Average Sea Surface Temperatures

Contents

  1. Overview and caveats
  2. Data processing and averaging
  3. Index page
  4. Map page
  5. Satellites
  6. Acknowledgements and feedback

Overview and Caveats

These pages provide access to contemporary satellite infra-red imagery processed to convey sea surface temperature. Multiple satellite images are averaged over periods of 1, 3 or 6 days to improve the chances of recording a cloud free observation. Typical accuracies achieved by the processing system for near real-time operation are temperatures better than 0.5 Celsius and positions within 1-1.5 km. Normally only the past 10-12 days of imagery are shown. A large archive of historical imagery (complemented by other ocean observations) is available via the IMOS OceanCurrent web site.

These data are being collected for research purposes but are made freely available subject to the terms of the Creative Commons Licence used by IMOS. Whilst every effort is made to keep the data as accurate as possible, users should take into account the specific conditions outlined in CSIRO's legal notice and disclaimer. Furthermore, although the service aspires (through automation) to 24x7 operation, it is important to note that it is primarily supported only during normal business hours, and then only as resources permit.

Data Processing and Averaging

Data from sensors on several satellite platforms are included. The data processing chain is a multi-stage system that merges imagery from a number of reception sites and organisations. As more data becomes available over time, the data is progressively updated to improve quality and spatial coverage. Typically this happens sub-hourly in the first 12 hours after acquisition and much less frequently thereafter. Although this web display system refreshes its images from the data processing chain every 20 minutes, the averaged images are not released until completion of the averaging period. Consequently the 1-day averages will always be delayed by about 1 day, the 3-day averages by 1.5-2 days, and the 6-day averages by 3-4 days. Quality control issues can sometimes delay imagery further. Users requiring more up to date data should use the shorter averaging periods, or visit the companion near real-time data web site, noting that single pass imagery can be strongly cloud affected. Note that there is substantial additional information about the data processing available at the IMOS GHRSST web page.

Index Page

The index page provides thumbnail graphics depicting all the satellite imagery available organised in order of increasing age (latest images first). The graphics are overwritten with the data averaging period (in dark blue text) and indicate the data coverage for the corresponding image. Clicking on a graphic links to the corresponding map page for viewing the data (see below). All satellites are included by default, check-boxes at the top of the page allow selection of specific averaging periods.

The date and time of each averaged image appears below the corresponding graphic, expressed as universal time (UT, denoted by the trailing 'z' character). The conversion between UT and local time depends on where you are in Australia and whether daylight saving is in effect. It is easy to look up the current UT on the internet (for example). Note that the times provided correspond to the centre of the averaging period.

Map Page

The map pages are reached by clicking on the thumbnail graphics. The index link at the top of the page can be used to return to the thumbnail graphics page.

The map page comprises a web map, initially centred on Australia, with some controls. The map can be zoomed in and out with the "+" and "-" controls or with a mousewheel. The map can be panned by using the mouse to click and drag a location.

The sea surface temperatures are displayed on the map, using the colour scale shown at the top of the map page. The upper and lower limits of this colour scale can be adjusted by entering values (in degrees C) in the fields labelled "Min" and "Max". Temperatures that are outside the range specified for the colour scale are shown in black. Where the processing system has determined there is an issue with the observations, such as cloud cover or a data transmission problem, data are not shown.

The data layer (showing the sea surface temperature) will normally update when the map is zoomed or panned, or when it detects that the colour scale range has been changed. A "refresh" button is provided to force an update if necessary. The current web server is perhaps a little underpowered for this application so a little patience is advisable when the page takes a while to update. It is intended that the system be migrated to a more powerful server in the near future (mid-2015).

Clicking on a point on the map will pop up a box reporting the longitude and latitude (in decimal degrees) and the temperature value (in degrees C) at that point.

Satellites

The satellite sensors observe infra-red radiation to estimate surface temperatures. They can image both at day time and in the night, but observations can not be made through cloud, which is why filtering out cloudy pixels and averaging multiple satellite scenes together produces better data coverage.

The NOAA series of polar orbiting meteorological satellites (POES) carry the AVHRR sensor and have been the backbone of sea surface temperature monitoring globally since the 1980s. These satellites orbit over the earth's poles (crossing the equator from north to south, and then from south to north) at an altitude of approximately 800km providing images 2400km wide with a resolution of just over 1km. A complete orbit takes approximately 100 minutes, and every point on the earth is observed at least twice a day. Two of these satellites, NOAA-18 and NOAA-19, are presently operational. Although imagery becomes available within a few hours of the satellite overpass, the data are not released to this site until the averaging interval is complete. This means the imagery are progressively more delayed for the longer averaging periods.

Acknowledgements and Feedback

These web pages data are provided by CSIRO using data sourced from satellite reception stations around Australia and processed by the Bureau of Meteorology and CSIRO with the support of the Integrated Marine Observing System (IMOS) - IMOS is a national collaborative research infrastructure, supported by Australian Government.

The satellite platforms and sensors are operated by NOAA in the US. Reception stations contributing data include:

For more information or to provide feedback, contact marine-remote-sensing AT csiro.au