\hypertarget{chapter1}{}
%%% CHAPTER 1
\chapter{Introduction}
This document consists of a Software Guide (\hyperlink{chapter2}{Chapter 2}) and Instrument 
Guide (\hyperlink{chapter3}{Chapter 3}). The Software Guide describes how to analyze XRT
data; the Instrument Guide gives a broad overview of the X-Ray
Telescope's hardware components. 
\section{Hinode and the X-Ray Telescope}
Hinode is a joint mission between the space agencies of Japan, 
United States, Europe, and United Kingdom. The craft carries three 
instruments, a Solar Optical Telescope (SOT), Extreme Ultraviolet 
Imaging Spectrometer (EIS) and X-Ray Telescope (XRT); together, they 
are designed to provide multi-wavelength data from the photosphere to 
the upper corona. The 875-kg craft was launched on September 23, 2006 
into a polar, sun-synchronous orbit at 600 kilometers with an
inclination of -98$^{\circ}$, allowing 9 months of continuous
observations and a 3-month eclipse season. Hinode provides
approximately 7 GB of data daily. \par

The XRT images coronal plasmas from 1 to approximately 20 million K 
with $2^{\prime \prime}$ resolution ($\approx 1^{\prime \prime}$
pixels). The XRT images through nine X-ray filters using two filter
wheels. The XRT also contains a visible light optic that takes G-band
images for alignment. The back-thinned CCD has 2048$\times$2048 pixels
and images over a 35$^{\prime} \times$ 35$^{\prime}$  field of view,
though partial frame images of various sizes can be read from select
areas of the CCD. XRT takes approximately 0.7 GB of data daily as 
lossless or one of nine forms of lossy JPEG compression. \par

The baseline duration of the mission is  3 years. Currently XRT, SOT 
and EIS are operated from the Institute of Space and Astronautical 
Science (ISAS) in Sagamihara, Japan. See the Instrument Guide 
(\hyperlink{chapter3}{Chapter 3}) for more information. \par
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% SYNOPTIC DATA
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\subsection {Synoptic Data}
The Hinode craft points at sun center for 10 minutes 2-4 times a day, 
enabling XRT to take synoptic data in the form of full-resolution,
full-disk images with both long and short exposures in one or more 
X-ray filters. The long and short exposures are taken to capture the 
dynamic range of the coronal plasma's X-ray emission and thus the 
saturated pixels from the long exposure are replaced with 
corresponding pixels in the short exposure pair. The pair is then 
available as one image in a form referred to as Level 2 data 
(See \hyperlink{datap}{Section~\ref{dataproducts}}). Synoptic Level 2 data is available at: \\
\url{http://solar.physics.montana.edu/HINODE/XRT/SCIA/latest_month.html}.
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% ECLIPSE SEASON
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\subsection{Eclipse Season}
The Hinode craft is in a polar, sun-synchronous orbit at 600 kilometers 
with an inclination of -98$^{\circ}$, allowing 9 months of continuous 
observations and a 3-month eclipse season. The eclipse season begins 
in May every year; eclipse durations are shown in \hyperlink{Fig1_1}{Figure~\ref{Figure1_1}}. 
Effects of atmospheric absorption will be visible in XRT images 
beginning $\approx$ 4 days before the season through to $\approx$ 
4 days after the season, for a total of $\approx$ 100 days. \par

\begin{figure}[h]
\hypertarget{Fig1_1}{}
\centering
\includegraphics[width=.65\textwidth]{eclipse.pdf}
\caption{Hinode eclipse season.}
\label{Figure1_1}
\end{figure}
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% OVERVIEW OF THE DATA ANALYSIS PIPELINE
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\section{Overview of the Data Analysis Pipeline}
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% DATA TRANSPORT
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\subsection{Data Transport}
XRT downlinks 15 times daily at the Svalbard Ground Station, a member
of the Norwegian Space Centre (NSC). Downlinks also occur up to four
additional times daily at any one of the Japanese Aerospace
Exploration Agency (JAXA) ground station network antennas, which
include two Japanese sites, in the Kagoshima and Ibaraki prefectures,
as well as three overseas sites: Maspaolomas, Canary Islands, Perth,
Australia, and Santiago, Chile. Downlinked XRT telemetry is sent to
the ISAS mission archive, the principal XRT data site, for
reformatting to create Level 0 data. Both QuickLook and Level 0 data are
then mirrored to the Smithsonian Astrophysical Observatory (SAO), in
Cambridge, MA. Using the data retrieval techniques described in
\hyperlink{obtaind}{Section~\ref{obtainingdata}}, users access machines at SAO to obtain XRT data. \par

