Remote Atmospheric Remote Atmospheric Sensing DeviceSensing Device
Team UNOTeam UNO
Team UNOTeam UNO
Donald SwartDonald Swart Cindy GravoisCindy Gravois René LangloisRené Langlois
UNO AdvisorUNO Advisor Lawrence BlanchardLawrence Blanchard
ObjectivesObjectives
Using the measurable quantities of Using the measurable quantities of UV intensity:UV intensity:• Measure total column thickness of the Measure total column thickness of the
ozone layerozone layer• Measure relative ozone concentration as Measure relative ozone concentration as
a function of altitudea function of altitude Measure UVB and UVC as it is Measure UVB and UVC as it is
transmitted and attenuated through transmitted and attenuated through the stratospherethe stratosphere
BackgroundBackground
What is Ultraviolet (UV) radiationWhat is Ultraviolet (UV) radiation How does UV help to detect ozone?How does UV help to detect ozone? Absorption cross sectionsAbsorption cross sections Ozone measurementsOzone measurements Beer-Lambert’s LawBeer-Lambert’s Law
Discovery of UVDiscovery of UV Johann W. Ritter Johann W. Ritter 1801 projected sunlight through a prism1801 projected sunlight through a prism Chloride in each color to see the outcomeChloride in each color to see the outcome Evidence of another wave form just barely higher Evidence of another wave form just barely higher
than the violet of visible lightthan the violet of visible light
What is UV?What is UV? Ultraviolet (UV) radiation is part of the electromagnetic spectrum from Ultraviolet (UV) radiation is part of the electromagnetic spectrum from
approximately 10nm-400nm that is emitted by the sun. approximately 10nm-400nm that is emitted by the sun.
UV rays can be made artificially by passing an electric current through a UV rays can be made artificially by passing an electric current through a gas or vapor, such as mercury vapor.gas or vapor, such as mercury vapor.
UV accounts for approximately 7% of total solar radiationUV accounts for approximately 7% of total solar radiation Wavelengths: Wavelengths:
• UVA - 320 to 400 nm UVA - 320 to 400 nm • UVB - 280 to 320 nmUVB - 280 to 320 nm• UVC - 200 to 280UVC - 200 to 280 nmnm• Vacuum or Far UV – 10 to 200 nmVacuum or Far UV – 10 to 200 nm
Determining total ozone layer Determining total ozone layer thicknessthickness
Recording ground intensitiesRecording ground intensities Using literature values for amount of Using literature values for amount of
UV within a specified wavelength UV within a specified wavelength rangerange
Using a longer wavelength sensorUsing a longer wavelength sensor Beer-Lambert LawBeer-Lambert Law
Beer-Lambert LawBeer-Lambert Law
Light transmission has an exponential dependence on:Light transmission has an exponential dependence on: Concentration or thickness of the gasConcentration or thickness of the gas Path length of the lightPath length of the light Wavelength of lightWavelength of light
m m represents the path length of lightrepresents the path length of light σσ represents the wavelength dependence represents the wavelength dependence
The value of the absorption coefficient The value of the absorption coefficient σσ varies between different absorbing varies between different absorbing materials and also with wavelength for a particular material. materials and also with wavelength for a particular material.
I0 is the intensity of the incident light
I is the intensity after passing through the material
m is the distance that the light travels through the material (the path length)
A is the concentration of absorbing species in the material is the absorption coefficient of the absorber.
20
10
0
10678.2
ln
ADU
mI
IA
eII Am
Determining relative concentrationDetermining relative concentration
Rates of ChangeRates of Change Density functionsDensity functions Relation of UV Relation of UV
intensity to column intensity to column thicknessthickness
13 )(
zmIdz
zdIz
dz
dAO
103 ln)(
mI
IdzzA O
How do we use UV measurement How do we use UV measurement to determine ozone amounts?to determine ozone amounts?
Variation of absorption levels due to Variation of absorption levels due to different wavelengths of UVdifferent wavelengths of UV
UVA is completely transmitted UVA is completely transmitted through ozonethrough ozone
UVB is partially transmitted through UVB is partially transmitted through ozone.ozone.
