Science DriversSpectroscopic SensorsMass SpectrometryIn Situ Mass SpectrometerIn Situ Mass SpectrometryLaser Raman SpectroscopyLaser Raman SpectroscopyLaser Raman SpectroscopyLaser Raman SpectroscopyLaser Induced Breakdown Spectroscopy (LIBS)LIBSVisual Reflectance SpectroscopyVisual Reflectance SpectroscopyVisual Reflectance SpectroscopyVisual Reflectance SpectroscopyVisual Reflectance Spectroscopy12.097 – Advanced Sensors: In Situ SpectroscopyScience Drivers• In Situ Sensors– Development of autonomous and remote platforms• ROVs, AUVs• Cabled observatories– Desire to analyze targets with discrete stability regions in the deep ocean• Hydrothermal vent fluid• Gas hydrates• Spectroscopic Sensors– Desire to analyze multiple species at once– Desire to analyze solid, liquid and gaseous targets– Desire for non-destructive, non-invasive analyses12.097 – Advanced Sensors: In Situ SpectroscopySpectroscopic Sensors• Mass Spectrometry– Atomic mass to charge ratio• Laser Raman Spectroscopy– Molecular vibrational modes• Laser Induced Breakdown Spectroscopy– Atomic emission• Visible Reflectance Spectroscopy– Reflected color12.097 – Advanced Sensors: In Situ SpectroscopyMass Spectrometry• Analytes (molecules, atoms) are differentiated based on their charge to mass ratio– Analytes are ionized– Ions are accelerated through a magnetic or electric field which alters the trajectory of the ion beam– The differentiated beams are focused onto a detectorhttp://www.atmosphere.mpg.de/enid/0,55a304092d09/Nr_ss_May_2__5_vegetation/CO2/R__Monitoring_carbon_dioxide_4ni.htmlImage removed due to copyright considerations. Please see:12.097 – Advanced Sensors: In Situ SpectroscopyIn Situ Mass Spectrometer• Gemini In Situ Mass Spec– Quadrupole mass spectrometer– Built by Rich Camilli, WHOI/DSL– 10 kg in air, 50 cm long, 5000 m depth rating– Measures molecules from 2 to 300 AMU– parts-per-billion detection limitImage removed due to copyright considerations.12.097 – Advanced Sensors: In Situ SpectroscopyIn Situ Mass Spectrometry• Advantages– Can analyze liquids and gases– Detects multiple species in a single measurement– Non-destructive– Requires no consumables• Disadvantages– Cannot analyze solids– Is invasive• Sample must be drawn into the instrument– Must maintain an ultra high vacuum (10-5Torr)12.097 – Advanced Sensors: In Situ SpectroscopyLaser Raman Spectroscopy• Raman scattering– Discovered by C. V. Raman• 1930 Nobel Prize• Inelastic scattering of monochromatic radiation– Sample is interrogated by a laser– Some of the backscattered radiation is frequency shifted– Shift in energy is equal to the vibrational energy of the molecule12.097 – Advanced Sensors: In Situ SpectroscopyLaser Raman Spectroscopy• Solids State laser for excitation– 532 nm, 785 nm– ~1-30 mW power• Notch filters for Rayleighline rejection• Holographic grating– Duplex grating splits the spectrum into two strips• Charge-coupled device (CCD) detector– Images full spectrumhttp://www.kosi.com/Image removed due to copyright considerations. Please see:12.097 – Advanced Sensors: In Situ SpectroscopyLaser Raman Spectroscopy• Raman spectrum provides a “fingerprint” of a substance based on chemical composition and crystal structure– Peak positions change with phase changes, pressure and temperature changes– Note that not all vibrational modes are Raman active• Depends on the polarizability of the molecule• Often complementary to IR spectroscopy12.097 – Advanced Sensors: In Situ Spectroscopyνν11νν22νν33Seawater Î water + sulfate12.097 – Advanced Sensors: In Situ SpectroscopyLaser Raman Spectroscopy• Advantages– Can analyze solids, liquids and gases– Detects multiple species in a single measurement– Non-destructive– Non-invasive– Requires no consumables• Disadvantages– Requires precise positioning to analyze opaque targets– Fluorescence can overwhelm Raman signal– Not all species are Raman active12.097 – Advanced Sensors: In Situ SpectroscopyLaser Induced Breakdown Spectroscopy (LIBS)• High power laser is used to “plasmize” a sample– Only picograms to nanograms are used• The spectral lines emitted from the plasma indicate the constituent elements• Work done by Anna Michel, WHOI/DSLCourtesy of Anna Michel. Used with permission.12.097 – Advanced Sensors: In Situ SpectroscopyLIBS• Advantages– Can analyze solids, liquids and gases– Detects multiple species in a single measurement– Non-destructive– Non-invasive– Requires no consumables• Disadvantages– Requires precise positioning to analyze opaque targets– Quenching of plasma by liquids12.097 – Advanced Sensors: In Situ SpectroscopyVisual Reflectance Spectroscopy• A target is illuminated with white light• The spectrum of the reflected light is analzed• Color can be used as a proxy for some mineral species (e.g., iron species tend to be red)http://imagers.gsfc.nasa.gov/ems/visible.gifImage removed due to copyright considerations. Please see:12.097 – Advanced Sensors: In Situ SpectroscopyVisual Reflectance Spectroscopy• Aerosol Dust Application– Iron is deposited in the ocean by aerosol dust– Iron may be a limiting nutrient for phytoplankton– Buoy sampler can collect and analyze samples in situimage credit: WHOI12.097 – Advanced Sensors: In Situ SpectroscopyVisual Reflectance Spectroscopy• Aerosols collected on filters show dust events• Color of the filter corresponds to iron contentCourtesy of Ed Sholkovitz. Used with permission.12.097 – Advanced Sensors: In Situ SpectroscopyVisual Reflectance SpectroscopyArimoto R., W. Balsam, and C. Schloesslin. "Visible spectroscopy of aerosol particles collected on filters: iron-oxide minerals." Atmospheric Environment 36, no. 1 (January 2002): pp. 89-96(8). (Elsevier Science)Image removed due to copyright considerations. Please see:12.097 – Advanced Sensors: In Situ SpectroscopyVisual Reflectance Spectroscopy• Advantages– Simplicity• No high vacuum• Not a weak signal• No high power laser– Non-destructive– Non-invasive– Requires no consumables• Disadvantages– Not necessarily species specific– Cannot necessarily differentiate between multiple species in a