CoAuthors

Tanvir Islam (JPL, USA)

The wet tropospheric correction is provided by dedicated microwave radiometers on all Jason-class altimetry missions. New calibration techniques and improvements to the instrument design for the upcoming Sentinel-6 mission promise to address past deficiencies, such as long term drifts and the accuracy in the coastal zone. Long term drifts observed in the microwave radiometers on Topex to Jason-3 have required significant corrections impacting the accuracy the derived global mean sea level (GMSL) trend. Prior to Jason-3, these corrections were made using on-Earth references that could introduce potential systematic errors in the GMSL time series. The Jason-3 mission was the first to implement dedicated cold sky calibration maneuvers which give a single, but absolutely stable calibration source independent of the Earth system. The Sentinel-6 missions goes a step further by including a dedicated external two-point blackbody calibration source in the instrument design. This promises to provide sub-mm stability for any 1-year period, benefiting the extraction of not only trends, but accelerations in the GMSL time series. We will discuss the current stability of the Jason-3 mission enabled by the cold sky calibration maneuvers and provide an estimate for the expected stability of the Sentinel-6 mission enabled by the on-board calibration system.

Sentinel-6 will also carry an experimental, high-frequency, high-resolution microwave radiometer (HRMR) for improving the accuracy of the wet path delay measurement in the coastal zone. This radiometer operates at 90, 130 and 166 GHz using the same 1m aperture of the traditional low-frequency radiometer. This means that the spatial resolution is 2-5km, providing estimates of wet path delay must closer to the coast than previous missions. We will describe the instrument and the predicted performance based on pre-launch test data from the radiometer.