UVC is totally attenuated by ozone.UVC is totally attenuated by ozone.
Ozone Absorption cont.Ozone Absorption cont.
““Screening” effectScreening” effect
Ozone peak absorption between 250 and 280 nm Ozone peak absorption between 250 and 280 nm
Absorption Cross SectionsAbsorption Cross Sections
Elements and compounds absorb Elements and compounds absorb certain wavelengths of light unique certain wavelengths of light unique to eachto each
Ozone (OOzone (O33) absorbs primarily UVB ) absorbs primarily UVB and UVCand UVC
The wavelengths of light (energy) The wavelengths of light (energy) absorbed is referred to as an absorbed is referred to as an absorption cross sectionabsorption cross section
Ozone Absorption Cross SectionOzone Absorption Cross Section
Y-axis: absorption cross section in cmY-axis: absorption cross section in cm22/molecule/molecule X-axis: light wavelength in nmX-axis: light wavelength in nm Hartley band 210 – 380 nmHartley band 210 – 380 nm Effectively creates a light “screen” that blocks light at Effectively creates a light “screen” that blocks light at
certain wavelengths better than otherscertain wavelengths better than others Nearly constant values for 255 ± 10 nmNearly constant values for 255 ± 10 nm
Atmospheric Cross SectionsAtmospheric Cross Sections
Ozone primarily Ozone primarily absorbs between absorbs between 200 and 325 nm200 and 325 nm
Other gasses Other gasses responsible for responsible for shorter wavelength shorter wavelength absorptionabsorption
Almost no Almost no absorption at absorption at wavelengths > 350 wavelengths > 350 nmnm
Air massAir mass
m=m=sec sec Determined from the prerecorded Determined from the prerecorded
solar zenith angles.solar zenith angles. Expresses the path length Expresses the path length
traversed by solar radiation to traversed by solar radiation to reach the earth’s surface.reach the earth’s surface.
Measuring OzoneMeasuring Ozone
Typical unit of ozone thickness is the Typical unit of ozone thickness is the Dobson Unit (DU)Dobson Unit (DU)
Defined such that 1 DU is .01 mm Defined such that 1 DU is .01 mm thick at STP and has 2.687e20 thick at STP and has 2.687e20 molecules/mmolecules/m22
STP is pressure at Earth’s surface STP is pressure at Earth’s surface (avg.) 101.325 kPa, and a (avg.) 101.325 kPa, and a temperature of 273 Ktemperature of 273 K
Payload DesignPayload Design
Electrical SystemElectrical System Mechanical SystemMechanical System Detection ArrayDetection Array Power SystemPower System Thermal SystemThermal System
Electrical DesignElectrical Design
Detector ArrayDetector Array• Filtered Photo diodesFiltered Photo diodes• Dark Current Dark Current
CompensationCompensation ControllerController
• PIC16F917PIC16F917• 8 16 Kb FRAM units8 16 Kb FRAM units
Pressure DetectionPressure Detection Temperature Temperature
Detection/RegulationDetection/Regulation
Electrical cont.Electrical cont.
PIC16F917 Circuitry solder connections
Mechanical DesignMechanical Design
BoxBox 8x6x5 inches8x6x5 inches Allows space for all Allows space for all
componentscomponents Reflective tape to Reflective tape to
prevent overheatingprevent overheating InsulationInsulation
Styrofoam sheetsStyrofoam sheets 1 inch of exterior foam 1 inch of exterior foam
retains heatretains heat Provides support for Provides support for
inner electronicsinner electronics
Detection ArrayDetection Array
PhotodiodesPhotodiodes 2 filtered2 filtered
Detect 255 ± 7 nmDetect 255 ± 7 nm 2 unfiltered2 unfiltered
Detect 230 – 305 nmDetect 230 – 305 nm Arrayed opposing each Arrayed opposing each
other at upper box other at upper box cornerscorners
ConnectorsConnectors Quick disconnect Quick disconnect
male/female connectormale/female connector
Photodiode and filter sensitivity relative to diode maximum
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
243.0 248.0 253.0 258.0 263.0 268.0
wavelength (nm)
sen
sit
ivit
y (
rel.)
