Thermal Infrared Remote Sensing Instruments Intro to TIR spectroscopy at Mars

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Thermal Infrared Remote Sensing Instruments
-Intro to TIR spectroscopy at Mars

• Lecture VEH7
• 10-16-03

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TIR Instruments at Mars

• Mariner 6/7 Infrared Spectrometer (IRS)
• Hyperspectral, limited observations only
  recently properly calibrated primarily aimed at
  atmospheric observations also carried infrared
  radiometer
• M9 Infrared Interferometer Spectrometer (IRIS)
• Hyperspectral, most observations during global
  dust storm primarily aimed at atmospheric
  observations also IRR
• Viking 1/2 Infrared Mapping Spectrometer (IRTM)
• Multispectral albedo and thermal bolometers
• Primary scientific objectives related to
  thermophysical properties, atmospheric
  observations
• first global A I maps, rock abundance, details
  of polar caps

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TIR Instruments at Mars, cont.

• Mars Observer/Mars Global Surveyor Thermal
  Emission Spectrometer (TES)
• Hyperspectral, with albedo and thermal bolometers
• Primary objectives include determining surface
  composition, atmospheric properties,
  thermophysical properties, polar processes
• Mars Odyssey Thermal Emission Imaging System
  (THEMIS)
• IR subsystem has 10 channels (_at_ 9 discrete
  wavelengths), one of which is for atm. studies
• VIS subsystem has 5 channels (5 wavelengths)
• Primary scientific objectives similar to TES,
  higher res.

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Mars TIR Instrument Summary
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TES Objectives

• Objective 1 Surface Mineralogy
• Covered most of this already - thermal IR
  excellent for compositional determination of
  virtually all minerals
• Objective 2 Atmospheric Properties
• Composition, particle size, and vertical
  distribution of aerosols (dust)
• Distribution and condensate abundance of H2O and
  CO2 clouds seasonal variations
• Abundance of gaseous species (water vapor)
• Pressure at surface and temperature/pressure vs.
  height (atmospheric dynamics)

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TES Objectives

• Objective 3 Polar Processes
• H2O and CO2 in caps physical properties,
  sublimation, seasonal characteristics
• Determine additional info about key parameters in
  models of above
• Effect of dust on surface frost albedo
  variations in dust abundance across caps
• Do CO2 hazes form?
• Effective scattering depth of dust, etc.

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TES Objectives

• Objective 4 Thermophysical Properties
• Thermal inertia
• e.g., particle size
• Albedo
• Rock abundance

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TES Instrument

• Conservatively designed to reduce complexity of
  fabrication
• Requirements (e.g., NEDT, resolution, etc.)
  defined by laboratory data, IRIS data,
  terrestrial remote sensing instruments (TIMS)
• Christensen et al. 1993 describes original
  design
• Christensen et al. 2001 describes TES II
  as-built

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From Christensen et al. 2001
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From Christensen et al. 2001
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Instrument Overview

• Michelson interferometric spectrometer
• Selectable 5 and 10 cm-1 sampling (Christensen et
  al. 1993 text erroneously uses resolution)
• Yielding resolutions of 10 and 20 cm-1,
  respectively
• 143 or 286 channels between 1600 - 200 cm-1 (6
  - 50 µm)
• Two broadband radiometers (thermal and visible)
• VNIR from 0.3 - 2.7 µm
• TIR from 5.5 - 50 µm (1800 - 200 cm-1)
• Spectrometer and radiometers share pointing
  mirror, but have separate telescopes boresighted
• Calibration targets internal to spectrometer

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VNIR/Thermal Bolometers
From Christensen et al. 2001
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Instrument Overview

• Spectrometer has 6 DTGS (deuterated tryglycine
  sulfate) detectors, arranged in a 3 x 2 array
• DTGS detectors do not require cooling lower
  responsivity, but wider spectral range
• Similar detectors and 3 x 2 arrangement for
  thermal and visible bolometers
• Spatial resolution nominally 3 x 3 km at each
  detector
• Image motion compensation required to attain
• IMC tested for, but is not used in 2 am orbit, so
  effective resolution is 3 x 6 km
• 6 spectra acquired every 2 sec 1 ICK
• 3530 individual 2-s observations per orbit (OCK)

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Mission Operations

• 200 days to acquire global coverage at equator
• Basic observation types
• Nadir pointing along ground track
• Nominally a 2 pm orbit, changed to 2 am due to
  solar panel damage during aerobraking
• Limb observations
• Use pointing mirror to view tangentially to
  surface through atmospheric column
• Emission phase functions (EPF)
• Observe same spot on ground using fore and aft
  views
• Surface mosaics
• Utilize planetary rotation to obtain spectra of
  areas adjacent to ground track similar to EPFs

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Mission Operations

• Interferometer can collect 64,512 bps
• Maximum data playback rates of 4992 bps
• Data volume reduction options
• FFT interferogram, onboard compression
• Spatial averaging (combining information from
  multiple detectors) can increase SNR (e.g., at
  poles)
• Spectral editing/masking (returning information
  from limited number of spectral channels)
• Temporal averaging (combining information from
  multiple instrument cycles)

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Standard Data Products

• Raw and calibrated TIR radiance at sensor
• Raw and calibrated VNIR/thermal bolometric
  radiance
• Atmospheric P/T profiles
• Thermal inertia
• Lambert albedo
• Atmospherically separated calibrated radiance
• Miscellaneous information about observations
  (ICK/OCK), pointing, position, quality flags,
  etc.
• Long term stability of MO TES was going to be
  assessed against pressure modulator infrared
  radiometer (PMIRR) on MO (bummer)

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