The Stratospheric Wind The Stratospheric Wind Interferometer for Transport Interferometer for Transport

StudiesStudies

SWIFT SWIFT

I. McDade, C. Haley, J. I. McDade, C. Haley, J. Drummond, Drummond, K. Strong, B. Solheim, T. K. Strong, B. Solheim, T. Shepherd, Y. Rochon, and the Shepherd, Y. Rochon, and the SWIFT TeamSWIFT Team

What is What is SWIFT ?SWIFT ?

© ESA

SWIFTSWIFT is the

SStratospheric WWind IInterferometer for TTransport SStudies

it is a Canadian satellite instrument designed to make global stratospheric wind measurements between 15 and 55 km

and provide simultaneous co-located ozone profiles.

Very few satellite measurements of stratospheric winds exist,

so this is something quite unique and of great interest to the international atmospheric science community

SWIFTSWIFT is just about to start Mission Phase B/C for implementation on a Canadian Space Agency Small Sat

mission called Chinook Chinook scheduled for launch in late 2010

SCIENCE OBJECTIVES OF SWIFTSCIENCE OBJECTIVES OF SWIFT

To provide global maps of wind profiles in the stratosphere in order to study:

•Atmospheric dynamics and stratospheric circulation

• Ozone transport from SWIFT’s co-located wind and ozone density measurements

•The potential of stratospheric wind measurements for improving medium range weather forecasts

 

Observational goals and required Observational goals and required performanceperformance

Obtain global vector winds to an accuracy of 3-5 m/s between 15 km and 55 km

Simultaneously obtain ozone number densities to an

accuracy of 5 % (15-30 km)

Vertical resolution 1.5 km

Horizontal sampling ~400 km along track

Continuous near-global coverage

How does SWIFTSWIFT work?

SWIFTSWIFT is based on the ‘Doppler Imaging Michelson’

concept already used by the WINDII instrument on UARS.

WINDII measured Doppler shifts in the wavelengths of airglow emission lines in the visiblevisible region of the

spectrum to determine winds in the upper mesosphere and thermosphere and made remarkable discoveries

about atmospheric tides and mesosphere and thermosphere dynamics

SWIFTSWIFT will do the same thing but use a single thermal emission line from ozone in the mid IRmid IR region

to push this technique down into the stratosphere

The Doppler Imaging Michelson concept as applied on SWIFTSWIFT

The wind produces a Doppler shift in the emission line

A Michelson interferometer produces the Fourier transform (right) of the input line spectrum (left)

The phase shift of a single fringe gives the ‘Line of Sight’ (LOS) wind speed as illustrated on the next slide

W avelength,

Inte

nsity

Path D ifference, D

Inte

nsity

~10 fringes5

Line Spectrum Interferogram

Using etalon filters, a single thermal emission line (an ozone rotation-vibration line near 9 m)

is isolated as shown in the left panel

Phase measurement and the LOS wind speedPhase measurement and the LOS wind speed

The interferometer is phase-stepped through four positions, yielding I1, I2, I3 and I4

From these the phase is computed, and from this the apparent LOS wind speed

This analysis is performed for each tangent height in the image field

A'

Iav

I1I4

Path Difference

I23I

Idrk

Ibkg

Fring

e I n

tens

i ty

SWIFT viewing geometry SWIFT viewing geometry (side view)

Image field 1X2 degree

(~ 50 km x 100 km)

SWIFT will take ‘pictures’ of bright line SWIFT will take ‘pictures’ of bright line emission from ozone in the IR regionemission from ozone in the IR region

Sample simulated SWIFTSWIFT images for phase steps 1,2,3 & 4 without noise

A'

Iav

I1I4

Path Difference

I23I

Idrk

Ibkg

Fring

e In

tens

i ty

SWIFT viewing geometry SWIFT viewing geometry (top view)

For each tangent height in the limb image SWIFTSWIFT obtains a LOS wind speed

(after correcting for the satellite velocity and Earth rotation components)

By observing at two orthogonal (or near orthogonal) directions as shown in the next slide, SWIFTSWIFT can resolve the wind speed and direction – i.e., measure the vector

wind profiles

SWIFTSWIFT viewing geometrySWIFT measures ‘line of sight ’ wind speeds in two orthogonal directions

Image field 1° x 2°(50 km x 100 km)made up of 81x 162 pixels each 0.64 km high/wide.Stratospheric coverage from 15 km to 65 km

SWIF

T

on Chin

ook

FOV 1 and 2

•Orthogonal FOVs resolve full horizontal wind vector

• Spacecraft velocity means ~8 minute delay between orthogonal components

SWIFTSWIFT Retrieval algorithm

Uses iterative Optimal Estimation with a forward model based on a SWIFT Instrument Simulator (SIS) and an atmospheric Radiative Transfer model, together with the Maximum a Posteriori (MAP) solver of Rodgers (2000), to find the FOV wind profile and ozone density profile most consistent with the observed phase-stepped images

MAP+DR

MAP

Unconstrained

SWIFTSWIFT Illustrative retrieval noise standard deviations

Wind and ozone random error standard deviations (lines) and sample retrieval errors from a single Monte Carlo realization/simulation (points) with measurement noise

Principal Investigator Ian McDade, York University, Toronto, Canada

Assistant to P.ICraig Haley (York U.)

Co.I. Co.I. Co.I. Co.I. Co.I Lead ID&C Lead GDR&SOC Lead GDV Lead GDA&M Lead ECUI&DA J .Drummond B. Solheim K. Strong T. Shepherd Y. Rochon (Dal. U. ) (York U.) (U. of T.) (U. of T.) (E. C.)

Plus the other Co-Investigators and student members listed below:

G. Shepherd, C. McLandress, W. Ward, D. Degenstein, R. Sica, W. Lahoz, C. Camy-Peyret, P. Rahnama, B. Quine, J. McConnell, E. Llewellyn, S. Turner,

etc.

ID&C = Instrument Development, Characterization and calibrationGDR&SOC = Geophysical Data Retrieval and Science Operations Centre

GDV = Geophysical Data ValidationGDA&M = Geophysical Data Analysis and Modelling

ECUI&DA = Environment Canada User Interface & Data Assimilation

SWIFTSWIFT Science Team

SWIFT on Chinook in 2010

Extra slidesExtra slides

SWIFT

SWIFTSWIFT Solid model