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