visible/near-infrared spectrometer, thermal infrared spectrometer, and neutron detector life in the...

Visible/Near-Infrared Spectrometer,Thermal Infrared Spectrometer,

and Neutron Detector

Life in the Atacama 2004Science & Technology Workshop

J. MoerschU. Tennessee

Life in the Atacama 2004 Workshop 2 Carnegie Mellon

Overview

Description of capabilities, operational considerations, and outstanding issues for three instruments in this year’s field test:

• Visible/Near-Infrared Reflectance Spectrometer

• Thermal Infrared Emission Spectrometer

• Neutron Detector

Life in the Atacama 2004 Workshop 3 Carnegie Mellon

Visible/Near-Infrared Reflectance Spectrometer

• Measures reflected light (from Sun or artificial source) off target as a function of wavelength.

• Ratio of (measured radiance / incident radiance) is Reflectance.

• Reflectance spectra in the 0.35 – 2.5 µm are diagnostic of a number of minerals and organic compounds.

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Vis/Near-IR spectra can be used to distinguish between broad classes of minerals

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Vis/Near-IR spectra can also be used to distinguish between minerals within a particular group

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Organic matter can also be identified (e.g. chlorophyll)

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ASD Portable Vis/Near-IR Field Spectrometer

Spectrometer

Laptop

Fiber Optic

Pan/Tilt Platform 1 deg. Foreoptic

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Some Specs:

Wavelength range: 350-2500 nm

Spectral Resolution: 3-10 nm

Field of View: 1° (1.7 cm @ 1m range)

Time req’d for one spectrum: 1-2 seconds in sunlight

Data interface: Parallel cable to computer

Data volume: 9kb/spectrum

Power: Internal NiMH (2 hour endurance)

Dimensions: 33 x 11 x 41 cm

Mass: 8.6 kg

Two of these instruments will be available – one on the rover (primary), one human-carried (backup).

ASD Vis/Near-Ir Portable Field Spectrometer

Life in the Atacama 2004 Workshop 9 Carnegie Mellon

ASD Vis/Near-IR Portable Field Spectrometer

Calibration accomplished by taking spectrum of a white reference standard every ~10 minutes (more often if conditions varying).

Spectra may be taken at night or under cloudy sky using an artificial illumination source. This also provides access to spectrum in the H20 absorption bands.

Life in the Atacama 2004 Workshop 10 Carnegie Mellon

Vis/Near-IR SpectrometerOperational Considerations

• Spectrometer mounted to rover, with 1-degree foreoptic mounted to mast, approximately co-located with panoramic cameras

• Images may be used to select targets. Instrument may also be pointed “in the blind” using azimuth and elevation angles.

• Targets can be individual points or raster patterns.

• Spot size is 1.7 cm @ 1m range. With artificial illumination source, spot size is about 5cm.

• Calibration target mounted on rover deck. “Dark current” calibration (internal to instrument) also possible.

• Data will be returned as binary files. RST will have software to turn these into spectra, and spectral libraries for compositional analysis.

Life in the Atacama 2004 Workshop 11 Carnegie Mellon

Vis/Near-IR SpectrometerOpen Issues

• Backup spectrometer will be shipped off to manufacturer for spectral resolution upgrade before field expedition.

• Best method for shipping to Chile?

• How to target if backup spectrometer used?

• Other issues on CMU side? Integration with rover? Software for targeting and data product tracking?

Life in the Atacama 2004 Workshop 12 Carnegie Mellon

Thermal Infrared Emission Spectrometer

• Measures emitted radiance from target

• Ratio of

(Measured target radiance /

Radiance of perfect blackbody at same temperature) is called Emissivity.

• Emissivity spectra are diagnostic of mineral/rock compositions

13After Christensen et al., 1992Christensen et al. 1985

Example Thermal IR spectra

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Boba Fett Hill Contact (Marsokhod 1999 experiment)

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16Instrument will be operated as standalone, simulated to be on the rover.

