Metop AVHRR Ice Surface Temperature and Validation
Dybkjær, Gorm; Tonboe, Rasmus; Høyer, Jacob L.
Danish Meteorological Institute, DENMARK
The ice surface temperature (IST) is an important boundary condition for atmosphere, ocean and sea ice models. An ocean observation user community agreed upon data delay and spatial breakthrough requirements for IST of 1-4h and 5km, respectively, with and accuracy of less than 4 degree for global applications.
An operational level-2 IST product using satellite Metop AVHRR infra-red data was developed at DMI in the MyOcean project. This production is currently running for the Northern hemisphere sea ice and it is presently under further development in the EUMETSAT OSISAF and will eventually have global coverage. Level-3/4 products are being prepared for the Arctic Ocean and the Baltic Sea. The production is in near real time, within 2.5h from data acquisition.
The IST estimates are based on multi-channel thermal infra-red data and it is therefore applicable in clear sky regions only. Clear sky conditions prevail during spring in the Arctic, while persistent cloud cover limits data coverage during summer. In the real time IST production the cloud covered regions are determined by the EUMETSAT cloud mask.
The IST level-2 product compares to 2m air temperature at the Greenland ice cap Summit within STD error of 3.14K and to Arctic drifting buoy temperature data within STD error of 3.69K. Case studies from land, sea ice and ship based platforms reveal that the STD error can be lower than 1K when compared to real skin temperatures and in positively clear sky conditions.
One year of cloud cover data from 8 automatic weather stations evenly distributed around the Greenland ice cap rim are used to quantify the errors emerging from the automatic Metop AVHRR satellite cloud mask. The results show that the cloud mask quality is strongly dependent on both season and on the presence of day light. The cloud cover at the automatic weather stations is estimated from long-wave radiation/near-surface air temperature relationships.
DMI is continuously expanding its data base of radiometric validation data for Arctic SST and IST, primarily from various deployments of the DMI-ISAR instrument. Deployment onboard commercial cruises between Greenland and Denmark continuously provide Arctic SST validation data and from dedicated sea ice field works we collect the radiometric IST in situ data.