Transcript Solar space instrumentations and techniques

UCL DEPARTMENT OF SPACE AND CLIMATE PHYSICS
MULLARD SPACE SCIENCE LABORATORY
Space Instrumentation
Louise K Harra
UCL-Mullard Space Science Laboratory
See text book ‘Space Science’ edited by Harra & Mason
Chapter on space instrumentation by Culhane.
Introduction
Spacecraft are used for
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Remote observation of the environment beyond Earth
In-situ observation of the extra-terrestrial environment
Observation of Earth’s surface from Space
This lecture will cover:
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Why we need to go into space.
Features of space instrumentation - and what conditions they have to
survive.
Use of multilayer coatings to reflect EUV and X-rays
Photon detection by CCDs
Choice of orbits and their restrictions
Future solar instrumentation
Design your own instrument!
Electromagnetic Spectrum
Quantum nature of radiation:
En = hn = hc/l
 Radio/Microwave
(Frequency/Wavelength)
→ THz, GHz, MHz, cm, m
 Infra-red/Sub-mm
(Wavelength)
→ mm, mm
 Visible/UV/EUV
(Wavelength)
→ Å, nm
 X-ray, g-ray
(Photon Energy)
→ eV
Regions of the Spectrum
Wavelength (m)
Frequency (Hz)
Energy (J)
Radio
> 1 x 10-1
<3 x 109
<2 x 10-24
Microwave
1 x 10-3 – 1 x 10-1
3 x 109 – 3 x 1011
2 x 10-24 – 2 x 10-22
Infrared
7 x 10-7 – 1 x 10-3
3 x 1011 – 4 x 1014
2 x 10-22 – 3 x 10-19
Optical
4 x 10-7 – 7 x 10-7
4 x 1014 – 7.5 x 1014
3 x 10-19 – 5 x 10-19
UV
1 x 10-8 – 4 x 10-7
7.5 x 1014 – 3 x 1016
5 x 10-19 – 2 x 10-17
X-ray
1 x 10-11 – 1 x 10-8
3 x 1016 – 3 x 1019
2 x 10-17 – 2 x 10-14
g-ray
< 1 x 10-11
> 3 x 1019
> 2 x 10-14
What gets through the Earth’s atmosphere
Photon absorption by the atmosphere of the Earth
•X-rays with E>50keV can penetrate to ~30 km above the Earth’s atmosphere
- hence can be measured with a balloon flight
•In practical terms you have to go into space to measure these wavelengths
•Even for the optical band (400-1000 nm) this is affected by turbulence - this
can be reduced by adaptive optics techniques which have best performance
in the IR with l<1mm
Telescope design
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Wolter type I telescope
• Grazing incidence: for short wavelengths EM
radiation behaves like ordinary light rays if it
strikes surfaces at a shallow enough angle.
• Normal incidence: the reflectivity of materials in
the soft X-ray/EUV range decreases with
wavelength - need multilayers to enhance R.
X-rays absorb - how do we measure them?
Traditional solution for X-ray/EUV astronomy:
grazing incidence telescopes
Chandra X-ray telescope
EUV Multilayer instruments for Solar Physics:
SOHO, TRACE…
Solar-B/EIS…
Multilayers enable operation at normal incidence.
[a-Si(38Å)/Mo(33Å)]x40
Introduction
Measured
Reflectance
d
~70Å
Fit, ~7Å
=3.0 deg
a-Si
Mo
Si substrate
Wavelength [Å]
For a periodic multilayer,
Bragg’s law, as in a crystal:
ml  2d cos 
• Schematic of the TRACE EUV telescope is shown below – a 0.3 m Cassegrain system
• Primary and secondary mirrors are sectored in four quadrants, three of which have Mo 2C/Si layers
• Quadrant shutter allows one sector at a time to view the Corona and register images on the CCD in
the appropriate passband
• Mo2C/Si layers have somewhat enhanced performance compared to Mo/Si
Remote Sensing of Sun
• Information only derived from solar radiation
• 4 ‘measurables’: t, x, y, λ
• Detectors are 2-dimensional, time obtained by
repeated exposures
• Something has to go!
– x, y or λ
Remote Sensing of Sun
• Two approaches
• Filtergrams
– Filter out a small portion of the spectrum, and take X-Y images
• Spectroscopy
– Throw out one of the spatial dimensions to obtain wavelength resolution
Filtergrams: EIT example
Spectroscopy: CDS example
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• 2D images are built up by rastering
MOSES concept
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We will achieve spectroscopy and imaging
SIMULTANEOUSLY over a large field of view
The MOSES rocket will now be launched on 31st
January - first results will be out asap after this.
