New Mexico Tech
Earth and Environmental Science

ERTH 471 / GEOP 572 - Geodetic Methods

Lab 8: Processing w/ gmtSAR: Timeseries; Getting SAR data

Note that you DO have to work on redoubt for some things today!

Introduction

This week you will process a prepared ENVISAT timeseries and learn something about where and how to get data you might be interested in. Ideally, we'd start you out on getting some data and then you'll process your own time series. However, as I mentioned in the lab, the time series processing is quite time consuming, so you'll have to use some canned data. Note that the point of this exercise is to get you to understand the processing; we'll look into exciting processes in a few weeks!

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.

1. gmtSAR - time series example

If things are unclear, refer to the gmtSAR documentation

Change to your working directory and copy the test data:

    $> cd $GEOP572
    $> mkdir lab08
    $> cd lab08
    $> cp /data/InSAR/gmtSAR_TEST/orignals/ENVI_2907_stack.tar.gz ./
    $> tar xfz ENVI_2907_stack.tar.gz
    $> rm ENVI_2907_stack.tar.gz
	

A directory listing should look similar to this:

    redoubt:/data/GEOP572/gps/lab08> ls
    align.in  intf.config  intf.in  raw  README.txt  topo
	

Follow the instructions in the README.txt file. Note that the alignment and interference steps take a while (about 30 mins-1 hr total, maybe more). During this time you can work on the rest of the lab, but keep an eye on what's happening with the processing.

• Explain the contents of the files data.in, align.in, intf.in. Use the commandline documentation for the respective programs, and/or the gmtSAR documentation.
• How many ENVISAT scenes are part of the dataset? Which scenes are interfered with one another?
• Does the intf_batch.csh program unwrap the entire region of the interferogram or just a subset? Check the input files for the program!
• At the end of the README file, step 4, instructs you to sum the LOS data to look at the residuals. The program used is grdmath which is a Reverse Polish Notation calculator. Write out the 2 equations in standard notation.
• The beginning of the README file states that this is a test for phase closure. With the entirety of the Internet, libraries and other imaginable sources at your disposal, explain what phase closure is, why one would do this, and whether or not the test succeeds. Feel free to include figures to make your point.

2. Getting Data

Just like with any data type: hunting is encouraged! The complexities involved with SAR data are that some data are only commercially available. Most are distributed over several archives, and the search interfaces are some times not quite intuitive. Download of the results may also not be very straightforward, but most places support command line based bulk downloads.

The algorithm that I would encourage for data discovery is:

• Check at Alaska Satellite Facility (ASF)
• Check at WinSAR
• Check with individual space agencies, e.g. ESA

Most places require you to register. But use is free (or commercial data are clearly marked). Some enable guest searches without registration. Register with ASF as you will need data access for homework #2. (Feel free to register with WinSAR. NMT is a Full Institutional Member. In fact, you should if you plan on becoming an active InSAR user. However, you'll have to fill out some license agreement forms and mail them to UNACVO; so this may take a few days.)

I highly recommend for you to read through the "Getting Started" guide at ASF.

Here are the links to some search interfaces:

• ASF: https://vertex.daac.asf.alaska.edu/
• WinSAR / SSARA: http://web-services.unavco.org/brokered/ssara/gui2.0
• JAXA (ALOS): https://auig2.jaxa.jp/ips/home?language=en_US?language=en_US (Japanese Space Agency)
• ESA (Sentinel): https://scihub.esa.int/dhus

Note that the WinSAR link takes you the "Seamless SAR Archive" (SSARA), which attempts to provide data from multiple collections (WinSAR/UNACVO, Geohazard Supersites, ASF, etc), however, the search may appear a bit rough.

For the following task keep in mind that in order to use SAR scenes for InSAR analysis, the scenes must have the same path/track and frame numbers. Using the ASF/WinSAR interfaces, search for data over an area and time of interest to you. Don't make the search area too large or you will have too many scenes to deal with.

• What's of interest to you in this area during this time?
• What sensors/platforms provide observations for your area? Write a couple of sentences on a sensor which you haven't heard before (time in orbit, space agency, waveband. etc.)!
• How many repeat pairs did you find that cover your area of interest in the time frame of interest? Provide all satellite-based observations.
• What are the path/track and frame numbers of the pairs? How far are they apart temporally?
• Are these ascending or descending observations? If they are ascending, do descending observations exist (and vice-versa), if so, provide track and frame numbers.

If your search didn't bring up anything, or you are not satisfied with the number of results, you can always check with the respective space agency. To give this a try find answers to the above questions for ALOS-2 PALSAR, ALOS-PALSAR by searching the JAXA archive for your area of interest. If you prefer Sentinel-1A data, search at ESA!

Deliverables: (submit via canvas!)

• An answer file (preferably PDF) with all answers to the questions above.