\section{\bf{Accessing Yohkoh files}}

\subsection{\label{readtapes1}How to Read Yohkoh Archive Tapes (GO\_RDTAP)}

The routine GO\_RDTAP allows access to the Yohkoh archive tapes.  Normally
the archive data are written on Exabyte (8 mm) or DAT (4 mm) tapes.
There is one archive tape for each week of data.  The first step to
accessing archive data are to determine which tape it is on.  Use the
WeekID table shown in the Reference Guide to figure out what tape you
need.  For example, if you wish to look at data on 27-Mar-92 you first
determine that it is week 13 in 1992, so the weekID is 92\_13.  You
can use the routine TIM2ORBIT with the {\it /print} option to get
the week number.  Put that tape into the tape drive.

You need to move to the directory where you want the data to be written.
\index{archive tapes, reading}\index{tapes, archive, reading}\index{archive tapes}

GO\_RDTAP is a menu driven program to retrieve data from the 
archive tapes via a menu driven program.  The ISAS and LPARL machines
have a copy of the directory listing for each tape saved on the
disk.  This means that you can simply type:
%
\idlinputa{go\_rdtap} \index{GO\_RDTAP}
%
and it will list all of the tapes that have been made.  You need to select
the tape that you are reading.  If your system does not have the XBD files
on-line, then type:
%
\idlinputa{go\_rdtap, /tape}
%
after you have loaded the tape, and the program will read the directory
listing from the tape.

\EEnumerate
\item A menu will appear with a series of weekly log files.  If you do not need any of
	the weekly files, then just select QUIT/EXIT.  
\item The next menu will be the
	file prefixes that are available.  Click on each file prefix that you wish
	to copy to the disk.  
\item When you have selected all of the prefixes you need, click on QUIT/EXIT.  
\item The final menu is the FileIDs that are on the
	tape.  Select the fileIDs you need, and then click on QUIT/EXIT.  
\item You will be asked whether you are ready to read
	the tape.  GO\_RDTAP will also display the number of kilobytes that you
	have selected to read, so check the available space on the disk selected
	before continuing.
\end{enumerate}

If the {\it /ydb} switch is used on the call to GO\_RDTAP, then the
weekly data files will be copied to their proper directories (the default
is to copy them to the current directory).

See the Reference Guide appendix for more detailed information on
the archive tapes.  

\subsection{\label{readtapes2}How to Read Yohkoh Database Tapes (RD\_YDBTAP)}

RD\_YDBTAP reads and installs Yohkoh Data Base (ydb) files from the
distributed ``ydb'' tapes.  A ``ydb'' tape contains data files which are
used by the Yohkoh analysis system. These may include both Yohkoh specific
data (e.g., Yohkoh pointing, ephemeris, observing logs, etc.) and
supporting data sets (GOES, BATSE).  Although some of the smaller database
(ydb) sets are available as compressed tar\footnote{{\em tar} is the Unix
backup utility} files and are included in the installation and upgrade
procedure, the ydb tapes are the recommended method for distribution of
large database sets (such as pointing data and observing log files).

RD\_YDBTAP Functions:

\IItem 
\item Provide graphical interface which allows user to specify database sets for
  extraction; selection may be by ydb file type and/or times.
\item Using ydb tape directory file, compare directory contents with user 
  requests and flag any discrepancies.
\item If output directory is not specified, use site specified Yokhoh environment
  to place files in proper locations.
\item Optionally create required directories which do not exist.
\item Using directory file information on file sizes and local output directory
  status, warn user if there is insufficient disk space to satisfy requests.
\end{itemize}

\index{YDB tapes, reading}\index{tapes, database, reading}\index{database tapes}\index{secondary database tapes}
The following example will allow the user how to interactively select times and
data sets for extraction and installation
%
\idlinputa{rd\_ydbtap}\index{RD\_YDBTAP}\index{YDB tapes}\index{database tapes, reading}
%
Several options are available on input -- if files are fully specified, no
additional user interaction is required.  The next example would extract and
install all data base files for the specified week using tape drive one.
%
\idlinputa{rd\_ydbtap, dev=1, weekid='92\_45', /all}
%
RD\_YDBTAP may function to ``boot up'' a remote system prior to implementation of 
a ydb network upgrade system.  Due to the potential of adversely impacting
the network, a network-based ydb upgrade system should be coordinated 
with the Yohkoh SW managers. They can provide some Unix scripts which 
assist in this task and allow some scheduling control. For more information 
on network upgrades of the Yohkoh data base, send e-mail to: 
\begin{verbatim}
        software@isass0.solar.iasa.ac.jp, SUBJ="ydb via network"
\end{verbatim}

\subsection{FTP Access to Yohkoh Archive, etc...}