\hypertarget{datap}{}
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% DATA PRODUCTS
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\subsection{Data Products}\label{dataproducts}

XRT data is available as FITS files, each of which include a data array and a metadata structure array containing a list of keywords (see \hyperlink{appendix}{Appendix 1}). Several types of data products are available: QuickLook, Level 0, Level 1, and Level 2. \par

QuickLook data are expedited to ISAS so XRT operation team members can view images a few hours after the data has been taken. However, these data have not been completely reformatted and thus the images may not be whole and the FITS keywords will not be populated completely or correctly. XRT team members use this data to make operations decisions but these data products are not suitable for scientific purposes. \par

Level 0 data contains whole images; in addition, the FITS keywords have been populated correctly by the reformatter. Level 0 data cannot be created until all the housekeeping data for a particular observation has arrived at ISAS, which may take up to 7 days. Level 1 data has been calibrated by \textbf{xrt\_prep.pro} and has units of instrumental Data Numbers. Level 2 data has been further processed into more physical units or into movies. The following table describes each of the XRT data products:  \par

\begin{table}[h]
\hypertarget{DataTypes}
\centering
\caption{\textbf{XRT Data Types}}
\label{datatypes}
\rowcolors{1}{}{gray!35}
\begin{tabular}{p{0.75in}p{1.5in}p{1in}p{2.1in}}
\midrule
\T {\bf Level} \B & {\bf Pixel values} & {\bf File format} & {\bf Purpose} \\
\T QuickLook \B & Data Number (DN) & FITS & Operations, \mbox{Data Verification,} QuickLook movies \\
\T 0 \B & DN & FITS & Basic science \\
\T 1 \B & DN/sec & FITS & Calibrated images \\
\T 2 \B & Physical units & Any & \mbox{Short and long exposures} \mbox{summed into one image;} \mbox{Differential Emission Measure;} \mbox{Temperature Maps} \\
\end{tabular} %The mbox was use above to clear an underfull hbox error that was causing the words to have larger than normal space.
\end{table}
XRT instrument data are available as single Level 0 FITS files with names in the the format \textbf{XRTYYYYMMDD\_HHMMSS.S.fits}. The files stored in directories organized by hour beneath directories organized by day, month, and year. An example of a directory structure to access an individual FITS file is as follows: 

\textbf{YYYY/MM/DD/Hhh00/}, or \textbf{2007/05/27/H1300}. 
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% REFERENCES
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\section{References}
\begin{table}[H]
\centering
\caption{\textbf{XRT References}}
\rowcolors{1}{gray!35}{}
\begin{tabular}{p{2in}l}
\midrule
\T Instrument paper \B & \citealt{Golub07} \\
\T Camera paper \B & \citealt{Kano08} \\
\T Calibration paper \B & \citealt{Kobelski13} \\
\T Measuring uncertainties \B & \citealt{Kobelski13} \\
\T Temperature Response \B & \citealt{2011SoPh..269..169N} \& \citealt{Narukage14} \\
\T Synoptic Images \B & \citealt{Takeda16} \\
\end{tabular}
\end{table}
XRT images in the popular media should be credited to SAO/NASA/JAXA/NAOJ. Please check the current Hinode data thesis projects webpage prior to publishing results. \\
%\url{http://hinode.stelab.nagoya-u.ac.jp/en/publ/hinode_thesis.shtml}
\url{https://hinode.isee.nagoya-u.ac.jp/thesis.input/}

For more information about Hinode XRT visit the website: \\
\url{http://xrt.cfa.harvard.edu}.
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% CONTACTS
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\section{Contacts}

For data analysis problems, contact {\tt xrt\_manager[at]cfa.harvard.edu}.

\noindent For science discussions, contact {\tt xrt\_science[at]cfa.harvard.edu}.  
