Sea surface temperatures from the NOAA-19 AVHRR sensor have exhibited larger than usual errors since 3rd September 2018, associated with the satellite passing for the first time into a fully sunlit orbit. NOAA-18 is expected to pass into a full-sun regime in late February 2019. Users are alerted to possible degradation in accuracy of IMOS AVHRR L3S SST products in coming weeks. The new operational IMOS Multi-Sensor L3S products are recommended for use.
IMOS has produced a 27-year suite of satellite-based sea surface temperature (SST) composites on a 0.02 deg x 0.02 deg grid, using locally received data from AVHRR sensors aboard the series of NOAA Polar-Orbiting Environmental Satellites (NPOES). From 2018, NOAA officially replaced the AVHRR sensor program with the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor program, after a long trial which began with the first VIIRS sensor launch in 2012 aboard the Suomi National Polar-orbiting Partnership (NPP) platform. IMOS has, since 16th November 2018, included the VIIRS SST from NPP in a new suite of Multi-sensor operational real-time SST products, resulting in improvements to overall quality, accuracy and coverage. This new product is intended to be a drop-in replacement for the existing AVHRR-only product set, with similar file format. For further information and data access please read this short article.
NOAA-18 and NOAA-19 are the last in the series of operational NPOES satellites to carry AVHRR sensors, starting with NOAA-6 in 1981, although they are still carried on the European Space Agency (ESA) MetOp series of polar-orbiters. Orbital decay of NOAA-18 and NOAA-19 during recent years has affected the accuracy of the real-time IMOS AVHRR SST products during some months. The AVHRR sensor on NOAA-19 was adversely affected by passing for the first time into a fully sunlit orbit on 13th September 2018, and from 29th September 2018 SSTs from this satellite have not contributed to the IMOS AVHRR-only L3S products. NOAA-18 is expected to pass into a similar full-sun orbit in late February 2019, with degradation in SST accuracy expected. It is therefore recommended that users requiring accurate 2 km SST composites over the Australian region consider using the new IMOS Multi-sensor L3S.