Spectroscopy of Stratospheric Molecular O3
Christy PredainaUniversity of Colorado at BoulderColorado Space Grant Consortium
April 4, 2005
Presentation Presentation OverviewOverview
Ozone in the AtmosphereOzone in the Atmosphere
SpectroscopySpectroscopy
Chemistry Chemistry
CX 1 Mission OverviewCX 1 Mission Overview
Three main science instrumentsThree main science instruments SpectrophotometerSpectrophotometer PhotometerPhotometer Ground Based Aerosol MeterGround Based Aerosol Meter
CX 1 Data Analysis & TOMS AlgorithmCX 1 Data Analysis & TOMS Algorithm
Ozone in the Ozone in the AtmosphereAtmosphere
Blocks all UV-C radiation 200-290 nm Blocks most UV-B radiation 290-320 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
SpectroscopySpectroscopy
What is Spectroscopy?What is Spectroscopy? The study of the interaction of electromagnetic The study of the interaction of electromagnetic
radiation with matterradiation with matter
Break down light into wavelengths using Break down light into wavelengths using a gratinga grating
Each wavelength intensity measured Each wavelength intensity measured separatelyseparately
Comparison of measured wavelength Comparison of measured wavelength intensities is basics of Spectroscopyintensities is basics of Spectroscopy
Hartley and Huggins Hartley and Huggins BandsBands
O3 AbsorptionO3 Absorption Hartley Band 200- 310 nmHartley Band 200- 310 nm Huggins Band 310-350 nmHuggins Band 310-350 nm
Chemistry of Chemistry of Stratospheric OStratospheric O33
Production of OProduction of O33
UV-C helps produce OUV-C helps produce O33
Protection of Earth by OProtection of Earth by O33
Chemistry of Chemistry of Stratospheric OStratospheric O33
Destruction of ODestruction of O33
Nitrogen OxideNitrogen Oxide ChlorineChlorine
Web Browser
AnalysisSoftwareDatabase
Web Server
Citizen Explorer Satelli teis designed and built byuniversity students usingrecent advances intechnology
Sun-synchronous orbitbrings satell ite overschools at 10am localtime
Ozone levels in theatmosphere aredetermined bymeasuring direct,reflected, andtransmitted sunlightat variouswavelengths
Direct
Sunlight
Reflected
Sunlight
Transmitted
Sunlight
Satellite transmits scienceand engineering datadirectly to low-cost receiversat K-12 schools across theUS and the world
K-12 students collectdata at their school using2 different hand-heldscience instruments thatmeasure the amount ofUV radiation reachingthe Earth’s surface andthe amount of aerosol(particles) in the air.
K-12 schools communicate withthe university and other K-12schools via the internet.
Global data is measureddaily, database andanalysis software madeavailable on internet
College s tudentsoperate satell ite fromthe University ofColorado at Boulder
CX 1 Mission OverviewCX 1 Mission Overview
CX 1 Data Collection CX 1 Data Collection OverviewOverview
Spectrophotometer measures backscattered UV to Spectrophotometer measures backscattered UV to determine ozone levelsdetermine ozone levels
Photometer measures albedo to calibrate Photometer measures albedo to calibrate backscattered signalbackscattered signal
K-12 students measure UV on groundK-12 students measure UV on ground
Students also measure aerosols (smog, brown cloud, Students also measure aerosols (smog, brown cloud, haze, etc.) which partially block visible and UV lighthaze, etc.) which partially block visible and UV light
CX 1 Science SubsystemCX 1 Science Subsystem
Photometer – “Mo”
Spectrophotometer – “Speck”
Spectrophotometer - Spectrophotometer - “Spec”“Spec”
Spec - Optical Layout
Optical Features• 280 - 350 nm Range• 5 nm Resolution• 7 x 0.5 ° FOV• Delrin/Graphite Baffles
Spec - Ray TraceSpec - Ray Trace
Ray trace for Speck showing the n= -1 diffraction from 280 - 350 nm.
Photometer – “Mo”Photometer – “Mo”
Measures albedo of Measures albedo of swath for calibrationswath for calibration
Consists of an Consists of an aperture, a lens, aperture, a lens, a filter, and a a filter, and a photodiodephotodiode
Ground InstrumentsGround Instruments
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
Reflected
Sunlight
Transmitted
Sunlight
CX 1 Data AnalysisCX 1 Data Analysis
ADS Mission Ops Photometer Weather Satellites
AtmosphericModel
Radiative Transfer ModelDISORT
SPECKPair Ratios
MatchingN-Values?
Mission Ops
Viewing Geometry Global Position Planetary Albedo Cloud Cover
Optical DepthSingle Scatter Albedo
D[O3], D[Aerosol]
N-Value
N-Value
[O3], [Aerosol]
Initial Guess
Yes
No
TOMS AlgorithmTOMS Algorithm
Wavelength Pairs MethodWavelength Pairs Method One sensitive to UV absorptionOne sensitive to UV absorption One insensitive to UV absorptionOne insensitive to UV absorption Ratio tells absorption by OzoneRatio tells absorption by Ozone
Combines all variables measured by satellite Combines all variables measured by satellite and ground such as:and ground such as: Wavelength Wavelength Viewing GeometryViewing Geometry Global positioning Global positioning AlbedoAlbedo Reflectivity / Cloud CoverReflectivity / Cloud Cover AerosolsAerosols
Produces ozone valueProduces ozone value
Presentation ReviewPresentation Review
Ozone in the AtmosphereOzone in the Atmosphere
SpectroscopySpectroscopy
Chemistry Chemistry
CX 1 Mission OverviewCX 1 Mission Overview
Three main science instrumentsThree main science instruments SpectrophotometerSpectrophotometer PhotometerPhotometer Ground Based Aerosol MeterGround Based Aerosol Meter
CX 1 Data Analysis & TOMS AlgorithmCX 1 Data Analysis & TOMS Algorithm
QuestionsQuestions
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
Mission RequirementsMission Requirements
Error BudgetError Budget
Item Error Passed Requirement
Statistical Sampling
< 10% Instrument S/N > 10
Modeling Scattering Line Profile
< 3%< 3%
< 5 nm BandpassPair-wise measurements within 20
nm of each other
Radiometric Calibration
< 10% Ground Characterization
Wavelength Calibration
< 1% Ground Characterization
Solar Irradiant < 5% Corrected in flight measurements
Total Error 15.6 %
Science Requirements
Mission Baseline/ Minimal Performance
Passed Requirement (Base/Min.)
Detectable Ozone Trends
2 / 5 % Daily measurements of same location
Ground measurements
Cost ~ $ 100.00 Simple remote sensing instrument
Instrument
S/NSpectral Resolution
Detector Thermal Noise < 10% of total detector noiseInstrument Thermal StabilityDynamic Range > 5000/1000Integration Time ~ 0.1/0.05 sec.2.5/5 nm
Detector Temp.< 10/22 CInstrument DT < 20 CVariable gain / 16 bit dataData RateInfrared Field of Vision (IFOV) =6.9/6.9 x 0.57x0.34 degreesFP(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 W15 V
< 1 W