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Furlanetto extend the usual elliptically-symmetric Sersic model for source galaxies to make the major axis a segment of a circle and the ellipse into an "ArcEllipse". They then explore ways of fitting this to pixelated, blurry data, and compromise on a method that underestimates flux but captures (quickly) the L/W ratio found by other methods. Since they base their measurements on SExtractor segmented images, this parameterisation could be adopted by Gavazzi et al's RingFinder code (if something equivalent is not already implemented). Interestingly, the number of parameters needed to specify an ArcEllipse is the same as that needed for a Sersic lensed by an SIS+Shear lens, though the predicted arc surface brightness is different.

Still reading the paper but... I remember that I talked to E. Bertin about how efficient SExtractor is to segment arc-like images. He was very negative about this. I'd like to hear your opinion on that!

In my experience SExtractor can do a very nice job at segmenting arcs. The tricky part is finding a SExtractor setup that works for arcs of all shapes, sizes and surface brightnesses. You can certainly bias your sample by choosing one setup over another. This is just a variant of the usual astronomical dynamic range problem of course - all methods have to solve this.

In this paper we estimate the number of gravitational arcs detectable in a wide-field survey such as that which will be operated by the Euclid space mission, assuming a LCDM cosmology. http://cgiocoli.wordpress.com/research-interests/moka/

Furlanetto et al selected 50-odd clusters in SDSS stripe 82 by richness, in two redshift bins, and then re-imaged in g, r and i at SOAR. Image quality is comparable to median LSST, but depth is only 22-23mag. Interesting sample for algorithm validation, but they are also interested in arc statistics