Help for Near Real-time Sea Surface Temperatures

This site provides access to the most recently available satellite images, processed to convey sea surface temperature (SST). By clicking on a thumbnail image you can explore the SST map in greater detail in your web browser. User registration (which is free) enables customisation by allowing you to save favourite areas of interest and provides access to an additional data exploration tool. The viewer available to registered users is particularly suitable if you have a low-bandwidth internet connection. The tabs below provide more information.

SST Page

The SST index page provides thumbnail graphics depicting all the satellite imagery available organised in order of increasing age (latest images first). The graphics include the shorthand name of the satellite (in dark blue text) and indicate the data coverage for the corresponding image.

screenshot of the home page

Clicking on a graphic links to the corresponding map page for viewing the data. All satellites are included by default, check-boxes at the top of the page allow selection of specific satellites.

The date and time of each satellite 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). Users in eastern Australia should add 10 hours to UTC to get local time (11 hours during daylight saving). Note that the times provided for each image are approximate; it takes between 10 and 20 minutes for a satellite to acquire a full-length image.

Map Page

The map pages are reached by clicking on the thumbnail graphics. The “SST” 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 position of the cursor in latitude and longitude is shown in the top right hand corner.

screenshot of the SST n18 map page

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. This image is a zoomed version of the one above, with a new temperature scale.

screenshot of the SST n18 map page detail

Left 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.

Registration (with an email address) is free and provides access to advanced features including user-customised map regions and a viewer with tools for exploring the data.

To register, click the ‘Login’ link at the top of the page to reach a login page.

screenshot of the SST registration page

Left 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.

Click ‘Create an Account’ button and a popup appears.

screenshot of the SST account creation page

Enter a valid email address, your password (twice) and the Captcha text. Hit the ‘Signup’ button and you will be sent an email with a link to confirm registration. Once you have clicked that link, you can return to the login page and log in. When you have logged in, the SST index page shows two new features – a ‘Settings’ link, and a drop down menu with a region name (default value ‘Australia’).

screenshot of the SST home page after logging in

Once logged in, SST images can be selected from the ‘SST’ page thumbnails as before. The map viewer page will show some additional buttons: ‘Save’, ‘Static Image’, and ‘Viewer’. There are also ‘Next’ and ‘Previous’ buttons which move to the next (more recent), or previous (older) image, without the need to go via the SST thumbnails page.

screenshot of the SST map page after logging in

The map can be zoomed and panned as before, and the temperature scale adjusted. Hitting the ‘Save’ button opens a dialogue box that allows entry of a name for the current settings (view region and temperature scale). In the example here, a group of settings with the name ‘Bass Strait’ is being saved.

screenshot of the SST detail page after logging in. Showing the 'add region' dialog box

Upon retuning to the ‘SST’ index page as a signed-in user, ‘Bass Strait’ will now appear in the drop down menu and thumbnails will be generated covering the chosen region, but only for satellite images that contain data in that region. Other passes are will not be shown.

screenshot of the SST home page after logging in, with an area selected

Now, when an image is opened from this region-selected SST thumbnail page, it opens already subset to the region, and with the temperature scale limits set.

screenshot of the SST detail page after logging in, with an area selected

Clicking the ‘Static Image’ button generates a plot of the displayed region that can be saved (by right clicking).

screenshot of a static image for downloading

Clicking the ‘Viewer’ button loads the image in a web page with additional tools and controls that allow exploration of the SST detail (see the ‘Viewer’ tab).

Choosing the ‘Viewer’ button, displays the satellite image in a page that, once it has loaded, can be used to manipulate and explore the data without further need for network access. This is especially useful for low bandwidth network connections.

The longitude and latitude of the cursor, and the temperature at that location, are continuously displayed in the top left corner. This display can be toggled on and off by the ‘o’ (o for oscar) key. If present in the region, the 200m depth contour (a proxy for edge of the continental shelf) is plotted in the image as a solid black line.

