Value til window.open

Hvordan får jeg selekteret option-value værdi indsat i window.open efter get-metoden?

<form name="mb" action="">
<select name="boe" size="1">
<optgroup label="Clouds">
<option value="00CLDIR_">Clouds (IR)</option>
<option value="00CLC03_">Cloud Cover (density)</option>
<option value="00CL203_">Cloud Cover(levels)</option>
</optgroup>
.
.
.
</select>
<input type="button" value="Choose" onClick="window.open('wypop.php','eupop','width=95,height=75,scrollbars=yes')"
</form>