Operational Status:
requestable, ready for deployment
General Description:
- The NCAR Airborne Oxygen Instrument measures O2 concentration using a vacuum-ultraviolet absorption technique. AO2 is based on earlier ship-board and laboratory instruments using the same technique, but has been designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system. To achieve the high-levels of precision needed, AO2 switches between sample gas and air from a high-pressure reference cylinder every 2.5 seconds. Atmospheric O2 concentrations are typically reported in units of one part in 1,000,000 relative deviations in the O2/N2 ratio, which are referred to as “per meg.” AO2 has a precision of +/- 2 per meg on a 5 second measurement. For comparison, this is equivalent to detecting the removal of one O2 molecule from 2.5 million molecules of air. At typical GV flight speeds of 300 kts or climb/descent rates of 1500 fpm, 5-seconds correspond to a horizontal resolution of 750 m and a vertical resolution of 40 m. The AO2 system consists of a pump module, a cylinder module, an instrument module, and a dewar.
- The system as used during HIPPO flights on the GV is shown in the following photograph:
- The system as used during HIPPO flights on the GV is shown in the following photograph:
- The NCAR Airborne Oxygen Instrument measures O2 concentration using a vacuum-ultraviolet absorption technique. AO2 is based on earlier ship-board and laboratory instruments using the same technique, but has been designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system. To achieve the high-levels of precision needed, AO2 switches between sample gas and air from a high-pressure reference cylinder every 2.5 seconds. Atmospheric O2 concentrations are typically reported in units of one part in 1,000,000 relative deviations in the O2/N2 ratio, which are referred to as “per meg.” AO2 has a precision of +/- 2 per meg on a 5 second measurement. For comparison, this is equivalent to detecting the removal of one O2 molecule from 2.5 million molecules of air. At typical GV flight speeds of 300 kts or climb/descent rates of 1500 fpm, 5-seconds correspond to a horizontal resolution of 750 m and a vertical resolution of 40 m. The AO2 system consists of a pump module, a cylinder module, an instrument module, and a dewar.
Measurement Characteristics:
- Overall estimate of uncertainty: 5 per meg
- Response time: 0.5 Hz (raw data sampled at 10 Hz)
- Precision: 2 per meg (5 s integrated measurement)
- Other measurement characteristics (comments on signal/noise, bias limits, etc):
- Measurements are relative to the Scripps O2 scale, with zero relative to a stored reference sample of air
