Note that you DO have to work on redoubt
for some things today!
Complete shift in gears now! We're moving from GPS processing into InSAR processing (for a bit, GPS processing will come back later). The goal for today is to get you comfortable finding you way around gmtSAR. We'll do data access next week.
A note of warning: there's a lot of vocabulary flying (ha!) around in InSAR processing. Most of these are standard satellite related terms. If there's something you don't understand, it's usually a good idea to search for the term, the satellite, and read up on it.
gmtSAR is an open source InSAR processing system. It makes use of the open source Generic Mapping Tools (GMT) (a tool very worthwhile learning in its own right!! We'll have some lectures on this later this semester in GEOP501; feel free to sit in!).
You can guess that ease of use is one of the main reasons I decided to use this tool in the class; other InSAR processors exist.
Read through sections 1.1 and 1.2 (no need to get into 1.2.1 - proper focus, right now) of the gmtSAR documentation and answer the following questions (in full sentences of well phrased English language):
Log into redoubt
(please use ssh -Y
or -X
to enable graphics forwarding!!) and
go into your $GEOP555
directory. On the command line enter:
$> gmtsar.csh
This lists all the shell scripts (recipes, in a sense) that are currently available
with GMT5SAR. The very bottom of the message gives a generic usage instruction 3 times
repeated. That's OK. Note that for most of these scripts you will
get a hint on how to use them if you just type their name
on the command line and hit enter (just like you did with
gmtsar.csh
above. Here are some questions:
Create a directory $GEOP555/lab07
and place
a gmtSAR test data set from /data/InSAR/gmtSAR_TEST/geop555/
into it.
Refer to the gmtSAR documentation, section 2.1, to understand what all the files are that gmtSAR produces during the processing. In fact, many things that you may not understand are likely explained somewhere in there. Feel free to get well acquainted with this document.
After changing into the lab07 directory, copy and unpack the data:
$> cd $GEOP555/lab07 $> cp /data/InSAR/gmtSAR_TEST/geop555/YOURDATASET.tar.gz ./ $> tar xfz *tar.gz
List the directory contents (ls
) and copy the output into your answer document.
You should have some form of README
document. Read it! And follow the instructions that are
in there. For some data sets you may need to create files with different names; it should all be spelled out in there.
Do it! Check that the raw
directory has the files listed in the README file.
The README
should also list a command to be executed on the command line. It should start with p2p_
for process 2-pass followed by the sensor name. The next two arguments are Master and Slave scene and the last
argument is a parameter file that controls gmtSAR's processing.
Open the config file config.
(the rest of the name depends on the sensor). You will find
sections for configuration. If you don't have any SLC
(single look complex) images in your raw
directory, make sure to set proc_stage=1
otherwise proc_stage=2
is OK. Note that this
is only important for the first run. If you decide to change parameters later to improve the processing (say
the phase unwrapping, you can skip all the prior stages by setting this parameter to the processing step you want to
play with!)
If a parameter doesn't have a value, gmtSAR uses a default. Leave that for now. Make sure the topo_phase
is being subtracted from the the phase! Obviously, that's when you need your DEM! Make sure it is in ./topo/
.
Leave all the other parameters the way they are, but read through the file!
snaphu.csh
on the command line if you can't figure it out from the config file.)
Now you're ready to run the processing - get the command line from the README file and execute it! This may take a while! (10s of minutes)
Once it's done, check which new directories were made (ls
). Compare to your previous listing Copy into
your answer file!
Your lab07 directory now should contain a intf
directory. In there is another
directory which notes which SAR scenes were interfered. Change into that directory and list
its contents!
WHOA! There's a lot going on! Copy the output into your answer file!
Here are some viewers for the various files:
.png
: eog
.grd
: ncview
.ps
: evince
.kml
: google-earth
(though currently not running on redoubt!)Remember to refer to the gmtSAR documentation, section 2.1, to understand what all the files are that gmtSAR produces during the processing.
Note that the (mask)_ll
files are projected into geographic coordinates.
phase
and unwrap
results. Is there any deformation in your interferogram? What might be the cause?corr
file. Does your interferogram have good correlation everywhere? How does correlation compare to information
in the interferogram (phase/unwrap)?
Repeat the following twice! Once with a very low correlation threshold for the phase unwrapping in snaphu, another time with a very high correlation threshold.
Save old result directory to save your previous run (run1, run2...
):
$>cp -r intf intf_run1
Edit the config.
file to change the snaphu parameter, also set the proc_stage
parameter to a value
that starts from phase unwrapping. Rerun your p2p_...
. Repeat the above for another snaphu parameter.
Copy the 3 unwrapped interferograms in the answer file and comment on the impact your changes had on the results.
rg <at> nmt <dot> edu | Last modified: October 04 2017 19:14.