Abstract's details
Long-term stability of ionospheric GIM corrections in satellite altimetry data sets
CoAuthors
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Quantifying Errors and Uncertainties in Altimetry data
Presentation type: Type Oral
Contribution: PDF file
Abstract:
High-accurate and long-term stable ionospheric delay corrections for satellite altimetry measurements are essential for reliable estimation of sea surface heights and global mean sea level (GMSL) trends. For most missions and applications, these corrections are directly computed from dual-frequency observations of the satellite altimeter. However, for single-frequency missions (such as SARAL or Cryosat-2) as well as for coastal and inland applications, external information is required. Usually, this is taken from GNSS-based Global Ionospheric Maps (GIM) as available from different analysis centers of the International GNSS Service (IGS). These corrections are also available in most altimeter data sets (e.g. Jason Geophysical Data Records, GDR).
When using GIM information for correcting altimeter measurements for ionospheric delay, the different orbit heights of GNSS satellites and altimetry satellites require an adaption of the GIM corrections to account for the free electrons in the topside ionosphere and the plasmasphere (i.e. between about 800 to 1300 km and 20.200 km). This scaling can be done using electron models, as well as by empirical estimated scaling coefficients.
This contribution investigates the impact of different ionospheric corrections and scaling approaches on altimetry-derived GMSL estimates. This is done based on open-ocean data of the Jason missions, for which dual-frequency corrections as well as GIM corrections are available in the GDR data sets. It will be shown that the widely used scaling approach based on the International Reference Ionosphere (IRI95) is not able to accurately scale the GIM models, since it disregards all information above 1400 km height. The impact of neglecting the plasmaspheric part of the atmosphere strongly correlates with the 11-year solar cycle and manifests itself as a trend error in GMSL. For the Jason period (2002 to 2021) a trend difference of 0.17 mm/year is shown, which is even larger for smaller periods (e.g. 1.0 mm/year for Jason-1 lifetime). The application of an additional constant scaling factor of 0.886 will reduce the trend differences to below 0.05 mm/year.
The Sentinel-6 MF observation period is still too short for reliable trend investigations. However, a similar impact is to be expected if the same scaling approach has been applied to the GIM data. First results for this missions will also be shown.
When using GIM information for correcting altimeter measurements for ionospheric delay, the different orbit heights of GNSS satellites and altimetry satellites require an adaption of the GIM corrections to account for the free electrons in the topside ionosphere and the plasmasphere (i.e. between about 800 to 1300 km and 20.200 km). This scaling can be done using electron models, as well as by empirical estimated scaling coefficients.
This contribution investigates the impact of different ionospheric corrections and scaling approaches on altimetry-derived GMSL estimates. This is done based on open-ocean data of the Jason missions, for which dual-frequency corrections as well as GIM corrections are available in the GDR data sets. It will be shown that the widely used scaling approach based on the International Reference Ionosphere (IRI95) is not able to accurately scale the GIM models, since it disregards all information above 1400 km height. The impact of neglecting the plasmaspheric part of the atmosphere strongly correlates with the 11-year solar cycle and manifests itself as a trend error in GMSL. For the Jason period (2002 to 2021) a trend difference of 0.17 mm/year is shown, which is even larger for smaller periods (e.g. 1.0 mm/year for Jason-1 lifetime). The application of an additional constant scaling factor of 0.886 will reduce the trend differences to below 0.05 mm/year.
The Sentinel-6 MF observation period is still too short for reliable trend investigations. However, a similar impact is to be expected if the same scaling approach has been applied to the GIM data. First results for this missions will also be shown.