Tag Archives: Software

Satellite Image Processing Revisited

Heard Island on Nov. 20, 2015, with image processing underway in QGIS.  Image credit: Bill Mitchell (CC-BY) with satellite imagery from USGS (EO-1 satellite, ALI instrument).
Heard Island on Nov. 20, 2015, with image processing underway in QGIS. Image credit: Bill Mitchell (CC-BY) with satellite imagery from USGS (EO-1 satellite, ALI instrument).

Following up on my earlier post about satellite image processing, I am happy to report that I have made progress in being able to process images myself! Through a fortunate combination of search terms, timing, and luck, I managed to come across two key pieces of information that I needed.

First, I found out how to make RGB images from raster data layers, such as different spectral bands on a satellite, fairly easily with QGIS. That was a big step forward from how I had been doing it previously, which was inelegant, inefficient, and only mostly worked. Stacking three layers (one each for red, green, and blue) into a virtual raster catalog was just a few clicks away (Raster | Miscellaneous | Build Virtual Raster (Catalog)).

Encouraged by the success with that project, I continued clicking around and stumbled across some mention of pan-sharpening (also pan sharpening), where a panchromatic (all-color) detector at high resolution is used to enhance the resolution of a colored image (sharpen). Alternately, you can think of it in the complementary way, where lower-resolution color data is added to a high-resolution greyscale image. So thanks to this blog post, I was able to find out what I needed to do to make that happen in QGIS (and Orfeo Toolbox).

Of course, it would be too easy for that to work. I didn’t have the Orfeo Toolbox installed which that needed, and ended up having to compile that from source code.* When the compiler finished and the program was installed, I went to tell QGIS where it was—but a bug in QGIS prevented me from entering the folder location. First, having just installed and compiled stuff, I attempted to get the latest version of QGIS and many of the tools on which QGIS relies. Being unsuccessful in making all of those and some of the compiler configuration software play nicely with each other, I eventually remembered I could get updated packages through apt-get, which gets pre-compiled binary files put out by the maintainers of Debian Linux. That solution worked, I added the folder location, and now I can have my pan-sharpened images.

Here for your viewing pleasure is my first properly pan-sharpened image: Heard Island on Nov. 20, 2015, seen in “true color” by the Advanced Land Imager (ALI) on the EO-1 satellite.** I’m not convinced it’s right, and I think the contrast needs to be brought down a bit, but I think it’s close.

Heard Island in true color on Nov. 20, 2015.  Image processing: Bill Mitchell (CC-BY) using data from USGS/EO-1.
Heard Island in true color on Nov. 20, 2015. Image processing: Bill Mitchell (CC-BY) using data from USGS (EO-1/ALI).

* Knowing how to compile software from source code is a rather handy skill.
** Emily Lakdawalla has written a great explanation of what “true color” means.

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Expedition Software

Preparing a Heard Island image taken with the NASA Aqua/MODIS instrument using GIMP.  Image credit: Bill Mitchell (CC-BY).
Preparing a Heard Island image taken with the NASA Aqua/MODIS instrument using GIMP. Image credit: Bill Mitchell (CC-BY).

Previously, I’ve written a little about the computer issues that may come up on the Heard Island expedition, as well as some of my views on open access (I’m generally for it). Now I’d like to talk a little bit more about the software which will be on the expedition computers.

For the most part, we’re using open-source software wherever it’s practical. My heart broke a little when I realized we would not be able to run Linux for many of the computers because of some of the programs needed to support the ham radio side of the expedition. I prefer open-source software because it can help encourage experimentation and learning among amateur programmers, it has code which is verifiable (not subject to security through obscurity), can be shared freely, and does a better job supporting open formats free of restrictive proprietary specifications that force vendor lock-in.

Here are some of the software packages which are coming with us:

  • GIMP (the GNU Image Manipulation Program), for raster graphics
  • Inkscape, for scalable vector graphics
  • Firefox, for standards-compliant HTML browsing
  • FileZilla, an FTP client for sharing files over the (local) network
  • PuTTY, a command-line client for accessing remote computers
  • VLC (VideoLAN Client), for playing sound/video files
  • Audacity, an audio recording/editing program
  • Pidgin, a chat client
  • LAMP (Linux, Apache, MySQL, PHP), a web server and related programs/languages (probably coming, but not confirmed)
  • QGIS, a mapping/geospatial information system

Just as with ecology, having a healthy, diverse software ecosystem is important. It allows new ideas a chance to thrive, and for users who know what they are doing to add features and patch bugs themselves. More and more academic research is turning toward open-source tools, from R (statistics) to Git (of GitHub fame) to WordPress. We are choosing as much open source software and as many open formats as possible to help preserve the data for the future. Proprietary formats are subject to the corporation changing the format to force upgrades, vendors going out of business, and other issues. It also happens with open-source projects, but there are generally compatible programs which can handle your data.

Most of these programs above are ones I have been using for quite a while, and have significant user bases. Online support is pretty easily accessed via search engine. Try them out at home, and you may find them quite to your liking!