The design is simple with no moving parts.
The reconstruction can be carried out by a simple
subtraction of the orders - this will give you a first
‘quick-look’ of the bulk flows observed.
For more detailed analysis, algorithms such as
SMART are used.
MOSES first results
CDS observation: 28 mins.
MOSES spectral image: 20s
Resolution limits
• Spatial resolution is limited by diffraction.
• The resolution of a given instrument is proportional to the
diameter of its objective, and inversely proportional to the
wavelength of the light being observed.
• So for example, when the spacecraft study of Orbiter
determined that the aperture had to be reduced because
of thermal problems, this had an impact on the resolution.
Charge coupled devices - behaviour
• Quantum efficiency: Not every photon falling onto a detector will
actually be detected and converted into an electrical impulse. The
percentage of photons that are actually detected is known as the
Quantum Efficiency (QE).
• Wavelength range: CCDs can have a wide wavelength range ranging
from about 400nm (blue) to about 1050nm (Infra-red) with a peak
sensitivity at around 700nm. However, using a process known as
backthinning, it is possible to extend the wavelength range of a CCD
down into shorter wavelengths such as the Extreme Ultraviolet and Xray.
• Dynamic range: the dynamic range of a CCD is usually discussed in
terms of the minimum and maximum number of electrons that can be
imaged. As more light falls onto the CCD, more and more electrons
are collected in a potential well, and eventually no more electrons can
be accommodated within the potential well and the pixel is said to be
saturated.
CCDs - more on
behaviour
a)
b)
• Noise: Dark current - i.e thermally generated noise. At room
temperature, the noise performance of a CCD can be as much as
thousands of electrons per pixel per second. Consequently, the full
well capacity of each pixel will be reached in a few seconds and the
CCD will be saturated. Dark current can be massively reduced by
cooling.
• Readout noise - the ultimate noise limit of the CCD is the readout
noise. The readout noise originates from the conversion of the
electrons in each pixel to a voltage on the CCD output node (a typical
value would be around 4mV per electron). The magnitude of this noise
depends on the size of the output node.
Challenges in orbit
• Vacuum of space: contaminants can readily move
from one part of an instrument to another, high
voltage discharge is an issue.
• Sun’s thermal radiation: typically a satellite will be
illuminated by the Sun on one side (T~6000K) and
the Earth (T~300K) or space (~4K) on the other.
• Ionising radiation - commercial electronics are not
suitable as they are not radiation hard
Launching
• The primary driver for cost of the launch is the
mass.
• This will then restrict the size of the spacecraft
• The instruments will be subject to severe vibration
and acoustic noise from the rocket motors.
Mechanical shocks will also be present caused by
e.g. the first stage separation.
Vibration testing
Solar-B going through its paces
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Telemetry
• Telemetry is a crucial constraint for solar satellite
observations, limiting the cadence of imaging instruments,
and reducing the quantity of spectral information produced
• Initially, EIT was allocated 1 kilobits/s (kbs) telemetry rate,
corresponding to only 6 full-disk images/day!
• SOHO has a standard science telemetry rate of 40 kbs
Choice of Orbit
• Low Earth Orbit (LEO) - orbit between the atmosphere and
the Van-Allen radiation belts. This minimises the damaging
effect of high energy particles. They are 200-1200km
above the Earth with an orbital period of 90-100 mins. Can
be prepared by the space shuttle (e.g. HST, SMM)
• High Earth Orbit (HEO) - is above the radiation belts more expensive to launch (e.g. XMM-Newton). Apogee >
30,000km.
• Geosynchronous orbit - has the same orbital period as the
sidereal period of the Earth. It has an altitude of 42,164km.
IUE was operated this way - it meant full time contact.
Leaving Earth Orbit
• The Lagrangian points are the 5 points in IP space where
a spacecraft can be stationary relative to the Sun and the
Earth (for example).
• SOHO flies at the Lagrangian point of the Earth’s orbit
about the Sun, in the same orbit as the Earth, & kept in
place by the shepherding effect of the Earth’s gravity.
• Ulysses was launched by the Space Shuttle Discovery in
1990. It headed out to Jupiter, arriving in February 1992 for
a gravity-assisted manoeuvre that swung the craft into its
unique solar polar orbit.
Where is Ulysses today?
STEREO’s orbit
Solar Orbiter’s orbit
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Take a break! Design your own instrument
• In the 10 min break think about what science
question you would like answered and can’t with
current/future instrumentation.
• Come up with science requirements that would
define the instrument - spatial, temporal, spectral
resolutions, field of view etc. etc.
