xml - XSL transformation - Namespace prefix undeclared -

i have xsl file convert xml file. xml file has been obtained renaming original file had .safe extension. here can see first lines

<?xml version="1.0" encoding="utf-8"?> <xfdu:xfdu xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" xmlns:gml="http://www.opengis.net/gml"  xmlns:xfdu="urn:ccsds:schema:xfdu:1" xmlns:safe="http://www.esa.int/safe/sentinel-1.0" xmlns:s1="http://www.esa.int/safe/sentinel-1.0/sentinel-1"  xmlns:s1sar="http://www.esa.int/safe/sentinel-1.0/sentinel-1/sar" xmlns:s1sarl1="http://www.esa.int/safe/sentinel-1.0/sentinel-1/sar/level-1"  xmlns:s1sarl2="http://www.esa.int/safe/sentinel-1.0/sentinel-1/sar/level-2" xmlns:gx="http://www.google.com/kml/ext/2.2"  version="esa/safe/sentinel-1.0/sentinel-1/sar/level-1/slc/standard/iwdp"> 

let's extract value ascending

<metadataobject id="measurementorbitreference" classification="description" category="dmd">   <metadatawrap mimetype="text/xml" vocabularyname="safe" textinfo="orbit reference">     <xmldata>       <safe:orbitreference>         <safe:orbitnumber type="start">11987</safe:orbitnumber>         <safe:orbitnumber type="stop">11987</safe:orbitnumber>         <safe:relativeorbitnumber type="start">15</safe:relativeorbitnumber>         <safe:relativeorbitnumber type="stop">15</safe:relativeorbitnumber>         <safe:cyclenumber>83</safe:cyclenumber>         <safe:phaseidentifier>1</safe:phaseidentifier>         <safe:extension>           <s1:orbitproperties>             <s1:pass>ascending</s1:pass>             <s1:ascendingnodetime>2016-07-03t17:02:32.742483</s1:ascendingnodetime>           </s1:orbitproperties>         </safe:extension>       </safe:orbitreference>     </xmldata>   </metadatawrap> </metadataobject> 

i'm trying in way

<xsl:template match="/"> <xsl:value-of select="/metadatasection/metadataobject/metadatawrap/xmldata/safe:acquisitionperiod/safe:starttime" /> </xsl:template> 

or (if call file external xml file)

<xsl:value-of select="document('file:///c:/workspace/s2_xsltest/s1_xsltest/new_s1manifest.xml')/metadatasection/metadataobject/metadatawrap/xmldata/safe:acquisitionperiod/safe:starttime" /> 

in both cases i'm getting following error:

error [main] jaxpsaxprocessorinvoker - namespace prefix 'safe' undeclared.

any suggestions appreciated because i'm begginner xsl transformation. i'm using windows machine eclipse version: mars.2 release (4.5.2)

you must include

xmlns:safe="http://www.esa.int/safe/sentinel-1.0" 

in xslt, best @ top level:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/xsl/transform"      xmlns:safe="http://www.esa.int/safe/sentinel-1.0" ...