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SalsaJ,
a software for data analysis
at school
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Notice:
SalsaJ is operational
but it is still a development version
http://www.euhou.net/
Feed back from TRA, pilot-school teachers and their pupils is
expected
Feed back from other interested users is most welcome
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SalsaJ: Introduction to
data analysis
� Educational tool derived from ImageJ (NIH/USA)
� Multilanguage interface
(8 languages of the project/regional setting of the system)
� Modification of menus and some tools (didactic
motivations)
� Introduction of astronomical functionalities (format,
photometry)
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SalsaJ:
a multilingual interface
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What is an image?
« Single-frame» images
� Acquired in one given
filter by CCD
� Pixel intensity coded
with false colours (or
B&W)
� Use of LUT
� Direct manipulation of
data
Format: FITS
RGB images= « real » colour
images (= 3 images)
� Obtained with webcam,
camera, web, etc.
� « True » colour
In astronomy:
� nice looking images
� relatively difficult to
produce in astronomy:
- 3 images of same area
- Registration, calibration
- Combination
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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Example of an RGB image:
470 x 441 pixels
(X,Y) coordinates
(row, column)
+ 3 intensity (RGB) values
for each pixel
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GreenRed Blue
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Look-Up Table (LUT) & False colours
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Look-Up Table (LUT) & False colours
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Look-Up Table (LUT) & False colours
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Back to astronomy…
Image of the galaxy M100 obtained with
the Faulkes Telescope Project
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Back to astronomy…
Image of the galaxy M100 obtained with
the Faulkes Telescope Project
GreenRedBlue
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Hubble Heritage Team ESA/NASA
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Hubble Heritage Team ESA/NASA
Colour images based on a
combination of 6 filters (~BVI)
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Understanding an image
Content:
Dynamic of the data/histogram
Classical image /astronomical image
Cuts: min/max; brightness and contrast tuning
Look-Up Table (LUT)
Astronomical context:
Sky background & photon noise
Variation of the observing conditions
Stellar objects
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Understanding an image
Content:
Dynamic of the data/histogram
Classical image /astronomical image
Cuts: min/max; brightness and contrast tuning
Look-Up Table (LUT)
Astronomical context:
Sky background & photon noise
Variation of the observing conditions
Stellar objects
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Variation of observing conditions:
2 exposures of the same field at 2 different epoch
+ shift (rotation) (pointing uncertainty)
+ transparency of atmosphere
+ sky background (Moon)
� Relative variation (flux ratio) between 2 stars on
one frame
� Corrections
Registration of frame
Calibration (Φ1=aΦ2+b)
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Correction of variations of
observing conditions:
Variable objects: supernovae, cepheids…
Moving objects: asteroids.
� Blink
� Subtraction of frames
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Scales, size &
cross-products
« Pixel size »:
�Physical size of pixel (e.g.15µm)
� angular size in sky (e.g. 0.3 arcsec)
[ depends on optical path followed by photons
provided with image ]
CCDXPIXE = 0.0000135 / [m] Size of pixels, in X:13.5um
CCDYPIXE = 0.0000135 / [m] Size of pixels, in Y:13.5um
CCDSCALE= 0.2783700 / [arcsec/pixel] Scale of CCD pixel on sky
SEEING = 5.252304E+00 / [pixels] frame seeing in pixels
Example for Faulkes Telescopes Project
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Dimensions &
size of craters
Image obtained with Mars Global Surveyor
(NASA/JPL/Malin Space Sciences Systems)
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Dimensions &
size of craters
Image obtained with Mars Global Surveyor
(NASA/JPL/Malin Space Sciences Systems)
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Dimensions &
size of craters
Image obtained with Mars Global Surveyor
(NASA/JPL/Malin Space Sciences Systems)
Pixel size=1500/(80-7)=20.54m/pixel
Crater size ~ (177-52)x20.54~2567.5m
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Subtraction of frames
and Galilean satellites
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Subtraction of frames
and detection of proto-
stellar discs
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Subtraction of frames
& proto-planetary
circumstellar discs
ESO
images
prepared by
D. Mouillet
(Grenoble)
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Subtraction of frames
& proto-planetary
circumstellar discs
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Subtraction of frames
& proto-planetary
circumstellar discs
Mouillet et al. 1997 A&A 324, 1083
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Registration of frames
and detection of supernovae
« Standard » procedure:
Shift, rotation (dilation – negligeable)
Subtraction
Blink or subtract
Qualitative alternative: plot profile
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Photometry &
stellar objects
Stellar objects = point sources
Convolved by the Point Spread Function (PSF) of the
« instrument » (atmosphere + optics)
PSF ~ bell-like shape function ~ Gaussian + tails
Characterised by its Full Width Half Maximum (FWHM) in
arcsec (cf pixel size)
Good sampling: FWHM ~2-3 pixel size
1/2
1/2
FWHM
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Photometry & distance
measurements in the Universe
with cepheids
Example of a cepheid star in the Small Magellanic Cloud:
measurement of the relative variation of stellar flux.
Data from
OGLE
collaboration
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Quick look: with plot profile
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Photometry & distance
measurements in the Universe
with cepheids
- Measurement of relative variation of cepheid as a function of
time
[ Absolute calibration of each frame (real luminosity in W or real
flux in Wm-2) difficult to obtain and of limited educational
interest. ]
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Aperture photometry
r1
r3
Fstar= Sum of intensity (pixels with r<r1) –Sky*N1
N1 = Number of pixels in the radius r1
Sky = Sum of intensity (pixels with r2<r <r3) / N23
N23 = Number of pixels in the corona r2 < r < r3
Use:
Instrumental value
proportional to the stellar
object flux (luminosity)
r2
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Aperture photometry &
distance measurements in the
Universe with cepheids
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Working with stacks and movies
Interval movie by Kinga Janusz
(Zespol Szkol Speckalnych No
3, Cracow, Poland)
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Working with stacks and movies
Interval movie by Kinga Janusz
(Zespol Szkol Speckalnych No
3, Cracow, Poland)
File/Import/Movie
Image/Stacks/Start animation
Image/Stacks/Convert stack to images
Image/Stacks/Make Montage
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Working with stacks and movies
Interval movie by Kinga Janusz
(Zespol Szkol Speckalnych No
3, Cracow, Poland)
File/Import/Movie
Image/Stacks/Start animation
Image/Stacks/Convert stack to images
Image/Stacks/Make Montage
Interval movie by
(Zespol Szkol Speckalnych
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Working with stacks and movies
Courtesy of M. Mayor et al.
Exercise on Extra-solar planet,
R. Ferlet
Application for the detection of planets by radial velocity
method: detection of a Doppler effect
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Perspectives:
- Addition of other astronomical functionalities (astrometry, PSF
photometry, etc.)
- Optimisation of the tool with intensive testing in schools
- Extension to biological imaging and developments of more
synergy with ImageJ (sustainability of the software).
- Translation in other languages
Sustainability
-Thomas Bouvier (UPMC) – technical and scientific referent for
future developments (link with ImageJ)
- Prospect to get additional staff support from UPMC