Finding Coverage Overlap between Radar Altimetry, SAR, and MODIS Imagery

Recently, I had to plot coverage overlap between Radar Altimetry, SAR, and MODIS imagery for a research proposal. It was an interesting little problem, and I want to point out the resources that could be helpful to others in solving a related or similar problem.


Radar Altimetry:

For altimetry, the requirement was to show the tracks for Jason-2 Poseidon-3 radar altimeter and Envisat Radar Altimeter 2 (RA-2). The pass locator GIS files are available on AVISO’s web page in the form of KMZ files and can be easily displayed in any GIS software tool. Since I did not have to perform any spatial analysis or queries, I used Google Earth for displaying all the required information. The individual tracks and track numbers for the altimeter tracks can be turned on / off as required.


Next I had to find SAR coverage for the following SAR satellites / constellations for a time period of Jan. – March, 2011: Envisat ASAR, TerraSAR-X / TanDEM-X, COSMO-SkyMed.

To find Envisat ASAR archive imagery coverage, ESA’s EOLi (Earth Observation Link) desktop software tool has to be downloaded. EOLi allows for customized search for Envisat ASAR archived scenes, and the search query results can be exported as KML / KMZ files.

TerraSAR-X / TanDEM-X archive scenes can be searched from Airbus Defense & Space TerraSAR-X Archive web system. KML files of selected scenes can be downloaded easily.

To search COSMO-SkyMed scenes, the user first has to make an account on the COSMO-SkyMed scientific and institutional users webpage (or here), after which archive search option is available. KML files of selected scenes can be downloaded easily.


Since MODIS scene is much larger in extent from all the other satellites, so only one MODIS scene extent needed to be shown as a sample. I downloaded a suitable MODIS Level-2 SST scene from the NASA Ocean Color Web data access system after looking at the preview images. However, my interest is just in the bounding box coordinates so I can display the corresponding polygon in Google Earth. I accessed the metadata information in the Ocean Color netCDF file through the ncdisp function in MATLAB, and noted down the minimum and maximum latitude / longitude values. Next I needed to draw a vector polygon with these bounding box coordinates. Various tools are available on the web for this task, and I used this KML generator tool. Entering the four corner coordinates in the text input tab generates a KML polygon which can be downloaded.

Final Coverage Overlay Map:

Overlaying all the KML / KMZ layers generated above and assigning them suitable colours / thickness etc., I got a really nice display map from Google Earth. The output was saved as an image, during which Google Earth allows the user to insert and manually place the North arrow, scale bar, title, and description. The final output map is shown above.

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About WQ

I received my PhD (2013) in Remote Sensing, Earth and Space Science at the Dept. of Aerospace Engineering Sciences, University of Colorado, Boulder, USA, under a Fulbright fellowship. Currently, I'm an Assistant Professor in the Dept. of Space Science at Institute of Space Technology (IST), Islamabad, Pakistan, where I have been a founding member of the Geospatial Research & Education Lab (GREL). My general expertise is in Remote Sensing where I have worked with various remote sensing datasets through my career, while for my PhD thesis I specifically worked on Remote Sensing using SAR (Synthetic Aperture Radar) and Oceanography, working extensively on development of techniques to measure ocean surface currents from space-borne SAR intensity images and interferometric data. My research interests are: Remote sensing, Synthetic Aperture Radar (SAR) imagery and interferometric data processing & analysis, Visible/Infrared/High-resolution satellite image processing & analysis, Oceanography, Earth system study and modelling, LIDAR data processing and analysis, Scientific programming. I am a reviewer for IEEE Transactions on Geoscience & Remote Sensing, Forest Ecosystems, GIScience & Remote Sensing, Journal of African Earth Sciences, and Italian Journal of Agronomy. I am an alumnus of Pakistan National Physics Talent Contest (NPTC), an alumnus of the Lindau Nobel Laureate Meetings, a Fulbright alumnus, and the Pakistan National Point of Contact for Space Generation Advisory Council (SGAC). I was an invited speaker at the TEDxIslamabad event held in Nov., 2014. I've served as mentor in the NASA International Space App Challenge Islamabad events in April 2015 and April 2016.

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