Power SystemPower System Main Payload and DiodesMain Payload and Diodes
Energizer CR 2025 Energizer CR 2025 batteriesbatteries
3 V, 170 mAh each3 V, 170 mAh each HeaterHeater
Energizer CR 2025 Energizer CR 2025 batteriesbatteries
Stacked to provide 6VStacked to provide 6V CR 2025 are very CR 2025 are very
lightweightlightweight 9 total used, less mass 9 total used, less mass
than standard 9 V than standard 9 V batterybattery
Can last 5 hours with a Can last 5 hours with a constant draw of 30 mAconstant draw of 30 mA
Thermal SystemThermal System
Heat SourceHeat Source 4 4 ΩΩ power resistors power resistors
in seriesin series Power SourcePower Source
4 CR 2025 batteries4 CR 2025 batteries 6 V, 340 mAh6 V, 340 mAh
Heat provided Heat provided primarily to the primarily to the microcontrollermicrocontroller
RadiationRadiation
Sensor CalibrationSensor Calibration UV SourceUV Source
Hg, quartz envelope, lampHg, quartz envelope, lamp CalibrationCalibration
1000 watt quartz-halogen 1000 watt quartz-halogen tungsten coiled-coil tungsten coiled-coil filament lamp Standard of filament lamp Standard of Spectral RadianceSpectral Radiance
.320 m spectrograph using .320 m spectrograph using a diffraction grating a diffraction grating
600 grooves/mm blazed 600 grooves/mm blazed at 300 nm.at 300 nm.
Calibrated according to Calibrated according to NIST standards to ±2.23%NIST standards to ±2.23%
Lamp was calibrated to Lamp was calibrated to within ±.25Å within ±.25Å
Hg Lamp Calibration
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
6.00E-05
225 245 265 285 305 325
Wavelength (nm)
Inte
nsi
ty (
mic
roW
cm
^-2
str
^-1
nm
^-1
)
Calibration cont.Calibration cont. Source cont.Source cont.
253.7 nm peak253.7 nm peak Power per steradian ~ 9e-11 W stePower per steradian ~ 9e-11 W ste-1-1
Solid angle of sensor as seen from diode:Solid angle of sensor as seen from diode: AAsensorsensor/distance/distance22
DiodesDiodes FilteredFiltered
Gain set such that 1.98e-16 W produced 1.5 VGain set such that 1.98e-16 W produced 1.5 V 1.32e-19 W/mV1.32e-19 W/mV
UnfilteredUnfiltered Gain set such that 1.98e-16 W produced 2.7 VGain set such that 1.98e-16 W produced 2.7 V 7.33e-20 W/mV7.33e-20 W/mV
Voltage changes were inversely proportional to the Voltage changes were inversely proportional to the square of the distancesquare of the distance
Data AnalysisData Analysis
Data AcquisitionData Acquisition In situ intensity measurementsIn situ intensity measurements PressurePressure
Other DataOther Data Solar zenith anglesSolar zenith angles Initial intensity (outer atmosphere)Initial intensity (outer atmosphere) Absorption cross section of ozoneAbsorption cross section of ozone
Data Analysis cont.Data Analysis cont.
Ground Ground measurementsmeasurements• Total ozone columnTotal ozone column
In situ In situ measurementsmeasurements• Track changes in Track changes in
intensityintensity• Determine relative Determine relative
ozone concentrationozone concentration
10ln
mI
IA
1
zmIdz
zdI
dz
dA
Expected ResultsExpected Results Flight profile:Flight profile:
0 to 30km0 to 30km Approximately 90 minute flightApproximately 90 minute flight Increasing UV intensity with Increasing UV intensity with
increasing altitudeincreasing altitude Largest change at about 15kmLargest change at about 15km
The curve shown on this graph The curve shown on this graph represents ozone density as a represents ozone density as a function of altitudefunction of altitude
Using ozone coverage Using ozone coverage estimates for the area of estimates for the area of Palestine, TX provided by NOAA Palestine, TX provided by NOAA and taken over the last 3 years and taken over the last 3 years during this week we should see during this week we should see about 320 DU of ozone about 320 DU of ozone coverage.coverage.
