Getting author URL outside the loop

I just put a piece of code from author.php file of TwentyTwelve theme:

<?php
    /* Queue the first post, that way we know
     * what author we're dealing with (if that is the case).
     *
     * We reset this later so we can run the loop
     * properly with a call to rewind_posts().
     */
    the_post();
?>

<header class="archive-header">
    <h1 class="archive-title"><?php printf( __( 'Author Archives: %s', 'twentytwelve' ), '<span class="vcard"><a class="url fn n" href="' . esc_url( get_author_posts_url( get_the_author_meta( "ID" ) ) ) . '" title="' . esc_attr( get_the_author() ) . '" rel="me">' . get_the_author() . '</a></span>' ); ?></h1>
</header><!-- .archive-header -->

<?php
    /* Since we called the_post() above, we need to
     * rewind the loop back to the beginning that way
     * we can run the loop properly, in full.
     */
    rewind_posts();
?>

Pay attention to how they get an author posts link. At the beginning they call the_post function outside the main loop to fetch first post. Then they get author information, like posts URL and display name. And finally they call rewind_posts function to reset loop.

You can use the same technique in your header.php file.