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the international space station support

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laboratories where research in a range

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of scientific disciplines is conducted

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and is also a stable platform orbiting

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the earth that supports a number of

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instruments that are looking down and

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gathering data about the planet in its

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systems

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one new such instrument is scheduled to

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fly on the station later this year on a

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dragon cargo ship

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dr joseph

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zudoni at the langley research center is

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the project scientist for the

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stratospheric aerosol and gas experiment

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known as sage iii and he recently talked

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with langley's

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kristen de medio about what sage will be

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well we're

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primarily an ozone and aerosol measuring

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system

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the sage series sage three is the third

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in the series

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has been going on for a number of years

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40 over 40 years now

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and

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the data is vital for

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measuring ozone seeing how it's changing

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with time

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and also aerosols which i'll get into in

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a little bit but they're

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important for climate

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can you tell me a little bit about what

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efforts this project has grown from

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so as i said this started uh 44 almost

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41 years ago with

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this little device this is the

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stratospheric aerosol measurement

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sam

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and it flew on apollo soyuz in the

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summer of 75 1975.

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very simple little instrument

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uh

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a diode at the end of this tube is aimed

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at the sun lined up with the site here

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this was just clipped into the window

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of the apollo spacecraft they aimed it

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at the sun and let the spacecraft be uh

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our platform

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it then watched the sun set

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and what happens is as that happens

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um sunlight

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is attenuated by the earth's atmosphere

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aerosols in particular

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this was a one channel instrument had

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made a single single measurement at one

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one micron

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in the infrared

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quickly after that

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followed sam ii which was on its own

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spacecraft it lasted for over 16 years

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shortly thereafter sage one was flown

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that had

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several channels that measured not only

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the aerosol at one micron but it also

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measured

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ozone for the first time from

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in occultation

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that lasted uh three years spacecraft

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battery systems failed on that

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then in 84 we launched sage ii which is

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probably our best known

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measurement system it lasted 21 years

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fabulous data set

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important period too because during that

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time ozone was first seen to be

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declining

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in the stratosphere upper stratosphere

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so the ozone layer is primarily in the

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stratosphere

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chlorine compounds freons in particular

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were

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causing the destruction of ozone in the

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and we saw that happening and

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by the mid 80s 1980s the

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community had come along and noticed

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that the ozone was declining started to

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take action trying to figure out exactly

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what was happening

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turned out

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pretty clearly from sage data and sbuv

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to sbuv data another nasa satellite

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system that measures ozone

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the pattern was such that we knew it was

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montreal protocol was was written up

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signed by virtually every country on the

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planet

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outlawing uh the use of freons

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and uh later in the 21 year mission

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lifetime of stage 2 the

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first evidence that the chlorine

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decreases were actually

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being seen in the ozone were found so it

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was a nice a nice long

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nice long

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mission

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near the end of that time we started to

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work on sage iii we built three of those

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uh the first one was flown in 2000 on

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the russian meteor

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lasted five years

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and now we're on

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the second sage iii and it was always

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designed to go on space station

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so this next

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piece of hardware stage three is

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scheduled to fly later this year can you

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tell me a little bit more about the

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hardware and where it's going to go on

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the space station

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place there's

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lots of places to mount things we're

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going out

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near the end of one of the arms on a

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place called elc-4

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our payload comes up on the dragon trunk

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in in two pieces this is uh the first of

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the pieces it's a nader viewing platform

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and all it does is it replicates an

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interface that's

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vertical relative to the earth and

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provides one that's horizontal that's

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why it's called nader viewing this flat

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place flat plate

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faces down towards the earth the second

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will also come up on the same flight

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and the robotic system will install this

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first this will be riding piggyback and

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then it'll take this

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and install it

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like that and then this completed

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assembly

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is is uh

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our hardware it's about 750 pounds if i

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record

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correctly

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the sage instrument itself

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and this uh allows us in this

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orientation we can see

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virtually 360 degrees to the to the

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horizon

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uh the limb of the earth

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we're looking at the uh the thin

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thin layer of

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air that you can see off at the off at

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the horizon and from orbit

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the instrument will rotate an azimuth to

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find the sun

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and then there's a scan mirror in there

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which scans the field of view across the

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sun up and down so we're making

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measurements of the solar brightness the

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limb darkening curve we look at it above

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the atmosphere

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and then as the sun sets we watch that

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uh light

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decrease due to scattering absorption in

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the atmosphere

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and we're measuring the uh

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the spectrum from 290 nanometers past

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one micron and then we have another

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channel single channel at 15 15

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nanometers

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and from that

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we measure a number of things we see the

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spectral fingerprints of gases like

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ozone

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nitrogen dioxide water vapor

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oxygen we measure temperature and

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pressure from that a few other trace

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species

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and then

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the broadband residual from all of that

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is is due to aerosol

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how is the data that ch3 is going to

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take going to contribute to our

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understanding of the atmosphere and how

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we can better protect it so since the

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montreal protocol

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was enacted and apparently is very

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successful we're expecting ozone to

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recover

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it

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minimum value

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in in the late late 90s there's no real

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clear signal yet despite it being 15

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years or more

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since that onset of recovery

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and it's just because the recovery is

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very slow and you need a very precise

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measurement in order to see such a small

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change that's where occultation is ideal

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the the instrument

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effectively can degrade with time

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but because it makes its measurement of

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the sun right before or right after

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taking the atmospheric data

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any changes that the instrument has

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can be taken taken out of that

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measurement so it's a very very stable

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so that record that we have by by the

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2015-2020 time frame so right about now

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we expect ozone to have recovered about

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halfway

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and so we're going to go up there and

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we're going to see how how that's how

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that's going what the pattern of

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recovery is

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and then we'll be able to use that to

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compare with models

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to see whether or not we understand the

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reason it's recovering the way it is