Remote Atmospheric Sensing Device Team UNO

Donald Swart Donald Swart Cindy Gravois Cindy Gravois René Langlois René Langlois UNO Advisor Lawrence Blanchard Lawrence Blanchard

Objectives Using the measurable quantities of UV intensity: Using the measurable quantities of UV intensity: Measure total column thickness of the ozone layerMeasure total column thickness of the ozone layer Measure relative ozone concentration as a function of altitudeMeasure relative ozone concentration as a function of altitude Measure UVB and UVC as it is transmitted and attenuated through the stratosphere Measure UVB and UVC as it is transmitted and attenuated through the stratosphere

Background What is Ultraviolet (UV) radiation What is Ultraviolet (UV) radiation How does UV help to detect ozone? How does UV help to detect ozone? Absorption cross sections Absorption cross sections Ozone measurements Ozone measurements Beer-Lambert’s Law Beer-Lambert’s Law

Discovery of UV Johann W. Ritter Johann W. Ritter 1801 projected sunlight through a prism 1801 projected sunlight through a prism Chloride in each color to see the outcome Chloride in each color to see the outcome Evidence of another wave form just barely higher than the violet of visible light Evidence of another wave form just barely higher than the violet of visible light

What is UV? Ultraviolet (UV) radiation is part of the electromagnetic spectrum from approximately 10nm-400nm that is emitted by the sun. Ultraviolet (UV) radiation is part of the electromagnetic spectrum from approximately 10nm-400nm that is emitted by the sun. UV rays can be made artificially by passing an electric current through a gas or vapor, such as mercury vapor. UV rays can be made artificially by passing an electric current through a gas or vapor, such as mercury vapor. UV accounts for approximately 7% of total solar radiation UV accounts for approximately 7% of total solar radiation Wavelengths: Wavelengths: UVA to 400 nmUVA to 400 nm UVB to 320 nmUVB to 320 nm UVC to 280 nmUVC to 280 nm Vacuum or Far UV – 10 to 200 nmVacuum or Far UV – 10 to 200 nm

Determining total ozone layer thickness Recording ground intensities Recording ground intensities Using literature values for amount of UV within a specified wavelength range Using literature values for amount of UV within a specified wavelength range Using a longer wavelength sensor Using a longer wavelength sensor Beer-Lambert Law Beer-Lambert Law

Beer-Lambert Law  Light transmission has an exponential dependence on:  Concentration or thickness of the gas  Path length of the light  Wavelength of light  m represents the path length of light  σ represents the wavelength dependence The value of the absorption coefficient σ varies between different absorbing materials and also with wavelength for a particular material. I 0 is the intensity of the incident lightintensity I is the intensity after passing through the material m is the distance that the light travels through the material (the path length)path length A is the concentration of absorbing species in the materialconcentration  is the absorption coefficient of the absorber.

Determining relative concentration Rates of Change Rates of Change Density functions Density functions Relation of UV intensity to column thickness Relation of UV intensity to column thickness

How do we use UV measurement to determine ozone amounts? Variation of absorption levels due to different wavelengths of UV Variation of absorption levels due to different wavelengths of UV UVA is completely transmitted through ozone UVA is completely transmitted through ozone UVB is partially transmitted through ozone. UVB is partially transmitted through ozone. UVC is totally attenuated by ozone. UVC is totally attenuated by ozone.

Ozone Absorption cont.  “Screening” effect  Ozone peak absorption between 250 and 280 nm

Absorption Cross Sections Elements and compounds absorb certain wavelengths of light unique to each Elements and compounds absorb certain wavelengths of light unique to each Ozone (O 3 ) absorbs primarily UVB and UVC Ozone (O 3 ) absorbs primarily UVB and UVC The wavelengths of light (energy) absorbed is referred to as an absorption cross section The wavelengths of light (energy) absorbed is referred to as an absorption cross section

Ozone Absorption Cross Section Y-axis: absorption cross section in cm 2 /molecule Y-axis: absorption cross section in cm 2 /molecule X-axis: light wavelength in nm X-axis: light wavelength in nm Hartley band 210 – 380 nm Hartley band 210 – 380 nm Effectively creates a light “screen” that blocks light at certain wavelengths better than others Effectively creates a light “screen” that blocks light at certain wavelengths better than others Nearly constant values for 255 ± 10 nm Nearly constant values for 255 ± 10 nm

