Transcript Stratospheric Ozone Experiment

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
• Measure relative ozone concentration as
a function of altitude

Measure UVB and UVC as it is
transmitted and attenuated through
the stratosphere
Background
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What is Ultraviolet (UV) radiation
How does UV help to detect ozone?
Absorption cross sections
Ozone measurements
Beer-Lambert’s Law
Discovery of UV

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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
What is UV?
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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
Determining total ozone layer
thickness

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Recording ground intensities
Using literature values for amount of
UV within a specified wavelength
range
Using a longer wavelength sensor
Beer-Lambert Law
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.


 I0 
1
A  ln sm 
I 
A
DU 
2.6781020
Light transmission has an exponential dependence on:




I  I 0 e sAm
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.
Determining relative concentration

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Rates of Change
Density functions
Relation of UV
intensity to column
thickness
 I0 
1
A   O3 ( z ) dz  ln sm
I 
dA
 dI z 
1




 O 3 ( z )   
s
m
I
z
dz
 dz 
How do we use UV measurement
to determine ozone amounts?
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


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.
Ozone Absorption cont.

“Screening” effect

Ozone peak absorption between 250 and 280 nm
Absorption Cross Sections

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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
Ozone Absorption Cross Section
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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
Atmospheric Cross Sections
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Ozone primarily
absorbs between
200 and 325 nm
Other gasses
responsible for
shorter wavelength
absorption
Almost no
absorption at
wavelengths > 350
nm
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.
Measuring Ozone
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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
Payload Design
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Electrical System
Mechanical System
Detection Array
Power System
Thermal System
Electrical Design
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Detector Array
• Filtered Photo diodes
• Dark Current
Compensation
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Controller
• PIC16F917
• 8 16 Kb FRAM units
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Pressure Detection
Temperature
Detection/Regulation
Electrical cont.
PIC16F917
Circuitry 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
Photodiode and filter sensitivity relative to diode m axim um
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
0.12
0.1
sensitivity (rel.)

0.14
0.08
0.06
0.04
0.02
0
243.0
248.0
253.0
258.0
w avelength (nm )
263.0
268.0
Power System

Main Payload and
Diodes
 Energizer CR 2025
batteries
 3 V, 170 mAh each

Heater
 Energizer CR 2025
batteries
 Stacked to provide 6V

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
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
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Power Source
 4 CR 2025 batteries
 6 V, 340 mAh


Heat provided
primarily to the
microcontroller
Radiation
Sensor Calibration
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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
6.00E-05
5.00E-05
Intensity (microW cm^-2 str^-1 nm^-1)

Hg Lamp Calibration
4.00E-05
3.00E-05
2.00E-05
1.00E-05
0.00E+00
225
245
265
285
Wavelength (nm)
305
325
Calibration cont.

Source cont.
 253.7 nm peak
 Power per steradian ~ 9e-11 W ste-1
 Solid angle of sensor as seen from diode:
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
Asensor/distance2
Diodes
 Filtered
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Gain set such that 1.98e-16 W produced 1.5 V
1.32e-19 W/mV
 Unfiltered
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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
• Total ozone column

 I0 
1
A  ln sm 
I 
In situ
measurements
• Track changes in
intensity
• Determine relative
ozone concentration
dA
 dI z 
1




 
s
m
I
z
dz
 dz 
Expected Results
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Flight profile:
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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
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“Atmospheric Absorption Spectrum.”
HELIOSAT-3. 20 March 2007.
<http://www.heliosat3.de/elearning/radiativetransfer/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
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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 cont.
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Physics Equations. 20 March
2007. Eric Weisstein’s World of
Physics. 20 March 2007.
<http://scienceworld.wolfram.co
m/physics/>
Solar Zenith Angles. 20 March
2007. Solar Radiation Research
Laboratory. 20 March 2007.
<http://www.nrel.gov/midc/solpo
s/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/dobs
on.html
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Ultraviolet radiation. 19 March
2007. Wikipedia. 20 January
2007.
<http://en.wikipedia.org/wiki/Ultr
aviolet>
UV Index. 11 January 2006.
National Oceanic and Atmospheric
Administration. 20 March 2007.
<http://www.cpc.ncep.noaa.gov/
products/stratosphere/uv_index/u
v_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/teach
er/ozone_overhead_v8.html>