• We’ll discuss this at the end of the lecture.
Solar-B
• Japan/USA/UK mission
• Follow-up to Yohkoh
• 3 scientific instruments
– X-ray imager (XRT)
– EUV spectrometer (EIS)
– Optical telescope (SOT)
• Launch 2006
• Mission aim:
– Solar-B will study the connections between fine magnetic field
elements in the photosphere and the structure and dynamics of the
entire solar atmosphere.
• The ‘Hubble’ of Solar Physics
Solar Optical Telescope
• 0.5 m optical telescope feeds the Focal Plane
Package (FPP)
– Telescope diffraction-limited to ~0.25 arcsec resolution
– Maximum field-of-view: 2.75x2.75 arcmin²
Focal Plane Package
• Spectro-Polarimeter
– Based on successful HAO Advanced Stokes Polarimeter
– Takes spectra at different polarisations to allow vector magnetic
field to be determined
– Raster images produced; pixel size 0.16 arcsec; 164x328 arcsec²
field-of-view
• Narrowband Filter Imager
– 0.08 arcsec pixels; 164x328 arcsec² field-of-view
– Vector magnetograms obtained by rapidly taking images at
different wavelengths and polarizations
• Broadband Filter Imager
– 0.05 arcsec pixels; 100x200 arcsec² field-of-view
– White light images; velocitygrams; magnetograms
Solar-B – XRT
• X-Ray Telescope
• Direct successor to the SXT on Yohkoh
• Key features:
– 2 arcsec resolution (1 arcsec pixels)
– Greater sensitivity to cool corona (1-2 MK)
– 34x34 arcmin² field-of-view (full solar disk)
EUV Imaging Spectrometer
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UK-led instrument (PI: Len Culhane, MSSL)
Spectra in 170-210Å and 250-290Å wavelength ranges
Field-of-view 6 x 8 arcmin²
Spatial scale: 1 arcsec pixels
Spectral scale: 0.02Å pixels
– Line centroids ~3 km/s; line widths ~20 km/s
Solar-B Co-Alignment
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EIS and XRT are physically attached to the SOT
XRT can not be pointed independently of SOT
XRT co-alignment performed by taking white light images
In order to obtain rasters, EIS has internal mirror motions
to change area being observed
• Co-alignment of EIS with XRT will be made through cool
XRT channels
STEREO
• Solar-Terrestrial Relations Observatory
• Two identical spacecraft leading and
following the Earth
• Launch 2005
• Four instrument packages
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SECCHI
PLASTIC
SWAVES
IMPACT
• Goal:
– Understand the origin and consequences of
CMEs
STEREO Mission Phases
• Phase 1 (first 400 days; α50°)
– 3-D structure of the corona
• Phase 2 (days 400 to 800; 50°α110°)
– Physics of CMEs
• Phase 3 (days 800 to 1100; 110°α180°)
– Earth-directed CMEs
• Phase 4 (after day 1100; α>180°)
– Global solar evolution and space weather
STEREO – SECCHI
• Instruments
– EUVI (EUV imager)
– COR1 & COR2 (white light coronagraphs)
– HI (heliospheric imager)
• EUVI and CORs are direct follow-ons to EIT and
LASCO
SECCHI – EUVI
• Successor to EIT
• Image channels: Fe IX 171, Fe XII 195, Fe XIV
211, He II 304
• Larger detector (2048x2048 pixels) leads to
– Higher spatial resolution (1.6 arcsec vs. 2.5 arcsec)
– Larger field-of-view (1.7 Rsun vs. 1.4 Rsun)
• Higher telemetry ensures higher image cadence
SECCHI – COR1 & COR2
• Two coronagraphs do a similar job to the three
coronagraphs of LASCO
• COR1
– 1.1-3.0 Rsun; 7.5 arcsec pixels
– Measures polarization
• COR2
– 2-15 Rsun; 14 arcsec pixels
– Higher spatial resolution and time cadence than LASCO C3
Heliospheric Imager (HI)
• UK-led instrument (PI: Richard Harrison, RAL)
• Will obtain a new type of solar data: imaging of
CMEs out to 1 a.u.
