|Title / Titel||Radiometric Terrain Correction for Radar Imagery|
|Abstract (PDF, 14 KB)|
|Summary / Zusammenfassung||In this project, the University of Zurich Remote Sensing Laboratories (UZH-RSL) works directly with ESA and other partners to develop a new kind of spaceborne SAR image product whereby many of the effects of topography on radar image brightness are modelled and corrected to better separate terrain-induced backscatter from the land cover signatures that are more generally the subject of study.
The new type of product offers several benefits. Comparing backscatter values from image acquisitions made from differing orbital tracks becomes possible. Flattening the terrain-effects on radar brightness enables significantly more frequent revisits to a given point on the Earth, particularly given the availability of a wide swath mode such as ASAR WS, RADARSAT-1 & 2 SCN & SCW, and ALOS PALSAR WB
This development enables a great improvement in temporal resolution, a parameter of critical importance in land cover monitoring, lowering the probability of missing the cusp of an event. Deep time series can be built up for a chosen area much more quickly from a single sensor given a wider variety of tracks (even combinations of ascending and descending passes). There is an added benefit: it becomes easier to integrate backscatter measurements from a diversity of sensors. Each sensor is typically characterised by the single orbital repeat period chosen at launch and the set of beam modes on offer. Different sensors therefore almost always implies differing tracks, modes, and nominal incidence angles that without terrain-flattening triggers incompatibility with a meaningful comparison. Only terrain-flattened backscatter, a product we call terrain-flattened gamma nought, offers the possibility of combining data from multiple SAR sensors acquired over terrain.
Future sensors such as the ESA Sentinel-1a and Sentinel-1b satellites, the first currently set for launch in 2013, offer the promise of possible daily images of Switzerland. Given the severe Alpine topography present, construction of backscatter time-series requires rigorous radiometric calibration that accounts for track-dependent effects of terrain. If a standard terrain-flattened backscatter product could be offered by ESA, that would simplify interpretation not only in Switzerland, but throughout the world.
|Publications / Publikationen||- Small D., Zuberbühler L., Schubert A., and Meier E.: Terrain-flattened Gamma Nought Radarsat-2 Backscatter, Canadian Journal of Remote Sensing (CJRS), (in press).- Atwood D., Small D., Gens R.: Improving PolSAR Land Cover Classification with Radiometric Correction of the Coherency Matrix, IEEE Journal on Selected Topics in Geoscience and Remote Sensing (JSTARS), (in press 2012).Small, D (2011). Flattening gamma: radiometric terrain correction for SAR imagery. IEEE Transactions on Geoscience and Remote Sensing, 49(8):3081-3093.Small, D; Miranda, N; Zuberbühler, L; Schubert, A; Meier, E (2010). Terrain-corrected Gamma: improved thematic land-cover retrieval for SAR with robust radiometric terrain correction. In: ESA Living Planet Symposium, Bergen, Norway, 28 June 2010 - 02 July 2010, 1-8.Small, D; Miranda, N; Meier, E (2009). A revised radiometric normalisation standard for SAR. In: 2009 IEEE International Geoscience and Remote Sensing Symposium (IGARSS 2009), Cape Town, South Africa, 12 July 2009 - 17 July 2009, IV-566.Small, D; Jehle, M; Schubert, A; Meier, E (2008). Accurate geometric correction for normalisation of PALSAR radiometry. In: ALOS 2008 Symposium, Rhodes, Greece, 03 November 2008 - 07 November 2008, 1-7.|
|Keywords / Suchbegriffe||Synthetic Aperture Radar (SAR), radiometric calibration, RTC, Radar terrain factors, Radar cross section|
|Project leadership and contacts /
Projektleitung und Kontakte
|Funding source(s) /
|Other Public Sources (e.g. Federal or Cantonal Agencies)
European Space Agency
|In collaboration with /
In Zusammenarbeit mit
|Duration of Project / Projektdauer||Dec 2002 to Dec 2012|