Zooming of the image is accomplished via the + and - keys, or using the scroll wheel on the mouse. The image can be panned by dragging the mouse (left click hold and move mouse).

screenshot of the viewer screen

Clicking the ‘Help’ button brings up an information box with a full list of the mouse and keyboard controls.

screenshot of the viewer help screen

Colour Controls

The colour scale can be modified interactively in three different ways.

  1. By left clicking, or shift+left clicking, on the colour bar itself, a new minimum (or maximum) temperature can be set. This enables a small temperature range to be represented by the full range of colours, so that small variations can be enhanced.
  2. A similar effect can be achieved using the Left and Right arrow keys can be used to move the temperature range represented up and down.
  3. The Up and Down arrow keys extend and compress the range of temperatures within the display range respectively.

Using the image above as an example, here the temperature range has been compressed using the Up arrow key, and then the centre of the range is increased using the Right arrow key. All changes can be reset to the default starting values with the 0 (zero) key.

screenshot of the viewer screen with the temperature compressed and range increased

Range and Direction

To facilitate measurement of distances and directions, a "ruler" function is provided. To activate it, hold the 'Ctrl' key, then at the starting point, left mouse click (and release), and then while holding 'Ctrl', move the mouse to the end-point and release 'Ctrl'. The endpoints will be marked with a solid line joining them. The information box at the top left reports the range in nautical miles and the bearing in degrees.

screenshot of the viewer screen showing a range and direction

A logged-in registered user has access to configuration pages via the ‘Settings’ link at the top of the page. This opens a page with 4 tabs that enable further customisation.

The first tab 'Settings' allows choice of the default viewer mode that opens when an SST thumbnail is selected. Two options provide customisation of the way locations are reported, and a drop-down menu is used to select what region is shown by default when a user first logs in.

screenshot of the settings page

The second tab 'Edit Regions' permits changes to be made to the bounding box and temperature ranges of saved regions, or for saved regions to be deleted.

screenshot of the edit regions page

The third and fourth tabs 'Change password' and 'Change email' do what they say, allowing registered users to change either their password, or even their username. Both changes require the re-entry of the existing password to confirm.

screenshot of the change password page

screenshot of the change email page

Satellites

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. This web display system refreshes its images from the data processing chain every 20 minutes.

Two series of satellites and sensors are presently in use. The 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.

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 and are referred to on these web pages by the shorthands n18 and n19 respectively. When everything is working well, NOAA imagery will initially become available on this site 1-2 hours after the satellite overpass.

The MODIS sensors are operated by NASA for Earth Observation. There are two instruments, one carried on each of the Terra and Aqua satellites, launched in 1999 and 2002 respectively. These satellites have similar over-the-pole orbits to the NOAA satellites, but the MODIS sensor makes a somewhat narrower 2300 km image. Both satellite missions have far exceeded their original design lives of 5 years. The two sensors are denoted "modisT" and "modisA" on this site. Various aspects of the MODIS sensor processing chain can delay receipt of these data by between 8-12 hours after the satellite overpass. Work is being undertaken to reduce this latency.

There are several additional satellite sensors, either planned or already launched, that could be used to complement the data currently available via this site. We plan to add imagery from these sensors as they become available and as resources permit.

Caveats

Typical accuracies achieved by the processing system for near real-time operation are temperatures better than 1 Celsius and position accuracy within 1-1.5 km. Normally only the past 48-60 hours 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.

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.

Some of the data were processed using the NCI National Facility in Canberra, Australia, which is supported by the Australian Commonwealth Government.

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

  • Hobart (CSIRO Oceans & Atmosphere Flagship)
  • Melbourne (Bureau of Meteorology)
  • Darwin (Bureau of Meteorology)
  • Alice Springs (Geoscience Australia)
  • Perth (WASTAC Consortium)
  • Townsville (Australian Institute of Marine Science)

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