Atmospheric Cross Sections Ozone primarily absorbs between 200 and 325 nm Ozone primarily absorbs between 200 and 325 nm Other gasses responsible for shorter wavelength absorption Other gasses responsible for shorter wavelength absorption Almost no absorption at wavelengths > 350 nm Almost no absorption at wavelengths > 350 nm

Air mass m= sec  m= sec   Determined from the prerecorded solar zenith angles.  Expresses the path length traversed by solar radiation to reach the earth’s surface.

Measuring Ozone Typical unit of ozone thickness is the Dobson Unit (DU) Typical unit of ozone thickness is the Dobson Unit (DU) Defined such that 1 DU is.01 mm thick at STP and has 2.687e20 molecules/m 2 Defined such that 1 DU is.01 mm thick at STP and has 2.687e20 molecules/m 2 STP is pressure at Earth’s surface (avg.) kPa, and a temperature of 273 K STP is pressure at Earth’s surface (avg.) kPa, and a temperature of 273 K

Payload Design Electrical System Electrical System Mechanical System Mechanical System Detection Array Detection Array Power System Power System Thermal System Thermal System

Electrical Design Detector Array Detector Array Filtered Photo diodesFiltered Photo diodes Dark Current CompensationDark Current Compensation Controller Controller PIC16F917PIC16F Kb FRAM units8 16 Kb FRAM units Pressure Detection Pressure Detection Temperature Detection/Regulation Temperature Detection/Regulation

Electrical cont. PIC16F917Circuitry solder connections

Mechanical Design  Box  8x6x5 inches  Allows space for all components  Reflective tape to prevent overheating  Insulation  Styrofoam sheets  1 inch of exterior foam retains heat  Provides support for inner electronics

Detection Array  Photodiodes  2 filtered  Detect 255 ± 7 nm  2 unfiltered  Detect 230 – 305 nm  Arrayed opposing each other at upper box corners  Connectors  Quick disconnect male/female connector

Power System  Main Payload and Diodes  Energizer CR 2025 batteries  3 V, 170 mAh each  Heater  Energizer CR 2025 batteries  Stacked to provide 6V  CR 2025 are very lightweight  9 total used, less mass than standard 9 V battery  Can last 5 hours with a constant draw of 30 mA

Thermal System  Heat Source  4 Ω power resistors in series  Power Source  4 CR 2025 batteries  6 V, 340 mAh  Heat provided primarily to the microcontroller  Radiation

Sensor Calibration  UV Source  Hg, quartz envelope, lamp  Calibration  1000 watt quartz-halogen tungsten coiled-coil filament lamp Standard of Spectral Radiance .320 m spectrograph using a diffraction grating  600 grooves/mm blazed at 300 nm.  Calibrated according to NIST standards to ±2.23%  Lamp was calibrated to within ±.25Å

Calibration cont.  Source cont.  nm peak  Power per steradian ~ 9e-11 W ste -1  Solid angle of sensor as seen from diode:  A sensor /distance 2  Diodes  Filtered  Gain set such that 1.98e-16 W produced 1.5 V  1.32e-19 W/mV  Unfiltered  Gain set such that 1.98e-16 W produced 2.7 V  7.33e-20 W/mV  Voltage changes were inversely proportional to the square of the distance

Data Analysis  Data Acquisition  In situ intensity measurements  Pressure  Other Data  Solar zenith angles  Initial intensity (outer atmosphere)  Absorption cross section of ozone

Data Analysis cont. Ground measurements Ground measurements Total ozone columnTotal ozone column In situ measurements In situ measurements Track changes in intensityTrack changes in intensity Determine relative ozone concentrationDetermine relative ozone concentration

Expected Results  Flight profile:  0 to 30km  Approximately 90 minute flight  Increasing UV intensity with increasing altitude  Largest change at about 15km  The curve shown on this graph represents ozone density as a function of altitude  Using ozone coverage estimates for the area of Palestine, TX provided by NOAA and taken over the last 3 years during this week we should see about 320 DU of ozone coverage.