• Images not Sun-centred (unlike coronagraphs)
• Two independent telescopes (HI-1, HI-2) with halfangle fields-of-view of 10º and 35º
Solar Dynamics Observatory
• Launch 2007
• Part of International Living with a Star Program
• 3 instrument packages selected by NASA:
– AIA (imaging and coronagraph)
– HMI (magnetograph)
– EVE (extreme ultraviolet irradiance monitoring)
• Geosynchronous orbit
– Very high telemetry rate (160 Mbs)
SDO
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HMI (Helioseismic and Magnetic Imager):The Helioseismic and Magnetic
Imager will extend the capabilities of the SOHO/MDI instrument with
continuous full-disk coverage at higher spatial resolution. PI: Phil Scherrer, PI
Institution: Stanford University
AIA (Atmospheric Imaging Assembly)The Atmospheric Imaging Assembly will
image the solar atmosphere in multiple wavelengths to link changes in the
surface to interior changes. Data will include images of the Sun in 10
wavelengths every 10 seconds. PI: Alan Title, PI Institution: Lockheed Martin
Solar Astrophysics Laboratory.
EVE (Extreme Ultraviolet Variablity Experiment):The Extreme Ultraviolet
Variablity Experiment will measure the solar extreme-ultraviolet (EUV)
irradiance with unprecedented spectral resolution, temporal cadence, and
precision. Measures the solar extreme ultraviolet (EUV) spectral irradiance to
understand variations on the timescales which influence Earth's climate and
near-Earth space. PI: Tom Woods, PI Institution: University of Colorado.
Solar Orbiter
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ESA mission to be run jointly with Bepi-Colombo
Launch ~2015-2017
Will get as close as 0.2 a.u.
Both in-situ and remote sensing instrument packages
Remote sensing:
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Visible imager and magnetograph
EUV imager
EUV spectrometer
Coronagraph
Orbit
XY-plane trajectory plot including extended mission
1.5
1
0.5
S
Y [AU]
• Each orbit is around
150 days
• Every 3rd orbit a flyby of Venus gives an
out of the ecliptic
kick to the spacecraft
• Orbit reaches
latitudes of ~30°
during extended
mission (> 4 years)
E
0
-1.5
-1
-0.5
0
0.5
1
1.5
t
V
-0.5
-1
-1.5
X [AU]
Solar Orbiter – Latitude Range
Getting started with AstroGrid: 3 steps
STEP 1
• Launch the AstroGrid workbench from
http://software.astrogrid.org/jnlp/workbench/workbench.jnlp
• Search for solar and STP data with HelioScope. (Look under the workbench “Data
Discovery” tab.)
• Load solar and STP data from HelioScope with Aladin, TOPCAT, and other tools listed at
http://plastic.sourceforge.net.
STEP 2
• Register for an AstroGrid account for access to remote applications and virtual storage.
Email email [email protected] for a username.
• Try out the solar movie maker parameterized workflow (look in “Science Examples” under
the workbench “Workflow” tab).
• Look for other solar and STP data analysis, visualization and modelling applications in
the Task Launcher (also under the workbench “Workflow” tab).
STEP 3
• Find out more about advanced data searches and applications by clicking the workbench
“Advanced” tab or looking at http://www2.astrogrid.org/documentation/ag-help-docs/.
Solar data with AstroGrid
The AstroGrid Helioscope tool finds solar and STP data from virtual
observatories in the UK, US and Europe.
How to:
1. Launch the AstroGrid workbench and click “HelioScope”.
2. Enter a start and stop time. Check “time series” and / or “graphic”. Click search.
3. Double click a “time bubble” to select data.
Current Datasets:
• Solar: TRACE; SOHO EIT,
CDS, MDI, and LASCO
• STP: Cluster, ACE, Wind spacecraft,
Ulysses, Polar spacecraft
Coming soon:
• Solar-B, Yohkoh
AstroGrid workbench “Data Discovery” tab.
AstroGrid HelioScope solar data search tool.
Solar data analysis with AstroGrid
The AstroGrid Task Launcher and Workflow Builder provide access to
remote processing tools, either as stand alone applications or as part
of a larger workflow.
How to:
1.
Launch the AstroGrid workbench and
click the “Workflow” tab.
2.
Click the “Science Examples” tab to
run a parameterized workflow.
3.
Or click the “Task Launcher” to run a
single application.
4.
Or click the “Workflow Builder” to
construct a complex workflow.
Solar and STP applications:
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Solar Movie Maker
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Solar Overlay
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Solar Data Reductor
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CTIP model and movie maker
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Plot STP
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GNUPlot
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ACE
AstroGrid application launcher showing application search
on “solar”.
Solar movie maker: example
1. Click “Science Examples”.
2. Log in and select “solar movie maker.”
3. Enter instrument name, start time and stop
time and press the OK button.
4. View finished EIT movie: (example)
http://www.mssl.ucl.ac.uk/~eca/Astrogrid/eitmovie.mpg
Future, future instruments
• What are they???