One of the aims of the International SST FRM Radiometer Network is to facilitate inter-comparisons between radiometers.The purpose of such inter-comparisons is not only to ensure traceability of the infrared radiometers but also field inter-comparisons to not only evaluate the measured skin SST but also the uncertainties.  The FRM4STS  project conducted the laboratory and limited water-based part of such an inter-comparison in 2016. The FRM4STS inter-comparison did not include a ship-based comparison but the ISFRN  carried out a demonstrator inter-comparison on the M/V Queen Mary 2  in 2015 with one ISAR and one SISTeR instrument (see information below for more detail). Another CEOS TIR radiometer intercomparison, funding through this project and hosted by NPL, was performed in 2022 and further details can be found here.

SST Inter-comparison on the QM2

The image blow shows the SISTeR (left) and ISAR (right) instruments mounted on the QM2 in Southampton. The inter-comparison between the two instruments was carried out between 11 September 2015 to 5 November 2015. Because of interference issues with the rain gauges, the usable data was limited to  22 October 2015 to 5 November 2015.

 

Inter-comparison of SISTeR and SIAR on the QM2 in 2015.

The following plots show the mean difference between the SISTeR and ISAR skin SST measurements, with ISAR skin SST measurements being cooler than the SISTeR skin SST measurements. Both instruments show a good agreement, with a mean difference of - 11 mK.  

The next plot shows the SISTeR-ISAR SST difference along the ship track.

One of the features of shipborne radiometers is the estimate of the uncertainty for each data point and one of the important features of the inter-comparison was to validate the SISTeR and ISAR uncertainty model at sea.  The plots below show the difference in the uncertainty values of the two instruments, which is mainly due to  the way the two uncertainty models deal with the sky variability and sea surface variability. 

 

 

A more detailed report on the inter-comparison will be published soon. 

The data from the inter-comparsion can be found here.