History / Background / Prior missions

The need for an instrument like HMI was recognized in 1996 with the conceptual design developed in 1998.

The SDO mission definition study in 2001 clarified the requirements, with real work on HMI beginning after a

competitive selection process in 2002. The Helioseismic and Magnetic Imager is a new and improved

version of the Michelson Doppler Imager (MDI) instrument on the Solar and Heliospheric Observatory

(SOHO). SOHO is a joint project of the European Space Agency and NASA. MDI was developed starting in

1988 by the same collaboration between Stanford and Lockheed teams that developed HMI. SOHO was

launched in December 1995. SOHO/MDI is presently still operating well and has completed helioseismic

and magnetic field observation of the Sun for all of solar cycle 23 and the beginning of cycle 24. HMI will

continue these important measurements from space into the next solar cycle. We hope and anticipate that

SDO/HMI will enable deeper understanding of solar processes during most of solar cycle 24.

Helioseismic & Magnetic Imager

Solar Dynamics Observatory

The HMI Team: Stanford University, Lockheed-Martin Solar and Astrophysics Laboratory,

High Altitude Observatory, and 22 Co-Investigator Institutions

HMI Major Science Goals

The primary goal of the Helioseismic and Magnetic Imager

(HMI) investigation is to study the origin of solar variability

and to characterize and understand the Sun’s interior and the

various components of magnetic activity. The HMI

investigation is based on measurements obtained with the

HMI instrument, one of the three instruments that make up the

Solar Dynamics Observatory (SDO) mission. HMI makes

measurements of the motion of the solar photosphere to study

solar oscillations and measurements of the polarization in a

specific spectral line to study all three components of the

photospheric magnetic field.

HMI produces data to determine the interior sources and

mechanisms of solar variability and how the physical

processes inside the Sun are related to surface magnetic field

and activity. It also produces data to enable estimates of the

coronal magnetic field for studies of variability in the

extended solar atmosphere which is where the Earth is. Solar

variability that effects the Earth is called “space weather.”

HMI observations will help establish the relationships between

internal dynamics and magnetic activity. In turn this will lead

to better understanding of solar variability and its effects. This

will lead to reliable predictive capability, one of the key

elements of the Living With a Star (LWS) program.

HMI investigation goals are to observe and understand these

interlinked processes of magnetic activity and internal

dynamics including:

SDO web link: http://sdo.gsfc.nasa.gov

HMI web link: http://hmi.stanford.edu

HMI/AIA JSOC data center web link: http://jsoc.stanford.edu

HMI Team

HEPL, Stanford U.

**Phil Scherrer

*Richard Bogart

*Rock Bush

*Tom Duvall, Jr.

