CoAuthors

Tanvir Islam (JPL, USA)

The Jason-3 mission was the first altimeter mission to implement special spacecraft calibration maneuvers for improving the long term climate calibration of the radiometer. The spacecraft is pitched to point the normally nadir viewing Advanced Microwave Radiometer (AMR) to cold space. In the microwave, the sky background is a stable cold calibration source that is used to provide a single point calibration baseline. A drift is observed in the Jason-3 radiometer calibration and has been attributed to drifts in the internal noise diode calibration sources. Similar drifts have been observed in past altimeter radiometers. But in the case of Jason-3, a single point cold sky calibration is able to stabilize the drift with minimal uncertainty since the cold sky brightness is absolutely known. Previously, on-Earth calibration references were required which have much larger uncertainties and are also coupled to the climate system. We will discuss the role the cold sky calibration maneuvers have in the Jason-3 radiometer calibration and estimate the resulting uncertainty in the long term climate calibration of the wet tropospheric path delay. We will compare this to the uncertainty that would result had the cold sky maneuvers not been implemented. Finally, we will discuss the further improvements expected for the Sentinel-6 mission which includes a climate-quality radiometer featuring on-board stable external blackbody calibration sources.