Transcript FRR Presentation

Stratospheric Ozone
Experiment
Team UNO
Team UNO
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Donald Swart
Christopher Barber
Michael O’Leary
Gregg Ridlon
Robert Sheffenstein
UNO Advisor
 Lawrence Blanchard
Objectives
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Measure ozone thickness as a
function of altitude using the
measurable quantities of UV intensity
Measure UVB and UVC as it is
transmitted and attenuated through
the stratosphere
Background
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What is UltraVoilet radiation
How does UV help to detect ozone?
Absorption cross sections
Ozone measurements
Beer-Lambert’s Law
Discovery of UV
Johann W. Ritter in 1801 projected a beam of
sunlight through the prism, which split the beam
into the colors of the spectrum. He them put
chloride in each color to see the outcome. The
red caused a small change while the deep violet
darkened the chloride. Ritter placed chloride in
the lightless area just beyond the violet and it
darkened as it were in a smoky fire. The was
evidence of another wave form just barely higher
than the violet of visible light. It is now known as
ultraviolet or UV light.
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What is UV?
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Ultraviolet (UV) radiation is part of the electromagnetic spectrum from
(200nm-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 - 3200 to 4000 Å
• UVB - 2800 to 3200 Å
• UVC - 2000 to 2800 Å
Determining ozone layer thickness
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Recording altitude dependent
intensities
Determining relative cloumn density
measurements above the payload
during the accent.
Beer-Lambert Law
Beer-Lambert Law
I0 is the intensity of the incident light
I1 is the intensity after passing through
the material
l 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.
I  e Am (1)
I
ln I  ln I  A (2)
 m
A
 DU (3)
2.6871016
0
0
In essence, the law states that there is an exponential dependence between
the transmission of light through a substance and the concentration of the
substance, and also between the transmission and the length of material that the
light travels through. Thus if l and α are known, the concentration of a substance
can be deduced from the amount of light transmitted by it.
The value of the absorption coefficient α varies between different absorbing
materials and also with wavelength for a particular material.
How do we use UV measurement
to determine ozone amounts?
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Variation of absorbtion levels due to
different wavelengths of UV
UVA is completely transmitted
through ozone
UVB is partially transmitted through
ozone.
UVC is totally auttenuated by ozone.
Ozone Absorption cont.
“Screening” effect
Ozone peak absorption between 250 and 280 nm (2500Å –
2800Å)
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
Atmospheric Cross Sections
Ozone Absorption Cross Section
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Y-axis: absorption cross section in
cm2/molecule
X-axis: light wavelength in nm (10Å)
Hartley band 2100Å - 3800Å
Effectively creates a light “screen” that blocks
light at certain wavelengths better than others
Air mass
m=sec q
Determined from the prerecorded solar
zenith angles.
Expresses the path length
transversed 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 2.687e16
molecules/cm2
STP is temperature and pressure at
Earth’s surface (avg.) 101.325 kPa,
298 K
Payload Design
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Electrical System
Mechanical System
Detection Array
Power System
Thermal System
Electrical Design
The photodiode signal
conditioning circuit is
intended to amplify the
output of the photodiode to a
readable analog voltage signal
which is then algebraically
summed and can be
measured by the ADC
included on the BalloonSAT
board. The combined
summing-amplifier circuit is
built to operate on a  9Volt
dual supply power source in
the form of dual 9 Volt
batteries. Power for the
payload is controlled by a
DPDT toggle Master switch,
which resides on a discrete
circuit board with the main
fuses.
Mechanical Design
The payload mechanical design will
be a cube approximately 16.5 cm
to a side. This size is optimum
allowing sufficient space for
electronics as well as the
insulation. A removable construct
is used to house the internal
components.
A shelf of foam board 10 cm by 12.5
cm with a 6.25 cm by 5cm hole in
the center will hold the
BalloonSAT. A lidless box of
dimensions 6.25 cm by 6.25 cm
and 6.25 cm tall will house the
batteries and heating element.
The box will be sized to fit
snuggly into the BalloonSAT shelf
in order to keep all components
close to the heat source to
maximize heat distribution by
conduction and radiation.
Detection Array
This system’s goal is to
collect digital data of UV
intensity in a specific
wavelength range which
will then be correlated to
effective ozone coverage.
The sensors’ wavelength
range is 2250 Å to 3200 Å
with peak sensitivity at
2800 Å. The photodiodes
are arrayed evenly around
the payload exterior, one
per corner.
Power System
Our payload will operate
on four 9V, 1200 mAh
batteries that are
capable of operating
in temperatures as
low as 233K. Two
batteries will power
our opamp circuit, one
will power the heater,
and a fourth will
power the BalloonSAT
itself.
Thermal System
The temperature control system
will consist of low mass
battery/resistor array that will
be activated by the
BalloonSAT when internal
temperatures reach 283K or
lower.
Heat will be distributed though
the payload primarily through
conduction. The heating
array will be placed in
immediate contact with power
supply for the BalloonSAT to
keep the battery at an
optimum operating
temperature. A heat sink will
be attached to the heating
elements to distribute the
heat to the BalloonSAT
components.
Sensor Calibration
We calibrated our mercury
emission at Stennis Space
Center using a 1000 watt
quartz-halogen tungsten
coiled-coil filament lamp
Standard of Spectral
Radiance and a .320 m
spectrograph/monochroma
tor using a diffraction
grating with 600
grooves/mm blazed at 300
nm. This standard was
calibrated according to
NIST standards to ±2.23%.
Our mercury lamp was
calibrated to within ±.25Å.
Calibration cont.
Using our calibrated
source we were able
to determine a voltage
change based on our
photodiodes’ exposure
to a known intensity.
The summed intensity
of all four photodiodes
was shown to be
approximately .374 V
when exposed to
intensities of ~.008W;
therefore, the average
voltage change per
photodiode is .094 V.
Data Analysis
In essence we will correlate voltage changes
to changes in the UV intensity that is
detected by our photodiodes. This will
provide us viable data that will be used in
eq. 2 to determine the column amount of
ozone. From that column amount it will
be an easy step to determine the
thickness of the ozone layer.
Tracking the changes in UV intensity
through the end of flight will also allow us
to “map” the ozone density through our
maximum altitude of 30km.
Expected Results
The flight profile will take us up
from 0 to 30km in
approximately 90 minutes. As
we climb in altitude we
naturally expect to see in
increase in UV intensity as our
payload rises above greater
amounts of atmosphere. The
largest change should be seen
at about 15km and increase as
we reach our flight peak of
30km.
The curve shown on this graph
represents ozone density as a
function of altitude; using
ozone coverage estimates for
the area of 31.78°N and
95.72°W provided by NOAA and
taken over the last 3 years
during this week we should see
approximately 305 DU of ozone
coverage.