*J.Todd Hoeksema

*Alexander

Kosovichev

*Jesper Schou

*XuePu Zhao

Jim Aloise

Art Amezcua

Taeil Bai

John Beck

Kelly Beck

Elena

Benevolenskaya

Sudeepto

Chakraborty

Keh-Cheng Chu

Millie Chethik

Nancy Christensen

Carl Cimilluca

Sebastien Couvidat

Priya Desai

Romeo Durscher

Christina Green

Thomas Hartlep

Keiji Hayashi

Tim Huynh

Stathis Ilonidis

Kevin Kempter

Irina Kitiashvili

Pavel Kosovichev

Anna Kosovicheva

Rasmus Larsen

Tim Larson

Yang Liu

Leyan Lo

James Mason

Rakesh Nigam

Konstantin

Parchevsky

Bala Poduval

M, Christina Rabello-

Soares

Brian Roberts

Kim Ross

Deborah Scherrer

Jeneen Sommers

Jennifer Spencer

Margie Stehle

Xudong Sun

Hao Thai

Karen Tian

Richard Wachter

Jeff Wade

Junwei Zhao

HEPL Staff

LMSAL

*Alan Title

*Karel Schrijver

*TedTarbell

Dave Akin

Brett Allard

Ron Baraze

M. Baziuk

Tom Berger

Paul Boerner

E. Bogle

Bob Caravalho

Brock Carpenter

C. Cheung

Roger Chevalier

K. Chulick

Tom Cruz

Jerry Drake

Dexter Duncan

Jay Dusenbury

Chris Edwards

Janet Embrich

Cliff Evans

Peter Feher

Barbara Fischer

Chuck Fischer

Sam Freeland

Frank Friedlander

Glen Gradwohl

Hank Hacook

Gary Heyman

Bob Honeycutt

Elizabeth Hui

Bruce Imai

Jerry Janecka

Romona Jimenez

Dwana Kacensky

Pete Kacensky

Claude Kam

Karen Kao

Noah Katz

Dave Kirkpatrick

Gary Kushner

Michael Levay

Russ Lindgren

Gary Linford

Andrea Lynch

Dnyanesh Mathur

Ed McFeaters

John Miles

Keith Mitchell

Sarah Mitchell

Ruth Mix

Margaret Morgan

Rose Navarro

Tom Nichols

Tracey Niles

Jackie Pokorny

Rick Rairden

Roger Rehse

J.-P. Riley

Lomita Rubio

David Schiff

Isella Scott

Cherl Seeley

Ralph Sequin

Dick Shine

Lawrence Shing

Araya Silpikul

Larry Springer

Bob Stern

Louie Tavarez

R. Timmons

Edgar Thomas

Darrell Torgerson

Shan Varaitch

Angel Vargas

Dale Wolf

Jake Wolfson

Ross Yamamoto

Carl Yanari

Kent Zickuhr

HAO

*Steve Tomczyk

Juan Borrero

Santiago

Gregory L. Card

Anthony Darnell

Rebecca C. Elliott

David Elmore

Jonathan Graham

Aimee Norton

Bruce Lites

Arturo Lopez Ariste

Matthias Rempel

Hector Socas-

Navarro

JPL

Michael Turman

U. of Colorado

*Juri Toomre

Benjamin Brown

Gwen Dickenson

Nicholas Fetherstone

Deborah Haber

Bradley Hindman

Swati Routh

Regner Trampedach

NASA Ames

*Nagi Mansour

*Alan Wray

NJIT, BBSO

*Phil Goode

Vasyl Yurchyshyn

NWRA/CoRA

*Doug Braun

*Tom Metcalf†

*Charlie Lindsey

Graham Barnes

Aaron Birch

Ashley Crouch

K. D. Leka

Orion Poplawski

Martin Woodard

NSO

*Frank Hill

*Rachel Howe

Walter Allen

Olga Burtseva

Irene Gonzalez-

Hernandez

Kiran Jain

Shukur Kholikov

Rudi Komm

Igor Suarez-Sola

Sushanta Tripathy

Predictive Science

Inc.

*Jon Linker

Michael Choy

Zoran Mickic

Pete Riley

Timofey Titov

Janvier Wijaya

SAO

*Sylvain Korzennik

Alisdair Davey

UCLA

*Roger Ulrich

U. of Hawaii

*Jeff Kuhn

Marcelo Emilio

Isabelle Scholl

UMCP

*Judit Pap

USC

*Ed J. Rhodes, Jr.

Shawn Irish

Johann Reiter

Anthony Spinella

Yale University

*Sarbani Basu

Charles Baldner

International

Aarhus University,

DK

*Joergen

Christensen-

Dalsgaard

Cambridge, UK

*Douglas Gough

ESA

*Bernhard Fleck

IIAP, IN

Dipankar Banerjee

Siraj Hasan

S. Paul Rajaguru

MPS, DE

*Sami Solanki

Raymond Burston

Laurent Gizon

Shravan Hanasoge

Yacine Saidi

MSSL, UK

*Len Culhane

Elizabeth Auden

NAOJ, JP

*Takashi Sekii

Kaori Nagashima

RAL, UK

*Richard Harrison

Sheffield Univ. UK

*Mike Thompson

Univ. Tokyo, JP

*Hiromoto Shibahashi

Industrial

e2v - CCDs

Gary Auker

Rob Wilson

RAL - Cameras

Nick Waltham

Light Machinery

- Michelson

interferometers

John Hunter

Ian Miller

Andover

Corporation &

Zygo Corporation

- Filters

John Cotton

H. Magnetics

- motors

Ralph Horber

• Convection-zone dynamics and the solar dynamo;

• Origin and evolution of sunspots, active regions

and complexes of activity;

• Sources and drivers of solar activity and

disturbances;

• Links between the internal processes and

dynamics of the corona & heliosphere;

• Precursors of solar disturbances for space-

weather forecasts.

