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TES Instrument Specifications

TES is a high-resolution, infrared, imaging Fourier-transform spectrometer with spectral coverage of 650 to 2250 cm-1 at a spectral resolution of 0.1 cm-1 (low resolution) or 0.025 cm--1 (high resolution), offering line-width-limited discrimination of essentially all radiatively active molecular species in Earth's lower atmosphere. (View a schematic diagram of the TES instrument optical layout.)

Requirement Specifications Comments
Spectrometer type Connes-type four-port Fourier transform spectrometer Limb and nadir viewing capability
Spectral sampling distance Interchangeably 0.0592 cm-1 nadir and 0.0148 cm-1 limb Unapodized
Optical path difference Interchangeably ±8.45 cm nadir and ±33.8 cm limb Double-sided interferograms
Overall spectral coverage 650-3050 cm-1 (3.2-15.4 µm) Continuous, but with multiple sub-ranges typically 200-300 cm-1 wide
Individual detector array spectral coverage (cm-1) 1A (1900-3050), 1B (820-1150), 2A (1100-1950), 2B (650-900) All mercury cadmium telluride photo voltaic at 65 K
Detector array configuration 1 X 16 All four arrays optically conjugated
Aperture 5 cm Unit magnification system
System étandue (per pixel) 9.45 X 10-5 cm2sr Not allowing for a small central obscuration from the Cassegrain secondaries
Modulation index >0.7; 650-3050 cm-1 >0.5 at 1.06 µm (control laser)
Spectral accuracy ±0.00025 cm-1 After correction fro finite field of view, off axis effects, Doppler shifts, etc.
Channeling <10% peak to peak; <1% after calibration All planar transmissive elements wedged
Spatial resolution 0.5 X 5 km nadir; 2.3 X 23 km limb
Spatial coverage 5.3 X 8.5 km nadir; 37 X 23 km limb
Pointing accuracy 75 µrad pitch, 750 µrad yaw, 1100 µrad roll Peak-to-peak values
Field of regard 45° cone about nadir plus trailing limb Also views internal calibration sources
Scan (intergration) time 4-s nadir and calibration, 16-s limb Constant-speed scan, 4.2 cm/sec (optical path difference rate)
Maximum stare time, nadir 208 s 40 downlooking scans
Transect coverage 885 km maximum
Interferogram dynamic range < 16 bits Plus four switchable gain steps
Radiometric accuracy < 1K, 650-2500 cm-1; < 2 K, 2500-3050 cm-1 Internal, adjustable, hot blackbody + cold space
Pixel-to-pixel cross talk <10% Includes diffraction, aberrations, carrier diffusion, etc.
Spectral signal-to-noise ratio As much as 600:1; 30:1 minimum requirement Depends on spectral region and target. General goal is to be source photon shot-noise limited
Lifetime 5 years on orbit Plus 2 years before launch
Size 1.0 m X 1.3 m X 1.4 m Earth shade stowed
Mass 385 kg Allocation
Power, average 334 W Allocation
Power, peak 361 W Allocation
Data rate, average 4.5 MBPS science only
Data rate, peak 6.2 MBPS Allocation

TES Optical Filters

The following table lists the optical-filter specifications and species in the atmosphere having absoption/emission features in the filter spectral ranges. Not all the filters are used in the global survey. Filters 2B1, 1B2, 1A1, and 2A1 are used in nadir global surveys, and filters 2B1, 1B2, 1A1, 2A1, 1B1, and 2A4 are used in limb global surveys.

Filter Identification Filter Half-Power Points (cm-1) Major Species
Array 2B (650 - 900 cm-1)
2B1 650 900 CO2, HNO3, CFC11, NO2
Array 1B (820 - 1150 cm-1)
1B1 820 1050 HNO3, NH3, CFC11, CFC12, O3
1B2 950 1150 O3, NH3, CFC11, CFC12, N2O
Array 2A (1100 - 1950 cm-1)
2A1 1100 1325 O3, N2O, HNO3, CFC12, SO2, CH4
2A2 1300 1550 O3, HNO3, CH4
2A3 1500 1750 H2O, NO2
2A4 1700 1950 H2O, NO
Array 1A (1900 - 3050 cm-1)
1A1 1900 2250 O3, CO, N2O, NO, OCS
1A2 2200 2450 CO2, N2
1A3 2425 2450 N2O
1A4 2600 2850 HDO
1A5 2800 3050 CH4, HCl, O3