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The Solar Occultation for Ice Experiment SOFIE

The Solar Occultation for Ice Experiment SOFIE. Mark Hervig, SOFIE Deputy PI Larry Gordley, SOFIE PI GATS Inc. Introduction. SOFIE was designed to measure PMCs and the environment in which they form Measurement challenges: PMCs occupy tenuous altitudes: 83 km / 0.006 mb

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The Solar Occultation for Ice Experiment SOFIE

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  1. The Solar Occultation for Ice Experiment SOFIE Mark Hervig, SOFIE Deputy PI Larry Gordley, SOFIE PI GATS Inc.

  2. Introduction • SOFIE was designed to measure PMCs and the environment in which they form • Measurement challenges: • PMCs occupy tenuous altitudes: 83 km / 0.006 mb • PMC particles: 50 nm radius / 80 cm-3 concentration • PMC signals are low • 100 times lower than PSCs • 1000 times lower than cirrus • Gas signals are 100 times lower than in the stratosphere • Solar Occultation can meet these challenges: • Brightest source • Relative measurements

  3. Solar Occultation The sun rises and sets relative to the spacecraft (30 times a day). SOFIE stares at the sun, measuring profiles of solar intensity during each rise & set SOFIE signals yield atmospheric transmission, a relative measurement:

  4. Measurement Objectives • Measurements in specific wavelength regions target specific gases or particles. • Measured transmission profiles are used to retrieve geophysical parameters: • Temperature • O3, H2O, CO2, CH4, and NO mixing ratios • PMC extinction • Vertical profiles from the tropopause to over 100 km, with 1.5 km resolution

  5. Measurement Geometry SOFIE sample volume length = 280 km Excellent vertical resolution Long horizontal path length ZT RE SOFIE vertical resolution, Z = 1.5 km

  6. Optical Layout

  7. Differential Absorption Measurements • Each SOFIE channel uses two detectors to make three measurements: • Strong band absorption • Weak band absorption • Difference signal, V = weak – strong • V reduces or eliminates common mode noise: • atmospheric interference, tracking jitter, chopper noise, sun spots Simultaneous measurements of: PMCs Temperature H2O

  8. Channel Description

  9. Retrieved Parameters • Vertical resolution: 1.5 km (over-sampled at 150 m) • Horizontal resolution: 280 km  4 km

  10. Geographic Coverage • AIM orbit is polar, noon - midnight crossings • SOFIE provides 30 occultations (soundings) per day • 15 sunrises in the south, 15 sunsets in the north • Consecutive measurements are separated by 1.6 hours & 900 km sunrises SOFIE coverage during one year sunsets

  11. Sun Sensor Megapixel FPA, 701 nm wavelength Pointing precision is 0.5 arcsec Measurements of solar extent provide refraction angle Refraction angles are used to retrieve temperature profiles

  12. PMC Measurements • Retrievals of particle extinction (optical cross section / volume = km-1) • 10 wavelengths from 0.33 - 5 m • Radiometer signals (10 's) •  = 0.330, 0.867, 1.04, 2.46, 2.94, 3.06, 3.12, 3.48, 4.65, and 5.01 m • Digitization limit = 1.1  10-7 (km-1) • Difference signals (2 's) • Ch 2:  = 0.95 m, gain = 300, digitization limit = 4  10-10 (km-1) • Ch 5:  = 3.09 m, gain = 120, digitization limit = 9  10-10 (km-1)

  13. Integral PMC Properties The infrared PMC signal is due to absorption which is directly proportional to r3 and therefore particle volume density, Vice, Vice = C () (1)) Where C is a constant, () is extinction in km-1, and Vice is in m3 cm-3.

  14. PMC Size Distribution Retrievals PMC measurements spanning 0.3 to 5 microns are key will allow retrievals of complete PMC size distributions. • Retrieval considerations: • Particle shape: • Spherical (Mie) • Non-spherical (T-matrix) • Size distribution form: • Lognormal • Gaussian • Discrete (# bins = # 's)

  15. Cosmic Dust / Smoke • Cosmic dust measurements are sparse and incomplete • Current understanding based on scant observations combined with theory • e.g., Hunten et al. [1980], Kalashnikiva et al. [2000]; Rapp et al. [2002] PMC volume densities are about 0.08 m3 cm3

  16. Smoke Signals in SOFIE Data • Predictions based on CARMA smoke model [Rapp et al., 2002] • SOFIE channel #2 (0.86 & 1.03 m) • Radiometer signals are below the digitization limit. • V signal of 90 counts at peak, but 30% of this is due to molecular scattering

  17. Correlative Measurements • AIM is seeking correlative measurements: Validation and enhanced science • Altitude: Focus on mesosphere, but SOFIE observes trop - 100 km • Latitude: 65 - 85 north & south • Time: focus on polar summer, desire other times • Measurements: PMC, PMSE, dust, aerosols, T, O3, H2O, CO2, CH4, NO • The AIM website (aim.hamptonu.edu) will provide • Measurement locations • Coincidence alerts (automated) • Coincidence criteria will vary depending on the geophysical parameter

  18. Summary • Continuous coverage of 65 - 85 latitude, north & south • Measures profiles of: Temperature • O3, H2O, CO2, CH4, and NO mixing ratios • PMC extinction • SOFIE online: sofiedata.org • AIM online: aim.hamptonu.edu

  19. Backup slides follow

  20. Sun Sensor • Two basic components: Fast steering mirror 1024 x 1024 focal plane array (FPA) • 701 (11) nm wavelength • 7.14 arcsec pixel dimension, 18 arcsec FOV (FWHM) • S/C is solar-pointing during SOFIE occultation SOFIE pointing should only manage S/C jitter • Testing indicates 0.5 arcsec precision

  21. System Technical Resources

  22. Commissioning Phase SOFIE commissioning will use SDL & GATS personnel

  23. Channel Separation Module

  24. SOFIE Overview • Vertical resolution: 1.5 km, over-sampled at 150 m • Horizontal resolution: 280 km  4 km • 16 bit digitization • Retrievals: • Temperature / Pressure • O3, H2O, CO2, CH4, NO • PMCs (10 wavelengths from 0.330 to 5.01 m)

  25. Implications of MAGIC Dust Measurements • Mesospheric Aerosols Genesis Interaction and Composition (MAGIC) • Rocket-borne particle collector using a carbon impact grid • Lab analysis reveals particle size, concentration, and composition • MAGIC flight over Wallops indicates cumulative smoke concentrations of 106 cm-3 • Cumulative over radii from 1 - 3 nm and altitude from 76.7 - 93.5 • CARMA model (Markus Rapp) gives cumulative concentrations of 2.2  104 cm-3 • MAGIC concentrations are 46 times greater than CARMA model

  26. SOFIE Signals Considering MAGIC Concentrations • CARMA smoke concentrations were scaled by 46 at all sizes and altitudes • SOFIE channel #2 (0.86 & 1.03 m) • radiometer signal is 30 times higher than digitization limit • V signal of 2800 counts at peak

  27. System Calibration Overview

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