HMI Implementation

The HMI instrument design and observing strategy are based on the highly successful MDI instrument, with several important

improvements. HMI will observe the full solar disk in the Fe I absorption line at 6173Å with a resolution of 1 arc-second. HMI

consists of a refracting telescope, a polarization selector, an image stabilization system, a narrow band tunable filter and two

4096² pixel CCD cameras with mechanical shutters and control electronics. The continuous data rate is 55Mbits/s.

Images are made in a sequence of tuning and polarizations at a 4-second cadence for each camera. One camera is dedicated to

a 45s Doppler and line-of-sight field sequence while the other to a 90s vector field sequence. All of the images are downlinked

for processing at the HMI/AIA Joint Science Operations Center at Stanford University.

SDO

and

HMI

HMI Optics

Package

*Co-Investigator, **Principal Investigator, HEPL: W.W. Hansen Experimental Physics Laboratory; LMSAL: Lockheed-Martin Solar and Astrophysics

Laboratory; HAO: High Altitude Observatory; JPL: Jet Propulsion Laboratory; NJIT,BBSO: New Jersey Institute of Technology, Big Bear Solar Observatory;

CoRA: Colorado Research Associates; NSO: National Solar Observatory; SAO: Smithsonian Astrophysical Observatory; UMCP: University of Maryland

College Park; ESA: European Space Agency; IIAP: Indian Institute of Astrophysics; MPS: Max Planck Institute for Solar System Research; MSSL: Mullard

Space Science Laboratory; NAOJ: National Astrophysical Observatory of Japan; RAL: Rutherford Appleton Laboratory. †Deceased.

HMI Electronics

Box

The Solar Dynamics Observatory will be placed into an inclined

geosynchronous orbit to maximize sunlit hours while providing

high bandwidth telemetry. Launch is scheduled for February 2010.

HMI Science: Solar Interior Dynamics and Photospheric Magnetic Fields

Helioseismology is the study of solar interior

structure and dynamics via analysis of the

propagation of waves through the Sun’s interior.

How HMI Works: HMI measures a long sequence of

Dopplergrams (maps of solar surface velocity) and magnetograms

(maps of magnetic field at the Sun’s visible surface, the

photosphere.) Each map of motion or magnetic field is computed on

the ground from a set of 12 images of the Sun, each obtained with a

different combination of wavelength tuning and polarization direction.

The wavelength tuning compared to the chosen solar spectral

absorption line is shown in this figure. The black line at the top

shows the solar iron spectral line profile. The colored lines show the

HMI filter transmission profiles at 7.6 pm tuning spacing. The black

The downward propagating waves are refracted upward by the temperature

gradient and the upward propagating waves are reflected inward by the

drop in density at the surface.

The Sun is filled with acoustic waves with periods The travel times of these waves depend on the temperature, composition,

near five minutes. These waves are made by the motion, and magnetic fields in the interior. The visible surface moves when

near surface convection.the waves are reflected. HMI measures this motion enabling the wave

frequency, phase, and amplitude to be measured.

Analysis of travel times over a multitude of interior paths enables inference

of internal conditions.

Solar Magnetic Fields: The Sun is permeated by magnetic fields on

multiple scales from “flux tubes” smaller than 70km to 30,000km sunspots

to the Sun-covering magnetic network. It is the dynamically changing

magnetic fields that is the source of nearly all solar variability that effects

the Earth and human technological systems.

HMI will provide the first full-disk continuous observations of solar magnetic

fields in all orientations. Prior measurements (e.g. MDI) measured only the

component of the field along the line of sight to the observer. The new

measurements should improve our understanding of the 3-D structure of

the evolving field. We can only measure the fields in the layer of the

atmosphere where most all of the light originates (photosphere) and we can

then compute estimates of the field in the upper atmosphere where AIA

observes the effects of the fields.

