Real-time, reference-free background oriented schlieren imaging system

A method of measuring a density object with a projected background oriented optical system, comprising:

• directing an incident light source having an image pattern through a field lens positioned between an image generator and a beam splitter, wherein the field lens is configured to focus the image pattern onto a downstream retroreflective background, wherein the beam splitter is configured to:
• reflect a first portion of the image pattern along a signal axis of the optical system;
• and
• transmit a second portion of the image pattern along a reference axis of the optical system towards a reference imaging sensor configured to store the transmitted second portion of the image pattern as a set of reference data;
• projecting the first portion of the image pattern past the density object to be tested and towards the retroreflective background, wherein the retroreflective background is configured to:
• receive the transmitted image pattern;
• and
• reflect the image pattern back through the test object and towards the beam splitter;
• passing the reflected image pattern through the beam splitter and towards a signal imaging sensor configured to store the reflected image patterns as a set of signal data;
• and
• processing the stored sets of reference data and signal data with a processing system operatively connected to the reference and signal imaging sensors, the processing system having a processor and a non-transitory computer-readable medium with computer-executable instructions that, when executed by a processor, cause the processor to at least:
• compare the received sets of signal data and reference data;
• and
• generate a set of flow data.

A method of measuring a density object in a test section of an instrument with an imaging system, comprising:

• directing an incident light source having an image pattern through a field lens and towards a beam splitter configured to:
• reflect a first portion of the image pattern as linear vertically polarized light (LVP) along a signal axis of the imaging system;
• and
• transmit a second portion of the image pattern along a reference axis to a reference imaging processor configured to store the transmitted image pattern as a set of reference data;
• passing the LVP light through a test window and into the test section;
• positioning a quarter-wave plate (QWP) between the test window and a retroreflective background;
• reflecting the LVP light back through the test section via the retroreflective background, wherein the LVP light is converted to LHP after passing back through the QWP;
• passing the LHP light back through the beam splitter towards a signal imaging sensor configured to store the reflected image patterns as a set of signal data;
• processing the stored sets of reference data and signal data in real-time with a processing system connected to the reference and signal imaging sensors, the processing system having a processor and a non-transitory computer-readable medium with computer-executable instructions that when executed by the processor, cause the processor to at least:
• compare the received sets of signal data and reference data;
• and
• generate a set of flow data.