SummarySummaryof Spectral Signaturesof Spectral Signatures

Labs in Bertinoro Labs in Bertinoro 23 Aug – 2 Sep 200423 Aug – 2 Sep 2004

Paul MenzelPaul MenzelNOAA/NESDIS/ORANOAA/NESDIS/ORA

Incoming solar radiation (mostly visible) drives the earth-atmosphere (which emits infrared).

Over the annual cycle, the incoming solar energy that makes it to the earth surface (about 50 %) is balanced by the outgoing thermal infrared energy emitted through the atmosphere.

The atmosphere transmits, absorbs (by H2O, O2, O3, dust) reflects (by clouds), and scatters (by aerosols) incoming visible; the earth surface absorbs and reflects the transmitted visible. Atmospheric H2O, CO2, and O3 selectively transmit or absorb the outgoing infrared radiation. The outgoing microwave is primarily affected by H2O and O2.

Solar (visible) and Earth emitted (infrared) energy

Solar SpectrumSolar Spectrum

VIIRS, MODIS, FY-1C, AVHRR

H2O

H2OH2O

H2O

O2

CO2

CO2

H2O

O2H2O

O2

MODIS IR Spectral Bands

MODIS

GOES Sounder Spectral Bands: 14.7 to 3.7 um and vis

II II I |I I ATMS Spectral Regions

MODIS

00.5

11.5

22.5

33.5

44.5

5

8.5

8.7

8.91

9.13

9.36 9.6

9.86

10.1

10.4

10.7 11

11.4

11.7

12.1

12.5 13

13.4

13.9

wavelength

Refle

ctio

n [%

]

Ice reflectance

High ice cld

Midlevel cldLow water cld

Midlevel cld

0.0

0.2

0.3

0.5

0.6

0.8

0.0 0.2 0.4 0.6 0.8 1.0

Ref

lect

ion

Func

tion

(2.1

42 µ

m)

Reflection Function (0.664 µm)

0 = 26°, = 40°, = 42°

32 µm

16 µm

8 µm

4 µm

2 µm

3224161284

2

c

re =

486

80

Variation with Particle Size (r eff )(IWP= 10 g m -2 ; 10.8-10 km)

Wavenumber (cm -1 )

Clo

ud F

orci

ng (K

)

0

10

20

30

40

50

60

70

700 800 900 1000 1100 1200 1300

4.5 micron

22.5 micron

Kaolinite montmorillonite

Kaolinite montmorillonite

Optical properties of cloud particles: imaginary part of refraction index

SW & LW channel differences are used for cloud identification{4 m - 11m}, {4.13 m - 12.6m}, and {4.53 m - 13.4m}

Imaginary part of refraction index

wavelength [microns]

0

0.1

0.2

0.3

0.4

0.5

0.6

1 3 5 7 9 11 13 15

Ice

Water

BT11-BT12 > 0 for ice BT11-BT12 < 0 for volcanic ash

Frank Honey 1980s

SO2 calculations from F. Prata

"Non-detection" of fog over snow surfaces with VIS channels:thick clouds and snow have the same reflectance

Fog Detection over Snow SurfacesFog Detection over Snow Surfaces

Emissivity as a function of wavelength and surface type

• Emissivity more variable near 3.9 m

• Sandy areas appear 5-10 K cooler at IR3.9 than at IR10.8 (at night, dry atmosphere)

• Different appearance of land surfaces during daytime, depending on surface typeIR3.9 IR10.8

Dry sand: 0.8 0.95

800 900 1000 1100 1200 13000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Wavenumber (cm-1)

n I

IceDust

Imaginary Index of Refraction of Ice and Dust• Both ice and silicate absorption small in 1200 cm-1 window• In the 800-1000 cm-1 atmospheric window:

Silicate index increasesIce index decreaseswith wavenumber

Volz, F.E. : Infrared optical constant of ammonium sulphate, Sahara Dust, volcanic pumice and flash, Appl Opt 12 564-658 (1973)

Dust and Cirrus SignalsDust and Cirrus Signals

wavenumber

Dust IR spectra – green clr sky vs dust particles of different size

Dust IR spectra – green clr sky vs dust layers at different heights

Fog and Low Stratus

Comparison of snow reflectance in VIS and NIR 1.6 channels

• Ch08 is in the centre of the O3 absorption band around 9

EnergyspectrumSource:EUMETSAT

Ch08

Figure 3c

Signals from lower parts of troposphere;But:Secondary maximum from higher than 100 hPa

WeightingfunctionsSource:EUMETSAT

AIRS radiance changes (in deg K) to atm & sfc changes 43

Aircraft S-HISLSE

Wavenumber (cm-1)

0.85

1.0

Bare Soil

Pure Vegetation

S-HIS OBS

12 m 9 m

Inferring surface properties with S-HIS high spectral resolution data - Note the large change, especially for bare soil, in surface emissivity between 960 and 1060 cm-1. The HES minimum mission would not cover both regions.

44