Quasi real-time analysis of mixed-phase clouds using interferometric out-of-focus imaging: development of an algorithm to assess liquid and ice water content

According to changes in aircraft certifications rules, instrumentation has to be developed to alert the flight crews of potential icing conditions. The technique developed needs to measure in real time the amount of ice and liquid water encountered by the plane. Interferometric imaging offers an interesting solution: It is currently used to measure the size of regular droplets, and it can further measure the size of irregular particles from the analysis of their speckle-like out-of-focus images. However, conventional image processing needs to be speeded up to be compatible with the real-time detection of icing conditions. This article presents the development of an optimised algorithm to accelerate image processing. The algorithm proposed is based on the detection of each interferogram with the use of the gradient pair vector method. This method is shown to be 13 times faster than the conventional Hough transform. The algorithm is validated on synthetic images of mixed phase clouds, and finally tested and validated in laboratory conditions. This algorithm should have important applications in the size measurement of droplets and ice particles for aircraft safety, cloud microphysics investigation, and more generally in the real-time analysis of triphasic flows using interferometric particle imaging.

[1]  Marc Brunel,et al.  Development of a spectrometer for airborne measurement of droplet sizes in clouds , 2015 .

[2]  Huanhuan Shen.  Interferometric out-of-focus imaging and digital holography for the characterization of droplets or bubbles : theory, optical design, characterization of a flow, synchronized experiments , 2014 .

[3]  M. Brunel,et al.  On the morphology of irregular rough particles from the analysis of speckle-like interferometric out-of-focus images , 2015 .

[4]  R. Adrian,et al.  Pulsed laser technique application to liquid and gaseous flows and the scattering power of seed materials. , 1985, Applied optics.

[5]  Marc Brunel,et al.  Determination of the Size of Irregular Particles Using Interferometric Out-of-Focus Imaging , 2014 .

[6]  Raymond A. Shaw,et al.  Airborne Phase Doppler Interferometry for Cloud Microphysical Measurements , 2008 .

[7]  Hans-Peter Kriegel,et al.  A Density-Based Algorithm for Discovering Clusters in Large Spatial Databases with Noise , 1996, KDD.

[8]  Jack Sklansky,et al.  Finding circles by an array of accumulators , 1975, Commun. ACM.

[9]  D. Massart,et al.  Looking for natural patterns in data: Part 1. Density-based approach , 2001 .

[10]  Pascal Lemaitre,et al.  ICONE15-10334 DEVELOPMENT OF RAINBOW REFRACTOMETRY AND OUT-OF-FOCUS IMAGING TO CHARACTERIZE HEAT AND MASS TRANSFERS IN TWO-PHASE FLOW AND AEROSOL COLLECTION PROCESSES BY DROPLETS , 2007 .

[11]  Jean-Louis Brenguier,et al.  Droplet Spectra Measurements with the FSSP-100. Part II: Coincidence Effects , 2005 .

[12]  Karim Faez,et al.  Fast Circle Detection Using Gradient Pair Vectors , 2003, DICTA.

[13]  Marc Brunel,et al.  Design of ILIDS configurations for droplet characterization , 2013 .

[14]  J. Tukey,et al.  An algorithm for the machine calculation of complex Fourier series , 1965 .

[15]  G. Konig,et al.  A new light-scattering technique to measure the diameter of periodically generated moving droplets , 1986 .

[16]  Marc Brunel,et al.  Real-time global interferometric laser imaging for the droplet sizing (ILIDS) algorithm for airborne research , 2010 .

[17]  J. van Beeck,et al.  Designing a maximum precision interferometric particle imaging set-up , 2007 .

[18]  N. Wiener.  Generalized harmonic analysis , 1930 .

[19]  Paul H. Kaye,et al.  Retrieving the size of particles with rough and complex surfaces from two-dimensional scattering patterns , 2012 .

[20]  R D Boyle,et al.  Interferometric laser imaging for droplet sizing: a method for droplet-size measurement in sparse spray systems. , 1995, Applied optics.

[21]  Marc Brunel,et al.  Limits on rough-particle sizing with low-defocus interferometric imaging , 2015 .

[22]  Christine Mounaïm-Rousselle,et al.  Droplet Sizing by Mie Scattering Interferometry in a Spark Ignition Engine , 1999 .

[23]  Marc Brunel,et al.  Interferometric laser imaging for droplet sizing revisited: elaboration of transfer matrix models for the description of complete systems. , 2012, Applied optics.

[24]  Richard Cotton,et al.  Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements , 2013 .

[25]  Koichi Hishida,et al.  Novel interferometric measurement of size and velocity distributions of spherical particles in fluid flows , 2000 .

[26]  R. Lawson,et al.  The 2D-S (Stereo) Probe: Design and Preliminary Tests of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe , 2006 .

[27]  Marc Brunel,et al.  Interferometric out-of-focus imaging simulator for irregular rough particles , 2014 .