This week’s guided exercise will look at the benefits of radar-based satellite observation, and will enable you to make a simple comparison between optical imagery and SAR (synthetic aperture radar) data in the same location, at roughly the same time.

For this exercise, we will use the Earth Images Lite tool from GeoCento.

Follow the steps below and then join the discussion to compare results and discuss ideas with other learners. Once you feel confident with the tool, you can explore other locations and data sets of your choice.

You may find it helpful to open the exercise in a separate window.

1. Go to Earth Images Lite. Choose ‘Type place name’ from the ‘Select A Place’ menu. Type ‘London’ into the search box. Select ‘London, UK’ from the list that appears. This creates a square around London on the map.

2. In the ‘Select Type Of Imagery’ menu, choose ‘Optical - Medium Resolution’.

3. in the date range menu, change the start date to Nov 01, 2015.

4. Click ‘Search’. The system will now search for the latest medium resolution optical images from several satellites relating to the selected area over London. These results will appear in the bottom half of the page after a few moments.

5. Search through the results and locate the thumbnail image for UK-DMC2, November 01 2015 at 09:13:21 UTC. (You can put the search results into date order by clicking on ‘Refine Search’ and then selecting ‘Acquisition Date’ from the ‘Sorted by’ menu).

6. Next click on the ‘double square’ symbol underneath the thumbnail image to open the image in a new window. This will give you a closer view and more information about the image. Note that the cloud cover in this image is extensive and London is not visible.

7. Next, go back to the ‘Earth Images Lite’ search/results page. Now select ‘Radar - X Band’ from the ‘Select Type Of Imagery’ menu at the top of the page, and click search.

8. Find the result from Terra SAR-X for the same date, November 01 2015 at 06:09:17 UTC and click on the ‘double square’ symbol underneath the thumbnail image to open the image in a new window. Now you will see a very clear view of London.

This exercise demonstrates how SAR (synthetic aperture radar) instruments enable us to observe the ground in detail even when there is substantial cloud cover.

You can repeat this exercise with alternative locations and by comparing different resolutions of optical imagery (VHR - very high resolution; HR - high resolution; MR - medium resolution) and also with different SAR bands.

You can search for a location either by typing into the search box, or by drawing a polygon onto the map. To do this, select a type of polygon from the ‘Select A Place’ menu, then click a location on the map to place your polygon and stretch it to cover the area you are interested in. Then click search. (Remember not every location will have results in every resolution).

Remember although Earth Images Lite is a very simple tool with only selected data available, its interface and the way it presents results is similar to aspects of other more detailed tools used professionally in EO and climate science.