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GEO

GEO Geohazards Supersite

Group on Earth Observations

Welcome to the Virtual Archive 4 Supersite

Virtual Archives are online archives that provide an easy access to EO data by coupling high bandwidth, large storage space and software. The Virtual Archive 4 provides a Cloud based service for storing and providing access to ESA Synthetic Aperture Radar (SAR) data.

This virtual archive represents ESA contribution to the supersites initiative. This huge amount of SAR data (today over thirty thousand products are hosted on Virtual Archive 4) is accessible to science communities dealing with interferometry, landslide and change detection.

The virtual archive is a Cloud solution providing Storage-as-a-Service for storing the data and is coupled with complementary services:

  • Data discovery implementing simple interfaces such as OpenSearch and results in Atom, RDF and KML format
  • Data access via common web protocols such as HTTP(s)

The virtual archive technical solution is based on research and development performed by Terradue and partially funded by European Commission Framework Programme 7 on the context of the GENESI-DEC and GEOWOW projects.

OpenSearch interface

OpenSearch is a specification and a collection of technologies that allow publishing of search results in a format suitable for syndication and aggregation that can then be aggregated by larger indexes. It is a way for websites and search engines to publish search results in a standard and accessible format. It originates in a community effort built around Amazon's A9.com and is made available under the Creative Commons Attribution-Sharealike 2.5 license and it's now maintained in a community process at opensearch.org

For more information about OpenSearch and the GeoSpatial and temporal extensions please check these links

OpenSearch description document

An OpenSearch description document can be used to describe the web interface of a search engine. Each collection has an unique document with the information of how to query it by using url templates. For example, in:

http://eo-virtual-archive4.esa.int/search/ER02_SAR_RAW_0P/description

we have a OpenSearch Description XML document where we'll find general information about the search service,

<OpenSearchDescription>
	<ShortName>ER02_SAR_IM__0P</ShortName>
	<LongName>Dataset Search ER02_SAR_IM__0P</LongName>
	<Description>
	This Search Service performs spatial, temporal and other queries [...]
	</Description>
	<Tags>
	 Supersite, ESA, NASA, GEO, NSF, JAXA, UNAVCO, Digital Earth Communities, Catalogue
	</Tags>
	<Contact>info@terradue.com</Contact>
	<Image height="16" width="16" 
		type="image/vnd.microsoft.icon">
		http://eo-virtual-archive4.esa.int/images/geoss.ico
	</Image>
	<Query role="example" geo:box="-25,30,45,70"/>
	[...]

followed by a list of the URL templates supported by the search service. For example:

	<Url type="application/atom+xml" 
		indexOffset="0" 
		pageOffset="0" 
		template="http://eo-virtual-archive4.esa.int/search/ER02_SAR_RAW_0P/atom/?
				count={count?}&;
				name={geo:name?}&
				startPage={startPage?}&
				startIndex={startIndex?}&
				q={searchTerms?}&
				start={time:start?}&
				stop={time:end?}&
				bbox={geo:box?}&
				[...]		
			" />

shows us the template necessary to request an ATOM feed with the ER02_SAR_RAW_0P entries. In this template, we see that the feed can be searched by free text, bounding box, start and end times among other queriables.

Requesting entries using free text

As seen in the URL template above, to request all the entries tagged with some free text information like california december 2007 we need to replace the {searchTerms?} template by the desired textual value and then requesting the following url

http://eo-virtual-archive4.esa.int/search/ER02_SAR_RAW_0P/atom/?q=california december 2007

to obtain all records the records that filling that condition. You can try that query by clicking here

Requesting entries using Temporal extension

The previous text query gives an fast but approximative result of all the entries that cover the December 2007 range. Also from the URL template above, one can see that to request all the entries that are precisely under a given range of dates it is necessary to include the precise date and time of the start and end of the range.

For that, it is necessary to replace the {time:start?} and {time:end?} templates by the actual date values, such as, 2007-12-01T00:00:00 (or just 2007-12-01) and 2007-12-31T23:59:59 and then requesting the following url

http://eo-virtual-archive4.esa.int/search/ER02_SAR_RAW_0P/atom/?q=california&start=2007-12-01&stop=2007-12-31T23:59:59

to obtain all records the records that filling that condition. You can try that query by clicking here

Requesting entries using GeoSpatial extension

Equivalently to the previous query, one may want to explicitly define a given bounding box to search a specific geographical area and that cover the December 2007 range. Also from the URL template above, it is necessary to replace the {bbox:geo:box?} template by the actual AOI bounding box, such as, -119,33,-115,36 and then requesting the following url:

http://eo-virtual-archive4.esa.int/search/ER02_SAR_RAW_0P/atom/?bbox=-119,33,-115,36&start=2007-12-01&stop=2007-12-31T23:59:59				
				

to obtain all records the records that filling that condition. You can try that query by clicking here