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Salsa

Salsa is a novel device which allows acquisition and analysis of four polarisation states.

Description

Salsa is being used in applications which require the detection of man-made objects in complex backgrounds, including military surveillance and remote sensing. This is because man-made objects generally have smooth surfaces which have a higher degree of polarization than natural objects. Degree of polarization imaging has been proved to be able to detect man made object in shadows

Salsa performs:

  • Fast linear Stokes polarization imaging in the visible
  • Passive and Active polarization imaging

Salsa enables:

  • Linear Stokes Polarization Analysis
  • Image contrast enhancement
  • Imaging through canopies and shades
  • Target Detection & Identification
  • Complex 3D surface reconstruction

The first polarization imaging systems were made with mechanical rotation of polarizer(s) and waveplate(s) between each frame. Those systems are usually quite slow and very sensitive to motion of the scene between frames. Bossa Nova Vision use a patented polarization filter based on ferroelectric liquid crystals (FLC) which dramatically reduces the time required to acquire the polarization frames. This architecture allows fast acquisition of four polarization frames that are later used to calculate the Stokes vector for each pixel of the image.

The critical point is to link the polarization raw frames to the Stokes parameters. BNV developed a calibration procedure to determine the calibration matrix that permits to calculate the four Stokes parameters for any incident polarization state, partial or total.

Principle of operation

Along with the intensity and the spectrum, the polarization of light carries abundant information. The Stokes formalism allows for complete description of any partial or total polarization state. While most of the available polarization imaging cameras perform only linear Stokes polarization imaging (only the linear polarization can be quantified), SALSA performs live measurement of the full Stokes vector for each pixel of the image at a video frame rate. Many polarization-related parameters can be visualized in real time such as the Stokes parameters (S0, S1, S2 , S3), the Degree Of Polarization (Linear or Circular), the Angle Of Polarization, the Ellipticity angle, etc.

SALSA software allows the acquisition in real-time of the raw polarization images and the calculation of the Stokes vector images. Different polarization images (angle of polarization, Degree Of Linear Polarization, Normal to the observed surface, etc.) are then easily computed at video rate.

Applications such as image contrast enhancement, imaging through canopies and shades, target detection and identification and complex 3D surface reconstruction can be easily carried out.

 

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