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Remote Atmospheric Sensing Device

Remote Atmospheric Sensing Device. Team UNO. Team UNO. Donald Swart Cindy Gravois René Langlois UNO Advisor Lawrence Blanchard. Objectives. Using the measurable quantities of UV intensity: Measure total column thickness of the ozone layer

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Remote Atmospheric Sensing Device

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  1. Remote Atmospheric Sensing Device Team UNO

  2. Team UNO • Donald Swart • Cindy Gravois • René Langlois UNO Advisor • Lawrence Blanchard

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

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

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

  6. What is UV? • 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 accounts for approximately 7% of total solar radiation • Wavelengths: • UVA - 320 to 400 nm • UVB - 280 to 320 nm • UVC - 200 to 280nm • Vacuum or Far UV – 10 to 200 nm

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

  8. Beer-Lambert Law 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 s is the absorption coefficient of the absorber. • 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.

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

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

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

  12. Absorption Cross Sections • Elements and compounds absorb certain wavelengths of light unique to each • Ozone (O3) absorbs primarily UVB and UVC • The wavelengths of light (energy) absorbed is referred to as an absorption cross section

  13. Ozone Absorption Cross Section • Y-axis: absorption cross section in cm2/molecule • X-axis: light wavelength in nm • Hartley band 210 – 380 nm • Effectively creates a light “screen” that blocks light at certain wavelengths better than others • Nearly constant values for 255 ± 10 nm

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

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

  16. Measuring Ozone • 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/m2 • STP is pressure at Earth’s surface (avg.) 101.325 kPa, and a temperature of 273 K

  17. Payload Design • Electrical System • Mechanical System • Detection Array • Power System • Thermal System

  18. Electrical Design • Detector Array • Filtered Photo diodes • Dark Current Compensation • Controller • PIC16F917 • 8 16 Kb FRAM units • Pressure Detection • Temperature Detection/Regulation

  19. Electrical cont. PIC16F917 Circuitry solder connections

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. Calibration cont. • Source cont. • 253.7 nm peak • Power per steradian ~ 9e-11 W ste-1 • Solid angle of sensor as seen from diode: • Asensor/distance2 • 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

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

  27. Data Analysis cont. • Ground measurements • Total ozone column • In situ measurements • Track changes in intensity • Determine relative ozone concentration

  28. 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.

  29. “Atmospheric Absorption Spectrum.” HELIOSAT-3. 20 March 2007. <http://www.heliosat3.de/e-learning/radiative-transfer/rt1/AT622_section10.pdf> Bevington, Philip. Data reduction and error analysis for the physical sciences. 1969. McGraw-Hill. Caroll, Bradley, and Ostlie, Dale. An Introduction to Modern Astrophysics. Second Edition. 2007. Addison Wesley. Finlayson-Pitts, Barbara. Chemistry of the upper and lower atmosphere: theory, experiments, and applications. 2000. Academic Press. Hamatsu Corporation. Photodiode Technical Guide. 2003. March 2007 http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htm Jacob, Daniel. Introduction to atmospheric chemistry. 1999. Princeton University Press: New Jersey. Jacobson, Mark Z. Atmospheric Pollution; 2002. Cambridge University Press Kistler.Piezoelectric theory and applications. 2003. March 2007. http://www.designinfo.com/kistler/ref/tech_theory_text.htm Mauersberger, K. Barnes, J. Hanson, D. Morton, J. “Measurement of the ozone absorption cross-section at the 253.7 nm Mercury line.” Geophysical Research Letters 13.7 (1986): 671 – 673. NASA. Studying Earth's Environment From Space(SEES). June 2000. March 2007 http://www.ccpo.odu.edu/SEES/ozone/class/Chap_9/9_6.htm References

  30. Physics Equations. 20 March 2007. Eric Weisstein’s World of Physics. 20 March 2007. <http://scienceworld.wolfram.com/physics/> Solar Zenith Angles. 20 March 2007. Solar Radiation Research Laboratory. 20 March 2007. <http://www.nrel.gov/midc/solpos/spa.html> The Aerospace Corporation. Microengineering Aerospace Systems. April 2006. March 2007. http://www.aero.org/publications/helvajian/helvajian-1.html Total Ozone Mapping Spectrometer. 5 March 2007. NASA. 20 March 2007. http://jwocky.gsfc.nasa.gov/dobson.html Ultraviolet radiation. 19 March 2007. Wikipedia. 20 January 2007. <http://en.wikipedia.org/wiki/Ultraviolet> UV Index. 11 January 2006. National Oceanic and Atmospheric Administration. 20 March 2007. <http://www.cpc.ncep.noaa.gov/products/stratosphere/uv_index/uv_information.shtml> Warneck, Peter. Chemistry of the Natural Atmosphere. Second edition. 1999. Academic Press. Ozone coverage. 5 March 2007. Total Ozone Mapping Spectrometer. 17 May 2007. <http://toms.gsfc.nasa.gov/teacher/ozone_overhead_v8.html> References cont.

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