XVIIIth Congress: XVIIIth Congress

Kraus, Karl; Waldhäusl, Peter

Bibliographic data

Multivolume work

Persistent identifier:: 1667435949

Title:: XVIIIth Congress

Sub title:: Vienna, Austria 1996

Year of publication:: 1996

Place of publication:: Vienna

Publisher of the original:: Austrian Society of Surveying and Geoinformation

Identifier (digital):: 1667435949

Language:: English

Editor:: Kraus, Karl; Waldhäusl, Peter

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing

Document type:: Multivolume work

Volume

Persistent identifier:: 1667438379

Title:: XVIIIth Congress

Scope:: 449 Seiten

Year of publication:: 1996

Place of publication:: Vienna

Publisher of the original:: Austrian Society of Surveying and Geoinformation

Identifier (digital):: 1667438379

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(31,B2)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist anhand des Copyrightjahrs ermittelt.

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Editor:: Kraus, Karl; Waldhäusl, Peter

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 18., 1996, Wien; International Society for Photogrammetry and Remote Sensing; International Society for Photogrammetry and Remote Sensing, Commission Instrumentation for Data Reduction and Analysis

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: THE EPOS SPECKLE FILTER: A COMPARISON WITH SOME WELL-KNOWN SPECKLE REDUCTION TECHNIQUES Wilhelm Hagg, Manfred Sties

Document type:: Multivolume work

Structure type:: Chapter

edge hing ision men- ional sing, stem. ence ata", ligital netry übler, roject Work. Jress, n Still sung, point t No. ETH semi- metric ce on 5, 9t o 3D- rift für , 193- (try for jects. emote D: on by ited to |, 9-19 ctronic 21(4), anding Digital eipke), ectural action. onsing, ophoto on the tations, THE EPOS SPECKLE FILTER: A COMPARISON WITH SOME WELL-KNOWN SPECKLE REDUCTION TECHNIQUES Wilhelm Hagg, Manfred Sties Institute of Photogrammetry and Remote Sensing Karlsruhe University Germany Email: {hagg,sties}@ipf.bau-verm.uni-karlsruhe.de Commission Il, Working Group 4 KEY WORDS: Remote Sensing, Radar, SAR, Speckle, Multiplicative Noise, Edge Preserving Filters, Comparison ABSTRACT Any classification process using SAR images presupposes the reduction of multiplicative speckle noise, since the variations caused by speckle does not allow a distinction between neighboring classes within the feature space. This may be done by smoothing the images with digital filter algorithms, which removes the high frequent noise but also causes distortions at the high frequent image contents, i.e. sharp edges. Several adaptive filter algorithms have been developed, which aim at the preservation of edges and single scattering peaks, while homogeneous areas are smoothed as much as possible. This task is rendered more difficult by the multiplicative nature of the speckle noise: the signal variation depends on the signal itself. The recently developed EPOS speckle filter is compared with other well-known algorithms in this paper. In order to enable an objective comparison, the smoothing capability of all filters is adjusted to a similar value. To achieve a measurement for the quality, speckle is added synthetically to an image, so it is possible to calculate the RMS-error for each filtering method. Since the RMS differ according to the image contents, typical areas for several geometric objects are used to calculate the RMS. Also different signal to noise ratios are take into account in the comparison procedure to achieve an exhausting overview of the algorithm performance. 1 INTRODUCTION solve for an operational SAR image interpretation. The availability of optical remote sensing data for landuse = Two categories of speckle reduction techniques are distin- applications is limited by the local weather conditions, espe- ^ guishable; (1) the averaging of several looks of the same cially by clouds. In addition illumination effects due to differ- ^ scene (multi-look processing), and (2) the smoothing of the ent sunsets aggravate the interpretation of optical datasets. ~~ image using digital image processing techniques. The multi- Therefore “Synthetic Aperture Radar” (SAR) systems were look processing is limited by the geometric resolution of the developed which use their own, well defined, microwave il- SAR instrument and the required resolution of the final im- lumination to penetrate clouds in the atmosphere. Another age. For the geocoded standard ERS-1 products three inde- reason to develop SAR systems is the total different backscat- ^ pendent looks are averaged to achieve a final resolution of ter behavior of microwaves due to the long wavelength of ^ about 25 meters. Both techniques use the fact, that averag- microwaves relative to optical systems. There is a lot of ing of several independent samples of a measurement reduces operational SAR systems on satellite platforms available as the variance of a signal. In the first case, several images are the European ERS-1 and ERS-2, the Japanese JERS-1 and averaged, while in the second case values of neighboring pix- the Canadian RADARSAT. In addition several experimental els are averaged. The most simple way of smoothing images systems were developed for a flight on board of a space shut- ^ with digital image processing techniques is to apply a mean tle. Recently the X-SAR/SIR-C mission resulted in the first filter within a moving window around each image pixel. The spaceborn multi-frequency images of the earth surface; the result will be a smoothed image with reduced speckle vari- instruments operate in the L- C- and X-Band. Also there ex- ation, but edges and single point scatterers, as they appear ists a lot of airborne SAR-systems for experimental purposes. in urban areas, are smoothed as well. Adaptive filter algo- rithms have been developed which aim at the preservation of edges and single scattering peaks, while homogeneous areas are smoothed as much as possible. For that purpose the fil- tering function has to be adapted to the local image contents to reduce the geometric distortions. It is obvious that the correction of a grey value, using the pixel values in the neigh- borhood, is efficient only in those cases where the neighboring pixels represents the same object on the ground. While the SAR-systems and SAR-processors are in an oper- ational state, the interpretation of SAR images is still under development due to several problems such as speckle noise and illumination effects in undulated terrain. SAR-processors are necessary to reconstruct the image from the synthetic aperture by coherently processing the returns from successive radar pulses along the flight path, and therefore they may be interpreted as the software component of the SAR instru- ment. Speckle noise is a system made consequence of the Most filter algorithms for speckle filtering are not fully sat- coherent radar illumination and appears as a granular pattern isfactory for the purpose of SAR image classification, since in the image. One of the most important feature of speckle the decrease of speckle caused variance is not sufficient for noise is its multiplicative character which links the amount of a distinction of neighboring classes within the feature space. noise to the signal intensity. The strong distortions of SAR Thus we developed a filter called EPOS (Edge Preserving Op- images by speckle noise often prevent an useful application of timized Speckle-filter) which is published in (Hagg and Sties, SAR images in remote sensing. Thus, an effective reduction 1994). The idea for the new algorithm was to adapt an area of speckle noise is one of the most important problems to geometry to the image contents in such a kind, that the as- 135 International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996

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