ANALYSIS AND INTER-CALIBRATION OF WET PATH DELAY DATASETS TO COMPUTE THE WET TROPOSPHERIC CORRECTION FOR CRYOSAT-2 OVER OCEAN

摘要

Unlike most altimetric missions, CryoSat-2 (CS-2), originally conceived for cryosphere studies, is not equipped with an onboard microwave radiometer (MWR) to provide the wet tropospheric correction (WTC) to the radar altimeter measurements, thus their correction currently relies on a model-based one provided by the European Centre for Medium-range Weather Forecasts (ECMWF). In the ambit of ESA funded project CP4O, an improved WTC for CS-2 data over ocean is under development, based on a data combination algorithm (DComb) through objective analysis of WTC values derived from all existing data types. The scope of this study is the analysis of the various available datasets for the computation of the wet path delay of altimeter measurements over ocean, and the inter-calibration of the derived WTC. Emphasis is given to the analysis of the WTC derived from water vapour products of different scanning MWR aboard various remote sensing (RS) missions. Together with wet path delays derived at Global Navigation Satellite System (GNSS) coastal and island stations and data from the ECMWF ReAnalysis (ERA) Interim model, these will constitute the main data sets for use in the DComb algorithm. A brief summary of the main issues regarding the computation of the WTC from all used data products is presented. For open ocean altimetry, an inter-calibration of scanning MWR derived WTC is performed, using the Advanced Microwave Radiometer (AMR) on board Jason-2 as reference. Moreover, the analysis of the orbital parameters of CS-2 and all other considered RS missions, as well as the respective scanning MWR characteristics, provides an insight into the expected impact of these data sets on the final derived WTC. The best approach for calculating the WTC from total column water vapour (TCWV) is investigated. The selected approach is shown to be well suited for accurate Level-2 scientific products.