Abstract's details
ACCRA : A Study on Future Microwave Radiometers for Atmospheric Correction of Radar Altimeters on Coastal Regions
CoAuthors
Event: 2015 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Corrections
Presentation type: Type Poster
Contribution: not provided
Abstract:
The wet tropospheric correction (WTC) is a major source of uncertainty in altimetry budget error, due to its large spatial and temporal variability: this is why the main altimetry missions include a microwave radiometer (MR) The commonly agreed requirement on WTC for current missions is to retrieve WTC with an error better than 1cm rms.
With the introduction of the along-track synthetic aperture processing, first implemented in CryoSat-2, and now in the upcoming operational altimetry missions such as Sentinel-3 and Jason-CS, more accurate altimetry data are anticipated for coastal and inland waters. Nevertheless, the quality of data in those areas are expected to be degraded with respect to those of the open oceans due to the rather wide field of view of the MR (-3 dB beam-width of ~20 km). As a matter of fact, the MR observations over those waters are subject to contamination by land brightness temperatures which fall within the MR footprint.
The present team has been selected by ESA/ESTEC to work on a MR instrument design for future operational radar altimetry missions. Such a design shall include the classical MR channels for ensuring observation continuity, augmented by a set of high frequency channels for enabling accurate altimetry over coastal and inland waters.
In this study team, the extensive systems and radiometric engineering experience of JCR Systems is complemented by a significant expertise of LOCEAN , CLS and CNRM in water vapour retrievals, a considerable experience in design and development of microwave and millimetre wave radiometer front ends from RAL and a substantial knowledge of SMT Consultancies in microwave and millimetre-wave antenna design.
We will present the first results of the on-going study on the selection of an optimal set of observation frequencies based on an analysis of both potential horizontal resolution and the value of the physical information provided. In order to properly select this optimal set for the wet tropospheric correction (WTC) retrieval over ocean and in coastal regions, the combination between all frequency candidates (including high frequencies such as 89 GHz, 157 GHz, 183 GHz) will lead to the definition of a set of retrieval algorithms based on ECMWF analysis, RTTOV radiative transfer model associated with an emissivity data base and a neural network inversion. The statistics on the algorithmic error defined as the difference between the retrieved WTC applied on simulated brightness temperatures (BT) and the ECMWF WTC will allow to quantify the performances and discriminate these algorithms over open ocean, land surface and polar ice. Eventually, design considerations are taken into account in order to select between different potential combinations.
With the introduction of the along-track synthetic aperture processing, first implemented in CryoSat-2, and now in the upcoming operational altimetry missions such as Sentinel-3 and Jason-CS, more accurate altimetry data are anticipated for coastal and inland waters. Nevertheless, the quality of data in those areas are expected to be degraded with respect to those of the open oceans due to the rather wide field of view of the MR (-3 dB beam-width of ~20 km). As a matter of fact, the MR observations over those waters are subject to contamination by land brightness temperatures which fall within the MR footprint.
The present team has been selected by ESA/ESTEC to work on a MR instrument design for future operational radar altimetry missions. Such a design shall include the classical MR channels for ensuring observation continuity, augmented by a set of high frequency channels for enabling accurate altimetry over coastal and inland waters.
In this study team, the extensive systems and radiometric engineering experience of JCR Systems is complemented by a significant expertise of LOCEAN , CLS and CNRM in water vapour retrievals, a considerable experience in design and development of microwave and millimetre wave radiometer front ends from RAL and a substantial knowledge of SMT Consultancies in microwave and millimetre-wave antenna design.
We will present the first results of the on-going study on the selection of an optimal set of observation frequencies based on an analysis of both potential horizontal resolution and the value of the physical information provided. In order to properly select this optimal set for the wet tropospheric correction (WTC) retrieval over ocean and in coastal regions, the combination between all frequency candidates (including high frequencies such as 89 GHz, 157 GHz, 183 GHz) will lead to the definition of a set of retrieval algorithms based on ECMWF analysis, RTTOV radiative transfer model associated with an emissivity data base and a neural network inversion. The statistics on the algorithmic error defined as the difference between the retrieved WTC applied on simulated brightness temperatures (BT) and the ECMWF WTC will allow to quantify the performances and discriminate these algorithms over open ocean, land surface and polar ice. Eventually, design considerations are taken into account in order to select between different potential combinations.