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)

3

AIRS Was Launched on the EOS Aqua Platform May 4, 2002

AIRS

HSB

AMSU-A1(3-15)

AMSU-A2(1-2)

Delta II 7920

MODIS

Aqua Acquires 325 Gb of data per day

4

IASI was launched on the MetOp-A Satellite on Oct. 19, 2006

Soyuz 2/Fregat launcher,

Baikonur, Kazakhstan

IASI

MHS

AMSU-A1

AMSU-A2ASCAT

HIRS

AVHRR

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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

CrIS 1305

IASI, 8461

Channels

CO

2

CO

2

O3 COCH

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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

Radiance Scan Mirror Telescope Spectrometer Entrance Slit Grating Array Detectors (HgCdTe Focal Plane Assembly)

http://www-airs.jpl.nasa.gov/

AIRS Spatial Coverage (1)

Swath: 1650 km

IFOV: 1.1° 13.5 km

http://www-airs.jpl.nasa.gov/

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Atmospheric InfraRed Sounder (AIRS) spatial coverage

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

Humidity weighting functionsTemperature weighting functions

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.

AIRS IR Specification

Infrared Spectral Coverage:3.74 m - 4.61 m [2674 – 2170 cm-1]6.20 m – 8.22 m [1613 – 1217 cm-1]8.80 m – 15.4 m [1136 – 649 cm-1]

Spectral Resolution: /=1200

Spatial Coverage:49.5 around nadir1.1 (~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 m0.35 K from 13.6 to 15.4 m

Power / Mass: 256 W / 166 kg

Lifetime: 5 years

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AIRS/AMSU/HSB DATA PRODUCTS

RMS Uncertainty*Horizontal Resolution

1 km below 700 mb2 km 700-30 mb

2 km in troposphere

Radiance Products (Level 1B)AIRS IR RadianceAIRS VIS/NIR RadianceAMSU RadianceHSB RadianceStandard Core Products (Level 2)Cloud Cleared IR RadianceSea Surface TemperatureLand Surface TemperatureTemperature ProfileHumidity ProfileTotal Precipitable WaterFractional Cloud CoverCloud Top HeightCloud Top Temperature

3%20%

0.25-1.2 K1.0-1.2 K

1.0K0.5K1.0K1K

15%5%5%

0.5 km1.0 K

15 x 15 km2.3 x 2.3 km45 x 45 km15 x 15 km

45 x 45 km45 x 45 km45 x 45 km45 x 45 km45 x 45 km45 x 45 km45 x 45 km45 x 45 km45 x 45 km

VerticalResolution

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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 < 1 K

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 1250-1370 1% H2O,HNO3

CO2680-795

2375-23950.5% 0.5%

H2O,O3

Volcanic SO2 1340-1380 1000% H2O,HNO3

HNO3860-920

1320-133040%25%

emissivityH2O,CH4

N2O 1250-13152180-2250

10%10%

H2OH2O,CO

CFCl3 (F11) 830-860 20% emissivity

CF2Cl (F12) 900-940 20% emissivity

CCl4 790-805 50% emissivityHaskins, R.D. and L.D. Kaplan 1993

ProductAvailable

Now

In Work

Held Fixed

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AIRS Surface Temp. & Water Vapor

T T

Q Q

Winter Summer

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AIRS Climate/Environmental Products

Monthly Temperature Monthly H2O

Ozone

Clouds

Level 3 Products

Ash & SO2

Aerosols

CO