References “Atmospheric Absorption Spectrum.” HELIOSAT March “Atmospheric Absorption Spectrum.” HELIOSAT March learning/radiative- transfer/rt1/AT622_section10.pdfhttp:// learning/radiative- transfer/rt1/AT622_section10.pdf Bevington, Philip. Data reduction and error analysis for the physical sciences McGraw-Hill. Bevington, Philip. Data reduction and error analysis for the physical sciences McGraw-Hill. Caroll, Bradley, and Ostlie, Dale. An Introduction to Modern Astrophysics. Second Edition Addison Wesley. Caroll, Bradley, and Ostlie, Dale. An Introduction to Modern Astrophysics. Second Edition Addison Wesley. Finlayson-Pitts, Barbara. Chemistry of the upper and lower atmosphere: theory, experiments, and applications Academic Press. Finlayson-Pitts, Barbara. Chemistry of the upper and lower atmosphere: theory, experiments, and applications Academic Press. Hamatsu Corporation. Photodiode Technical Guide March /html/ssd/si-photodiode/index.htm Hamatsu Corporation. Photodiode Technical Guide March /html/ssd/si-photodiode/index.htm /html/ssd/si-photodiode/index.htm /html/ssd/si-photodiode/index.htm Jacob, Daniel. Introduction to atmospheric chemistry Princeton University Press: New Jersey. Jacob, Daniel. Introduction to atmospheric chemistry Princeton University Press: New Jersey. Jacobson, Mark Z. Atmospheric Pollution; Cambridge University Press Jacobson, Mark Z. Atmospheric Pollution; Cambridge University Press Kistler.Piezoelectric theory and applications March tech_theory_text.htm Kistler.Piezoelectric theory and applications March tech_theory_text.htm tech_theory_text.htm tech_theory_text.htm Mauersberger, K. Barnes, J. Hanson, D. Morton, J. “Measurement of the ozone absorption cross-section at the nm Mercury line.” Geophysical Research Letters 13.7 (1986): 671 – 673. Mauersberger, K. Barnes, J. Hanson, D. Morton, J. “Measurement of the ozone absorption cross-section at the nm Mercury line.” Geophysical Research Letters 13.7 (1986): 671 – 673. NASA. Studying Earth's Environment From Space(SEES). June March /class/Chap_9/9_6.htm NASA. Studying Earth's Environment From Space(SEES). June March /class/Chap_9/9_6.htm /class/Chap_9/9_6.htm /class/Chap_9/9_6.htm

References cont. Physics Equations. 20 March Eric Weisstein’s World of Physics. 20 March Physics Equations. 20 March Eric Weisstein’s World of Physics. 20 March m/physics/ m/physics/ Solar Zenith Angles. 20 March Solar Radiation Research Laboratory. 20 March Solar Zenith Angles. 20 March Solar Radiation Research Laboratory. 20 March s/spa.htmlhttp:// s/spa.html The Aerospace Corporation. Microengineering Aerospace Systems. April March /helvajian/helvajian-1.html The Aerospace Corporation. Microengineering Aerospace Systems. April March /helvajian/helvajian-1.html /helvajian/helvajian-1.html /helvajian/helvajian-1.html Total Ozone Mapping Spectrometer. 5 March NASA. 20 March on.html Total Ozone Mapping Spectrometer. 5 March NASA. 20 March on.html on.html on.html Ultraviolet radiation. 19 March Wikipedia. 20 January Ultraviolet radiation. 19 March Wikipedia. 20 January aviolethttp://en.wikipedia.org/wiki/Ultr aviolet UV Index. 11 January National Oceanic and Atmospheric Administration. 20 March UV Index. 11 January National Oceanic and Atmospheric Administration. 20 March products/stratosphere/uv_index/u v_information.shtmlhttp:// products/stratosphere/uv_index/u v_information.shtml Warneck, Peter. Chemistry of the Natural Atmosphere. Second edition Academic Press. Warneck, Peter. Chemistry of the Natural Atmosphere. Second edition Academic Press. Ozone coverage. 5 March Total Ozone Mapping Spectrometer. 17 May Ozone coverage. 5 March Total Ozone Mapping Spectrometer. 17 May 2007.