Digital Geography

Observing deforestation with Sentinel-1

While preparing for an upcoming presentation at the annual meeting of the American Geophysical Union (AGU) I came across a topic that I thought might make an interesting blog post.  The presentation is about using data from the Sentinel-1 mission for Earth Science applications.  The Sentinel-1 spacecraft are C-band SAR systems launched and operated by the European Space Agency (ESA).  An innovative aspect of this mission is that the collection scenario devised by ESA is systematic and very broad in coverage.  Using Sentinel-1 we can monitor Earth using SAR data like never before.

Short Announcement: SRTM 1 Data Worldwide

The digital elevation dataset resulting from the SRT Mission in the year 2000 is probably the most widely used digital elevation dataset in the world. It was first released with a 90 at ground resolution in a more or less global level (56° S to 60° N). In 2014 the White House announced the release of the 30 m original solution dataset. So they released parts of the dataset one-by-one. Our author Christoph just mentioned an update via Twitter.

Freeware SAR processing, Part II: PolSARPro

In this post I’ll take you through some simple functions in the freeware polarimetric SAR processing package, PolSARPro. The software is distributed by the European Space Agency (ESA) and supports a wide range of dual- and quadpol datasets, including Radarsat-2, Envisat ASAR, SIR-C, EMISAR, and AIRSAR. I’ll be processing ALOS PALSAR in this example. The steps I will show are: Importing and Extracting data, calibration, speckle filtering and multilooking. We will finish by producing an Entropy-Alpha-Anisotropy dataset. Getting Started We start by identifying the directory in which our data lies. To do this we click on the first icon (highlighted…

Freeware SAR processing (Part 1.)

One thing about working with synethic aperture radar (SAR) data is that regular image processing functions are often unsuitable. This is because most processes were design to deal with issues related to passive multispectral data in the visible-thermal infrared wavelength range. SAR imagery is derived from an active sensor which introduces particular problems or rather requires special solutions. The wavelength range is also very different meaning that the interaction between the energy and target is dissimilar to that of visible-infrared radiation. Hence we need a different set of tools to work with SAR data. If you have the money there…

What is the synthetic aperture in “Synthetic Aperture Radar” (SAR)?

Talking to a colleague recently about monitoring changes to the magrove forest of the Rufiji Delta in tanzania, he commented on the relative scarcity of satellite data over the region. It’s too cloudy. Some Landsat TM data exist: we found four images between 1989 and 2010 with less than 20% cloud over the northern delta. To observe the forest we will develop tools that use cloud penetrating synthetic aperture radar (SAR) data. SARs transmit microwaves at centimetre wavelengths (normally) that can penetrate cloud and can image the surface day or night. The intensity and polarisation of reflected or “backscattered” radar…

Free Sources of Geospatial Raster Data

I’m always looking for good sources of free data, so I thought I would post a few here in case they were useful to others. The sources listed below tend to be larger providers of regional to global level data, however, please post suggestions in the comments if there are other sources you like and think should be added. I had initially planned to include vector data here, but I think that will be another post as this one got quite long. SAR Data Free Synthetic Aperture Radar data can be some of the hardest to find, but it is…