Remedy 1: Use of GNSS-RO temperature profiles as a reference dataset for satellite Cal/Val

Primary gap remedy type: 
Technical
TRL 5 – technology development / demonstration
Secondary gap remedy type: 
Research
Proposed remedy description: 

As a first step, we propose the inclusion of GNSS-RO bending angles and derived temperature profiles and their uncertainty estimates in the GRUAN processor. It is important to keep the bending angles, as well as the temperature profiles, since the latter have additional sources of uncertainty due to the need for prior information in the retrievals. This first step would involve some technical work. It would also require work by GRUAN sites to improve scheduling to match with GNSS-RO profiles within reasonable colocation criteria. EUMETSAT has developed a tool that has been shown to be able to forecast occultation positions with >98% skill up to two weeks in advance. This can forecast optimal launch times to create a full profile from the surface to 5hPa that coincides with a polar orbiter overpass.

A second step would be to carry out a research study comparing the NWP forecasts with GNSS-RO bending angles and derived temperature profiles and evaluate whether the mean differences fall within the uncertainty estimates. This would lead to an indication of the uncertainties in NWP temperature fields, as indicated by comparison with GNSS-RO observations.

The final step would be to evaluate these uncertainties in radiance space for different satellite instruments. The proposal here follows the procedure that is currently being used for GRUAN data in the GAIA-CLIM project. 

Relevance: 

The solution proposed here addresses the lack of reference observations for temperature at atmospheric heights 40 – 5hPa. This is important for the calibration/validation of stratospheric temperature sounding channels. An additional benefit would be increased global coverage of reference temperature-sensitive observations. 

Measurable outcome of success: 

Firstly, development of the GRUAN processor to include GNSS-RO observations and uncertainties. Secondly, a documented study of the comparison between GNSS-RO temperature profiles and NWP temperature fields in both geophysical space (temperature-height) and radiance space (radiances by channel) for different satellite instruments. 

Expected viability for the outcome of success: 
  • High
Scale of work: 
  • Single institution
  • Consortium
Time bound to remedy: 
  • Less than 1 year
Indicative cost estimate (investment): 
  • Low cost (< 1 million)
Indicative cost estimate (exploitation): 
  • No
Potential actors: 
  • EU H2020 funding
  • National Meteorological Services
  • WMO
  • ESA, EUMETSAT or other space agency