The misr_time program calculates block center times for a MISR Level 1B2 
file using the RANGE_BEGINNING_DATE and RANGE_ENDING_DATE from the
file's core metadata.  It returns values to the nearest second, and
in comparison with block center times stored in files produced
beginning in August 2003, these values are with one second of the 
results calculated during processing.  A block center time data file 
is created with the same name as the MISR L1B2 file, with the addition 
to the file name of _block_centers.txt and without the original file's 
.hdf suffix.

The program is written in ITT Visual Information Solutions IDL language and can be
run with a licensed version of that software.  In addition, a .sav file 
is included in the misr_time tar package which can be run using the IDL 
Virtual Machine.  The IDL Virtual Machine is a free version of IDL available 
from ITT Visual Information Solutions at http://www.ittvis.com/idlvm/.  The IDL VM 
software may be downloaded from that site or ordered from ITT VIS on CD at no 
cost.  The site provides installation instructions.

The files in the misr_time.tar delivery package can be extracted using
the command
    tar xvf misr_time.tar
on Unix systems or using a file extraction utility such as WinZip on
PCs running Windows.   A directory named misr_time will be created and the 
files in the delivery package will be written there.

To run the program:

1)  If you have a licensed version of IDL, start the IDL development 
environment and from the idlde file menu, open the project misr_time.prj 
which is located in the misr_time directory.  From the idlde Project menu, 
choose Build and then choose Run.  

2)  To run using the IDL Virtual Machine, on a Unix system at the Unix 
command prompt, type
    idl -vm
or on PCs, double click on the IDL VM desktop icon.  The IDL VM splash screen 
will be displayed.  Click anywhere on the splash screen and then use the dialog
box that appears to navigate to and select the misr_time.sav file.  Or, on
a PC, you can drag the misr_time.sav file from a Windows Explorer window onto
the IDL VM desktop icon.

3)  At this point, a dialog box for selecting the MISR L1B2 data file will appear;
navigate to and select the desired data file.  When the processing is complete,
a message pop-up notification window will appear.  The block center data output
file is written to the current IDL directory.


NOTES:

1)  A time of 00-00-0000 00:00:00 UTC for the start block center indicates
that data in that first good data block begin after the block center.  
Likewise, if the end block center is 00-00-0000 00:00:00 UTC, data in the
last good data block end before the block center.

The following notes apply to those working with a fully licensed
version of IDL:

2)  This program is written to work with Level 1B2 data in the
stacked block format.  To use this program with Level 2 data, it will
be necessary modify the code to choose an appropriate parameter to search 
for the start of data.  The grid name and field name for that parameter
need to be modified in the call to the read_grid_field routine.

3)  The program is written to work with a parameter whose fill value is
positive, so if a parameter with a negative fill value is used, the
comparisons with fill value used in calculating the first good data line
and the last good data line would also need to be modified.

4)  The path in the DIALOG_PICKFILE call can be edited to specify the 
directory path for MISR data files.