236
M. Krug et al.
12.2 Data
Three IR SST datasets are compared: the Pathfinder version 5.2 (hereafter referred
to as Pathfinder v5.2), the Moderate Resolution Imaging Spectometer (MODIS) onboard the US National Aeronautics and Space Administration (NASA) satellite Terra
and the Ocean and Sea Ice Satellite Application Facility
1 (OSI-SAF) experimental
hourly SST products.
The Ocean Pathfinder SST project consists of a reprocessing of all Advanced Very
High Resolution Radiometer (AVHRR) data on board the US National Atmospheric
and Oceanic Administration (NOAA) satellites from 1981 to present with the same
algorithm (Kilpatrick et al. 2001; Casey et al. 2010). The aim of this project is
to produce consistent long term SST for research, modelling, and trend analysis
(Casey et al. 2010). SST is derived using two channels in the thermal IR (10.8 and
11.4 μm). Monthly composites were computed from the daily daytime Pathfinder
v5.2 at a 4 km spatial resolution. A quality flag of 4, considered as the lowest quality
level for acceptable data (Kilpatrick et al. 2001), was imposed for our application.
SST data from MODIS Terra has been available since 2000. The MODIS SST
dataset aims to provide high quality global measurements at a high spatial resolution.
The MODIS SST is derived using two channels in either the thermal IR (11 and 12 um)
or in the mid-IR region (3.8 and 4.1 um) (Minnett et al. 2002). Level-2 MODIS data
were downloaded from the Ocean Color website
2 and processed at a 4 km resolution
using the SeaWiFS Data Analysis System
3 (SeaDAS). The processing method is
described in Dufois et al. (2012). Only the daytime passes were processed, allowing
us to use the cloud flag (SST quality flags were not used). The daily data were then
averaged to obtain monthly data. This product is hereafter referred to as Reprocessed
MODIS.
The OSI-SAF hourly SST product is available on a 1/20
◦ grid (5 km) and processed
by the French Centre ERS d’Archivage et de Traitement (CERSAT). The OSI-SAF
SST consists in the best hourly SST images sampled from the Spinning Enhanced
Visible and Infrared Imager (SEVIRI), onboard the geo-stationary Meteosat Second
Generation 2 (MSG-2) satellite. It is calculated using a classical multi-channel formulas applied to the 11 and 12 μm channels (Le Borgne et al. 2006). SEVIRI has
been imaging the Earth since June 2004 at a 15 min sampling interval using 12 spectral channels (4 visible/near-IR and 8 IR channels) with spatial resolutions of 1 and
3 km. For comparisons purposes, our analysis of the OSI-SAF SST was restricted to
daytime observations (from 7:00 to 19:00).
A weekly composite of SST data collected from the Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E), on board the US NASA
Aqua satellite, was used to illustrate some of the limitation of microwave radiometry
in the Agulhas Current. Global maps of AMSR-E SST data are available on a 1/4
◦
1 See www.osi-saf.org
2 At http://oceancolor.gsfc.nasa.gov
3 For details see http://seadas.gsfc.nasa.gov
M. Krug et al.
12.2 Data
Three IR SST datasets are compared: the Pathfinder version 5.2 (hereafter referred
to as Pathfinder v5.2), the Moderate Resolution Imaging Spectometer (MODIS) onboard the US National Aeronautics and Space Administration (NASA) satellite Terra
and the Ocean and Sea Ice Satellite Application Facility
1 (OSI-SAF) experimental
hourly SST products.
The Ocean Pathfinder SST project consists of a reprocessing of all Advanced Very
High Resolution Radiometer (AVHRR) data on board the US National Atmospheric
and Oceanic Administration (NOAA) satellites from 1981 to present with the same
algorithm (Kilpatrick et al. 2001; Casey et al. 2010). The aim of this project is
to produce consistent long term SST for research, modelling, and trend analysis
(Casey et al. 2010). SST is derived using two channels in the thermal IR (10.8 and
11.4 μm). Monthly composites were computed from the daily daytime Pathfinder
v5.2 at a 4 km spatial resolution. A quality flag of 4, considered as the lowest quality
level for acceptable data (Kilpatrick et al. 2001), was imposed for our application.
SST data from MODIS Terra has been available since 2000. The MODIS SST
dataset aims to provide high quality global measurements at a high spatial resolution.
The MODIS SST is derived using two channels in either the thermal IR (11 and 12 um)
or in the mid-IR region (3.8 and 4.1 um) (Minnett et al. 2002). Level-2 MODIS data
were downloaded from the Ocean Color website
2 and processed at a 4 km resolution
using the SeaWiFS Data Analysis System
3 (SeaDAS). The processing method is
described in Dufois et al. (2012). Only the daytime passes were processed, allowing
us to use the cloud flag (SST quality flags were not used). The daily data were then
averaged to obtain monthly data. This product is hereafter referred to as Reprocessed
MODIS.
The OSI-SAF hourly SST product is available on a 1/20
◦ grid (5 km) and processed
by the French Centre ERS d’Archivage et de Traitement (CERSAT). The OSI-SAF
SST consists in the best hourly SST images sampled from the Spinning Enhanced
Visible and Infrared Imager (SEVIRI), onboard the geo-stationary Meteosat Second
Generation 2 (MSG-2) satellite. It is calculated using a classical multi-channel formulas applied to the 11 and 12 μm channels (Le Borgne et al. 2006). SEVIRI has
been imaging the Earth since June 2004 at a 15 min sampling interval using 12 spectral channels (4 visible/near-IR and 8 IR channels) with spatial resolutions of 1 and
3 km. For comparisons purposes, our analysis of the OSI-SAF SST was restricted to
daytime observations (from 7:00 to 19:00).
A weekly composite of SST data collected from the Advanced Microwave Scanning Radiometer—Earth Observing System (AMSR-E), on board the US NASA
Aqua satellite, was used to illustrate some of the limitation of microwave radiometry
in the Agulhas Current. Global maps of AMSR-E SST data are available on a 1/4
◦
1 See www.osi-saf.org
2 At http://oceancolor.gsfc.nasa.gov
3 For details see http://seadas.gsfc.nasa.gov