On-orbit calibration of HALOE detector linearity

Area of Science:

• Atmospheric science
• Remote sensing
• Instrument calibration

Background:

• The Halogen Occultation Experiment (HALOE) provided crucial satellite solar occultation measurements for 14 years.
• Accurate long-term atmospheric trend studies depend on understanding instrument performance, including response linearity.

Purpose of the Study:

• To assess the stability of the HALOE instrument's response linearity over its mission lifetime.
• To quantify any changes in nonlinearity that could affect the reliability of HALOE data for trend analysis.

Main Methods:

• Utilized a calibration wheel with neutral density filters for ground and on-orbit measurements.
• Analyzed solar occultation data collected over 14 years (ending November 21, 2005).
• Evaluated instrument response linearity using a combination of calibration techniques.

Main Results:

• On-orbit measurements suggest that any instrument response nonlinearity changed by less than 2% throughout the HALOE mission.
• Measurement uncertainties prevent a definitive quantification of the exact nonlinearity, but the trend is minimal.
• The stability of the response linearity was confirmed via on-orbit calibration data.

Conclusions:

• The minimal change in response nonlinearity (<2%) over the HALOE mission lifetime validates the data's suitability for long-term atmospheric trend studies.
• This finding reduces a significant potential source of uncertainty in HALOE-derived atmospheric trend research.
• The HALOE instrument demonstrated remarkable stability in its response linearity, enhancing its legacy value.