IGF::OT::IGF THE PHASE II PROJECT WILL LEAD TO THE DESIGN, CONSTRUCTION, AND FIELD-TESTING OF A PROTOTYPE PHOCS INSTRUMENT FOR ATMOSPHERIC COLUMN RETRIEVALS OF OXYGEN AND CARBON DIOXIDE. THE CARBON DIOXIDE WAVELENGTH RANGE MAY ALSO BE EXTENDED TO ADD METHANE AND CARBON MONOXIDE MEASUREMENTS DEPENDING ON LASER PERFORMANCE. THE PROTOTYPE WILL INCLUDE THE IMPROVEMENT TO HETERODYNE SPECTROSCOPY INVENTED IN PHASE I. THE PROJECT WILL MOVE MESA PHOTONICS' TECHNOLOGY TOWARD COMMERCIALIZING COMPACT, PORTABLE INSTRUMENTS THAT COMBINE HIGH SPECTRAL RESOLUTION WITH HIGH SENSITIVITY AND RAPID DATA ACQUISITION.