Php and Simple XML with namespace

<?php
$xmlString=<<<XML
<?xml version="1.0" encoding="ISO-8859-1"?>
     <Processrere>
    <ProcessDispositionDocumentResponses>
        <ProcessDispositionDocumentResponse>
            <ns0:Rsere> SCANNER.TIF302.42.236</ns0:Rsere>
        <ns0:Doser>1545421</ns0:Doser>
         <ns0:Caseser>130803</ns0:Caseser>
       </ns0:ProcessDispositionDocumentResponse>
  </ns0:ProcessDispositionDocumentResponses></ns0:Processrere>
XML;

$modifiedData = str_replace("ns0:", "", $xmlString);
$xml = simplexml_load_string($xmlString1);
$xml = simplexml_load_string($modifiedData);

//echo $xml->getName() . "<br />";

foreach($xml->children()->children()->children() as $child)
  {
 if ($child->getName() ==="CaseNumber"){
     $caseNumber=$child;
 }
  }
  echo $caseNumber;