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Volume 17, issue 24
Atmos. Chem. Phys., 17, 15069-15093, 2017
https://doi.org/10.5194/acp-17-15069-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 17, 15069-15093, 2017
https://doi.org/10.5194/acp-17-15069-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Dec 2017

Research article | 20 Dec 2017

How long do satellites need to overlap? Evaluation of climate data stability from overlapping satellite records

Elizabeth C. Weatherhead1, Jerald Harder2, Eduardo A. Araujo-Pradere3, Greg Bodeker4, Jason M. English5,6, Lawrence E. Flynn7, Stacey M. Frith8, Jeffrey K. Lazo9, Peter Pilewskie2, Mark Weber10, and Thomas N. Woods2 Elizabeth C. Weatherhead et al.
  • 1University of Colorado, Boulder, Colorado, USA
  • 2Laboratory for Atmosphere and Space Physics, University of Colorado, Boulder, Colorado, USA
  • 3School of Science, Miami Dade College, Miami, Florida, USA
  • 4Bodeker Scientific, Alexandra, New Zealand
  • 5Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 6NOAA Earth System Research Laboratory, Global Systems Division, 325 Broadway, Boulder, Colorado 80305, USA
  • 7NOAA, NESDIS, College Park, Maryland, USA
  • 8Science Systems and Applications, Inc., Lanham, Maryland USA
  • 9Consulting LLC, Gunnison, CO, USA
  • 10University of Bremen FB1, Bremen, Germany

Abstract. Sensors on satellites provide unprecedented understanding of the Earth's climate system by measuring incoming solar radiation, as well as both passive and active observations of the entire Earth with outstanding spatial and temporal coverage. A common challenge with satellite observations is to quantify their ability to provide well-calibrated, long-term, stable records of the parameters they measure. Ground-based intercomparisons offer some insight, while reference observations and internal calibrations give further assistance for understanding long-term stability. A valuable tool for evaluating and developing long-term records from satellites is the examination of data from overlapping satellite missions. This paper addresses how the length of overlap affects the ability to identify an offset or a drift in the overlap of data between two sensors. Ozone and temperature data sets are used as examples showing that overlap data can differ by latitude and can change over time. New results are presented for the general case of sensor overlap by using Solar Radiation and Climate Experiment (SORCE) Spectral Irradiance Monitor (SIM) and Solar Stellar Irradiance Comparison Experiment (SOLSTICE) solar irradiance data as an example. To achieve a 1% uncertainty in estimating the offset for these two instruments' measurement of the Mg II core (280nm) requires approximately 5 months of overlap. For relative drift to be identified within 0.1%yr−1 uncertainty (0.00008Wm−2nm−1yr−1), the overlap for these two satellites would need to be 2.5 years. Additional overlap of satellite measurements is needed if, as is the case for solar monitoring, unexpected jumps occur adding uncertainty to both offsets and drifts; the additional length of time needed to account for a single jump in the overlap data may be as large as 50% of the original overlap period in order to achieve the same desired confidence in the stability of the merged data set. Results presented here are directly applicable to satellite Earth observations. Approaches for Earth observations offer additional challenges due to the complexity of the observations, but Earth observations may also benefit from ancillary observations taken from ground-based and in situ sources. Difficult choices need to be made when monitoring approaches are considered; we outline some attempts at optimizing networks based on economic principles. The careful evaluation of monitoring overlap is important to the appropriate application of observational resources and to the usefulness of current and future observations.

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Satellite overlap is often carried out as a check on the stability of the data collected. We looked at how length of overlap influences how much information can be derived from the overlap period. Several results surprised us: the confidence we could have in the matchup of two records was independent of the offset, and understanding of the relative drift between the two satellite data sets improved significantly with 2–3 years of overlap. Sudden jumps could easily be confused with drift.
Satellite overlap is often carried out as a check on the stability of the data collected. We...
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