Measuring 3D Forest Structure through Radar Remote Sensing

3DWald_tomo_xl

Polarimetric L-band F-SAR image of the study site in southeastern Bavaria, Germany. The image is shown in false color: forest areas appear green, while surfaces with low vegetation are shown in blue / red. Image credit: DLR

Radar remote sensing can enable us to see and construct a full 3D view of forest structure and trees. In a joint research study conducted last year, NASA and DLR proved this concept in airborne flights over a test region in southeastern Bavaria, Germany, where both agencies flew their own airborne radar sensors over a period of a few days. NASA flew its well-known L-band UAVSAR sensor, while DLR flew its F-SAR system. The F-SAR system is unique as it does coincident radar imaging at L-, C-, and X- bands. Radar remote sensing analysts know well that lower frequencies like L-band can penetrate right down to the forest floor, C-band frequencies penetrate the canopy to some extent, while X-band frequencies are reflected from the top of the tree canopy. Utilizing these three frequencies simultaneously for forest imaging allows full 3D mapping of the forest, from the upper section of the forest crown, canopy, branches, down to the under-canopy vegetation and forest floor.

See the DLR official press release for more info.

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Example vertical profile of radar backscatter from F-SAR. Backscatter is scaled in shades of green. Solid green lines represent liar-measured heights of forest floor and crown. Image credit: DLR

Many other research groups are also pursuing similar goals to measure forests in 3D using SAR remote sensing. One such technique which can be applied to both airborne and spaceborne SAR sensors is POLinSAR (Polarimetric Interferometric SAR).

The Finnish Geodetic Institute is leading a research effort to measure 3D forest structure using a multiple active sensors, including SAR imagery from Sentinel-1, TerraSAR-X / TanDEM-X, and ALOS-2 PALSAR, along with optical satellite stereo imagery, and Airborne Laser Scanning (ALS). Learn more about their research here and here.

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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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