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>>

Bevington, Philip. Bevington, Philip. Data reduction Data reduction and error analysis for the physical and error analysis for the physical sciencessciences. 1969. McGraw-Hill.. 1969. McGraw-Hill.

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

Jacob, Daniel. Jacob, Daniel. Introduction to Introduction to atmospheric chemistryatmospheric chemistry. 1999. . 1999. Princeton University Press: New Jersey.Princeton University Press: New Jersey.

Jacobson, Mark Z. Jacobson, Mark Z. Atmospheric Atmospheric PollutionPollution; 2002. Cambridge University ; 2002. Cambridge University PressPress

Kistler.Piezoelectric theory and Kistler.Piezoelectric theory and applications. 2003. March 2007. applications. 2003. March 2007. http://www.designinfo.com/kistler/ref/thttp://www.designinfo.com/kistler/ref/tech_theory_text.htmech_theory_text.htm

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.

Ozone coverage. 5 March 2007. Ozone coverage. 5 March 2007. Total Ozone Mapping Total Ozone Mapping Spectrometer. 17 May 2007. Spectrometer. 17 May 2007. <http://toms.gsfc.nasa.gov/teach<http://toms.gsfc.nasa.gov/teacher/ozone_overhead_v8.html>er/ozone_overhead_v8.html>