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
