Remote Atmospheric Sensing Device

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-Lamberts 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 280 nm
• 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
• s represents the wavelength dependence
• The value of the absorption coefficient s 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 gt 350 nm

15
Air mass

• msec q
• Determined from the prerecorded solar zenith
  angles.
• Expresses the path length traversed by solar
  radiation to reach the earths 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 Earths 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 O 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

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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
References

• Atmospheric Absorption Spectrum. HELIOSAT-3.
  20 March 2007. lthttp//www.heliosat3.de/e-learnin
  g/radiative-transfer/rt1/AT622_section10.pdfgt
• 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/kistle
  r/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

30
References cont.

• Physics Equations. 20 March 2007. Eric
  Weissteins World of Physics. 20 March 2007.
  lthttp//scienceworld.wolfram.com/physics/gt
• Solar Zenith Angles. 20 March 2007. Solar
  Radiation Research Laboratory. 20 March 2007.
  lthttp//www.nrel.gov/midc/solpos/spa.htmlgt
• The Aerospace Corporation. Microengineering
  Aerospace Systems. April 2006. March 2007.
  http//www.aero.org/publications/helvajian/helvaji
  an-1.html
• Total Ozone Mapping Spectrometer. 5 March 2007.
  NASA. 20 March 2007. http//jwocky.gsfc.nasa.gov/d
  obson.html

• Ultraviolet radiation. 19 March 2007. Wikipedia.
  20 January 2007. lthttp//en.wikipedia.org/wiki/Ult
  ravioletgt
• UV Index. 11 January 2006. National Oceanic and
  Atmospheric Administration. 20 March 2007.
  lthttp//www.cpc.ncep.noaa.gov/products/stratospher
  e/uv_index/uv_information.shtmlgt
• Warneck, Peter. Chemistry of the Natural
  Atmosphere. Second edition. 1999. Academic
  Press.
• Ozone coverage. 5 March 2007. Total Ozone
  Mapping Spectrometer. 17 May 2007.
  lthttp//toms.gsfc.nasa.gov/teacher/ozone_overhead_
  v8.htmlgt