HMI Specifications

Central wavelength

Filter bandwidth

Filter tuning range

Central wavelength drift

6173.3 Å

76 mÅ

680 mÅ

0.1 Å (Fe I line)

10 mÅ fwhm

68 mÅ

< 10 mÅ during any 1 hour period

Field of view

Angular resolution

Detector resolution

Focus adjustment range

Pointing jitter reduction factor

Image stabilization offset range

Pointing adjustment range

Dopplergram cadence

Camera Image cadence

Timing

Science telemetry allocation

Instrument design lifetime

> 2000 arc-seconds

better than 1.5 arc-seconds

0.50

0.01 arc-second / pixel

4 depths of focus

> 40 db with servo bandwidth > 30 Hz

>

>

14 arc-seconds in pitch and yaw

200 arc-seconds in pitch and yaw

dashed line is the profile used for the continuum filtergram. A

picture is made for each tuning and the results are used to

compute velocity and magnetic field strength at each pixel.

The polarization selector needed for magnetic field

measurements is a set of waveplates that can be rotated to

different angles for detection of different polarization

parameters (called Stokes I,Q,U,V)

The wavelength selection and tuning is accomplished with a

set of successively narrower bandpass filters. These are the

front window, blocking filter, a five element Lyot filter, and two

Michelson interferometers. The last three filter stages can be

tuned by rotating retarder waveplates. The combination results

in a 7.6 pm bandpass that can be tuned over 68 pm and is

centered on the 617.3 nm solar line. (1 pm = 10 mǺ)

Doppler Velocity

Cadence45 s

Precision13 m/s

Zero point accuracy0.05 m/s

Dynamic range±6.5 km/s

Line-of-Sight Magnetic Flux

Cadence45 s

Precision10 G

Zero point accuracy0.05 G

Dynamic range± 4 kG

Continuum Intensity

Cadence45 s

Precision

Accuracy pixel to pixel

Vector Magnetic Field

Cadence

Precision:

Polarization

Sunspots (1kG<|B|<4kG) *

|B|

Azimuth

Inclination

Quiet Sun (0.1kG<|B|<2kG) *

|B|

Total flux density

Azimuth

Inclination

0.3%

0.1%

90 s

0.22%

18G

0.6º

1.4º

220 G

35 G

15º

18º

< 50 seconds

< 4 seconds

< 1 µs stability, < 100 ms absolute

< 55 Mbits/s

> 5.3 years

Examples of science data

products from SOHO/MDI.

Improved versions of these

can be made with HMI

observations.

A. Sound speed variations relative

to a standard solar model.

B. Solar cycle variations in the

sub-photospheric rotation rate.

C. Solar meridional circulation and

differential rotation.

D. Sunspots and plage contribute

to solar irradiance variation.

E. MHD model of the magnetic

structure of the corona.

F. Synoptic map of the subsurface

flows at a depth of 7 Mm.

G. SOHO/EIT image and

magnetic field lines computed

from the photospheric field.

H. Active regions on the far side of

the sun detected with

helioseismology.

I. Vector field image showing the

magnetic connectivity in

sunspots.

J. Sound speed variations and

flows in an emerging active

region.

B – Solar Dynamo

J – Sunspot Dynamics

C – Global Circulation

HMI Optics Package Principal Components

Shutter Assembly

Focal Plane Assembly

ISS Beam-splitter Assembly

Limb Sensor Assembly

ISS Electronics Box

Fold Mirror Assembly

BDS Beam-splitter

Michelson Interferometer

I – Magnetic

Connectivity

A – Interior Structure

D – Irradiance Sources

Alignment Mechanism

Filter Oven Assembly

Camera Electronics Box

Telescope Assembly

Lyot Filter Assembly

Oven Controller E-Box

ISS Mirror Assembly

H – Far-side Imaging

E – Coronal Magnetic Field

Primary Lens Assembly

Front Door Assembly

Z

Focus Mechanism

G – Magnetic Stresses

F – Solar Subsurface Weather

Hollow Core Motors

X

Optical Characteristics:

Effective Focal Length: 495 cm

Telescope Clear Aperture: 14 cm

Y

Secondary Lens

Mechanical Characteristics:

Box: 0.84 × 0.55 × 0.16 m

Over All: 1.19 × 0.83 × 0.30 m

Mass: 44.0 kg

First Mode: 73 Hz