IMC 2016 June 2-5, Egmond - the Netherlands Martin Dubs, FMA, Switzerland Koji Maeda, Nippon Meteor Society and University of Miyazaki, Japan Meteor Spectroscopy, calibration

IMC 2016 June 2-5, Egmond - the Netherlands Content n Wavelength calibration, linearization of spectra n Processing and extraction of meteor spectra n Instrument response, flux calibration n Conclusions Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 2

IMC 2016 June 2-5, Egmond - the Netherlands Starting point n Camera with wide angle lens n Transmission grating –mounted perpendicular to optical axis! n Problem: –Moving meteor –Curved spectra with nonlinear dispersion –Cannot be stacked Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 3

IMC 2016 June 2-5, Egmond - the Netherlands Vector notation, wavelength calibration* n Grating perpendicular to optical (z-)axis, Rowland H. A. (1893), n Unit vector (A B C) for incident direction n Components of diffracted beam A' = A + mλG (x-axis) B' = B(y-axis) C' = sqrt(1 – A' 2 – B' 2 ) n Spectrum on CCD plane –Nonlinear dispersion –Hyperbolic curvature n Spectrum straight linear in A',B‘ n Rotational symmetry of transformation correction of lens distortion *Dubs, M. and Schlatter, P. (2015), A practical method for the analysis of meteor spectra, WGN, 43:4, p94 Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 4

IMC 2016 June 2-5, Egmond - the Netherlands Gnomonic and orthographic projection n Gnomonic, TAN, CCD plane –R = f*tan(  ) –Great circles  straight –Optimum for path, radiant –Latitude circles  hyperbola n Orthographic, SIN –R = f*sin(  ) –Great circles  ellipses –Latitude circles  straight –Optimum for spectroscopy Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 5

IMC 2016 June 2-5, Egmond - the Netherlands Image transformation, original Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 6

IMC 2016 June 2-5, Egmond - the Netherlands Transformation to orthographic projection Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 7

IMC 2016 June 2-5, Egmond - the Netherlands Orthographic projection, result Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 8

IMC 2016 June 2-5, Egmond - the Netherlands Orthographic transformation, result n Frames converted to b/w, linearized, registered n colour Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 9

IMC 2016 June 2-5, Egmond - the Netherlands Extraction of spectra n Use of standard spectroscopy software to extract spectra Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 10

IMC 2016 June 2-5, Egmond - the Netherlands Full processing n Wavelength calibration  n Flux calibration Correct for: –Background subtraction! –Vignetting, field of view flat field correction –Correction for image transformation in pre-processing oApply image transformation oExtract spectrum, calibrate wavelength n Instrument response –Grating efficiency –Camera spectral sensitivity (lens, CCD) instrument response –Atmospheric transmittance Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 11

IMC 2016 June 2-5, Egmond - the Netherlands Instrument response, theory n Grating efficiency, dependent on incidence angle: (Gsolver V4.20b, n CCD efficiency: quantum efficiency from manufacturer –Convert to flux by dividing by wavelength (E = hc/λ) n Atmospheric transmission: Ta(λ) ≈ exp[-τ(λ)/cos(z)] Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 12

IMC 2016 June 2-5, Egmond - the Netherlands Measured reference spectrum n Venus spectrum Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 13

IMC 2016 June 2-5, Egmond - the Netherlands Instrument response n Spectrum of known object (Venus, Sirius) –IR(λ) = measured spectrum(λ) / flux calibrated reference spectrum(λ) n Meteor spectrum, wavelength calibrated  flux calibrated spectrum –Flux calibrated spectrum(λ) = meteor spectrum(λ) / IR(λ) Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 14

IMC 2016 June 2-5, Egmond - the Netherlands Conclusion n Grating mounted perpendicular to camera axis n Image transformation gives linear spectra! n Precise flux calibration depends on many factors, approximations used n Looking for low cost, sensitive, high resolution, high dynamic range video camera n Full format colour camera (e.g. Sony) +Color  easy interpretation +Orders can be separated +High resolution  Bayer matrix lower sensitivity  Difficult to analyse (Instr. Resp.)  cost n Video camera (e.g. Watec) +High sensitivity +Spectral range +Low cost  Small field of view or  Low spectral resolution  Overlapping orders Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 15

IMC 2016 June 2-5, Egmond - the Netherlands Spectrum recording and processing software n UFO Capture for trigger and record video ( n IRIS and ISIS ( astronomical image processing and spectroscopy softwarehttp:// –Both by Christian Buil n ImageTools by Peter Schlatter (private communication) n Linear calibration: or _2015.pdfhttp://arxiv.org/abs/ _2015.pdf Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 16 Links

IMC 2016 June 2-5, Egmond - the Netherlands Acknowledgment n FMA (division of Swiss (Amateur) Astronomical Society) for data, discussion –Jonas Schenker, Roger Spinner (website, database) –Network of stations (Photo, Video, All sky fireball detection, Radio, Seismic), complementing Spectroscopy –Linked with EDMOND database n Peter Schlatter (Image tools) Martin Dubs, Koji Maeda, Meteor Spectroscopy, IMC 2016 page 17 Thank you!