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Spectroscopy of Stratospheric Molecular O3
Christy Predaina University of Colorado at Boulder Colorado Space Grant Consortium April 4, 2005
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Presentation Overview
Ozone in the Atmosphere Spectroscopy Chemistry CX 1 Mission Overview Three main science instruments Spectrophotometer Photometer Ground Based Aerosol Meter CX 1 Data Analysis & TOMS Algorithm
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Ozone in the Atmosphere
Blocks all UV-C radiation nm Blocks most UV-B radiation nm 320 to 400 UV-B and UV-C radiation are harmful to living organisms because they can be absorbed by the nucleic acid in cells A 1 % decrease in atmospheric ozone causes UV-B to increase about 2 % at the Earth’s surface
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Spectroscopy Break down light into wavelengths using a grating
What is Spectroscopy? The study of the interaction of electromagnetic radiation with matter Break down light into wavelengths using a grating Each wavelength intensity measured separately Comparison of measured wavelength intensities is basics of Spectroscopy
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Hartley and Huggins Bands
O3 Absorption Hartley Band nm Huggins Band nm
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Chemistry of Stratospheric O3
Production of O3 UV-C helps produce O3 Protection of Earth by O3
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Chemistry of Stratospheric O3
Destruction of O3 Nitrogen Oxide Chlorine
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CX 1 Mission Overview
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CX 1 Data Collection Overview
Spectrophotometer measures backscattered UV to determine ozone levels Photometer measures albedo to calibrate backscattered signal K-12 students measure UV on ground Students also measure aerosols (smog, brown cloud, haze, etc.) which partially block visible and UV light
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CX 1 Science Subsystem Spectrophotometer – “Speck” Photometer – “Mo”
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Spectrophotometer - “Spec”
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Spec - Optical Layout Optical Features 280 - 350 nm Range
5 nm Resolution 7 x 0.5 ° FOV Delrin/Graphite Baffles
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Spec - Ray Trace Ray trace for Speck showing the n= -1 diffraction from nm.
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Photometer – “Mo” Measures albedo of swath for calibration
Consists of an aperture, a lens, a filter, and a photodiode
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Ground Instruments Measure aerosols in atmosphere
Reflected Sunlight Transmitted Measure aerosols in atmosphere Measure UV light reaching ground Study UV absorption of aerosols Compare ground measurements to satellite measurements Compare theoretical and experimental intensity readings Provide a hands on learning experience for students Create a ground based map of aerosols
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Radiative Transfer Model
CX 1 Data Analysis ADS Mission Ops Photometer Weather Satellites [O3], [Aerosol] Viewing Geometry Global Position Planetary Albedo Cloud Cover Initial Guess Atmospheric Model Optical Depth Single Scatter Albedo Radiative Transfer Model DISORT N-Value Matching N-Values? D[O3], D[Aerosol] No N-Value SPECK Pair Ratios Yes Mission Ops
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TOMS Algorithm Wavelength Pairs Method
One sensitive to UV absorption One insensitive to UV absorption Ratio tells absorption by Ozone Combines all variables measured by satellite and ground such as: Wavelength Viewing Geometry Global positioning Albedo Reflectivity / Cloud Cover Aerosols Produces ozone value
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Presentation Review Ozone in the Atmosphere Spectroscopy Chemistry
CX 1 Mission Overview Three main science instruments Spectrophotometer Photometer Ground Based Aerosol Meter CX 1 Data Analysis & TOMS Algorithm
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Questions
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Mission Requirements Requirement Met By: Detectable Ozone Trends
Operations Nadir FOV = 6.9 x 0.57 degrees Structure / Mounting Low thermal noise / thermal stability Passive cooling Integration times ~ 0.1 sec. Dynamically chosen in flight Dynamic Range > 1000 Multiple OpAmps Spectral Resolution < 5 nm Telescope / Slit geometry
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Error Budget Item Error Passed Requirement Statistical Sampling
< 10% Instrument S/N > 10 Modeling Scattering Line Profile < 3% < 5 nm Bandpass Pair-wise measurements within 20 nm of each other Radiometric Calibration Ground Characterization Wavelength Calibration < 1% Solar Irradiant < 5% Corrected in flight measurements Total Error 15.6 %
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Passed Requirement (Base/Min.)
Science Requirements Mission Baseline/ Minimal Performance Passed Requirement (Base/Min.) Detectable Ozone Trends 2 / 5 % Daily measurements of same location Ground measurements Cost ~ $ Simple remote sensing instrument Instrument S/N Spectral Resolution Detector Thermal Noise < 10% of total detector noise Instrument Thermal Stability Dynamic Range > 5000/1000 Integration Time ~ 0.1/0.05 sec. 2.5/5 nm Detector Temp.< 10/22 C Instrument DT < 20 C Variable gain / 16 bit data Data Rate Infrared Field of Vision (IFOV) =6.9/6.9 x 0.57x0.34 degrees FP(700 km)=168/168 x 14/8.4 km Payload/Spacecraft Internal Volume Instrument:15 x 15 x 8 cm Payload: 16 x 16 x 9 cm Weight Instrument: 1 kg Payload < 1.75 kg Power < 0.75 W 15 V < 1 W
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