MEADOW

FOREST

MEADOW

SAND

FOREST

LAKE

SUNRISE NOON SUNSET

COOL

WARM

TE

MP

ER

AT

UR

E

LAKE

EARTH

WATER

DAWN NOON SUNSET MIDNIGHT

6 12 18 0

COOL

WARM

TE

MP

ER

AT

UR

E

Thermal Diurnal Signature

Radar Signatures

TIME(Near Range)(Far Range)

RE

TU

RN

IN

TE

NS

ITY

IMA

GE

TO

NE

RA

DA

RS

IGN

AT

UR

E

TE

RR

AIN

FE

AT

UR

E

SP

EC

UL

AR

(SM

OO

TH

)S

UR

FA

CE

CO

RN

ER

RE

FL

EC

TO

RS

DIF

FU

SE

SU

RF

AC

E

SH

AD

OW

HIG

HL

IGH

T

RANGE (LOOK)DIRECTION

AZI

MU

TH (F

LIG

HT)

DIR

EC

TIO

N

DEPRESSIONANGLE

TRANSMITTEDPULSE