The quality of satellite images used for the generation of SST (Sea Surface Temperature) composites can be affected by the presence of undetected clouds or ice, or by an occasional malfunction of a satellite sensor. Temperature values computed over pixels exhibiting those imperfections then become incorrect.
Various levels of filtering are applied to images in order to remove bad pixel values, giving rise to various versions of the composites.
SST product types available on SLGO
The "Data type" drop-down menu holds four entries related to SST composites.
"Mean Temperature" represents the union of L0 and L1 products; the L1 version (more reliable) is always offered when both L0 and L1 versions exist for a given product. Unfortunately, an L1 version does not become available until at least a month after the underlying images have been acquired; therefore the L0 version is used when being the only available version. In fact, the L0 version is returned, so that users are not misled into thinking that no products are available for the most recent days.
Unfiltered Temperature (L0)
This level corresponds to the absence of any filtering other than the basic one allowed by the TeraScan system (www.seaspace.com). Composites at this level are computed from SST maps generated just a few hours after the satellite passes become available. They can exhibit wrong temperature values at various spots.
Temperature with cloud and ice filters (L1)
At this level, composites are produced using images subjected to a series of three distinct filters.
Temperature with climatological filter (L3)
Composites of this level are produced using images which are first filtered similarly to the L1 products. A fourth climatological filter is then applied.
L2 daily composites were used just as intermediate products in the process of producing more accurate climatologies. They are not made available.
WMS (Web Map Service)
SST composites are made available through a WMS service, so that a user equipped with a GIS software supporting WMS connections can easily access the temperature maps over the internet. In fact, the SLGO portal directly relies on this service for browsing through the SST image catalog when used in basic display mode.
The WMS service can be reached at the following basic URL that can be used when the GIS software requires the identification of the WMS service:
The above URL gives access to products of the "Mean Temperature" category available for the most recent day. Those will always be of L0 type (see "Availability" above).
Two custom parameters can be appended to the URL to select the category and the time period for which to return products. When used, a '?' character must prefix the first appended parameter. When both are used, they must be separated by a '&' character. No space should appear in the appended string.
|coll=cat, where 'cat' identifies the product category. It must be one of|
|msst||select "Mean Temperature" category; this is the default|
|msst-L0||select "L0 category"|
|msst-L1||select "L1 category"|
|msst-L3||select "L3 category"|
|period=per, where 'per' identifies the wanted time period. It can be entered as a single value, or a series of comma-separated values. A date value can identify a single day, or a time interval composed of a starting and ending date separated by a '/' character.Both value formats can be intermixed. A date value is entered in the 'yyyy-mm-dd' format. For example:|
|2011-03-01||March 01 2011|
|2011-03-01,2011-10-10||March 01 2011 and March 10 2011|
|2011-03-01/2011-03-07||From March 01 2011 to March 07 2011|
|2010-03-01/2010-03-07,2011-03-01/2011-03-07||First 7 days of March 2010 and March 2011|
By default, the products of the most recent day for which they are available are selected.
For example, using the following URL when identifying the WMS service inside the GIS tool will result in the tool asking the service to return layers pertaining to level L1 SST composites available for the first 5 days of July 2006 :
NOTE. The above URL is NOT a valid WMS command. The GIS WMS tool will take care of appending the parameters needed to turn it into a valid WMS command.
Connectivity to the WMS service can be checked by sending the service a 'getcapabilities' command similar to the one sent by a WMS client to query the service about what it has to offer. Enter the following URL in an internet browser :
The service should reply with an XML document formatted as per the OGC WMS specification.