Highly accurate in-situ determination of the refractivity of an ambient atmosphere

A measuring unit utilizing in-situ determined refractivity of an ambient atmosphere to provide a highly accurate quantity measurement in said ambient atmosphere, said unit comprising:

• measuring means exposed to said ambient atmosphere providing an electrical signal output indicative of a predetermined quantity to be measured;
• light conducting means adapted to provide light from a stabilized light source;
• refractometer means exposed to said ambient atmosphere the fractivity of which is to be determined, said refractometer means, upon receipt of said light from said light conducting means, providing an optical interference fringe pattern having a dependence upon the refractivity of said ambient atmosphere;
• optical imaging system for receiving said interference fringe pattern from said refractometer means and providing an output indicative of the far field of said pattern;
• multi-element detector means for receiving said output from said optical imaging means and, responsive thereto, providing an electrical signal output indicative of said far field fringe patter;
• and
• processing means for receiving said electrical signal outputs from said measuring means and said multi-element detector means, said processing means determining in-situ the index of refraction of said ambient atmosphere and, responsive thereto, correcting said quantity measurement to thereby provide a highly accurate quantity measurement output.

A method for providing accurate in-situ determination of the refractivity of an ambient atmosphere, said method comprising:

• providing a concentrated source of light at different angles;
• utilizing said concentrated source of light at different angles in an ambient atmosphere to form an optical interference fringe pattern having a dependence upon the refractivity of said ambient atmosphere with said refractivity-dependent optical interference fringe pattern being measurable as modulation of the input angular distribution from said concentrated source of light;
• detecting the phase of said measurable refractivity-dependent optical interference fringe pattern and providing an electrical signal output indicative thereof;
• and
• processing the electrical signal output to determine the index of refraction of said ambient atmosphere.