ReferencesReferences ““Atmospheric Absorption Spectrum.” Atmospheric Absorption Spectrum.”
HELIOSAT-3. 20 March 2007. < HELIOSAT-3. 20 March 2007. <http://www.heliosat3.de/e-learning/rhttp://www.heliosat3.de/e-learning/radiative-transfer/rt1/AT622_section1adiative-transfer/rt1/AT622_section10.pdf0.pdf>>
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Caroll, Bradley, and Ostlie, Dale. Caroll, Bradley, and Ostlie, Dale. An An Introduction to Modern AstrophysicsIntroduction to Modern Astrophysics. . Second Edition. 2007. Addison Second Edition. 2007. Addison Wesley.Wesley.
Finlayson-Pitts, Barbara. Chemistry Finlayson-Pitts, Barbara. Chemistry of the upper and lower atmosphere: of the upper and lower atmosphere: theory, experiments, and theory, experiments, and applications. 2000. Academic applications. 2000. Academic Press.Press.
Hamatsu Corporation. Photodiode Hamatsu Corporation. Photodiode Technical Guide. 2003. March 2007 Technical Guide. 2003. March 2007 http://sales.hamamatsu.com/assets/http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htmhtml/ssd/si-photodiode/index.htm
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Mauersberger, K. Barnes, J. Hanson, D. Mauersberger, K. Barnes, J. Hanson, D. Morton, J. “Measurement of the ozone Morton, J. “Measurement of the ozone absorption cross-section at the 253.7 absorption cross-section at the 253.7 nm Mercury line.” nm Mercury line.” Geophysical Geophysical Research LettersResearch Letters 13.7 (1986): 671 – 13.7 (1986): 671 – 673.673.
NASA. Studying Earth's Environment NASA. Studying Earth's Environment From Space(SEES). June 2000. March From Space(SEES). June 2000. March 2007 2007 http://www.ccpo.odu.edu/SEES/ozone/chttp://www.ccpo.odu.edu/SEES/ozone/class/Chap_9/9_6.htmlass/Chap_9/9_6.htm
References cont.References cont. Physics Equations. 20 March Physics Equations. 20 March
2007. Eric Weisstein’s World of 2007. Eric Weisstein’s World of Physics. 20 March 2007. Physics. 20 March 2007. <http://scienceworld.wolfram.com<http://scienceworld.wolfram.com/physics/>/physics/>
Solar Zenith Angles. 20 March Solar Zenith Angles. 20 March 2007. Solar Radiation Research 2007. Solar Radiation Research Laboratory. 20 March 2007. Laboratory. 20 March 2007. <http://www.nrel.gov/midc/solpos<http://www.nrel.gov/midc/solpos/spa.html>/spa.html>
The Aerospace Corporation. The Aerospace Corporation. Microengineering Aerospace Microengineering Aerospace Systems. April 2006. March 2007. Systems. April 2006. March 2007. http://www.aero.org/publications/http://www.aero.org/publications/helvajian/helvajian-1.htmlhelvajian/helvajian-1.html
Total Ozone Mapping Total Ozone Mapping Spectrometer. 5 March 2007. Spectrometer. 5 March 2007. NASA. 20 March 2007. NASA. 20 March 2007. http://jwocky.gsfc.nasa.gov/dobsohttp://jwocky.gsfc.nasa.gov/dobson.htmln.html
Ultraviolet radiation. 19 March Ultraviolet radiation. 19 March 2007. Wikipedia. 20 January 2007. Wikipedia. 20 January 2007. 2007. <http://en.wikipedia.org/wiki/Ultra<http://en.wikipedia.org/wiki/Ultraviolet>violet>
UV Index. 11 January 2006. UV Index. 11 January 2006. National Oceanic and Atmospheric National Oceanic and Atmospheric Administration. 20 March 2007. Administration. 20 March 2007. <http://www.cpc.ncep.noaa.gov/p<http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_roducts/stratosphere/uv_index/uv_information.shtml>information.shtml>
Warneck, Peter. Warneck, Peter. Chemistry of the Chemistry of the Natural AtmosphereNatural Atmosphere. Second . Second edition. 1999. Academic Press.edition. 1999. Academic Press.
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