AIRS
(Atmospheric Infrared Sounder)
Instrument Characteristics
AIRS onboard of AQUA
• NASA’s EOS spacecraft
• Aqua launched May 4, 2002
• 705 km orbit (polar-orbiting)
• Early afternoon (1:30 PM) equator crossing
time heading north
• AIRS system on Aqua:
 AIRS (Atmospheric infrared Sounder)
 AMSU-A (Advanced Microwave Sounding Unit)
 HSB (Humidity Sounder Brazil)
• Other instruments:
 MODIS (Moderate Resolution Imaging
Spectroradiometer)
 AMSR-E (Advanced Microwave Scanning
Radiometer for EOS)
CERES (Clouds and the Earth’s Radiant
Energy System)
AIRS Was Launched on the EOS
Aqua Platform May 4, 2002
AMSU-A1(3-15)
MODIS
AMSU-A2(1-2)
AIRS
HSB
Aqua Acquires 325 Gb of data per day
Delta II 7920
3
IASI was launched on the MetOp-A
Satellite on Oct. 19, 2006
IASI
HIR
S
AVHRR
MHS
AMSUA1
ASCAT
AMSUA2
Soyuz 2/Fregat
launcher,
Baikonur, Kazakhstan
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AIRS & IASI are making 4 global
measurements per day
• Initial Joint Polar System:
An agreement between
NOAA & EUMETSAT to
exchange data and
products.
– NASA/Aqua in 1:30 pm
orbit
– EUMETSAT/IASI in 9:30
am orbit (Oct. 19, 2006)
– NPP-JPSS/CrIS in 1:30 pm
orbit (2011)
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Spectral Coverage of Thermal Sounders
(Example Radiances: AIRS, IASI, & CrIS)
AIRS,
2378
Channels
IASI,
8461
Channels
CrIS
1305
6
CO
O3
CH
CO CO
AIRS – Grating Spectrometer
• Array grating spectrometer
• Operating range: 3.7 – 15.4 m
• Spectral resolution: /=1200
• Infrared energy dispersed across arrays of
HgCdTe detectors (2378 detectors in 17 arrays)
AIRS – Grating Spectrometer Basics
Different wavelength are diffracted into
different angles
m = d (sin + sin)
where

wavelength

incident angle

diffraction angle
d
groove spacing of grating
m diffraction order (integer)
AIRS – Grating Spectrometer Optics
Radiance
http://www-airs.jpl.nasa.gov/
Radiance  Scan Mirror  Telescope  Spectrometer Entrance Slit  Grating  Array Detectors (HgCdTe
Focal Plane Assembly)
AIRS Spatial Coverage (1)
http://www-airs.jpl.nasa.gov/
Swath: 1650 km
IFOV: 1.1°  13.5 km
Atmospheric InfraRed Sounder
(AIRS) spatial coverage
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AIRS Spatial Coverage (2)
AIRS data is collected in 6 minutes junks = 1 granule
135 scanlinesx90 footprints=12150 pixels per granule (~125 MB)
240 granules per day (120 ascending daytime and 120 descending nighttime granules)
AIRS Spatial Coverage (3)
AIRS Spectral Coverage
• IR sounder: 2378 channels
• spectral ranges: 3.7 - 4.61 m, 6.2 - 8.22 m , 8.8 - 15.4 m;
AIRS Spectral Coverage  Vertical Resolution
Jacobian matrix K=dBT/dX is the matrix of partial derivatives of the
Brightness temperature with respect to the input parameter X. The
weighting functions (=rows of K) reflect the relative contribution from
each level to the total measured radiance.
Temperature weighting functions
Humidity weighting functions
AIRS IR Specification
Infrared Spectral Coverage:
3.74 m - 4.61 m
6.20 m – 8.22 m
8.80 m – 15.4 m
[2674 – 2170 cm-1]
[1613 – 1217 cm-1]
[1136 – 649 cm-1]
Spectral Resolution: /=1200
Spatial Coverage:
49.5 around nadir
1.1 (~13.5 km dia) IFOV (Instantaneous Field of View)
Sensitivity (NEDT):
0.14 K at 4.2 m
0.20 K from 3.7 to 13.6 m
0.35 K from 13.6 to 15.4 m
Power / Mass: 256 W / 166 kg
Lifetime: 5 years
AIRS/AMSU/HSB DATA PRODUCTS
Radiance Products (Level
1B)Uncertainty*
Horizontal Resolution
RMS
3%
15 x 15 km
AIRS IR Radiance
20%
2.3 x 2.3 km
AIRS VIS/NIR Radiance
0.25-1.2 K 45 x 45 km
AMSU Radiance
1.0-1.2 K 15 x 15 km
HSB Radiance
Vertical
Standard Core Products (Level 2)
Resolution
1.0K
45
x
45
km
Cloud Cleared IR Radiance
1 km below 700 mb
0.5K
45 x 45 km 2 km 700-30 mb
Sea Surface Temperature
2 km in troposphere
45 x 45 km
Land Surface Temperature 1.0K
1K
45 x 45 km
Temperature Profile
15%
45 x 45 km
Humidity Profile
5%
45 x 45 km
Total Precipitable Water
20
5%
45 x 45 km
Fractional Cloud Cover
Thermal Sounder “Core” Products
(on 45 km footprint, unless indicated)
Radiance Products
RMS Requirement
Current Estimate
AIRS IR Radiance (13.5 km)
3%
< 0.2 %
AIRS VIS/NIR Radiance
20%
10-15%
AMSU Radiance
0.25-1.2 K
1-2 K
HSB Radiance (13.5 km)
1.0-1.2 K
(failed 2/2003)
Geophysical Products
RMS Requirement
Current Estimate
Cloud Cleared IR Radiances
1.0K
<1K
Sea Surface Temperature
0.5 K
0.8 K
Land Surface Temperature
1.0K
TBD
Temperature Profile
1K/1-km layer
1K/1-km
Moisture Profile
15%/2-km layer
15%/2-km
Total Precipitable Water
5%
5%
Fractional Cloud Cover (13.5 km)
5%
TBD
Cloud Top Pressures
0.5 km
TBD
Cloud Top Temperatures
1.0 K
TBD
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Trace Gas Product Potential from
Operational Thermal Sounders
gas
Range (cm-1)
Precision
Interference
UTH
1400-1500
15%
T(p)
O3
1025-1050
10%
H2O,emissivity
CO
2080-2200
15%
H2O,N2O
CH4
CO2
1250-1370
680-795
2375-2395
1%
0.5%
0.5%
H2O,HNO3
H2O,O3
Volcanic SO2
HNO3
1340-1380
860-920
1320-1330
1000%
40%
25%
H2O,HNO3
emissivity
H2O,CH4
N2O
1250-1315
2180-2250
10%
10%
H2O
H2O,CO
CFCl3 (F11)
830-860
20%
emissivity
CF2Cl (F12)
900-940
20%
emissivity
CCl4
790-805
50%
emissivity
Haskins, R.D. and L.D. Kaplan 1993
Product
Available
Now
In
Work
Held
Fixed
22
AIRS Surface Temp. & Water Vapor
T
T
Winter
Summer
Q
Q
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AIRS Climate/Environmental Products
Monthly Temperature
Monthly H2O
CO
Clouds
Ash & SO2
Ozone
Aerosols
Level 3 Products
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