Optical head

Computer controller

Foreoptic

Mike

Life in the Atacama 2004 Workshop 17 Carnegie Mellon

Some Specs:

Wavelength range: ~8 – 12 µm

Spectral Resolution: 6 cm-1 (0.04 - .09 µm)

Time req’d for one spectrum: <10 minutes

Field of view: 4.8° (8.2 cm @ 1m range)

Data interface: Integrated computer

Data volume: 36 kb/spectrum

Power: 12V 7-hour battery pack

Dimensions: 36 x 20 x 23 cm

Mass: 7 kg

Coolant: Liquid nitrogen in on-board dewar

ASU D&P Thermal Infrared Field Spectrometer

Life in the Atacama 2004 Workshop 18 Carnegie Mellon

D&P Portable Thermal-IR Field Spectrometer: Calibration

• Each target spectrum requires four measurements:

• Target spectrum

• Hot blackbody spectrum

• Cold blackbody spectrum

• Downwelling radiance spectrum measurement

• Calibration of raw spectra will be accomplished by the RST using supplied software

Life in the Atacama 2004 Workshop 19 Carnegie Mellon

Thermal-IR SpectrometerOperational Considerations

• Spectrometer is not mounted to the rover – operated by field personnel in a stand-alone mode at the end of each sol.

• Instrument can only be used in “single point” mode – rastering not possible because it has no precise az/el pointing (it’s pointed by eye).

• Calibration spectra will be acquired with each spectrum or set of spectra at a single site.

• Spectral acquisition can be cumbersome. At beginning of field test, a limit of 6 spectra per sol will be imposed. If we find we can handle more, we will advise the RST of a higher limit per sol.

• Data will be returned as raw radiance spectra of the target and calibrators. RST will have software to turn these into spectra, and spectral libraries for compositional analysis.

Life in the Atacama 2004 Workshop 20 Carnegie Mellon

Thermal IR SpectrometerOpen Issues

• Need to find a source of liquid nitrogen in town

• Best method for shipping to Chile?

• How to identify targets?

Life in the Atacama 2004 Workshop 21 Carnegie Mellon

Neutron Detector

• Counts neutrons coming up from the surface in two different energy ranges: a) all energies, b) energies above the Cd-cutoff (epithermals)

• Ratio of [(All – Epithermal) / Epithermal] is sensitive to amount of hydrogen within sensing radius (0.5 – 1m)

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Neutron Detector: Physical processes

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Neutron Detector: Sensitivity

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1.0

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4.0

5.0

6.0

7.0

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PERCENT WATER

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Life in the Atacama 2004 Workshop 27 Carnegie Mellon

Detection of Buried H

Horizontal Displacement from Center of 3"-Deep Target (feet)

-3 -2 -1 0 1 2 3

Ep

ithe

rmal

s/T

herm

als

0.0

0.1

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Neutron Detector: Systematic Traverse Measurements

“Pure Dry”

“Pure Wet”

Traverse measurements

Life in the Atacama 2004 Workshop 28 Carnegie Mellon

Some Specs:Time req’d for one measurement : ~10 minutes

Sensing radius (depends on density) : ~ 0.5 – 1.0 m

Data interface: Serial RS-232 to Tablet PC

Data volume: A few bytes per measurement

Power: 14V laptop batteries

Radiation source: Encapsulated pellet of 252Cf (gives about 104 neutrons/second)

Neutron detector

Life in the Atacama 2004 Workshop 29 Carnegie Mellon

Neutron DetectorOperational Considerations

• Instrument is not mounted to the rover – operated by field personnel in a stand-alone mode at the end of each sol. Instrument will be wagon-mounted to keep the geometry of the detector tubes fixed.

• Instrument is not “pointable” – it simply senses hydrogen abundance within a certain range.

• Measurements with this instrument should not yet be interpreted in terms of absolute H abundances, but as relative abundances (e.g., “wetter” or “dryer”).

• Not possible to distinguish between possible sources of H – could be water, could be in minerals.

• At beginning of field test, a limit of 6 measurements per sol will be imposed. If we find we can handle more, we will advise the RST of a higher limit per sol.

• Data will be returned as a single number at each position, the ratio of thermal/epithermal counts.

Life in the Atacama 2004 Workshop 30 Carnegie Mellon

Neutron DetectorOpen Issues

• Co-I was recently in an accident – may or may not be healed in time. His presence may be critical to the success of this instrument.

• Finding an appropriate isotopic source and getting it to/from Chile is a big issue not yet resolved.

• Need to buy a wagon in Chile.

• Best method for shipping instrument to Chile?

• How to identify targets from RST?

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Personnel

Jeff Moersch (UT):

Field team lead on all three instruments

Darrell Drake (LANL):

Field team – neutron detector

Mike Wyatt (ASU):

Field team – thermal infrared spectrometer

Mike Rampey (UT):

Field team

Jen Piatek (UT):

Remote science team lead on all three instruments