ATSR Reanalysis for Climate --------------------------- ----------------------- File Naming Conventions ----------------------- AT{s}_AVG_3PAARC{yyyy}{mm}{dd}_{l}_{type}.nc Where: s satellite which may be "1", "2", or "S" for ATSR-1, ATSR-2 or AATSR respectively yyyy year mm month dd day l length of averaging period, always "D" for daily files type four character identifier for the type of retrieval described below day/night flag nadir/dual view combination <2|3> number of channels used cloud mask used: full Bayesian or Minimal bayesian The Minimal bayesian cloud mask uses only the 11 and 12 micron channels so it operates identically both day and night. It is intended for use with ATSR-1 as the 3.7 micron channel failed shortly after launch and the 1.6 micron channel was not calibrated as it was for the later sensors. ------------------------------------- SST Estimates and Time of Observation ------------------------------------- The NetCDF files contain data for both the skin SST and the SST estimated for depths of 0.2 and 1.0 m (corresponding approximately to drifter and moored buoy depths). The skin SSTs correspond to the satellite overpass time i.e. they are as observed. However, the depth SST are adjusted to a common local equatorial crossing time (LECT) so that the difference between the ATSR-2 and AATSR overpass is not present as a step change between the sensors. ERS-1 and ERS-2 carrying the ATSR-1 and ATSR-2 instruments have a LECT of 10:30, while the Envisat platform carrying the AATSR instrument has a LECT of 10:00. This 30 minute difference in local time of observation will lead to a step change between ATSR-2 and AATSR SSTs from the diurnal cycle in SST. Therefore the AATSR estimates of SST depth are adjusted to be an estimate of the sea state 30 minutes after the observation time. --------------- Recommended SST --------------- The recommended night-time SST is the dual-view three channel retrieval (type code: nD3b) The recommended day-time SST is the dual-view two channel retrieval (type code: dD2b) Where maximum consistency between day and night retrievals, or with ATSR-1, is required then the dual-view two channel SST should be used at night as well (type code: nD2b). For consistency in the quality of cloud screening, the Minimal bayesian mask can be used (type codes: dD2m and nD2m). Note that this will lead to an overall lower quality cloud mask as it only uses information from the 11 and 12 micron and discards all other channels Nadir-only SSTs are also provided, but they should be used with caution. The nadir-only retrievals are not robust to stratospheric aerosol and are more sensitive to atmospheric variability. However, the nadir retrievals are combined with a nadir-only cloud mask and can therefore have more extensive spatial coverage. Furthermore the nadir-only 3-channel retrieval (type code: nN3b) has very low noise and can be considered where low noise is the primary requirement.