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MLS Instrument Science
Contact: Bob Jarnot


Summary

Good Aura MLS science quality is dependent upon accurate calibration knowledge in three key areas: radiometric, spectral and field-of-view responses. To achieve this required careful attention to instrument design and fabrication, careful pre-launch performance verification, and comprehensive pre-launch calibrations. Many minor performance issues were uncovered during pre-launch performance testing, and all were resolved prior to the start of calibrations. An important philosophy behind calibrations was that they were performed end-to-end whenever possible, and all crucial calibration data were taken in this manner. The results of these calibrations are documented in a comprehensive (4 volume) Instrument Calibration Report, and all calibration data required by Level 1 and Level 2 data processing are available in electronic form.

In-orbit tests are performed periodically to monitor such important calibration data as the radiance differences between cold space views via the Switching Mirror and Antenna. In over 5 years of operation these tests have shown remarkable stability, with overall changes typically smaller than 20 mK in all bands. Another valuable in-orbit calibration has come from the brief opportunities during which MLS can scan across the Moon. These measurements have sometimes required coordinated spacecraft maneuvers to allow the relatively narrow MLS field-of-views to scan across the appropriate portion of the lunar disk, and have significantly lowered the uncertainties on the pre-launch measurements of boresight (pointing) differences between the various radiometers, as well as indicated that the shapes of the antenna FOV's have remained stable. Another area in which in-orbit data has added to our knowledge of measurement accuracy is in the area of standing waves on radiometric calibration views. Tracking (as opposed to scanning) the lunar disk has provided quantitative information on the impact of standing waves on radiometric calibration accuracy that was not available from pre-launch calibration data. Signal levels seen when observing cold space via the main GHz antenna indicate no significant changes to the reflectivity or emissivity of the 3 antenna mirrors. The observed positions of atmospheric spectral lines as seen by the 30+ spectrometers on MLS indicate the absence of frequency drifts within the instrument. The one area in which signals have been changing for the duration of the mission is that the signal powers to the nineteen 25-channel spectrometers have steadily decreased. These decreases arise from radiation effects on low-dropout voltage regulators that were added to the spectrometers late in the instrument fabrication phase. The dropping signal levels have been periodically compensated by changes to programmable attenuator settings, and the regular in-orbit radiometric calibration sequences completely compensate for these small drifts. Extrapolating the declining signal levels indicates that these degradations are unlikely to be a life-limiting factor for the data from any measurement band.

MLS publications related to instrument science

2011

  1. Pumphrey, H.C., "Microwave Limb Sounder observations of biomass-burning products from the Australian bush fires of February 2009", vol doi:10.5194/acp-11-6285-2011, num 11, pgs. 2, 2011. Reprint Preprint

2008

  1. Wu, D.L., "Validation of the Aura MLS Cloud Ice Water Content (IWC) Measurements", vol doi:10.1029/2007JD008931, num 113, 2008. Reprint Preprint

2007

  1. Mueller, E.R., "Terahertz local oscillator for the Microwave Limb Sounder on the Aura Satellite", num 46, pgs. no. 22, 2007. Preprint

2006

  1. Cofield, R.E., "Design and field-of-view calibration of 114-660 GHz optics of the Earth Observing System Microwave Limb Sounder", num 44, pgs. no. 5, 2006. Preprint
  2. Cofield, R.E., "Instrument Packages", vol ISBN: 0470051507, pgs. W. Imbrial, chapter 7, 2006.
  3. Jarnot, R.F., "Radiometric and spectral performance and calibration of the GHz bands of EOS MLS", num 44, pgs. no. 5, 2006. Preprint
  4. Pickett, H.M., "Microwave Limb Sounder THz Module on Aura", num 44, pgs. no. 5, 2006. Preprint
  5. Schoeberl, M.R., "Overview of the EOS Aura Mission", num 44, pgs. no. 5, 2006. Reprint Preprint

2003

  1. Waters, J.W., "Observations for Chemistry (Remote Sensing): Microwave", 2003. Reprint Preprint

2000

  1. Gaidis, M.C., "A 2.5-THz Receiver Front End for Spaceborne Applications", num 44, 2000. Preprint

1997

  1. Woodard, S., "Experimental investigation of spacecraft in-flight disturbances and dynamic response", 1997. Preprint

1996

  1. Jarnot, R.F., "Calibration of the Microwave Limb Sounder on the Upper Atmosphere Research Satellite", num 101, pgs. D6, 1996. Preprint
  2. Lau, C.L., "Characterisation of MLS 1/f noise parameters", num 17, 1996.

1993

  1. Barath, F.T., "The Upper Atmosphere Research Satellite Microwave Limb Sounder Instrument", num 98, 1993. Reprint Preprint
  2. Waters, J.W., "Microwave Limb Sounding", 1993.

1989

  1. Waters, J.W., "Microwave limb-sounding of Earth's upper atmosphere", num 23, 1989.

1984

  1. Waters, J.W., "A balloon-borne microwave limb sounder for stratospheric measurements", num 32, 1984.


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