Envisat MERIS sensor captures sand and dust from the Sahara Desert blowing across the Atlantic Ocean along the coasts of Mauritania (top), Senegal (middle) and Guinea Bissau (bottom). The cloud-covered Cape Verde islands are visible off the coast of Senegal. The Medium Resolution Imaging Spectrometer (MERIS) is a imaging spectrometer that measures the solar radiation reflected by the Earth, at a ground spatial resolution of 300m, with 15 spectral bands in visible and near infra-red and programmable in width and position. MERIS allows global coverage of the Earth every 3 days.

Sandstorms, or dust storms, are usually the result of atmospheric convection currents, which form when warm, lighter air rises and cold, heavier air sinks. Dust from the Sahara Desert can be transported over thousands of kilometres by convection currents, which also cause other meteorological conditions, such as thunderstorms. Sandstorms are very common over the Sahara, which is a major source of mineral dust, and large concentrations of it can be found in the tropical Atlantic and the Caribbean.

image credits: ESA

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Earth observation (EO) products have specific characteristics like the orbit number, processing center and acquisition station that follow a specific logic inherent to the EO community of users of satellite datasets.

Typically a EO product contains information regarding the:

• Platform or satellite from where it originates (e.g. SPOT, ENVISAT)
• The Satellite number (if exists)
• The sensor used to acquired the data
• The specific dataset identifier
• The processing center responsible for its elaboration together with the date and software used for the processing
• The date of acquisition
• The geographical footprint or coverage of the data present in the product

While the last two items are already covered by the time and geo opensearch specification extensions, all the others are currently only accessible through the generic searchTerms. This entry describes an extension proposal for OpenSearch that will provide a standard mechanism to query a resource based on those Earth observation elements. The naming of the elements follow the “GML 3.1.1 Application schema for Earth Observation products OGC 06-080r4“[OR2] normative that describe the EO Metadata format within the Heterogeneous Mission Accessibility (HMA) project. This elements present here are an initial set that were identified in this project phase. More elements will be added upon further analysis and discussion.

Namespace

The proposed XML Namespace URI for the OpenSearch Earth observation products extension is:

http://www.genesi-dr.eu/spec/opensearch/extensions/eop/1.0/

Example

 <?xml version="1.0" encoding="UTF-8"?>
 <OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/"
                        xmlns:eop="http://www.genesi-dr.eu/spec/opensearch/extensions/eop/1.0/">
   <ShortName>Web Search</ShortName>
   <Description>Use Example.com to search the Web.</Description>
   <Tags>example web</Tags>
   <Contact>admin@example.com</Contact>
   <Url type="application/atom+xml"
       template="http://example.com/?q={searchTerms}&orbit={eop:orbitNumber?}&amp;
                 acqstation={eop:acquisitionStation?}&amp;pw={startPage?}&amp;format=atom"/>
   <Url type="text/html"
       template="http://example.com/?q={searchTerms}&orbit={eop:orbitNumber?}&amp;
                 acqstation={eop:acquisitionStation?}&amp;pw={startPage?}"/>
   <LongName>Example.com Web Search</LongName>
   <Image height="64" width="64" type="image/png">http://example.com/websearch.png</Image>
   <Developer>Example.com Development Team</Developer>
   <SyndicationRight>open</SyndicationRight>
   <AdultContent>false</AdultContent>
   <Language>en-us</Language>
   <OutputEncoding>UTF-8</OutputEncoding>
   <InputEncoding>UTF-8</InputEncoding>
 </OpenSearchDescription>

Parameters

platform

A string identifying the platform from which the product originated (e.g. ENVISAT, SPOT)

http://example.com/?q={searchTerms}&pw={startPage?}&platform={eop:platform?}

This tag name corresponds to the Xpath description eop:platform/eop:Platform/eop:shortName

sensorType

A string identifying the sensor type from which the product originated. The possible values are: OPTICAL, RADAR, ALTIMETRIC, ATMOSPHERIC

http://example.com/?q={searchTerms}&pw={startPage?}&sensor={eop:sensorType?}

This tag name corresponds to the Xpath description eop:sensor/eop:Sensor/eop:sensorType

instrument

A string identifying the instrument from which the product originated (e.g. MERIS, AATSR, ASAR, HRVIR).

http://example.com/?q={searchTerms}&pw={startPage?}&instrument={eop:instrument?}

This tag name corresponds to the Xpath description eop:instrument/eop:Instrument/eop:shortName

resolution

A real number interval requesting the range of Sensor Resolution given in metres (i.e. uom=’m’). This parameter is a range or a group of integer number defined as [n1,n2] (meaning n1 <= resolution <= n2). It uses typical mathematical notation to define the interval with:
• [n1,n2] equals to n1 <= resolution <= n2
• [n1,n2[ equals to n1 <= resolution < n2
• ]n1,n2[ equals to n1 < resolution < n2
• ]n1,n2] equals to n1 < resolution <= n2

http://example.com/?q={searchTerms}&pw={startPage?}&res={eop:resolution?}

This tag name corresponds to the Xpath description eop:sensor/eop:Sensor/eop:resolution

orbitNumber

A integer number interval requesting the range of acquisition orbit number. This parameter is a range or a group of integer number defined as [n1,n2] (meaning n1 <= orbit <= n2). It uses typical mathematical notation to define the interval with:
• [n1,n2] equals to n1 <= orbit <= n2
• [n1,n2[ equals to n1 <= orbit < n2
• ]n1,n2[ equals to n1 < orbit < n2
• ]n1,n2] equals to n1 < orbit <= n2

http://example.com/?q={searchTerms}&pw={startPage?}&orbit={eop:orbitNumber?}

This tag name corresponds to the Xpath description eop:acquisitionParameters/eop:Acquisition/eop:orbitNumber

acquisitionStation

A string identifying the station used for the product acquisition (.

http://example.com/?q={searchTerms}&pw={startPage?}&acqStation={eop:acquisitionStation?}

processingCentre

A string identifying the processing centre from which the product was elaborated (e.g. PDHS-E, PDHS-K, DPA, F-ACRI)

http://example.com/?q={searchTerms}&pw={startPage?}&procCentre={eop:processingCentre?}

processingSoftware

A string identifying the software used when product was elaborated (e.g. ASAR/3.06, MERIS/5.04, MEGS-PC/7.4). This element shall return all the elements similar with the request as in LIKE or MATCH query. As such, a query for ASAR/3 will return all the products processed with any of the release of version of 3 of the ASAR processor.

http://example.com/?q={searchTerms}&pw={startPage?}&procCentre={eop:processingSoftware?}

processingDate

This queries the element for a time interval between two time points as defined by the ISO8601.

http://example.com/?q={searchTerms}&pw={startPage?}&procDate={eop:processingDate?}

The processingDate should be replaced by a string containing the time interval in the format YYYY-MM-DDTHH:mm:ss/YYYY-MM-DDTHH:mm:ss

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This entry is an initial proposal and further elements might be added in the future. Please send any comments, doubts or suggestions.

Earth observation products have specific characteristics like the orbit number, processing center and acquisition station that follow a specific logic inherent to the Earth observation community. This entry describes an extension for OpenSearch that will provide a standard mechanism to query a resource based on those Earth observation elements. [...]

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