Abstract's details
Performances and stability assessment of Sentinel3 Microwave radiometers
CoAuthors
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Propagation, Wind Speed and Sea State Bias
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Sentinel-3B was launched the 25 April 2018, two years after Sentinel-3A. The two radiometers are identical in design. The pair of satellite will increase coverage and data delivery for Copernicus service. For routine operation, Sentinel-3 configuration is such that both satellites will fly with a 140° separation.
The two-channels microwave radiometer (23.8 and 36.5 GHz) on board the two missions is similar to the Envisat and ERS MWR sensors. It is combined to the altimeter in order to correct the altimeter range for the excess path delay (WTC for wet tropospheric correction) resulting from the presence of water vapor in the troposphere.
The wet tropospheric correction (WTC) is a major source of uncertainty in altimetry budget error, due to its large spatial and temporal variability. It also contributes significantly to the uncertainty in the long term mean sea level trend.
In order to better quantify the WTC trend, it is important to focus on the detection of potential instrumental drifts. The long-term stability of each radiometer will be assessed using different methods.
First, vicarious calibrations are statistical selections of coldest and hottest temperatures over the ocean and the Amazon forest respectively. They are commonly used for the in-flight calibration during commissioning phase, but also for long-term monitoring.
Second, the double difference accounts for frequency, Earth Incidence Angle, and orbital differences between platforms. To calculate the double difference, the single differences for each radiometer are first computed. The single difference is found by taking the difference between a reference statistic of the observed radiometer brightness temperatures (TBs) and a reference statistic from simulated TBs. The double difference is then the difference between the single differences of the two radiometers. Single differences suffer from the discontinuities introduced by evolutions of the Numerical Weather Prediction model due to improvements in the operational version or modification of the assimilation scheme. By construction, double differences cancel out the impact of these evolutions.
Third, comparison to Fundamental Climate Data Record will be performed for overlapping periods. FCDR are homogenized and intercalibrated brightness temperatures to ensure long term stability suitable for climate related applications.
Finally, conclusions can be drawn on the stability of the WTC.
The two-channels microwave radiometer (23.8 and 36.5 GHz) on board the two missions is similar to the Envisat and ERS MWR sensors. It is combined to the altimeter in order to correct the altimeter range for the excess path delay (WTC for wet tropospheric correction) resulting from the presence of water vapor in the troposphere.
The wet tropospheric correction (WTC) is a major source of uncertainty in altimetry budget error, due to its large spatial and temporal variability. It also contributes significantly to the uncertainty in the long term mean sea level trend.
In order to better quantify the WTC trend, it is important to focus on the detection of potential instrumental drifts. The long-term stability of each radiometer will be assessed using different methods.
First, vicarious calibrations are statistical selections of coldest and hottest temperatures over the ocean and the Amazon forest respectively. They are commonly used for the in-flight calibration during commissioning phase, but also for long-term monitoring.
Second, the double difference accounts for frequency, Earth Incidence Angle, and orbital differences between platforms. To calculate the double difference, the single differences for each radiometer are first computed. The single difference is found by taking the difference between a reference statistic of the observed radiometer brightness temperatures (TBs) and a reference statistic from simulated TBs. The double difference is then the difference between the single differences of the two radiometers. Single differences suffer from the discontinuities introduced by evolutions of the Numerical Weather Prediction model due to improvements in the operational version or modification of the assimilation scheme. By construction, double differences cancel out the impact of these evolutions.
Third, comparison to Fundamental Climate Data Record will be performed for overlapping periods. FCDR are homogenized and intercalibrated brightness temperatures to ensure long term stability suitable for climate related applications.
Finally, conclusions can be drawn on the stability of the WTC.